The GMC CCKW

I was woundering can I mount 900x20s on 750x20 rims.Were do you find other rims for these trucks? Are there other sizes and configurations of rims avliable and what are there off of ?

Thanks,Matt

there is a post thread about them i read, it started with a pic of
a listers truck, looked good, but Joel pointed out had 9.00 tyres,
you might seach for that thread, the owner saying he got a good deal etc.

Dr Deuce said somewhere that whilst higher maximum speed can be acheived, a corresponding loss of torque will be felt badly going uphill.

I think that 7.50 tyres would be strongly recomended by most listers.

Having said that I am curious about what is the max practical tyre size

The rims are the same but I believe that most would prefer the 7:50 suze as that is what the trucks were designed for. Still there are posters on this site that have the 9:00 tires due to their being readily available at a reasonable costs from a surplus dealer.

I think you will find that there is not enough offset or dish in the 7.50X20 rims. The wider 9.00 tire will not have any space between the tires side walls on the rear dual mounts and will interfere with each other.

As I recall, those who have converted CCKW and Chev's have to use 9.00X20 rims from a later M series truck in order to allow for the wider profile on the rears.

Can't remember if there is a difference between M-211 and M-35 Rim's? Don't think so but not sure.

Cat Man

I believe CAT man is correct. My Annie the crane has wheels and tires off of a 1956 GMC civy-mil tanker truck. The M35/M211 wheels would be a good bet too.

I believe that you would have a hard time assembling the 9x20's on the 7.50x20 wheels and that they would almost impossible to get apart due to having to the the tire away from the ring.

Hi Matt
I don't want to contradict any one but , I bought a 1 1/2 ton chevy with a good set of 900X 20 tires mounted on 750x20 rims clearance between the duals was not a problem ,and fender clearance was not an issue , but the truck was never fully loaded either.
The previous owner stated that he mounted the 900s on because he had them and 750 tires for this truck were shot and he would not by new ones.
The owner stated that he had a truck tire dealer do the mounting for him,
I don't how difficult it was to mount the 900s on the rims but they sure broke -down and came off real easy,
I bought and installed the correct tires 750x20
I still have have the 900s they are free to anyone interested.
Hope this helps
John

Thanks for all the info.

Chris in Chowcilla set me up with a good used set of tries.

So my problems are over for now.

I see pictures of these trucks with duals on the front. That has to be hard on the running gear and the brakes!

Thanks again Chris !!!!

Hope everyone has a happy new year.

SEE YOU NEXT YEAR,Matt

hi miner matt,
putting duals on the front looks mad and i know someone who did it and told me the steering was very hard, he tried it on a hard surface so that might be why,as it was intended for soft ground!!!!!!!!!!! glad you got your tyre s sorted

I had 7.50 tires on my truck and with internal engine modifications was able to increase its horsepower and torque. Once that was accomplished, I put 8.25's on the truck (scout /half-track tires). It gives me about 5 mph more and I feel a better look.

P.S. The tires fit fine on the 7.50's CCKW rims with no problems.

Virually everyone agrees that WW2 trucks had tires 1 or 2 sizes too small. I have never figured out why the Dodge 3/4 tonners had "appropiate tires' when all the rest, especially the CCKW and Chev did not.

Agreed with all of the above. The 8:25 always looked like a good alternate to me, Still these trucks were 1930's technology and the tires at that time were natural rubber and cotton fabric so perhaps the tire technology of the time was not advanced enough to build larger tires for that much weight that would hold up uder the conditions they built the trucks for. If I remember the forerunner to the CCK series, the early GMC's had 7:00x20 tires on them.

I think that more than anything it had a lot to do with the designers at the time. There was a lot of maturing in the large truck designs and manufacturing between the 1930's and 1945. You look at a the post war large trucks on the civilian market and they are far more developed than pre-war trucks. Just for instance take a look at all of the wood that was used in pre-war trucks for spacers, stiffeners, shims etc. I think up until WWII many companies were still in the horseless carriage mindset. Once the war got fired up the rubber supply was strained which probably didn't help matters. WWII was the first highly mechanized war and I don't think that the designers fully realized how the vehicles would perform in mud, soft terrain etc over the long term.

Ryan that is a very good point.

We went and measured some origianl rims from our CCKW, and they're about 5 1/2 inches wide inside of the rim. That would be awfully narrow to mount a 900/20 on. Our truck now has 8.25/20's and they're on 7 inch wide rims. Mounting too wide of a tire on a narrow rim makes the height of the tire taller, but gives you less width than what the tire's designed for (besides being a pain to put on), but I understand your pain, a new set of 7.5/20's at $150-$170 a piece = WOW