Suspension springs

[David Ramsbotham]

I would like to lower my rubber bumper roadster to the same ride height as the chrome bumper cars.
Can someone explain how the higher ride height on the rubber bumper cars is achieved ie is it just longer springs at the front and leaf spring configuration at the back?
Thanks, David.

[Peter Cresswell]

Hi David,
I think the rubber bumper cars use a different front crossmember which has a 1in plate welded to the top to space it out from the chassis rail and longer more bowed rear springs.
Easiest way to lower a rubber bumper car is to buy the kit sold by all the main suppliers, but do a price comparison - and make sure you include the VAT!

[David Ramsbotham]

Thanks for that Pete, so I guess all front springs are the same length! Could easily have fallen into a trap there and purchased chrome bumper second hand springs only to find out they are the same size! That will teach me not to try to do things on the cheap!
Cheers, David

[Peter Cresswell]

Hi David,
Since my reply above I had discovered that the rubber bumper MGBs use the MGB GTV8 front crossmember and the plate is 1/2in. The kits allow you to keep the Crossmember you have and provide suitable front springs to bring the ride height down to chrome bumper levels and use spacers at the rear to lower the ride height and keep the springs you have.
See: https://mgbhive.co.uk/product/mgb/mgb-m ... tube-axle/

[Rick Benson]

Hi David,

I lowered my rubber bumper car some years ago, one thing I did some years after that ( I wish I had done it sooner!) was fit some reduced height front bump stops. I had seen them advertised which prompted me to have a look, there was evidence they had been in use (marking on rubber) and the suspension travel before they came into contact appeared to be very small.

After fitting there was noticeable improvement with less harshness over the bumps. I guess with our lovely roads you need all the travel you can get.

I think I got them from Moss but you might be able to find elsewhere or perhaps it is possible to modify the originals. Certainly something to check when fitting the shorter springs.

Best Regards
Rick

[Ian F]

Just a quick couple of comments from me on this subject.

I think if you want to have the suspension operating as designed without any misbehaviour as described by Rick above, it would be best to copy the whole suspension set up from a CB car. This would mean a replacement s/h crossmember. Additionally, with spacers at the rear you are allowing a certain amount of leverage to be applied to the spring from the axle, especially on acceleration - perhaps not an issue on a gently driven road car, but could be an issue for some. Lowered springs may be a better bet here?

Ian F.

[Peter Cresswell]

Ian is right about lowering blocks, but they are a cheap and convenient way of correcting the ride height at the rear. Interestingly I acquired an article about Ron Gammons car which was published in Classic and Sports Car in December 1989 and they were very impressed by the handling of the car. B&G do offer a 'Rally leaf spring MGB as JYH part No. STN7000'. I understand these are slightly harder than standard springs for roadster to take into account the weight fuel in the long range tank fitted to the car, but this should be around the same weight as a boot full of luggage. So these might work well with harder springs (Ron's car had 600lb spring at the front) and uprated 25% damper valves all round. Another option is to use reverse eye spring, where the eye on the shackle end goes down instead of up. These springs will lower the car by one inch, but they are around twice the price of standard springs. MGB suspension is something of a mystery when it comes to changing it from standard, as there is no clear guidance (that I have found) that gives ride heights for different springs. Some years ago I had a couple of Ford RS cars (Mk1 RS2000 and Mk2 RS Mexico) and these were a doddle to modify. Fit these springs and struts and you get this ride height. So simple but no so for the MGB!

Under racing start conditions the axle will still tramp badly but this is due to the poor location of the axle, which doesn't use radius arms. You can overcome this fitting radius arms or by using very high revs off the line and using the clutch to control wheelspin through first gear. This breaks traction so quickly the axle doesn't tramp. Not really suitable for the traffic light grand prix on the way to work, but it does make for a fast start, although the clutch life is drastically shortened. I used this technique for getting my racing MG TC off the line (6,000 rpm and feed the clutch in) and the Toyota Corolla GT I had for sprints and hillclimbs - 6,500rpm and feed the clutch in until the acceleration slows, then full throttle to 7500 rpm and change gear keeping the engine at full throttle and on the rev limiter during the change. Brutal but that's motorsport!

[Rick Benson]

Ian and Peter make good points. I like the idea of the c/b cross member but wonder if the body shell is the same in that area as I have not seen the crossmember swap advertised or promoted.

Certainly the lowering kits don't warn of potential problems, with the shorter front springs the angles of the wishbones are quite different at rest. I assume this will change the roll centre (and other things I don't know much about but have read about)


Rick

[Peter Cresswell]

In Clausager's book 'Original MGB with MGC and MGBGTV8', all rubber bumper cars used the MGBGTV8 front crossmember plus longer front springs to achieve the higher ride height of 1.5in. The crossmember has 0.5in steel pads attached at the mounting point to the chassis, so the spring gave a 1in increase in ride height. So just changing the crossmember from the RB one to a CB one will lower the car by 0.5in, but then you get into the realms of which spring. The obvious choice is the CB roadster springs. You then have consider the rear springs, and again the obvious choice is the CB springs. This is where you will hit a snag as the car will almost inevitably ride tail high. You will be told they will settle quickly - they won't! So then what do you do?
This is where the conversion kit comes in. You don't have to change the crossmember and the front and rear spring are (or should be) compatible. I would suggest you buy from one of the quality suppliers. You might pay a few quid more but they have a reputation to maintain.

Roll centres are a very complex subject, but unless you are prepared (and able) to re-engineer the front suspension you are stuck with what MG gave you! The rear is simple - the roll centre is in the centre of the diff housing and you can't change that without changing to an independent rear suspension set up. at the front as you lower the car the angle of the front arms changes from pointing down from the pivot point on the crossmember to the bottom of the king pin to pointing up from the pivot to the bottom of the kingpin. I can though confirm that this doesn't necessarily produce an evil handling car, as my car is lowered 2in at the front and 1in at the rear, and now has a level stance (the chrome line is parallel to the road), but I gone much further than this as the front spring are 8.5in free length and 600lb/in rate, it has 1 degree negative camber and 4deg caster (compare to 1deg positive camber and 7deg caster) and a 3/4in anti roll bar.
The effect of all this can be seen in the pictures below. I do need to beware of sleeping policemen and going on and off ferries - but it has got a ver strong exhaust system!
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[Peter Cresswell]

I don't know why the first picture disappeared, so here it is again:

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