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i have a 1973 kawasaki g3ss 90cc.
according to the owners manual, stock tires were 2.75 x 18
the tires that are on there are 3.00 x 18.
front tire has LOTS of rubber and NO sun damage as it has spent the last 20 years in a garage (not being ridden at all).
rear tire needs replacing immediately due to very low tread.

with those numbers, can i assume that these are bias ply tires ?
if they are bias ply, does the same rule apply to two-wheelers as to cars/trucks ... i.e. no mixing of bias and radial ? (obviously i am thinking of using the existing front tire if possible).
what was gained or lost by going away from the 2.75" to the 3.00" ?
what size should i replace it (them) with, keeping in mind that this is going to be ridden 99% city, 99% solo, with only the occasional, short, stretch of highway use.

thanks
joe
 

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Retired twice: Navy and as a govt contractor
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The rubber in a 20 year old tire will be hard and lack good traction regardless of how much thread is on it. Replace both.
 

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what was gained or lost by going away from the 2.75" to the 3.00" ?
1/8" was added to each side of the tire In other words, nothing much was gained or lost. It was probably a matter of not being able to find a 2-3/4" tire but a 3" tire was available.

The numbers don't indicate whether it's a bias or radial tire. If there's a "B" or an "R" on the side, that would indicate which. If not? I'm not sure how much difference it would make on a 90cc bike putting around city streets.

Generally no, don't mix tire types on a bike unless the manufacturer designed the bike to do so. A few do come from the factory with both a radial and a bias ply tire.
 
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