Understanding Wheels

[BenIS]

Can someone help me with understanding all the different wheel sizes please. Like this for example, "Tyres 245/40R18 and on its 8Jx18H2 ET40

Obv 114.2 x 5 pcd" I get all the tyre sizes but just the wheels i dont.

Also what wheel nuts do IS200 have?

Thanks

[mikey's IS]

ok so

Tyres - 245 is the width - 40 is the profile ( sidewall ) R18 is the rim diameter

Wheels - 8J is the width ie 8 inches wide - 18H2 is 18 inches in diameter ( not sure what H2 is ) - ET40 is the offset which will determine how far the mounting face is away from the centre of the wheel ( see attached for explanation ) hope this helps.

Mike

[steve2006]

That's a very good explanation.

Just to expand a little , using the example above the tyre is a 245/40/18 so the tread width is 245mm, the aspect ratio is 40 this means the side wall is 40% of the tyre width i.e. 40% of 245mm or 98mm high. The tyre is for 18" rims.

For some reason tyres sizes are a confusing mix of both metric and imperial

[BenIS]

brilliant guys thankyou cant ask for better than that !

[mikey's IS]

That's a very good explanation.

Just to expand a little , using the example above the tyre is a 245/40/18 so the tread width is 245mm, the aspect ratio is 40 this means the side wall is 40% of the tyre width i.e. 40% of 245mm or 98mm high. The tyre is for 18" rims.

For some reason tyres sizes are a confusing mix of both metric and imperial

Not sure where you have herd that from but i dont think it works like that the sidewall on a 245/40/18 is not 98mm or near 4in as im running 255/35/18 this would make my side wall 89.25mm

as showen in the picture i have just taken they are no where near that.

Mike

[mikeyv]

I'm pretty sure Steve is correct.

[mikey's IS]

^^^ care to explain how

[mikeyv]

Sure, though I didn't think explanation was required.

Aspect Ratio

The aspect ratio of a tyre is the height of the tyre sidewall expressed as a percentage of the tyres width. To understand this more you need to recognise the meaning of the size markings on the sidewall of a tyre.

For instance a typical tyre size used today is 205 / 55 R 16 and this size can be broken down into 3 major areas:

205 - this is the width of the tyre expressed in mm.

55 - the aspect ratio, or profile of the tyre, in this case 55% of the tyre width.

16 - diameter of the rim the tyre is designed to be fitted to (in inches).

In this case the tyre sidewall height would be 113mm (205 x 55%).

That;s lifted directly from etyres site, and for me confirms what Steve wrote, and I agreed with.

[mikey's IS]

Come on why was an explanation not required all you said was steve is correct when there is a photo there to prove this is not correct also this is sombody esles explanation ( what are your veiws )

Not having a go but have you actually measured a 205 / 55 / 16 to confirm that this is correct.

edit just poped outside and took a picture of a 205 / 55 / 16 and these are the results. dosnt look anywhere near 113mm so you still belive etyres & steve ?

Mike

[mikeyv]

Take the tyre off the rim and try again, this time on a new tyre with full tread, and from the actual inside edge of the tyre, not the wheel rim.

And yes I do believe both, you obviously don't.

Oh, and I still believe clarification wasn't necessary, if somebody says something, and I say I think they're correct, where's the ambiguity?