Ok to increase Aspect ratio?
Discussion
I have 245/35/R21 tyres on my Volvo V90......beautiful wheels but not suited to a lot of my journeys up to rural Cumbria, Scotland etc. I have a set of 18 wheels with winter tyres and thinking of buying a set of high aspect ratio tyres for summer use. The Volvo "approved" 18" tyre is 245/45R18.
Can I only use aspect ratios as approved by Volvo? Would there be any issue with MOT / accident investigations if I fitted a 50 or 55 ratio?
Ta
Can I only use aspect ratios as approved by Volvo? Would there be any issue with MOT / accident investigations if I fitted a 50 or 55 ratio?
Ta
You're not limited to manufacturer-specified tyre sizes, no.
Increasing the aspect ratio with the same width means an increased sidewall. At some point the larger tyre will contact part of the car wheelarch or whatever, which is worth avoiding. It will also lengthen the gearing and make the speedo under-read, as you increase the rolling radius over what you have now.
245/50 R18 is the closest match to your current rolling radius (the outer radius of the tyre itself), so that would seem like a good safe bet (0.4% smaller). 55 would likely be fine as long as there's clearance for the slightly bigger tyre.
Increasing the aspect ratio with the same width means an increased sidewall. At some point the larger tyre will contact part of the car wheelarch or whatever, which is worth avoiding. It will also lengthen the gearing and make the speedo under-read, as you increase the rolling radius over what you have now.
245/50 R18 is the closest match to your current rolling radius (the outer radius of the tyre itself), so that would seem like a good safe bet (0.4% smaller). 55 would likely be fine as long as there's clearance for the slightly bigger tyre.
I would just stick to the manufacturers recommended sizes.
Why mess with something that they have tested and is known to work in extremis? I fitted non standard tyres to a car once, same wheel, slightly different width (10mm wider) and profile (5% shallower). Online sources and the tyre fitters said it was fine. The car however, when pressing on didn’t behave in the same way. Honestly cacked myself on my first spirited corner, because the car deviated from its normal understeer biased behaviour and felt unsettled.
Personally I wouldn’t risk messing with fitting something non standard, unless you know what you are doing or have a specific reason.
Why mess with something that they have tested and is known to work in extremis? I fitted non standard tyres to a car once, same wheel, slightly different width (10mm wider) and profile (5% shallower). Online sources and the tyre fitters said it was fine. The car however, when pressing on didn’t behave in the same way. Honestly cacked myself on my first spirited corner, because the car deviated from its normal understeer biased behaviour and felt unsettled.
Personally I wouldn’t risk messing with fitting something non standard, unless you know what you are doing or have a specific reason.
Edited by wyson on Tuesday 13th June 21:07
https://www.volvocars.com/uk/support/car/v90/artic...
If your car doesn’t have the bigger brakes or active 4c suspension, you can drop to 17’s and use 225 / 55 r17 tyres.
If your car doesn’t have the bigger brakes or active 4c suspension, you can drop to 17’s and use 225 / 55 r17 tyres.
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