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MG Midget and Sprite Technical - Frontline rear dampers

My first posting ,i have searched the archive but can't find what i was looking for.
I have been talking to Frontline about their rear damper conversion and have read favourable reports, however i am concerned about the limited suspension travel that will result.(total travel on damper 100mm)
What would the standard system travel be and would 100mm
be enough?

If i go this route i will make up a support to carry the bottom mount sized to suit,with this in mind what sort of compression of the bump stop should i be looking at?

The car has full fibreglass rear bodywork is lowered with the lowest springs i could get from Moss and has 25mm lowering blocks.(It still sits way to high but as it hasn't been driven yet,i am sure the springs will settle)

The front already has the Frontline kit with 7.5 inch uprated springs.

The car will be used on the road and for track days,maybe a little open class hill climbing.
S BREEZE

Full droop of the rear suspension is the length that the check straps will allow the axle to fall. Then the full up of the axle is obviously the moment the axle bump stops hit the pads. I found when measuring this that the total travel was about 5 inches. Obviously the full droop only occurs when the backen goes light over a bridge or what ever and so the 5 inches could be reduced. so 100mm would be 4 inches and ought to be alright if the fully compressed state is in the correct position. (ie on the bump stop) bear in mind that the bump stop will compress a bit so make allowances for that compression.
Robert (Bob) Midget Turbo

rear suspension travel is governed on compression by squash of the bump stops, and on rebound by the length of the axle straps. As you have lowered it your resting point will not be standard but will be nearer the bump stops. If you fit shorter axle straps you can limit movement in the opposite direction. With measurement and a bit of trial and error you can find a strap length that will keep movement within the 100mm limit of the Frontline spec. Having said all that, 100mm sounds far too little to me; best handling IMO is found with normal travel and soft-ish shocks - very many racers keep the back end standard (just lower). Especially for hillclimbing, if the back end is too stiff then the inside rear wheel loses drive on tight bends and you go nowhere...
David Smith

cross-posted, but I don't think we contradict each other too much ;-)
David Smith

David,

If the downward travel allowed by the dampers or check straps is too little you can also lift the rear inner wheel and you can't put any power down unless you have an LSD (not Torsen).

IIRC when I fitted the later 1/2 elliptic hollow rubber bump stops to my frogeye I assumed worse case they might compress to about half their standard height so from memory that would be about another inch travel.
David Billington

Having spent lots of money on FL parts I personally strongly recommend you buy them from somewhere like MGOC/Moss where you will have a full warranty back up


the check straps are removed and dampers in their place

photo below of my standard road going car r/h/s rear on FL fixing bracket to spring, adjuster facing front of car


Nigel Atkins

S Breeze.

WHY Frontline...?

My suggestion is to use the std lever-arm type.

DON'T over develop your car without knowing how the original set up works first. OK, lower it but not too much (you can stuff up the steering geometry quite nicely here). Stiffer front springs and stiffer anti-roll bar will be a good basis to start from.

Develop YOURSELF first.... get used to the car and alter to suit once you know what you are doing. Study corner weights and balance... Don't just bolt on bits that are sold to you as being able to do a job.

Frontline are good at marketing, but that doesn't necessarily mean that they know what is good for you and your car.

My opinion only...

Mark.
M T Boldry

To a certain extent I ten to agree with Mark but I must say every race car I have driven that has been competitive has been super stiff.

If I decided to build a midget now for racing then I would be strengthening the bump stops and lowering the suspension to them, both front and back. Then as soon as there was any body roll it would be instantly addressed by the rubber stops

If my car was lifting the rear wheel in a corner then I would think that the front end was too soft and the outer front wheel/suspension was diving. However I don't want to start WW3 here about what creates best handling and state that is only my opinion!! :)
Robert (Bob) Midget Turbo

Many many thanks for all of your comments,just to clarify -my concern with this set up is the limitation on the droop, as has been stated, this may cause the inside wheel to lift therfor losing drive as i do not have an lsd. The 5 inches of travel from the std system(thanks Bob)is less than i was expecting so the reduction in travel is less than i thought. The uprated front springs are on the stiff side of rigid so should go some way to controlling the rear. The rear springs are very soft.
Any ideas on how far the bump stops will compress?
I do understand where Mark is coming from,the car has been two years plus in rebuild and the frontline kit is a simple fit and as far as i can tell it is the best route for this style of damper. Future development will be dependent on where the car is most used.
I also have a sprite with a 1275 turbo engine,this runs uprated lever arm units,lowered but all steel body, it's a really great car to drive however with the midget i wanted to try something else.I have tried to keep the weight down(lever arms are very heavy) and gone for a 1380 normally aspirated engine.
Stuart
S BREEZE

If you buy the Frontline rear tele-kit everything needed is in the kit so you don't need to make extra brackets.

Also, if you fit the Frontline rear tele-kit you no longer have check straps as the damper becomes the check strap (re-reading this I see Nigel said this!). What you have to watch then is not so much rebound but bounce. If your car is standard ride height you might have some issues but if the car is lowered than 4"/100mm of travel will be plenty. On my road car i have 2.75" of travel before the axle meets the bumpstops and they've never met yet.

Frontline are very good are marketing and getting magazine publicity but it seems they need to brush up their sales pitch in your case!

The Frontline rear telekit is a lot nicer to drive than the rear Spax kit.

I haven't said it for a while so I guess I can say it now - there are books with this stuff in, they even have pictures of this stuff...
Daniel Thirteen-Twelve

Robert (Bob),

I was playing around with my rear bump stops as I found in use that when they came into effect it upset the handling. My frogeye has fibreglass front and rear but also the softer (more conical) early front bump stops and had the standard rubber brick rear bump stops as wasa fitted to 1/4 elliptic cars. I found in use that the transition when cornering from rolled to rolled + bump was a noticeable sudden change to oversteer, the change to the later softer bump stops on the rear made the transition much smoother. Maybe this is one of the reasons the later cars had stiffer front bump stops and softer rears. I think all to do with the action of the bump stops changing the spring rates when they come into play and potentially upsetting the handling.
David Billington

you can soften the rear bump stops further by cross-drilling 13mm holes in them.
David Smith

Bob..

"Then as soon as there was any body roll it would be instantly addressed by the rubber stops"

By doing this, you would be transferring suspension loads directly from the springs to the tyres an almost certain way of a quick exit from the track...

Suspension MUST 'work' and it has to do this in a smooth transition and not via spring to bump stop then tyre.

If you have a lot of rear body roll, this should be controllable by front set up...

It's all a compromise but with development and not a salesman, you end up with what YOU want..

Mark.
M T Boldry

To chuck in my two penneth, I agree David. I have never raced midgets but to me hitting the bump stops whilst cornering just seems a recipie for a crash!

The spring and dampers job combined is to control the movement of the wheel relative to the body. 'Safe' handling is created by tuning the rates of all the front and back springs and dampers to work together. The springs on each corner have a linear stiffness. As soon as you hit the stops you have a sudden change in the spring stiffness on one corner. Completely changing the dynamics of the car an tossing you into the bushes! Twitchy, unpredictable mid corner handling is hardly confidence inspiring or good for speed.

As said, this is not based on experience, just a bit of plain thinking.

Cheers,
Malcolm
Malcolm Le Chevalier

Hi Mark

Makes me wonder how I won 3 championships?

Never had the problems described?

However each competitor must do what he feels suits his style and makes them faster, the only advice that is sound is to experiment yourself and find what works for you. If you end up at the back of the grid then you are not doing the right things if you end up winning then it is a pretty good indication that you are on the right lines. (Especially if you are a crap driver!!LOL)

As many grand prix commentators have described the main suspension on a Formula 1 car is the tyres.

But as I said I do not want to start WW3 about handling!! LOL.
Bob Turbo Midget England


OK With any luck WW3 can be avoided.
From the above i have an idea that the compression on the bump stop will be half the length of said stop at maximum.
If the damper stroke is used up before the bump stop has done it's thing, all that load will be transfered to the damper mountings, not the best idea.
I do understand that driving style and conditions will determine just how far the stops are compressed so in the absence of hard facts i think it is better to be safe.
The frontline kit has 100mm of travel,if we say 25mm for the bump stops, leaving 75mm, the distance from the bump stop to the chassis is 70mm so 5mm of droop in the static condition. (with the lever arms the droop would be limited by the check straps so would be 57mm)
I did a mock up with some mini dampers,i think i will get the car going on these and try to take some video to see what is actually happening and whether or not the lack of droop is an issue and just how far the bump stops actually go.
I also got a reply from protech shocks ref a custom build but i will do the research before going to much further with that.
All i have to do now is finish the rebuild,hope to be done for spring!!!
Thanks again for your comments, this has been very informative.
Stuart
S BREEZE

Stuart,

My experience with lack of droop was after fitting a Spax 1/4 elliptic kit to the rear of my frogeye in about 1986, it reduced the droop travel to about 1" and that kit stayed on for all of 3 days before it was removed and the lever arms put back. The lack of droop resulted in the inner wheel being picked up and loss of drive even through relatively slow speed corners. I eventually fitted telescopics to the rear giving longer travel than standard. The Spax rears ended up on the front.
David Billington

I fitted to the front and back FL suspension on my Frogeye (1/4 eliptic). I am happy with it.
You will have to remove the strap and alter the fixing point. The instruction of FL is clear about this. But (at first) it was not possible for me to restrict the inward travel, so the damper botommed.
I then welded a 10 mm thick steel plate (50 x 50 mm) to the body where the rubber stop hits the body to limit the travel.
No problem since.
J.W. Vlaanderen

Bob, no WW3 but just to put discussions into perspective, I did not win three, two or even one championship, but I have built quite a few cars that have... :-)

Spridgets don't run on F1 tyres or any of their technology.

Horses for courses... :-)

Mark.
M T Boldry

In my opinion 100mm of travel isn't enough. I used to have mini front shocks on the back of mine, mounted to the check strap bolts at the top and standard bottom mounts. They had about 4" of travel and no matter how I altered the bottom position they would either bottom out slightly or worse still lift the inner wheel on hard cornering.

Last year I got round to fitting some Mini rears and they are about perfect. I think they have 5 3/4" travel and cost me £12 on ebay. They are some cheap standard ones but seem to be fine from a damping point of view for my hillclimb car. My intention was to try the cheap ones out then replace them with some adjustable ones once I know the Mini rears work. I'm leaving them for now.

The big problem with this mod is that the Mini rears need a small turret welding in so although cheap there is quite a bit of work and probably not something you would want to do to a decent shell.

From the top before fitting:


John Payne

From below - you can just make out the top mount:



John Payne

Lifting the rear wheel with the old shocks - fairly extreme situation but it still used to do it on lesser bends. Could probably do with stiffening up at the front but it's a road car as well:



John Payne

Thanks for that info jonn , as it's been close to 30 years since i played about with mini's, can you tell me if they have a droop stop built in to the damper.
Are your springs the moss lowered ones with the upside down eyes?
stuart
S BREEZE

Stuart, not sure about the droop stop, not really sure what one is to be honest! They don't have a rubber stop anyway.

My springs are some old Peter May ones that were 1.5 inch lower. I also have some 3/4 inch spacers. I could do with some new springs really as these are a bit twisted but I can't seem to find any.

I got some of the reverse eye ones from Moss when I was rebuilding it last spring. I didn't even try them on the car, I offered them up to the old ones and they worked out to be about an inch and a half higher! Not only that but the quality looked awful so they went straight back.

John



John Payne

john, I may have the ones you sent back, we will just have to see how they work out.

The good news is that i have found a set of adjustable lever arm dampers. The one adjuster is jammed so i will get them reconditioned. I have mailed Peter May to see if he can do them.
S BREEZE

<The good news is that i have found a set of adjustable lever arm dampers.>
...and said so casually, like you come across a pair more than once every 5 or 10 years! Can't remember when I last saw any for sale.
David Smith

Ha.. the 'pair' of adjustable ones I have are both the same side...! :-(

Mark.
M T Boldry

To be honest I got the impression the ones I had might have been returned before as well! When I spoke to Moss about them it was almost as though they knew what was coming!

I would definately try the lever arms. (or flog them on here!)
John Payne

David- In all honesty,"found" is not strictly true. In comparison to you folks on this forum I know very little about these cars, two years ago when I got this one I knew even less. Thats the excuse over with then, when I took the car apart these were already on it and i simply did not notice they were anything other than standard shocks. When I pulled them out from the old bits pile I couldn't believe my luck. Think I will have another look through said bits pile.
S BREEZE

well then you'll be pleased to know they can fetch 400 the pair s/hand...
David Smith

I wish I had that sort of luck!
John Payne

This thread was discussed between 05/01/2012 and 11/01/2012

MG Midget and Sprite Technical index

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