RATIO

I was hoping someone could answer a question.

What would be viable rear gears for a CAT CT660 15L tractor running 11R24.5 tires and 4.30 rears, in order to get the best fuel mileage I can, and still keep as much pulling power as possible?

It will be used for light loads (10K to 40K, usually in the 20K range), running 400 mile daily round trips on relatively flat roads with small hills, and speed limits ranging between 45 and 70 mph.

I have an '01 Pete 387 with 336 rears and stage 1 PDI tuned 6NZ motor which averages ~ 6.3 mpg running hard up to 72 mph (72 on flat lands will tac at 1500-1600 rpm).

Thanks in advance for any help.


***Sorry, the CAT has an 18-Speed Manual, With Double Overdrive & Double-Lo

 

Sorry to be negative but that's the wrong truck for the work you described...... And the 660 is a pos.



P.S. Most guys are going >3.55

 

Most guys are going with 3.55 when? With work similar to mine?
I would love to keep the 4.30 rears for next year when I start hauling timber, but I just don't want to be burning an extra $1200 in fuel per month until that happens.

I was thinking of 3.70 or even 3.90 as a nice compromise...

Thanks for your thoughts on the 660. It looks OK to me.

 

3:55 are the rears you want man. The work your describing with an 18 spd is a great set-up for 3:55's. The 18spd will give you all the low end you need for hauling timber. If you didn't have all those gears on the low side, 3:90's would be better. But the 18spd trans was built to give guys low end gears with the same overall drive of .73 same as the 13 spd to get best fuel mileage on highway as well.

 

Thats what I was thinking, thanks.
I'll be under 90K gross with the timber so nothing too insane.
I was also considering the 3.70, the more I look at it, but not sure yet....
THoughts?

 

3:55 and 3:70 are pretty similar. I think either way you go will be fine. 3:55 are gonna put you at 74 mph at 1500 Rpm. 3:70 will put you a lil slower. Both are gonna pull great.

 

Thanks for the input.
I'll probably just go with the 3.55 and depending on what the core charge is, ask to keep the 430 rears...

 

Only advantage to the 430 is when you let the clutch out in low gear on a very hard pull ,otherwise 3.55 or :3.70 will do fine once rolling due the to 18 speed besides the 430 gear will run outta it's rpm range by 60 mph 430 was fine with mechanical engines screaming at 2000 rpm not so hot with new engines though

 

Yea, I sometimes wish I knew how to work on those old mechanicals...

 

my t600 with 3.70 and 10 sp has 3.70 and gets 5.7 mpg.