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MG Midget and Sprite Technical - Anti-roll bar

Hi :)

As my midget (1972 - 1275cc) is not sleeping during winter, I had the opportunity to drive her under the cold-but-sunny days we had recently :) Hence more questions for you...

I fell that the car, especially the front, is "pumping" when changing direction on narrow road... She is "bending/pumping/compressing the suspension like a Citroen or a boat on the wheel which is opposite to the turn direction...

I checked the car, and I have genuine anti-roll bar, and, I guess, genuine rubber mounts... I think they deserve retirement :)

= Should I go to higher anti-roll bar ? 5/8 or 11/16 ?
= I only need to change the anti-roll bar and rubber mount/bushes, everything else stay the same ?
= Should I forecast anything difficult/tricky, more than the usual rusty nuts ?

Thanks :)




CH Hamon

I would suggest you need to look at some stiffer springs. Springs around the 340 - 360 lb/in stiffness work well on road Spridgets. A little harsher, but it makes the handling so much sharper.

Big changes in handling attitude come from spring changes, then ARBs should be used for fine tuning.

Or to put it a different way, a fat ARB shouldn't be used to compensate for a too low a spring rate.

Malc.

(Edit: Sorry... I have done that thing that people do on the internet and not actually answered your question!)
Malcolm Le Chevalier

That's fine, it is definitely a good advise! Especially that you have an interesting car, so I listen carefully ;) My target is to improve the car handling as things come along (my front bushes are getting perished little by little...), so I will put the springs on my list :)

Car is so small, narrow and light: she definitely deserves some improvements :)
CH Hamon

Cedric,
I think this might tie in with your perceived tyre problems. Firstly are you sure -
. all suspension fittings are secure and tight
. all suspension bushes are in good condition
. your dampers are working correctly (and securely fitted)
. as Malcolm puts, springs are not tired
. kingpin fitting is good and not too much play
. steering secure.

Uprating the ARB and/or front road springs should be done only after all other issues above (or others) are dealt with.

If/when you change uprate springs go to Kim Dear at Magic Midget (I can thoroughly recommend his 9.5" freelength 360lb) and he does ARBs.

For bigger ARB, as I was told (and discovered) the plates on the bottom of the chassis legs need to be beefed up and you will also need larger straps, bushes and end stops.
Nigel Atkins

Might be worth checking the front wheel toe in first. That can result in kicking back through the steering wheel as well
GuyW

Good point Guy but I think that would have been included in Cedric's thread about tyres. Earlier in Cedric's tyre thread I put I thought the tyres might be disguising other issues. IIRC something was done on the LA dampers but as we know these dampers can be pretty poorly sorted in modern times.

When Cedric drove my Midget he said his Midget drove about the same which disappointed me and got me to check mine, I think mine is driving better now.
Nigel Atkins

Have you considered polyurethane bushes, negative front camber and a panard rod?

Flip
Flip Brühl

Thanks for the feedbacks !

Polyurethane are on the list, when the actual ones will be (too) perished :)

For the moment, I am not really looking at making the handling chirurgicaly precise and responsive: already have a lot to do on other topics before doing this :)
I am just trying to decrease this "boat"/"pitch" effect while turning: the outer suspension compress "a lot" when turning sharp... Similar to an hydractive Citroen :)
CH Hamon

>> the outer suspension compress "a lot" <<
That doesn't sound right, I think you need to raise the front and support it and have a good look around.

Are you sure it is nothing to do with the counterbalance of the considerable weight of spares and tools in the boot, although I cannot think they would move around a lot as they are so densely packed in there. :)
Nigel Atkins

Or shagged shocks!

I tried to find some pictures to show the difference between the 271 lb/in springs with the 360 lb/in. The attached is the best I can rustle up at work.

+1 for Kim @ Magic Midget!

Malc.


Malcolm Le Chevalier

Malcolm, the pic just explained my words :)
CH Hamon

I did hint at the dampers, that IIRC have received some previous attention or been changed, but I'm so subtle and polite (or prolific and know-it-all-but-don't) and it's always best to get other advice/opinions than mine.

I'm very glad to see Cedric changing his 10 year-old, little-used tyres but I doubt their major contribution to problems with straight line driving and again the front springs might dip too much under braking and sharp cornering but wouldn't normally be so noticeable on straight line driving on reasonable road surfaces unless they're in pieces.
Nigel Atkins

So you did Nigel, I missed that :-)
Malcolm Le Chevalier

Malc,
I wasn't commenting on your post, two(?) great minds thinking alike, I was just having my usual drip reminders to poor Cedric, but you know these kids take no notice of their elders. :)

You'd certainly be better to advise and help with the dampers.

I think the ARB angle in your photos tell a story.
Nigel Atkins

Nah! I think the driver of the car on the left just ate too many pies. And doesn't have a passenger to weigh the nearside corner down.
GuyW

Well a lot of work was put into the car between photos and I don't just mean putting the hood up, driving controls at least.

I remember Malc as looking like he was quite slim but perhaps being married has made him more comfortable - massive crash helmet though if it's a tight fit then perhaps the centre of gravity is too high in the car. :)
Nigel Atkins

I doubt there's been much adaptation of the driving controls, Nigel!
GuyW

There's been a lot between those two photos - bigger screen or opticians' visit for YOO Guy! :)

Did you see wot I did there, oh, no, perhaps you can't. :)

Nigel Atkins

On yes, I see. He's changed his tyres.
GuyW

He's also sitting in the wrong seat. And he's put his number plate on back to front.
😆
Greybeard

Quite!
GuyW

"He's also sitting in the wrong seat. And he's put his number plate on back to front."

He was clearly in a reflective mood that day! 😆😆



C Mee

YOO, very clever! :-) Yeah, not a true like for like. But I was driving in both instances so won't have been dawddling.

I always liked the first pic as it shows everything flexing and straining! That is standard springs, 155/70 tyres at Shelsley. Pic two was the stiffer springs, a smidge of extra camber, 175/50 tyres Castle Combe

I found another pic, further round (I think) the same corner on the standard springs at Shelsley. Almost scraping the sills it is leaning so much!

And the less said about married life the better... ;-) ha ha.

We have digressed... sorry Cedric!

Malc.






Malcolm Le Chevalier

That's fine, no worries !

Springs are on my list now, have to check how rusty are the nuts around there :P
CH Hamon

Definitely poor wheel control.
Before changing anything, tyre the bounce test. Get some good quality reconditioned dampers from magic midget or peter may, or a frontline telescopic kit.
Dan Cusworth

Put a bar on it, you know you want to-
Don't stuff about go straight to 19mm, that's where you'll end up one day anyway

willy
William Revit

William,

A mates Austin Sprite had a 7/8" (22.22mm) front ARB courtesy of a previous owner that worked for Stothert and Pitt. I think the chassis probably flexed more than the ARB and we did have to beef up the ARB mountings in the chassis rails.
David Billington

David
I tried a 7/8 bar but it was just a bit hard but then I was using 550lb springs to get my travel correct, it was a really good combo on flat tracks where you could hold the power on all the time but just a bit too understeery for my favourite hillclimb- You could adjust it out but then it would be tracky up the straights
3/4"/550lb was the perfect combo
As you say the ARB mounts on the chassis are an issue, I had to bolt right through the rail and angle brackets around onto the bumper mounts to stop them breaking away
William Revit

William,

On my frogeye I have standard springs IIRC but the ARB is 9/16" but with 2" box section outriggers and stiffer wider rubbers from an A40 Farina at the bends in the ARB and the same box section between the front chassis rails, the effect is to support the whole torsion length of the ARB. The problem with the standard ARB is that it is supported well inside the main torsion length so suffers from bending and torsion, the changes I've made support the ARB at the end of the torsion zone so make the smaller diameter ARB more effective.
David Billington

Anyone know a good source of high quality standard rubber roll bar bushes if Cedric does not want to go to Polyurethane upgrade?
M Wood

yes I have standard springs on my frog. I was using a 5/8 bar but the N/S ARB mounting failed. I repaired it and installed the 9/16 bar to reduce the stress. I found with decent tyres (rainmasters) the handling on the road was fine.
Bob Beaumont

Sounds like a good mod David
When you look at that last pic. that Malc. put up , it really shows up the daggy mounting spacing of the std. setup
Like you I ended up mounting outside the rails with a plate under the rail with a 50x50mm angle mounted on top of it bolted to the bumper mounts, it really does make a differance ---as you say, the further apart they are the better the bar will work
Bit hard to tell from this pic ,but it's the only one I've got of the front working hard


William Revit

11/16 ARB. 400lb springs. Considerable air gap (saves on tyres). Suspension controlled well on the outside. Rear on the bumpstop.

And yes, it does do it on right handers as well. Just not as amusingly.


Rob Armstrong

William,

In the 1st image Malcolm posted 5 March at 8:24 it seems fairly clear the shallow S bend the front ARB is doing as the result of the standard mounts being inboard of the ends of the torsion section.
David Billington

I hadn't noticed that. It demonstrates it pretty well. I wonder how much it stiffens the ARB moving the mounts out?
Rob Armstrong

David
Yep ,That's the pic I meant, I didn't see the one under. It really shows up the mounting points being wonky, they're getting close to only being about 1/3 of the bar apart
Rob
By rights , in theory it should actually soften the bar by extending the length of the active section of bar although it will shorten the arms-- in practice it takes all the soggy out of the mountings having them further apart so the overall gain will be stiffer and more precise (earlier acting)
'Your' main issue isn't in the front though-
If you're getting air like that all them adjustments to camber caster toe springs etc are a waste as they do nothing without the wheels on the ground
If you're on the bump stops and hanging a front like in the pic the rear is probably too soft

4 tyres on the ground will always be faster than 3

With a wheel off the ground the bar has zero effect till it lands

As soon as you hit the bump stop on a wheel then the wheel rate for that corner goes out the window and usually results in a spin (if it's in the rear)
William Revit

This thread was discussed between 04/03/2020 and 06/03/2020

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