HaveGun

If I go from a 32" tall tire, to a 33" tall tire on my SUV, and do not correct the speedometer, how many fewer miles a year will show on my odometer in a year, or 12,000 miles of driving?

Was talking to my dad about lifting my SUV and going to a 33" tire and he pointed out that doing so would show less miles on the vehicle after some time. How many less is a mystery since I suck at math. I've tried to figure out a formula, but it makes my head hurt.

Meridian7750

Formula for circumference is 2* pi* radius. Pi is approx 3.1416
2*16=32. 32*pi=100.5”, or 8.38’ per revolution of your tire.

At 33” (16.5” radius), you travel 103.67”, or 8.64’ per revolution.

That’s a 3% increase, so you would show only 97% of the actual miles driven in any given period of time.

If you drive an actual 12,000 miles, your odometer will show 97% of that...
11,640 miles.
All numbers are approx, but close enough to get the gist.

awshoot

If I go from a 32" tall tire, to a 33" tall tire on my SUV, and do not correct the speedometer, how many fewer miles a year will show on my odometer in a year, or 12,000 miles of driving?

Was talking to my dad about lifting my SUV and going to a 33" tire and he pointed out that doing so would show less miles on the vehicle after some time. How many less is a mystery since I suck at math. I've tried to figure out a formula, but it makes my head hurt.

pi*diameter=circumference
Told=pi*32=100.531
Tnew=pi*33=103.673

The odometer will show fewer miles than you actually travel. You want to know the distance per revolution in a proportional manner of the old to the new tires:

proportion=Told/Tnew=0.96969317
miles recorded=12000*proportion=11636.3

The speedometer will under-report your speed and "think" you go less distance per revolution, so you want to know the proportion of the new distance to the old distance, actual speed will be Tnew/Told=1.03*speedometer reading. So 50 mph would 51.5 mph etc.

I think. ;-)

PaulB47

Just multiply your odometer mileage times (33/32) to get the true mileage. Or go back the other way to get the odo mileage from the true mileage, except how are you going to know what the true mileage really is?

I think odometers are usually off some even with standard tires, just the same way speedometers are. The car manufacturers don't seem too worried about getting exact numbers, and anyway that would be hard to do since tires decrease in diameter during their useful life.

The Heretic

Many modern vehicles have electronic ODOs and also have a setting for adjusting it for different sized tires/wheels.

Certaindeaf

Sounds like a Seinfeld can deposit arbitrage caper.

I can see why his head hurts!!

Unicykle

Havent you heard math is racist, lets keep it clean here guys.

What isn't anymore?

HaveGun

Awesome! Thanks for the responses! So roughly 400 less miles a year on my vehicle; excellent!

Bajablast

This website works well for me:

Just put in the tire sizes and go from there.
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