Going up a tire size? Will it rub/drag?

[Jsneeb]

I have a 2002 BB TC2000 29ft bus. It was originally Las Vegas school district and ran mostly a city route.
It came with 255/70r22.5 tires.

These tires are now 7 years old and show signs or their age, though the tread is fine.
The fronts have already been replaced with virgin steer tires in the same size.
Im looking to replace the rear's with a slightly larger size and something cheaper than virgin tires.

I'm, looking at these right here, which look like a decent deal on a set of 4 retreads.

https://classifieds.ksl.com/listing/60544043

The size is 295/75/r22.5
cost is $170 per tire.

My reason for going to a larger tires size is to help reduce my cruising engine RPM.
Currently 2300rpm @ 62mph, and 2500 at my max governed speed of 67.
With these tires I'll drop it down to 2100 at cruising speed 62mph, and bump up my max speed by about 6.3 mph, also nice for occasional passing.


So my understanding is they will fit the rim, but clearance to the body is going to be tight.

The tire size calculator gave me this information when I compared both tire size options.

Size 1Size 2
Diameter
36.6"
39.9"
+9%

Width
10"
11.6"
+16%

Sidewall
7"
8.7"
+24.3%

Circum.
114.8"
125.4"
+9%

Revs/Mile
552
505
-47

The good news is I have air bag suspension, and an adjustable rod with which I can bring the front or rear up a few inches to make sure that during driving the tires dont make contact with any part of the body.
But when the bus isn't driving, and the air suspension settles, which it does after a week or so of sitting, the rear tires will infact touch the inside of the wheelwell. When I dropped my air bags and measured with the current wheels on there, I had 1 inch from the top of the tire to the body, and with the 3.3" larger tires I will need 1.65 inches above the tire. So that means that about half an inch of tire would be compressed and in contact with the wheel arch.

Do you think this is a problem?

Should I stay with the dinky little tires?

I dont mind the speed I cruise at. I get between 9.5-10.5 mpg as it is now.
My uphill / mountain climbing capability is amazing. Stays in OD and pulls most grades at 55.
I would hope to see even a bit of mpg improvement, but really im most interested in these because they are a good price.

[joeblack5]

I like the idea of larger tires, lower price, better mileage, lower rpm.


I would look at the bump stops and see if a spacer can give you the 0.65" needed. The good side effect would be that the air bags do not completely get pressed down while sitting. so a longer time before stress cracking in the rubber.
I have our bus frame on blocks for that reason.



My 0.02


Good luck
Johan

[Jsneeb]

Thanks Joe. I thought about bump stops made out of like 6 spare body mounts that I have.

Is it bad for the air bags to sit deflated? Mine sit like that quite often.

I figured it was ok since they are designed for the weight and they must have considered that a vehicle will at some point sit on a bag with no air in it

[joeblack5]

I am no specialist on that but.. if you look how crumpled up they are when the air is gone after a week then I can't believe that is good for them. I does not long for a flat tire to get side wall cracks.


Also this is commercial equipment .. it gets uses every day in normal life and when all is well it should not completely air down during in a couple of hours of sitting.



But to me it seems only positives.


johan

[joeblack5]

Maybe say it different.. use every day and sit aired down very little versus sit most of the time and use ones every month .
Mine set mostly for 8 month during conversion and was fine but i sure did not like to see how folded those bellows were.



Johan

[Meathead]

Nah. You’re good.