MK2Ed Posted January 7, 2008 Report Posted January 7, 2008 The tyre size given to me for some slicks was 20/54/13 I take it that the '54/13' is the normal measurement given for tyres in mm and inches? (although I've never heard of 54 as a size, more 50, 60, etc). But, what does the '20' stand for? The guy selling them was a bit vague... I'm more used to the standard measurement for tyres, i.e 185/175, etc... Can anyone explain? and what size 20 is closest to in normal measurement? Ta.
danny69 Posted January 7, 2008 Report Posted January 7, 2008 I thought it was 20cm as in 200mm? The 54 might be a percentage of the width as it is normally? So somewhere between a 50 and a 60 profile? More questions than answers
Messenjah Posted January 7, 2008 Report Posted January 7, 2008 20 is thw width and is 200mm inbetween a 195 and a 205 tyre 54 is the profile and on slicks im not sure if it is the % but usually is which would give you a 108mm profile .... which is as said between a 195/60 and a 205/60 .... so its basically the tyre inbetween those two
MK2Ed Posted January 7, 2008 Author Report Posted January 7, 2008 Ah percentage... Nice one... I'm guessing 200 will be too wide for a standard RS 4 spoke rim?? without giving the fitter the hump and RSI. While on that one offhand does anyone know what maximum width tyre will go on a standard 4 spoke rim... 195 ?? Ta
Messenjah Posted January 7, 2008 Report Posted January 7, 2008 theoretically for a tyre with a profile of more then 50% then the rim width should be 70% of the tyres section width and 200mm = 8 inches roughly so 70% of that would be a 5.6 inch rim ... to the closest half inch thats 5.5 and if they are mk1 rs 4 spokes then they would be theoretically perfect .... but at a guess they are "6 rims but again you would be FINE with 200mm tyre son a "6 rim
Retromotorsport Posted January 7, 2008 Report Posted January 7, 2008 20=200mm used tyr surface 54=540mm overall diameter of the tyre the reason for giving the overall tyre diameter is so we can work out the gearing quickly and is much more accurate than the aspect ratio of a standard road tyre as the width marked on road tyres is never whats acctually on the road .. some class as much as 40mm on the sidewalls so a 200/70/13 road tyre may only be 160 wide .. The race tyres will be with a few mm of the width dimension
Retromotorsport Posted January 7, 2008 Report Posted January 7, 2008 for handling round bends .. the tyre width should be smaller than the rim width, ie a 5.5 rim should have a 5" tyre or a 125 wide race tyre a 10" rim should have a 9" tyre .. or a 230 wide race tyre some hillclimb single seaters, because of compounds, will run 2" under rim on the rears sat a 10" tyre on a 12" rim due to the high cornering loads they achieve
Messenjah Posted January 7, 2008 Report Posted January 7, 2008 i stand corrected and i was going from vistas link in the how to room which was for road tyres (oops) gary to the rescue
Retromotorsport Posted January 7, 2008 Report Posted January 7, 2008 not sure if this pic shows it up to clearly but thats a 195 tyre on the back .. and as you can maybe see its lot wider than a 195 road tyre go and measure your road cars tyres ... but only the bit thats in contact with the road .. what you measure is what race tyres are numbered up at ... be good to see the biggest difference between sidewall number and the actuaul contact patch measurement .. think the biggest i've seen is a 175 that had 125 in contact with the ground .. 25mm of the tread was down the sidewall
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