Progressive or linear coilover springs
Turbo Mini Forums

What's peoples thoughts and recommendations for 1.9 coilover springs. Some people supply progressive, others linear. I plan on using protech front and rear coilovers. Car will weight about 510-515kg 35-65% rear-front. I have already bought 100lb linear rear springs (rear ARB)

Car will be road legal, but mainly used for trackdays

Class C 3rd Place Avon 2011 14.18 @101mph

When I spec'd to protech for my coilovers I was recomended 265/340 progressive with a vehicle weight of around 550kg.

Personally I would always go progressive but I prefer the feel

Drives
-Ford S-max Mk2 Ecoboost
-Rover 100 VVC #2 - track project

Searching is all you need on TurboMinis

i ran the original progressives on the back , i think they were around 90 lbs , way too soft. now have 150 lbs linear , still too soft i think .car weighs around 650 kg .

Medusa + injection = too much torque for the dyno ..https://youtu.be/qg5o0_tJxYM

I must admit the 100lb rears do feel very soft, compared to the standard subframe setup with red cones. If I stand on the rear boot lid lip the wheels touch the arch and the top KAD calliper hits the boot floor lip.

I was recommend 100lb / 325lb by protech based on weight of car and running A rear ARB.

There seems to be such a variance in opinions, across the forums threads. I guess it's all about trail and error. Spring pre load also makes a big difference I guess.

Huddersfield Shiny Spares supply 265-340lb progressive fronts as standard apparently.

Edited by alaskanow0 on 12th Nov, 2014.

Class C 3rd Place Avon 2011 14.18 @101mph

I went through all this when messing with mine. Never really got anything sorted but came to the same conclusion as you that it would be trial and error.
It also seams that like camber / castor etc its all down to personal preference !, there isn't really an ideal fast road / track set up.
But realistically its allways nice to have a ball park to start with .

The main problem with coilovers on a Mini is that the std cone sprung car is non linear, very aggressively at the front and less so at the rear.

So a Cone sprung car gets stiffer in both roll and bump travel, the more it rolls or the more it compresses the stiffer it gets.

So 'progressive' springs are supplied with some coilovers.

The problem with 'progressive' springs is that they are usually anything but 'progressive', dual rate is usually a better description, so at some point in the spring travel one section of the spring essentially becomes coil bound and at this point the second 'stiffer' rate kicks. This transition (depending on how much of a rate change occurs) between the two spring rates can feel pretty unpleasant especially if it happens in the middle of the corner.

So, depending on how low the car is and how much the 'progressive' rear spring has to travel before it's rate increases will drastically effect how one car feels relative to another, which I think is why opinions vary so much.

Ideally your 'progressive' spring should be in the 'softer' area as you drive along in a straight line at a relatively constant speed and then as soon as you steer and start to generate a bit of lateral acceleration move into the 'stiffer' area and stay in this area throughout the whole of the corner or say during heavier braking.

Or you just stick with a linear spring and keep upping the rate until it handles how you wan't but this will almost always mean that the 'ride' / comfort driving in a straight line at a steady speed will be harsh to stop the car from feeling like its 'falling over' in corners or just plain running out of travel.

The other side effect of 'progressive' rate springs is that if you use them on the front the car will lift more under acceleration and if you use them at the rear, the rear will rise more under braking.

All of this ignores any bump stop / rubber effects and assumes you have enough suspension travel to just be assessing the springs, if you are near the bump stop or into it during a manoeuvre then anything could be happening.

I calculated for a 600kg car, 65/35 weight split that 17.5 N/mm (100 lbs/in) rear spring gives about the same rate as a std cone when at static std ride height but is hopeless in practice as it 'falls over', so as Robert suggests, with a linear rate spring (especially on a lowered car) I'd start around 150 lbs/in and have to live with the ride comfort & being a bit 'skitty' over uneven 'B' road surfaces.

You could also experiment with proper bump rubbers (like most modern cars have on the damper shaft) which add rate in bump travel and not the aggressive bump 'stops' that a std Mini has which are just to stop it going metal to metal or running out of joint angle.

Cheers

Edited by Aubrey_Boy on 28th Nov, 2014.

Thankyou for your detailed explanation. I've made a decision to ditch the front coilover setup, as per my build thread. This is partly down to the lack of weight saving, but mainly down to concerns of how they will perform. Having spoken to a few people, I think cones are probibly a safer bet. I'm concerned about lack of droup, harsh ride etc. on coilovers.

Then again do rubber cones become to harsh on a very light mini or does them been progressive maintain the ride quality.

What's your opinion on the best setup then?

Edited by alaskanow0 on 13th Nov, 2014.

Class C 3rd Place Avon 2011 14.18 @101mph

Just my opinion... As far as the 'best' set up goes it would have to be a qualified 'best'

I think it depends on how comfortable someone is with designing / making parts to get what they want

My personal 'best' choice is coilover - But my version of 'coilover' is making all your own coilover mounting points to make them do what you want. I couldn't get what I wanted without resorting to the inboard coilover setup which was done just for this reason.

My project specific reasons are packaging and that a coilover setup is lighter as it allows a tubular front subframe and rear subframe removal, which in my case is roughly 20kg just for the subframe changes. 14kg rear, 6kg front.

Coilovers give much more tuning options, spring rate, suspension travel, damping.

For a road car, If I had to choose between cones and an 'off the shelf' coilover conversion (and I wasn't bothered about weight and I could package cones) then no question, I would choose cones, fit and forget, everything is easily available, difficult to get it too wrong.

For a light track car I think you have much more chance of making coilovers (assuming your using an off the shelf coilover conversion) work as the consequences of running stiffer spring rates are much less of an issue on a smooth / even surface. Your not worried about ride quailty and can keep tweaking the rate front or rear to suit you.

My other concern is staying cone sprung at one end, i.e. the front cones and coilover rear. I think this would be difficult to resolve for a road car, mainly I would worry about how a lightweight rear end with stiff rear coilovers would behave on fast A / B road if you have to lift off mid corner or encounter an uneven patch of road.

It's not to say you can't get to an acceptable compromise but it will no doubt involve a few spring rate changes to get to something that is acceptable, but there is no way in the world if you were designing a car from scratch that you would start this way as you MUST have a much higher rear wheel rate than should be the case to maintain a sensible roll couple and lateral load transfer distribution front / rear. Also because of this you would run out of available suspension travel even in a straight line so again have to run a stiffer wheel rate or a high ride height to compensate.

As far as your question about cones becoming too harsh on a lightweight mini I wouldn't worry too much, on a std cone rate, assuming a 65 / 35 weight split for both (although the lightweight will in reality be more front biased), then say going from a standard Mini weight of 650kg to a lightweight 510kg is the equivalent to about a 14% stiffer front wheel rate and about 16% stiffer rear wheel rate, most after market 'tuner' springs for road cars are circa +20% over OEM so this increase should be fine.

Cheers

Edited by Aubrey_Boy on 28th Nov, 2014.

i suppose the thing to d on the rear , is move the top coilover mount forward to the bulkhead .

Medusa + injection = too much torque for the dyno ..https://youtu.be/qg5o0_tJxYM

And as if by magic

Yes Robert, here's one I prepared earlier



Black is the standard rear cone, I didn't exercise the model over it's full travel but it looks pretty linear / constant
Red is the coilover, you can see it's non linear and ultimately falling rate
Blue is moving the standard damper top mount forward

The horizontal axis is wheel travel in mm, bump to the right, rebound to the left

The vertical axis is the change in wheel rate, up = increase in rate, down = decrease in rate

The wheel travel = 0 mm position is for a 12" mid 90's Mini as it left the factory in terms of static ride height

(Black curve - std cone) You can see that as you lower a cone equipped car the wheel rate gets higher

(Blue curve - fwd top mount) you can see forward it is roughly twice the amount of required change.

These are taken from a fully elasto-kinematic model which is why there is some hysteresis shown between loading and unloading of the suspension.

It is one of the options I am considering as well as an arrangement similar to the front which would bring the coilover into the car

Cheers

Edited by Aubrey_Boy on 28th Nov, 2014.

Ok I think I'm following this. I'm I right in thinking the coilover has to be mounted in relation to the direction of travel of the bottom arm.

Now, does that fact that I've mounted the rear turrets 25mm higher make it better or worse.

As you can see the coilover sits a lot closer to the turret at the rear About 14mm further back than normal due to the beam.

It's is worth slotting the top hole closer to the front

Edited by alaskanow0 on 14th Nov, 2014.

Class C 3rd Place Avon 2011 14.18 @101mph

Moving the top mount up 25mm will make it very slightly worse but likely to be tiny in reality

Moving the lower coilover mount rearwards is better

Moving the trailing arm pivot axis up is better (subject to clearance / making clearance).

Little gains in each of these areas will mean you get you closer and mean you need to run a less stiff coilover rate to replicate the cones without going to the extremes of moving say the top mount forward .

Edited by Aubrey_Boy on 28th Nov, 2014.

Thanks for all your help. I'm still a little confused why the different angle makes such a difference. I've try to search online, but can't fine any thing that explains it.

Also what effect does tightening the spring platform have. If like to run a 1" shorter spring to lower the car further. Or do a get a stronger spring with less pre load?

I've held off sending the front coilover back today just in case. How's does Nicks setup look to you with the modified top arm brackets.

Edited by alaskanow0 on 14th Nov, 2014.

Class C 3rd Place Avon 2011 14.18 @101mph

If you need any decent pics or anything of how i've cobbled mine together just shout.

I'll be honest and admit i've no idea about suspension setup, I've literally just done it all by eye

it sounds like what paul h did with his donuts up against the seat rail ,was a good idea .


http://www.turbominis.co.uk/forums/index.php?p=vt&tid=447470

Edited by robert on 15th Nov, 2014.

Medusa + injection = too much torque for the dyno ..https://youtu.be/qg5o0_tJxYM

This is a great thread. Excellent information.

I'm about to fit coilovers to the back of mine purely as a weight saving exercise. I'm tempted to fit turrets now and angle them toward the rear bulkhead. The rear end is tripped anyway so i have no excuse really.

In the 13's at last!.. Just

That was a awesome idea, good thread

The thing we are concerned about is called motion ratio, that is the relative motion of the wheel centre in a pure vertical sense versus the displacement of the coilover (spring travel if you like) along the coilover axis.

If the wheel centre moves 1mm vertically and the coilover also moves 1mm we have a motion ratio of 1/1 = 1, if the wheel centre moves 10mm vertically and the coilover 9mm we now have a motion ratio of 10/9 = 1.11 as per the typical coilover installation on a Mini. As you go further this usually gets worse and worse. 20/17 etc etc...

The reason the coilover is now moving less is because the top wishbone moves in an arc and the lower coilover mount moves towards the centre of the car as well as compressing the spring along it's own spring axis. In the case of the front coilover this is all too obvious when coilovers are mounted using the 'off the shelf' lower brackets as per Nicks early photo and we can instinctively see that something is not right.

As we lower the front ride height the top wishbone angle is even more acute and the motion ratio problem is even worse. So as Nick did you have to move the lower mount out and the top mount.

I went inboard coilover to try and resolve this issue. I could do this on the passenger side but not on the drivers side due to the subframe tube having to pass around the stupid big engine and occupying the same space that I would have needed.

Robert,

I guess this is similar, a scheme I looked at a while back, good for keeping the weight low down but quite a lot of effort compared to moving the coilover top forward for what I need, still not decided but 'phase 1' will be relatively simple (hopefully)



Ignore the fact that some tubes pass through the tyres! The software simply connect two points together with a straight tube graphic, the kinematics are unaffected and you can edit the graphics if you want full gaffer dazzling but not necessary.

The prop is there as I have done some AWD dynamic tests but I can turn it's functionality ON / OFF but the graphic still shows.

Cheers

Edited by Aubrey_Boy on 28th Nov, 2014.