3.55 and 3.58 ratio difference

I have a 10sp .73 and 3.55s. If I had a 13sp it would pull much much better. I have to wind out 9th to 1500 so I can get a quicker spool in 10th and not smoke out the freeway trying to lug the motor.

Honestly I can pull hills decent unless my mph goes under 58 then it's game over. A 13 or 18 is a must and will probably be my upgrade purchase next year.

 

No, it would not. It would be easier for you to choose gear and apply power to wheels, coz on on 13/18 each step is 17% difference, not 33% as on 10sp.

 

It's hard to apply the power to the wheels with a big turbo if it don't spool quick. So higher rpm's in my next gear helps a lot to keep the turbo lit. So if I can split the shift at 1500 rpm's it would pull amazing.

 

Its depends of the engine. My particular engine doesnt like very much rpm higher than 1500. I switch down on 1150-1300. Anotger truck I use to drive was very capable and easely went 1700rpm and higher. So it was easier to use same 10sp gearbox on that particular truck. As for 13 all I want to say it doesnt resolve the problem of weak truck, it just makes process of shifting gearbox a bit easier. If truck is weak it would crawl same hill with same speed no matter 10 or 13 gearbox is in it.

 

3.58 if you're doing a lot of uphill loads since it will pull a bit harder, but i don't think you will see that big of a difference between 3.55 and 3.58 on the highway..

 

I have a CAT C15 with an 18 speed with 4:11 ratio's (1575rpm) @ 100kph would changing to 4:33 ratio's (1675 rpm) @ 100 kph make a big difference to fuel economy?

 

K w what cat engine do you have? How much weight do you pull on a regular basis? For heavy work 115000 and up. I would keep cruise rpm around 1400 to 1500. With an 18 when you drop half a gear for rolling hills etc you still would be at a reasonable rpm. 1675 in high gear is a bit much in my mind.@'

 

Swap that simple overdrive tranny out for a double overdrive 18. All your profits going out your exhaust. Changing just the rears would put you at 95kph at the same rpm. If you swap the tranny and the rears you'll be at 100kph but with 1500 rpm rather than 1675.

http://www.roadranger.com/ecm/groups/public/@pub/@eaton/@roadranger/documents/content/ct_062746.swf

play around with that tool. CAT's like low rpm

 

I have a 9NZ C15 Cat @ 550hp with an RTLO 20918B 18 speed. i pull a B'Double grossing around 60000kgs. 4:11 & 4:33 ratios are very common in australia.

 

Very nice set up, I actually run quite similar. 7CZ CAT @ 600 HP, RTLO20913B, 3.90 ratio and haul 100-180k. 4.11 and 4.33's are common for heavy haul set ups. Are you sure your tranny is a double overdrive? Your RPM's should be considerably lower, even with the extra weight