Hi,

I recently lifted and installed the Revo 285's and I'm wondering if there is a formula to determine my real speed. I curios at 60mph and 80mph--I know it has to be off by a good margin--My last few tanks of gas have been on the low side to--245 miles vs. 330 before the tires. I can't say the 4Runner feels slower--maybe becuase I have a stick?

 

I actually clocked myself this morning on the way to work versus a co-workers speedo and when he was doing 75 mph my speedo read about 64-65 mph, so about 10 mph off. No wonder I was zipping by folks when I was going 70 mph because it was actually about 80 mph! I was adding about 1 mph for every 10 but that looks like a bad estimate it seems, so probably more like 1.25-1.5 mph for every 10 mph you are going would be a more conservative estimate.

My gas mileage also now sucks, but I don't drive more than back and forth to work and on the weekends, so I don't really care too much about gas mileage.

I have 285/75/16 Goodyear MT/Rs on Tech 1 Rockcrawlers.

 

Go to the following site. It is real easy to use. Put in your original tire size and the new size and the site calculates how much your speed is out.
www.miata.net/garage/tirecalc.html

 

That is a great site--if your lazy you can use this formula:
speed*1.073

60=64.3
70=75.11
80=85.84

Thanks for the help

 

You should test your speedo for accuracy against another vehicle. I don't think a cop is going to buy an excuse like "oops my math was off" if you get caught speeding.

 

I live in Mexico--$20 usually takes care of it! But I do want to get a gps to verify.

 

I always verify my speedo with my handheld GPS. Just a thought for those who have access to one.

 

Isn't that the truth!

One time we got pulled over in Cabo and my dad just took off!

Good thing we were driving a fast car, the VW Bug.

(Sorry about the threadjack)