CMP Value

[huxley]

Another question came up in my feeble mind. If this is in fact a F60 it should have 20" wheels, yes? Has anyone gone back down to the 16" wheels to cut weight, overall ride height, tire/tube/liner cost, etc. No clearance problems?

I fear this 60cwt truck is overkill for my needs... even after shortening to 134" wheelbase.

Cheers!

H

[Grant Bowker]

I know people have put 20" rims onto the lighter trucks that originally had 16" rims. I don't know of anyone who has done what you suggest. I suspect there could be interference between the brake drum and wheel, but don't know this for sure. If you want, I can try to figure out the brake drum size tonight when I get home if nobody can tell us first hand that it either works or does not.

[huxley]

Thanks Grant!

But it is not an issue at this time... I am still blue skying this project.

[Phil Waterman]

Hi

There are some of the 60 series that have the smaller brake drums to use the 16" which are 8 lugs these trucks will take either 16" or 20" see picture of my C60L during change over. The 16" wheel brake drums backing plates on those trucks measure approximately 16 1/2 diameter while the 20" wheel brake backing plates are 17 1/2". The 16" wheels don't fit the larger drums I tried.

Difference in wheel size had to do with use truck, weight and date of production. I've heard that the smaller tires were also used to save on rubber and to make some vehicles like ambulances, easier to load. Also the smaller diameter tires would deliver significantly more torque to the ground at the expense of speed. This would explain their use for towing anti-aircraft guns. From experience with my C60L the torque makes shifting out of 1st gear difficult but use of 1st is also limited. With the 16" wheels you can expect to be pasted by people on bicycles.

[huxley]

Never thought of the changing of the gear ratios from 20" to 16"!

Good call!

H

[Phil Waterman]

Originally Posted by huxley

Never thought of the changing of the gear ratios from 20" to 16"!

Good call!

H

Hi-

Quick look through CMP parts book shows only one ratio for all.

Manual specs show the C30 and C60 series as being 7.16 to 1 while the parts book lists them as 6:43 ratio (same thing).

Though your point is well taken if you could find a pair of ring and pinion gear sets from the heavy civi chevy truck, that used the same differential carrier, you could go to 6:39. This would give you better road speed while slowing down the drive train which would be a good thing for the road. But this option would only work if you were also up engineing as the 216 engine just doesn't have power.

All in all the tire size, gear ratios, and engine size for the CMPs are probably a very good balance for conditions they were design for. The off road performance of CMPs is down right impressive. After 30 years of club trail rides people are still amazed that my HUP will climb anything a Jeep or M151 can climb. CMPs just do it slower.

[hrpearce]

Taken from MB-C2 the diff ratios were different for the different rim sizes;
C-8A 5.42 to 1, C-15 6.17 to 1, C-15A 6.5 to 1, all others as mentioned 7.16 to 1.