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Is a 170/60/17 interchangeable with a 180/55/17?

Discussion in 'Technical and Troubleshooting Torque' started by pringa8, Jan 16, 2009.

  1. Or is it strictly as per manufacturers specs with motorcycles tryes?

  2. you can check the size (rolling circumference) differences here http://www.miata.net/garage/tirecalc.html which will tell you if there is a difference in speedo reading but others here will have to comment on the effect of width and profile changes
  3. Thanks mate, looks like it only covers cars though (185, 195, 205 increments of 10 every 5, doesn't have even numbers for bikes)
  4. in that case you can do the calculation of rolling circumference by hand.

    in fact you don't even need to do that

    calculate tyre 1 height = 0.6*170=102mm
    calculate tyre 2 height = 0.55*180=99mm

    which means that the 180/55 will have a smaller rolling radius than the 170/60 as they are on the same rim


    3mm on radius is less than the tyre wear through its life so I reckon that in terms of reading speed correctly you will be okay

    I think the different tyre width, and profile and their effect on handling would be more of an issue but I'm not experienced enough to help onthat one I'm afraid.
  5. This is more my concern, effects on handling. Not stressed about the 10m width, mainly the profile.
  6. Easy answer dont ...The price factors is about the same. I can post up pages and pages of info from all the tire makers and its all the same stay with standard ..bigger maybe but smaller cant be good..It will effect steering,tip in ,lean angle, braking , balance ,speedo ,rake and trail and suspension..
  7. I'm experienced with car tyres only i'm afraid but the above quote seems sound advice for bike application, changes in characteristics were instantaneous when fitting alternate sizings to cars. In order to counter / take benefit of such changes suspension modifications were your first point of call. Probably best to speak to some experts in bike suspension and glean info there ? Also as posted rolling diameter is a calculation and can be applied across to bikes, but factoring in sidewall flex and internal pressure absorption characteristics is something i'd tip only a seasoned traveller could give advice on.

    Perhaps track-day regulars or some of the racers here could add more ?
  8. Too many factors to consider, try it is the only way to know.
  9. Shouldn't make that much of a difference,
  10. Yes, go one size smaller.

    All the top racers drop down a tyre size on the rear. The benefits equate to much quicker turn in and general chuckability of the bike.

    I've been doing it for the last 10 years on all my road bikes and recommend it as the single best handling improvement you can make on any road bike.

    The best way for you to corroborate this is to ride two identical bikes back to back - one with the regular tyre and one with one size smaller.

    Garry from Oz.
  11. Should be fine. A Ducati 748 and 998 have the same rim sizes and frame geometry. The 748 comes with a 180/55/17 rear and the 998 with a 190/50/17. The only reason for the fatter tyre seems to be cosmetics, it does look better. Like the last post said, the narrower generally improves the handling. Put a 180 on mine and find it much better.