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Wheel sizes

Discussion in 'Technical and Troubleshooting Torque' at netrider.net.au started by jd, Oct 30, 2007.

  1. Okay another question relating to that wonderfully weird era of Japanese bikes, this time on the mix of wheel sizes used on some bikes ie fitting a 16 inch front but an 18 inch rear etc.
    I can see how changing both the front and rear to larger/smaller sizes would have an affect on lean angle/stability but curious to know what the reasoning was behind mixing them given that modern sportsbikes seem to just run 17 front and rear.

  2. My understanding has always been that it was to minimise gyroscopic effect, allowing quicker turn-in and generally lighter steering.

    Supposedly, it worked rather too well, resulting in a generation of bikes with twitchy handling. The manufacturers of aftermarket steering dampers did rather well though.

    Can't say I ever noticed on my old GSX 550, in spite of pushing it pretty hard on occasions, but, these days, you're rather limited in tyre choice. For that reason alone, if I had another bike with a 16 incher, I'd serously consider devising a change to 17 or 18, even if it involved a bit of engineering.
  3. Kawasaki GPX-750 and the Hornet 600 early models ran 17 rear and 16 front. It was thought in GP racing that a 16 front gave a more aggressive turn-in, and it did too, but most manufacturers found that riders thought it resulted in a 'nervous' feel to the front end, and abandoned the idea. Later Hornet 600s have a 17. Plus, personal opinion only, the 16 is a real handlful on dirt or rutted surfaces.
    And, as Pat says, tyre choice is now limited, in my experience. I cannot get BT-021s for the front of my bike; I have to use BT-014 instead. Up side is that the BT-014 is a bit stickier.
  4. Yeah I've already discovered the limitations with tyre sizes, because of the 16 and 18 inch rims the Kat seems to be limited to the Michelin Macadams it's currently running. Not too bad though given I've got no real intention of trying to ride a 22 year old, 250 kilo "sports"bike all that hard anyway.
  5. As Pat said, it's about gyroscopic effect and the speed of steering.

    18" used to be the standard, then the japanese started mucking around with 17" and eventually in the late 80s, 16" (Guzzi did too)

    16" wheels were found to be borderline as they were potentially unstable over uneven surfaces.

    So now we are left with mainly 17" wheels as they are good at both performance and street applications. There is also a good selection of rubber for them.

    Personally I believe 18" wheels are still preferable for road only work, but tyre selection is limited to sports touring compounds.

    It would probably take and alliance between a couple of bike manufacturers and tyre manufactures to seriously change back to 18" wheels now.
  6. There are other reasons for mixing wheels also, but not knowing much about the specific era of bikes and their design justifications it might not be of any relevance. A 16.5 on the front, matched with an appropriate tyre, allows a taller sidewall while maintaining the same overall diameter as a 17" tyre. All sorts of advantages come from that.
  7. The 919RR has a 16 inch front wheel, tyre choice sucks