Stiffened rear ARB

[handpaper]

Copied from someone else on here (I've been trying to find the thread and can't); I just had to try it

The closer the pick-up point on a torsion spring is to the rotation axis (centre of the bush), the higher its effective rate; an ARB is a simple torsion spring.
I did something similar a couple of years ago with a front bar.

To provide the extra lugs I chopped up an old Peugeot wheelbrace and bent it to shape with vice and lump hammer.
Welding them on was just possible with my 100A MIG; I had to use max current, minimum wire feed rate, and zig-zag the weld. (Note to self : get a better welder)



Not the best pic; I should have taken it before painting . I've welded the extra lug on top of the bar as it will sit when mounted; this should give the most available movement (limit is the ARB link hitting the underside of the car)

The new lugs are half as far from the pivot point as the originals, for twice the effective stiffness, equivalent to having a 16.5mm bar.



This will be going on my Touring in the next day or so; I'll update later with how it feels/whether it fouls anything/if it breaks

[GeoffBob]

Well done. Welding looks pretty good to me, nothing to be ashamed of there.

Out of interest, why do you want such a stiff ARB?

[handpaper]

Well done. Welding looks pretty good to me, nothing to be ashamed of there.

Out of interest, why do you want such a stiff ARB?

The Touring, while handling quite nicely, rolls a lot more than than I like. This may have something to do with my previous road car (now morphing into a track-day toy) running stiffly-sprung coilovers all round

Also, I have a little track day coming up (June 17th, Llandow) and I want to get some drifting in

[GeoffBob]

I would think the touring rolls more due to greater mass? What about stiffening up the springs on the touring as well? I'm a big fan of all round coil-overs

[handpaper]

A Touring weighs c. 100Kg more than a saloon and it's all at the back
For the track day I'll bolt on the coilovers (and brakes, and LSD) from the track car , but the OE stuff will be going back on afterward - it's a road car after all, and I don't want to spoil the ride. Shopping brought home in a car running the equivalent of 630lb/in rear springs is not a pretty sight

[UweM3]

handpaper why don't you use an ARC welder for the bigger stuff? Gives better results with less expensive equipment (than MIG) AND stronger welds.

[GeoffBob]

A Touring weighs c. 100Kg more than a saloon and it's all at the back
For the track day I'll bolt on the coilovers (and brakes, and LSD) from the track car , but the OE stuff will be going back on afterward - it's a road car after all, and I don't want to spoil the ride. Shopping brought home in a car running the equivalent of 630lb/in rear springs is not a pretty sight

Good stuff! Sounds like you're pretty serious about taking your touring on a track day. That's a lot of work to swop that lot over, so good on you for the effort. Makes sense though that you are puting the stiffer springs with the stiffer ARB. I wouldn't recommend that you try your stiffer ARB without the stiffer springs as your rear suspension will likely become "dependent", as opposed to "independent". She may even cock a leg going round a corner, like the little FWD's with torsion beam rear suspensions. Not what you want in a rear wheel drive .

630lb/in on your rear springs! Yeh, those are some serious springs you have there. In my language that's about 110kg/cm. On a touring that probably has around what, about 400 to 500kg over the rear axle (I'm guessing here), not counting the unsprung mass which always shows up on the scales, that sounds about right.

I didn't realise she was a daily driver. Not the sort of car to put your dozen eggs in the back of unless you want them scrambled, so I understand why you would want to go back to the OEM suspension afterwards.

Thanks for the info and good luck. I'd be very interested to hear how your modified ARB performs.

[UweM3]

GeoffBob, I am running 1000lbs in the rear and was thinking to go up a little
(but that's undrivable on the road(

[handpaper]

handpaper why don't you use an ARC welder for the bigger stuff? Gives better results with less expensive equipment (than MIG) AND stronger welds.

I'll have to try that. I have an arc welder, but I've never used it. Something else to learn....


Geoff, the track car (with coilovers) was also my road car for about six months. The spring rates are 650lb/in front, 225 lb/in rear*. Uwe would say that that's undriveable on the road, but that's because he's soft After I'd used it for a few weeks and my lumbar vertebrae had fused together, it was fine

The consensus on stiff springs and ARBs seems to be that it's either/or (except on the rear, for drifting).
A stiff ARB can help reduce body roll in an otherwise softly sprung car, improving comfort and precision where the reduction in grip isn't so important.
Harder, track oriented suspension makes ARBs less useful as the spring rates allow less body roll. It's very common for VLN saloons to remove the rear ARB for wet races to increase rear grip, while a few very stiffly sprung race cars don't run them at all.

The 'cocking a wheel' that FWD hatches are famous for is caused by the combination of a very light rear end and the stiff rear ARBs used to balance out the chronic understeer these cars suffer from. It's usually observed when turning-in, especially when still on the brakes.
The Touring has a slight weight bias to the rear (unstripped); this, along with the difference in driving style (I release the brakes as or before I turn in) and the even stiffer front bar should keep the roll centre in a sensible place.
Coincidentally, I saw an excellent demonstration of this the last time I went to Llandow as I was filling up the list for the Saxo Sports Club
In the 325i I was second quickest of the day, behind a very well sorted VTS.
This time I'm tagging along with Scoobynet - if I'm lucky I'll be second slowest

*The rear suspension is full coilover, picking up on the shock mount, not the OE spring seat (as Uwe's does). Because of the greater leverage a spring in this position has, its rate must be altered (by the square of the lever ratio, in this case, 1:2.8 ) To match Uwe's 1000lb/in springs in the OE location, I would fit 360lb/in springs on the coilovers.
Apologies if you already knew this

[UweM3]

Geoff, the track car (with coilovers) was also my road car for about six months. The spring rates are 650lb/in front, 225 lb/in rear*. Uwe would say that that's undriveable on the road, but that's because he's soft After I'd used it for a few weeks and my lumbar vertebrae had fused together, it was fine

oouii careful here Keep in mind I am an old man with brittle bones. Your rear springs are softer than mine and I can't open up the damping for the road like you can. Mine is really not a pleasure to drive on the road. And I am fed up with strapping in and out of the harness just to go to the petrol station.
I use the car where it is so much more fun, on a race track.
Got a nice comfy 5 series tourer to tow it

[GeoffBob]

The 'cocking a wheel' that FWD hatches are famous for is caused by the combination of a very light rear end and the stiff rear ARBs used to balance out the chronic understeer these cars suffer from. It's usually observed when turning-in, especially when still on the brakes.

Yes, and equally observable on a short wheel base RWD car with an ultra stiff ARB while under heavy braking in a corner (for reasons that I will go into below). The two situations are basically the same, although obviously the outcome for the RWD car is quite different.

My concern with any ARB (and this is not intended as a criticism of your work) is that it essentially binds the vertical movement of one wheel to the other (reducing the independence of the suspension). This has its place, off course, in order to reduce body roll. However, the tendency of a body to roll is, in the first place, a function of its mass, the height of its COG, and, quite importantly, the distance between the COG and the roll centre. All of which an ARB can do nothing about, except to limit the resultant roll. Sadly, this comes at the expense of increased vertical load on the outside wheel, and decreased load on the inside wheel, which can lead to a loss of traction on the inside wheel. This is why ARB's are commonly removed in wet conditions - since traction has been reduced to the point where the slight reduction of vertical load on the inside rear wheel while cornering can have unhappy consequences.

The Touring has a slight weight bias to the rear (unstripped); this, along with the difference in driving style (I release the brakes as or before I turn in) and the even stiffer front bar should keep the roll centre in a sensible place.

What you say makes good sense! I don't claim to have all the answers and I certainly don't claim that ARB's don't have their place in motorsport, but I would suggest that you consider what I have said above with regard to the reduced vertical load on the inside wheel. Despite your rearwards weight bias, the weight is effectively shifted forward during braking. Combine this with reduced vertical load on the inside wheel and any combined cornering and braking could be disastrous for you (hence you brake before corners, I understand). I certainly can't see this situation getting any better with an even stiffer rear ARB. I am not saying you will lift the rear inside wheel like a little FWD hatch (I doubt that you would in a tourer), but there will be a very real and substantial reduction in weight on that inside rear wheel (which, and I mention this purely out of interest, cannot be seen by putting a USB camera over the coil spring, due to the fact that it’s due to the action of the torsion-spring ARB).

I think that what I have said is in direct agreement with your statement:

A stiff ARB can help reduce body roll ”¦. where the reduction in grip isn't so important.

With the exception that I have just bored poor Uwe to tears again with an overly detailed explanation of how the clockwork ticks .
Sorry Uwe .

However, this does beg the question, if a stiffer ARB reduces bodyroll at the expense of traction, then unless a) you have limited suspension travel (which has its own solution), or b) your roll centre is shifting up and down markedly (which also has its own set of solutions) then why bother with ARB's? Surely not for comfort (at least not on a track car)? Once again, not a criticism, just stimulating the conversation.

[UweM3]

With the exception that I have just bored poor Uwe to tears again with an overly detailed explanation of how the clockwork ticks .
Sorry Uwe .

However, this does beg the question, if a stiffer ARB reduces bodyroll at the expense of traction, then unless a) you have limited suspension travel (which has its own solution), or b) your roll centre is shifting up and down markedly (which also has its own set of solutions) then why bother with ARB's? Surely not for comfort (at least not on a track car)? Once again, not a criticism, just stimulating the conversation.

Don't worry I am still with you
I am thinking about ARB's for a long while. First I followed the usual advice (because one doesn't know better) but as more as I get into the details of it I wonder if I am not making things worse with the wrong ARB spring combination.

Of course on a road car it is quite common to up the ARB's to reduce body roll but for me that's going in the wrong direction.
Sure upping the spring rates has negative effect on the comfort but there is no such thing as free lunch.

I found my previous suspension setup a good compromise for road and track. Yes a little bit comfort (for road) was traded in for less body roll (on track) but the whole setup was juuust working ok in the two different environments.

my friends back in Germany are doing slalom racing (Auto-X?) and they all run without rear ARBS but MEGA stiff springs. (220-240N!)

I will just do what I usually do when I am undecided. I will disconnet the rear ARB and see what happens
I have one or two places on the Ring where I can feel the inside back wheel lifting! (Ex-Muehle for example) And I am sure there are a few others I don't even realise a little bit of back wheel lifting.
My ultimate dream still is adjustable ARB's......

[GeoffBob]

Handpaper, one thing you said has been bothering me. I initially commented on it in my last post, but then deleted my comment as I thought I must be having a daft moment. However, after some thought, I have to disagree with your comment that:

Because of the greater leverage a spring in this position has, its rate must be altered ”¦ by the square of the lever ratio

I'm pretty sure that you alter the spring rate in direct proportion to the lever ratio, not the square of the ratio. To satisfy my concern I have proven this to myself by both balancing the bending moment about the pivot point (the point where the arm connects to the frame), as well as proving it by the method of conservation of work. Either way, it works out the same. I have a sneaky suspicion that your "ratio squared" relationship comes from Herb Adams book Chassis Engineering. If so then be careful, there's a lot of good information in that book, but there is also a lot of nonsense. He presents a lot of good experience accumulated over many years of work in the motor industry, but doesn't have as much grasp on the theory as he claims to have. I realised this when I first saw him muddling up units in some of his equations.

I am thinking about ARB's for a long while. First I followed the usual advice (because one doesn't know better) but as more as I get into the details of it I wonder if I am not making things worse with the wrong ARB spring combination

Personally, I opt to solve as much of the roll as possible with stiffer springs. Unfortunately, there is only so much that can be done with stiffer springs. For example, to halve your roll angle would require springs that are twice as stiff, and increasing your spring stiffness this much could lead to other problems (assuming they are already very stiff). Thus, I opt only to fit ARB's after I have exhausted all options with springs. This is why I have very deliberately built a light car with a low COG and I do not use ARB's. A heavy car with a high COG, however, has limited options.

Of course on a road car it is quite common to up the ARB's to reduce body roll but for me that's going in the wrong direction. Sure upping the spring rates has negative effect on the comfort but there is no such thing as free lunch.

I fully agree. My car is not built for comfort, its built for the track. I do however find that wearing my harness extra tight helps as it cuts off the blood supply to those parts of my body that hurt

my friends back in Germany are doing slalom racing (Auto-X?) and they all run without rear ARBS but MEGA stiff springs. (220-240N!)

Aah, ein Deutscher, Ja? Das erklärt die Abwesenheit des Humors und der Liebe von WÃarsten. Ich bin glÃacklich, in der Nähe von einer Brauerei zu leben, die ausgezeichnete Weis und Alt Bier, etwas macht, dass ich vermute, dass Sie im England nicht haben. Ich wÃarde Ihnen einige senden, aber es ist zu gut, um sich zu teilen.

EDIT: OK, I won't try that again. My German is a bit rusty, I struggle with masculine and feminine objects.

Units! N/m or N/cm please! I tend to agree with this policy of running with stiff springs and without ARB's though.

I will just do what I usually do when I am undecided. I will disconnet the rear ARB and see what happens I have one or two places on the Ring where I can feel the inside back wheel lifting! (Ex-Muehle for example) And I am sure there are a few others I don't even realise a little bit of back wheel lifting.

Sounds good to me. I don't think there's anything wrong with testing this way? I've left my ARB mounting points intact in case I ever have to put one or the other back.

[Jhonno]

One thing the arb's do offer is the ability to adjust the balance of the car.. Yes this can be done with springs also, but not as easily or cheaply..

Also, correct me if I am wrong (I often am.. ) but arb's also have less effect as the spring rates increase, seeing as they don't adjust their stiffness with the springs..

I would agree about your comment of the spring rate full coilover vs. platforms being directly proportional is correct, simple moments and leverage

[GeoffBob]

One thing the arb's do offer is the ability to adjust the balance of the car.. Yes this can be done with springs also, but not as easily or cheaply..

I'll have to think about this one Jhonno. Adjusting the balance of the car is a critical aspect/point of the suspension setup which I personally think is quite easy to adjust by means of the springs. But that's just my opinion and I guess I am just used to doing it this way. Of course having adjustable spring seats and an assortment of springs to play with helps. For the most part, I adjust the balance simply by adjusting the preload on the springs (in other words, adjusting the seats up and down). So long as my adjustments don't severely limit the suspension travel, that is to say, don't bias the wheel predominatly up or down. If it does then its a case of changing the stroke of the dampers as well. OK, maybe playing with ARB's is easier, and certainly cheaper ...

Also, correct me if I am wrong (I often am.. ) but arb's also have less effect as the spring rates increase, seeing as they don't adjust their stiffness with the springs..

Sorry Jhonno, not sure if I understand this question. Are you referring to non-linear springs that increase or "change" their spring rate as they are compressed (which ARB's don't do, so far as I am aware, unless torsioned to near their breaking limit) or are you talking about actually "changing" the springs rate by swopping or "changing" it out, but leaving the same unchanged ARB behind?

[UweM3]

my friends back in Germany are doing slalom racing (Auto-X?) and they all run without rear ARBS but MEGA stiff springs. (220-240N!)

Aah, ein Deutscher, Ja? Das erklärt die Abwesenheit des Humors und der Liebe von WÃarsten. Ich bin glÃacklich, in der Nähe von einer Brauerei zu leben, die ausgezeichnete Weis und Alt Bier, etwas macht, dass ich vermute, dass Sie im England nicht haben. Ich wÃarde Ihnen einige senden, aber es ist zu gut, um sich zu teilen.

EDIT: OK, I won't try that again. My German is a bit rusty, I struggle with masculine and feminine objects.

Not bad your german actually! But you do me wrong justice with the humor thing. Believe it or not germans have humor (ok not all off'em..), I have surprised quite a few people with not fitting in the usual pattern.

Cars are so damn complictated! I am much better with bikes. Two wheels only and the steering nicely in the centre axis. Job done! Actually not as easy as it looks like at first sight, as soon the thing starts to lean over the problems are showing up. But that's another story

Have a look at Jhonno's sig picture. That's my previous suspension setup he is running.

[GeoffBob]

Not bad your german actually! But you do me wrong justice with the humor thing. Believe it or not germans have humor (ok not all off'em..), I have surprised quite a few people with not fitting in the usual pattern.

'Was only kidding Uwe . Strange, after reading some of your earlier posts on this forum I had you pegged as a Welshman , particularly after you said you were foreign . Oops, now I'm in for it.

[UweM3]

'Was only kidding Uwe . Strange, after reading some of your earlier posts on this forum I had you pegged as a Welshman , particularly after you said you were foreign . Oops, now I'm in for it.

you're pushing you luck.......

[Jhonno]

One thing the arb's do offer is the ability to adjust the balance of the car.. Yes this can be done with springs also, but not as easily or cheaply..

I'll have to think about this one Jhonno. Adjusting the balance of the car is a critical aspect/point of the suspension setup which I personally think is quite easy to adjust by means of the springs. But that's just my opinion and I guess I am just used to doing it this way. Of course having adjustable spring seats and an assortment of springs to play with helps. For the most part, I adjust the balance simply by adjusting the preload on the springs (in other words, adjusting the seats up and down). So long as my adjustments don't severely limit the suspension travel, that is to say, don't bias the wheel predominatly up or down. If it does then its a case of changing the stroke of the dampers as well. OK, maybe playing with ARB's is easier, and certainly cheaper ...

You can adjust in smaller steps.. Pretty much like fine tuning

Also, correct me if I am wrong (I often am.. ) but arb's also have less effect as the spring rates increase, seeing as they don't adjust their stiffness with the springs..

Sorry Jhonno, not sure if I understand this question. Are you referring to non-linear springs that increase or "change" their spring rate as they are compressed (which ARB's don't do, so far as I am aware, unless torsioned to near their breaking limit) or are you talking about actually "changing" the springs rate by swopping or "changing" it out, but leaving the same unchanged ARB behind?

Sorry, all I meant, was the stiffer you go, the smaller part the ARB's play in the system, seeing as they are simply torsion bar with a set rate.. Does that make any sense now?

[Jhonno]

'Was only kidding Uwe . Strange, after reading some of your earlier posts on this forum I had you pegged as a Welshman , particularly after you said you were foreign . Oops, now I'm in for it.

you're pushing you luck.......

Hmmm sheep 'enthusiast' or sun lounge hogger.. I think I'd rather be German!

[UweM3]

'Was only kidding Uwe . Strange, after reading some of your earlier posts on this forum I had you pegged as a Welshman , particularly after you said you were foreign . Oops, now I'm in for it.

you're pushing you luck.......

Hmmm sheep 'enthusiast' or sun lounge hogger.. I think I'd rather be German!

I can give you some lessons, got a spare towel.....

[Jhonno]

Is it the lack of beaches in Germany, that when you finally get to one you get all over excited?

[GeoffBob]

Sorry, all I meant, was the stiffer you go, the smaller part the ARB's play in the system, seeing as they are simply torsion bar with a set rate.. Does that make any sense now?

OK, I follow you now. The way I always look at springs and ARB's is as follows: Springs provide what's called common mode suspension, while ARB's provide what is called differential mode suspension. That is to say, springs resist the vertical displacement of each wheel with a force that is proportional to the diplacement of each wheel, while ARB's resist the vertical displacement of each wheel with a force that is proportional to the difference in displacement between two adjacent wheels.

In other words, as a car drives over a sleeping policeman (speed bump), say, the torsion bar offers no resistance to the vertical wheel travel since there is no differential movement between the two wheels (the two wheels move up and down the same, assuming the axle is cossing parallel to the bump). All the suspension work is done by the springs.

However, while cornering, the body will tend to roll and thus the outside wheels will be displaced upwards, while the inside wheels will be displaced downwards (relative to the rolling body). The ARB will thus tend to resist/limit this differential displacement between the inside and outside wheels as the bar torsions.

Thus, the springs and ARB's respond to different (but related) inputs, and essentially function independent of each other. Changing the value of one actually has no effect upon the force exerted by the other. It is, however, quite true to say that increasing the stiffness of the springs (or more specifically increasing the stiffness of the outside spring) will resist body roll. And thus, the stiffer the springs, the less noticable the influence of the ARB on the system compared to the effect of the springs, to the point where the springs might be so stiff (in theory at least) that an ARB would have no effect at all.

This makes perfect logical sense if you think about it: If you replaced your springs with the stiffest springs possible, something like a length of solid steel round-bar, the effect of the ARB, regardless of its torsional stiffness, would be zero. In fact you might as well just throw your ARB away (along with your spine, kidney, spleen and teeth).

Having said all this, both common-mode and differential mode suspensions have their place on cars, and I am very interested to hear how handpapers uprated ARB performs. Sorry Handpaper if I've hogged your thread.

[handpaper]

Hog away, I love this kind of discussion (ask Uwe )

First point, the 'ratio squared' thing. I was given that calculation by 'Pooky' (on northloop.co.uk and bmwtrackzone.com). He's a suspension designer/engineer for Jaguar. I used it as rote initially, but thinking about it further it does make sense. Not only does the coilover spring have more static leverage than the OE spring, but it is also compressed more in the same ratio.
Here's a simple diagram :


Let's assume the lower position in the diagram is with the suspension fully unloaded and the upper is at static sag.
Each spring must provide a force, in the compressed position, sufficient to support the weight of the car. We'll assume for simplicity's sake that this weight acts through the coilover point as opposed to the hub (which sits a short way pivot-ward) and also that the OE spring perch is half-way between the coilover point and the pivot.
One side of the rear of an E30 weighs c. 250Kg, so this is the force that must be developed.
The OE spring is at a disadvantage here as it acts on a point half-way up the trailing arm; it must therefore develop 500Kg in order to support the car, where the coilover spring need develop only 250Kg. This is the static leverage ratio.
Now let's consider how these forces are developed. Look at the arcs described by the movement of the spring attachment points - these show how much each spring is compressed. Notice that the coilover spring is compressed twice as much as the OE spring for the same suspension movement. This means that it will develop the same force as the OE spring with only half the spring rate.
The coilover spring therefore need only develop half the force of the OE spring on being compressed twice as much, so its rate will be 1/4 as high - the square of the ratio of distance from the pivot.
Does that make sense now?

Aaaand back to ARBs

If I was serious about going fast on this upcoming track day, I'd either leave the stock rear ARB in place or fit an even softer one.
But I'm not. The day was organised on Scoobynet; most of the cars there will have twice as much power as me, some even more, so I'm just going to go as sideways as I can and have a laugh. To this end, a stiffer rear bar will reduce rear grip nicely and let me play

I'm in full agreement with the comments made about high spring rates making ARBs redundant.

Re : Jhonno's point about using ARBs to tune suspension....
What you can do with adjustable bars is to move the roll centre forward or backward. This can have a large impact on the car's handling; see my point above about using stiff rear bars in FWD hatches.
I would hesitate to attempt altering the weight distribution of a car by meddling with spring perch heights, though this adjustment is useful for corner-weighting. If weight distribution needs altering, move some weight!

The pic of Jhonno's car is a little misleading; it's about mid-way around the Karussell so it's cornering at over a G, on 45 degree banking.

I'm fairly Welsh......

[GeoffBob]

Excellent explanation Handpaper! Many thanks for the work you put into that. I'll need a little time to mull it over and digest it, and then I'll respond.

If I was serious about going fast on this upcoming track day, I'd either leave the stock rear ARB in place or fit an even softer one.
But I'm not. The day was organised on Scoobynet; most of the cars there will have twice as much power as me, some even more, so I'm just going to go as sideways as I can and have a laugh. To this end, a stiffer rear bar will reduce rear grip nicely and let me play

Yeh, that's the way to do it!! Nothing wrong with sideways - helps limit space for others to overtake . Forget the pictures, I want to see the videos!

I would hesitate to attempt altering the weight distribution of a car by meddling with spring perch heights, though this adjustment is useful for corner-weighting. If weight distribution needs altering, move some weight!

Point taken, I figured I'd get nailed on this one. I wouldn't advocate this method for major adjustments, but it can be used. If a major adjustment is required, then fair enough, move some mass. The point I want to make here, however, is that the tendency to over or understeer is a function of the dynamic movement of the COG. A subtle change to the static weight distribution can have a marked effect upon the dynamic weight distribution. This assumes that one has a car with good weight distibution to start out with and that there's nothing left to move around (my missus is getting fed up with having to sit in the boot of the car). This technique is put to good effect on banked circuits in Nascar for example by wedging (adding preload to a spring). The amount of pre-load that is added is dictated by the circuit conditions at that time and preclude the option of redistributing the static weight. Of course this only works where the turns are all in one direction only, so I'm not suggesting anyone try this. I mention it purely as an example of where adjusting the pre-load on a spring is employed to adjust the tendency towards over or understeer.

[GeoffBob]

Handpaper,

OK, I understand now. I studied you explanation in detail and managed to derive the same mathematical relationship myself in line with your explanation.

My mistake was in thinking that the problem went no further than a simple balance of the bending moments about the pivot point (which results in a linear relationship). Once it dawned on me that the distance through which the two spings would move is different (also a function of the ratio) then the penny dropped, and out popped the ratio squared relationship.

Thanks again for the excellent explanation.

BTW, could you post a few pics of how you fitted your rear coil-overs. I'm still using adjustable spring seats on the rear and really like this idea of yours of moving the spring back closer to the hub. Uwe, you're still busy building, maybe this would be of interest to you as well?

BTW Uwe, this evening I am drinking a most excellent Rauchbier. You wouldn't believe the most fantastic German stuff that is brewed down here.

[handpaper]

No problem on the explanation, it was your asking about it that prompted me to derive it for myself

Video system is ready to go; I'll post any decent footage I manage to get. It's a rather crude collection of cheap bits running off a home-made power supply, but it does work.
Late 2007 it recorded this 'Ring lap

My coilover thread is HERE. Uwe built his at about the same time; he chose to use an adjuster on the rear spring perch.

The ARB....
Well, there's a problem with the 'uprated' ARB. I fitted it this afternoon and the link arms won't reach the new pick-up points
Longer link arms will almost certainly foul the underbody under suspension compression; extending the trailing arm pick-up points rearward will probably cause similar problems. As far as I can see, the only solution is to reposition the ARB pick-up points so that the link arms can reach them. Whether the bar will still be usefully stiffer I don't know.

Staroslav, so cold it pours like gel, is currently easing the pain

[UweM3]

just a thought, is there a place where I can get a custom ARB made??

[GeoffBob]

Excellent thread that Handpaper! Thanks for pointing me to it. I'm definitely going to fit rear coil-overs at some point. It's the whole "ratio-squared" thing that has done it for me. Locally, I have so much more to choose from in terms of softer springs compared to the rock-hard ones required closer to the pivot point. Maybe its different in the UK, but I suspect that the job of rear spring selection may become a little easier for other serious tracksters if they take a page from your book in this regard.

BTW, I have a very different set of coil-overs on the front of my car. As you may or may not be aware, I built my own E30 space-frame to which the E30 subframes attach (see here http://www.e3024v.com/board/index.php?topic=514.0). The frame has an R5Turbo body on top (mostly GRP), just to be different and to confuse the hell out of everyone. To fit the R5Turbo GRP nose I had to lower the strut towers by 30mm (compared to a standard E30). This immediately precluded the use of standard parts.

I'm currently running 50kg/cm (280lb/inch) springs, which may sound soft, but the whole car only weighs a touch over 750kg (180kg per front wheel). Cornering at speed is just sooooo easy in this car. The dampers are adjustable Konis for one or other Toyota corrola. The big advantage of the dampers is that they are secured through a hole drilled in the very bottom (underneath) of the strut. Thus there is no need to fight with any locking ring at the top of the damper body. The Corolla damper has three little bumps around it's top edge to locate it securely inside the 51mm strut tube, and a little rubber booty to keep the damp out. I fitted camber plates with integral spherical bearings at the top of the struts.

[Jhonno]

just a thought, is there a place where I can get a custom ARB made??

I think whiteline do a variety of thicknesses..

[UweM3]

just a thought, is there a place where I can get a custom ARB made??

I think whiteline do a variety of thicknesses..

I am not after thicker or thinner standard bar, I need a different designed bar. Just a straight bar with longer levers than E30

[handpaper]

Geoff, one of the most compelling reasons for fitting coilovers, front or rear, is the huge selection of spring lengths and rates available. It's why I went for full coilovers on the rear, despite the greater cost.

The 'right' spring (and damper) rates aren't the hardest you can fit, but the softest. All suspension is a compromise between compliance and control; it's no use being absolutely certain where your wheels are if they're not on the ground.

Yours is an interesting build, though I would advise adding some form of strut brace. There doesn't seem to be mch preventing the front strut tops from moving together under cornering
I have a Reliant Kitten chassis leaning against the side of my house awaiting a suitable drivetrain. It looks very similar to your early box-section frame!


Uwe, I'd speak to Faulkner about a custom ARB. Since it's simply a torsion spring that hasn't been coiled up, they should be able to make one quite easily.
What is it for?

[UweM3]

Uwe, I'd speak to Faulkner about a custom ARB. Since it's simply a torsion spring that hasn't been coiled up, they should be able to make one quite easily.
What is it for?

hmmm, didn't think about Faulkner. Worth a try. But will he have the right thickness of raw material?

I had to move the ARB from the back of the subframe to the front. Although I am happy with how it turned out (just need to make longer drop links) it could be much more easy with an ARB that hasen't got the kink in the middle the E30 ARB (to clear exhaust and wishbones) and while at it a bit longer lever arms as well.
I will look at some E36 ARB's but from memory they have even a deeper kink. But I might tbe wrong here and it's worth finding a off the shelf ARB before spending money senseless.

May need some help to work out ratios and forces if you don't mind

[GeoffBob]

The 'right' spring (and damper) rates aren't the hardest you can fit, but the softest. All suspension is a compromise between compliance and control; it's no use being absolutely certain where your wheels are if they're not on the ground. ?

I quite agree, no need to emphasise this point. My point was, however, its easier to find a wider variety of softer springs than harder ones, and because the rear sping is more than half way up the the trailing arm from the hub, a stiffer spring is required (and thus less to choose from), even though this equates to a softer sping rate at the hub. I wasn't advocating fitting the stiffest springs possible, heaven forbid!

Yours is an interesting build, though I would advise adding some form of strut brace. There doesn't seem to be mch preventing the front strut tops from moving together under cornering

Each strut tower has a length of 42mm diameter, 4mm wall thickness, EN36 pipe which connect to the integral cage.

[handpaper]

The 'right' spring (and damper) rates aren't the hardest you can fit, but the softest. All suspension is a compromise between compliance and control; it's no use being absolutely certain where your wheels are if they're not on the ground. ?

I quite agree, no need to emphasise this point. My point was, however, its easier to find a wider variety of softer springs than harder ones, and because the rear spring is more than half way up the the trailing arm from the hub, a stiffer spring is required (and thus less to choose from), even though this equates to a softer sping rate at the hub. I wasn't advocating fitting the stiffest springs possible, heaven forbid!

Not emphasising, just agreeing with you
I'd disagree, though, on the availability of different rates in stiffer springs - HERE is Faulkner's standard list of 6" springs, roughly the length Uwe used on the rear for his conversion.
As you can see, it's (roughly) a 10% scale - each spring is 10% stiffer than the previous one - at both the softer and harder ends.

Yours is an interesting build, though I would advise adding some form of strut brace. There doesn't seem to be much preventing the front strut tops from moving together (Edit - they move apart ) under cornering

Each strut tower has a length of 42mm diameter, 4mm wall thickness, EN36 pipe which connect to the integral cage.

I saw the bars that tie the strut tops into the cage, the problem is that they're pointing the wrong way to do the work of a strut brace.
Think about it like this : each bar looks to be about 500mm long. If you had that length of bar welded firmly to something at one end, you would still be able to move the free end sideways a few mm by hand - standing on it would displace it by 10mm or more.
This is comparable to the load this area would see during hard cornering, where 10mm of movement translates to 1 degree of negative camber lost

hmmm, didn't think about Faulkner. Worth a try. But will he have the right thickness of raw material?

I had to move the ARB from the back of the subframe to the front. Although I am happy with how it turned out (just need to make longer drop links) it could be much more easy with an ARB that hasen't got the kink in the middle the E30 ARB (to clear exhaust and wishbones) and while at it a bit longer lever arms as well.
I will look at some E36 ARB's but from memory they have even a deeper kink. But I might be wrong here and it's worth finding a off the shelf ARB before spending money senseless.

May need some help to work out ratios and forces if you don't mind

E36 ARB (from realoem)


Available in 22.5, 23, 24, 25 and 25.5 mm. Lever arms look longer than the e30 ones, too - maybe too long?