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MG Midget and Sprite Technical - Front tyres fouling wheel arches

I have an almost standard 1971 Mk3 midget, with a few minor tweaks - including mildly lowered front suspension (from memory it's about 15mm lower - see pic).
Its done about 20,000 miles since the full rebuild 10 years ago. Standard front & rear suspension - the front shocks new (not rebuilds), the rears the ones removed from the donor car, with unknown provenance (but no MoT problems). New (standard) springs all round at the time - all suspension components from Welsh MG. Those lovely translucent blue plastic bushes throughout (forget the name now).

For the last couple of years I've had a problem with the front tyres rubbing on their wheel arch lip, whenever I turn in at fairly moderate speeds (say 20-ish plus) and at the same time hitting a mild surface change, ramp, or worse, a Hampshire pothole. Getting the obvious loud scuffing noises and a rubber deposit on the inner arch lip. It's brief - one or two secs depending on steering angle and speed. At the same time the handling is starting to feel a little more 'skittery' - not an oversteery loss of rear-end grip, more a feeling that the front end has a less than perfect relationship with the road after ten years.

What does the group think? Front shocks? As I say, they were 'new' units from MGBHive (not cheap rebuilds), appear leak-free and haven't been an MoT issue from a long-established garage that I know knows their old cars.

Thoughts, ponderings welcome.



Steve Clark

Nice car, does it have 4X4 rock crawler transfer case also... hahaha

Your issue is None of the above, im going with huge freaken ballons for tires, even I can see those are not 145s

Prop
Prop and the Blackhole Midget

My first question was going to be about the size of the tyres, but Prop beat me to it.
Dave O'Neill 2

Dunlop 155/80-13s.
Never a problem for the four years between lowering the front, until when it started.
Steve Clark

Oh - and standard front ARB.
Steve Clark

With that size I dont think you can get any bigger without mods, id say its just the car getting older things tend to relax out a bit, and becomes more mellow

You said you lowered the front by 15mm (3/4 inch) maybe take that back out and see if that helps.. I just dont think your going to find anything out of wack, testing will.show its within spec

Arie debest from here, has a secret trick...using a heat gun and a baseball bat that pushes the wing edges out a bit for extra clearance with no body work or damage... id say rattle his cage for the details and I bet that will solve your delima

Prop
Prop and the Blackhole Midget

As to aries secret trick... I dont mean that in jest... it really is a legitimate trick he has done to his car, I just dont recall the finer points of his concept

Prop
Prop and the Blackhole Midget

Most likely the springs have settled a bit.

Is it happening on both sides?
Dave O'Neill 2

Yes Dave.
Steve Clark

Steve are you sure this isnt going to be something you can live with?, I fear your going to be replacing good parts for perfect parts and repeating the cycle every couple of years... due to parts just relaxing

What about going to a 1500 wing, I want to say the wheel hole is a bit bigger then the privios models...

Or maybe even a stiffer spring... like a 400 pound instead of a 320 pound...I dont know if that would work,

But id say start with puting back the 15mm back into the ride hieth that was removed

Or I hate to say it, smaller rubber tires....the bigger tires fill in the voids nicely, and does give the car some nice ground clearance esp for pot holes and bumps in the road.

But to keep everything as is, I think it will require some wing modifications ...the question is how much

But I wouldnt get into that trap of replacing good parts for perfect parts to maintain a minume road clearance

Prop

Prop
Prop and the Blackhole Midget

fatter ARB'll fix it in most situations by resisting individual wheel movement. Harder springs'll also fix it.

I ran 155/80s on mine till they were worn out with no catching, then 175/70 with minimal catching (including 5mm spacers on each side), and now 185/65 14 which catch a little if I'm trying hard on bumpy corners. Though I've got harder dampers, harder springs and a fatter ARB all helping with those.

I'm surprised (but don't doubt!) that the 155s are catching, I would have thought that they'd go up inside the wheel well just fine.

Have you got a pic from the front showing arch clearance?

Soggy shocks might be causing sloshyness, and reduced damping causing catching. Happens on dad's car, but he's got 175s on. and have diagnosed as shocks getting old. First thing to check with handling weirdness is always the tightness of the rear spring pads.

The trick that Arie did that Prop's referring to was on the rear arches, and involved jacking them out a little.

Guy of this parish has done a mod on the inner arches at the front that shortens the height of the bit that catches, wings off and welder out for that one though.
Rob Armstrong

I wonder if your front shocks are giving up the ghost. THere have been a number of threads about shocker quality and even the so called "new" units don't seem to have the life of the originals.

I've done about 4000 miles on Moss-supplied new units and I'm damn sure they don't feel as positive as they did when they were originally fitted.
Graeme W

I had that exact problem with mine. Lowered at the front, and with 165/70 R13 tyres. Going over yumps and sumps you could hear - and sometimes smell - the rubber as the front wheels caught. On inspection, they were catching on the flanged edge of the inner wheel arch, not the outer as I at first thought.

After attempts to alter the clearance I eventually modified the radius of the inner wheel arch flange. With outer wing removed, I used a thin cutting disc I slit between the outwards facing flange and the vertical edge of the inner wing, leaving the flange attached at front and back. I then added in about 1 3/4" steel piece in the middle, so increasing the circumference, and seam welded it back along the slit edge. This left a downwards projecting edge of steel that I ground flush. Easier to do than try and describe in words! Photo shows the flange sliced of, cut in the centre of the arch, but still attached at front and back. Its not easy to work out exactly what is showing at first, but keep looking and you will see the cut edges.


Guy Weller

And here's a photo of the end result. It may not be that obvious without another to compare, but the vertical depth to the inner wheel arch between the flat top and the curved lip at the top of the arch is about an inch less than the original.

Incidentally, I doubt it is directly caused by worn shocks. Shocks don't ultimately control the amount of suspension travel, they just reduce the speed at which the suspension compresses. Go through a sudden dip in the road at sufficient speed and the suspension will still compress to the same extent, however good your shocks.


Guy Weller

1500 wings have a lower wheelarch to compensate for the raised ride height.

On the Sprite I chopped a big piece off the inner arch, but it was considerably lower than standard.

I also had to trim the lip off the outer arch.



Dave O'Neill 2

Steve,
my thoughts as well as dampers is springs

I'd strongly recommend you contact Kim Dear of Magic Midget about springs and things

I've got his '9.5" freelength 360lb rate. Retains standard ride height to overcome sleeping policemen, rough surface autotests/auto-solo's etc, whilst reducing body roll/ brake dive. 27.50 each' as I previously had grounding issues and they're great

http://magicmidget.co.uk/

if you're lower then if you've not already got one then the next size up from standard ARB could also make a good improvement in handling

my car originally came with 155/80/13 tyres and the nose pointing down and whilst I had no issues with tyres catching I did with dipping on braking, so I originally had the front lever arm dampers swapped (for uprated too) but this just exposed that the front springs were weak so I swapped them too
Nigel Atkins

Now Dave,

Is that a dryer vent hose in the photo of your car ???

Tis tis tis

Prop

Prop and the Blackhole Midget

So steve,

With all the new insights people are providing, whats your thinking on this

Im very interested in this thread as well as I was planning the same size tire with my future upgrade , and mine is a 71 also, I certinaly wasnt aware of any issues


Prop
Prop and the Blackhole Midget

I have 155/80s on my fronts with standard set up, original wheels, springs, no arb, and refurb shock absorbers last year. The tyres were new last year and have done about 6000 miles. They do not catch or rub at all.

Yours looks lower at the front than mine.

The distance from the top of the wheel arch to the rim of the offside front wheel is 6 3/4 inches.

Hope this helps, Dave
Dave Squire

155/8's are not the problem.
Dampers are not the problem.

springs are the problem.
ARB could help to fix it but harder springs are the real answer.

Dampers do not control the amount of bump and rebound of the suspension (better said they should not)
Springs control that and can be helped by an ARB but this is mainly to combat other suspension issues.

If you lower a midget at the front with shims below the spring pan you are doing just that.
But what you are not considering is that the suspension and spring rate where designed to have a deflection of an X amount with a bump of Y amount and then should not hit the body.

You have just changed the starting point of that equation by lowering it but not changing the spring rate.
So now with bump Y you get a deflection of X+ the amount lowered and it hits the body.

See where this is going?

If you lower and increase the spring rate then by increasing the spring rate you make sure that with bump Y you get a deflection of X- the amount lowered and don't hit the body.

Onno K

Surely if the shocks are worn the body movement on a change in direction will not be restricted by the shocker and so will move more freely and therefore faster. Higher momentum will cause the spring to compress more until it overcomes the inertia of the body.
Under static load the spring is compressed and the system balanced. The spring only compresses further by the additional force created by the car movement in a vertical direction. As force is the product of mass and acceleration if the acceleration is greater (due to ineffective shockers) the spring compression will be greater.
Graeme W

as put before, I go with Onno that the springs need considering but also think that worn dampers could perhaps contribute to the problems

if the dampers are 10 years old they may need attention

passing an MoT means very little other than they meet the minimum standard at that one point in time to one expert's opinion it doesn't mean that those or the car as a whole is in good condition and running as well as it could or should

many classic owners accept mediocrity in their cars because they've never driven better examples to be able to make the comparisons against their car - their classic will go and be acceptable but possibly no where near as good as it could or should be
Nigel Atkins

How about negative camber trunnions or off center bushes? That would bring the top of the wheel inwards slightly and perhaps clear the wheel arch.
I have the same issue with rubbing but have no ARB and running 175/70-13 with 10mm spacers
Andy Phillips (frankenfrog)

I Suspect, as Graeme does, that dampers unavoidably do affect the amount of bump and rebound, at least in terms of wheel movement.

They won't affect the total travel (except in some situations - when they're set so hard that the weight of the car over a bump can't compress them) and they won't affect the ride height, but by limiting the response of the spring then they automatically stiffen the system.

I've got adjustable dampers on mine, and I can adjust them so hard that I get almost no suspension movement, as a higher proportion of the energy created by going over a bump is used by the damper. The extreme example of this is a solid bar instead of a telescopic damper. This doesn't change the spring rate on the spring, but the overall stiffness is increased, reducing wheel movement and reducing grounding and catching.

While I had my old ARB on I used to have the dampers set harder to stop body roll and stop the wheels catching - this worked really well.

Hence my logic that softening the damper will increase wheel movement for a given 'hump' thus cause catching on things. If you took the valve out of the lever arm you'd be looking at an extremely wallowy spridget (due to lack of damping) but also one that hit the bumpstops more readily.

Of course, that could all be rubbish and I've misunderstood somewhere!
Rob Armstrong

Sorry rob

Not wallory, much more like oceany without a mast on a tom sawyer raft

The 1st.drive I took my car home, all 4 shocks where a completely dead stick and no arb fitted, that thing floated on the road and just had a rolling rythem of xyz axis...it was almost relaxing in a freakish way due to the motion of the ..... it just rolled side to side, front to back, and courner to courner...but I was still smiling ear to ear that day, but took an hour for the blood to flow back into my white knuckle kun fu grip

Prop
Prop and the Blackhole Midget

Rob and Graeme
Yes the shocks can cause the tyre hitting the wing.
But they should not!
It just shows the suspension setup was wrong to begin with.
Onno K

Well to turn this thread all about me

On my future set up, im going the frontline kit with there adjustable tele shocks, and barry king wish bones and a 3/4 or 5/8 inch arb bar, I plan on doing the same size as steve 155 / 80s but wont be lowered and use the same stock springs I have now

Everything will be revamped and upgraded,

Whatz the odds ill have clearance issues

Should I consider a spring upgrade to a 400 lbs

Prop
Prop and the Blackhole Midget

Agree with that Onno :) Prop you'll be fine without harder springs in that setup.
Rob Armstrong

None of the above will be the actual cause of the tyre making contact with the wing. They will all make it happen more easily, but the only cause can be that the suspension is travelling too far when it hits a bump.

What limits the travel is the bump stop.
Steve describes a bit of provocation for it to happen: "whenever I turn in at fairly moderate speeds (say 20-ish plus) and at the same time hitting a mild surface change, ramp, or worse, a Hampshire pothole."
Undoubtedly what has caused the CHANGE in behaviour is one or (most likely) a combination of the above suggestions, but the underlying cause is that there is too much suspension travel before the bump stop takes effect.

Steve says that he has a lowered car but still has standard springs, so presumably this was acheieved via spacing down the sping mount from the wishbone as Onno noted above. If this has been done, then the suspension has to travel up further before contacting the bump stop, as the bit that makes contact with the stop is part of the spring pan and so is sitting further down compared with the wishbone.

If the shocks, springs etc are tired then the suspension will travel more/be further up on full deflection than it should for a given bump situation, making contact more likely. Even worn inner lower bushes will cause the car to sit lower statically and so make bump stop contact more likely.

The cheapest fix to this problem would be to add, to the bump stop's contact area in the centre of the spring pan, a spacer plate of thickness equal to those used to lower the car.

The best fix would be to take out the spacers and achieve the lowering by fitting the appropriate springs. At the same time uprated springs could be fitted if desired.

Another easy fix, quite a bit cheaper than the new springs, would be to fit a new bump stop, as the new ones are much broader on the pointy end so won't deflect as far. It does make for harsher contact though so my preference would be the spacer or lowered springs.

Whichever method is chosen, the other issues rraised should also be checked while everything is apart.
Paul Walbran

This thread was discussed between 21/08/2014 and 23/08/2014

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