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#556577 - 29/01/19 04:48 PM Tyre Pressures
Gambalunga Online   content

Member of the Inner Circle

Registered: 03/09/11
Posts: 11129
Loc: Mandello del Lario, Lake Como,...
Every so often someone asks advice on tyre pressures and I have tried several variations over the 6 plus years during which I have owned the Plus 4.

During that time there have been several changes in the suspension configuration and a change of tyres. Interestingly the changes in suspension configuration seemed to also have an influence on what seemed to be optimal tyre pressures. Quite naturally the change of tyres also had an effect.

With the original factory supplied Yokohama 195/60 R15 tyres and I found 1.5 Bar (22 psi) does not feel good. No doubt the car grips well at that pressure but it feels as though the tyres are under-inflated and a bit squirmy in corners.

I now have Michelin CrossClimate 195/65 R15 tyres fitted. They may not be optimal in summer on hot dry roads but they are quite acceptable, fantastic on wet roads and good in snowy conditions. In part they are fitted because in this area you must have snow tyres or carry chains from 15 November to 15 April.
I currently run 1.6 bar (23 psi) front and 1.7 bar (25 psi) rear.

My findings, in general terms with different pressures are as follows:
1.5 Bar (22 psi) - comfortable ride, particularly on rough roads, slightly heavier steering and the feeling that the rear is slightly under-inflated (depends on the make and model of tyre
1.6 bar (23 psi) - a reasonable compromise between comfort and general feel.
1.7 bar (25 psi) - the car feels better planted on the road and the perception of body roll is reduced.
1.8 bar (26 psi) - great on smooth surfaces but feels harsh over minor bumps or a broken road surface. Steering is lighter.

I think it is very much a matter of personal choice and how the car feels with different tyres and pressures. With such a light car small changes can make a big difference. Too high a pressure definitely makes the ride harsher and too low a pressure may make for a feeling of underinflation in cornering.

#556718 - 30/01/19 09:42 AM Re: Tyre Pressures [Re: Gambalunga]
MOG 615 Offline

Has a lot to Say!

Registered: 24/09/14
Posts: 1349
Loc: London

I am in 100% agreement that drivers should experiment with tyre pressures for each type of driving they do.

With my (TR engined) +4 I needed to run higher front pressure than rear to help minimise the understeer. On the road I would run 24/22 for light loading , and 28/26 for heavy (I had an 18 gallon "Sebring" tank)
For circuit racing I used to start with 38/36 on road tyres (otherwise the tyres would rolloff the rims under limit cornering) , but 26 all round on racing tyres (Dunlop M section radials , but I used the stickier 232 compound on the front and the harder 184 on the rear) The racing rubber was much more stable on the rims Most drivers vary the pressures according to the circuit and the conditions on the day.
From his autobiography we learnt that Lawrence used 50 all round on his Dunlop L section cross ply racing tyres for Le Mans, but that is a very specific task.

Now I would not dare advocate that drivers change tyre pressures for each drive , but develop a range that they are happy with from previous experimentation. Your range of 22 to 26 would suit the +4 , I think the lighter 4/4 could possibly be a few psi lower and the heavier +8/Roadster a few more.

Personally I found 24 psi all round when touring with my +8 is a good compromise, and with a full load about 2psi extra in the rears. However with the SSL front/rear suspension I think I will try some further experimentation. The more compliant ride leads me to think that I can raise the pressure an amount , but the greater grip suggests that I could lower it . As soon as the salt disappears from the SE UK roads I will doing some trials.
Andy G
1999 +8 , Indigo Blue.
Ex-John McKecknie/Mike Duncan 1955 +4 racer.

#556726 - 30/01/19 11:08 AM Re: Tyre Pressures [Re: Gambalunga]
brownbaker Offline

Talk Morgan Regular

Registered: 23/09/10
Posts: 850
The number of times drivers have pointed to my reat tyres and told me I had a
Flat tyre !

#556887 - 31/01/19 07:35 AM Re: Tyre Pressures [Re: Gambalunga]
xc68anc Offline
Just Getting Started

Registered: 16/11/18
Posts: 54
Loc: Germany, Rhein-Main Area
In cause there is an important difference in driving with a little difference in the tirepressure it makes sence to use allways the same pressure gauge.

I a lot of years ago I had an scooter accident, caused in wrong working tire pressiongauge a the gasstation. The tire pression was about nearly 50% to low.


#556888 - 31/01/19 07:44 AM Re: Tyre Pressures [Re: xc68anc]
Gambalunga Online   content

Member of the Inner Circle

Registered: 03/09/11
Posts: 11129
Loc: Mandello del Lario, Lake Como,...
I agree. I have carried a tyre pressure gauge in my motorcycle kit for ages and when I bought the Morgan it was natural to get one to keep in the glovebox. Even though it always registers the same as the gauge on my compressor I still check with the tyre pressure gauge.

In the case of the Morgan the range of pressure I use is very small and I prefer to know exactly what it is.

Andy. I too increase the rear tyre pressure when touring with luggage. Given that most of the extra weight is over or behind the rear wheels. In that case I up it to 1.8 bar (26 psi).

Edited by Gambalunga (31/01/19 07:51 AM)

#557460 - 02/02/19 03:09 PM Re: Tyre Pressures [Re: Gambalunga]
Geir Karlsen Offline
L - Learner Plates On

Registered: 22/03/10
Posts: 180
Loc: Norway
I think Peter is right.

1,7 bar is the best for my 4/4.
Lower pressure the steering gets heavier and acceleration slower.
At 2,5 bar the steering is very light ad the ride harsh. I only use this pressure when the car is laid up before winter, as the tyres leaks.
I can´t give a n exact reprt son tyres, but they do have an aimpact on noise and ride too.
I also check tyre pressure once a month as tempereature and leakage has an impact on my ride.

Edited by Geir Karlsen (02/02/19 03:17 PM)
4/4 2 seater 2001 model

#557537 - 02/02/19 09:48 PM Re: Tyre Pressures [Re: Gambalunga]
The Austrian Offline

Talk Morgan Addict

Registered: 17/10/14
Posts: 3415
Loc: Austria, close to Vienna
I ended up at 1,7 to 1,8 bar as the best option for my type of driving style.
once: Green M3W; 2013
now: Red 4/4 Sport; 2011
and some practical cars for use in real life


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