Tire Size VS Gear Ratio

[Dana]

Info:
Well, that didn't work....

 

[Dana]

How about this?

 

[Poisonous Mods]

Dana the Circumference is based on the fact that its on full PSI right?

So ud just have to drop the PSI to bring back up the Gear ratio?

Great Post :beer:

 

[Dana]

yes, all the tires were measure with about 26 pounds of air pressure.

All tires expand on acceleration, especially the slicks - ET Steets.
I don't know if changing the air pressure will make much difference to them as far as diameter or circumference goes under racing conditions.


OK, I just dropped the presure in the ET Streets to 13 #'s and the diameter is the same. I think that if you drop it low enough, you would observe a small difference, but it would have to be close to zero #'s.
Remember this is off the car. I'm sure this would have increased the contact patch, and their effectiveness, but that's not what were talking about here.

Dana

 

[Poisonous Mods]

Originally posted by Dana
yes, all the tires were measure with about 26 pounds of air pressure.

All tires expand on acceleration, especially the slicks - ET Steets.
I don't know if changing the air pressure will make much difference to them as far as diameter or circumference goes under racing conditions.


OK, I just dropped the presure in the ET Streets to 13 #'s and the diameter is the same. I think that if you drop it low enough, you would observe a small difference, but it would have to be close to zero #'s.
Remember this is off the car. I'm sure this would have increased the contact patch, and their effectiveness, but that's not what were talking about here.

Dana

But the Gear Ratio doesnt change on the stock tires with 26psi?
How did u come to the figure out the gear ratio with each tire?

Contact Patch is totally different area i realize.

 

[Dana]

The stock gear ratio on the car is 3.55 to 1.
The stock F - 1 tire size is 275X40X17.

26 PSI is what I normall run my tires at on the street.

The circumference was measred with a string and placed on a ruler. Stock Circumference=81 inches.

The diameter is determined by Circumference divided by pi (3.1416).
then it is just a matter of ratios.

3.55 * 25.78 = 91.59 (where 25.78 is the diameter of the stock tire)

divide 91.59 by the rest of the tire diameters and the result is the gear ratio.

91.59/25.78=3.55
91.59/25.95=3.52
91.59/27.21=3.36

Dana

 

[Poisonous Mods]

Dana, thanks for the formula... Very helpful to know when u go to the 1/8 or 1/4 track.:thumbsup:

 

[Blade]

Yea, it's from a Vette site, but this is the one I always use.

http://www.c5-corvette.com/tirecalc.htm

 

[Dana]

Blade,
I don't know where you saw that formula before, but that is from high school math and is just basic stuff. Ratios and proportions.

The problem with the other calculators is that they assume a certain tire size has certain dimensions, which is not always correct. That was why I posted the actual measurements of these 3 tires. They are very handy for general use though.

They list ~ the same diameter for the 2.75 and the 3.15 sizes that are listed above, and obviously that is incorrect.

Anyone care to add to the ACTUAL measurements of any of the other replacement sizes we're using?

Dana

 

[Poisonous Mods]

Dana,

Kuhmo MX Series tires.
Rears are 295x35x18
PSI @ 25
Circumference @ 81"

ended with 3.549
81 / (3.1416) = 25.78
25.78 x 3.55 = 91.519

91.519 / 25.78 = 3.55 rounded off.

Only short run but it wasnt hot hot such as a burn out hot.

Does this work?

 

[Poisonous Mods]

Think after a burn out situation im sure the tires will have a bit higher air pressure & as u take off on the run the tires will expand. So my final drive surely will change. If i had the tires at its full 35psi damn should of checked out first come to think of it now.

Oh Dana...u got a formula for added weight on the tires?
Got some new rims & added 6lbs to each rim on the rear.

I hear that 1lbs weight = 16lbs rotational weight...basically once the tires start rolling....is that true?

 

[PhillyCobra]

There is actually little or no expansion of radial tires with rotational speed. Totally different than regular drag slicks.

 

[Dana]

Now you're getting way out of my league. You're going to need someone with a backround in engineering to step in and work with those numbers with regard to the degree of expansion on acceleration and rotational weight. Sorry.

I'll add the Kumho's to the list though.

Thanks,
Dana

 

[Dana]

P'sns Mods,

Which wheels are these tires mounted on? type and width?

Thanks,
Dana

 

[Poisonous Mods]

Originally posted by Dana
P'sns Mods,

Which wheels are these tires mounted on? type and width?

Thanks,
Dana

AFS Rims.

 

[Poisonous Mods]

Sorry Dana, But cant post same pic's. Following thread has better pics.
http://svtperformance.com/forums/showthread.php?s=&threadid=45070

18x10.5" AFS

Now problem...just a friend of my sister came by yesturday & he was talking about weight VS rotational speed & all this theory stuff.

 

[Poisonous Mods]

Originally posted by Dana
yes, all the tires were measure with about 26 pounds of air pressure.

All tires expand on acceleration, especially the slicks - ET Steets.
I don't know if changing the air pressure will make much difference to them as far as diameter or circumference goes under racing conditions.


OK, I just dropped the presure in the ET Streets to 13 #'s and the diameter is the same. I think that if you drop it low enough, you would observe a small difference, but it would have to be close to zero #'s.
Remember this is off the car. I'm sure this would have increased the contact patch, and their effectiveness, but that's not what were talking about here.

Dana

Any one else with some Michellen or some other brands?

ttt