#41 or #42 speedo gear?

[Brad’s Tj]

Hi all, I have a speedo gear question thats about like some old threads but further questions. I just re geared my 05 tj from factory 3.73 to Revolution 5.13’s. 4.0, 42RLE auto, sye kit, RME with Dana30/Dana44, 35” bfg a/t’s.
I have checked out the speedo gear charts and determined that a white 42 tooth gear should be best for a rolling height 35” tire(?). Am I wrong being the charts show a red 41 tooth gear? Any results from anyone with this set up for proper gear? I have tried to put the white 42 gear in numerous times, indexed the housing, greased the gear, only to have no speedometer! How can I get it to work as I can’t really feel a good gear meshing, I do have some light smashed like areas on the new gear now and wondering if the shaft gear needs replaced now too?! I put a red gear in for now but off 10 mph.

 

[Rickyd]

Verify your speed with gps and find what percentage your speedo is off by. Use your current tooth count and that ratio to find what tooth count you need. It might be different than what you get off a chart and will be more accurate.

Idk what to say about the meshing if it is set for the right tooth count range. Hopefully you don't need a 42

 

[Brad’s Tj]

Verify your speed with gps and find what percentage your speedo is off by. Use your current tooth count and that ratio to find what tooth count you need. It might be different than what you get off a chart and will be more accurate.

Idk what to say about the meshing if it is set for the right tooth count range. Hopefully you don't need a 42

Hi Rickyd, thank you for your reply on this. Would you mind giving me an example on the math of figuring that out? I’m not that young anymore lol. As I said, charts show a 41 gear for 35’s with my set up but I’m not so sure that they consider the rolling height of said tires. Thanks again!

 

[Rickyd]

Yep,actual tire height differences make the chart a guess.

This guys post got me the start i needed-

Post in thread 'TJ Speed Gear Issues' https://wranglertjforum.com/threads/tj-speed-gear-issues.67779/post-1261642

 

[Brad’s Tj]

Yep,actual tire height differences make the chart a guess.

This guys post got me the start i needed-

Post in thread 'TJ Speed Gear Issues' https://wranglertjforum.com/threads/tj-speed-gear-issues.67779/post-1261642

Yep,actual tire height differences make the chart a guess.

This guys post got me the start i needed-

Post in thread 'TJ Speed Gear Issues' https://wranglertjforum.com/threads/tj-speed-gear-issues.67779/post-1261642

Thank you Rickyd! I’m almost certain that the speedo is showing 10 mph faster than my phone gps. I’ll recheck it today and figure this one out as it’s only 2:30 am here. lol. Will any specific speed work better to be accurate?

 

[Jerry Bransford]

Charts are for the an average tire using its measurement molded onto the sidewall so 35" in your case. I'd go with the 41 tooth. I did several tire size and axle ratio changes over the years on my previous TJ and using the tire's "official" tire size on its sidewall always yielded an accurate speedometer from speedometer gear charts.

 

[Rickyd]

Thank you Rickyd! I’m almost certain that the speedo is showing 10 mph faster than my phone gps. I’ll recheck it today and figure this one out as it’s only 2:30 am here. lol. Will any specific speed work better to be accurate?

At half the speed it will only be 5 mph off.it is a ratio not a set number. Read that whole thread to understand the numbers hes plugging in to the equations

 

[Brad’s Tj]

Charts are for the an average tire using its measurement molded onto the sidewall so 35" in your case. I'd go with the 41 tooth. I did several tire size and axle ratio changes over the years on my previous TJ and using the tire's "official" tire size on its sidewall always yielded an accurate speedometer from speedometer gear charts.

Hi Jerry, just wanted to say thank you for your reply. Been busy with life lately! I ordered a 41tooth gear yesterday, finally!

 

[Brad’s Tj]

At half the speed it will only be 5 mph off.it is a ratio not a set number. Read that whole thread to understand the numbers hes plugging in to the equations

Thanks again for your help Rickyd! Late reply here!