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Regearing the speedo?

L

lapisxj

NAXJA Forum User
Location
Huntsville, AL
I am looking to regear my speedo. I just went to chrysler and got a list of gears that they offer. Right now I am running 3.07 axle gears with 32" tires. I am planning to go up to 4.11 gears with my 32" tires. My question is which speedo gear would I need for this?
 
Find a post by GoJeep, go to his webpage that's listed in his sig, and find the section about changing the speedo gear. There's a nice chart and it will tell you how to do the change.
 
You might want to reconsider the 4.10's and go 4.56's with your 32's. I'm running that combo on my daily driver, and it works great with my 5 spd. I'm also running a 40 tooth speedo gear, and I'm with 1 mph accurate.

Many others that have run 4.10's with 32's wished they would have gone with 4.56's.... I learned from their mistakes :)
 
Last edited:
Thanks for the help, that site had lots of good info. I put the 37 tooth gear in with my 4.10 gears and 32" BFG tires and the speed is within a 0.5 mile accuracy to my GPS, I couldn't ask for better than that. Thanks
 
Ivan said:
You might want to reconsider the 4.10's and go 4.56's with your 32's. I'm running that combo on my daily driver, and it works great with my 5 spd. I'm also running a 40 tooth speedo gear, and I'm with 1 mph accurate.

Many others that have run 4.10's with 32's wished they would have gone with 4.56's.... I learned from their mistakes :)
Click to expand...

I second that. I installed 4.10's w/32's and 8 months later put in 4.56's. That was an expensive mistake. I can still drive well over the speed limit on the highway and not over-rev the engine. Look at the rpm charts based on tire size and gear ratio and take into account your tranny setup. I have an AW4 4-speed auto w/4.0L. Also, my gas mileage went from 13 mpg to about 17 after the 4.56's were installed, but I'm heavy on the gas pedal.
 
He has the manual tranny, you have an auto. The manual usually goes one step less than the auto in gearing. The manual tranny XJ start (from the factory) with 3.07 and the auto tranny comes with 3.55.

bburge
 
what about 30's, automatic... but i'm towing. I am thinking that 4.56's seem like they would be too much, but 4.10's may be too low? any help is appreciated, BTW it's a 4,300 lb. trailer. and yeah yeah yeah, i know i should get atleast a d44 in the rear, but i'm trying to find out if i can afford it right now... i just dropped like 2K from intake to exhaust tip.
 
I run 4.56s and 32s with an automatic. I love it...Mileage went from 12 to 19 when I regeared from 3.55s... For 30's I'd still go 4.56. you will, on some point, go larger.
even with 30s 3000rpm is ~85mph. I wouldn't tow any faster than that.
 
yuppiexj- the most i will go is 31's,what rpm are you at with the 32's and 4.56s at 65 in 3rd gear?
 
Not trying to belittle GoJeep's/Jason's research, but I wouldn't trust just the chart itself. Case in point, my XJ had a 29 tooth speedo gear, stock. It's a 98 Sport with an AX-15 and NP231. Not sure what the stock size was since I got it used (presumably 225/75R15), but the door jamb says 215/75R15. I went up to a 30x9.50 MT/R, and checked my speedo with a GPS unit. Comparing the satelite speed to my dash speedometer, the dash speedo read 2MPH faster than I was actually traveling. This means that my rig should have come with 31s from the factory if the speedo was to be anywhere near correct!

GoJeep's chart said I would need a 28 tooth gear, but a 30 tooth gear is what I needed. Ordered the 30 tooth unit from the stealership, installed, and checked it, and it is 99% accurate with the GPS unit, almost no margin of error.

I would say if you can get a hold of a GPS unit, use that to calculate how much your speedo is off, see what tooth speedo is in your t-case (it takes like 2 mins to check, it's stamped right on the plastic gear), and calculate how many more teeth you need/don't need.
 
SyCo said:
Not trying to belittle GoJeep's/Jason's research, but I wouldn't trust just the chart itself. Case in point, my XJ had a 29 tooth speedo gear, stock. It's a 98 Sport with an AX-15 and NP231. Not sure what the stock size was since I got it used (presumably 225/75R15), but the door jamb says 215/75R15. I went up to a 30x9.50 MT/R, and checked my speedo with a GPS unit. Comparing the satelite speed to my dash speedometer, the dash speedo read 2MPH faster than I was actually traveling. This means that my rig should have come with 31s from the factory if the speedo was to be anywhere near correct!

GoJeep's chart said I would need a 28 tooth gear, but a 30 tooth gear is what I needed. Ordered the 30 tooth unit from the stealership, installed, and checked it, and it is 99% accurate with the GPS unit, almost no margin of error.

I would say if you can get a hold of a GPS unit, use that to calculate how much your speedo is off, see what tooth speedo is in your t-case (it takes like 2 mins to check, it's stamped right on the plastic gear), and calculate how many more teeth you need/don't need.
Click to expand...
If GPS is not available just use the "Your Speed Is:" radar trailers that the local PDs set up from time to time.
 
There are a couple different formulas on GoJeeps site (depending on what info you have on hand). My speedo was within 1/2 mph accurate (on GPS) when running 30.25" tall tires, 3.55 gears, and a 33 tooth speedo gear.
I now have 4.10's and same 30.25" (ProComp's 31 x 10.5 x 15" tires :rolleyes: ) and the speedo was OVER-REPORTING by ~15% (had a cop clock me....on purpose *tax dollars at work* ;) ) GoJeep said ~3% per tooth if you know that your speedo was accurate before the gear change. That put me at 38 teeth, but DC doesn't make a 38 tooth gear, so I went to 37 tooth. Gear was <$10 at dealer.
BLUTO
 
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