What will smaller tires do for me in numbers?

I am pretty sure everyone knows my setup, most of the details are in the signature.

What I want to know is, when the track opens back up, and I take off my 27" tall 255/60s and put on 25" tall 215/60s, what kind of ET improvements should I expect?

I was less than satisfied when I swapped from open 2.79 with stock 14" tires to the 3.80 spooled rear because I also went up to 245/60r15s. And it almost looked like I picked up no improvements...just canceled out my gear with larger tires. I drive 255/60 to keep the highway rpms low, but plan on going to the track this season with 26" slicks, and the 25" 215/60s and am wondering if I will see much improvement on my times.

Is there a general percentage rule to how much you gain by losing an inch of tire?

 

Scott, I honestly don't think you'll get those tires to hook (I hope I'm wrong).

You've done some pretty nice HP add-on's since last time out haven't you?

If they hook, I believe your 60' will improve but you will start losing that advantage passed the 1/8th.


Wait a sec : I see where you're going to be using 26" slicks anyway. Perfect.


I think there's a calculator out there on the Interweb that claims to tell you what rpm's you'll be running at the stripe. (I know, you hate using Google )

 

So, you think I will lose time with the BFG 215s due to breaking loose, but might make the time back plus some with the 26" slicks?

Cool

I just think that my car feels faster than the 14s car that it proves itself to be. Know what I mean?

My other fear is that the slicks will hook enough to crater my transmission

Which will give me an excuse to buy a decent one...

 

its going to be like adding a higher gear , like you have 3.80 now it would be kinda sorta like putting a 4.11 in it kinda

 

Here's a formula I got from TCIauto.com to calculate your optimum tire size. It's based on your estimated MPH and your desired RPM at the stripe. You can use 10-15% for converter slip and your trans ratio is 1.

Opt. Tire Ht.=(rearend ratio*MPH*336.136*trans ratio*converter slip)/RPM

I think the theory is that you're trying to stay in the power band of your engine throughout the race and especially at the top end. So you need to estimate (or know) your optimum power band...it's usually related to the cam/heads/intake.

I'm definitely no expert, just trying to help.

 

Found a calculator and found this.

3.80 gears with 27" tires at 5000 rpms is 106mph
3.80 gears with 26" tires at 5000 rpms is 102moph
3.80 gears with 25" tires at 5000 rpms is 98mph

so it looks like (for my setup and similar, at least) 4% increase per loss of inch per tire, at least in these ranges. Which calculates to approx 12 hp gain per loss of an inch.

I hope to try it out on the track and take all three sets of tires and actually do it and see what happens...

Just don't know if/when the track will open...

 

whats a moph?

 

you use a "moph" to get the doghair off the tile floor

I was going to correct that, but figured everyone would know what I meant, and decided to leave it alone.

I was WRONG

 

I run 26 inch tires with my 3.40 gears. My 60ft could have been better(best was a high 1.7 or low 1.8) My springs were to low in the frt. If it would bite, though you could feel it in the car. I feel I needed the weight transfer as I would blow the tires off otherwise. I needed it for a good plant. Car was so inconsistant as a result. Ran mid 12's one day ,mid 13's the next . Either way I feel the 26 inch slick will improve your time overall.

I tried some 28 inch slicks. It just bogged my car down......

 

i thought it was for removing the effects of to much boxed wine.

 

Fast

 

Sorry guys...this was a question that dealt with MY car with MY setup, with MY tires, with MY etc.

get the hell off of MY thread, unless you have info that will help ME!!!

sorry, need a chill pill

 

2000 lbs.
575 hp.
6500 trap spd.
27 in. tires


9.5 all day.

whats walter brennan say???? no brag, just fact!



or


3500lbs.
1200 hp.
8k trap speed
33 in. tires


8.4 all day




zzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzz.

 

i think your car should be in the 13.50s-90s

i think the such low compression is hurting you , around 14-1 should do you right

 

i dont care who you air... that right thar is funknee