Fast06Z06

I've heard so many different theories on this. Want some feed back from others. What is the relationship if any to changing your tire size to a smaller or larger overall diameter in mph in the quarter if any? Im not asking if it changes your gear ratio or accelerates faster if small etc. Just in relates to your mph in the quarter mile would it be more or less or unchanged?

Fast06Z06

I guess no one knows or has an opinion on here either. Mine is that your mph would be the same regardless. Whats yours.

atomicfusion

There are facts that will effect your MPH in the 1/4 based on tire height...

In reality what you are adjusting is your final rear end gear ratio.

If you take the same car and give it a 3.23, 3.42, 3.73 and then 4.10 gear and run it down the track with all other things equal you will have very different times.

a 4.10 gear will give you more low end torque and you should loose some top end MPH while a 3.23 will leave much softer (less torque) and have more "available" MPH on top end. The caveat to this is final trans gear ratio, meaning if you change into a new gear it will adjust things further.

Your stock tire is 325/30x19 or 26.68 inches and you have a 3.42 gear, if you adjust your tire size to a 345/35 x 18 (M&H Drag radial on 18" wheel) then your tire height changes to 27.51 inches and your final gear ratio now becomes 3.31 which will allow for more MPH but will not lauch as hard. The reverse is also true... for example, Ranger's fastest pass in a stock car on drag radials was on BFG 315/35x17 tires with a height of 25.7 inches. His rear gear ratio now becomes 3.55 and it will now take less power to propel the car the same speed. With this added torque you can now go faster sooner given the same power and as long as you have enough RPM left at the end of the track you will go faster.

Since in a M6 car you can finish the race at the end of 3rd with a stock tire, a smaller tire will require you to shift sooner getting you into a higher gear (4th) allowing for more MPH. That is why you can put a smaller tire AND get more MPH since your final trans gear ratio now becomes smaller.

There are many usefull calculators online and some that I found are HERE

Hope this clears up the issue.

355Spider

I race with C5Z06 wheels and tires which are noticably smaller than the stock rims. My mph stays the same. My time goes down though because of traction.

Nice car and rims atomicfushion.

atomicfusion

Well that too is a caveat to changing the rear gear ratio... If you increase the rear gear ratio to say 3.55 and now have increased torque, you must have enough contact patch to plant the power. If you go to a narrower wheel/tire you now have less contact patch to work with and will need to "tinker" with other settings in order to achieve maximum 60' times.

When I was stock on stock tires I was pulling ~1.79 60' times. When I first got my Nittos on the exact same setup, I was only getting ~2.0 60' times. I had to adjust my driving and eventually got the tires to hook better and got to ~1.75. Then I went to BFG drag radials with a wider contact patch and had to start all over. Finally I got them down to about where the Nittos were, but I was still not happy.

I then went with a taller tire and slightly less contact patch with the M&H, but since the compound is so much better and the sidewall was taller the car hooked up better.

Overall tire height will affect the final gear ratio but can create more spin, so you have to have the proper side wall, tire compound, suspension setup and driving skills to use what you have created.

Without these things you will litterally be just "spinning your tires"

Fast06Z06

Thanks for the info. Makes sense. Good information. Only thing I dont get is that if you are shifting into fourth gear it doesnt necessarily mean that you will get more mph. Heres why i believe this. If you had two cars with the exact same horsepower and everything except one has 3.42 gears and the other 4.11 gears. At the same rpm, same gear the car with the 4.11 would actually be going slower in mph without the speedometer being recalibrated. Yes it would accelerate faster to go to that point but at the same rpm and gear the 3.42 car would actually be going a fast mph. Do you see what I mean? This is were im confused. Wouldnt a car with smaller tires than another have a lower trap speed with equal horsepower? Man there are so many variables. I guess the other way to look at it is if you had different gears two cars with the same mph on the speedo with have different rpms. the 4'11's high rpms for the same speed. Same rpms matched then the 4'11's mph would be slower. Man its confusing haha

atomicfusion

You can calculate all the variables with the link I Posted earlier...

Fast06Z06

Yes I took a look at the link. Thankyou. Just trying to figure out the concept overall . Basically does smaller tires equal lower mph trap speeds or do larger overall diameter tires mean higher mph. My guess would be smaller equals lower trap speed. thanks very much for your input though im atleast half way there.