13 replies to this topic

[TopCatCustom]

Just to see if anyone has experience of using a rear beam (not a beam axle) and coilovers on particularly rough driving ground. I'm considering them on my project but am aware that the mini wasn't designed with them in mind, though I will be tying a multi-point cage in throughout the car and into the rear shock towers- so they will be plenty strong enough to deal with the forces involved I am 100% sure of that, I'm just not sure about the actual shock absorbing and ride etc.

On the front- I'm dubious because the front suspension wasn't designed for such long travel- and could cause driveshaft joint problems with the extreme travel that coilovers could offer. Again if I was sure they would work well I would bring the front of the cage through the bulkhead and tie it into the top mounts, then down to the front of the subframe similar to drag car fronts before they shell them up. This would be superior to a couple of bits of 25mm box bolted on as well as using a flip front.

Any input appreciated!

(Cooperman I know where you traditionally stand with this topic- but do you think my spaceframe/cage would change things, or am I right to be dubious about the driveshafts?)

[bmcecosse]

I used it on my much abused Autocross and Sprint car - absolutely excellent. I could lift the rear of the car and wheel it like a barrow. But you would need to keep the weight of the car down to a minimum. The 'beam' needs to be solid enough to keep the tracking right - I used the front part of a subby - braced in the center to the heel board. It was 40 years ago!

[Cooperman]

I think if the events you are going to do will be smooth tarmac, like disused airfields, coil springs and, maybe, a rear beam may work as well as rubber cones, but I doubt that your times would be any better overall as it's not so much saving the last kilogram of weight, as it obviously is for race, sprint and hillclimb cars, it's more the handling on unpredictable rally surfaces and the ability to put the power onto the road. Plus, of course, the strength to take a few big bumps if and when you go off the road a bit or if the surface becomes broken and bumpy.
The reason rubber cones are so efficient in rallying is because they are true variable and increasing rate springs in the truest sense.
You could go for coils, but how would you actually know how to set the variable rate figures? Constant rate, which many coil-overs sold are would simply not work for rallying. If the car is light, you would want a very low rate for the first inch or so, then an increase to a higher figure as maximum suspension travel is neared. I guess you could measure a rubber cone on a spring measuring machine and replicate that and get the springfs wound to those figures.
I don't think drive shaft retention will be an issue so long as the car is not raised by a huge amount so long as you don't go to massive negative camber which has the effect of lengthening the required overall shaft length. It's normally full lock, power and rebound which can cause the shafts to 'pop'.
With regard to flip fronts, you would have to do so much bracing to be safe and satisfy the scrutineers that the weight would probably increase. I prefer to have a good strong steel front with defined structure. If you go off and roll at over 80 mph, as a friend of mine did recently at Caerwent in a Rover 25, you need all the strength you can get! The interior is fine with an FIA cage properly fitted, but a strong front is also good to have.
All the quick Mini rally cars that I've been involved with in 49 years of rallying have had normal rear sub-frames and rubber springs. That's not to say other types of spring/sub-frames wouldn't work, just that I don't know of any successful cars where this has been done. For racing, hill climbing or sprinting, I would say go for lightness and coils if the regs allow.

Peter

[Cater_Racer]

I did The Rally of the Tests last week, in truly dreadful conditions. Using Adjustrides, standard cones & KYB's (all brand new) I had to adjust the rear twice on the event, probably due to the set-up settling. I was running Hakka tyres. I would suggest they were a good set-up despite thick mud everywhere and plenty of gravel stages. I'd be reluctant to add weight, which coil-overs would do, or have I got that wrong?

Edited by Cater_Racer, 26 November 2010 - 11:11 AM.

[Cooperman]

How did you get on on the 'Rally of the Tests'. It's a good event for a Mini. A load of my old friends were out marshalling.
The idea of a beam rear suspension is to save the weight of the sub-frame and to take all of the loads from the rear suspension through the heel-board mountings and at the damper top.
My reservations are: 1) That backwards/forward loads which are normally taken out into the structure at front and rear of the rear sub-frame will have to be resolved only through the heel board mountings and, 2) That the coil springs will need to be variable rate (VR) and set to suit the light rear end with no specific rate being known as the race ones will not be suitable. You could 'wind' loads of different rate springs before getting a pair which work. The initial rate needs to be very low, with the increase and the actual rate of increase being an increasingly steep graph up to the point where the bump stops stop any risk of coil-binding.
It all seems a bit of a task when rubber cone springs are known to work so well in rallying.
If the back is lightened it may cause directional in stability over 'yumps' and cause the car to do what used to be known as 'ecking', which is when the rear lands after a bump, then bounces up out of line a few times and usually ends up with the car rolling (been there, done that!). Too high an initial spring rate and too hard a damper setting just makes it worse and even more so if the rear end is too light.
The requirements for rallying are just so different from racing and other smooth road disciplines.
I did wonder a while back if using VR coils springs could help with rallying if the rear wheel arches were modified and raised i height with much longer coil-overs and dampers to increase the available suspension travel by a couple of inches, but to do the same at the fromt would not be easy due to geometry limitations and there is no point in only doing one end, so the best option I've found is to use Hi-lo's, with the suspension raised a bit and good adjustable dampers set not too hard.

[Cater_Racer]

Thanks for the info Cooperman, I don't think beam rear suspension is for me.

On the Rally of the Tests I got 4th in class and mid field, but was doing better, but missed 2 regularities and two tests on the Friday morning due to collapsing front wheel bearing. It cost me 1 hour 10 mins in penalties and lost me 2nd in class.

Very difficult for a '64 car, because it's classed in with the Lotus Cortinas and Saab 96 V4's. Which is tough for a 998cc. If I'd been 997cc I'd qualify for the mini's/ Ford angela/Standard 10 class (Designed in 1950's) But the 998cc MK1 is deemed to be a 1960's design, so in the 1960's upto 1800cc class.

Edited by Cater_Racer, 26 November 2010 - 01:32 PM.

[Cooperman]

I'm pleased to see my friends Paul and Nigel finished 2nd.
It's strange all those Alfas turning up - I thought they had all rusted away!
Still good to see those Minis in there.

Edited by Cooperman, 26 November 2010 - 01:39 PM.

[TopCatCustom]

Thanks for the replies. Yes indeed getting the spring rate correct for such a light rear end was/is one of my concerns. I reckon I'm going to have a long think over the weekend before going ahead with anything!

The other reason for considering it is that the cost of new rubber springs, hi-los and good adjustable dampers is not far off the cost of coilovers! Also what is the difference between standard cones and rally ones that mini-spares offer?

[Cooperman]

By the time you get the spring rates correct, the springs could have cost a lot.
Personally I would never consider coil springs for a rally application, but maybe that's because I'm 'old skool'. For racing, coils and beams are established as excellent and you can ask for the spring rate data as used on successful cars. Where you could start on a rally car I don't know. I certainly don't have any data. If fitting a beam for a rally application, I would be inclined to plate the heel board each side with 3 mm steel plates and add fore & aft steel webs welded to a re-inforced floor to get the rearward shock loads out.
You would, of course, require a really good hard rubber rear bump stop as if you got coil-binding it would be disasterous. The spring must stop compressing before it goes 'solid'. I have been working on a Peugeot 106 rally car where that was not done, the springs coil-bound and the damage was extensive to both the struts and the mountings.
It could be an interesting engineering design project. Thinking as we go, maybe on the front suspension special ultra-short 'trumpets' acting as the platform for longer VR springs could increase the suspension travel with large bump stops built into the inside of the springs. Again determining the rate would not be easy and a bit of trial & error would be necessary. The 'trumpets could be machined from aluminium bar with a screw thread and separate spring platform to enable height to be set. Not cheap to do, but for those engineering-types it would be a good challenge.
What do you guys think.

Edited by Cooperman, 26 November 2010 - 02:34 PM.

[Cooperman]

Forget to add that I don't know the actual differences in spec of the comp & standard ones that Mini Spares do, but call Richie at the Harrogate branch and I'm sure he'll know, or 'simon@minispares on here may have the data. In my rally 'S' I run the top quality ones from MS and these have done over 30 rallies, a lot of them on gravel/mixed surface and they are still fine. I don't run Hi-los as when I built it there was some doubt about eligibility for historics. They are now approved so when necesssary I'll put a set in. I set my ride height just slightly above standard using washers and that works OK. I've always found the VR rubber cones to be fantastic as a suspension medium.

[Cater_Racer]

Rally of the Tests

[Cooperman]

Rally of the Tests

Here is mine on The East Anglian Classic

Attached Files

•  CNX_EAC_2006_4.jpg   350.37K   36 downloads

[John Clayton]

Thanks for the replies. Yes indeed getting the spring rate correct for such a light rear end was/is one of my concerns. I reckon I'm going to have a long think over the weekend before going ahead with anything!

What did you decide?

I've had to beef up the L brackets on my beamframe as they have broken on both sides over the course of several rough off-road events. The inboard L brackets that attach the trailing arms to the beamframe are the problem; they now have fillets welded into them which will hopefully make them a lot stronger.

[TopCatCustom]

John- see the last pics on this page, I made my own beam and radius arms. Just have to see how well they hold up to abuse, they are actually stronger than they first appear with internal welding etc. http://www.theminifo...t/page__st__120