Rear Suspension Options- Opinions Please!
Turbo Mini Forums

Hi all, I'm building my mini up for rallying, not historic as I have modified the shell too much anyway.

I have a full cage I have welded in, rear are tied into the shock mounts (and include 4" diameter turrets to house coilovers) and I have decided to ditch the radius arm suspension.

I have 2 options I'm not sure which to take, 1. fabricate a rear axle on triangulated 4 link setup, Vizard said when built correctly this is a big improvement over standard, or 2. use front suspension parts and fabricate a new rear subframe to have IRS.

I think both would be as easy/hard as each other, but I'm leaning more towards making a new subby to take the same double wishbone type setup the front has, and use coilovers.

Just after some opinions really, the car is a bare shell with no rear seat, boot etc at the moment so there's about the same amount of work in both options! Also someone reminded me that the GTM mini based kit car used a front subframe (with engine) in the rear and they handled very well.

Any input welcomed!

Thanks, TC

www.topcatcustom.co.uk

If i recall correctly, Vizard's system was based on a rear wheel drive Escort setup i.e. a beam (Axle) with trailing radius arms and an adjustable Watts linkage to raise and lower the rear roll center. It was said to work very well but took a lot of fiddling to get it right. The system is not however independent. I believe he designed it in conjunction with Aldon Automotive some time in the 70's. There was a brief description in his book 'How to modify your Mini' Good luck.:)

It's not the age that makes me creak it's the mileage

Yes I have that book, it is a beam axle (which so many people keep confusing with the common beam subframe things!)

It was that that initially made me want to change the standard subby, but I am now thinking about using front suspension parts as they are light, and allow for easy change of camber and toe in/out.

And thanks!

www.topcatcustom.co.uk

I don't know much about the MSA rules on rallying, but are these kind of modifications allowed in production cars. I know that historic is very restrective, but how do the rest of the classes work? I am just interested to know, I have the blue book, but I guess you already know and will save me having to read it.

Edit for poor engrish.

Edited by Ben H on 5th Oct, 2011.

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http://www.hillclimbandsprint.co.uk/default.asp

A man without a project is like a like a woman without a shopping list.

Have a look at paul h mate i belive he put a modded front subby at the rear, could this work for you? Could work out alot cheaper

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What I thought the rules in rallying were currently, is that there quite open with subframe modifications, so you can go all tubular up front but they have to use original mounting points... not sure how that stands up if your say, loosing the rear mounts but still using the fronts for the rear beam, or making a few additional say in the centre of the heal board. Bosses building a tubular subframe for the 205 but using the original mounts, same at the rear

David.

I think the car is already quite far gone and probably past some of the MSA general rules, no rear seat at all or boot floor (yet), anything that doesn't do anything has been removed including pieces of the shell, fg front end etc. I'll look into Paul H when I get in tonight!

Have thought about a tubular front subframe too but thought that's a mod I can do later when the car is actually running, as not sure how much of a worthwhile mod it is!

www.topcatcustom.co.uk

Why the reason for ditching the radius arms??

Stick to what works, independant rear is better than a fixed axel .
Front subframe in the rear just seams like a lot of work ,weight and hastle setting up for little gain.

rick

I figured it would involve a fair bit of work.

The reasons being- standard radius arms weigh a ton, radius arm type suspension is rubbish for tyre contact when body roll occurs, and also I've ripped off a couple of the side mounts when going a bit sideways on rough ground.

Fixed axle although not perfect on uneven big bumps leaves both tyres flat on the ground around corners, and an axle with all links would weigh about the same as a radius arm.

I don't mind the work, and there are gains to be had, Vizard I think said his fixed axle transformed the handling, so theres more to it than you think!

www.topcatcustom.co.uk

I really would check what is eligible before you start building something. In the blue book R48.4.1 basically limits you to original type of suspension using the original mounting points.

If you have chopped a lot of the car out then you may fall into R46.3, but that looks like a lot of effort to get it fit for a rally.

It is up to you, but it really is best understanding the rules before starting a build or you end up with a car you can't use.

http://www.twin-turbo.co.uk
http://www.hillclimbandsprint.co.uk/default.asp

A man without a project is like a like a woman without a shopping list.

So use a standard subframe, KAD cast ALU rear arms, protech shocks and alu bits and bob's to hold the frame on and for back brakes. you'll save a shit load of weight, time and money. piece of cake.

But you still have the issue that for every degree in body roll you also get one degree in camber change.

Interesting topic came up today at work... while at the moment you can use foregn designed suspension, different mounting points etc etc... from next year you wont be allowed it and you wont even be able to do single venues... see Andy Burtons Cosworth powered pug' 306. Theres also a car down the road from me at work, A Micra with a Lotus engine, the bulkhead modifications and subframe alterations are meaning it wont be allowed from next year... soo head these if you can, altho not sure whats going to happen seeing as youve altered the firewall

David.

The rear "beam" setups also. As the radius arms are fixed at parallels to the body.

what about fabricated radius arms that arnt mounted paralell to the heal board, such that there is bump induced camber.

turbo 16v k-series 11.9@118.9 :)

Denis O'Brien.

no you don't

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This thread may be worth a look, for something slightly different.

http://www.turbominis.co.uk/forums/index.php?p=vt&tid=264092

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1/4mile in 13.2sec @ 111 terminal on 15psi

Can you explain that one to me Carl? if the rear sub frame is mounted to the car, and the rear arms are mounted to the rear sub frame. Its all a linear relationship. So say you turn left. the rear outside wheel will tip to the right because its in a linear relationship to the body. The inside wheel will tip i nthe same direction. Or am I going mad here?

ignoring toe in.

Edited by Sam on 7th Oct, 2011.

You have one degree of bodyroll, and thus 1 degree of chande in the angle between the tarmac abd the tyre, but thats not the same as camber. My project linked to above have camberchange with compression/bodyroll.

Thats what I always thought, hence one of the reasons I wanted to stray away from standard rear suspension.

Miniminor63 I had a quick look at your project thread, its surprising how much camber you get considering your radius arm roll centre is not anywhere near parrallel to your wheels, looks great though!

www.topcatcustom.co.uk

Surely as the wheels is fixed that will change?

But what you've just said has made something click, the Tyre then deforms most at the outer edge.

I guess that's what you and Carl are getting at. Because its not a camber change as its not changing in relation to the body.

Edited by Sam on 8th Oct, 2011.

Can't comment on rules but camber in relation to road surface will change proportionally to body roll. Bad news. You can compensate for some of this by using -ve camber brackets. This is probably main reason cars in general switched to semi trailing arm suspension.
Use wishbones and arrange the pick ups correctly and you will get camber gain (-ve) in bump which compensates for a +ve camber change due to body roll . Careful where you put the top spring/damper pick up or you can get decreasing rate suspension.
Remember if you go to rear wishbones and presumably discs, you'll need a mechanical handbrake assy to stay road legal . Rally design do them around £50 a piece. Also, you'll have to change steering pick up points on the hub if you want to optomise (or ideally get rid of) bump steer. Kit car boys have made some weird and wonderful bracketry to try and sort this sort of thing.
Lot of work. If you don't get it all right you could finish with something worse than what you're trying to get of.
Good luck

I used to talk to myself a lot until I realised I wasn't listening.

Here is my take on all of this. Although the mini rear suspension in isolation looks poor you have to consider the car as a whole package. The rear suspension on a mini has very little to do. All the hard work is done by the front, hence the decent twin wishbone set up. If you make the rear all fancy and gain loads of grip you will just end up with lots of understeer. Fine you can dial it out with adjustment, but if you just left it alone you would just be in the same position without the hassle.

The rear can be improved, with spring rate, dampers, toe and camber adjustment, plus an anti-roll bar. With all of this a mini can handle and grip superbly, there really is no need for twin wishbone or semi-trailing suspension to make a mini work. By all means give it a go though.

http://www.twin-turbo.co.uk
http://www.hillclimbandsprint.co.uk/default.asp

A man without a project is like a like a woman without a shopping list.

the migs handle very well and the rear wheels spend most corners in the air!!!

i believe they still use a normal rear subby arrangement

My build thread..

http://www.turbominis.co.uk/forums/index.php?p=vt&tid=542985