Alternative Size(s) To 225/50 R17

[JohnD]

Careful here.
If you fit rims and tyres different from the ones specified by the manufacturer in your manual, in case of a serious accident the insurance will start being a pain in the backside.
My car can only run on 225/50R17 XL, so I have no choice apart from the speed rating which goes H and above.

my car has 20" rims with low-profile tyres, but the manufacturers options, for different versions, go down to 17", and different profile tyres to give the same rolling radius.

I have a set of 18" for winter use. mine has extra-big brake discs so the 17" were not an option.

Reputedly the smaller wheels with bigger tyres run less bumpily.

You will normally need wheel-nuts of different shape to go on steel wheels.

 

[Stivino]

A wee bit about aspect ratios;
In the old days, when tyres were marked (let’s use 155x13 as an example) the aspect ratio was 80%. That hasn’t changed. A tyre that doesn’t state the aspect ratio will be 80%. i.e. 155x13 will be 155x80x13.
So, say you had a Cortina, it probably had 165x13’s (165x80x13) fitted as standard, and you wanted to fit wider tyres. In order to keep the circumference the same, you had to go up two widths, from 165 to 185 and down 10% on the aspect ratio. So, you would fit 185x70x13, to keep the gearing and speedo the same.
Any tyre that doesn’t have the aspect included in the size should be considered as being 80%. And, any tyre below 80% should be considered as a “low profile tyre”.
That is how it was explained to me many moons ago.

 

[EFLImpudence]

Does anyone know how this system came about?

It would seem to be a lot easier to just state the 'height' of the tyre - possibly also in inches to match the wheel size.

Then a tyre could be 185/3/13 and the diameter easily worked out to be 19 inches.

 

[Mottie]

Showing my ignorance here. If 225 is the width of tyre and R16 is the rim diameter, what is the 50 after the 225?

Aspect ratio. It means the height of the sidewall of that tyre is 50% of the width of the tyre. I.e. 225mm x 50% =112.5mm.

It is a bit confusing - you have millimetres, inches and percentages to explain the size!

 

[Mottie]

155x13 will be 155x80x13.

Slight correction Stivino. 155x13 will have an 82% aspect ratio and 80% aspect ratios are the only two sizes that can be legally mixed on the same axle.

From the testers manual:
" 'Standard’ car tyres have a nominal aspect ratio of 82% (unless marked otherwise) and these are almost identical in size to tyres with an aspect ratio of 80%. They can be safely mixed in any configuration on a vehicle".

 

[Stivino]

Slight correction Stivino. 155x13 will have an 82% aspect ratio and 80% aspect ratios are the only two sizes that can be legally mixed on the same axle.

Thanks, I was close but no cigar.

 

[Captain Nemesis]

When the Ferrari 365 GTB-4 Daytona was launched its 215/70 tyres were considered "low profile".