adam_r Posted June 15, 2012 Report Share Posted June 15, 2012 This may be a tricky one.. well it is for me! I understand rolling radius's and why size tyres can be put on a wheel... anyway this is bugging me somewhat. I have 17x7jj rims on my accord. i know i can fit: 225/45/17 215/45/17 and possibly 205/45/17 but they are on the small side. Now apart from increase in radius what would happen to the handling / general performance of the car if 235/40/17's or 235/45/17 tyres where fitted to the rims. does handling deteriorate due to the sidewalls being pushed out further from the 'outside' of the rim, so when cornering the tyre wall would not support the car correctly ? my knowledge of this area is very poor so please be kind Adam Quote Link to comment Share on other sites More sharing options...
Tony Posted June 16, 2012 Report Share Posted June 16, 2012 The real change in the size of the contact patch between 225-215 is about 2mm so virtually nothing. Problems arise when the need to maintain the aspect ratio reduces the side-wall. Reason this is a problem is the smaller profile tyre tends to have extra load sidewalls. Thw reduced lateral flex communicates road irregularity's "tramlining". Additional problem is the tyre is less progressive so the grip coefficient saturates. Quote Link to comment Share on other sites More sharing options...
adam_r Posted June 16, 2012 Author Report Share Posted June 16, 2012 Thanks for that Tony. So if i where to say choose between the following tyres: 215/45/17 225/45/17 235/45/17 The 212/45/17 would show most tramlining effects, and the 235/45/17 would be a more predictable ride. Reason for these questions is.. at the moment i have 17 x 7jj rims with 225/45/17 tyre fitted. The handling is ok and grip is progressive but im suffering with very bad tramlining. Im hoping a step up to 235/45/17 would help reduce this annoyance without really raising tyre costs... Any input on this? Im well aware that it will kick my speedo out a bit but i can cope with that and it would still be within mot limits Quote Link to comment Share on other sites More sharing options...
parthiban Posted June 18, 2012 Report Share Posted June 18, 2012 From my experience I think the tyres themselves can be more of a factor than the size. I moved from 17s to 18s but have less tramlining now since the car's been on Goodyears and now Michelins compared to the OEM Dunlops. My brother had a similar experience with the runflats on his Z4, the OEM Bridgestones would make the car jump around like crazy with anything on the road but since swapping to Michelins (still RFT) the car is far more settled. Quote Link to comment Share on other sites More sharing options...
Tony Posted June 19, 2012 Report Share Posted June 19, 2012 To keep the correct rolling radius the tyre size would move to.... 215/45/17 225/40/17 235/35/17 As you can see the aspect ratio gets smaller and stiffer. Quote Link to comment Share on other sites More sharing options...
adam_r Posted June 19, 2012 Author Report Share Posted June 19, 2012 To keep the correct rolling radius the tyre size would move to.... 215/45/17 225/40/17 235/35/17 As you can see the aspect ratio gets smaller and stiffer. hmm yes. my speedo reads very low at the moment and im running 225/45/17. on my speedo it reads 70mph (ish) and on my GPS speedo it says im doing about 64mph. Would i get in trouble if i fitted say 235/45/17 tyres to the car ? Quote Link to comment Share on other sites More sharing options...
parthiban Posted June 19, 2012 Report Share Posted June 19, 2012 To keep the correct rolling radius the tyre size would move to.... 215/45/17 225/40/17 235/35/17 As you can see the aspect ratio gets smaller and stiffer. If you're maintaining the rolling radius surely the sidewall isn't actually getting any smaller? The number is getting smaller as it's now a smaller percentage of a wider tyre but the sidewall should still be the same size? However with the sizes above won't the rolling radius be decreasing? For example, 235/40/17 would be a closer match in overall diameter to 215/45/17. Quote Link to comment Share on other sites More sharing options...
Tony Posted June 19, 2012 Report Share Posted June 19, 2012 To keep the correct rolling radius the tyre size would move to.... 215/45/17 225/40/17 235/35/17 As you can see the aspect ratio gets smaller and stiffer. If you're maintaining the rolling radius surely the sidewall isn't actually getting any smaller? The number is getting smaller as it's now a smaller percentage of a wider tyre but the sidewall should still be the same size? However with the sizes above won't the rolling radius be decreasing? For example, 235/40/17 would be a closer match in overall diameter to 215/45/17. I meant numerically smaller. Quote Link to comment Share on other sites More sharing options...
Tony Posted June 19, 2012 Report Share Posted June 19, 2012 To keep the correct rolling radius the tyre size would move to.... 215/45/17 225/40/17 235/35/17 As you can see the aspect ratio gets smaller and stiffer. hmm yes. my speedo reads very low at the moment and im running 225/45/17. on my speedo it reads 70mph (ish) and on my GPS speedo it says im doing about 64mph. Would i get in trouble if i fitted say 235/45/17 tyres to the car ? Have a go with the tyre calculator here> http://www.wheels-inmotion.co.uk/forum/ind...hp?showforum=33 Quote Link to comment Share on other sites More sharing options...
adam_r Posted June 19, 2012 Author Report Share Posted June 19, 2012 interesting... playing about with that: stock tyre size = 205/55/16 = speedo would read '60' @ 60mph... even though we know there is a % underthat. current tyre size = 225/45/17 = speedo would read '60' @ 60mph. going up to 235/45/17 = speedo would read '61' @ 60mph. so i would still have a speedo that under reads speed if i went for that size. but going back to my first question.. will there be any performance issues if i fitted a 235 / 45 / 17 to a 17x 7jj rim ? Quote Link to comment Share on other sites More sharing options...
Tony Posted June 19, 2012 Report Share Posted June 19, 2012 Yes because it should be on a 8.5j to 9.0j wheel. Quote Link to comment Share on other sites More sharing options...
adam_r Posted June 19, 2012 Author Report Share Posted June 19, 2012 Yes because it should be on a 8.5j to 9.0j wheel. right. is that due to the side wall being forced out past the rim due to the contact patch instead of being verticle / slightly angled in ? so does not give the correct support for the tyre overall ? excuse my complete ignorance on this subject but its one thing i have never understood properly Quote Link to comment Share on other sites More sharing options...
Tony Posted June 19, 2012 Report Share Posted June 19, 2012 The profile will be V shaped and have to much roll in the wall during yaw. Think of it like the wheel moving in and out of tyre. Quote Link to comment Share on other sites More sharing options...
adam_r Posted June 19, 2012 Author Report Share Posted June 19, 2012 interesting Tony . So would a 215/45 tyre be more appropriate for a 7jj rim than say a 225/45 tyre ? the 215/45 tyre on a 7 inch wide rim would show less 'yaw' during lateral grip. going to the other extreme.. i understand why drifters used 'stretched' tyres as this almost removed sidewall flex & allows a greater contact patch to regain grip, but at the same time with reduced sidewall flex to 'loose' grip easier due to the amount of power the cars have. i have just never understood the implications of putting a tyre that is too 'big' for the rim. Quote Link to comment Share on other sites More sharing options...
parthiban Posted June 19, 2012 Report Share Posted June 19, 2012 The profile will be V shaped and have to much roll in the wall during yaw. Think of it like the wheel moving in and out of tyre. Does that mean the sidewalls of the tyres will actually be leaning inwards ever so slightly with the wider tyre? So would a 215/45 tyre be more appropriate for a 7jj rim than say a 225/45 tyre ?the 215/45 tyre on a 7 inch wide rim would show less 'yaw' during lateral grip. The OEM wheels on the IS200 are 17x7 and the standard fit tyre is 215/45/17 - I assume Lexus probably knew what they were doing when they chose that tyre size Quote Link to comment Share on other sites More sharing options...
adam_r Posted June 19, 2012 Author Report Share Posted June 19, 2012 The profile will be V shaped and have to much roll in the wall during yaw. Think of it like the wheel moving in and out of tyre. Does that mean the sidewalls of the tyres will actually be leaning inwards ever so slightly with the wider tyre? I presume its the opposite going on Tonys info... The outer rim lips are not far enough apart causing a 'mushroom' shape above the rim. Quote Link to comment Share on other sites More sharing options...
Tony Posted June 19, 2012 Report Share Posted June 19, 2012 The stretch tyres on the drift cars are inherently unstable and easy to saturate. Quote Link to comment Share on other sites More sharing options...
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