rayinkrabi Posted June 10, 2016 Share Posted June 10, 2016 Hi all, I had new Michelin City Grip tryes fitted a couple of days ago and decided to try a slightly oversize one on the rear, 120/70-14 to replace the stock 100/90-14 (I went for the stock 90/90-14 for the front). I've read on various forums that others have done this and they were quite happy with the results. The ride home from the Honda garage was not good and I found the twit had put over 80 psi in them! I then realised that the rear tyre appeared smaller than I thought it should be and when I measured it is just under 110 mm across. Michelin online (who I bought them from) were quick to answer my message on this and told me that it is because the wheel rim is too small for this size and the tyre is now 'squeezed' thus decreasing the width. I've never heard of this problem and am really concerned whether I have compromised the safety and handling..any ideas please? I am quite prepared to replace this with the correct 100/90 if I have to. Link to comment Share on other sites More sharing options...
VocalNeal Posted June 10, 2016 Share Posted June 10, 2016 Your bike has a 2.15" rim and 120/70 requires ideally a 3.5" rim or compromise of 3 minimum. Have you been on the PCX forum? Link to comment Share on other sites More sharing options...
taichiplanet Posted June 10, 2016 Share Posted June 10, 2016 depends on the width of the rim, you can see that cast into the wheel rim somewhere. if it is 2.5" wide rear rim then max recommended tyre would be 120/80. for a 120/70 tyre you'd need at least a 3"wide rim. Don't know if dangerous or not, but squeezing a tyre onto a smaller than recommended rim will change the characteristics of the tyre to what it was designed for. Also going for lower profile will make the bike ride a little bit harder, but some people like that. chart of recommended tyre to rim sizes http://www.maxxis.co.uk/know-your-tyres/motorcycle-tyre-safety/wheels-and-rims Link to comment Share on other sites More sharing options...
VocalNeal Posted June 10, 2016 Share Posted June 10, 2016 ^ Got my info from the Bridgestone site. Link to comment Share on other sites More sharing options...
taichiplanet Posted June 10, 2016 Share Posted June 10, 2016 ^ Got my info from the Bridgestone site. you are right about the rim size, i checked a PCX150 in the car park and the rear rim is 2.15 wide. it has a 120/70 tyre fitted. looking at a Pirelli catalogue for a 120/70-14 X-ply tyre it recommends a rim of 2.75 to 3.75 depending on the type of tyre. Attached is a table for recommended rim/tyre size by the Tyre & Rim Assoc. Australia TRAA Bike Rim Table 2012.pdf Link to comment Share on other sites More sharing options...
johng Posted June 11, 2016 Share Posted June 11, 2016 One good thing about fitting over wide tire's is that they act a bit like "run flat" tires ,often I find mine with just 2-5 psi the bike has noticeable poor acceleration and lower top speed. But its still perfectly rideable no damage to rim or tire and its never come off the rim (no I don't drive it on a racetrack and its only a 150cc bike ) The downside is that there is actually less usable rubber in contact with the road the more the tire is squeezed. Link to comment Share on other sites More sharing options...
rayinkrabi Posted June 12, 2016 Author Share Posted June 12, 2016 Thanks all for your input, been very helpful indeed and has helped me to make my mind up on changing the tyre back to either the stock size of 100/90-14 or maybe 110/80-14 (?) The reason I'm considering the 110 is (if I've read the charts correctly) it will fit the rim without the 'sqeeze effect' (??) and will only make a 2mm difference to the height which I calculate will make under 1% difference to the speedo / odo. Thanks again for all your help :-) Link to comment Share on other sites More sharing options...
BSJ Posted June 12, 2016 Share Posted June 12, 2016 The rule of thumb for many years is go one size up on the same size rim. Link to comment Share on other sites More sharing options...
rayinkrabi Posted June 12, 2016 Author Share Posted June 12, 2016 Duh..After doing all the maths the old fashioned hard / long way using the pai formula I just found this excellent site that has a great calculator for just this :-) at least it confirmed my numbers and may be of help to fellow members here? Oh Oh..sorry but just remembered the forum rule about posting web addresses..sry seedy! PM me if anyone wants this link. Tire Size ComparisonSpecification Sidewall Radius Diameter Circumference Revs/km Difference100/90-14 90mm 268mm 536mm 1683mm 594 0.0%110/80-14 88mm 266mm 532mm 1670mm 599 -0.7%120/70-14 84mm 262mm 524mm 1645mm 608 -2.2% Link to comment Share on other sites More sharing options...
rayinkrabi Posted June 12, 2016 Author Share Posted June 12, 2016 Thanks BSJ, I've also read this but have also read elsewhere where folk have changed to 140/70 (using the appropriate spacers) supposedly successfully. I now realise this is absolute nonsense and would distort the tyre profile much worse than my 120/70...unless of course they also changed the wheel itself for one with a much wider rim? Ah well, I've learnt a lot from this experience and will bite the bullet and replace my rear tyre for a 110/80 as soon as I get confirmation that it will fit on the 2.15 rim without any distortion. Any one want a 'slighty used' 120/70-14 City Grip tyre? :-) Btw, I'm certainly no expert, but can already notice an improved ride with the new rubber. Link to comment Share on other sites More sharing options...
rayinkrabi Posted June 12, 2016 Author Share Posted June 12, 2016 It does seem that the 110/80-14 is the way to go but I'm still having trouble searching to confirm it is ok on the 2.15 rim. Any ideas what bikes / scoots the 120/70-14 will fit correctly? Link to comment Share on other sites More sharing options...
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