All these threads about tyres has reminded me:
Is there any chart or conversion to quickly compare rim sizes and therefore the appropriate tyres to retain the overall diameter of the wheel.
I understand the rim diameter in inches, the XXX/XX size being the width of the tyre itself in millimeters and the second figure giving tyre wall (rim to edge?) as a % of the tyre width. Am l right so far?
For example if l wanted to change a 14" rim 185/65 tyre to 16" rim what XXX/XX figure should l be looking at to keep the overall wheel size?
I have tried working it out manually but what with the rim being in inches then adding 2 X the % of the width in millimeters it is frankly pissing me off and l don't really know what l'm doing.
Can anyone help?
dan
P.S. Can anyone also tell me of any ill effects from increasing the width of the tyre (regardless of rim size) to say 225mm for example?
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Any alloy wheel supplier will be able to tell you which tyre size you need to maintain the rolling radius based on your existing wheel/type combination. I went through this a few months ago, and couldn't find anywhere that had this kind of info.
Going to wider types will make the car more prone to tramlining and aquaplaning, since the weight of the car is now spread over a larger area. There is also the risk of the tyre rubbing against the inside of the wheel arch when on full lock if the wheel offset isn't right. You also tend to find that it's difficult to simply increase tyre width without increasing the rim size.
Andy
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Dan
You may find what you want on the following site.
www.miata.net/garage/tirecalc.html
David
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Increasing the tyre width, as Andy says, can cause problems with handling.
Another major factor is the rolling resistance, as well as the 'roll and slip' factor.
In essence, in the event of losing lateral traction, the car may be more prone to 'dig in', and roll, as opposed to just sliding.
Even if it doesn't tip over, with more area on the road, and therefore more grip, the dampers and other suspension parts will take more of a hammering as well.
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Dan
Try the tyre bible on
www.geocities.com/chrislonghurst/
which has coversion charts, or contact Micheldever tyres and get their 'Sportsmode' brochure.
Regards
John
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On your PS, you will find poorer grip in the snow. This is why rally cars use narrow tyres for snowy routes.
I am more aware of snow problems as I live 1000 feet up a Welsh hillside!!!!
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Cheers guys,
I spent ages trying to find this info.
Thanks again.
dan
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