I had a brief chat to a local tyre supplier today who has been telling customers to run 38psi in their 18" tyres. I reckon this is far too high and said 32-34max. Anyone got any views? They aren't mine by the way, just looking for some feedback.

 

I would think, correct me if im wrong, that the normal wheels run on 28ish, so 18's wouldnt require more. theyre just a lower profile/larger diameter tyre. same pressure rules should apply.

too high and you'll end up sliding around the road

 

My thoughts exactly. I've heard of others being told by this bloke to use 38psi!

 

Normal 17" tyres are 33 front and 32 rear if you use book pressures.

 

Mark - LOL, who is this bloke then?

 

You should know, you were there!

 

Mark,
Had to laugh when you pulled in. Quote from the bloke "how will he know he's no tyre specialist"

 

subaru sticker that i got with my 18" P1 wheels (225/35/18) says 33 front 28 rear if that helps at all

 

Vito, obviously the bloke who sold you the tyres isn't as clever as he thinks he is!

 

LOL, well, it lightened up an otherwise frustrating day didn`t it Mark?

Vito, bang 38psi in and then go down to morrisons car park when its empty and attempt some cornering, should be fun, and you wont break anything when it understeers to ****! lol

 

got a p1 with upgraded 18" alloys 225/35/18,subaru sticker on door panel says 38 front and 35 rear,hope this helps

 

im running 37psi front and 32psi rear with no problems. you can notice the ride is alot firmer as a daily driver.

 

you're dead right, i've got the std 16" pressures in my head

do you actually run 38 in the fronts? how does it drive?

worrying thing is my car drives ok with 33/28 should be a bit better then with nearer the correct pressures in

 

in my P1 (225/35/18 ) i run 37&35

 

On my newly-arrived Forester STi with 18 inch wheels the door pillar sticker says 2.3 bar front, 2.2 bar rear (that's about 33.5 front, 32 rear). However, I'd been using 38 front and 36 rear 'cos that's what it had in it when delivered and I didn't have a handbook.... but I had a sneaking feeling that the skating around roundabouts and terminal understeer wasn't quite right...


Yesterday I dropped pressures when cold to 34 F 32 R and the increase in grip (and drop in noise) is astonishing.

 

eh? - I thought tyre pressure was related to tyre size and car weight - therefore how can someone say that all 18" tyres should be **psi.

confused

 

I run 36 front 34 rear no problems with it.

 

I believe that the pressure increase is related to the profile rather than outright tyre size.

i.e.If 18" wheel means you've got a 35 profile (instead of 40 or 45) then there is less cushioning for the wheel. Higher pressure assists with keeping the road away from the rims.

F1 cars use high profile tyres so that they can run low pressures and increase the contact area between tyre and road.

 

I run 37psi all round on mine with 17"s on.

Bob

 

Although I have just checked and I should be running 37Front and 32Rear.

http://www.whiteline.com.au/articles...on_rails_1.pdf

Bob

 

Woah!! this is interesting reading. I always thought i was pushing it running 32Psi all round. The fronts always look flat, so going to try 37psi in them later.

Im running 225/35/18 Toyo Proxes T1 S by the way.

 

I spoke with Mike Wood at Prodrive about this, and he confirmed (in good faith + with the usual caveat about don't sue me etc) - that in relation to the P1, running 18 inch PZeros that the recommended tyre pressures were 38 Fr 35 rear - as the sticker in the door says. Personnaly I found these way too hard and bounced all over the shop with car feelign quite skittish. Currently run approx 35 front and 33 rear which works pretty well for me.

 

38 in fronts,to much understeer,i use 35 front,34 rear works ok with me
but im no expert

 

Im running 36/35 on some 215/35/18s. I found that 32 meant that uneven roads and cats eyes that werent flush with the road would clonk the rim at speed