Tyre size width question

[den9112]

Hi, i have a Suzuki swift booster jet 2018 that currently as 185x55x16 tyres on ..I was told when i had a puncture and had to replace the tyre that i could upgrade to 195x55x16 as they are easier to get hold of compared with the 185x55x16..My question is my rear have plenty of tread left and really don't need replacing just yet ,however the front are ok but i would like to change them and put 195x55x15 on the front ,then do the same to the rear when they need doing,is that legal and fine to do or do i need to replace all 4 ..Thanks

[ssray]

My MK1 focus had 205/50/16 tyres I replaced with 205/55/16 as they were half the price, you should have plenty of clearance

[SlimJim16v]

I don't know what your insurance company would say. I would only change all 4 together and would use 195/50x16 instead, which I think is an OE fitment.

[Aunty Pasty]

Going from 185 to 195 increases the width of the tyre making it slightly fatter. It doesn't affect the diameter of the wheel. Increasing by another 10mm should be fine. The rolling resistance will be a tiny bit higher.

Having different width tyres from front to back is legal. Some cars come from factory like that.

[craig1912]

Aunty Pasty said:

Going from 185 to 195 increases the width of the tyre making it slightly fatter. It doesn't affect the diameter of the wheel. Increasing by another 10mm should be fine. The rolling resistance will be a tiny bit higher.

Having different width tyres from front to back is legal. Some cars come from factory like that.

Won’t the sidewall be slightly deeper so the diameter is very slightly larger but acceptable.

Edit yes it will but only very slightly
https://tiresize.com/comparison/

Edited by craig1912 on Tuesday 28th June 17:30

[den9112]

185x55x16 are OEM i would be going to 195x55x16 but only at the front for now ..

[Aunty Pasty]

craig1912 said:

Won’t the sidewall be slightly deeper so the diameter is very slightly larger but acceptable.

In theory yes but we're only talking a few mm here. I don't think the ratio values are exact tbh.

[Scrump]

I made exactly the same change in tyre size on Mrs Scrump's car.
I switched round the front and rear tyres so that all 4 needed changing at the same time.

[mmm-five]

Aunty Pasty said:

Going from 185 to 195 increases the width of the tyre making it slightly fatter. It doesn't affect the diameter of the wheel.

Not the wheel, but it does affect the tyre radius/diameter.

The '55' part of the tyre size is the sidewall height (the profile) as a percentage of the width...so if the width increases but the profile stays the same, you will have increased the sidewall height (and thus the radius) by 10mm x 55% (x2 for diameter).

Whether this materially impacts the ride/performance/clearance is another argument

[den9112]

Thanks all for the replies ,it was only the guy at the garage saying the 185 are not as popular as 195 and the 195 easier to source if you had a flat that made me think about changing when they needed doing..Think i might just stick to 185 ...

[stevieturbo]

Legality irrelevant.

Changing the rolling circumference of a tyre across or either axle, will screw up ABS or stability systems which can be dangerous.

All your tyres must have the same rolling circumference, which your change from 185 to 195 on only 2 tyres will not be the same.

And if an actual legit tyre place has suggested you do this, they are dheads and best avoided.

But a change of all 4 tyres is likely easily doable.