I bought my 92 4runner in 1998 with 235's on it. The information on the door panel states that stock tire size is 225.

Well, about 1.5 years afterwards some new 31x10.5 BFG's were purchased and put on the truck when it had 116k miles. My current odometer reading is 164K miles. Based on odometer vs. mile marker comparisons over the past few months it appears that for every mile I actually go, the odometer reads about 0.9 miles. If this is the case I actually have about 4-5k more miles on this truck than the odometer states because of the larger tire size.

Here's the math: 1 actual mile/0.9 odometer miles=1.111 correction factor. 164k-116k=48k miles with larger tires. 48k*1.111=53.33K actual miles on the vehicle. 116K+53.33K=169.33K miles on the vehicle.

Instead of 164K miles on my 4runner it appears that it is actually almost 170K miles! Am I thinking/calculating right about the effect of the larger tire diameter? Someone please correct me if I'm not. Thanks for your help.


Scott

 

My truck came with the 31's from the factory and doing the mile-marker comparison I found mine is off too. I see pretty close to .9 for every mile also. I'm hoping when I upgrade to slightly taller tires this fixes this. Also - I need to find one of those roadside radar machines that displays your speed. I want to see how far off my speedometer is after the tire upgrade since obviously its off a little right now.

 

Mine is 10% off since i have 31's on it. its geared for the 225s as well..but i like the 31s better. you might also what to see what your gear ratios are and check out this page.

 

You won't get an accurate reading... They generally don't calibrate them, which is good because they cannot use them in court.

Just pull up to an officer running radar on a not real busy street. The worst he can say is "no."