So just fitted winter boots to car and have followed the handbook and put an extra 0.2bar in each tyre. This led me to look more closely at recommended pressures. Why is the front pressure lower than the rears? 2.0 vs 2.1 bar? I wouldve thought with the heavy engine over front wheels it should be higher for the front wheels.

Also if the car is fully loaded the sticker recommends 2.3 bar for fronts and 3.0 for the rears. That seems a big jump for the rears?

Someone please educate me!?

Edited 24 November, 201015 yr by evan15281

Mine says 2.1 for the front and 2.0-2.8 for the rears + 0.2 for winter.

Probably passengers plus luggage plus a full fuel tank load the rear tyres more than the front?

I agree that the full load pressure for the rears takes a lot of pumping. I have ben mocked by owners of other marques who say the pressures do not need to be adjusted for their 'wonderful' cars.

Probably passengers plus luggage plus a full fuel tank load the rear tyres more than the front?

I agree that the full load pressure for the rears takes a lot of pumping. I have ben mocked by owners of other marques who say the pressures do not need to be adjusted for their 'wonderful' cars.

just would've thought in an unloaded car that the engine weight over the front wheels would mean higher pressures required for the fronts.

Probably passengers plus luggage plus a full fuel tank load the rear tyres more than the front?

I agree that the full load pressure for the rears takes a lot of pumping. I have ben mocked by owners of other marques who say the pressures do not need to be adjusted for their 'wonderful' cars.

Funny you should say that, I get the use of a Jag XJ8 for around 9 months of the year. There are no different pressures on this front and back...Just High Speed and comfort Guess what they are on now!!

There has been a lot of discussion about vRS tyre pressures in the past and a strong consensus that the OE recommended pressures are too low.

Personally I used to run 2.3bar front & rear in the winter and 2.35bar front & rear in the summer. This IMHO tightened up the handling nicely with no particular degradation of ride quality and certtainly no adverse affect on tyre wear.

As for the + 0.2 bar for winter tyres, this will likely be due to winter tyres having a generally softer construction and more pliable sidewall. I would suggest this will also depend on whether you are using standard size 225/40 18s or have gone the whole hog with winters and got, say, 205/60 16s.

If anyone's interested......

The tyres I got fitted were Marangoni Meteo HP from Kwik Fit, mainly for convenience reasons. I went for the straight tyre swap solution, no extra set of alloys. So sizes 225/40 18. Obviously not true skinny snowploughing winter tyres, but likely better than the summer dunlops. Admiral insurance were happy with this if that helps anyone.

Obviously a bit too early to tell regards how they will perform, but first thing I've noticed is the ride is definitely a bit softer - compared to the OEM Dunlop summer tyres. Front Dunlops needed to go in the bin as they were right down to their wear markers centrally and the tyres have not been overinflated. Maybe it's the fact there's now some rubber between me and the road cushioning the ride.

I'll report back when the tyres have bedded in.

Edited 24 November, 201015 yr by evan15281

There has been a lot of discussion about vRS tyre pressures in the past and a strong consensus that the OE recommended pressures are too low.

Personally I used to run 2.3bar front & rear in the winter and 2.35bar front & rear in the summer. This IMHO tightened up the handling nicely with no particular degradation of ride quality and certtainly no adverse affect on tyre wear.

As for the + 0.2 bar for winter tyres, this will likely be due to winter tyres having a generally softer construction and more pliable sidewall. I would suggest this will also depend on whether you are using standard size 225/40 18s or have gone the whole hog with winters and got, say, 205/60 16s.

Thanks for that information. I wondered whether the lower temps in winter meant that pressures are lower (I'm thinking that's Boyle's law or something from my distant chemistry past!), and to keep same inflation at a lower temperature requires higher pressure. Certainly the more pliable compound makes sense as well. I've stuck with original 225/40 18 sizes so again assume that pressures need to be a bit higher than with higher profile tyres (e.g. road bicycle tyres need higher pressure than comfy mountain bike tyres)

Why higher pressures during the summer if you don't mind me asking?

I guess erring on the side of slightly higher pressures would slightly reduce the contact area with the road, essentially making the tyre a bit narrower, and they do say narrow tyres are better for snow. Might give the new tyres a little pump up tomorrow.

cheers

Tyre pressures are determined using three main parameters:

1. Maximising contact area (even wear, good grip etc).

2. Reducing heating of the tyre due to sidewall flexing.

3. Optimising grip

Rears often have a high 'fully loaded' pressure to reduce sidewall flexing and hence overheating of the tyre on a high speed run.

Front and rear pressures are often tweaked to obtain the handling balance that the car manufacturer is aiming for.

Increasing the pressures will often make the car feel 'sharper' - but what you are doing is effectively stiffening the sidewall - this reduces the slip angle (and possibly also the contact area) so at the end of the day the actual maximum lateral grip is reduced. You won't go far wrong sticking with the manufacturer's recommendations.