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gears vs. tire sizes

3K views 19 replies 6 participants last post by  Soccerluvr4 
#1 ·
The best I can determine, increasing the tire diameter by about 2" would effectively be equal to a rear gear ratio change of from 3.31 to 3.55.
Is that right?
Does changing the tire size have the same effect as changing gears?
I know I must be missing something here.
 
#3 · (Edited)
Yeah I can see where the rpm per mph is the same but is the effect the same?

Edit: like there's a torque change when you increase the diameter of the tire but I guess it is offset by the toque increase of the higher speed.???
 
#6 ·
Yeah thats what I did. That's why I had to check on the final results of power to the road.
 
#8 ·
#12 ·
Let me add my 2 cents here for clarification.
A numerically higher gear is a lower gear and a numerically lower gear is actually higher numerically.

Confused?

4:10 is a lower gear than 3:55 but it's higher numerically because the numbers are bigger.
It's the ratio that matters. The pinion will turn 4.11 times while the axle will turn once.

Make sense?
 
#15 ·
The width doesn't matter too much. Its more the sidewall. Which remember is expressed as a %.

The difference between say a 275/35-18 and a 305/35-18 is only .8" so its not a huge difference. Might feel like going from a 3.15 to a 3.00. You most likely won't feel a difference.

Now say you went from a 275/35-18 to a 305/40-18 then its a difference of 2" and you will notice the difference.
 
#16 ·
When I ordered my MPT tunes, they wanted to know the gear ratio as well as the tire size. All are factors in tuning for my V6 auto. Just 2 more cents :thumb:
 
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