Largest circumference tyre on 18" wheels

[Juzman]

Hi,

I've just gone to 18 inch wheels with 245/40 tyres. I know it's not recommended but just wondering if anyone knows what is the maximum tyre circumference you can go before there are serious guard and rubbing issues. Can I get around it with rolling the guards?

I just want a little comfort back, finding the 18s giving me a little too harsh ride and was hoping I could up the side wall a little.

Also on a side note what is the minimum psi I could run the tyres at for 18s?

Cheers
Justin

[Dave_Obsession]

235/40 or 245/40 is all I've ever heard of AU's running on 18's......if you up the sidewall while keeping your 18's, the tyre diameter will become too big and it will throw your speedo and odometer out......

If 18's are too harsh for you, go down to some 235/45 17's??? That should give you a little bit of extra comfort you are after?

As far as minimum psi......as low as you want! Your tyres won't last as long, but you may find the ride a little more comfortable......I run mine at 38psi (235/40 18's) and I find the ride quality is excellent.

Perhaps have a play around with some different psi settings on your tyres, and find what feels best for you. It's a personal choice thing.....what I may consider soft, you may consider too harsh etc....it's difficult for anybody else to advise you what you need.

But personally, if you're determined to drop your tyre pressure, I wouldn't go below 30psi if your on 18's......I just think it will sacrifice your tyres too much.

[ronwest]

Originally Posted by Juzman

I just want a little comfort back, finding the 18s giving me a little too harsh ride and was hoping I could up the side wall a little.

Yeah, I found the same thing. I had the 18's on for a trip to Adelaide and back and ended up back on 17's.

For long trips it's the best compromise between looks/comfort, imo.

[T3man]

The problem with higher profile tyre on the 18s will be the upper ball joint not your guards. A 245/45-18 tyre will be 12mm taller (radius) and there is not 12mm clearance under the ball joint.

You will have to go to a 17" wheel to use a 45 series tyre.

I would not run a 40 series tyre on less than 36 psi on the front (40 is best) - you risk sidewall damage if you do. 4 psi lower for the rear unless fully loaded.

Even a 45 series should be at 36 psi but you could drop it to 34.

[JC]

You'd have to go to a 225/45/18, but that would look a little skinny and may not be legal fitment on an 8" rim (would be Ok on 7" or 7.5" though)

[Juzman]

thanks for the advice guys, I've been experimenting with different psi... hard to actually notice that much difference between 35 and 40... perhaps a little more forgiving.

Sounds like larger tyres are not going to work, oh well... I guess the firmer ride was to be expected.

You'd think with technology these days cars should almost be bump proof!

[Mont5.0]

they probably are when you run them on the factory 16's (or XR 17's) with larger side walls.