23 replies to this topic

[tiger99]

Also, the very thick coils used on a Mini (they have to be thick due to the lever ratio of the suspension, and the need for high stiffness) are very much more prone to fatigue fracture than the normal thin coils used on coilovers or on conventional cars. Fatigue is causes by strain, not stress directly, and, simplistically, when a thick thing flexes, the strain at the surface is higher than if it was a thin thing. There have been instances on this forum of not very old coils breaking.

Worse, to get a variable rate from the springs, which is absolutely essential, the coils have to progressively come into hard contact with one another as the spring compresses. That abrades the paint, which allows corrosion, and corrosion pitting is where the majority of fatigue fractures in coil springs start.

I do like a nice ride quality, but would never use coils on a Mini, as the engineering is utterly wrong in every single respect. Some aftermarket mods which are sold are about as useful as the infamous snake oil, marketed by similar charlatans.

If you want soft, controllable, suspension that does work properly with short travel suspension, and a variable load in the car, you really want to be thinking about a Citroen style hydropneumatic system. Constant ride height and natural frequency independent of load, with the possibility of a height selector on the dash, so you can let it down for high speed cruising, or raise it over rough stuff.

Edited by tiger99, 26 March 2013 - 01:45 PM.

[MRA]

You can have progressively smaller radii of coils allowing them to fit inside each other this allows a lot more travel, but is full of other surprises that are not wanted.

[MRA]

I've just had a brain wave.....why not use some rubber devices, rubber offers all of the positives but with few negatives,it's ideal

Edited by mra-minis.co.uk, 26 March 2013 - 09:29 PM.
Allsorts of unwanted text removed,

[tiger99]

Sorry, Issigonis and Moulton beat you to it!

[Cooperman]

It really is hard to see how the rubber cone springs can be improved on in an overall sense. For racing a coil spring with a constant high spring rate works very well, but it would be so harsh on a normal road as opposed to a totally smooth race track that the ride would be unacceptable. For a softer ride than rubber cone, the initial rate will need to be lower, so the amount of initial suspension travel will be greater. This means that the rate at which the rate increases will need to be high and coil-binding must be avoided at all costs. In fact, in order to cater for different overall load differences it will probably be necessary to fit a big rubber bump stop to give a very high final spring rate, which brings us back to rubber cone suspension.

[Carlos W]

I blame the government

[tiger99]

I blame Microsoft!

[firstforward]

So from that answer I assume you have never owned these as Cooperman has never, for me that says it all really, minimad also says he has his car 1 inch off the ground, again that says it all. For your information the ones I use are progressive rate. May I suggest you do not give out advice you are not qualified to, or if you do let it be know its just an opinion.

You can get rising rate coil springs, there are a few ways to achieve this, that where not readily available 50 years ago.

However once a coil spring bottoms out it will do so with a massive shock loading that the rest of the car would not take kindly too, I appreciate this is going to be fairly rare, just that the chance is increasing as the roads are deteriorating. Compared to rubber suspension medium, i.e. the standard system, which as it is compressed it rises in it's ability to support that load and changes to suit, anyone who has bottomed a standard mini's suspension will also know that the shock can be quite severe, just not as severe as coil spring suspension.

you can't get around the fact that at least a quarter (and sometimes more ) of the minis weight is carried by one bolt not designed to carry that much weight

Bungle are you confusing this topic with "coil over" type suspension which although similar is quite different.

I agree with you, the coils must not bottom out and if set up correctly so the bump stop comes into play so coil binding will not happen. The bump stop on rubber cone setup is contacted many times and ultimately is the point of no more travel also, no different to a coil. For me I am after a road car that can be driven faster rather than slow but with as much comfort as possible, I find the coil pretty much achieves that. There are downsides, namely a coil spring can fatigue and I would bet most that do break early are because they were not setup and adjusted correctly. They are really to be setup as standard, not lowered or too high for that matter for all the obvious reasons that many seem to miss.

Many cars of old used torsion bar suspension, I remember Porsche 911's used to not so many years ago. I was amazed to find that if the coil of a mini is measured unwound it would have a length of just under 1 meter, some 32 inches. I don't think the 911's were much longer if they were even that long so there is plenty of torsion available on that length.

I have often wondered if a solid rubber tube ( for want of a better description ) could not fit inside the coils, in part to make Cooperman a bit more happy on the subject of coils if nothing else!! Would this give a bit of both and be an overall winner? just a thought.

[The Matt]

i have used springs for agesss, so much better than donuts

only problem is the rear ones can pop out if you have a mini on 10" wheels, tubbed rear arches and sitting an inch off the ground
other than that they are absolutely fine

In this instance, lowered height (or maybe custom height) dampers should be used. This would also happen on a Mini with traditional rubber donuts if it's lowered beyond the point of the rear suspension being compressed when the wheel is off the ground.