What he said.

Thanks for reviving this thread made my search easier. I need to do this to my 98 now and I need some help with what gear I need. I'm running 315/75/16 tires on my truck with m5od.

 

What he said.

Thanks for reviving this thread made my search easier. I need to do this to my 98 now and I need some help with what gear I need. I'm running 315/75/16 tires on my truck with m5od.

 

Need to know what your Diff Ratio is.

For your tires the formula is:

(8 x Diff Ratio x 582.88868445262189512419503219871) / 1000 = the number of teeth you need on the speedo gear.

I suggest going one gear tooth higher than your answer. For example with my stock tires the formula gives an answer of 19.098. But the stock gear has 20 teeth. Also when I did the formula with my tires, the answer was close to 17 and I went with the 18 tooth gear. My speedo is now nearly dead on to the GPS, I'd say as close as it was with the factory size tires and gear.

Doug

 

yea i saw the formula after i posted and since my gearing is so bad (3.08) it gave me a 14-15 tooth gear haha

 

I've changed my wheels from stock 245/75R16 worn coopers to 305/60R18 MT. The ratio of my F250LD is 3.31 and it had a 20t gear. Since I got the truck I've been wondering about the shifting points and -time of the transmission. With the new wheels I now use a 17t gear (as the formula says) and now it shifts a little bit earlier, smoother (even with edge programmer on) and the warp display says it's running exactly in accordance to my gps. Difference is 3 teeth...

 

so is the stock gear a 20 tooth? cuz with my new gears i get a 21 tooth so i should be very close

 

Seems like in most trucks stock gear is a 20 tooth. you better check it with a gps device.

 

looks like ill be getting a 21-22 tooth gear then hopefully this week

 

Reviving this thread with a question. Where did you get the '8' (drive gear teeth) from for the formula. I'm not doubting you...just would like to know where I can find the info to save for later reference.

Kevin

 

i looked alot of this up before i ordered mine and it was between a 7 and 8 tooth gear and the easiest way to verify you have an 8 tooth drive gear is to pull your gear out and plug it into the formula and solve for drive gear teeth.

but most likely its gonna be 8

 

The 8 tooth drive gear is what I have according to the formula. Thanks. I just thought there might be a chart/info out there that might be easily available.

Kevin