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Classic Mini radius arms

Classic Mini radius arms

Classic Mini radius arms

(OP)
Hi
I have a classic Mini with a B16 Honda VTEC engine fitted. Needless to say, this has altered the weight distribution, from an approx. 58:42 to 62.5:37.5 front to rear. I have, after much trial and error, got the front suspension to behave acceptably using coilover units, but the rear has me a bit baffled. I am using standard Moulton rubber cones, and with a 360lb cornerweight (gross), the rear suspension is extremely stiff.
Problem 1 is that I cannot find any information on the spring rate for the rubber cones. Added to the problem is that they're progressive not linear.
Problem 2 is that the suspension leverage figure is huge (if my understanding is correct). The rubber cone is compressed via a knuckle and solid bar from a lug underneath the radius arm, 40mm below the radius arm pivot point. The radius arm stub axle / pivot point centre-to-centre is 300mm - see attached image. To me, this gives a very large leverage (SL) figure of 7.5, which squared gives 56.25. Is this understanding correct ?
Using damper travel of 5" - this is also the wheel travel figure if the full range is used - the cone gets compressed 3/4".
Problem 3 is; how can I determine the spring rate of the rubber cone? Could I compress it using a hydraulic press fitted with a force/pressure gauge, measuring force every 5mm perhaps. I would like to know the spring rate in order that I can work out how to make the rear less stiff.  

RE: Classic Mini radius arms

Jack up the back end and put a scale under each rear wheel. Measure where the rear wheel is without any load on it, then lower the car down a step at a time and plot force versus deflection. Put sandbags in the back of the car to see what it does beyond static weight.

RE: Classic Mini radius arms

I'm not sure why you would wish to keep the "cones" since you have already made enormous changes to the car's front end...The stock style cones come in a couple varieties...stiff and very stiff, but why keep the stock rear when you have already converted the front to coil springs?  
Alternate, adjustable suspension setups are readily available here in the US and from multiple sources in the UK.  Why re invent the wheel?   Several Honda conversions are about.  I've seen several that are quite well done. Some even utilizing the stock suspension! In the UK, you can perhaps get a copy of the February, 2006 "MINI Magazine" that includes possibly the most definitive Honda conversion I've ever seen.

Rod
 

RE: Classic Mini radius arms

Rod

The D series Honda engine and gear box is considerably lighter (and cheaper) than the B series vtecs. They should make an easier conversion for a Mini, allowing the use of the original suspension..

Regards
Pat
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RE: Classic Mini radius arms

(OP)
Evelrod. Had coilovers in the rear too, but even with 120lb/in springs, the rear was very stiff. Couldn't put softer springs in as the tyres rubbed on cornering. Then fitted a rear ARB, and still couldn't go down on the spring rate. Seems the Mini suffers from poor rear roll stiffness.
A colleague has a standard Mini and you can compress the rear by hand, so thought I should revert back - it is better but not much better however, certainly not as soft as his car. I don't understand, as I was under the impression that new rubber cones gave a better ride than old ones !!

RE: Classic Mini radius arms

That other Mini wouldn't be one with Hydrolastic suspension, would it?

RE: Classic Mini radius arms

(OP)
No Brian, rubber cones.

RE: Classic Mini radius arms

Well, about the best I can say is that you have an unusual problem.  With a 360 lb. corner wt and a 120 lb/in wheel rate...ya just gotta expect 'stiff'...

My race Mini, ~1400 empty and 1700 all up race ready with me in the seat (225lb.) it has 490 on each front and 360 on each rear.  Stock (very old and hard) cones, GAZ and 1/2" rear bar.  Yup...it's stiff but not all that far off of a few street vintage Minis I've driven.
Like I mentioned, the Honda conversions are quite popular and I've seen several.  We even have a rear engined version about.  I've heard no complaints about being too stiffly sprung. Perhaps you should get in touch  with Don Racine of Mini Mania here in the U.S. as he does these conversions on a regular basis.  On your side of the pond...I just cannot imagine that you can't find knowledgeable Mini gurus.  Nick Swift, Keith Calver, etc.  I've done business with them and they get a thumbs up from me.

Rod

RE: Classic Mini radius arms

Rod, I smiled when I read this from your first reply

''The stock style cones come in a couple varieties...stiff and very stiff''

I remember them acting as automatic cigarette ash tippers too, the ashtray becoming your lap or floor!

BG

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