car tyres, a serious question.

[treaclefight]

honestly not a repeat question. can you Expalin what tyre sizes mean.. example 215/45/17, i know that the 17 is wheel diameter and 45 is the offset but what is 215? what would be the physical difference going from a 215/45/17 to a 225/35/18?

[RCP]

That figure is the width of the tyre, so you'll generally find small cars (except for teenagers' Corsas) having 145 or 155 wheres larger or more sporty types having 195 and above.

[wildwood]

It is also worth noting that in order to change your tyres from 215/45/17 to 225/35/18 you also need to change to 18" wheels! The lower the tyre profile, the larger the wheel size needs to be. This is to compensate for the difference in circumference of the outside of the tyre, or else the car's gearing and speedometer will be (dangerously) out of sync.

[treaclefight]

so to confirm, the 215 or 225 figure refers to the circumference or diameter of the tyre. so when the wheel is fitted to the car and viewed from the side, the difference between the figures will be the height of the tyre?

[j2buttonsw]

I read here ( http://www.wrx.com.au/forum/topic.asp?TOPIC_ID=478
2 ) that the first bit is to do with the tyre width (215 or 225, unsure what units they use) the second bit is the sidewall height as a percentage of the width ( 45% of 215 or 35% of 225, again unsure of the units) and the last bit is the wheel diameter in inches (17" or 18").

[sft42]

The first number is the amount of tread surface on the road measured in Millimetres, the second is as already said the tyre wall height expressed as a percentage of the width and lastly the easy bit that most people know the teen no is the wheel size in inches....following on from that the letter after the numbers is a speed rating used to rate the tyres maximum rated speed usually towards the end of the alphabet with the possible exception of H.

[paulz]

Treacy - blimey mate you know more than I do, I now understand what they say @kwik fit, I know last time i got stitched up talked into buying better tyres than I needed cheers :+)

[treaclefight]

lol paulz, the reason i had to find out is because the other half's very flash car has had the wrong very flash tyres put on its very flash wheels. we thought they were fine but they scrape the wheel arches if you have anyone over the age of 9 in the back. info supplied by answerbankers has enabled us to go back to the very flash garage and get it sorted out. :-)