The importance of tyre pressures.

**britten_mark** · Friday 19th February 2010, 11:58

Have had my R for a few weeks now, and having sorted the binding handbrakes shoes that kept it immobile for a while have now had chance to get to know the car a bit better.

Have to say I was not overly impressed with the ride or handling, had basically dismissed the 4C as cack and yearned for some regular shocks. Well on checking tyre pressures last night they were all down to mid 20s; pumping them up to the right specs, well wow, the magic carpet "comfort" ride is back (not that I ever had it), no more shimmying on rough roads, can't wait to try it out in sport

Being a tyre geek already I know the importance of decent boots and the right pressures on any car, but the difference to an electronic damping setup seems to be multiplied many times over. Just shows you have to check the basics out before jumping to conclusions. I'm off on a half day now to have some fun with it!

**abdul** · Friday 19th February 2010, 12:16

going to check mine

**t5_monkey** · Friday 19th February 2010, 16:50

I can feel the difference between 30 and 34 when I drive mine...Check em at the end every month to be on the safe side.

**crespo** · Friday 19th February 2010, 18:47

What PSI should mine be.? 225/45/17's.

straight5 · Friday 19th February 2010, 20:50

Originally Posted by crespo

What PSI should mine be.? 225/45/17's.

On my S60 with same size wheels; its 29psi on normal loads. look inside your filler cap for the guide.

Makes a massive difference.

**LeeT5** · Tuesday 23rd February 2010, 02:35

Originally Posted by straight5

On my S60 with same size wheels; its 29psi on normal loads. look inside your filler cap for the guide.

Makes a massive difference.

I would double check that as my '99 V70R AWD with 215/45 ZR 17s on was 36psi on all 4 corners! Also my current '03 V70R AWD with 235/35 ZR 18s runs with 35psi all round. I know the AWD cars should run with the same tire pressures all round but 29psi seems too low for a S60 T5. Even my old '96 T5 estate with 205/50 ZR 16s had 33psi front and 30psi rear.

**thebadger** · Tuesday 23rd February 2010, 10:05

Originally Posted by straight5

On my S60 with same size wheels; its 29psi on normal loads. look inside your filler cap for the guide.

Makes a massive difference.

Strange, my cap says 36psi on that size?

I use this & it feels great, less than 30psi feels "bendy" in the handling.

Also my Tyres look slightly flat at 30psi & normal at 36psi.

Just my thought but have you checked with a dealer?

**Flatout Phil** · Tuesday 23rd February 2010, 14:19

42R 45F works for me. And yes, you really can tell when the pressure is a few pounds out - mind you, new anti-roll bar will help a bit too...

straight5 · Tuesday 23rd February 2010, 14:27

Originally Posted by thebadger

Strange, my cap says 36psi on that size?

I use this & it feels great, less than 30psi feels "bendy" in the handling.

Also my Tyres look slightly flat at 30psi & normal at 36psi.

Just my thought but have you checked with a dealer?

I've taken another look at my filler and it has left me more confused, rather than less. There are 2 columns one for heavily loaded (picture of 5 people and a load of luggage) and one for medium loads (three people).

Each column is divided into two rows though with a picture of a speedo at 160 kmh. First column shows 0-160 and shows tyre pressures of 29 all round.
Second shows as follows: "160-" with tyre pressures of 38.
Its pretty ambiguous what this means. Does this mean if I spend a lot of time at speeds over 160 kph which is virtually 100 mph I want them at 38 psi, but if Im generally doing 0-100mph Im better at 29??? I often do 130mph on a favourite country lane (private road of course) but inevitably I spend most of my time closer to zero. Well zero is usually where I start from anyway haha.
Seems a very confusing way to put a guide. (Mine dont look too flat at 29)

(Also not sure about Badgers "bendy in the handling" lower pressure means more grip and higher means lower grip but less fuel consumption)

**LeeT5** · Tuesday 23rd February 2010, 16:35

Originally Posted by Flatout Phil

42R 45F works for me. And yes, you really can tell when the pressure is a few pounds out - mind you, new anti-roll bar will help a bit too...

Over inflating your tyres will massively reduce tyre wear. These pressures Phil are too high for your R.

**britten_mark** · Tuesday 23rd February 2010, 16:39

Tyre pressures are always going to be a compromise if you vary your loads and type of driving. I use the middle values unless going on a long trip with sustained loads/high speeds, then I'll pump them up.

Originally Posted by LeeT5

I would double check that as my '99 V70R AWD with 215/45 ZR 17s on was 36psi on all 4 corners!

I had the same Vredesteins as you on my old R and agree 36 was IMHO the best compromise pressure

**princepugh** · Tuesday 23rd February 2010, 17:12

IMO anything outside of the 30-40 band could well result in uneven tyre wear and would certainly be noticeable through the wheel. My P2 T5 carries varying loads but I compromise around the 35 mark.

**mds** · Tuesday 23rd February 2010, 17:12

Lee is spot on the handbook advizes 225/45/17 @ 250 kPa Front and Rear = 36 psi or 2.5 bar Normal running and 280 kPa all round = 40 psi loaded

**pookie** · Tuesday 23rd February 2010, 23:06

On my 850R I use 36psi all round for general urban running around, if I go out on the B roads I'll up them a couple of lbs - also the same for long distance m/way runs.

Pookie

**thebadger** · Tuesday 23rd February 2010, 23:15

By "bendy" I mean that the grip drops off in very tight corners (mini roundabouts & the like) but is far better at 36psi.

The filler caps list is pish anyway, if I were driving a car at over 100mph everywhere, I'd be in Germany? No?

Too much pressure will mis-shape the running surface on the tread & cause bands of wear on both edges.

I'm for 35-40psi (more keen at 35ish) for daily use.

**v70torslanda** · Tuesday 23rd February 2010, 23:51

Too much pressure will mis-shape the running surface on the tread & cause bands of wear on both edges.

Over pressure in the tyres will cause centre tread wear, under inflation will give you high edge wear.

Also that 'little label' is what your insurance company will use to wriggle out of paying your claim if they really feel like it. It's not 'pish', it has a basis in law.

**Flatout Phil** · Wednesday 24th February 2010, 13:44

Originally Posted by LeeT5

Over inflating your tyres will massively reduce tyre wear. These pressures Phil are too high for your R.

(Oops - got my R and my F back to front) But if you look at page 4:4 of the 850 Owners Manual 42f 46r is the spec for motorway at full load - so that suits my usage. 41f 39r is the recommendation for general usage on 205/45/17 on turbo estates doing runs over 60mph. Under that 33f 32r is the recommendation - although I have to say that I find that set-up to be flaccid and soggy.