Tyre pressure

[Bakdraft007]

Is the ROM desire for tyre pressure to be 26 psi front and 30 psi rear, typically what people are using?

Its just that they seem a bit low, as soon as you drop a tiny bit the tyres start to bulge... or at least they do on my Stag

Of course I am happy to accept that those recommendations are just fine.

Dave

[sujitroy]

my car label in glove box says the same

[trunt]

The book is always a good place to start but try a few psi changes and see what they feel like

I’m running 30psi all round, as like you felt the fronts looked a bit flat, perhaps as I have modern lower profile tyres. The handling has improved, too early to comment on wear but they will probably rot before I wear them out!

[dasadrew]

.... and, to disappear down the rabbit hole next to the steering geometry one, at what temperature do the pressures apply? On the cars I've had with tyre pressure monitors I have to change the pressures for winter / summer and street / garage parking to stop the warning lights flashing all the time.

[Dieter H. Marschall]

Hello all,
personally I find 1.8 bar (26 psi) most comfortable.
Best wishes,
Dieter - from Germany.

[Hughesy]

34 psi on 65 profile tires.

[jbuckl]

195 (mm) 70 (%) 14 (“) 28 (psi) all round apologies for mixing units

[Paul Kelley]

Given that our power steering is on the light side, I've experimented with front tyre pressures and I reckon 25 psi provides a bit more feel and weight without any adverse effects. I use 28 psi at the back. I'm using Pirellis 15 x 65 x 6 so may vary by tyre brand and wheel size. Another angle is to pump your pressures well up, 32 + if you're laying the car up for a considerable time. This is to reduce the risk of flat spots, but better to also mark a wheel position with tape and move the car around a bit to shift the weight to different parts of the tyres.

[Stag About Town]

Given that our power steering is on the light side, I've experimented with front tyre pressures and I reckon 25 psi provides a bit more feel and weight without any adverse effects. I use 28 psi at the back. I'm using Pirellis 15 x 65 x 6 so may vary by tyre brand and wheel size. Another angle is to pump your pressures well up, 32 + if you're laying the car up for a considerable time. This is to reduce the risk of flat spots, but better to also mark a wheel position with tape and move the car around a bit to shift the weight to different parts of the tyres.

This is good advice to move the car now and then when laid up. This also helps preserve wheel bearings. Regardless of whether the tyres are the original sizes or have changed profile as above, and if the important OD and rolling radius is maintained as it should be, then the volume of air in the tyre is the same. The tyre is just thinner and higher on the sidewall or wider and fatter. The pressure is exactly the same. I changed from 175HR14 to 19570HR14 on Stag alloys and stick to the recommended pressures 26 front 30 rear. Over-inflation is always better than under-inflation but checking when cold is critical. John

[richardthestag]

This also helps preserve wheel bearings.

How so? do you not lube them up with a high melt point grease that is stickier than something very sticky indeed? then are they not tightened to the required preload. I would imagine that if so then there would be no discernible change in the bearings if they were left for decades.

You could use tyre savers but I have generally found that even after long periods of no use that any wheel vibration goes away within a couple of miles. If it doesn't then the compound may have gone bad and you should look at new tyres - especially so if they are coming up for their 10th birthday.

By the way I now enter and exit all of my cars "Dukes of Hazard" style to avoid any potential wear and tear to the door hinges and catch mechanism



Richard

[Stag About Town]

How so? do you not lube them up with a high melt point grease that is stickier than something very sticky indeed? then are they not tightened to the required preload. I would imagine that if so then there would be no discernible change in the bearings if they were left for decades.

You could use tyre savers but I have generally found that even after long periods of no use that any wheel vibration goes away within a couple of miles. If it doesn't then the compound may have gone bad and you should look at new tyres - especially so if they are coming up for their 10th birthday.

By the way I now enter and exit all of my cars "Dukes of Hazard" style to avoid any potential wear and tear to the door hinges and catch mechanism



Richard

No idea not being highly technical but this is a common problem with caravan wheel bearings when the van is left parked for months at a time. The mechanic told me that it is because with the weight bearing down on the same point for a long time the grease eventually leaches out leading to hot bearings when running. I saw mine when he pointed this out and they had clearly overheated and had to be changed. He said that classic cars can have a similar problem if not moved now and then. No idea if he is right or wrong ? Tyres I do know about and flat spots were a problem back in the day when a lot of nylon was used in manufacture. In particular, trucks would return to base on a Friday on hot tyres and would develop flat spots standing over the weekend. Monday morning and they would go off down the road as if running on threepenny bits until warmed up.With modern radials any distortion will be minor, if any at all, and any vibration will soon go.

[richardthestag]

Fair point Stag about town, I can understand about caravan bearings as they are not often used and less responsible owners never consider servicing the running gear of them.

I should play more nice and I apologise for taking the michael a little

I can assure you that the front and rear wheel bearings on a stag are industry standard roller bearing design as pioneered by Timken a 100 or so years ago. They run truer the tighter you get them BUT there is a point at which they will wear more if over tightened. So there is a specific setting at which the bearing it just about tight enough but not so loose as the wheel wobbles. This is the end float that I mentioned.

The hub that each of the bearings sits inside is a sealed'ish space that should contain a lot of a suitable LM grease. this stuff is extra sticky and will have coated each roller, cage and seat for each bearing on the axle. Unless you are underwater or leaving the car is extreme heat I would expect that the bearings would be unaffected by a reasonable length of time without moving.

There are other considerations about waking a car up after a long lay up but to be honest a few months and you shouldn't need to worry too much if everything on the car was already in good order.

[jakesmig]

I used to set my MG Midget tyres (14,195 65) at 17psi at the start of a track day at Knockhill and after 5 laps or so they would be up to 26/27 psi which the car was comfortable at. If the tyres started off at higher pressure they would end up too hard and the car would slide and bounce.
I crew for a Mk2 Escort on the rally circuit and it gets sent out of service at 25psi and the driver resets the pressures before going into stage to about 23
Generall if you are driving gently the tyres won't heat up too much and the pressure will not rise too much, if you're being enthusiastic then the tyres will heat up and the pressure will increase. If the pressure gets too high the tyres will slide more, bounce about a bit and the braking performance will drop slightly.

John.

[Stag About Town]

Fair point Stag about town, I can understand about caravan bearings as they are not often used and less responsible owners never consider servicing the running gear of them.

I should play more nice and I apologise for taking the michael a little

I can assure you that the front and rear wheel bearings on a stag are industry standard roller bearing design as pioneered by Timken a 100 or so years ago. They run truer the tighter you get them BUT there is a point at which they will wear more if over tightened. So there is a specific setting at which the bearing it just about tight enough but not so loose as the wheel wobbles. This is the end float that I mentioned.

The hub that each of the bearings sits inside is a sealed'ish space that should contain a lot of a suitable LM grease. this stuff is extra sticky and will have coated each roller, cage and seat for each bearing on the axle. Unless you are underwater or leaving the car is extreme heat I would expect that the bearings would be unaffected by a reasonable length of time without moving.

There are other considerations about waking a car up after a long lay up but to be honest a few months and you shouldn't need to worry too much if everything on the car was already in good order.

This reminds me of a time many years ago when my company-owned Fiat Miafiori was serviced by the local garage in Watford. Next day, doing about seventy on the M25, the front nearside wheel locked solid with a loud screech and a puff of blue smoke. The steering wheel was yanked out of my hands and I finished up shaking on the hard shoulder. The bearing was practically welded in the hub. The garage were quick to the rescue and admitted to tightening the bearing too much. Scary.

[richardthestag]

Fiat Miafiori