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Tyre Sizes

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  • Tyre Sizes

    I have rebuilt my RAS replica over winter and the last job is replacing the perished race tyres. It has 18" WM1 and WM2 rims fitted. I was going to fit Heidenau race tyres but they are only available 2.50 x 18 and 3.00 x 18- they say a 3.50 is too big for the rear? I think 2.50 is too small on the front?, so could I fit 3.00 F & R ?
    Bear in mind I haven't used a race tyre since 1977 and the RBS I raced in the 60s had Dunlop Triangulars on, and it will be parades only at the moment. So, any recommendations??????????? Dogsbody

  • #2
    A lot of people seem to use Avons these days. However, I have a Dunlop KR825 on the front and an Avon AM22 (I think) on the rear and these seem to work OK. My Silverstone had WM1's front and rear and I used a 2.75 front and 3.25 rear, both Dunlops as that was all there was really back in the 70's.

    I don't know off hand the sizes on the Yam as they are in these strange 90/90 measurements but will have a look tomorrow.

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    • #3
      I used Avon Roadrunner race compound tyres on my RDS for years, 80/90 front and 90/9 rear. These profile well on a WM1 front and WM2 rear rims. However, I put on a set of Heidenaus at the end of the 2012 season and have used them since, 2.75 front (K45R) and 3:00 rear (K65R) and I am really impressed with the grip, both in the dry and in the wet. Plus they were half the price of the Avons, over in Canada anyway. I reckon that these are as large a tyre as required on a 250 and that most bikes are over-tyred now. Something to do with bigger must be better.
      Stan

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      • #4
        Stan, Thanks for that. Gone with your recommendation, fitting to the wheels tomorrow. What tyre pressures do you run? Colin

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        • #5
          That's a good question. I used to run 27psi front and 29psi rear in the dry with the Avons, dropping a couple of pounds in each in the wet (although I was reading something recently about increasing the pressures in the wet to decrease the contact patch and therefore increase the lbs/sq in to cut through the water film better??).
          I am not sure how I came up with these pressures as, when I checked the Greeves RDS Service Notes recently it states pressures as 21psi front and rear for the 2.75 Dunlop triangulars that were fitted at both ends originally. So .... I dropped the pressures in the Heidenaus to 23psi front and 25 rear and they seem to work OK, but maybe I am not pushing hard enough to feel the difference
          The rule of thumb that seems to be used as a guide here, among the vintage bike racers anyway, is that the pressures should be used that give a 10% increase in tyre pressure between cold (before going out) and hot (just off the track) but have to admit I haven't checked this out yet. Note to self that I need to get more serious about this racing thing
          Stan

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