Speedo gear for 31's?

[Grifter]

what speedo gear do i need to make it close with 31's.
Going from 235/75/15 stockers to 31's with 3.27 rear, A4LD.

 

[metstalker]

i would guess the 17 tooth one i had the 16 tooth in mine and it was a 3.08 gear with stock tires

how far off is the speedo? that should give you a better idea

 

[Grifter]

dont know yet, i have to get the tires off my ranger first and swap them to the Ex..just thinking ahead, so i might have parts ready to drop in..

 

[metstalker]

dont worry its not too big of a job just one bolt and a clip and then bolt back on

 

[Grifter]

oh yeah, i have changed them before, just wanted to have the right one on hand when i do it, so i can get it all done in one shot..

 

[Bashman]

When I put the 31's on mine, the speedo read correctly. A few others on this board have had the same result.

 

[Grifter]

Well, i will find out this weekend..They are going on, and for the ride home, the GPS will tell me how far off i am..

 

[Maniak]

If your speedo is correct with 235x75xr15 tires.. going to 31 tires will make it read incorrect.

235x75xr15 is roughtly a 28.5" tire.. a 31" tire is actually about a 30.5" tire..
thats a 7% difference.. that means if your speedo is dead on now, it will be 7% off..

You need to change the gear (driven gear) 7% (or as close as you can get)..

If I didn't get myself confused again.. it will read 7% slow.. Assume you have a 17 tooth gear, you would want to replace it with an gear 1 tooth down (thats as close as you will get).. you will still be 2% off or so..

If I got it backwards (smaller vrs larger gear to speed up the speedo, someone will bring it up)..

~Mark

 

[Grifter]

well, right now its at 72.4 at 70 on the speedo, so thats what, 3%? if i go the other way, 4%, thats 68ish when it says 70, close enough i would say
if it works out that way

 

[Grifter]

turns out its 9-10% slow, almost exactly at 10%..