Tyre pressure preferences

[Hound]

I have 225/40ZR18 tyres on my C70 T5, and run them at 34F/32R (the label on the door says 33F/30R, but that's for 225/45R17).

They always look a bit flat to me and I wondered whether 36 all round (Volvo's recommended pressure for a full load) might be better.

Obviously I don't have to think about the same kind of load-carrying requirements as, say, a V70 or 850 estate. But I don't want the ride to be much harsher.

I'm sure I could just try it and see, but thought I'd invite opinions and anecdotes from your varied experiences!

[LeeT5]

I have 235/40ZR18s and as per the fuel filler flap lid on my R, I run them at 35 psi F and 35 psi R. Your tyres are exactly the same profile and size wheel, just 10mm less in width. Due to the lower profile, the tyre needs to run a slightly higher pressure.

I would either speak to Volvo and find out what the new C70 tyres are and what pressures they run at because I'm certain they have 18" or even 19" wheels. Other than that I would run them at 35F and 33R and see how it goes.

[jamesy12345]

I was wondering about this also......as soon as I get hold of a decent thermometer, was going to try....

http://www.race-technology.com/upload/products/NewImages/new%20products/Tyre_pressure_temps.jpg

Rough arsed way would be to work out the difference in volume of different tyres & increase/decrease the pressure accordingly

[foammanmark]

My C70 T5's on 225/45 R17's and runs at 33 front, 30 back as per the label.

[jamesy12345]

Just cos I've really got nowt better to do..the volume of a 225/45 x 17 tyre is about 10% bigger than a 225/40 x 18.

On my S70 there's a 215 tyre instead of a 205.......which is about 10% the other way - so I should be reducing pressure if that method is to be believed

I left them as is (about 33 front / 30 rear) & it feels OK for the way the car is being driven/loaded

[Doingitsideways]

Holy ££££ James, that's boredom fella!

The internet also has pornography you know?!

[Hound]

I looked online and found people running anywhere between 36 and 41 but with no real explanation as to why. Nice to see more sensible responses here, thanks!

Car feels ok, tyres just look a bit flat to me - I suppose it's just a heavy beast.

[Biff]

I usually run 35 all round.
I was told years ago that bigger wheels & tyres made no difference to the psi. It always stayed same.

[Ettienne]

I run 37 psi, run too low psi in a p2r you can risk denting a rim, with the low profile tyre.

It's meant to be 35 normal 39 loaded up, I've usually got a load of crap in the car and the kids so just went in the middle, seems to work well for me.

[Hound]

I took Volvo's "normal load" figure and added a pound or two to cater for the Fat B@stard factor... :frown:

28280

[Rnash2002]

I run 34 all round.

[RollingThunder]

36psi all round on my V70R AWD. Seems OK and the tread appears to be wearing evenly which must be the bitter test? Keep an eye on the wear - if its wearing more on both outer edges than the central band then you're under inflating. More wear on the central band and you're over inflating.

Greater wear on just one outer edge usually means your tracking is out of course.

[jamesy12345]

Holy ££££ James, that's boredom fella!

The internet also has pornography you know?!

The reason I've got a semi on about this is: my R5 orignally came with metric wheel/tyres & now has proper sized minilites & Yoko tyres

It would be nice to get the pressure right, particulary at the back - so next time I drive backwards through a hedge it will be safe in the knowledge that it was the bell end driving it rather than too hard tyres

For anyone interested, some numbers:

The manual states 1.5 bar at the front & 2 bar at the rear, with the rock hard compound TRX

190/55 x 340 front now 195/50 x 15 = 3% increase in volume...will leave it as is instead of reducing by 1psi))

220/55 x 365 rear now 220/50 x 15 = 8% decrease in volume....so pressure should be increased to 31 psi

then keep an eye on the temperatures/wear and maybe I'll get it right some day!

[Doingitsideways]

Mate, I'd get a semi every time I sat in that 5! ;)

[foammanmark]

I took Volvo's "normal load" figure and added a pound or two to cater for the Fat B@stard factor... :frown:

28280

I have nivos on the rear of my C70 for the same reason, although I've lost nearly 2 stone now so could go back to standard:)

[Hound]

Cool, I didn't know Nivos would work on a C70!

Congrats on your weight loss (tries not to look jealous)