rickrides Posted April 22, 2018 Share Posted April 22, 2018 Got a nail in my ZRX's rear tire with only 4K miles. So, bought a new tire. The Avon 3D Ultra 170/60 will be patched/plugged from the inside. The rear tire on my FJ09 is worn out and I want to try to use the Avon. Has anyone fitted a narrower tire? Thanks, Rick Link to comment Share on other sites More sharing options...
shigeta Posted April 23, 2018 Share Posted April 23, 2018 Fitting a different sized tire on the bike will change it's profile. Changing the profile changes the bike's attitude. In other words, the bike will turn in differently. Typically if you stretch a narrower tire on a wider rim, you will have a "flatter" profile. That means that it will respond or turn in more sluggishly. It also means that you won't have as much tire to lean onto. Also, tire dimensions are not standardized. A 170/60 =/= 180/55 tire. Find the measured dimensions of the tire from Avon and whatever you have on the FJ-09 currently. Keep in mind, the first number is the "width" of the part of the tire that can touch the road (tread) in millimeters. The 2nd number is the height as a ratio of the measured width. For example, the height of the 170/60 tire is 60% of the measured width. Manufactures are allowed a small variance in width, so a 170 Michelin isn't necessarily the exact same width as a 170 Avon. That means that although your Avon 170/60 should be a measured 170mm, there is wiggle room for what it actually measures out to. For the sake of the conversation, let's assume your 180/55 tire and 170/60 tire have true measurements. That means that your current tire has a measured width of 180mm and a height of 99mm (180*.55=99) That also means that your 170/60 tire has a measured width of 170mm and a height of 102mm (170*.6=102) Again, these dimensions change if the rim width change. On a rim that was designed to properly fit a 180/55 tire, by stretching on a 170/60 tire, you've made the profile flatter. Looks like the 3D Ultra is a more "v" shaped profile, so you've made it more rounded. (read: harder to turn in.) Also, you've effectively changed the rear ride height. Since you've stretched a 170/60 tire wider, it's actual height is lower than the 102mm and therefore likely shorter than that of the stock 180/55 tire. By lowering the rear ride height and keeping the front the same, you've effectively increased the front rake and therefore made the motorcycle harder to turn in—albeit more stable in a straight line. Link to comment Share on other sites More sharing options...
koth442 Posted April 23, 2018 Share Posted April 23, 2018 I'm also concerned about the tire beading properly. A 170 is designed for a narrower rim. '15 FJ09 Link to comment Share on other sites More sharing options...
rickrides Posted April 23, 2018 Author Share Posted April 23, 2018 Shigeta, thanks for that in depth analysis. I will just keep the 170 for when the new rear on the ZRX wears out and put a new 180 on the FJ. It's my wife's FJ and it's been lowered, so why add anything else weird for her to deal with. Link to comment Share on other sites More sharing options...
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