What Speedometer gear?

[High2by]

Here are the specs for the truck:

'89 2WD 4.0/AW4. Stock tire size was 205/70/15, 26.3" diameter. Current tire size 295/50/15, 26.6" diameter. 

Stock gear 3.55. Current gear 4.10.

I have read that both a 39 tooth or a 41 tooth gear will work. I'm not sure which one. Do you guys have any thoughts or suggestions?

 

Thanks!

[88mancheman]

For the 4.10 ratio and rounding up to 27” tires the “correct” Speedo gear would be between a 39-41 tooth Speedo gear

There seems to be lots of charts on the old inter webs of Speedo gear charts but these two seem to be the most reputable, also reminder that running a smaller gear will make the Speedo run off by a few miles faster and going larger will make it read a few miles slower so if I where you I’d run the 39 tooth Speedo it should be the more “correct” Speedo gear and if nothing else will read 2-3 mph too fast over actual speed which Ought to keep you outta some trouble with the black and whites ;)


Here’s 2 links to verify :)

http://www.novak-adapt.com/catalog/transfer-case-parts/np-speedometer-gears


https://jeepey.com/media/workspace/files/speedometer-gear_3.pdf

[Drahcir495]

https://www.quadratec.com/c/reference/jeep-speedometer-gear-tooth-chart

 

Try this

[derf]

Go look up the specs for your exact tire.  It should have a number for revs per mile.  Then run the numbers:

 

Revs x axle ratio x 13 ÷ 1000

 

Round up.

 

[High2by]

8 minutes ago, derf said:

Go look up the specs for your exact tire.  It should have a number for revs per mile.  Then run the numbers:

 

Revs x axle ratio x 13 ÷ 1000

 

Round up.

 

 

10 hours ago, 88mancheman said:

For the 4.10 ratio and rounding up to 27” tires the “correct” Speedo gear would be between a 39-41 tooth Speedo gear

There seems to be lots of charts on the old inter webs of Speedo gear charts but these two seem to be the most reputable, also reminder that running a smaller gear will make the Speedo run off by a few miles faster and going larger will make it read a few miles slower so if I where you I’d run the 39 tooth Speedo it should be the more “correct” Speedo gear and if nothing else will read 2-3 mph too fast over actual speed which Ought to keep you outta some trouble with the black and whites ;)


Here’s 2 links to verify :)

http://www.novak-adapt.com/catalog/transfer-case-parts/np-speedometer-gears


https://jeepey.com/media/workspace/files/speedometer-gear_3.pdf

 

 

According to derf's calculation, I get 40.4 which rounded up is 41.

 

I like 88mancheman's train of thought on keeping out of trouble though, so I think the 39 tooth is where I'll land. Not because I would ever speed, but in case the wife drives the truck...

 

Thanks for all the input guys, I appreciate it!

[High2by]

10 hours ago, Drahcir495 said:

https://www.quadratec.com/c/reference/jeep-speedometer-gear-tooth-chart

 

Try this

 

I reserve the right to change my mind...

 

After doing some more digging here, it appears I can get a 40 tooth which is gonna put it almost dead nutz on. Thanks Drahcir495!

[Drahcir495]

Glad it helped