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ZZR250 - New Tyres and Revs

Discussion in 'Technical and Troubleshooting Torque' started by tyrelever, Jun 1, 2007.

  1. Hi all,

    Another noob question here...

    I have just got my first set of brand spanking new tyres for ol' girl and have noticed a change in the revs while cruising.

    Before the new set went on it sat dead on 8000rpm at 100Kph, now it sits on 9100 at 100kph. I was expecting maybe a small change due to the now thicker tire but not that much.

    Is this normal?

  2. I replaced tyres on mine a week or two ago and noticed a change as well. It is normal since difference in wheel circumference does effect gearing. I used to be 9000rpm for 100kmh, now its more like 8650.
  3. Thanks for the reply phizog,

    I would expect the rev to be at a lower level with new tyres, but in my case they have gone up instead.

    I was think they maye have put the wrong sized sprocket or something but none of that was changed.

    Any ideas about what it could be anyone?
  4. Simple, it would appear that if ONLY tyres were changed the rolling circumfrence of the new tyre is smaller than that of the older, compare the tyre size of old and new, if the profile is different, or the width is different yet profile number is same, then both scenarios will contribute to a change in rolling circumfrence.
  5. Yup
  6. No. New tyre must be smaller or lower profile if RPM is actually up.
  7. Thanks guys!

    Im going to have a look at the profile tomorrow morning

    I suppose what im asking is that are there any adjustments that could have been made (assuming the tyres are the same as the old ones) that could cause this to happen?

  8. If the tyres were replaced with ones identical in size, there is no adjustment to make this occur. They tyres are different I will bet!
  9. Yep thats it, different profile tyres... Grr....

    Off to the bike shop tomorrow.