GMC C7000 Larger Tire Size

[davargo]

I have a 1986 GMC C7000 with 9.00-20 tires on Dayton style wheels currently. I know many of these trucks came with 10.00-20 tires as well. I am working on upgrading to tubeless, I have 4 new-to-me 22.5 wheels and 4 good 11R22.5 drive tires. I am having trouble finding good used steer tires at a reasonable price/distance/size. I came across some 12R22.5 steer tires with 50% tread that are mounted on open center wheels already, are these going to be way too big for this truck? I'm worried about them getting into the fenders or leaf springs when turning. Anybody running 12R22.5 on a similar truck? For about triple the price I could also buy two new wheels and pick up some good condition 295/75R22.5. I know these are basically the same width as the 12 but about the same diameter as my 9.00-20's. This truck is not used commercially, less than 500 miles a year going to the dump and local truck shows.

 

[MG84]

This truck is not used commercially, less than 500 miles a year going to the dump and local truck shows.

If this is the case why are you going through all the trouble to swap out the 900-20 tires and wheels?

 

[Deere500a]

Past drove 86 gmc Topkick 32k gvw same looking truck stock wheels were 11r22.5

 

[davargo]

If this is the case why are you going through all the trouble to swap out the 900-20 tires and wheels?

The current tires badly need replacing due to dry rot, seems logical to upgrade to something readily available and repairable anywhere by anyone since I need to buy something regardless

 

[MG84]

The current tires badly need replacing due to dry rot, seems logical to upgrade to something readily available and repairable anywhere by anyone since I need to buy something regardless

If you were using the truck every day I'd say that's a worthwhile upgrade, for limited use it seems like a lot of trouble to me. A 11r22.5 is a good bit taller than a 900-20, you're going to effectively be raising the gear ratio of the truck as well as throwing off the speedo/odometer. Buy some good 900-20 tubes and good steer tires and put something cheap on the rear, and you'll probably never have to mess with them again. I have two trucks still running 900-20 tires on split ring wheels, I personally find them easier to deal with than the 11r22.5's on budd wheels on my other trucks.

 

[Deere500a]

86 7000 OEM was 10r or 11r 22.5 or Dayton r20's were option. Most time I see r20 there are on c60 or lighter trucks

 

[cuttin edge]

Is it a gas job? Just seeing it makes me hear it run, even if it wasn't gas.

 

[DDoug]

If you were using the truck every day I'd say that's a worthwhile upgrade, for limited use it seems like a lot of trouble to me. A 11r22.5 is a good bit taller than a 900-20, you're going to effectively be raising the gear ratio of the truck as well as throwing off the speedo/odometer. Buy some good 900-20 tubes and good steer tires and put something cheap on the rear, and you'll probably never have to mess with them again. I have two trucks still running 900-20 tires on split ring wheels, I personally find them easier to deal with than the 11r22.5's on budd wheels on my other trucks.

Probably rub on the insides when turned to the stops as well.

 

[Truck Shop]

. I am having trouble finding good used steer tires at a reasonable price/distance/size.

Finding decent used steers is not really common, those have a tendency to be well used.
For the fact most will spend a little extra for better quality on steer and run them down
to Lincolns head. Especially in these times with tire prices the way it is. You would be
better off with lo-pro 22.5's for height against 900/20's. IIRC 10R 22.5 is same as 900/20.

 

[JaredV]

I don't know how many other outfits do this, but our steer tires are recapped for drives. Works well for the work we do.

Check around with your tire shops, they might have a pair of 10r22.5s that they want to move. I got a set of 9r22.5 drives for my old IH dump truck that originally had 8.25-20s for fairly cheap because they aren't commonly used.

 

[Old Doug]

I have a 1964 Ford F600 . I got it a few years ago to kind of experiment on how useful some thing like it would be. I have used it alot . It has 8.25-20 tires . I replaced the steer tires with new ones and have been able to find good used tires for the drives . What i use it for i dont have to load it heavy more bulky. I can stay off heavy traveled roads so speed isnt a big deal. I thought when i started using it I am using it so much I need a newer better truck but then I thought why ?? Something I would like to have to try is a dump trailer because I have a newer single axle truck that has 22.5 tires. I bought this truck so I could have one truck instead of three . I have the f600 it has a 16' flat bed dump, a IH winch truck with poles and a 1996 GMC 7000 with airbrakes and winch. I thought I would keep the GMC get a dump trailer have one truck one set of easy to find tires ,one insurance,one license,one expense ? If a guy just had a crystal ball .

 

[davargo]

Is it a gas job? Just seeing it makes me hear it run, even if it wasn't gas.

8.2 diesel. Not the most desirable engine but it runs really well and should be fine for my purposes

 

[cuttin edge]

8.2 diesel. Not the most desirable engine but it runs really well and should be fine for my purposes

Nothing wrong with that. I like the gas jobs for nostalgia. Remember my father in under the hood of them. Never interested in getting into diesel. He always said if it got to the point where he couldn't fix em anymore it was time to retire

 

[Willie B]

I have a 1986 GMC C7000 with 9.00-20 tires on Dayton style wheels currently. I know many of these trucks came with 10.00-20 tires as well. I am working on upgrading to tubeless, I have 4 new-to-me 22.5 wheels and 4 good 11R22.5 drive tires. I am having trouble finding good used steer tires at a reasonable price/distance/size. I came across some 12R22.5 steer tires with 50% tread that are mounted on open center wheels already, are these going to be way too big for this truck? I'm worried about them getting into the fenders or leaf springs when turning. Anybody running 12R22.5 on a similar truck? For about triple the price I could also buy two new wheels and pick up some good condition 295/75R22.5. I know these are basically the same width as the 12 but about the same diameter as my 9.00-20's. This truck is not used commercially, less than 500 miles a year going to the dump and local truck shows.


View attachment 360723

I had a 1976 C65 with open center wheels, nobody had 1:00-20 tires to sell. I drove a lot trying to find serviceable tires. I was 500 miles from home spending a week, blew a trailer tire. The very small tire dealer was a pleasure to deal with, I asked about 10:00-20 tires. He said: "I don't have them in stock, but I'll have them Wednesday." He sold me Double Coin, they were a fine tire.
My present truck is 1990 GMC Top Kick C7000. It too was on 10:00-20. Bought new wheels & 11R-22.5 for it, virtually the same dimensions.
Mine has lots of room around the tires. Your engine/transmission/ differential are a question. Can you live with a slightly higher gear ratio?

 

[davargo]

I had a 1976 C65 with open center wheels, nobody had 1:00-20 tires to sell. I drove a lot trying to find serviceable tires. I was 500 miles from home spending a week, blew a trailer tire. The very small tire dealer was a pleasure to deal with, I asked about 10:00-20 tires. He said: "I don't have them in stock, but I'll have them Wednesday." He sold me Double Coin, they were a fine tire.
My present truck is 1990 GMC Top Kick C7000. It too was on 10:00-20. Bought new wheels & 11R-22.5 for it, virtually the same dimensions.
Mine has lots of room around the tires. Your engine/transmission/ differential are a question. Can you live with a slightly higher gear ratio?

A slightly higher gear ratio would be good actually. It currently tops out around 55mph, I almost never use the low range in the axle. I wouldn't mind a few more mph. Rear tires should be no problem on clearance, just concerned about the front

 

[Willie B]

My 1976, and my 1990 have the same cab, but the 1990 is much taller. There is a pedestal the cab sits on raises it a bunch. Both handle the 11R-22.5 tires just fine.
I'll guess yours is a gas engine. I find with a diesel, controlling engine speed gives most power. Mine, a V8 Cat gets its peak torque a little shy of 2000 RPM. Higher engine speed, I lose torque.
The lower 1976 truck had plenty of room in the fenders for the slightly bigger tires.

 

[crane operator]

You can make a cardboard "template". A 1/2 -3/4 Moon at the larger diameter tire size, hold it on top of your existing tire, and turn the wheel each way and see if it clears.

Assuming you are getting rims with the same offset as you currently have.

Sometimes a change in offset , throwing the tires further away, can help with clearance, but there's probably not a lot of offset options in that wheel style anymore.