Gear Ratio Adjustment

kicks6000 · **Posted:** Sat Dec 31, 2005 6:00 pm

I've had my BFGoodrich A/T tires for a few months now. I never thought to have this done, but should I have my gear ratios adjusted? I had P215 (minivan tires

) and now I have P245s. My local dealership charges $97 for the work. Does this sound fair for a stealership?

Eddo · **Joined:** Thu Jul 07, 2005 7:01 pm **Posts:** 1214

My dealer was only going to charge me 40 and I though that was high

ManicMechanicJoe · **Posted:** Sat Dec 31, 2005 7:15 pm

$97 to change gear ratios???? Thats a steal, unless you mean adjust the speedometer so it read accurately, then $97 seems close. They generally charge you for diagnostic work when they do this (any time they plug in the OBDII reader you get charged $80 or so for an hours worth of diagnostics) and adjust it. Figure a downtime of about 5-10 minutes. Sorry no loaner car for this one!!!

Jeepjeepster · **Posted:** Sat Dec 31, 2005 7:21 pm

Can you tell a difference in performace? thats a big difference.

ManicMechanicJoe · **Posted:** Sat Dec 31, 2005 7:23 pm

a 245 doesn't have to be taller then 215's, keep in mind that the first number is width in millimeters, I am sure his are taller-just throwing that out there

camper · **Posted:** Sat Dec 31, 2005 8:24 pm

are you sure your tires aren't an LT series (light truck) instead of P (passenger)....with an E rated sidewall construction....I'm just splitting hairs with you....but if you're going to list them in your signature, you may want to recheck your sidewall letters....

I have the rusty's 2 1/2" coil lift....I run the bfg all-terrain t/a LT245/75/r16 on an '04 with the 42RLE automatic transmission....I was too cheap to take it to the dealer to have the speedometer recalibrated....about 18 months/24k miles now.....I'm a slowpoke driver usually.....I haven't noticed any problems leaving it as it was....

I don't think the difference in diameter is great enough to worry about....maybe someone will confirm or criticise my lack of concern....

kicks6000 · **Posted:** Sat Dec 31, 2005 9:41 pm

You're right. They are LTs. Stupid me!

oldhockeyvb · **Posted:** Sun Jan 01, 2006 12:21 am

I remember seeing a post on the old site that the difference in speedometer reading was only like 5 mph at highway speed.

KJ04 · **Posted:** Sun Jan 01, 2006 8:44 am

Not getting the speedometer recalibrated will also add extra mileage to your odometer and shorten the warranty life.

bighause · **Posted:** Sun Jan 01, 2006 11:17 am

Actually with bigger tires the speedometer and odometer will read slower than you are actually going because the tires make fewer revolutions than smaller ones at the same speed. That would actually give you slightly more warranty time!

AdamIsAdam · **Posted:** Sun Jan 01, 2006 12:21 pm

You give them the tire revs per mile (there was a long exhaustive thread on this in the old forum). For BFG 245/75x16 the number that worked best was 696 as I recall. It was slightly off from BFG's number. Keeping in mind that this number actually changes as the tires wear. But I can tell you that my dealer did it while I waited for about $29 out the door (15 minutes of time maybe?) with tax. And using my wife's NAV system in my KJ, I know that I'm EXACTLY correct in my speed (and thus my odomoter too).

I thought about leaving it alone for the extra warranty, but would rather have correct speedometer. Besides, I've got a 100k B2B warranty anyway.

Get it changed. It's the right thing to do. Cheaper than speeding tix.

ManicMechanicJoe · **Posted:** Sun Jan 01, 2006 4:58 pm

The difference is not a constant 5 miles per hour. It's actually a percentage of your claimed speed. I believe mine was like 5% off. So if I was doing 100 mph then I would really be doing 105. Around town (30 mph) it was like 1.5 mph off. It really isn't a huge difference untill you step up to 35's from stock or something like that.

Gear Ratio Adjustment

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