Speedometer Gearing

[BenXJCA]

I have not addressed this after installing a lift and larger diameter tires. Does anyone have or know of a chart that tells how many teeth the gear has to have to compensate for specific differential gearing and tire size? Also, does anyone have a link or a company name of a supplier of the speedometer gears?
TIA you guys rock

[GSequoia]

Here's a link to Cherokee America's speedo chart: http://www.off-road.com/jeep/cherokee/98/07_jul/speedo/speedo.html

I've heard of people getting them from the dealer, not sure of other sorcues.

[Pat]

http://go.jeep-xj.info/HowtoSpeedoGears.htm

that should give you what you're looking for...

i got my speedo gear from the dealer.

Pat
NAXJA member

[atticus032]

Does it hurt anything if you don't get a new speedo gear? I have an automatic. Plus, if I plan on getting 32s instead of the 31s i currently have should i go on and by the speedo gear that for the 32s?

[Lincoln]

Doesn't matter except your reading will be off. Just know how fast your going.

I didn't read the articles, but here is the most accurate way:
1. Find out how much your speedo is off. Preferable at a faster speed. Around 60.

2. Take your reading divided by the speed you knew you were traveling. Ex. 55/60 = .91667

3. Pull the gear you have and check how many teeth it has and times that number by the above. Ex. 27*.91667 = 24.75

4. Find a gear that is close to that number. Less teeth make the speedo read faster. 24 teeth if you want it to read a little fast and 25 teeth if you want it a close as you can get it.

Later,
Lincoln

[Eagle]

Originally posted by atticus032
Does it hurt anything if you don't get a new speedo gear? I have an automatic. Plus, if I plan on getting 32s instead of the 31s i currently have should i go on and by the speedo gear that for the 32s?

Most 31s measure about 30-1/2, and most 32s measure about 31-1/2. I'd get the gear for a 31" tire. I bought a gear based on 3.73 gears and 30" tires, and with 31x10.50s mounted it is EXACTLY accurate, as confirmed by those radar trailers some police departments are now deploying.

[Gojeep]

Originally posted by atticus032
Does it hurt anything if you don't get a new speedo gear? I have an automatic. Plus, if I plan on getting 32s instead of the 31s i currently have should i go on and by the speedo gear that for the 32s?

It does effect the lock up convertor. It will lock up at the wrong speed as it uses the speedo gear pulses to know at what speed to lock up. The ECU also uses it for other things as well. You can notice a small change in performance after changing to the right gear as mentioned by a few people.

My chart also takes into account the real height of the tyres ( namely BFG's ) and after being tested with a GPS on as many gear tyre height combos as possible.