Tire size effect on gear ratio ?

Currently running 4.56 gear with 33.5 tire. What will staying with 4.56 gear and switching to 34.5 tire change my effective gear ratio too at 4500 rpm's ?

 

I am not sure I understand your question but if you want to know what gear change would net you the same result as that tire change the answer would be approx. 4.6343 or not much different from a 4.56

 

tire size

What is the 4500 RPM's for? I think the back of an old NHRA rule book has that equation.or just try + Google it. should fine something. Don

 

Just multiply the tire hiegth by 3.14 that will give you the roll out then divide that number by the rear end ratio that will give you the inches travelled in one rotation of the driveshaft.



33.5x3.14=105.19 divided by 4.56=23.0679
34.5x3.14=108.33 divided by 23.0679 = 4.696136

I did it in my head earlier when I got the 4.63, I was off by about 1/3th of a ring gear tooth its actually 4.696136 give or take.

And as pointed out by Don, RPM has nothing to do with it.

 

Richard, next time I have a math issue can I call you..very impressed.Dave

 

What I am trying to do is get my wheel speed down without changing rear gear.

 

Secondwindracing, see what a 8th grade education will do for you

Mightymouse,

I would post up the type of car you are running and your wheelspeeds, 60s etc. and what you are trying to achieve.

I am sure some of the guys on here have run a simalar setup and can give you a some good information on what changes you should expect to see with the tire change, myself I know a little math and a little engine and computer stuff but my experience with launching different setups is very limited.

 

Richard, ahh, sorry mate, but you've got it back to front. Putting a taller tire on the same gear ratio has the effect of making the overall ratio taller. When dealing with ratios, we must work with the diameters, not the circumference;

4.56 / 33.5 = 152.76
4.56 / 34.5 = 157.32
100 / 152.76 * 157.32 = 102.98

So a 'ratio' change of approximately 3% (taller).

Paul.