# probably a dumb question about tubes/tires

Discussion in 'Thumpers' started by projectmrod, Mar 1, 2013.

1. ### projectmrodn00b

Joined:
Mar 26, 2011
Oddometer:
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So ive got a Kenda k761 that im going to put on my rear, its size is 120/80/18 and the tube i got is a 110/100-18 (it lists 2 other sizes but thats the closest) anyways

I took it to a honda dealer cuz they usually do a quick install.

Anyways, the guy wanted to wait 3 days for a new tube to get delivered because he wanted to order a 120/80/18 exact tube.. and i was like uhh i'm pretty sure this guy will fit..

just wondering what your thoughts are
2. ### crypto666Long timer

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Can you imagine what women go through watching the guy deal with a condom?

I wouldn't be too concerned about it, it tends to be restricted to a certain size by the tire and rim.
3. ### markk53jack of all trades...

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Dec 20, 2007
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Obviously the dealer service manager or whomever made that uneducated decision has no mathematical sense.

My bet is the cross sectional area of a tube made to fit a 120/80 (slightly oval with a major diameter of 120mm and minor diameter of about 100mm) will be so close to that of a tube made to fit a cross sectional area of a 110/100 (perfectly round) that there is no rational physical reason to not use the 110/100 in place of the 120/80 tube. The guy is a dim bulb.

The math for this would be that between the 110/100 and the 120/80 there is 10mm difference in width - less than 1/2" going from a 120mm to a 110mm width - BUT the difference from the 110/100 height to the 120/80 height is about 1/2" (that 80 indicates a 20% reduction in profile)... Can you say "the same"? I thought you could.

Try explaining this to that guy that wanted to order the 120/80 tube. But don't don't be surprised if it just goes right over top of his head...

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