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MG MGB Technical - A Couple of Lindsey Porter Q's

I was browsing through Lindsey Porter's Haynes mgb restoration guide (the second edition, 1998), and it raised a couple of questions which I know have been well picked over, but what the heck - this is a BBS after all!

1)His Michelin-derived tyre pressure recommendations for modern radials seem a fairly low 21 psi for fronts and 24-6 on the rears for modern radials. What are you guys using?

2)He feels the moss coil-over telescopic front conversion is one of the best upgrades an owner can make...now I've read many, many opinions that well setup stock renders other options expensive for little gain.
Curtis Walker

Curtis. Porter built a car to allow him to write a book. He covered a lot of things which were possible, but did not seem to make, to my mind, some valid comparisons. For instance, he did not make a side by side comparison between a factory front end, freshly rebuilt, and the modified front end, freshly installed. Either results in a significant improvement over an old, worn front suspension.

As to tire pressures, I run 35 PSI, all around, on my cars using Michelin tires. Lower pressures will give a slightly more confortable ride and a slightly less well handling car. The reason the front tires are listed as being pressurized at a lower value than the rears is to introduce an element of understeer to the car. Many believed that an understeering car was better suited to "the average driver" than a more neutral steering car. Many years ago, I owned a BMW Bavaria sedan. It used four psi greater front tire pressure than rear to attempt to cut down on its bad understeer problem. Play with the tire pressures and see what suits you for ride comfort and performance.

By the way, Porter sold the car he build (actually, mostly had built by someone else) shortly after the publication of the book.

Les
Les Bengtson

If you feel like doing a little experimenting, Barney Gaylord shows you how to determine your optimum tire pressure, starting here:
http://mgaguru.com/mgtech/tires/tt102.htm
Rob Edwards

Thanks, guys. I run 32 PSI all around (on 185/70's), and am about to add uprated, reconditioned lever arm shocks and new coil springs to my somewhat tired OE set up.
Curtis Walker

Curtis, based on Porter's and others wild exuberent testimonials, I popped a wad to convert all 3 roadsters to tube shocks. I was so unimpressed, I contacted World, and purchased six pair of rebuilts and threw the tubers in the garbage. Now that difference was notable. The stock rebuilt dampers, rendered improved, much better cornering, bump supression, and high speed float. I admit on 2 though, I also installed Doug Jackson's composite leaf spring which makes the rear feel butter-like. Spend the saved doe on a new distributor as it will make a noticeable difference for the moola. FWIW Vic
vem

I've always run the factory figures of 21/24, never seen any reason to do any different. A friend said he did run about 30 in Ireland, the roads were so potholed that he needed it to be able to take quicker avoiding action.

Tubulars on the rear are *definitely* a waste of time, unless you also go for parabolic leaf springs and positive axle location at considerable extra expense. I'm in the process of junking the POs Spax setup and going back to lever-arms. I can't see how coil-overs at the front would make any difference unless they also used a different alignment and/or damping, and the latter at least can be obtained with lever-arms. More and more people are finding that for 'normal' road use the original setup was just fine, and many so-called enhancements can actually make things worse.
Paul Hunt 2

Another interesting discussion about an old chestnut!

Some of the 'reconditioned' lever-arm dampers are very cheap - MGB Hive at £13.75 each, for example - but are they any good? (I do not know anything about the MGB Hive's dampers; I am merely qwuoting their price as an example from EMG).

If cheaply rebuilt lever-arm dampers are poor, is there any known source for good lever-arm dampers?

Peter
P L Hills

Tire design has changed over the years. In the '60's and '70's tires were designed for low pressure and improved to provide a better ride and still handle ok. 24 psi (US) was a typical factory spec.

Check a new performance radial and they are all at or above 30 lbs reccomended. 1/ The tires roll easier with higher pressure(better gas mileage); 2/ The engineers have changed designs in both tire and suspension so that you can have a good ride with higher pressure.

If you are using an oversize tire with a light car - typical with wide modern low profile performance tires on an MGB with wide alloy rims - you can get away with relatively low pressures (in the 20's) and still have good handling. I found with my car running 195-55-15 tires on 6" wide wheels that my car handled best at 26-28 front and 23-24 rear. Tire Manufacturer's spec is 32 lbs.

Barry
Barry Parkinson

Tire design has changed over the years. In the '60's and '70's tires were designed for low pressure and improved to provide a better ride and still handle ok. 24 psi (US) was a typical Detroit factory spec.

Check a new performance radial and they are all above 30 lbs reccomended. 1/ The tires roll easier with higher pressure(better gas mileage); 2/ The engineers have changed designs in both tire and suspension so that you can have a good ride with higher pressure.

If you are using an oversize tire with a light car - typical with wide modern low profile performance tires on an MGB with wide alloy rims - you can get away with relatively low pressures (in the 20's) and still have good handling. I found with my car running 195-55-15 tires on 6" wide wheels that my car handled best at 26-28 front and 23-24 rear. Tire Manufacturer's spec is 32 lbs.

Barry
Barry Parkinson

fantastic thread ,do you mean to say after all these years that the factory set up of rear lever arms is best ?44 years a bit late never mind. so some of us agree that factory set up is good enough . as for rear shocks yes i do agree buy them new there are some sources that still supply them new i bought two pairs for my cars recently.
s curtis

I've the Ron Hill front suspension conversion using Bilsteins with new top wishbones doing away with the lever arm altogether, it's very good particularly on bumpy corners but somewhat pricey, I've a Spax rear conversion and I don't like it, too stiff even at the softest setting.
I run 15" wheels with 185/65s at 22/24psi, and wouldn't like to go a lot higher than that on a wet road, has anyone considered the insurance implications of running with the tyre pressure significantly higher than recommended?
Ron
R. Algie

Hello,

Front suspension...

Have a look at that site:

http://www.hawkcars.co.uk/parts/mgbsuspension/mgbfsusp.html


Cheers,

JGC
Jean Guy Catford

I've only ever bought reconditioned units at that sort of price. I did get one (out of probably four) which leaked again within a year, but it's replacement has been fine. They are only as good as the exchanged core which is then rebuilt, but it is still a damn-sight cheaper than buying new, and they have only (relatively) recently become available again. I'd be much more hacked-off with a new one failing prematurtely than a reconditioned. Also 'new' stuff these days has just as much chance of being faulty or shortlived compared to the originals. An even then, my 1973 Morris Marina which only had two faults in 6 years and 60k miles, one of them was the left-hand front damper (the other was the interior light bulb).
Paul Hunt 2

interesting thread, i have recently looked at spax but am now worried about the handling implications.

my car has had new rear tyres recently and has become a lot more tail happy, in that i can push and the front stays planted whereas the back tends to slide about.

i figured spax may help this, but by reading this thread maybe i should just lower my tyre pressures at the rear....
d buck

I have found that tyre choice makes a far bigger difference to handling than most things that can be done to an MGB. I've been able to compare cars with and without rear tubulars (no difference except harshness) and with and without a rear anti-roll bar (slightly improved axle location with). But having fitted a new pair of rear tyres, and driving significantly slowly to bed them in and because it was a bit damp, had the rear end fly right out on a roundabout I drove round regularly significantly faster. It was so bad and I got so fed up with pussy-footing everywhere that eventually I swapped fronts and rears over which restored the rear grip, and whilst understeer is a bit more noticeable when pushed I can live with it.
Paul Hunt 2

the modern marshall tyres i have fitted have far less contact area than the goodyears they replaced.

the thing is the marshall gaves me a bigger overall diameter so i would like to keep them.
d buck

Contact area of the tires should be a function of tire pressure, with a small variation due to sidewall stiffness. The weight of the car is supported on the contact area of the tires on the pavement. Tire pressure in psi, times the total contact area, should give the weight of the car. Since the weight of the car (at any given instant in time) doesn't change then decreasing contact area means increasing tire pressure.

Tire design does make a difference in the shape of the contact patch, with older tire designs having a longer narrower contact patch and the wider low profile tires having a shorter wider contact patch.

There is a detailed discussion of this in the archives somewhere.

FWIW

Larry
Larry Hallanger

the difference between tires is far greater than suspension in my opinion. On my detroit coupe I changed brands of tires (not size) and transformed the car from a sloppy handling slip and slide car to one that stuck to the road wet and dry like glue and still broke loose with lots of warning. From a subjective point of view, it felt like a 40-50 % increase in traction. The tire size was unchanged.

According to tire testing on Tire Rack, some of the best tires will not only have great transient response and stickiness on dry pavement, but will have up to 98% grip in wet compared to dry conditions. I can go over a twisty mountain pass, nearly as fast wet as dry. It is scary to start pushing it in the wet and still be in control, when you know from past experience you should be out of control. Assuming you drive sanely, there is also additional safety.

If you like to drive fast choose your tires carefully. Tires aren't like spark plugs -- there is a huge difference from brand to brand and between cheap and expensive. And more expensive, generally does mean better, but not always. Objective test reports are really helpful in my experience. Tire rack has tables where you can compare objective test ratings and user ratings on various tires.

A few years back I bought a cheap set of H rated "performance" tires for the rear of a pickup. Every time it rained, I had trouble keeping the rear of the truck where it belonged. I bit the bullet and abandoned relatively new tires for new ones that had a reputation for performance wet & dry. It was a lesson well learned.
Barry
Barry
Barry Parkinson

I agree that the tires make a tremendous difference. I recently replaced all-season Yokohamas with new BFG G-Force T/A KDs...what a revelation! The car seems to stick to road with unbelievable tenacity...at speeds that would have felt like ice-skating on the old tires!
Question:
My car came equipped with the Spax tube shock conversion, installed by the prior owner; this conversion has been roundly criticized here; what is the favored replacement?
Martin
Martin Connolly

My guru put 4 Spax on my 1970 roadster when the lever shocks gave out. I don't go into spasms over these shocks, but the car does corner a bit flatter on the medium setting and haven't been a problem.

But then I don't intend to paint a number on my doors, either.


Dan Robinson

Martin. Do you need to replace the shocks? Are you happy with how they are currently performing?

The original question dealt with an assertion by Porter that the tube type shocks were a very decided improvement over the factory system. A statement made without any form of test data to back up such a statement. Nor, with any indication that Porter had, himself, made any tests, whatsoever, to back up such a contention.

Thus, the contention that tube type shocks are a "must have item" and "offer significantly better handling" must remain suspect until someone actually takes a rebuilt front end, does some testing of it, converts it over to the tube type shocks, performs the same tests as was done with the factory style system, and supplies verifiable data to indicate that there is a performance increase to justify the cost of the tube shock package.

This does not mean that someone who has tube type shocks, in good condition, should go out and convert back to the factory system. We also lack convincing evidence that the factory system is superior to the tube shock conversion.

If it is working, do not mess with it.

Les
Les Bengtson

Dampers just alter the resistance to up and down movement - unless you hit the end-stops in which case they will also limit suspension travel at the expense of an extremely hard ride! The only way they can make the car corner flatter, as far as I can see, is if they are so stiff that even under sustained cornering forces they do not move as far as the originals. And if they are doing that you effectively have no springs. When the weather gets warmer I have lever-arms, drop-links and bottom plates all ready to go on the V8 instead of Spax (now non-adjustable).
Paul Hunt 2

My car still has the adjustable Spax, which seem to do ok...the ride is stiff, but much of that has to do with 50-series tires and lowered springs. Les makes a good point in that I really have no basis for comparison. I think I'll leave the Spax on for now, and when the mood strikes (or they show marked deterioration in performance), I'll replace them with something like Bilsteins or Konis.
Cheers,
Martin
Martin Connolly

Thanks for your considered input, Les et al...reaffirms what I'd read elsewhere after being thrown by the comments in LP's book. Now I'm more than happy to rebuild the front end using dampers (plus V8 or nylothane bushes - have yet to decide that one!). Cheers.
Curtis Walker

This thread was discussed between 11/03/2006 and 22/03/2006

MG MGB Technical index

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