TEDSgrad

iTrader: (4)

No, I'm not talking about the flu!

Let's discuss unsprung weight vs wider footprint - contact patch & suspension articulation. Let's assume most of us aficionados have completed steps 1-4 below.
What is needed to have more "favorable geometry to use a larger footprint?" And what is the point of diminishing returns?
2 yrs ago this month, Dean wrote this:
The biggest gain is how the car is weighted. So of course the light V6 is going to sacifice HP.
Since these are full size cars, I focused alot on polar weight reduction. Basically getting alot of the weight in between the wheelbase and chassis strength. The reduction of polar weight also helped reduce chassis flex.

Its really not all about what you buy, but more how you set it. That Scott as you kind of know with race cars is a person think to each individual vehicle based on its componants and weights to get balance.

If the question is "what are the main weaknesses in these cars?" then I will say first and foremost-
1) stock strut mounts suck. Replace them with solid bearing type mounts t eliminate strut shaft movement.
2) Reduce chassis flex- this is done many ways combined, not just SFC's, but also repositioning weight like stated above.
3) best shiocks money can buy
4) best tires money can buy

from there, it is a matter of unsprung weight reduction to increase the sprung weight ratio and improve chassis stabilty and grip over road imperfections. This costs $$$$$ for exotic lightweight parts.

Things like my drilled axles, carbon fiber driveshaft, aluminum wheel hubs, aluminum calipers and rotor hats, alum front bumper, reduction of heavy rear exhaust routing and addition of I-pipe muffler, lightweight gears and overall axle assembly weight reduction, lighter wheels and tires (Most people with larger tires do not always have favorable geometry to use a larger foorprint. Often they have a smaller contact patch through articulation without realizing it. Sometimes, just by usaing all of a smaller tire contact patch will be better than a heavier whell/tire combo. Just adds unnecessary unsprung weight and alot of times more scrub radius and poor lateral track front to rear.

I did alot of bracing, but what I also did that I never really showed anyone is I trimmed off every bracket that was belyond my range of use. I was starting to eliminate excess weight like the excess panhard adjustment braacket, the excess LCARB material, axle housing material around the panhard mount (factory area). These alxe assemblies are HEAVY and are in need of atttention. This is where a shorter Tqarm setup I think would pay off in unsprung weight, but you need to focus on acheveing this without brake wheelhop through higher rate rear springs, lower rear RC and shock valving.

SlickTrackGod

First and foremost, you can not really have any factual data without using a pyro.

The old shoepolish on the tire edges trick will work for camber and tire pressure adjustments, but the pyrometer will tell you the temp across the tires footprint, not just that the tire is touching at points of the footprint on certain times on the track. Temp will tell you how much it is being touched/or used.

For example- you can shoepolish (We'll just say SP) the edges of the tire tread going onto the sidewall. Lets say we make 1 run on an autox course and the SP is scrubbed off the inner mark over the sidewall 1/4", and not to the sidewall edge by a half inch on the outer- result? you have a little too much negative camber AND slightly high tire pressure. If its a front tire (lets say the factory 245/50-16) that depending on the tire quality may be a reduction of about 0.5 camber setting (which would bring both SP marks to about 1/8" above tire sidewall edge and maybe a 1 psi drop based on tire tread makeup. SOme tires you want to leave as much as 1/4" srub marks above the sidewall tread edge- its all about quality and testing lap times.

NOW- with the above stated on SP testing. you could then put a pyro on the tread to get avtually tire temps and still find out the tirew middle and outer tread sections are the hottest. Meaning it may be touching the inside edge only on inside cornering, but then riding mostly on only the outer center to edge of the tire footprint on straights and corners. You want pretty even temp across the tire footprint. A general rulle is usualy about 10% hotter on the inside edge on long courses (typically a long course will have a tire running on tmore the inside edge (due to static camber) on straightaways, and then set more onto the entire tread when the car is set into a corner.

Here is a closeup of me reading the pyro at the track with Val. If you do not have one, buy one and learn how to use them- it is the best tool money can buy for making adjustments and getting longevity out of tires as well.

TEDSgrad

iTrader: (4)

Will my infrared thermometer used for my rotors work, as well?

SlickTrackGod

Teds(Brian) - The question of how much is too much tire/wheel width realy boils down to surface smoothness and the amount of use- as opposed to ride comfort and handling when the grip factory comes into play.

Lets take probably one of the fastest small track cars on these boards- Pablo. He is running very wide CCW wheels and I believe it is Hoosier A6 315's up front and 335's out back. TIre width on a short track will trump anything as long as the footprint is decent and temps are fairly even (especially R or even A compound race rubber). Where Pablos car will eventually fall short (And Pablo, I am not trying to bash you here, I commend you on a very fast and fun build you did and you are using your car in the perfect forum for it)- but if Pablo were to put those wide footprint,wide offset tires onto a high speed road circuit the tires would burn up very quickly and wear out fast on the fronts due to 2 factors...1) is the poor ackerman these cars have, and 2) is the massive scrub radius he has. They will work great for a few laps, but then times will start dropping as the tires heat unevenly and start to wear rapidly.

Now whats my point and how does this go back to topic?
Pablo could not put regular DOT 200 or above street tires on that car and drive it for 20-30K miles on the street, He would probably get about 5-10k out of them. Thats fine though, he did not build the car for that so all is good, this is just an example of what you need to think about when you secide on wide tires and the cars overall general use.

Now as for weights of the wider wheels, he is running pretty much the best wheel out there- the very lghtweight CCW's (bow to the wheel gods- these are top shelf) Most peoples choice in street wheels are much heavier when going wider and larger diameter.. This increase in size is a decrese in sprung to unsprung weight ratio (which is everything to ride quality of a vehicle) Also, the wider outer footprint of the tire (even when the centerline is the same as fatory) will increase the wheel movement leverage. It is like holding you arm out to the side fully extended and have someone force it upward while you try and resist- then hold it a little closer (with elbow bent) and have someone try the same. You can resist the upward thrust motion easier the closer the leverage distance. THink how this is effected when the wheel hits a bump and the wheel/brake assembly thrust upward. The more it weighs and/or the more leverage, the more it will leverage the shock rate and move upwward. To lessen movement we have to increase spring rate-BUT- increased spring rate now starts to lift and unsettle the chassis more. Light wheel assemblies allow for a little lighter spring rates- and thus here is the real clincher- will allow for longer suspension arms that will reduce chassis attitude change in the same suspension travel (I probabl should not say that because it will entice people to build wider suspensions- but you'd better understand the high dollar cost in lightweight parts as well as know it also will effect the already bad steering geometry and lack of ackerman.

Ever notice how long an Indycar or F1 car's front suspension links are in comparison to the body width. They are generally carbon fiber bladed control arms and magnesium wheels with inborad bellcrank type light unspruung weuiight shock and swaybar setups- that's how they all work so well on a little light sprung weight chassis that is very narrow.

SlickTrackGod

no. THat will only read a very rapidly decreasing surface temp. You need core tread temp- it is alot more stable and gives better time to jump out and get rradings when you do not have a crew to do so( actually its still better even with a crew. Here is a shot of me getting right on tire temps at the NASCAR track right in the winners circle down in front of the crowd on the start finish line. THis is how I got a few month nickaname of "Booger". Nicknames are earned, not choosen (that one friggin sucked...lol) I have the team hustle onto the track on a place or win becasue the top 4 cars generally stay on the track for throphy presentation and interveiw. Makes for alot of huslte to get out there quick enough before temps drop too much. We would record tems, staggars, and PSI as quick as possible This is the best data for reference charts on individual setups based on race length and ambient temps (ie-summer, winter, night, day, sunny, shaded etc)
https://www.thirdgen.org/forums/memb...my-first.htmps

ps- Slick track god is earned

TEDSgrad

iTrader: (4)

Prof. Sake', too I bet, is earned.

No matter how committed I am to my first love (low unsprung weight), I always find myself seduced/tempted away by the new sirens, pretty baubles, etc. Spending more time with one's first love, keeps the bond tight/secure. Sometimes I just need to go over the old, old story for refreshment, and remember why I chose it as my first love. Hey, I could start preaching, here.
I've never thought too much about rear unsprung weight. My 9bolt is holding up, but I just put in the stock LS2 (382 rwhp: further plans for L92 heads, intake, & cam will blow the rear for sure). Strange 60 or 12bolt is a lot of weight - is that so bad with the V8 - car weight balance vs rear unsprung weight? Your brake hop comments got me thinking. Here, it's rear end strength tempting me away. If only I could find a Dana 44. I've never had a stop-light ego, so I might be able to make a lighter rear work.
I readily agree with you on higher aspect ratio with higher speeds for safety sake (not for sake' sake). What affect do aspect ratios have on tire temps? Wider low profile tires would heat faster, correct? The higher aspect ratio favors tire patch and absorbs some impact - especially for big, heavy cars.
I'm trying to think ahead, while staying with my first love - it's not so easy being committed with all these temptations. Bank account is trashed: suspension, brakes, interior, LS2/4l65e swap, and now paint - will finally be sprayed and baked next week. I'm not bragging, I'm hurting - must be close to 40k in 2 yrs. Right or wrong sequence, I've left wheels til last.

SlickTrackGod

I would think the lighter weight the axle is the less likely for brake hop because the weight would counteract the heavy chassis better than a lighter rearend. We are talking peanuts though when talking 400lbs agasint 2000 lb compared to 375 lbs against 2000 lbs when you add up the axle, brakes unsprung suspension weight, and wheels and tire that make up the total unsprung weight movement compared to chassis sprung weight.

Ideally- lets look at what causes wheel hop and try to reduce or eliminate that- then you can focus on using a lighter unsprung weigh toatl rear assembly.

We know that a Tqarm will lift the chassis in acceleration. Where it lifts at is where the length of it attaches to the chassis. The shorter the TqArm the more it will lift towards the rear of the car and produce more antisquat under hard acceleration. It promotes tire bite. No on the reciprical, the shorter Tqarm will rotate downward in thrust on hard braking and pull the rearend down (which in turn pulls the axle up and causes less pressure on the rear tire contact patches.. As the weight is pulled down the car has to rebound from that in spring recoil reaction pushing it back up, and grip pulls it back down again through Tqarm leverage- this causes one type of brake hop. Note a shorter Tqarm helps reduce the "rear jacking effect" these chassis are notorious for- but at a price of brake hop. THus you can get away with using stiffer rear springs and a lower rear roll center and not have bad jacking when those rear spring release energy under chassis motion from front brakes. The lower rear roll center keep the roll axis front to rear down in the back- so any motion of lateral roll will help keep the inside rear tire weighted better under hard braking into turns- its the straightline braking we more worry about.

So the shorter twarm allows you to use stiffer rear springs? yes. The stiffer rear spring would normally jack the car under braking becasue the Tqarm was too long to pull the back down and hold the stiffer rear spring from jacking under braking. Too shirt a TRarm now gives you the reverse situation. WHat is a good length? a happy medium- only found through testing- testing needs to be done individually on each different car with each different set of variables of modificatiosn and weight issues.

This is where we now focus of the 2nd culprit of wheelhop- poor LCA geometry aids to it also. Just as an inverted (higher towrds the rear) LCA will cause wheelhop under acceleration, it will too cause wheelhop under deceleration if the rear angles too much down also. Some front nose dive of the car is good- to much makes a cars attitude change too much and is hard to control. Nose dive gets the CG moving more into the spndles rather than over them (in a sense of 'direction of motion'). This squat reduces the strut length antilift leverage I talked of in prior posts The shorter the overall strut length from spindle to top mount point, the less leverage that weight transfer will jack the rear of the car under braking. ALso the lighter weight progressive rate springs will also reduce forcing the rear chassis weight up as their rate decreases when they relax towards free height.

Weight placemetn on a car is critical. The very best feature a 3rd gen can probably have in chassis weight reduction "in my belief" is replacing the heavy latch glass with lexan to get rid of that heavy upper rear wieght bhind and above the car's cg. yes the Cg will lower, but the overall weight that wants to transfer over it in polar movement is greatly reduced so the overall chassis weight is brought closer to the pole of CG in braking.

Catch22? yes, you have now reduced the ride ratio of sprung to unsprung weight which will give a more poor ride quality. Add dynomat to the lower floorbaord to make up for it and aid roll weight under the lateral cg- just another tip. THere are tons of gives and takes, it is wheat makes each car the owners personal choice and outcome. Knowledge is power.

Do posts like this frustrat people? I am sure it does discourage alot of people. It take work to dial in cars, and it also take work to keep a car fast on a track with ever changing conditions and equipment.

paul_huryk

First of all, third gens through the years have shown that a wider wheel and tire does increase grip - especially in the corners. The change from a 215-65-15 tire to a 245-50-16 one from the factory is a large factor in the handling of a so equipped IROC or WS6 Trans Am. Ditto for the SLP Firehark which used very heavy 17" x 9.5" wheels to mount a 275-40-17 all around - another large leap in cornering grip. The cars respond to wider tires like few other cars - a combination of the simple suspension design and ability to improve the factory suspension parts.

It has been proven a few times that lighter wheels and tires can help acceleration, help handling, extend the life of suspension components, and even affect gas mileage.

But is the lightest, most exotic wheel and tire combo worth it? Depends on the application and strength needed. For example, Dymag carbon fiber wheels are ultra light, ultra expensive, and also ultra fragile on the street - there have been countless wheel failures under a 3200lb Porsche that may not happen in a 1000lb lighter car under the same conditions. Also - is the extra strength of say a fully forged 1pc lightweight wheel necessary (they are stronger than a 3pc, but not as repairable) under anything other than maximum effort cars on the track? I can't say no to that, but $800 and up a corner would stop me from pulling out my plastic on a $10k car CCW, Fiske, Forgeline, Jongbloed...).

As a manufacturer of wheels (CTW Motorsports), we understand the balance of weight, strength, and brake clearance (proper fitment is a given ). For example, the 16" factory wheels vary in weight and also brake clearance depending on design. Another example is the Ronal wheels that SLP used on the Firehawk - it fit a 275-40-17 tire, but were 26lbs each and won't clear a lot of modern brakes. Ditto for TT2's and a lot of aftermarket 17" and larger wheels that fit the cars.

Taking all of that into consideration was something we tried to accomplish and not have to charge $4k a set for; thankfully our wheels came in at 20lbs, can fit most 14" brake kits, and cost around $1,100 a set. Strength-wise they certainly won't compare to a 1pc forged wheel using the best alloys - but unless your car pulls over 1.75g, you probably won't need them anyway, BTW - their strength is compareable to rotary forged wheels.

Suspension geometry is a concern, but quite a few issues can be improved or resolved with modern aftermarket parts and/or some home brew engineering. Most street cars that aren't too low and have a well balanced suspension would be affected at a pretty small level - race cars are another story altogether.

One item I want to point out is tire sidewall considerations - the trend has been to make that smaller in the last decade or so and it affects how these cars handle. First - the suspension is pretty simple and needs more sidewall cushion than a modern car with 4 wheel double wishbones all around. Second is the weight involved with a larger wheel diameter, which increases with size - thicker spokes, more cc of metal in the barrel.

The point of no return (on a third gen) of grip vs weight vs brake clearance vs cost is somewhere around the 275-40-17 sized tire from what I have seen with actual testing and also from people who have used them, myself included.

SlickTrackGod

I would closely agree, but with a 245/45-17 up front. The 275 will rub and will also wear out quicker on the street for handlling AND longevity having to run it on a wider wheel.

TEDSgrad

iTrader: (4)

That's an excellent suggestion
Maybe Paul would offer a second choice of front wheel to compliment the current set. Maybe even account for say .3" for BBK.

paul_huryk

Under full lock, our wheels rub - but so do stock 245-50-16 tires on OEM wheels. Never had a problem with rubbing on the street, neither do my customers (that I have heard of).

There is no real advantage of running a 245-45-17 tire over a 245-50-16 one except for brake clearance. Sure you may have a bit less tire squirm with 1" less sidewall - but on a front heavy car, you want as much rubber under there are you can fit reasonably. Even BMW 3 series with 50:50 weight distribution handle better with 255 tires under all 4 corners than the 225/255 factory stagger.

Can't comment about the longevity.

paul_huryk

Our wheels work with both factory brakes and BBK that push the wheels out a bit.

It makes no sense to offer a wheel with a 0.3" different offset - so we made it fit both scenarios; unlike SLP that used a Brembo specific offset on their Firehawk wheels that required spacers to use with 1LE or other factory brakes (if you bought them loose for your own car).

TEDSgrad

iTrader: (4)

Lack of Grip in 16" tire options are forcing us guys to 17," then we scramble for fitment options. Like your set, Paul, but drop spindles keep me to 8" wheel. I have considered 8.5" and go 255 like you just mentioned. I'm nervous about being that close to the tie rod for just that little amount, but it might be a possibility.

paul_huryk

I see now what you are talking about! Cars with stock suspension items can fit the wheels no problem - have had the wheels on at least 6 or 8 cars here at the shop and not one hit anything on the suspension up front.

What is the backspacing you need to get an 8" wheel to fit in? That would help me to guestimate if the wheels are a no go from the start.

We are looking into an 8.5" wheel for the front of the 2nd gen cars - may also fit the last g-body generation also...

RTLACY

Just out of curiosity and before I install the drop spindles, what would the trade off be if using stock spindle - thus tie rod clearance - and a much wider 10.5 to 11" tire?

paul_huryk

You can fit a 10.5" width in front - if you have an 18" or larger wheel with the right BS. Drop spindles may prove that not possible though.

TEDSgrad

iTrader: (4)

10.5 is big! Paul's 9.5 giving you 275 is excellent especially if you drive on street. You would have to ditch the drops and get extended ball joints. I like the drops, but it limits, but I can live with it and the discussion, here, confirms that.

Paul, I'm still running the stock formula deep dish rims. Stock offset is fine.

RTLACY

Paul,

Do you feel the wider wheel makes up for using a stock height spindle? I definitely see the advantages to lower the car 2" with minimal bump steer issues.

Ray

87350IROC

iTrader: (2)

I am by no means a suspension expert but I will add some info on tire width. Conventional "rigid body" dynamics suggests that the amount of lateral grip is based solely on the weight on the tire and the coefficient of friction between the tire and road. In other words, tire width makes no difference.

However, what we must realize is that tires are not rigid bodies, they "easily" deform. Based on the SAE test data that I have seen, it suggested that doubling tire width would provide 15% more lateral grip for the same car and same compound tire.

So this suggests that moving from a 245 width tire to a 275 width tire would net roughly a 1.7% increase in lateral grip. Certainly not bad, but not earth shattering either.

John

TEDSgrad

iTrader: (4)

Ray,
It depends!
I'm married to low unsprung weight. Tubular a-arms, alum hubs, 2 pc rotors, and 6pot narrow calipers - they all fit under my stock deep dish rims. If my desire was to go wider when I go bigger (17's), I might have made different decisions on the brakes. Then I'm seduced away from my commitment. My brakes are great - needing bigger and better is not necessarily the truth. Same goes for wheels - where is the diminishing returns line?
Paul is serving the largest base of customers - good thing for a business. When most people go bigger wheels, they also go wider. This discussion debates that course of action - grip & weight. As a business, you have to follow the customers. I'm in the minority for my commitment to unsprung weight. Not everyone needs/wants to go to my extreme. Both Paul and Dean are close in their advice with the exception of the front. Add brakes/rotors in the mix for weight, too. If you have great brakes that are small, why add big wheels? not for fitment!
I don't see drop spindles as a negative by any means, and they fit into this discussion; as so many have discounted them because of this fitment issue. Since Dean landed on 17x245, drops fit with his recommendation. With Paul's 17x275, you'll have to go the extended ball joint route (a solution, but not better than drops). Majority of people would go this route and Paul was right to serve this larger group. Then, we'll have to debate weight and suspension articulation - but again, most would never need/want this discussion.
I don't find this discussion frustrating at all. When I uncover more reasons to support the course I've already taken, I'm happy, even with snow on the ground!

Brian

paul_huryk

John,

Indeed cars are not rigid bodies and neither is anything on cars, everything deflects and pulls you away from the optimum, including aerodynamic lift.

But I will say this regarding street cars - you can typically get back 20 to 50% of the increase in tread on the ground in terms of handling - and in the case of the third gens on the street, it runs about 35 to 40% believe it or not. Tests have shown a 0.03 to 0.05g increase in lateral grip by going from a 245 to a 275 tire with either stock or modified suspensions. Some cars with very advanced and compliant suspensions show more like 20 or 25% improvement.

Check this out - not the same tires, but still an indicator:

http://thirdgenfbody.wordpress.com/2...eptember-2003/

paul_huryk

Ray,

As I don't have a car with drop spindles, I can't comment on that.

But the third gens do respond very well to wider tires - stock suspension or heavily modified. 120mm is a big jump in rubber on the ground for our cars.

My cars are lowered about an inch each - partially to clear stuff and also to minimize the bump steer and other suspension issues that can surface with a big drop.

RTLACY

There is a lot of very good information in this thread. Thanks to all of you for helping me decide how to proceed.

Ray

rlewi771

in a couple months I will have some data with regards to drop spindles vs. a wider tire. I have ran numerous road course events on my drop spindles, but will be going back to stock spindles this season and running 295/30/18 Hooiser R6's on all 4 corners. I have run very consistent lap times in the past and look forward to seeing the difference. I am predicting a significant drop in lap times. I am aware that it wont be a "controlled experiment" and there will be other variables that can affect lap times, but if nothing else, i'm sure the seat of my pants combined with lap times will have an opinion on which setup is faster.

87350IROC

iTrader: (2)

Excellent. You were running R6's before as well right?

To be honest I don't think anyone here can really argue if the larger tire + all the other goodies (extended ball joints, bump steer kit) or the drop spindles and a factory sized tire is actually better.

It will be really interesting to see your results.

rlewi771

No, I was running the Nitto Nt01's which is a 100 treadwear tire. 245/50/16. I probably went through 4 sets and had nothing but very good results. So yes, tire compound will be a factor as well in the change, but fairly close.

Now if only the weather will change and we can get out there and burn some rubber!

SlickTrackGod

Paul, in all due respect, that article even states they took "aged Pirelli tires on stock rims' and tested them in lateral grip agaisnt a brand new 275-40-17 performance tire. I can not find what the old Pirelli is but it lt lloks like an old P600 H rated 400 tw tire that is probably 10 year old hard rubber at the time of the test.

Now to test a 245/50-16 KDW against a 275/40-17 KDW both new would not be hardly a difference if any- at most I will give you a generous 5%. especially since they are not talking about any alignment tweaks from factory specs.

Heck, if youtook the tires the other way around and put 10 year old hard and morn KDW's on the car compared to brand new maufaturer date Pirelli's, youd find almost the exact same lateral #'s- at most give up .02g' for poorer average perormance tire compounnd and tread design if the age of tires were reversed. The new 16" tire would outperform the aged and worn wider 17" tire hands down- ---and Ill put big bucks on that statement.

paul_huryk

Definitely apples to oranges, but 4 or 5% is a large difference - in terms of tires only, especially on the street. A car that pulls .95g on 245-50-16 tires would be able to pull close to .99g with just a tire change if this were true.

Why would GM have gone to a 275-40-17 on the later years C4 Corvette when a 255-50-16 do just as well; or a 4th gen with 275-40-17 over baseline 245-50-16? Same with the C5 Z06 vs. base C5 wheels and tires...

Grip is directly influenced by tire patch on the ground.

Pablo

iTrader: (1)

I did a very unscientific back to back on tire width. I ran 17x9 SS wheels with brand new kumho V700s - 245 front, 275 rear. Fastest lap time I ran at the local track was a 47.7

I then got a hold of the CCWs with used Hoosier R6s (not A6) 315 front 335 rear. At the same time I had to minitub the rear and put in a 6 point bar, changed the rear springs to 250 lb/inch, installed a dana 44 with 3.73 (vs 3.08 which I think was a better gear for the track actually, and the diff in the 44 quickly stopped working. I repaired it and can say that I think the functioning diff was worth maybe around .3-.4 or so) I also lowered the rear roll center (hence the 250 springs), and I shortened the wheelbase 1.25". - So, a lot of changes

I went back to the track and ran a 45.3 after playing with the sway bars to get it balanced out. The car had way more grip. I especially felt the difference on the only sweeping turn on the track. The difference in steady state grip was dramatic. I also felt like braking improved a great deal as well.

So not a scientific test but just some data. I will say that just going from garbage street tires to the Kumhos made a bigger difference than anything else. Huge difference would be an understatement.

Yes you can feel the larger scrub radius, driving on the street becomes a bit of a task. I'm working on tucking them in some more which is going to require a tie rod relocation which I'll do in conjunction with an ackerman fix.

TEDSgrad

iTrader: (4)

If we assume 5%, that's with all four changing from 16x245 to 17x275. It would be less with 17x275 on the rear for both cars, just a front difference of 245-->275.
I'm guessing but maybe a 2# difference in wheel/tire combo, here on fronts. Add drop spindles which save 3# over stock, and you have a savings of 5# per side. That really helps with articulation and contact patch. Then throw in all the numerous advantageous of the drops; RC, CG, nose dive characteristics - Deans weight movement into spindles mentioned above, brake zone improvements, you certainly are set up going into lateral grip well.

87350IROC

iTrader: (2)

Is that 3# lighter than an OEM spindle or an OEM spindle that has been modified for aftermarket brakes? A modified spindle is probably in the neighborhood of 10#. I can't imagine you could drop 3# easily. On the other hand maybe that is why we have someone here who has broken one.

I guess the question would be, which is better.

1.
- 17x8, with 245 tires
- 2" drop spindles

2.
- 17x9.5 (or 10.0 or 10.5) with 275 tires (or 285 or 295)
- oem spindles modified for a brake kit
- extended ball joint
- bump steer corrected
- lowered 2" on shorter springs

Now most of our setups are sprung pretty firmly with limited suspension travel. For this reason, I'm not sure the camber curve is all that important, and the extended ball joints should help.

I recon setup 2 will weigh 3-5lbs more. It is hard to say what the final result is.

IMO the choice of tire compound will be a lot more important than the differences between setup 1 and setup 2.

TEDSgrad

iTrader: (4)

Thanks John, as soon as I posted I thought I should have mentioned ext bj and mod spindle. 3-5# difference, taller springs, better nose dive still w/ option 1.

SlickTrackGod

need I remind everyone that I pulled a documented 1.07 g's (left hander, 1.04 to the right) on a 220tw DOT street tire in a factory sized 245/50-16 on factory 16x8 IROC rear wheels on all 4 corners. If I needed more grip I would not go larger width, I would go stickier tire compund. More width is a cost of unsprung weight as well as rotational weight which effects acceleration, handling and braking performance. You are all just focused on lateral grip. Get the car's unsprung weight low, the chassis weight bias closer, the roll weight more neutral from massive positive roll, and some good percise footprints that are very stable through calculated geometry both inside trak and outside track radius' and you have an wicked gripping car on skinnies. (yes I had good grip on the inside tires also because of my chassis weight tricks.

TEDSgrad

iTrader: (4)

No grip anymore in 16" tires forces move to 17". Dean, are you saying stay 17x8 on all four? What if your build approaches 500rwhp? Wouldn't a 9.5 on the rears make sense in this scenario?

Good reason to fit 6pot brakes inside factory wheels, though. Track days can see r compounds on those 16x8's.

paul_huryk

And I agree that is one way to go for added grip - stickier tires... In some cases.

But as an example the CMC guys all have spec tires in their series and are allowed only certain suspension modifications, so going to a larger tire (255-50-16 to a 275-40-17) is one of the few ways to add grip and stay legal. I'll also point out I am selling CTW Wheels to them as the 16" spec tire has been discontinued. These cars are not allowed any sort of non-stock lightweight suspension (or unsprung) items (except for BBK), so it is all about tire patch on the ground.

And even the 3rd gen chump car I am sponsoring is only allowed a 180 wear tire or higher (no rules on which tire), so they are going from a 245-45-17 to a 275-40-17 (on a 1.5" wider wheel) for more grip. This car is dominant in the region and should become even more so with the wheels (which are 10lbs lighter each too). I'm pushing them toward the Falken 615k or Nitto NT05 as they are the gripiest that the tire wear rating will allow.

87350IROC

iTrader: (2)

Based on the same SAE test as I quoted before, for acceleration or braking grip, the tire height is actually the more critical dimension as more tire height will make the contact patch longer which is the dimension where the grip is required. Just like for lateral grip we really only care about tire width. Think of a top fuel dragster. The tire dimensions are skewed to be quite tall. Granted there are other disadvantages to running a taller tire.

paul_huryk

I think the car companies have all moved to larger diameter tires due to that SAE finding (been common knowledge for a while actually) and also the load requirement and brake systems of modern cars (while still keeping a tallish sidewall for ride).

Dodge really started the trend doing that with cars on the 300 and Magnum, both 4000lb+ behemoths, then the Gen 5 Camaro and even the GT-R. All of these cars run tires 2 to 4 inches taller than our OEM 25.7" diameter ones. I don't think a 12" brake system is going to do much good on a 4500lb Magnum SRT8, neither would a 1500lb load rating per tire in a 245-45-17 size. So they increased the size.

I'd love to see what an aftermarket 22" fitment with street tires would weigh on a 5th gen, for kicks.

TEDSgrad

iTrader: (4)

3 Grip Factors:
1) Coefficient of Friction - tire to road surface
2) Size of Contact Patch - wide & tall tires
3) Vertical Load - weight and aerodynamic downforce

To achieve max grip, proper tire temp (pyro) and a certain slip angle needed (say, 4-10% range). So one should prefer the lowest possible slip angle while maintaining grip/heat in tires.
Heavier vehicles (weight and grip is not linear) & bigger/heavier wheel assemblies will kill grip, and bounce on road surface killing contact patch and its vertical load consistency.
What effect does same vehicle, different wheel/tire combo have on slip angles? Again, more unsprung weight but wider less aspect ratio.

SlickTrackGod

I think I am the only guy on here that focused entirely different on my build for handling. I keep unsprung weight light, and I also focued mainly on chassis weight and getting everything I could outside the alxes 9fore and aft) into the center of the axles and lower to help reduce polar weight as well as reduce the positive roll weight. I purposely added dynomate to my cockpit floorboard because it was heavy and weights the car low underneath the roll axis.

Also in yawing my roll axis with suspension geometry (especially the rear) the roll axis migrates rappidly toward the outside rear of the car with the progressive rate springs I used. THis makes for a heavier weigth of the chasss in leverage on the inside rear tire of the car (think of a teeter totter with the pivot moved towards one end). The longer side is harder to lift so yu have to push on the shorter side [Example: RF tire] in order to lift chassis weight off the LR tire.

Also withthe rear rc lowered, and the front rc raises a little with extended ball joints (both in direct comparison to the CG) the yawed roll leverage is also at more of an uphill lift to roll rather then an over & down motion in direction of advantage.

These tricks help keep weight on all four tires and not just focusing on making to two outside tires wider and heavier. Also- what happens when those larger weight percentage outside tires hit bumps or dips when set into a corner (not big ones, I mean even the littler road imperfections- they change the contact patch footprint and cause the car to slide. Less weight on individual tires with all weight more evenly distributed on four tires will make the footprints of each tire stay more stable. Stable is grip. When the load can corner on 4 tires rather than two, the car will turn faster, harder, and with less roll leverage. It will transition ALOT quicker- That car I had steered like a jetfighter. Trust me, I have raced(driven) alot of 3rd gen cars around tracks and nothng was nimble like the one I built- but it also was the only built V6 car you will ever see because everyone wants big hp. I do not care about big hp, I like big brakes and a car that will carry its speed. Said this before but I will repeat: Id rather have a car that does corner to corner 40mph-70mph-40mph, than a car that does 35mph-80mph-35mph. The V6 climbed 30, and braked 30, where as the V8 to do the same lap time would have to change 45 up and 45 down in speed making alot more work for the driver and chassis bobble.

SlickTrackGod

#4 and most impotant- Stability of the contact patches. A medium size aspect ratio will remain most stable over imperfactions because the sizewall can give a little to absorb it. The shorter sidewall will remain the same slip angle but willskip over the other side of the bump airbourne.

Best way I can describe the difference is like suspension bushings. you want ones that will articulate, but not be sloppy. A lower aspect tire is more like a urathane bushingthat has strain in movement. "Things need to bend a little, if they do not bend they will break"- this same priciple relates to tire grip. Ths is why low aspect tires that are narrow will grip to a point but then slip unexpectedly. A meduim aspect tire will not flex too much, but just enough to give predicabilty in grip.

You aht to remeber this fact- if a road where 100% perfect then the low aspect tire would win every time- but that at not perfect to the least. Even if asphalt dips a 1/4" in 5 feet and then bumps 1/4" in the next 10 feet (this is VERY FLAT ROAD) the tire is still hitting imperfections and changing weight load upon the contact patch. SOme of that is taken up with the suspeion and some of it taken up with the tire sidewall stiffness.

More on slip angles- my car also induced roll understeer very rapidly- why? to keep the rear tires closer in slip angles to the front tires for heat balance across the pyro readings

Th only reason cars like the vipers and ZR1 vette are running low aspect tires is becasue they are also very wide tires. The wider the tire the lower you can get in aspect and it will absorb the same as a narrower taller tire.

SlickTrackGod

I know Jasen Swindle (CMC champion)I have actually worked with him. He knows alot more on vehicle dynamics then most of the yahoos in CMC (att least back int he early 2000's(aprox 2002-3). Alot of those competitors where simply trying to copy eachother. I spent a day at the track talking with alot of them and going over their cars. I had my car there at the time and was only about half built- compared to how it evolved in by 2007. I had run my car (full creature comforts- full street weigth and street tires) the day before on the same track at California Speedway as the race tire CMC cars. From what I remember there were about 22-23 cars there and my lap times the day prior was faster in that little underpowered V6 then 5 (FIVE) of those CMC cars. I had run a 2:04 from what I recall, and the fastest guy in a Mustang was running around 1:54, but most the others were 1:58-1:59 qualifying times. I dod not have the brakes I later put onto it, nor alot of the chassis tweaks that came later. Alot of those cars were lighter than me also.

I learned alot more of this lack of knowledge when I got into NASCAR. It was unbelievable to me how everyone is picking everyone elses brains for chasiss setups and everyone is monkey see monkey do. The top teams are doing are own things and everyone else is in that mid group pack with all the same setup.

TEDSgrad

iTrader: (4)

Here's a visual from Ross Bentley. If steady state is 10 traction units per wheel=40; then cornering reduces overall traction but outside wheels increase. 36 number is just for visualizing not scientific.
So your induced understeer sets the outside weight xfer quickly, then the progressive springs start to resist -after that quick weight xfer.
Not so jarring with a v6, either.
Lower unsprung weight on inside tires will help keep contact patch better than wider/heavier wheel? I would think vertical load (spring & damper) considerations would trump patch width (at the dimensions we're talking about).

paul_huryk

That I fully understand from talking to some (but not all) CMC guys regarding CTW wheels - their knowledge of suspension is really based on the rules and keeping more or less what is working - not necessarily changing things looking for better handling. It seems like some of those cats can really drive and can overcome deficits in their car when compared to less skilled drivers.

SlickTrackGod

I do not agree with that graph at all. My first impression is weight- and the graph would be wrong because weigh does not dissipate in gravitaional force regardless of lateral force....
...but the graph talks about "grip" not weight- so even more wrong. Are we talking lateral grip? No, becasue the factors would be 0 not 10 at static straight line because we have no dynamic lateral force upon them. Also if we are talking static lateral grip (as if someone we pulling the car sideways dragging) each fator would have to be considered 100% the max on each wheel and the factors between each would be irrelivant (toss out the 10 on each all equal 40). The camber at static lateral "drag we will call it is usually about 2/3rds the contact patch for straight line friction reduction on a typical aprox race car spec tire(note that a tire will somewhat grow in diameter ffrom centricfical force -and thus the contact patch will narrow- at very high speed straight line. The poorer quality the tire structure, the more previlant) So put this factor at about 75% on the outsides taking into account for sidewall lateral distrotion slightly growing the contact patch from 66% while being dragged. The insides would do the opposite and reduce from 66 down to about 52% giving the same reverse effect.

Now put the suspension into dynamic loading of the suspesnion in lets say 3g ,2.5- 3* chassis roll and the suspension will set into camber gain (on a properly setup race suspension- in an ideal world) that outside tire will now gain to about 100% grip with the loading squish of the suspension weight, as well as the camber gain (without loading squish- tire PSI can be reduced to get the same footprint, or increased to reduce this. Now to the inside wheels- its all about Caster specs and camber loss in articulation and roll. The inside tire will release and actually aid a little in growing the tire contact patch, but the less load (even with chassis tricks, this inside load will never equal outside load, just impposible- but can be alot closer or further aparts based on chassis settings) can be as high as about 75% my estimate on an indy type car with a sight negative roll rate(this is where supesnion lateral connection points come into the chassis higher than the cg. It would staticly be higher, but dynamic load of weight even with negative roll will lift pressure off the insides and put it outward in centrifical lateral force thus lessening the wieght on the inside tires- the psi of the tires lifts the contact patch and makes it slightly smaller than the static size- -------now should we go to downforce or am I going to get alot of "my head hurts"-


That graph illustrator would have done better giving each wheel a weight factor of the chassis or a weight percentage, rather than trying to discuss grip. His chart makes no logical sense.

Brian- You are off track with this:
{So your induced understeer sets the outside weight xfer quickly, then the progressive springs start to resist -after that quick weight xfer.
Not so jarring with a v6, either.
Lower unsprung weight on inside tires will help keep contact patch better than wider/heavier wheel? I would think vertical load (spring & damper) considerations would trump patch width (at the dimensions we're talking about}

Induced understeer has nothing to do with weight transfer speed, it has to do with tire slip angle as lateral roll increases. We will always have some degree of positive lateral roll (unlike an Indy car discription above) becasue of how are suspension mount points come into our lateral chassis cg. The reduction of this postive roll rate slows weight transfer, but the car will still go into roll with grip. Its just that the inside tires will grip more before the outside tires go to full grip and then beyond to slip.

The unsprung weight part of the statement you missed also. I was refering to the uneven pavement will not shock load a tire to change the contact patch as much as a heavier tire when the pavement thrusts it upward on a bump. Less positive chassis roll AND less unsprung weight will account for the ABILITY to run lower spring rates. This will allow for the suspension to absorb more on each individual wheel and the tire contact path not deform as the suspension is hitting and unloading- hop[e that makes sense becase its hard as hell to explain in words.

Dean

TEDSgrad

iTrader: (4)

Prof. Sake, I remember at TEDS where most students would not risk their opinions or voice their thought processes for fear of being wrong and exposed in class. Some Profs. correct mildly, sometimes they do not. Better to be off track in class than...Thanks for correcting me!
I understand where I went wrong with unsprung weight part, and how the graph is not all that helpful.
I don't fully understand the induced understeer has nothing to do with weight xfer speed (speed yes, but still weight xfer is producing slip angle). The quicker one get "set," - find the proper slip angle - the better off you are to complete the corner. The speed of weight xfer is a positive - just not equivalent to "induced understeer." Maybe my choice of words were not the greatest, or am I still missing some comprehension, here.

SlickTrackGod

Roll induced understeer is simply put= rear wheel steer. So lets just go over basics.

The rear wheels on a solid axle can change direction based on the arch of the LCA attachment arms. When the arms are out at starightest point (parallel to the ground) they are at their longest geometry.

When both lcas are at the same angle thier is no thrust angle of the axle (this is ideal with a proper alignment, given the proper aftermarker adjustments with adjustable LCA's)

However, when the car body rolls, the rear swaybar will try and keep the LCA's the same but they still differ. If you can keep the LCA geomerty on the inside wheel to articlulate to where the INSIDE LCA stays parallel to the ground while the OUTER LCA archs upward towards in geometry from the chassis mount to the axle, this parallel distance between the mount and the axle vertical centerline will decrease as the axle on that side will be pulled forward more than the other side of the axle. This causes rear steer.

Now with rear steer, the rear wheel pointing towards the corner of turning will cause the car not to rotate as the car leans to set. It wants to hold the back of the car towards the inside of the corner. Roll induced oversteer would throw the rear of the car outward and would make it harder to recover- and ths harder to retrieve the car back to straight tracking becuase of increased momentum of the chassis. So whith that said, I hope you can understand how roll UNDERsteer will resist polar motion and allow the car to hold the rearend tight, as well as help bring the rear end back staight after steadystate and going into corner exit.

The added benefit of this is the roll understeer makes a little more slip angle beause of the rear wheel steering- just like how front wheel steering does this, we are matching the rear a little closer to the front rather than the rear being neutral with only load slip angle. The rear now has load and steering angle just as the front does so the footprints are much closer if veiwed from under the road.

Please read this- It will talk about slip angles and slide angles. Remember also that the inside of the car is better weighted when the overall car gets to set mid corner chassis roll. To best example this, lets say if most cars did 100% outside and 60% inside, mine was doing 100% outside and 75% inside

http://www.mgf.ultimatemg.com/group2...slip_angle.htm

SlickTrackGod

To continue the discussion in the above post-

The last example of the 100% outside and 75% inside senerio as opposed to the 100% outside and 60% inside would be related to contact patch size at steady state. TO increase this outside contact patch size you would have low tire psi. To decrease it you would have high psi obviously- so testing and pyro readings generally give the best psi rating when you see heat distrubuted into the core of the tire tread: outside/middle/inside readings. Higher readings on RF to RR would mean more load is being exerted on the RF of the car than the RR of the car so chassis balance is needed to bring heat to the rear. If you are experiencing wheel spin- this heat will build artifically raising rhe readings so testing needs to be done with proper throttle control.

Now lets take weights into those percentages- and we will see how those weights of the chassis affect load. We will try to transfer contat patch size into load figures just for educational purposes so it is better understood. This is not exact figures, it is simply an educated guess on my part. Ithere is no way to figure this exactly unless you drove the car with scales under each wheel at all times- which you can not- this is where data acquisition gear is optimum. On the fly pyros underneath the fenders pointing down on the tires is best (Like in top team NASCAR testing) but those of us in the real world pocketbook can simply best use a handheld pyro after the fact and not actually real time data in corner load.

Lets say my V6car had 3100 overall weight with a 54/46 bias (lets just pretend it lived in a perfect world in left/right bias to take that out of the equation to make this simpler- no driver weight) both front tires are about 837 lbs each (75% contact patch via psi and neg camber) in static load and both rear tires are about 713 each (85% contact patch via psi and camber)in static load.. A 3400 lbs V8 car at 57/43 bias is in comparison of 969 lbs fronts/ 731 rears (and alot more polar weight percentage of that is towards the front and rear bumpers- think of spinning you body with arms close and stoping spin motion compared to spinning your body with arms outstreached and stopping that motion. the 2nd is harder to start AND stop rotation.- this rotation affects slip angle stabilty and causes it to go into "slide angle" easier.

Now to dynamic laod weights.- My V6 car for example would go in 2.5* roll to set outside footprints at 100% load on LF and 75% load on RF in a right corner set.
Rears would go about 90% LF and 70% LR due to lack of comaber settings on a solid rear axle. NOW- considering how I yawed my roll axis and weighted my lower chassis- as well as my roll center static and dynamic heights as opposed to a stokc or even altered V8 car, This would weight on each wheel in mid corner set of about 957lbs LF/ 717 lbs RF and 802 LR/ 624 RR.

To compare a typical V8 lowered sightly without chassis corrections you will get about

100% LF/ 60% RF and about 90% LR /50% RR which would compare in tire load #'s of 1211 lbs LF/ 727 lbs RF and 940 lbs LR/ 522 RR.

You can see how radically different each tire takes a load on the V8 compared to what my little skinny tire lightweight V6 car was doing. Its why I could pull 1.07 g's on street tires becasue I was distributing weight more evenly on all four tires. I was using all the tires better in the corner rather than adding wider tires and just using the outside tires for more grip.

SlickTrackGod

Seeing is believing-

Watch the end of each of these Video's. First is me on 245-50 16's all around, the second is a car on lightweight 11" wide sportlines in the rear with pretty much brand new summer performance tires (I think Mike ran Michelin Pilots- I can't remember). My tires were already otwo years old and worn- and actualy replaced the next day (Goodyear GS-D3's). The end of the runs across the finish line will show how controlable the cars differed. Mike is a very good driver- We have driving the "same" car on a track identical times on several occations. He is a very god driver. The difference was chassis setup and tire weighting. His tires were much wider and newer so he "should have" had the advantage if everyone thinks wider is the only better (wider is better than skinny- but its not the only way. This shows how skinny beats wider by using better use of chassis loading on skinnies)

SlickTrackGod

Alos note that this was in 2003-4 timeline. I was in development with this car. I had the Wilwood rears on it, but not the fronts, I had no made changes to the SAI, had not weighted the chassis to reduce positive roll (no race seats yet so no Dynomat inside chassis floor) and no front extended ball joints as well as the crappy heavier rear exhaust. Also no front alum bumper I later installed. i also later added that custom lower chassis brace as the stering brace spreader bar across the nose of the V6 and welded the STB 3rd point brackets from flexing. So alot of fairly drastic improvements were made still after this video.

Roostmeyer

iTrader: (3)

In terms of wider=better or not, a lot of times adding extra width adds scrub radius which causes caster jacking. This unloads the inside rear tire when the front tires are turned and causes inside wheel spin on corner exit. Changing the springs/bars to take understeer out of a car with wider rear tires will do this too.

stock front 16x8 is zero offset
CTW 17x9 is zero offest
z06 18x10.5 with 1.75" spacer, 6.25" backspacing. Works out to be 12mm positive offset.

So the z06 wheel'ed car has 1/2" less scrub radius and can fit another 20%-25% wider rubber under the car. Or you can take it to the extreme, and put an 18x11.5 CCW wheel under the car and have the same scrub radius as stock...

In terms of extended ball-joints or lowering spindles a strut suspension is always going to have a unfavorable camber curve. For a race car its easy enough to deal with, dial in more static negative camber and stiffen up the car to reduce roll. To fix the roll center mismatch its much easier to lower the rear roll center than to raise the front. I'm in favor of extended balljoints, but not if it keeps me from running a larger front tire.

Yes the larger wheel is going to increase unsprung weight, but barring a terribly bumpy course, the 20-30% increase in tire size should make up for it.