Tire Tube Sizing

[Doc Sprocket]

Hey folks-
I've got a set of 22x11-8 knobbies for my project. They're not in the greatest condition, so I'm going to install tubes. Locally, I can get 18x9.50-8 tubes for a good price, but they don't have 22x11-8. I'm trying to keep costs down. I imagine that these tubes will do the job, but I'd hate to find out I'm wrong. Any thoughts, fellas?

 

[r97]

it might be like running on a somewhat deflated tire, but im not shure

 

[Doc Sprocket]

See, neither am I. I know that with enough air volume in it, it WILL expand enough to fill the tire. With it being expanded that much, obviously, the rubber is stretched more. I don't think it'll just blow, but I'd like to know ahead of time if it'll be a problem...

EDIT- Dunno if this helps, but I test mounted one on a 7 inch wide rim (original was 8-inch) without a tube, and aired it up to a decent pressure. It came out smaller than advertised as they often do, at about 21" diameter including tread, and about 10 inches wide.

 

[redsox985]

Uum bust out that math book and find the volume of the tire and volume of the tube. The tube doesn't care about an inch in this direction or that.

If I found the right info online it's

A tire on a wheel is basically a torus.

Formula for Volume of a torus= 2*(pi)^2*R*r^2

Where R=distance from center of wheel to center of tube
r=radius of circle formed by tire/wheel (cross section)

http://forums.13x.com/showthread.php?t=200537

 

[Doc Sprocket]

Okay, interesting. I can do that, and probably will, but as we all know, theory and practise are two different things. For starts, we have no idea how far out those numbers can be out before it actually causes a problem.
I appreciate the info, but I think I need some real-world, experience based comments...

 

[Kenny_McCormic]

Might make the stretch, might not. If there is one nearby, try tractor supply, they have around 8 feet of shelving dedicated to tubes, all the way up to car and tractor tires.

 

[redsox985]

Ya, I know that numbers aren't real life experience but it's worth a shot.