Thoughts on Proper gear ratio

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Transmission Ratio RPM Calculator | Spicer Parts

Tall 22.5 3.91 is exact same effective ratio as tall 24.5 4.10..

3.58 is pretty far off from a 4.10, but off by maybe 2.2mph tall rubber 3.58, 22.5 to 3.91, 24.5..
Now 3.58 with lo-pro 22.5 is pretty close to 3.91 tall 24.5

 

You want to run one of them 63,500kg (140,000lbs) Canadian jobs in the mountains with 3.58's.?

I'm just a 4 axle silly flatlander out of FL, but that sure don't sound right too me.. 4.10, maybe even 4.30's is what I'd be looking at depending if I went tall 2's or tall 4's..

 

Don't know if it'd be necessary to go that low. My old man's last truck was tridrive with 4.10 rears and a 530 ISX. He grossed slightly less than OP at around 54k or 55k kg but had no real issues out in the off-road logging roads with it. I see a lot of trucks with the 600 Cummins running 3.91 rears now too.

 

I have a good friend that is a journeyman at Detroit diesel. He said that Detroit is on their 3rd or 4th generation of emissions. He said they removed the air dosing from the emissions and they are seeing very few issues. Do your research before people spout off that they are junk. They had issues but are much better and he's seeing them running 750k to million without issues.

 

That's because of the torque multiplication.

The higher number gear ratio with tall tires will always have more torque than the lower numbered gears with shorter tires but the same RPM at a given speed.

A taller tire changes the roll out but does not affect the gear ratio.

 

With 11r22.5 id go with 3.90s personally.

 

TBH, I think the difference in fuel economy from 4.10 to 3.90 is negligible at super b weights and mountain pulls.

 

Without this chart those other calcs mean little.

235/80-R22.5 vs 255/70-R22.5 Tire Comparison - Tire Size Calculator | Tacoma World

 

22.5 and 24.5 are the rim diameter and have very little to do with tire height.