radial tyres putting extra load on suspension

[martin418]

just a thought having seen a couple of trunnion failures i was wondering if running radials at a much higher pressure is not helping the wear and load on the suspension as the original tyres running 24 psi have a good amount of give thus absorbing road shock

[liammonty]

No, I doubt it. Radials need a higher pressure than a cross ply precisely because they are 'squabbier' than a cross ply. I don't think trunnion failure is a new thing to be fair - we just didn't used to be able to let people know about it on the Internet in the olden days so perhaps word didn't travel so fast! I'm off to check my trunnions now I think!

[chesney]

Poly bushes would have a similar effect, no?
I've run poly bushes for over 30,000 miles on my Minor with no adverse effects, though it is greased every other weekend (do 1000 miles a fortnight in mine).
More of a problem is wider tyres/rims I imagine, though not on the trunnion. I've seen fatigue of the eyebolt/chassis leg which is no doubt exasperated by the greater grip/faster cornering/strain in general of wider tyres.

[John Naylor]

At the risk of re-starting the old arguments on tyre pressures:
Radial tyres do not require much higher pressures than cross plies! Michelin recommended 20 front 22 rear on 145 14 MX's and 22/ 24 for other manufacturers (saloon normal loading) quite different to the commonly advised 30+psi on this forum.
I replaced the aged rubber on Bertie (a Traveller) with new 145 R14 Bridgestones initially set at 30+psi and was still unhappy with the ride. Having taken BMC's advice on W40 oil in the shock absorbers I was much happier but then reduced the tyre pressures to 24/ 26 and was astounded at the improved ride. My wife, who is not a driver, noticed the difference and said it feels like a new car! So far, I haven't felt any deterioration in handling. The fronts used to be disturbed on corners by pot holes but now stay in contact with the road surface being much more predictable.
Most of us now run tubeless which are safer than tubed tubeless tyres as they are at much lower risk of rapid deflation. As standard rims are not Tubeless it is necessary to avoid excessively low pressures which could cause the tyre to leave the rim under extreme cornering but that is no excuse for over inflating.
Tyre pressures are a personal preference but you won't risk anything by reducing to recommended settings and you may well be surprised at the improved ride!

[martin418]

i was indeed basing the'' higher pressure '' from posts on here

[bmcecosse]

At the low pressures - the side wall bulging and heat build-up in the tyres is alarming!

[martin418]

i can see why the radials bulge as i had 155 s on the wheels i repainted and the 155's did not sit on the bead at all well and having looked at several tyre to rim charts it would appear 155's are to wide for minor rims , i am glad i went for the original spec tyres so no messing about with pressures and gearing etc

[John Naylor]

At the manufacturer's recommended pressure they don't bulge excessively and shouldn't have excess heat build up. Some people look at radials and think that the flex in the sidewall is a weakness and want to add pressure to get better steering response (false!) and make them look more like a cross ply. That is defeating the objective of the tyre which is to maintain the correct contact patch with the road in all circumstances. Excess pressure distorts the contact patch and not only gives increased wear but reduces grip. The only 'down side' in reducing from 30+psi to correct settings is slightly heavier steering at low speeds, not noticeable over 10 mph.
John

[bmcecosse]

Just feel the sidewalls after a good run if you are running daft low pressures. ALL modern cars on radials specify pressure of 30 psi and above.....there's a good reason....

[smithskids]

I have Toyo 155X14 radials on my MM and they work fine at 25 all round. Its a tourer so it will be a bit lighter than a saloon I suppose. I also did the BMC oil trick on the dampers and it holds the road well and is comfortable

[ManyMinors]

Just feel the sidewalls after a good run if you are running daft low pressures. ALL modern cars on radials specify pressure of 30 psi and above.....there's a good reason....

Tyre pressures vary from car to car depending on weight largely. By modern standards a Minor is a light car hence the recommended pressures from both the car and tyre manufactures being fairly low. ALL modern cars do NOT run with pressures of 30psi and above. The manufacturer recommends 26psi all round for my Mazda MX5 and anything higher certainly has a negative effect on it

[bmcecosse]

Aye -but these are extreme low profile tyres I suspect.....

[ManyMinors]

They're 185/60/14. Hardly extreme by today's standards. 26psi is simply the manufacturers recommended tyre pressure for the car with standard sized wheels and tyres. It's a fairly light car. So is a Morris Minor. No need for high tyre pressures.

[bmcecosse]

I bet it hasn't got the tyres fitted to massively undersize rims !!

[ManyMinors]

This thread is about radial tyres in general. Why would you assume people are running such tyres on "massively undersize" rims?
On my own Minor I have radial tyres. They are the size recommended by the car manufacturer and I run them at the pressure recommended by the manufacturer too. I have experimented over the years with different sizes and different pressures but this suits the car best for my purposes. Why do you feel owners should run greater pressures than the tyre and vehicle manufacturer recommend?