The Stovebolt Site Forums The Parking Lot Big Bolts Tire size

I got a set of 7.50 X 20 Denman Highway Express tires for the front of my '39 for Christmas. I compared them to the ones that were on my truck originally and they are a lot bigger. They fit the rim but the outside circumference is about 5" wider overall than the original 7.00 X 20 tires. The truck is in pieces so I cant mock them up. Does anyone know if they will rub the front fenders? Can anyone tell me why 7.50s are so much bigger than 7.00s? Can anyone tell me what the 7.50 or 7.00 means? I am an idiot when it comes to tires. Thanks

7.50's are a half inch wider across the tread than 7.00's.

They SHOULD (and I am not positive on this) be the same diameter/circumference as the 7.00's.

If the diameter is different, they may be a heavier ply (ie 8 ply vs 4 ply) or the old ones may have just been worn down that much. Do you have ply ratings on both sets?

To become schooled in tire sizes, I used this website .

I hope this was helpful.

I wouldn't anticipate a problem if you're only one size from the stock size; you'll find enough room on pretty much any vehicle to go up at least one size. The factory designs enough room into cars and trucks to go up at least one size,just in case the driver can't get a replacement correct size tire for some reason,and also to accomodate any mid-year changes in tire specs that might happen. You might be able to go two sizes up,but may have tire to spring clearance issues at full lock.
Speed

The side wall height ratio was the same for all the tires with the same wheel diameter while the simple number system was in use. I think it's like 75% (don't quote me on this), so an example would be a 7.00x20 would have a 5.25" sidewall and a 7.50x20 would have a 5.63" sidewall making the 7.50 tire taller by 3/4".

This then gets confusing when you get into mixing tube type with tubeless type tires. The ratios are not the same. Example, a 9.00x20 is the same diameter as a 10.00x22.5 and a 10.00x20 is the same as a 11.00x22.5. So the 22.5 must have a smaller "ratio" number than the 20's have.

Happy New Year!

Mike

You seem to have the tire conversion program down pat... Can you help lead me to find a conversion for a 7.50R20? I have the 8.25R20's all around but they rub the frame on a lock to lock turn. Not a big deal but "if" I can find a couple of 7.50R20 steering tires, I'll feel better. So how or what would a 750R20 convert to? Thanks.

nothing anything better Virginia, unless you go back to the bias ply 750's, which are scarcer and more expensive, but prolly available at Coker

I had 825's on my 46 and they rubbed a bit like that too - just hafta not use that last 1/4 turn of the wheel!

Bill

That is what I'm finding the more I search. But you know that firefighters never give up!

Red 58;
Isn't there an adjustable stop on each spindle,or was that just on smaller trucks?
Speed

Is it possible to use a spacer and longer studs to extend the wheel clearence? Even 3/8" per side would make a bit of difference.