C5 ride

[Dormouse]

I have done a quick calculation for the final axle weights of Pint Pot and I suspect that my final pressures will be 46/48 front and 48/50 rear. Anyone who studies my posts will think I pull these figures out of thin air but I can assure you there is a wealth of technical information for calculating tyre loadings and hence pressures out there. The only problem is finding it.

This is part of an engineering paper primarily for commercial vehicle tyres but such information is also available for caravan tyres to achieve the best performance within the tyre's operating envelope.

[white exec]

I haven't digested all of your figures, so must acknowledge that.

However, for saloon cars like C5, running on standard tyres, there would be precious little comfort to be had with such high pressures. This is particularly true of Hydractive suspension, where the first line of shock absorption is the tyre itself. We know that over-inflating by even just 2psi (above the standard 30psi or so) produces a hard and thrashy ride.

Calculations of loading, foot-print, etc may well produce a result for commercial vehicles - especially those carrying a heavy load - but the lightly-loaded rear end of a lightweight passenger car is possibly something else.

[aneesh84]

On my c5 2005 it says front tyre pressure 2.5 bar on the door pillar which is around 36 psi. i am currently putting 2.4 bar. won't 30 psi be too less and cause early tyre wear. i already see the outer parts of the tyre wear faster, probably due to the roundabouts.

[white exec]

Aneesh - I was just using 30psi as an example, and making a point about over-inflation.
Recommended pressures will vary from car to car.

[Peter.N.]

I have run hydropnumatic Citroens since the '80s (apart from the X7s) and although the high speed comfort is superb they all have a tendency to ride hard a slow speeds over rough surfaces i.e. forest and farm tracks of which there are many of down here, I have found that this can be improved by lowering the tyre pressures by a couple of psi. The choice of tyres can also make a tremendous difference.

The steel sprung X7 with the softer springs actually rides better over these surfaces but not of course over most others, that was what sold it to me when I first drove one. I have only driven one XM that really gives that magic carpet ride and that is among those sitting at the top of the field, why it rides like that I don't know but it is superb, had it been a 2.1 I would probably have it on the road.

Peter

[Dormouse]

I haven't digested all of your figures, so must acknowledge that.

However, for saloon cars like C5, running on standard tyres, there would be precious little comfort to be had with such high pressures. This is particularly true of Hydractive suspension, where the first line of shock absorption is the tyre itself. We know that over-inflating by even just 2psi (above the standard 30psi or so) produces a hard and thrashy ride.

Calculations of loading, foot-print, etc may well produce a result for commercial vehicles - especially those carrying a heavy load - but the lightly-loaded rear end of a lightweight passenger car is possibly something else.

I agree. Tyre Safe . org have an online calculator for tyre pressures and it is ok as far as it goes = like most databases it is not totally correct. So understanding this limitation is essential. When I tweak tyre pressures and wheel alignment I do it fully understanding the negative effects as well. Most of the comfort in a car comes from the suspension so playing around with other bits is more personally subjective than definitive science. All I will say with certainty is that all cars are different, all tyres are different and all people are different.

[Dormouse]

What I have found is that seats vary enormously in comfort so, for me, I start with the seating before I play with anything else and if that doesn't work we discuss this and either get rid of the car or I set it out with various pads, cushions and foams under a seat cover until I can live with it. Some cars I just couldn't. The best car we both found especially comfy was an Audi 100 Avant auto early 5 cylinder. I liked my dad's Austin Ambassador for seat comfort but LOML never drove it so it doesn't get the seal of approval.