MPH picks up with 26" tires??

[3.8vsix]

I don't hardly understand why this is. I bought some 28 by 9 Goodyears and my best mph was 112, I then put on my nitto drag radials and my mph picked up to 115?? Was the 28" to much for my car. I have new valve springs since the sig below. Should I try some 27" tires? Thanks

 

[GREG O'Brien]

you'll typically lose mph when you go to a larger tire - and maybe even some ET... do the effective change in gear ratio and the effect of the heavier tires.

when it comes to slicks - you want the smallest, narrowest slicks you can hook on...

for example - if you have 28x11.50" tires - but can hook on 26x8.50" tires - run the 26x8.50" and you will always be faster as long as you don't have too much gear (over revving through the traps)

 

[RealFastV6]

Originally posted by GREG O'Brien
you'll typically lose mph when you go to a larger tire - and maybe even some ET... do the effective change in gear ratio and the effect of the heavier tires.

when it comes to slicks - you want the smallest, narrowest slicks you can hook on...

for example - if you have 28x11.50" tires - but can hook on 26x8.50" tires - run the 26x8.50" and you will always be faster as long as you don't have too much gear (over revving through the traps)

Not always true... Especially with Buicks. Because we dont make peak power at redline, often times we'll pick up going to a 28" tire, even though the car isn't reving out on a 26" tire.

 

[NCTURBOS]

Every car I have ever ran has always mph'd better with a radial tire. My guess is more due to the less rolling resistance compared to a "sticky" tire.

 

[ALBERTAN]

/me waits patiently for UNGN to show up...

 

[UNGN]

Originally posted by 3.8vsix
I don't hardly understand why this is. I bought some 28 by 9 Goodyears and my best mph was 112, I then put on my nitto drag radials and my mph picked up to 115?? Was the 28" to much for my car. I have new valve springs since the sig below. Should I try some 27" tires? Thanks

A couple points here:

1.) What was the tire pressure in the nittos vs. slicks?
2.) What was the weather condition differences between the slick runs and the nitto runs?

With your mods, 112 mph with 28X9 goodyears means something was off, and it wasn't the tire height. Given you 1/8th mile time and mph, your car should be running 118 mph in the 1/4.

28" tires are EASIER to pull above the HP peak of the same car with 26" tires so it usually will mph higher. The HP peak of a stock motored car in drive is around 90-95 mph. Above this point, if the car had 28" tires vs. 26" tires it will accellerate faster. This is same day/same track/same everthing else. Throw variables in like new valvesprings and apple to apples comparisons are no longer valid.

Should you try 27" tires? Sure. If you still have the 28" tires why not try them again?

 

[TurboDave]

My vote says stick with the 28's and get some more runs on them. Something else must have changed to account for loosing MPH when going up in tire size.
Track, track conditions, weather, density air, etc, etc, etc.

With your setup, you should have at least picked up some mph going up to the 28's.

 

[GREG O'Brien]

hmmmm.... i'm proven wrong then... so are you guys saying that even if you gear a car properly they'll still pull harder with 28" tires

*never* seen that to be the case with any of my turbo cars -- but i don't own a Buick so i guess there something I am not taking into account

i've typically seen a loss of MPH/ET, but a gain of consistancy with 28" tires in pretty much all cars until you are running deep into the 10's.

going back into turboford lurking mode...

 

[Ed Valvo]

How much timing is in your chip down low? When I ran 28" ET Streets and a street chip with low timing, my launches were disappointing. It acted like the 28" tall tires made the gearing too long. With higher timing race chips, it would blast out of the hole and my sun visor would hit me in the face.

 

[blackbuick87]

Greg since your car is a four banger it probably likes the rpms and addtl hp. Since ours are all about torque and not hp (peak hp with stock cam is 4400rpm ) they dont like to rev high. This is also helped by our rediculously small cams.

 

[turbov6joe]

I agree with the last response. EVERY turbo Regal or TTA I have seen that switched to taller (28") tires picked up in mph considerably! Now, as the last guy said, your 4 banger prolly likes the RPM when compared to our 6's that are good for about 6k rpm tops (unless it's a stage block or girdled or course)...My buddy with a 2.3 turbo in his Mudstang used a 26x9x15 slick and ran LOW 11's all day long. Put a taller tire on it and slowed down a fuzz...not enough torque...not enough rpm to make the motor happy!

 

[GREG O'Brien]

was that Sean from MC racing?

 

[3.8vsix]

My 60' times were off also with only 1.69 to 1.71, lanching at 10psi. When I had 26x10s my 60's where 1.59 to 1.63 range. The times above 1/8th mile times where in the 7.50 range at 90 to 91mph, which was a 11.90@112 with the 28's. My Chip is a precision turbo and engine, with 26 deg timing, and 110 oct. I have the tires sold, so I want some et streets or quick time pros. What size should I get?

 

[forcefed3.8's]

You will lose about 20hp at the wheels from the lower air pressure and non radial construction.

 

[3.8vsix]

20 hp is a lot at the rear wheel. That may be why my times where off with the 28's. The tire pressure was 15psi in the slicks and 25psi in the nittos.