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i have a 5in on my 450smr and i personally think its too wide. i have a 160 conti road attack on there and i have clearance issues. only problem is that when i get a smaller wheel (4.25) the 160 will ride different. my ducati has a 4.5 and i use the same exact tire on the ktm and the ktm tire looks to have a better profile, where the duc looks like its too narrow. when i was using the stock 170 slick, the chain would hit the wheel really bad, and chewed up the whole way around, but with the 160 conti i have no issues with it hitting the wheel but i do have a nice little "X" pattern all the way around the tire.

 

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it will depend on the tire itself. my 160 conti road attack barely fits. i had to have the tire a little bit off straight to keep it from rubbing the chain constantly. in all honesty, i probably moved the tire over 2-3 mm where it would have hit the chain.

but every tire is a little different. the 170 slick i pulled off is narrower than the 160 i replaced it with. i plan on keeping it a 160 because now i only have to remember one rear tire size for both my bikes.

edit: i just read your post again and i dont think its a problem with the size of the rim trying to run a 170 tire, but rather a clearance issue between the tire and the chain.

 

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if you have a 5in rim on there now and its not hitting that rim you should be fine. i honestly dont think the chain will hit the rim anymore now that i have the wider tire on there. the old tire i had was the stock 170 slick and it is a good bit narrower than the 160 conti thats on there now. the chain does hit the tire just a bit, enough to put a "X" pattern on the tire in 150ish miles, but it hasnt hit the rim anymore that i have noticed.