Hi all, i want to buy a set of 18" CJ Lancer VRX rims and put them on my '08 380 SX (17") 225/55/17 question is, what size tyres do i need to buy to keep the same size diameter overall?

Stock 380 is 215/55/17... a set of 225/45/18s would have an overall diameter of about 8mm less. They're an appropriate size - I wouldn't be keen to go wider than 225s on a 7" rim.

Sorry, my mistake, your quite right meant to say 215/55/17

So a 225/45/18 shouldn't throw the speedo out by much?, not that my speedo is super accurate anyway, always indiates about 6-8 km/h faster than i'm going anyway...

Most of my customers with 380's running 18's are all running the 225/45/18, is a fairly common tyre size, fits the wheel nicely and also keeps the speedo fairly close

Ok, many thanks

So a 225/45/18 shouldn't throw the speedo out by much?, not that my speedo is super accurate anyway, always indiates about 6-8 km/h faster than i'm going anyway...
If they're 8mm out, they'll probably throw out the speedo by 1.5-2km/h at most. Legally you can go +/-15mm, so it's still legal.

235/45/18 would keep your rolling diameter virtually the same (so no change in speedo), but I would be very reluctant to run a 235 tyre on a 7" rim.

Running a 235 tyre with not probs

Running a 235 tyre with not probs

You don't know how bad it is until you get a correct fitting tyre warren!

Toyota do it..

17x7s and run a 235/45/17 out of the box..

Food for thought maybe..

SuFz

You don't know how bad it is until you get a correct fitting tyre warren!

Tyres are too skinny otherwise IMO

its more about look for me

Does the change from 17's to 18's have a major effect on ride comfort?

All things equal you'd likely notice that your ride was a bit firmer, but unless you're super anal about ride comfort, it wouldn't be a major effect.

I went from 17s to 18s on my Magna and noticed a difference - but it was in part because my new tyres had a significantly stiffer sidewall than my 17s. So your tyre choice will definitely play a role.

not really worried about comfort TBH