6 Speed Manual performance difference?

[Direwolf]

Would anyone with a Sport, 3:45 s MT chime in ? Those P245/75/R17 are about 31.2", would like to know how it pulls in 1st gear, thanks

I did some of the math in another thread, pasting here. Sport tire circumference is approximately 98.86" and Rubicon is about 102.76". So multiplying that all out and converting to mph...

1st gear sport: 1000rpm / 3.45 / 5.13 * 98.86" * 60m/h / 63360"/mi = 5.29mph per 1000rpm
1st gear Rubi: 1000rpm / 4.10 / 5.13 * 102.76" * 60m/h / 63360"/mi = 4.63mph per 1000rpm

6th gear sport: 1000rpm / 3.45 / 0.72 * 98.86" * 60m/h / 63360"/mi = 37.69mph per 1000rpm
6th gear Rubi: 1000rpm / 4.10 / 0.72 * 102.76" * 60m/h / 63360"/mi = 32.96mph per 1000rpm

Basically, the Rubicon is geared about 12.5% higher than the sport and its speed in any gear at the same RPM is roughly 87.5% of the sport's. That's assuming that I did all the math correctly, of course... Feel free to double-check and put it in a spreadsheet or something.

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[AZCrawl]

I did some of the math in another thread, pasting here. Sport tire circumference is approximately 98.86" and Rubicon is about 102.76". So multiplying that all out and converting to mph...

1st gear sport: 1000rpm / 3.45 / 5.13 * 98.86" * 60m/h / 63360"/mi = 5.29mph per 1000rpm
1st gear Rubi: 1000rpm / 4.10 / 5.13 * 102.76" * 60m/h / 63360"/mi = 4.63mph per 1000rpm

6th gear sport: 1000rpm / 3.45 / 0.72 * 98.86" * 60m/h / 63360"/mi = 37.69mph per 1000rpm
6th gear Rubi: 1000rpm / 4.10 / 0.72 * 102.76" * 60m/h / 63360"/mi = 32.96mph per 1000rpm

Basically, the Rubicon is geared about 12.5% higher than the sport and its speed in any gear at the same RPM is roughly 87.5% of the sport's. That's assuming that I did all the math correctly, of course... Feel free to double-check and put it in a spreadsheet or something.

Great job. Can you do the math for a Rubicon on 37's for proper gearing that maintains the stock RPM ranges?

 

[That One Guy]

My money says it will pull better or at least as well as a JK rubi with 4.10 gearing. That 1st gear is LOW.

What mph does 1st top out at?

after, uh, engine break-in of course

 

[DanW]

What mph does 1st top out at?

after, uh, engine break-in of course

I'll have to check, but it comes quickly, for sure.

 

[Direwolf]

Great job. Can you do the math for a Rubicon on 37's for proper gearing that maintains the stock RPM ranges?

It's all linear... A 37" tire is 13.12% larger than the stock Rubicon 285/70R17 (32.71"), so you'd need to bump up your axle ratio by the same percentage to maintain stock RPM ranges. That's 4.64, which is probably not available, but 4.56 would put you very close.

Notice that a Rubicon on 37's (13.12% from stock Rubicon) is just a little off from the sport (12.53% from Rubicon).

 

[That One Guy]

I'll have to check, but it comes quickly, for sure.

Especially with those 4.10's.

In fact, it'd be great if you and a member with the regular diff ratios posted max speeds in the first few gears one day. Nice little comparison.

 

[DanW]

Especially with those 4.10's.

In fact, it'd be great if you and a member with the regular diff ratios posted max speeds in the first few gears one day. Nice little comparison.

I've got a grat speedometer app that will greatly aid this. It snapshots top speed, so I should be able to give a pretty accurate report on it, after work, of course.

 

[That One Guy]

I've got a grat speedometer app that will greatly aid this. It snapshots top speed, so I should be able to give a pretty accurate report on it, after work, of course.

Bonus points, if no one with a manual sport/sahara manages to do this before me, I will

 

[DanW]

What mph does 1st top out at?

after, uh, engine break-in of course

Remember, I'm running 35s. It will be different for Rubi with stock 33's.

 

[That One Guy]

Remember, I'm running 35s. It will be different for Rubi with stock 33's.

Ah. Curious, did you get your speedometer recalibrated? I've wondered if that's easy.

Back in the day I brought my 4Runner from 29's to 35's, but regeared the diffs approximately back to stock, so I didn't end up having an off speedometer. But I probably wouldn't regear a Sport on 33's. Wondering if the Wrangler will take a tire size upgrade in the future and have a cost-effective way to maintain an accurate speedometer.

 

[DanW]

Ah. Curious, did you get your speedometer recalibrated? I've wondered if that's easy.

Back in the day I brought my 4Runner from 29's to 35's, but regeared the diffs approximately back to stock, so I didn't end up having an off speedometer. But I probably wouldn't regear a Sport on 33's. Wondering if the Wrangler will take a tire size upgrade in the future and have a cost-effective way to maintain an accurate speedometer.

I haven't recalibrated yet. I'm about 4mph faster than indicated speed at an actual 55mph. Maybe 3.5.

 

[Billy]

I haven't recalibrated yet. I'm about 4mph faster than indicated speed at an actual 55mph. Maybe 3.5.

Isn't it a quick adjustment through the touch screen?

 

[AZCrawl]

It's all linear... A 37" tire is 13.12% larger than the stock Rubicon 285/70R17 (32.71"), so you'd need to bump up your axle ratio by the same percentage to maintain stock RPM ranges. That's 4.64, which is probably not available, but 4.56 would put you very close.

Notice that a Rubicon on 37's (13.12% from stock Rubicon) is just a little off from the sport (12.53% from Rubicon).

4.56 was my guess, thanks.

 

[AZCrawl]

Isn't it a quick adjustment through the touch screen?

Nope.

 

[DanW]

Isn't it a quick adjustment through the touch screen?

I've not seen that and it is doubtful. That would be all to easy to commit odometer fraud.

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