As above, pro's and con's, 1.9" or 2.25" and whats the ride quality like

1.9's are more compact and will fit in smaller spaces but there is more choice of lengths and spring rates in 2.5's.

The ride quality depends on your choice of springs and whether you get it right or not but at least with coil springs you know what the rate is and can alter it in a controlled way rather than drilling holes in, or machining lumps of rubber.

Can anyone add any spring rates/lengths based on standard mounts or otherwise

I would imagine that if you could fit the after market type front Mini coilover conversion at the back of the GTM the spring rates should be close but at the front I have no idea.

I can tell you that my front springs are 275 lb/" but that's through a 2.5 : 1 rocker ratio so their effective wheel rate is 48 lb/". They are a little soft but OK.

My rear springs are 380 lb/" operating through a rocker ratio of 1.9 : 1 so their wheel rate is 105 lb/". They are fine.

If you know the lever ratio on your car (wheel movement/spring movement) then you could work backwards from my figures to get the spring rates you need.

Spring rate = Wheel rate x lever ratio squared

Thanks John, i also looked at your other post regarding springs

Tim,

I'm running AVO Comp Coilovers (Rose jointed) and I'm currently playing round with spring weights, so far I have got 250lb in the rear and 225lb in the front, the shocks are set midway on adjustment. With this setup it handles really well and would probably be a good race setup but I think its a little stiff for the road. I'm going to try 225lb in the rear and 180lb on the front. Once I have done this I will let you know further.

Thanks Andy

Tim,

I have successfully got the coilovers working on the coupe, 250lb rear and 200lb front, I may still drop the front ones slightly but have not had a chance to really push the car and see what the understeer is like. I would say if I did change them it would be to 180lb rate.

I have had to modify the top and bottom mounting points and significently stiffen the top one up to prevent movement.

All in all a nice ride and much better looking.

I will attached some photos once a remember the camera.

I forgot I had this.



The lever ratio on the front of a Mini using the standard damper mounting pin is approximately 1.5 : 1 so if you work out what you want the wheel rate to be then the spring rate should be 2.25 times greater (1.5 squared). For road use I would think 180lb/in would be firm and 150lb/in would be better but that's just a best guess.

Some of the conversion kits mouint the damper further out on the top arm though so that messes up the sums again I'm afraid.

Thanks Andy and John. I have'nt finished the rear subframe yet, so its an ideal time to make any mods Andy what length units and springs are you using

I converted my Mini in 1991 when there was not as much kit around as there is today. 2.25" meant there was much more choice. I opted for spax on price and reputation, you do not have to buy springs from spax, there are plenty of spring suppliers about and nowadays you can get dual rate springs which is seriously worth considering if you push the car to any degree but still want 'down to the shops' comfort. My overall experience of coilovers was that it changed the mini from a go kart to a modern comfortable car and allowed easy set up of corner weights.

At the front of the mini, there was the issue of clearance (have 13" wheels) hence the top mount was fabricated and welded to the body. With the GTM it is a similar simple case of fabricating a decent bracket to attach securely to the car. Looking at the GTM, the body work I used on the Mini was not available on the GTM so rather than jump in and develop this mounting, I have elected to stay with rubber cones for now but that is not to say I wont be looking at going coilover in the future.

Spring rates we calculated were 275lb front and 120lb for the rear. These were ok in fact they were wonderfull on the road and on bumps but when the car was pushed on tarmac circuits, there was a bit too much body roll, I would go for 350lb next time or use dual rated springs (damn the expense). The moral here is you ought to consider adding a percentage uplift to the calculated rates if you are seriously pushing the car.

Another piece of useful information we learnt was the bottom mounting. Our Mk1 suspension sat on a plate located on the bottom arm which all looks nice and tidy. The coilover put too much stress on the bottom ball joint which exploded on me during a road rally. The Mk2 suspension now picks up on the standard shockabsorber mount. We use a new HT 12.9 bolt and torque correctly after every 6 or so events and we have not had any trouble. Hope this helps.

I have made new top mounts based on the original coupe setup but alot more solid and braced against the body to stop twisting and upward movement. To allow the shock to sit properly ie not facing inwards I fabricated some custom botom mounts that push the bottom mount further towards the balljoint. I am looking at maybe incorporating the balljoint mount in the bracket too for additional rigidity. I will be in the garage tonight so will take a couple of shots and post. As the car is still to be taxed etc I haven't had the opportunity to really push the car, it has been on the road and say the ocasional donut for spectators but nothing more. It's still a work in progress but its much much better than cones and donuts.

The other Tim,

Sorry I didn't get back earlier, I'm playing round with Avo Comp shocks part # WA100, 1.9 springs the only reason for this is because I use these on my single seater and it was an easy option, I may look at the next length up say WA120 or WA140 just for a little more travel, but at the mo it seems to work. I found on my old race mini that there was a lot of wasted suspension travel on the car and they almost always work at near full compression +/- 50mm. This is what I have adapted for the coupe.

Anti roll bars

I have done alot of calcs on the springs rates i should be needing on my coupe when i eventually get around to it, and from some of the calcs an anti roll bar may be very useful for fine tunning the balance. I want to see what the current spring rate is [cone] front and rear which means divising a way of measuring, then a can compare the calced values with my current set up.

Oh peter any chance you could edit your post with a smaller picture as its a little large

WEST

Thanks Andy and Peter, some food for thought Would moving the bottom coilover mount out and the top one in (towards the centre of the car) add a degree of rising rate

You get a rising rate if, as the suspension compresses, the angle between the spring/damper and the top arm gets nearer to 90 degrees.