Tire size

[Greezy56]

So my N Line S has 235x50R 19" tires as manuf spec,
Could I fit a 235x55 or 60. Thinking more comfort. What are the downsides, are there any upsides by increasing side wall?

[daibill]

If you change the rolling radius of the tyre, doesn't that throw the speedo out???

[joolstdi]

Yes that will increase the speedo speed, what psi are you running in the car? Try 34 psi all round that will make it more comfortable for you, but if you are carrying a load or towing you will need the extra psi in your tyres.

[Indalo]

my N Line S has 235x50R 19" tires as manuf spec,

Manufacturers spend a lot of time testing tyres in conjunction with tyre companies and the upshot of thousands of miles of testing in all conditions produces tyres that provides the best compromise of all the various properties. The tyres may vary between markets due to particular weather patterns and typical road conditions within different regions.

That said, for all normal intents and purposes, those tyres provided by your car’s manufacturer in UK models are regarded by expert test drivers as the best in terms of size. Other tyre manufacturers provide their take on the OE tyres utilising the same dimensions.

Choosing to move away from the OE tyre dimensions is not a decision that should be taken lightly and before embarking on such a project, it would be prudent to contact your insurance company as they will undoubtedly consider it a modification. Whether or not they would wish to alter your premium, I really can’t say but in the event of any serious collision, their assessor (or perhaps a police traffic officer) might question the wrong tyre size. Insurers like to use any possible get-out to avoid paying out and many would seize such an opportunity to do just that.

As mentioned by ‘daibill’, a change to the rolling circumference would have an effect on the speedometer reading, albeit marginal, calibrated as it is to the OE tyre size.

I can’t really comment on the merits or demerits of the kind of change you are contemplating but I doubt that you would improve the comfort aspect noticeably by such a change. Road testing over the years has concluded that car models with eg, 15” wheels on a poverty spec car ride better than their more salubrious sibling with 17” wheels. Yours has 19” wheels! A read of articles concerning winter tyre sizes might help provide answers to some of the questions you may have but quite honestly, unless you live on the top of the pennines or the cairngorms, you won’t have too many problems on OE tyres.