In a previous topic about going with various rim and tire sizes that are considerably larger and/or wider than stock, several guys differed in opinion. I just wanted to start a new topic based on where we left off.

Check out the last statements!!

Steve91Z28 L98, I hear you man, and I understand what you mean, (the 17x9.5 / 17x11 setup definately looks awesome) but in terms of ride quality (during hard cornering) and that damn tire scrape, you've got to admit... having the right size rims with the right offsets and the right tires to go with them 'is to NOT go overboard with width for the sake of looking cool!

Maybe it's just me. I've seen guys with 11s in the rears of their thirdgens and it looks cool as ****! But those guys KNOW that they are RISKING THEIR RUBBER by LOOKING that good!!

I'm sure you guys know where I'm coming from. Now, CrazyHawaiian considered mixing up wheel sizes and his ideas are pretty cool. I'm just trying to help him see the downfall of going with a certain setup for the sake of looks alone.

p.s. Here's a photo link of a '91 Formula with C5 rims (17s front, 18s in rear). Like I said, LOOKS cool, but this guy's wheelwells probably chew on his tires periodically!
http://www.skulte.com/TmyhreC5rim.jpg
Check it out!!

Well what do you guys think? all replies are welcome! Thanks!

p.s. (04/25/01) I had to edit this! You guys were on me like flies on ****! LOL! ...but I really appreciated you guys doing that! Geez, I'll watch how I phrase **** from now on. Thanks again. nFORM91

[This message has been edited by nFORM91 (edited April 25, 2001).]

 

I think you have the relationship between tire size and handling backwards. Wider tires give -more- traction, so those cars with 275/40 or 315/35 tires will handle much better than those with thinner tires. In defining handling, I mean both steady-state cornerning (like a skidpad) and in transistional handling (like a slalom). Trust me, all of the world's car manufacturers don't install wider wheels/tires as an upgrade just for looks.

------------------
Greg Westphal
'87 IROC 305TPI/A4

 

Why would you say it handles worse? I have the 17x9.5 17x11 combination and the cornering capability is awesome. I will be using this setup for autocross events. From testing this weekend( on-off ramps at high speeds and a few Virginia Department of Transportation pylon courses) I'm very excited about this setup! More tire more grip.

 

forgot to mention, I have no scraping or interference at all.

 

Well the 17x11s come off corvettes which handle better than us....i believe vipers have 335/xx/xx in back...they handle better than us too...oh yea and my car handles much better with 275/40/17s in back and 245/45/17s in front than it did with the 215/65/15s that were stock...although I lost a lot of sidewall too but I do get much better grip

[This message has been edited by TwicK91 (edited April 24, 2001).]

 

More rubber=More grip.
More grip is good.
Larger wheel diameter=shorter sidewall
shorter sidewall=better response
better response=better handling

The only downside to larger/wider wheels and tires is that ride quality suffers, and of course the cost.

------------------
Karl Hunter
Hunter Motorsports
Vancouver, B.C. CANADA

 

I know that "wider is better". But, tire edges that look like minced meat at the end of hard slalom run doesn't make f*cking sense! (not to me anyway)

Guys, don't get me wrong, please! My point is simply; don't sacrifice your car's tires just to look good!

It's obvious that wider wheels and tires, especially wide, short-sidewall tires give better traction and handle better. We have all seen many cars (including FBodies) that had an aftermarket wheel/tire setup which may have been wider, but was for instance WAY OFF in terms of offset (or backspacing).

...WTF, the '91-'92 Firehawks are among my most favorite cars of all, they came with 17x9.5s and handle like a MOTHER F*CKER!!! (in case your're wondering... I'm saying that they handle VERY VERY GOOD!) There's a way of doing things right. That's all I mean!

In other words, if you do proper research on wheel and tire size comparison for upgrades, instead of just ordering bigass wheels and tires, you'll come out alot better on the performance end. Many muscle/sportscar owners lack this approach and as a result, their cars end up looking kinda cool with but handle like **** and their tires look like minced meat after awhile.

Would you let your wheelwells eat your tires just to handle alittle better?? and that's my point. Now, if you go back and read my first post you should see what I meant all along. In fact, I agree with all you guys who responded cause more DOES handle better.

p.s. ...perhaps I should've said 'this guy's wheelwells probably chew on his tires periodically'. Gotta admit though, those C5 rims do look cool on that Formula...

 

Maybe instead of "You OVERsized rim guys beware!!", your topic should have been "Choose the correct offset wheels and/or use wheel adapters to minimize tire/body interference. I have 17x9's all around (chrome 96/97 SS 5 spokes) with Bridgestone Potenza RE730 245/45's F and 275/40's R. Maybe I should trade them for some nice 15x7 rally wheels and 215/60's huh?

------------------
-Jason M. 1991 Camaro Z28

 

To add to my post in the other topic, the IROC that I have seen did not have any wheel rub or body interference whatsoever. The car looked AND handled incredible. Just ask the other guys on the board who have ZR1 wheels. If you get the correct wheel adapters then you will be fine. If your suspension is in good shape then there should be no reason for there to be that much travel in the suspension as to have the tires rub the wheel wells.

------------------
1991 Z28 - 350 TPI, T56, McLeod street clutch, LT4 pressure plate, Pro 5.0 shifter, ported plenum & runners, AFPR, Holley Annihilator ignition box and wires, Hooker shorty headers w/o AIR, Flowmaster muffler, homeade ram-air, SSM subframe connectors, Kenny Brown STB, Global West steering box brace, Steve Spohn adjustable torque arm and T56 crossmember

 

I don't believe anyone has any real problems with any 3rd/4th gen or vette wheels fitting properly and improving handling...some do need spacers tho...the only wheels I think look bad are those ones that people by from kmart or someplace where more than half the tire is completely outside of the wheel well...those have to make handling worse

 

I have a friend with a '95 Mustang and he has 315's on the back. The edges of his wheels are all chewed up. So this question is for Twick...is this OK for handling or is he just Polish?

 

well he is polish


[This message has been edited by TwicK91 (edited April 24, 2001).]

 

Jason M 91Z,... no, definately keep the SS 5 spokes and Potenzas, it's a great setup!

I know now that I should not have phrased the subject of this topic the way I did. It came off as if I was against upgrading our cars with wider rims and tires. and I did not mean it that way! I am all for making f-bodies better at what they already do great. Sorry if I gave the wrong impression.

I just can't stand to see an f-body owner who bought some expensive 17s or 18s without doing any homework on offset and correct fit. With tires sticking out two inches past the fenders. Some cars just look rediculous. But I'm all for more "meat" filling the wheelwells (and even alittle beyond the wells IF it's tastefully done!

Alot of tireshop guys don't give a **** what our cars end up looking like as long as the bolt pattern fits and the wheel generally fits the car (thus selling the wheel).

This is why I emphasize that we do some research and calculations ourselves so we can stay ahead of the game and have awesome results based on what we want to achieve for our cars.

I've got alot of respect for you guys on this message board and by reading your responses I see that many of you know exaxtly what you're doing regarding this topic of rims and tires and also have some awesome rides to show for it!

 

That's Trevor's (BLOWNWS6) Formula. He bought those wheels cause he got a deal from his boss who was selling them off his Vette. He has spacers and they fit fine. At first the outer side wall was getting scraped in the rear because of a metal "lip" that is on the inside of our 1/4 panels. After he rolled that lip in (basically just smoothed it out so it didnt protrude) they were fine. No more rubbing and bad a$$ looking C5 wheels on his Formula.

Also, C5 wheels werent meant for thirdgens and arent popular additions to them. With ZR-1 rims you can get perfect spacers that make them fit exactly.

Also, the 315's on the 17x11 ARE Viper size.

 

They might be sacrificing ride quality but cornering performance will go through the roof!!!!

You have NO clue what you car talking about. You are confusing "ride" with "handling". For example: A Caddy rides like a dream but handles like a boat, a 4thgen Z28 rides and handles good. A WS6 thirdgen will handle better than a stock 4thgen Z(not SS) but it won't ride better.

-Tas
'89 Formula WS-6

P.S. the '92 Firehawk had 17x9" rims all around.


305, TBI, auto, 14x3 chrome flat based open element with K&N, Milodon 160* thermo, functional Formula hood, cross-flow Flowmaster, '99z28 rear pipes and tips....

Soon to be installed:
Hooker 1-5/8" 50 state legal headers, Dynomax 3" I pipe (PN 44063 and 43248), Catco 3" cat, and injector spacer.

Super GRK_Taz World
F-Body Dual Exaust
EFI & Intake Options
AOL IM: superGRtaz


[This message has been edited by Tas (edited April 25, 2001).]

 

I believe I should step in here with a few comments based on the principals of physics. I may not totally have the right idea, but this is how I understand it:

First of all, Friction between the ground and the tire is nearly the same whether the tire is wide or narrow. The main purpose of wider tires (225s and larger) is to reduce heating and wear. Interestingly, functions such as braking, accelerating, and cornering are not affected by the contact patch, but the amount of wear those tires experience is directly related to the size of the contact patch. For those doubtful, get out your old physics book and have a field day.

Next, for those of you interested in increaced cornering grip, look no further than your suspension. If you minimize roll, lower the center of gravity, and strenthen the chassis, you will get suprisingly good results for the dollar...even with your 245/50R16s .

All other things equal, a 225 tire will allow nearly (incredibly near) the same cornering/accelerating/braking ability as a 335 tire...but if you go with a 225 just dont expect to retain that handeling capactiy for too long, as your tires will fall victim to premature wear.

Kyle

------------------
1990 Firebird Formula 350 speed density TPI; K&N, air foil, throttlebody coolant bypass, underdrive pullies, MSD 6AL, MSD HEI coil, 8.8mm wires, adjustable fuel pressure regulator, Hypertech Thermomaster chip, 160* thermostat, fan switch, B&M stage 2 shift kit, Edelbrock 1&5/8 headers, gutted dual cats, Flowmaster 80 series muffler, 3.73 posi rear end

 

Actually, the Viper's rear tires are 335 mounted on a 17" or 18" by 13" rim.

Matt


[This message has been edited by Matt_91RSTPI (edited April 25, 2001).]

 

dude is right about friction and our cars don't "need" big rims to handle well. I have a old book on handling and with a budget of $3000 they got an IROC to pull over 1G consistanly. They used 16x8" Momo rims and very good tires. Funny thing is that they had the same budget with a '89 Mustang GT and they could barely get it to stock IROC specs. yea for our team!

 

MellowYellow,

This same topic came up a few weeks ago I think. I agree that friction is always taught with no reference to contact patch, but rather with coefficient of static (or sliding) friction and magnitude of normal forces (perpendicular to the ground). I can't remember who it was, but somebody brought up the concept of "rolling friction" and how it differs from static friction. Now I like to think that there is something that they have not been teaching us with the book lernin, because I believe that wider tires handle better (ie: Indy cars/F1 cars). Been meaning to read up on this (and either learn it or try to remember it, depending on if I never knew it, or knew but forgot), but there is just too much going on around here since finals are next week.

Later,
MikeS

 

Man-oh-man... OK, (04/25/01) I had to edit this! You guys were on me like flies on ****! LOL! ...but I really appreciated you guys doing that! Geez, I'll watch how I phrase stuff from now on. Thanks again.

In a previous topic about going with various rim and tire sizes that are considerably larger and/or wider than stock, several guys differed in opinion. I just wanted to start a new topic based on where we left off.

Check out the last statements!!

Steve91Z28 L98, I hear you man, and I understand what you mean, (the 17x9.5 / 17x11 setup definately looks awesome) but in terms of ride quality (during hard cornering) and that damn tire scrape, you've got to admit... having the right size rims with the right offsets and the right tires to go with them 'is to NOT go overboard with width for the sake of looking cool!

Maybe it's just me. I've seen guys with 11s in the rears of their thirdgens and it looks cool as ****! But those guys KNOW that they are RISKING THEIR RUBBER by LOOKING that good!!

I'm sure you guys know where I'm coming from. Now, CrazyHawaiian considered mixing up wheel sizes like a C5 (17s in front and 18s in the rear. His ideas are pretty cool. I'm just trying to help him see the downfall of going with a certain setup for the sake of looks alone.

p.s. Here's a photo link of a '91 Formula with C5 rims (17s front, 18s in rear). Like I said, LOOKS cool, but this guy's wheelwells probably chew on his tires periodically!
http://www.skulte.com/TmyhreC5rim.jpg
Check it out!!

Now, that's the way it should have read all along.

nFORM91

 

Kyle, good point! kinda ties in with my thoughts of having a car that handles superbly without having the biggest, widest rims and tires and (in some cases) looking utterly rediculous.

I always believed that lowering the car's center of gravity and giving it some notable suspension upgrades in combination with lighter, correctly fitted wider rims and tires would bring out the car's optimum handling performance. All while looking professional (like the owner knew what he was doing before investing all that money).

This is kind-of a touchy subject, because what's cool to one guy might be regarded as BS to another. Cool looks, great handling, and the many variations and opinions thereof, just tells me that this topic is quite subjective.

Hey, just have fun with whatever project or plans you have for your car! If anything, at least you'll appreciate it ...and that's all that really matters.

 

Maybe I'm dumb but this does not sound right. Can you maybe explain a little better.

It seems to me that a given area of contact will be able to handle a given ammount of force before it begins to loose traction... If that area changes, the ammount of force that it can handle should change proportionally.

A practical example would be a drag car that overpowers a set of 8 inch slicks can step up to a set of 10 inch slicks made of the same compound and short times will improve as a direct result of contact patch.

------------------
1988 T/A,
9" Ford, 3.50 gears, Auburn posi, 700r4 -w- 2100 converter, 360ci, 9.8:1 cr,
AFR 195 Heads, Weiand #7525 intake, Lunati roller 219/227, .479/.480, 112 LSA
Holley 700cfm 4bbl on TBI truck 7747 computer and chip by Howell-EFI

 

That is exactly what I have been wondering. It is common knowledge that more rubber=more traction, but I can't prove it by anything I've ever been taught in school. All the books point to Kyle being right about this, but it feels so wrong! All I can come up with so far is that as the contact patch grows, the weight of the car is spread out over more so effectively every square inch of tire on the ground has less force holding it to the road. Now I know that the force (weight) has an effect on friction. I just want some math to back up my gut feeling here.

 

This is a quote from Serway & Beichner's "Physics for Scientists and Engineers" 5th Ed.

"The coefficients of friction are nearly independent of the area of contact between the surfaces. To understand why, we must examine the difference between apparent contact area, which is the area we see with our eyes, and the real contact area, represented by two irregular surfaces touching (Picture two saw-toothed surfaces on top of each other)... When we increase the apparent area (without changing anything else), there is less force per unit area driving the jagged points together. This decrease in force counteracts the effect of having more points involved." Pg. 133

Sounds to me like the only thing that is improving the "grip" is the that the force per unit area is decreasing. The actual force of friction is not changed.

Hope this sheds a little light on the debate.

Dale

------------------
The Bird
1986 FireBird
2.8L MPFI
Gutted Cat, No muffler (Sweet Sound)
Was 700-R4 --> Now T5

[This message has been edited by 86Chicken (edited April 26, 2001).]

 

As I stated previously, "I might not have the totally right idea," but after reading 86Chicken's response, I think I have a soloution:

I still believe that the main purpose of using a wider tire is to reduce heating and wear, as the loads of driving distributed over a wider contact patch are smaller per square unit than a tire with a smaller contact patch.

However, I can conclude by the same token that the same force of acceleration/braking/cornering distributed over a wider contact patch will demand less performance per square unit from the tire than a tire with a smaller contact patch. Therefore, all things being equal, a tire with a larger contact patch can handle more load than a tire with a smaller contact patch before a loss of traction occurs.

Whew!

I correct myself and clarify thing for others at the same time. Isn't this board great?

Bear in mind, however, that it is very inefficient to slap big rims/tires on a car unless you have a finely tuned suspension, as body roll will cause inside tires to lift, reducing your overall contact area.

Anyway...Its been fun, guys!

------------------
1990 Firebird Formula 350 speed density TPI; K&N, air foil, throttlebody coolant bypass, underdrive pullies, MSD 6AL, MSD HEI coil, 8.8mm wires, adjustable fuel pressure regulator, Hypertech Thermomaster chip, 160* thermostat, fan switch, B&M stage 2 shift kit, Edelbrock 1&5/8 headers, gutted dual cats, Flowmaster 80 series muffler, 3.73 posi rear end

 

MelloYello, you must've been reading my mind! Your highly intelligent, distinctly descriptive and inciteful explanation of how the relative element of physics and it's comprehension is pertinent to our understanding of even the most basic concepts of automotive performance handling ...utterly astonishing!

LOFL!!! I'm sorry guys... I just couldn't resist! Hey Mello... I aint making fun of you man, just havin some fun with that. Some guys on this board are so damn good that what they say sometimes goes over your head.

 

Ouch, man . Anyway, its not like I relish in adjectative/adverb use, but when I need to say something, I prefer to use a few clear words to describe what I am trying to say rather than rambling. Language is a wonderful thing, and I use it to my advantage.

Also, I just thought I'd mention that I just recieved my Jamex 1.5" lowering springs - $99 - (probably none left now, as when I ordered them over a week ago I got one of the last 6 sets). Now all I have to do is save up $419.00 (quoted by www.shox.com) for my Bilstein sport shocks and struts and I'll be set to corner (Spohn stuff comes later)...All on my FACTORY 16x8s mind you .

------------------
1990 Firebird Formula 350 speed density TPI; K&N, air foil, throttlebody coolant bypass, underdrive pullies, MSD 6AL, MSD HEI coil, 8.8mm wires, adjustable fuel pressure regulator, Hypertech Thermomaster chip, 160* thermostat, fan switch, B&M stage 2 shift kit, Edelbrock 1&5/8 headers, gutted dual cats, Flowmaster 80 series muffler, 3.73 posi rear end

 

"When we increase the apparent area (without changing anything else), there is less force per unit area driving the jagged points together. This decrease in force counteracts the effect of having more points involved."

If I read that right, it is saying that grip would be virtually independant of contact patch. With a larger area of contact, each point (on an atomic level at the most detailed) has less force driving it towards the ground, reducing the frictional force per contact point. Sounds to me like this theory says grip would be the same for wide and skinny tires. Wide ones have lots of contact points, but less force per point, while skinnys have few contact points but lots of force.....resulting in virtually the same about of frictional force.

could be wrong though,
later,
Mike

 

NOOOOOoooooooooo!!!!!
go here: http://www.ws6.com/f-bodygp.htm

------------------
-Tas
'89 Formula WS-6

305, TBI, auto, 14x3 chrome flat based open element with K&N, Milodon 160* thermo, functional Formula hood, cross-flow Flowmaster, '99z28 rear pipes and tips....

Soon to be installed:
Hooker 1-5/8" 50 state legal headers, Dynomax 3" I pipe (PN 44063 and 43248), Catco 3" cat, and injector spacer.

Super GRK_Taz World
F-Body Dual Exaust
EFI & Intake Options
AOL IM: superGRtaz

 

MellowYellow, I'm glad that you have a sense of humor and didn't take offense to my last post. BTW, sounds like you've got a good lowering plan for your Formula!

I'm lowering my '91 'Form this Weds., 05/02! I Already got my Eibach Pro Kit and KYB struts and shocks. I'll post pics when the work's done. I'm also running 16x8 T/A charcoal Diamondspokes. Hope to see pics of your car too when it's ready!

[This message has been edited by nFORM91 (edited April 27, 2001).]

 

I believe we have all our info FU@Ked up. What you are saying is that the more weight you have, the more grip, this is totally true, but what we are failing to take into account is cintrifugal force. more pounds per square inch of contact equals more cintrifugal force per square inch, cancelling out the extra grip and totally negating this theory, so what makes all the difference is the contact patch. I'm not a physics major, but none of us are. What do all of you think?

 

Some of us were. I don't know enough about the physics of tires to take a stab at the problem (I was more interested in atmospheric physics), but it's important to remember that introductory physics courses and texts teach the principles through examples using ideal cases with perfect non-deformable bodies. Systems in the real world are always many times more complex than the simple case in a textbook.

 

Ok, I lied. I'll take a shot...

Larger tires have increased traction, not increasted friction.

Physics textbooks describing friction use examples of smooth flat objects sliding over one another. They attribute friction to temporary "welds" between surface imperfections in each object on a microscopic scale, the size of an individual "bump" on the surface is insignificant when compared to the sizes of the objects. Also, the example ideal objects do not deform each other in any way. If you were racing with steel wheels on a glass track, then you would notice no difference in traction regardless of contact area.

Tires and asphalt on the other hand have surface imperfections on a macroscopic scale, the sizes of the imperfections are significant when compared with the sizes of the objects. These bumps are also large enough and the tires are soft enough that there is some deformation of the tire. The tire actually deforms around the bump and "pushes" against the side of the bump. A narrower tire has a lower probability of being in contact with a significant number of bumps in the road that it can push against than a wider one. Soft tires such as slicks also deform around the surface imperfections in the road more than hard ones, providing more push. The combination of this pushing force and friction is what we call traction.

[This message has been edited by Apeiron (edited April 28, 2001).]

 

Apeiron, that's basically the idea that I was thinking of a way to convey. Take the above sawtooth example. Unless I completely misunderstood it, bear with me...

Imagine two flat lines rubbing against each other. Then imagine one line as a sawtooth line rubbing on the straight line. The friction would be decreased because the actual contact area is reduced to just the points. But say the straight line was deformable (like rubber). It molds in and out of the pattern and provides more surface area in contact than just the straight line, thereby providing more friction.

You know what forget it. At 4:50am, I just don't have the brainpower left. G'nite, I'm goin' to bed.

 

anyone know who makes a 275 45 r16? i was told 275 was the biggest a camaro lowered 2 in can handle...preciate the feedback

------------------
1992 RS 25th anniversary..305 tpi conversion,slp headers,jet chip,3 inch flow master exhaust,3:73 richmond gears,big block style hood,80 degree tint,black outs,b&m megashifter,high rise spoiler,and much more.

Stereoioneer 8000R with organic screen,2 memphis 1000d amps(1100rms each) 4 memphis shp 12's 2 capasitors,audiobahn line driver,memphis crossover,stinger dry cell battery.

 

But what I want to know is why. With twice as much possible contact area you also have half as much weight per square inch, resulting in the tire not deforming as well. I have emailed Louis A. Bloomfield about this, he is a professor of physics from the university of virginia, so hopefully he can shed some light...

------------------
With this car, it's never a question of "can I...", only "will I..."!

 

Yes, but remember that the tire deforms in the other direction as it pushes as well. The tire exerts a force on the bumps parallel to the road. The opposing force to this one exerted on the tire by the road deforms the tire and causes the the tire to slide up and over the bumps when traction is lost. A wider tire exerts less force per square inch normal to the road making it deform to the road less, but the road also exerts less force per square inch in the direction of travel, lowering the tendancy of the tire to slip off the bumps.

If I keep thinking about this any longer I'm going to end up drawing my first free-body diagram in about 10 years.

[This message has been edited by Apeiron (edited April 28, 2001).]

 

Hey howzit nFORM 91, I just wanted to say thank you for all your help. I really want everyone's input on this kinda stuff cuz I want to go as big as I can but I dont want any weird adverse effects ... like weird treadwear on the tires, wheelewlls eatting tire (like you said), tires bottoming out really bad, or just plain crappy handleing. I just looked saw another post about 18's on front, and there is a guy in the UK who is running 18x9 in front with a drop, and no rubbing. I hope I can get more information about this setup!! If I can do it, I would like to run 18x9's all around. I'm even willing to bang out wheelwell!!! :P thanks again

------------------
--- Currently ---
Maroon 1989 Camaro RS
Crappy 305 TBI / Auto
Hypertech Stage 2 Chip (and 160/ThermoStat)
2.5" Pipes, No Cat, Flowmasters (Dual)
GT Grant Wheel

Planned: just tint!! (its a lost cause!)

--- Next Project ---
1992 Camaro z28 (5.7ltr / Auto)
K1 Interior Kit, Sparco Seats, Tweeded Interior, 6 pt Rollcage
TurboCharged L98 w/ internal work and T56 Tranny swap
Full Suspension (Eibach, Sphon, Undecided Shocks), Brake Upgrades (Baer), 18x9 Cobra R's all around
LOTS of bodymods and House of Kolor Chameleon II Black/Green Paint

 

Ok Apeiron, let's see if I'm understanding you correctly. Now, (in as close to layman's terms as I can get), the wider the tire's contact patch is to the road, the less deformation the tire undergoes while encountering bumps and other road variances hence greater traction, thus enabling more force (or speed) to be applied to cornering.

In other words, wider tires experience less 'stress' due to less deformation in hard cornering situations (basically, the sidewalls 'sway' side to side on the rim alot less). Wider short sidewall tires then obviously need the appropriate rim size to maximize their effectiveness (which is less sidewall sway and less deformation under cornering loads). ...by George, I think we've got it!

 

if i got 315's on the rear of my car, i would roll the under and inside edge of the fenderlip, then i would DECREASE the back spacing to get the tires kinda inside where they dont look gay and all sticking out....that way...they wouldnt ruin your sidewalls and it still "looks" cool....i'd only decrease the back spacing by about an inch or two.......

------------------
1991 RS LO3
mods: 14" chrome air cleaner, straight-piped after cat exhaust with one chrome dual tip on the left side.
future mods: headers, removing smog equipment, and as many cheap mods as i can find
aol s/n: budman8503

GONE MUSTANG HUNTING.......
BACK IN 10 SECONDS

 

Hey CrazyHawaiian! good to hear from you again! Listen, no wheelwell banging is needed if you do alittle research and correctly calculate the offsets and width figures of your new wheels.

Let's take a look. Alright, the 18x9s you want, size them up in relation to stock rim specs. Factory 16x8s for thirdgens (i.e., IROC rims/GTA rims) are a good reference and have 0 offset for fronts (which is also a 4-1/2" backspacing). Rears have a 16mm positive offset (which is 1" and a 5-1/2" backspacing).

OK... first you've got to have a basic understanding of 0 offset as well as POSITIVE and NEGATIVE offset. Backspacing, simply put, is the distance measured from the inside wheel mounting face to the back edge of the rim.

In simplest terms, 0 offset, means a center mounted wheel - the wheel and hub mount perfectly at the center of the wheel.

Positive offset, means the area where the wheel and hub mount is located closer to the OUTSIDE (thus causing a wheel to sit inside the wheelwell more).

and Negative offset means the area where the wheel and hub mount is located closer to the INSIDE (thus causing a wheel to stick out of the wheelwell more).Remember the old hotrod "Deep Dish" Cragars? That's negative offset out the &SS!!


I did the math for you based on an 18x9 wheel upgrade;

To make an already long story short you'll need the fronts to have a 4-1/2" backspacing.

For the rears, you'll need an 8mm positive offset (5-1/2" backspacing). These are spec to spec figures for an upgrade to 18x9" rims for a thirdgen f-body. CrazyHawaiian, please keep us posted. Good luck and hope I didn't bore you too bad explaining this.

 

Alright guys! I think it was so simple I never would have thought of it. For some reason, the whole concept of the tire deforming around and into imperfections in the pavement just escaped me. That's why soft compounds give better traction than hard ones. I guess I was wrong in equating friction with traction (although it does come down to friction on a small enough scale, with the deformed sections of tire grabbing and pushing against the "bumps" in the road. Thanks for pointing out my mistake aperion (sp?). Just one more question and then I think I'll give up on the subject....
the statement about less force per sq inch in the direction of travel lowering the tendency to slip off bumps....
This sounds backwards to me. Once you get down to this small scale, it would get to be more a matter of actual friction as opposed to the deformations interlocking. As the car is being accelerated forward, the wheel tries to rotate with the back edge moving upwards, tending to slide the deformed section of tire off upwards off of the bump in the road. Anyways, guess it doesn't really matter. I've just really enjoyed the discussion. And the picture i've ended up with in my head is like a fractal or whatever they are called, where the same pattern repeats over and over as you magnify it and look closer and closer at it. Each deformed part of tire is in turn deformed into more deformations that are deformed....ok, its getting late, back to studying for me. Later, Mike.

 

Well Guys, Its actually pretty Simple. Ideally, anyway.


Two Directions of Force, One Parallel To the tires width, and One Perpindicular.


Straitline traction and Cornering ( sorta )


Ideally, a Wider tire will yelid more friction, and therefor more traction, When the Force is perpidicular to the Width of the tires tread, IE braking and accellerating.


It will, however, not yeild any more friction IE traction when the force is parallel To the width of the tires tread ( contact patch )ex: car moving sideways ( wich happens more often than some of us would like to admit! ) haha

Now, Of course its not that Simple. Why ?

For drag, it essentially Is I suppose, Not alot of non-strait vector forces Involved, So a Wider tire is what You want. all force from lauch to brake is perpidicular to the tires tread width, So up to the point where No loss of traction is experianced, a Wider tire is desired (providing the increased friction at speed is not detrimental down the 1/4)

For Roundy Round, It all changes. Alot more Forces Involved, Rather, Direction of forces.

When Involved in Cornering, We are not simply Pushing our cars sideways. If we were, then any structurally sound tire, Of any width, would provide the same amount of friction. ( ignoring the molding theory's, wich is signifigant, but will get to that later) But we arent. The Front wheels are (usually, haha) Turned, What does this Do ? it changes the Direction Of the Force vector, It is no longer purely parallel to the width of the tread, but a combiantion of perpidicular and parallel, SO a Wider tire is beinifit, Because the effective width of tread perpidicular to the force is increased. Allowing the car to Turn More sharply Before it starts to Push

So, In theory, You could run Fat tires in front, and Really narrow tires in back, and corner just as well. Would have some trouble coming out of the turns However ( lets not forget that our rearends dont stay exactly paralell either, but that all Minute compared to the relative forces ) Also, Rarely in cornering is the centrifugal Force purely perpindicular to the centerline of the vehicle, Maybe if we drove Constant speed around a perfect circle all day, But we Don't. So You get forces going every wich way.


Now, All the talk about the tire moulding around imperfections in the surface is true as well, and adds to this. So All in all, a Wider tire is better. But Not For the reason's You may think. Of coruse, this is only up to the point Where the friction from that Increased Contact patch starts to actually slow you Down, as your motor struggles to Turn It at speed. Weight is also a Factor. Don't think this is signifigant ? Take a look at the front tires of any serious Dragster. The reduced friction Can be worth several tenths, even in the 13-14 second Range.


So, Ideally you want just Enough tread width On the ground perpidicular to the Force, To keep the Car where its supposed to be, at any given time and combination of Forces. Any more and your slowing yourself down, any less and your In the sand. But we don't have magically changing tire widths, So we have to come up with compromises, just like the rest of our cars composition.

Then there is coefficient of static friction Compared to that of "already moving" friction (for lack of a better term) Wich Comes into effect Once you start to slide ( Slide slide Slippity Slide, when your livin' In the city, its Do or Die )

Thanks, Coolio.

btw, Last semster i received an "F" In Physics 50, oops.


Oh, and A related Question, Whats the Widest tire I can fit on stock 15x7's? I saw a camaro with 265's and It looked Sound, But I have heard not to Go bigger than 235.


Lastly, tire composition turns out to matter More than tread Width. IE a better Tire is Going to give more traction than a Cheaper, Wider tire.




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60 Ranchero - Project ( Money Hole )
85 Sport Coupe LG4 - Daily Driver
Reader's ride -> My Ride

Just another Hot Rod kid, or thats what they all tell me.
Livin' the Stereotype

 

Ok, so this is what everybody has convinced me are the keys (in order of significance) for producing traction:

1. Tire compound..softer/stickier=more tract.
2. Weight of car. Friction increases
linearly with weight.

(ok, so 1 and 2 might be mixed up, I don't
really know).

3. Tire width...applies to traction through
the deformation of the rubber (see 1).

4. Got to add sidewall height. Tall walls
allow shifting of the wheel with respect
to the tread of the tire, letting the
tire "roll" off of the best part of the
tread pattern.

bort,
physics 50? what class is that/where is it?
Just wondering cause the numbering is so different than mine was.

Ok everybody, I'm sure nobody wants to hear it anymore, so I guess I'll stop now.

 

I am running 275/60/15 in the rear of my camaro. I think they might be slowing me down a bit because they are so tall. They look good with my new rims and my bump in the rear but do you think I made a mistake?

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'89 RS camaro: 305 TBI, 700R4. Upgrades: Edelebrock proflow air filter open element, Dynomax Superflow cat, Stage 2 Jet performance chip. 160 thermostat. New paint job.

 

San Jose State.




------------------
60 Ranchero - Project ( Money Hole )
85 Sport Coupe LG4 - Daily Driver
Reader's ride -> My Ride

Just another Hot Rod kid, or thats what they all tell me.
Livin' the Stereotype

 

YYyaaawwwnn... zzzzz... OH!! sorry! ummm, I think we all got the physics lesson now. I also think this topic is getting kinda old... FAST! can we move on now? Thanks guys

 

Its interesting Nform

If any of these topics ever Got old, I wouldnt have the car I have

I could talk about any aspect of my, or anyone elses car, Till You were blue in the face.

I guess that makes me Socially mal adjusted, Oh well !

( Ill be Socially Mal adjusted, In front of you! )



------------------
60 Ranchero - Project ( Money Hole )
85 Sport Coupe LG4 - Daily Driver
Reader's ride -> My Ride

Just another Hot Rod kid, or thats what they all tell me.
Livin' the Stereotype

 

Yeah, same here.
Love the car and what makes it work.
But I'll give it a rest now.

Mike
Ga Tech

 

What?!? ...uhhhh, I was talking about the physics lessons in this forum getting old! (and they are... to me). C'mon dude, read! I'll NEVER get bored with thirdgen stuff. Just save the intricate physics (lectures) for college.