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MG MGA - Tyre pressures

OK Steve what tyre pressures do you recommend? I have New Vredenstein 155s. As to power steering. One day. (I am 77) And what about wife's arm power. I love these BBs.
H L Davy

You mean to say you let your wife drive the MGA!!

I run 27 all round on my Firestone 165s. In the recent shock absorber thread one ran 26 while another had 26 front 28 rear.

If my memory recalls correctly (probably not), other threads have highlighted handling issues that have been traced to over inflated tyres; i.e. 30 or above. The opposite also applies, that under inflated tyres also course issues, such as heavy handling at low speeds.

What pressures are you running?

I guess this topic will get a mention in Barney's parallel thread on handling.

As an aside, I wonder how many of us can vouch for the accuracy of our tyre pressure gauges? I have seen wide variations between commercial gauges at filling stations, garages, my own compressor adapter and other gauges I have in my garage.

Steve
Steve Gyles

I seem to remember on an earlier thread that someone said you should not run less than 30 lbs in a radial tire. Any truth to this?

John
John Progess

My wife doesn't drive the MGA. I actually want her to know how to as a back up if I become ill since I do longish trips on the Continent. I was running 26 all round. Vintage Tyres fitted new tyres and gave me the car back on 20/22. I will try 26/28 fully loaded.I have two guages which agree and avoid garage ones.
H L Davy

HL. Nor does my wife drive ours. I am not sure her feet will touch the pedals!. Pressures look in the range most of us go for.

Not sure about the not less than 30lbs that John says. let's hear what others say.

Steve
Steve Gyles

apologies for this aside but my wife drives the MGA but only when we've been to the pub and I've imbibed more than a pint- she absolutely hates driving it, I think for following reasons:

stiff steering -no power steering
low seated position
quite high geared steering
hard suspension
'notchy'gearbox with small gate
no syncro on first
controls not on steering column
fierce clutch (original mga not diaphragm)
no vanity mirror
difficult getting in and out of the car
difficulty in finding headlight dimmer switch

need I go on - but she loves the car!
J H Cole

When I bought my A, I was concerned there was a problem with the very heavy steering. I asked the PO when he last checked the tyre pressures and he said he always checked it carefully, using the figure in the handbook. That meant 17psi on the front! So that was the easiest fix ever!
I have 28 all round.
Graham M V

I always run my MGA's (with steel radial tyres) at 30 psi. I find that this gives the best compromise between roadholding and comfort.
Barry Bahnisch

I run 30 psi all round too, not saying its correct but it suits me.
Vin Rafter

I am working on a 74 jeep and the handling was aweful.Amongst a million other comments I was advised the best way to get the right press. in my new 31in truck size tyres was to drive to a large to a large flat area ,put a wide band of chalk across the treads of all tyres and then drive forwards and backwards straight (ie with no steering) a few times and examine the chalk. If chalk remains in the centre inflate, if on the outside deflate until even chalk removal acrooss tread. I did this on the jeep and it gave it better steering and roadholding ( press. about 28psi). Theory obviously is that all of the tread should touch the ground ( should also even out the wear). I keep the mga tyres hard ( 32psi )to reduce steering load but.....!! I will try this on mga in near future but would appreciate comments..
Neil Ferguson

My understanding of tyre dynamics is that you want the minimum pressure to keep the tyre from distorting on the rim. This gives you maximum contact area with the road and stops heat build up. Low profile tyres need less pressure to keep their shape i.e. 25 psi maybe ideal for 195/55/15 for road and track while 165/80/15 might need 30 psi for road and 40 psi for track.
What do you guys think of this logic?
Does Fred Puhn cover this subject in his book "How To Make Your Car Handle"?
The MGAguru discusses this issue in http://www.mgaguru.com/mgtech/tires/ti102.htm and I quote one of the paragraphs below.
"Now in general, lower pressure puts down a larger footprint and gives a better grip, up to the point that the tire may start to roll over on the sidewall and pick part of the tread off the ground, when it loses grip and gets really mushy. At just slightly higher pressure where it is doing none of these nasty things, you get maximum grip".
Mike
Mike Ellsmore

I run 26/28 psi.

My wife drives our car especially useful after a session or for long drives. She was even doing 30 mile commuting for a few months last autumn.

The only problem is that she pulls the seat so far forward that it fouls the handbrake and it doesn't always stay on.
Dan Smithers

The original spec for the crossply Goldseal Dunlops was 17F/20R. I like to keep that same differential as there must have been a reason for it. As I've said previously here, I have run the radials at 24F/27R (MGOC advice) for at least the last 13 years on the same tyres.
Is there perhaps some good reason like the near 50/50 weight distrubution for instance, to run them at the same pressure all round?
Pete
P N Tipping

First, radial tires need more pressure than bias ply tires. And yes, MGA has very close to 50/50 weight distribution with one or two passengers on board.

Second, most MGA originally had no front anti-sway bar, and they have relatively stiff rear springs. Run the car into a fast tight corner and it will pick up the inside rear tire. This leaves half the weight of the car on one rear tire. That moderately overloads the tire leading to loss of grip efficiency, and the tail will swing wide causing significant over steer. Adding a little pressure to the rear tires helps carry the higher load, reduces squirming of the tread and sidewall, and reduces the tendency to over steer. Therefore original MGA specification is for a few pounds more pressure in the rear tires. For fast driving add a few psi all around. For trailer towing add a few psi in the rear to prevent the tail from wagging the dog.

Add a front sway bar and the corner to corner weight distribution changes. The front sway bar puts more weight on the outside front tire and less weight on the inside front tire (same total weight in front). That's how it reduces body roll. As a result of less body roll, you get less weight on the outside rear tire and more weight on the inside rear tire (same total weight in rear). Effectively the sway bar is shifting weight distribution to opposite corners.

When the outside rear tire carries less weight in a fast turn) it has a better lateral grip that reduces the tendency to over steer. With less weight on the outside rear tire you can run lower pressure in the rear tires. Exactly the opposite happens in front. The outside front tire carries more weight and then needs a little more pressure. Therefore, the stiffer the front sway bar the more pressure you need in front relative to rear.

After installing the 3/4" front sway bar, for street radial tires I run 25 psi all around for casual touring (soft ride). When I get a little frisky I add 2-3 psi in front for quicker steering response. For competition it needs more pressure to prevent the tire tread from squirming and rolling on the sidewalls during harsh cornering maneuvers. For the same street radials I may run 30 psi front and 27 psi rear (depending on pavement condition).

When I installed the 7/8" sway bar for competition on race tires, the pressure bias for street tires got to be a little more. Now I commonly run 28 psi in front and 25 psi in rear for casual cruising. For competition maybe 30-32 front and 25-27 rear.

One last caveott for radial tires, never less than 25 psi in any tire to prevent the squirmy feeling. Different tires may like slightly different pressure. Older "P"-metric radials need about 5-psi more. Some modern radials can do with considerably more pressure.

Bias ply car tires typically said "32 PSI Maximum" on the sidewall. Radials commonly say "35 PSI Maximum". P-metric radials may specify something between 38 and 42 psi maximum. Some modern radial tires have significantly higher maximum pressure tagged on the sidewall (tending toward lower rolling resistance for better fuel economy). The MGA (being a sports car) uses tires larger than necessary to carry the load, so you never need to run pressure anywhere near the maximum shown on the sidewall.
Barney Gaylord

This thread was discussed between 18/05/2011 and 21/05/2011

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