From what I can gather the 140/80 tires are measured in a different way (as others have said) and are FIM competition specification tires. I think the FIM spec is designed to produce a tire that has less flat contact area and therefore does not make ruts as easily as a normal spec tire.
That's how I understand it - I'm not going into the science of whether or not this is true, cause I've no idea about that.
What I do know from first hand experience, is that 140/80 tires look like a balloon when compared to an ordinary 110/100 tire. Looks like more 'roundy' sidewall and less contact area.
Definitely not a fan of how they work - I refer to the Michelin balloon that came stock on my Gasser. The tire just seemed to spin and wouldn't dig in and hook-up like a 'normal' spec size tire.
If you don't have to run FIM spec tires, I'd stay away from the 140/80 stuff.
But what do I know? I'm sure there is an expert with a better answer.
Jason
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