FRMULA88

4.11 with 26" tall tire

or

4.44 with 28" tall tire

on paper these will both cross the finish line at the same RPM, MPH & ET.

6700 RPM
126.4 MPH
10.24 sec

The calculated ET MPH is based on a 3600 # car and 597 rear wheel HP


The question is do I keep my current tire size (26") and just change my carrier to a 4.11 and spool or also step up to the taller tire with the 4.44 ?


Is there any real mechanical advantage with taller sidewall on a car with a rear suspension?

To give the car the proper stance and a 1" more ground clearance should I make the front tires 28" tall as well?

Thanks,

Orr89RocZ

iTrader: (20)

Taller tire offers more contact patch for more traction.

Tires are easier than gear swaps, i'd go tires with 4.44

And true 597 whp traps closer to 135-137 at 3600

FRMULA88

I just used a HP calculator based on MPH & weight.

the number it spit out was 603 but I do not know if that is flywheel HP or WHP it did not specify.

But I don't really care because using another calculator and that value for HP my current gearing etc... I run my timeslip...


I need to check my dyno run to see how much HP (flywheel) I make at 6000. I know at 6700 thru 6900 we are at 668-669

so safe to say at 6000 rpm 597-600+ is very likely true.

FRMULA88

The point is I am leaving plenty of ET & MPH on the table with my current rear gearing
since I am crossing the finish line a little over 6000 rpm.

Dropping the gear to a 4.11 or 4.44 with the corresponding tire height should have me crossing the line at the top of my power curve, not the bottom.

By contact patch you mean the tire has a bit more circumference ? we are only talking
the difference in 2piRad between 26" tire and 28" tire seems like that is not much and splitting hairs since the tires are the same width. (10" wide) now if I tubbed / back-halved the car and put steam rollers on it that would be a different topic.

I guess after all these years I still prefer to be a small tire guy..

mw66nova

iTrader: (13)

it's more longitudinal contact patch, which spreads out even more at the release of the brake. it will make a difference.

that said, the 26x10.0Stiffwall m/t (3053S) looks cool as crap on a 15x10 and is what i'm trying to make work on my car. the 28 (3055S) is easier to make work.

Orr89RocZ

iTrader: (20)

I like the way 26" tires fit. 28" is talll and fills up well so much it requires alot of clearancing. Atleast on my lowered car.

AlkyIROC

The proper way to do it is to stuff the tallest tire possible under the fenders then adjust the gears to match the rpm range of the engine for those tires.

A taller tire has a longer contact patch on the ground. That means any point on the tire will be in contact with the ground for a longer period of time (dwell) which should create better traction.

I run 32" tall tires and wish I had the room to go to 33's or 34's but I already have enough traction to pull the front wheels sky high. Even on a cold unprepped track I have better traction that cars with smaller tires.

You spin, you lose.

mw66nova

iTrader: (13)

yeah, but that's boring. making a small tire work on stock suspension is so much cooler

DIGGLER

iTrader: (1)

seems like i was turning around 6800ish with a 3.89 gear and 275's. trapping 139mph.

articwhiteZ

iTrader: (56)

26" tall are sorta small looking. swaping to a 28" tall tire. every thing stayn the same.. i picked up 4mph
and it looked better..

i also stepped up to 29x13x15s now.

mw66nova

iTrader: (13)

well, looking better is subjective.

personally, i think this looks pretty slick

FRMULA88

I have Hoosier 26 X 10 slicks which are the same height as the
OEM P245 50 R16 tires that came on the car from the factory.

Personally I like the look of a "stock sized" tire.

There are plenty of cars running in the 7s on 275 drag radials and 10" slicks so it can be and has been done. So for my goal of low 10s a small tire seems reasonable to me.

Doing some quick math C = pi D

3.14 X 26 = 81.64

3.14 X 28 = 87.92

difference in circumference = 6.28"

The tire widths are the same so the only mechanical advantage I see is the 28" tire will spin slower which is why you need a lower gear to compensate.

Once you do that then both tires are spinning at the same speed.

If that is true what advantage is there? Both sizes tire are spinning the same speed and are the same width. So there is no additional contact patch, dwell time, or whatever "scientific term" you want to use.

To me it seems pointless to use are slightly taller tire that is the same width.

A much taller and much wider tire I can see making a lot more sense:
28" tires you can't go much wider than 26s, BUT with 30s and taller you can get some pretty wide tires. Then you are going to mini-tub and or backhalf the car to fit them. Not something I want to do at this time..

FRMULA88

It just looks right to me ! so why mess with perfection?

LOL

mw66nova

iTrader: (13)

the difference in circumference of 6.28" is what makes the taller tire work better/easier though. as a result there is more surface area on the ground since the area front to back grows with the larger circumference. since this increased area is also in the direction of travel, it helps with traction during acceleration.

does that make sense?

at the end of the day, making a car fast on a small tire is way cooler to me though.

mw66nova

iTrader: (13)

your key to making the smaller tire work sir:

Orr89RocZ

iTrader: (20)

There most certainly is an increase in contact patch on the ground. Not easily seen but there is. Taller sidewall also helps wrinkle action, even radials wrinkle some.

FRMULA88

You picked up MPH because you did not change the rear gear, the taller tire raised your rear gear ratio.

which probably means you had too low a gear with the shorter tire.

tire swaps are easier than gear changes, but it my case I need lower gearing since I already have a "small" tire I need to change the ring gear & pinion.

if I go to a taller tire... well then I just need a slightly lower gear to compensate.

FRMULA88

adjustable rear shocks, send me some more info.

I have been using Lakewood 50/50 rear shocks for years.

FRMULA88

yes it does on both counts..

but if 28X10 X15 fit I can try them out. they should look just fine and still a small tire by comparison.

My 26x10x15 are over 10 years old but plenty of life still left on them.
I suppose I got my moneys worth.



Dear Santa.. I have worked hard all year. For Christmas I want a Strange 9" aluminum carrier with 4.44 gears, 31 spline spool, and 1350 moly yoke.

A pair of Hoosier 28x10x15 slicks would be nice also but I can get those on Fathers' Day.

FRMULA88

Bench racing season has begun !

mw66nova

iTrader: (13)

they fit fine:



the shocks are vikings, i got them from UMI on their black friday sale for $170/each. they're normally $190/each so even at full price they're a steal. i hope to have results in early spring for everyone as they're still a new brand and not much exposure yet.

if youre tires are 10 years old, they're WORE OUT. not because the tread dept is gone, but because all the moisture/oils in them has dried out. i swap mine every season to avoid this. with the smaller 26x10.0 on the car now and the additional shock of the clutch, i may be swapping them even more often.

Orr89RocZ

iTrader: (20)

Good grief!! How do they still work at all? My bias plys after 2 years got hard and dry, burnouts needed to be longer and longer to get them to hook and eventuall they lost the ability. New set and practically no smoke burnout dead hook.

FRMULA88

Did you install taller tires up front to keep the stance of the car "even" ?

I think mine will look like a stink bug with 26s up front and 28s in the back.

my front runners are over 10 years old too.. LOL I have had this car A LONG time.

mw66nova

iTrader: (13)

no, i just have the back that low, lol. that's a 26" front runner.

time for new rubber man, don't want a front runner coming apart at speed on you cause ya let them get too old and dry

FRMULA88

no signs of any dry rot or stress cracks, but why take the chance.

New tires are a lot cheaper than paint and body work or worse.

Looks like Hoosier makes 28" tall front runners.. that will be the direction to take

plus the 1" extra ground clearance will be nice

mw66nova

iTrader: (13)

here's an old picture with 28's up front and a 29x9 on the back



this was before i saw the light and went to a m/t tire.

FRMULA88

no luck getting the Hoosiers to hook?

I have M/T 26x10 slicks
my fronts are Dunlop metric series radial

I need to check M/T website for sizes especially for matching height front runner

LOL I just replaced my front motorcycle tire last month.
it only had 8000 miles but was 19 years old and starting to show stress cracks (dry rot ) on the sidewalls.

the rear I replaced in 1999 because of flat. Still looks great !


you would not have those 28" front runner tires in storage would you? would you consider selling them?

paul_huryk

If you go by the pure math, a 28" tire will put about 7.7% more tire on the ground than a 26" one.

mw66nova

iTrader: (13)

no, i don't have the 28's anymore, lol.

the hoosiers just didn't have great longevity. after 40 passes i had chords showing.

mw66nova

iTrader: (13)

whew man, just looked, trim those rear coils down a bit!

1991sleeper

iTrader: (-3)

Do u think those 29*9's would fit a stock rear setup car ? No mini tub etc. ... I do have tubular LCA's and panhard bar ALL adjustable ... Why is the biggest street tire I could fit ? It's stock ride height with new moog springs also I have 18" wheels

mw66nova

iTrader: (13)

my car is not mini tubbed. i cut the bump stops out and bfh-modded the inner fenders till they cleared. car has stock width rearend with 15x10/6.5" backspacing.

DIGGLER

iTrader: (1)

i had a set of hoosier 28x10.5's. c07 compound. never had a problem with them not hooking. 1.30-1.33ish 60's usually. had about 50-60 passes on them when i went to a drag radial and they still had over half the tread depth left.

FRMULA88

I suppose I should trim the rear coils.

I trimmed 1/2 coil out of the front ones just to get them to fit, they were just too tall to compress and re-install otherwise.
Even the instructions said some trimming may be needed.

LOL, that was almost 10 years ago when I replaced the stock front coils with Moroso Drag springs. But I never trimmed the rear springs to compensate.

That is easy enough to do, this car still has the original rear springs I never saw the need to replace them.

FRMULA88

Or if I want to spend some money I can install this:


http://www.spohn.net/shop/1982-1992-...le-Shocks.html

then I can tweak the ride height and the shock rate..


otherwise Eibach has rear springs that will lower the rear 1.75

http://www.spohn.net/shop/1982-1992-...ng-Spring.html


it's never just one part is it.. but a combination...


seems to me the rear coil over is the best option since you can adjust ride height for any tire size..

mw66nova

iTrader: (13)

I just trimmed my stock rear coils

FRMULA88

rear coil overs are bit too much for now.

SO I will trim my rear springs also, how much did you remove the get right stance on yours ?

I should wait to trim them until I get my tire combination sorted out first.

then try some adjustable shocks...

mw66nova

iTrader: (13)

1 coil

85SILVERBULLET1

Sorry to hijack but how much of your rear coil springs did you cut out to get "the stance" That thing looks killer.

crap somebody else asked this. lol I got my answer.

FRMULA88

Sorry for reviving this tread, but I picked up a set of M/T ET Drags over the weekend.

They are 28x10.5x15 any issues with fitment in a stock wheel well?

M/T does NOT make a 28x10 tire.. BUT reading the specs I see this.

My old 26x10 tread width is actually 9.6 "
My new 28x10.5 tread width is actually 10.0"

The real difference is only .400 " so some massaging with a BFH or wheel spacers should do the trick if there is a fitment issue.

BTW I also ordered some new 29x4.5-15 front runners. These should help fill up the wheel wells versus the 26"s, but more importantly even out the stance and gain some much needed ground clearance. It's only 1.5" up front and 1" in the back but I will take it. LOL !!

This week I am going to remove the center section to see if have the "big" or "small" bearing unit (I don't remember) so I can order the new ring & pinion. Strange Engineering is minutes away from me, so I will give them a call to see if they can install the new parts on my carrier.
after doing some more calcs.. I think 4.30 is the one to use on my combo with a 28" tall tire but I will talk with their tech dept.

FRMULA88

update:

the 29X4.5s front runners were are big mistake, I don't know what I was thinking. They went back same day.

M/T does make 27.5x4.5 front runners and these will look just right and help balance the stance of the car, especially with 28X10s in the back.

On close inspection my 26x4.5 did have signs dry rot but it was between the treads..
so it was time to change them.. not a bad run considering I mounted them in 2001. I would say the lived a good life LOL !

mw66nova

iTrader: (13)

i wondered abou the 29.5" tall front tire but was willing to stay quiet and wait for results with them installed. i have ran a 28" hoosier on the front before. i prefer the m/t tires over the hooser now-a-days. i'd go for the 27.5" in a heart beat. might be worth putting on my car when i go back to the 28" tire.

FRMULA88

Yes it was a hasty decision but I ordered the M/T 27.5X4.5 fronts yesterday, they should be perfect with the 28s on the back.

I also dropped of my carrier at Strange yesterday for the gear swap. LOL, no UPS cost there, so nice that they are local to me. Looking at their catalog they make a front drag brake kit specific for 3rd gens with no mention of a "weight limit". so that is something to consider for upgrade next year.

I am still on the fence with doing coil overs. Once I finish this tire and gear change we will see how the car 60' and take it from there. On paper the 4.30 gear should be good for 132 MPH @ 6800 RPM in the 1/4, we shall see.

If I pick up 6 MPH and drop a few tenths then this was a must to optimize my setup.

anything after that is a "bonus"

TB2

iTrader: (1)

Would love to go to the 28x10.5 with a 4.30 gear. But the car spends a lot of time on the street. I run a T400, 3.90 gear and the stock crosslace wheels with 255/50x16 on the street. They are short! 26" tall at best. On the xway I'm in the right lane with the motor screamin away at about 35-3700rpm. So I have to compromise with the 26x10 slicks to go with the 3.90 gear for the track.

FRMULA88

BY memory I know 3.70 with 26" tall tire gives the same final drive ratio as a 4.10 with 28" tires.

so with a 3.90 and short tires you would be better off with taller tires for the street.

or just do the 4.30 with 28s because it t will be pretty close RPM wise to what you have now.. check out Wallace calculators..

1991sleeper

iTrader: (-3)

Yes !... All ur gear ratios are BASED on a 26" tall tire so 4.10's with a 28.5" tire are actually real close to a 3.73 with 26's ... so if u run a 26" tire u are getting the actual gear ratio u are running ... I run 4.10's with 29" tire and 3000rpm is about 92mph in 5th gear according to GPS on my phone

91' bird 305 TBI T-5, trick flow heads, 4.10 gears, full UMI setup, track times coming soon!

TB2

iTrader: (1)

Agreed. The problem is that you can't get a taller standard street tire for the Crosslace 16" wheel. And since the car spends a lot of time on the street, my drag setup has to work with what I run on the street. There are options, but I'm not really comfortable with any of them. And right now it is hooking good on a 26" slick and the gear ratio is not far to off from optimum.

FRMULA88

26" tall tires are fine but the taller tire will yield better 60' times.

I recall that 15"crosslace wheels were also made by GM. You could find a pair of crosslace 15s for the rear to run a taller tire.

There are ALOT more tires sizes available with the 15" wheel.
Just something to consider.

FRMULA88

http://www.ebay.com/itm/91-92-FIREBIRD-WHEEL-15X7-ALUM-DIAMOND-SPOKE-557817-/200856766348?pt=Motors_Car_Truck_Wheels&hash=item2ec3ff078c&vxp=mtr
you can always have the stock 15x7 crosslace wheels widened to make them 15x8..

another option is the 2nd gen 15X8 snowflake wheel.. which I think looks pretty darn
good on the 3rd gen.

FRMULA88

http://www.stocktonwheel.com/powder_coat.html

Stockton can narrow or widen wheels..