How do bigger tires effect my speed?

[aggieEB]

I just put 265/75/R16 BFG A/T KOs on a my pretty much stock EB. How will this effect my speedometer? Is my speed going to be higher than what is registered on it and if so by how much? Can any of you guys help me out?

 

[02XSport]

Here you go:

http://www.4lo.com/4LoCalc.htm

 

[Robert]

Yes, your speed will be higher by 5% than it was with your factory 255 70R16s. You can fix this by changing the $10 speedometer gear in your transfer case and about 10 minutes of your time. It'll also let your transmission shift correctly again. You need a gear with one less tooth than the one that is in there. If your '97 is like mine, then you probably have a 20 tooth black gear in there now. If you do, you need a 19 tooth pink gear. It's held on by one bolt and is easily accesable.

 

[xcelratr]

Aggie,

Check your speedo first. Find some mostly flat and mostly straight freeway where you can set your cruise for while. Set your cruise at 50 on your speedo and time yourself over 4 or 5 1-mile stretches with a stopwatch. Then do it again at 60 and 70.

For each speed, average the times to minimize timing errors and milemarker placement errors.

Then use this formula: (1/S) x 3600 = mph to calculate your actual speed.

Then divide the actual mph by the indicated mph to find out what percentage your speedo is off by. Doing it at the three different speeds and averaging the times just helps to reduce errors.

When I went to 5.6% bigger tires, my speedo ended up off by only 2.8% (when my speedo says I'm doing 75, the radar gun says I'm doing 77), so that means it was wrong with the stock tires. Such a small error to me isn't worth correcting. Check yours and then you'll know if it's worth doing or not.

Hope this helps.

 

[aggieEB]

Thanks Guys!

I just wanted to thank everyone who responded. This was exactly the info I was looking for.

 

[tenikiwon]

Where can you get the gear?