Tyre Pressures and Suspension

[jon3000]

I ran my car on about 60 miles a few days ago, Scottish roads are rougher than much of the rest of the UK, and did feel I was bouncing around a bit more than I would like. I think I will reduce my tyre pressure tomorrow to see what the effect is. I am not sure what I set it to in the past or even what it is currently as I put some air in without too much thought,  but on reflection now I think to make sure its below 20 PSI.  My tyres are getting old now and may be harder, they have low mileage and are in excellent condition so I am reluctant to change them without knowing it will have a positive effect.

I am wondering what tyre pressures people are running. I have adjustable SPAX, I vaguely recall playing with this in the past. My initial thought was to reduce the setting, however but when I checked it they were near minimum so, actually I am wondering if I don't have enough damping.  I am wondering about other experience with this topic.

[Nigel Haldane]

I run at around 20psi, and around 6 clicks on the sockets, I did have to put stiffer springs on the rear I think they were around 160

[jon3000]

Thanks Nigel,

I have never been particularly pedantic about tyre pressures but this car is likely to make me so.  I checked my tyre pressure it was just about 20-21 PSI on my gauge perhaps. I reduced the PSI to about 19-20 and set the rear shocks around 5 clicks (  the first one or two were not positive enough that I could say sure.) That seemed to help a lot, I reduced the tyre pressure down to 18 and at the moment I am happy. Passing over uneven surfaces much less of an event!. Previously the quarterlight to windscreen chatter was also an issue, it was noticeably quieter. Vibration of the roll-bar is the most noticeable rattle I would like to improve on.

[Nigel Haldane]

I was advised by Avon that my car should be running at 14 psi front and 16rear but this could cause seal problems, the low pressure is because they said my car was grossly over tyred e.g the 94w after the size is the weight ratings, but I didn’t know this at the time and just fitted them, I haven’t seen any bad ware exsept fo when I first put it on the road and left most of the rear tyres on the road.

[jon3000]

Thanks Nigel,
I just learned something. I did not think about tyres having a weight rating. My tyres are AVON too, I think mine are 92V but I will check. I did not think about the risk of deflation, although I have seen that in cold weather.

You reminded me of an issue that came up on my SVA regarding design weights. I got the design weight numbers from Pilgrim which I put in the paper work. Then I failed my SVA because my car exceeded the declared design weight! As the car is build pretty standard clearly the Pilgrim design weight was wrong! Anyhow I got Pilgrim to send me an official letter declaring "corrected" design weights to show I did not just pull the numbers out my a*se, which what I suspect they did

Anyhow my "official" design weights are 490Kg front Axle and 580Kg Rear Axle. It amazes me that the rear axle weight is heavier than the front but I assume that is with allowance for passengers and luggage. I also have weights from the car at the SVA, I assume that was without me in it but I don't recall the specifics.

Anyhow armed with this I will look on the internet for how to calculate the tyre weight rating and perhaps tyre pressures

PS I did not understand your comment about leaving the tyre on the road.

[Nigel Haldane]

Tires on the road! You can spin them quite easily so they ware out. Quicker. I emailed Avon for the tyre pressures

[simon3000]

i run my tyre pressures at about 17-20 psi,seems ok.if the ride is "bouncy" check your shocks are ok.due to den making a few chassis "improvements" the rear shock mounts had been moved resulting in the shocks being out of line.this resulted in the shafts being slightly stressed and premature wear and failure of the seals.protech recommended spherical bearings on the shock top mount and its all ok since

[jon3000]

Thanks,

I will check the shocks for leaks, I think they are fine, I did not notice any leaks but I will look again. I hope my car escaped any "improvements". I may try setting the shocks with increased damping to see if it get better still.

I think I just had them set wrong before. On good roads it was not too noticeable, but where I live the roads whilst not terrible they they have enough frost damage and repairs that I  was not happy with the ride on minor roads.  Reducing the tyre pressure from just over 20 to about 17-18 seemed to be helpful too. It see at least we have consensus on optimal tyre pressures.