The Unusual Suspension Thread
Discussion
OK, how about a thread to discuss the pros and cons of unusual or innovative suspension systems?
I'll kick off with some views on the Dax Camber Compensation System.
I'll kick off with some views on the Dax Camber Compensation System.
Edited by Sam_68 on Saturday 20th December 13:13
Picking up on a discussion in General Gassing:
Basically, it uses a pair of cross-links to adjust the position of the upper wishbone mounts relative to the chassis, thus cancelling out camber change in roll.
Like everything, it's not perfect (in many respects, it's no better than a simple beam axle - perfect wheel geometry in dive/squat and roll, but not so good in single wheel bump), but it is very clever and effective.
Geometrically and dynamically, it's probably best to think of it offering the benefits of a well-located beam axle, but lower unsprung weight (so you can use more compliant springs) and decoupled to avoid the gyroscopic effects you get with a beam.
Is it in any way similar to the NIK link fitted to Radicals?
Why don't you start a thread "unusual suspension systems" and lets see where it goes. I'll chip in.I think Dax might have fitted it at the rear, too - they've certainly listed rear CC as an option.
I suspect that the main difficulty is that diagonal weight transfer is one of the main tools in tuning handling, and it's mainly managed by varying the relative heights of the geometric roll centres and by use of anti-roll bars.
As far as I can determine, roll centre on the dax system is fixed (on the vehicle centreline, at the height of the bottom wishbone pick-ups) and fitting anti-roll bars would partly defeat some of its better characteristics. Without these, the only real tool you've got left to vary the relative front and rear roll stiffness are the spring rates themselves, and of course changine spring rates has global side effects on ride and handling...
Since there aren't such big advantages with unsprung weight at the rear (it's easy enough to build a lightweight de Dion), and you don't need to worry about the effects of gyroscopic forces on steering, it's probably cheaper and simpler to use a beam axle instead of the CC&AR system at the back... that way you can use a variety of linkages to fix the roll centre height (hence diagonal weight transfer characteristics) where you want.
Sam_68 said:
bobthemonkey said:
The Dax is the one with the trick suspension, isn't it? I had it explained to me once in a pub using whatever was to hand; it's something akin to an extra ARB, but designed to limit changes in camber resulting from compression/extension IIRC.
It's a bit more complicated than that and, as it happens, doesn't use an anti-roll bar at all (it doesn't need to, since the geometric roll centre is so high and there isn't significant camber change under roll, any way).Basically, it uses a pair of cross-links to adjust the position of the upper wishbone mounts relative to the chassis, thus cancelling out camber change in roll.
Like everything, it's not perfect (in many respects, it's no better than a simple beam axle - perfect wheel geometry in dive/squat and roll, but not so good in single wheel bump), but it is very clever and effective.
Geometrically and dynamically, it's probably best to think of it offering the benefits of a well-located beam axle, but lower unsprung weight (so you can use more compliant springs) and decoupled to avoid the gyroscopic effects you get with a beam.
spyder dryver said:
Sam_68 said:
.....useful info regarding Dax Camber Compensating suspension....
Hi Sam. Would similar benefits be gained by fitting it on the rear also? I don't think Dax do so.Is it in any way similar to the NIK link fitted to Radicals?
Why don't you start a thread "unusual suspension systems" and lets see where it goes. I'll chip in.
I suspect that the main difficulty is that diagonal weight transfer is one of the main tools in tuning handling, and it's mainly managed by varying the relative heights of the geometric roll centres and by use of anti-roll bars.
As far as I can determine, roll centre on the dax system is fixed (on the vehicle centreline, at the height of the bottom wishbone pick-ups) and fitting anti-roll bars would partly defeat some of its better characteristics. Without these, the only real tool you've got left to vary the relative front and rear roll stiffness are the spring rates themselves, and of course changine spring rates has global side effects on ride and handling...
Since there aren't such big advantages with unsprung weight at the rear (it's easy enough to build a lightweight de Dion), and you don't need to worry about the effects of gyroscopic forces on steering, it's probably cheaper and simpler to use a beam axle instead of the CC&AR system at the back... that way you can use a variety of linkages to fix the roll centre height (hence diagonal weight transfer characteristics) where you want.
Hi Sam.
In the early 90's I was heavily involved in the design and build of a highly successful TR7 V8 circuit racer.
That had no anti roll bars either. The front had a compression strut/ macpherson type arrangement but the rear was (at the time) very novel. All the standard TR links were ditched. We fitted an "A" frame from the lower pickup points behind the seats to a spherical bearing attached to the bottom of the diff casing. The two rear links from the top of the axle went rearwards and ended up in the boot area, just above floor level. Arm lengths were chosen carefully to be the same, effectively, as the "A" frame. The upper pickups on the axle and the spherical on the bottom of it were equispaced with regard to the axle tube centreline. Viewed from the side it resembles a Watts linkage.
Are you with me so far?
The roll centre height was 4" at the front, rising slightly to just under 5" at the rear. Spring rates were 440front and 280rear. All IIRC. Basic characteristic was for slight understeer going into a corner, corrected by early throttle application to give a neutral /very slight oversteer on the way out with full throttle being achieved quite early.
Following an extended test at Mallory, respected motoring journo and author Jeremy Walton ( The Lion of Spa) said it was one of the best handling front engine cars he had ever driven. The car was featured in CCC and suseqently in MTORSPORT follwing Jeremy driving the car in the last round of the TR championship at Cadwell and winning.
Do you know any other cars using this arrangement. It looked good enough on paper at the time for us to invest considerable effort in. We liked the idea of the slightly rising roll axis and the fixed roll height at the rear. Can your analytical eye see any other reason why it proved to be so good, even without anti roll bars?
We must give credit for some inspiration to Fred Puhn.
And we'd seen rearward links on TVR's.
Geoff.
In the early 90's I was heavily involved in the design and build of a highly successful TR7 V8 circuit racer.
That had no anti roll bars either. The front had a compression strut/ macpherson type arrangement but the rear was (at the time) very novel. All the standard TR links were ditched. We fitted an "A" frame from the lower pickup points behind the seats to a spherical bearing attached to the bottom of the diff casing. The two rear links from the top of the axle went rearwards and ended up in the boot area, just above floor level. Arm lengths were chosen carefully to be the same, effectively, as the "A" frame. The upper pickups on the axle and the spherical on the bottom of it were equispaced with regard to the axle tube centreline. Viewed from the side it resembles a Watts linkage.
Are you with me so far?
The roll centre height was 4" at the front, rising slightly to just under 5" at the rear. Spring rates were 440front and 280rear. All IIRC. Basic characteristic was for slight understeer going into a corner, corrected by early throttle application to give a neutral /very slight oversteer on the way out with full throttle being achieved quite early.
Following an extended test at Mallory, respected motoring journo and author Jeremy Walton ( The Lion of Spa) said it was one of the best handling front engine cars he had ever driven. The car was featured in CCC and suseqently in MTORSPORT follwing Jeremy driving the car in the last round of the TR championship at Cadwell and winning.
Do you know any other cars using this arrangement. It looked good enough on paper at the time for us to invest considerable effort in. We liked the idea of the slightly rising roll axis and the fixed roll height at the rear. Can your analytical eye see any other reason why it proved to be so good, even without anti roll bars?
We must give credit for some inspiration to Fred Puhn.
And we'd seen rearward links on TVR's.
Geoff.
Hi here's a couple of link's to vid's best viewed in high quality, of the camber compensation suspension working(first shake down for the silver Dax few more on youtube )
http://uk.youtube.com/watch?v=H1uSzccAW6k
http://uk.youtube.com/watch?v=RBVY-MFgWZo&feat...
http://uk.youtube.com/watch?v=H1uSzccAW6k
http://uk.youtube.com/watch?v=RBVY-MFgWZo&feat...
Edited by busa turbo on Saturday 20th December 13:11
spyder dryver said:
Viewed from the side it resembles a Watts linkage...
Do you know any other cars using this arrangement.
If I'm understanding you correctly, I'm sat about 30 feet from one!Do you know any other cars using this arrangement.
It sounds not dissimilar to the system that live axle Sylvas (very successfully) use... basically longitudinal, asymmetric Watts links for longitudinal axle location? The Sylva uses a conventional Panhard rod for lateral location, whereas by the sound of it you used a lower 'A'-frame?
The Sylva works well without an anti-roll bar because in roll the Watts linkages 'fight' each other and try to twist the whole axle tube. In reality, it's not the axle that twists, but the rubber bushes used at the ends of the arms of the Watts linkages that compress, but the net effect is the same - the linkage gives inherent roll resistance.
It sounds as though your set-up would do the same thing, albeit trying to twist only half the axle, and resulting in some predictable rear steer?
Edited by Sam_68 on Saturday 20th December 13:36
busa turbo said:
Hi here's a couple of link's to vid's best viewed in high quality...
Fascinating to watch the car cornering absolutely flat, despite what obviously (from the squat and dive inder acceleration and braking) quite a compliant set-up?What spring rates are you running?
And how are the springs actuated - unless my memory is playin tricks with me, the only Dax CC&AR cars I've seen have had outboard springs, with conventional lower wishbones>>>chassis mounting?
Sam_68 said:
spyder dryver said:
Viewed from the side it resembles a Watts linkage...
Do you know any other cars using this arrangement.
If I'm understanding you correctly, I'm sat about 30 feet from one!Do you know any other cars using this arrangement.
It sounds not dissimilar to the system that live axle Sylvas (very successfully) use... basically longitudinal, asymmetric Watts links for longitudinal axle location? The Sylva uses a conventional Panhard rod for lateral location, whereas by the sound of it you used a lower 'A'-frame?
The Sylva works well without an anti-roll bar because in roll the Watts linkages 'fight' each other and try to twist the whole axle tube. In reality, it's not the axle that twists, but the rubber bushes used at the ends of the arms of the Watts linkages that compress, but the net effect is the same - the linkage gives inherent roll resistance.
It sounds as though your set-up would do the same thing, albeit trying to twist only half the axle, and resulting in some predictable rear steer?
Edited by Sam_68 on Saturday 20th December 13:36
On another matter, what is your opinion of the "zero droop" setup used on the front of some Radicals, particularly in the US? Also favoured by some in Formula Ford and similar. I am interested to know if the theory might be applied to a Phoenix. And what is the NIK link all about?
Geoff.
spyder dryver said:
In our setup the "A" frame was the only link forward of the axle. It locates the axle both fore/ aft and sideways. There were no other forward links. I don't think any parts were fighting one another.
But you also had a pair of upper leading arms as well? Or do I misunderstand you?Very difficult to describe on here, but if that's the case, the 3 location arms (2 x leading arms plus the A-frame) will be describing 3 separate arcs, so will cause a certain amount of rear-wheel steer (not necessarily a bad thing, if you know what it's doing and you can manage it).
spyder dryver said:
On another matter, what is your opinion of the "zero droop" setup used on the front of some Radicals, particularly in the US?
It's another item in the suspension engineer's toolkit, is about all you can say about it. It's another tool to allow management of diagonal weight transfer without some of the side effects of anti-roll bars.spyder dryver said:
And what is the NIK link all about?
I've never worked on a Radical, so I'm not that familiar with the Nik Link, but from what I understand of it, it's basically a bell-crank arrangement whereby the coilover is compressed from both ends. It thus multiplies the amount the coilover is compressed, for a given wheel movement. The advantage is that unless you use very expensive dampers, small movements are not very accurately controlled; bigger movements are easier to control, so by multiplying the damper compression in relation to the wheel movement, you can get more precise damping with relatively cheap dampers.Yes, that bar is an anti-roll bar.
Damned if I can describe very well how it works, without resorting to sketches, but basically it's s long S-shaped spring, set up so that one side of the suspension pushes on the end of it in bump, while the other pulls on it in bump.
...so if both sides of the suspension rise or fall (ie. bump or squat), it just shifts across width of the car without being compressed. In roll, when one side of the supension rises and the other falls, it is either compressed or stretched; either way it resists roll like a conventional anti-roll bar, except that the Radical arrangement gives slight rising-rate roll resistance.
Damned if I can describe very well how it works, without resorting to sketches, but basically it's s long S-shaped spring, set up so that one side of the suspension pushes on the end of it in bump, while the other pulls on it in bump.
...so if both sides of the suspension rise or fall (ie. bump or squat), it just shifts across width of the car without being compressed. In roll, when one side of the supension rises and the other falls, it is either compressed or stretched; either way it resists roll like a conventional anti-roll bar, except that the Radical arrangement gives slight rising-rate roll resistance.
Sam_68 said:
Picking up on a discussion in General Gassing:
Basically, it uses a pair of cross-links to adjust the position of the upper wishbone mounts relative to the chassis, thus cancelling out camber change in roll.
Like everything, it's not perfect (in many respects, it's no better than a simple beam axle - perfect wheel geometry in dive/squat and roll, but not so good in single wheel bump), but it is very clever and effective.
Geometrically and dynamically, it's probably best to think of it offering the benefits of a well-located beam axle, but lower unsprung weight (so you can use more compliant springs) and decoupled to avoid the gyroscopic effects you get with a beam.
Is it in any way similar to the NIK link fitted to Radicals?
Why don't you start a thread "unusual suspension systems" and lets see where it goes. I'll chip in.I think Dax might have fitted it at the rear, too - they've certainly listed rear CC as an option.
I suspect that the main difficulty is that diagonal weight transfer is one of the main tools in tuning handling, and it's mainly managed by varying the relative heights of the geometric roll centres and by use of anti-roll bars.
As far as I can determine, roll centre on the dax system is fixed (on the vehicle centreline, at the height of the bottom wishbone pick-ups) and fitting anti-roll bars would partly defeat some of its better characteristics. Without these, the only real tool you've got left to vary the relative front and rear roll stiffness are the spring rates themselves, and of course changine spring rates has global side effects on ride and handling...
Since there aren't such big advantages with unsprung weight at the rear (it's easy enough to build a lightweight de Dion), and you don't need to worry about the effects of gyroscopic forces on steering, it's probably cheaper and simpler to use a beam axle instead of the CC&AR system at the back... that way you can use a variety of linkages to fix the roll centre height (hence diagonal weight transfer characteristics) where you want.
Hi here,s a another link to how the Camber Compensating suspension worksSam_68 said:
bobthemonkey said:
The Dax is the one with the trick suspension, isn't it? I had it explained to me once in a pub using whatever was to hand; it's something akin to an extra ARB, but designed to limit changes in camber resulting from compression/extension IIRC.
It's a bit more complicated than that and, as it happens, doesn't use an anti-roll bar at all (it doesn't need to, since the geometric roll centre is so high and there isn't significant camber change under roll, any way).Basically, it uses a pair of cross-links to adjust the position of the upper wishbone mounts relative to the chassis, thus cancelling out camber change in roll.
Like everything, it's not perfect (in many respects, it's no better than a simple beam axle - perfect wheel geometry in dive/squat and roll, but not so good in single wheel bump), but it is very clever and effective.
Geometrically and dynamically, it's probably best to think of it offering the benefits of a well-located beam axle, but lower unsprung weight (so you can use more compliant springs) and decoupled to avoid the gyroscopic effects you get with a beam.
spyder dryver said:
Sam_68 said:
.....useful info regarding Dax Camber Compensating suspension....
Hi Sam. Would similar benefits be gained by fitting it on the rear also? I don't think Dax do so.Is it in any way similar to the NIK link fitted to Radicals?
Why don't you start a thread "unusual suspension systems" and lets see where it goes. I'll chip in.
I suspect that the main difficulty is that diagonal weight transfer is one of the main tools in tuning handling, and it's mainly managed by varying the relative heights of the geometric roll centres and by use of anti-roll bars.
As far as I can determine, roll centre on the dax system is fixed (on the vehicle centreline, at the height of the bottom wishbone pick-ups) and fitting anti-roll bars would partly defeat some of its better characteristics. Without these, the only real tool you've got left to vary the relative front and rear roll stiffness are the spring rates themselves, and of course changine spring rates has global side effects on ride and handling...
Since there aren't such big advantages with unsprung weight at the rear (it's easy enough to build a lightweight de Dion), and you don't need to worry about the effects of gyroscopic forces on steering, it's probably cheaper and simpler to use a beam axle instead of the CC&AR system at the back... that way you can use a variety of linkages to fix the roll centre height (hence diagonal weight transfer characteristics) where you want.
http://www.walker-partnership.com/
Interesting thread for me as I need to improve the handling of my mk1 escort classic race car. Just look up my profile and the evidence of the problem is perfectly exhibited.
Tail happy escorts might be crowd pleasers but I would rather lap quicker without the sideways drama. Front suspension is bump rebound height adjustable avo 300lb coilovers, compression struts, adj bottom arms, eccentric top mounts, no arb. Rear suspension is similar avo 180lbs coilovers in turrets,(no leafs), 4 linked with panhard rod. Tyres are obligatory for series Advan 048 medium 205x60x13.
The car actually goes very well and is competitive apart from all the sideways stuff. It turns in nicely but lacks traction exiting slower corners where the throttle has to be modulated to keep it tidy at the expense of speed.
Rally Design sell a Watts linkage for the english axle and I'm considering fitting one, I'm reluctant to fit drop links and arb as the car understeered badly with the original arb.
Any suggestions appreciated.
Tail happy escorts might be crowd pleasers but I would rather lap quicker without the sideways drama. Front suspension is bump rebound height adjustable avo 300lb coilovers, compression struts, adj bottom arms, eccentric top mounts, no arb. Rear suspension is similar avo 180lbs coilovers in turrets,(no leafs), 4 linked with panhard rod. Tyres are obligatory for series Advan 048 medium 205x60x13.
The car actually goes very well and is competitive apart from all the sideways stuff. It turns in nicely but lacks traction exiting slower corners where the throttle has to be modulated to keep it tidy at the expense of speed.
Rally Design sell a Watts linkage for the english axle and I'm considering fitting one, I'm reluctant to fit drop links and arb as the car understeered badly with the original arb.
Any suggestions appreciated.
Kinkell said:
The car actually goes very well and is competitive apart from all the sideways stuff. It turns in nicely but lacks traction exiting slower corners where the throttle has to be modulated to keep it tidy at the expense of speed.
The Watts link certainly ought to help, as they tend to let you put the power down better when exiting a corner than a Panhard rod, but seeing as this is a thread about unusual suspension designs, how about considering a WOBlink or a Scott-Russell link? Both would give you the accuracy of roll centre location that you get with a Watts link, but allow you to adjust the rear roll centre height (which will in turn influence the diagonal weight transfer, hence understeer/oversteer balance).I'd also be thinking in terms of angling the rear trailing arms to provide a little roll-understeer. This won't affect your turn-in, as it will only come into play as the body leans though the corner, to give maximum effect as you are ready to put the power down to exit the bend.
On a more mundane level, if you haven't already done so, check the following:
- If you are allowed to run an LSD, think about adding one (or increasing the degree of lock-up).
- Despite your reluctance to fit an ARB, I'd be inclined to fit both front and rear adjustable ARB's. Set the front stiff and start off with a fairly light setting on the back, progressively increasing the rear to see how it reacts.
- Have you checked the camber and toe at the rear? You ideally want a little toe-in (toe out will certainly result in corner exit oversteer) and slight negative camber. I know it's a live axle, but with care you can adjust these slightly by heating the axle casing with a blow torch. The tube will expand when heated, but then contracts slightly less when it cools down again. Heating the back of the axle tube will therefore increase toe-in, slightly, and heating the underside of the casing will slightly increase negative camber. The bearings (which I assume you've already checked for play?) will stand a little such mis-alignment without too much distress.
You've got me thinking right enough and I would be more than happy for the escort to handle like one of the Mallocks with a WOBlink. The LSD is being rebuilt while the axle is out and I have noticed a front to rear 6" split in the shell above the panhard rod and I think the watts linkage would prevent this worsening.
I am going to try this as a first stage before fitting arbs. The best handling escorts tend to grip on the rear and lift an inner front wheel when cornering hard.
I am going to try this as a first stage before fitting arbs. The best handling escorts tend to grip on the rear and lift an inner front wheel when cornering hard.
Nice thread!
The Dax suspension is (pardon the pun) very lateral thinking! I was thinking along a similar lines the other day actualy! D a m n it!!!! Someone else always seems to have my ideas done before I think of them!!!! It all seems very clever in practise though! Do you think this would work on a single seater? From a theory/dynamic point of view ignoring the packaging headache. Is the roll centre high because it has been designed that way or can it not be any lower?
The radical website has plenty of decent pictures of the NIK link suspension on their website for those interested. Couple those with Sam's descriptions and it will all make more sense.
Not really that unusual compared to the above however recent F1 front suspension designs seem to have moved towards short upper and lower wishbonbes both tilting upwards. This seems contrary to all the "classic" suspension theory I have been reading about and I can't see why? Surely there will be side ways scrub out with bump movements. Is an increase in front track adavantageous with suspension travel? I know most reasons behind F1 suspension will be driven by aerodynamics but there must be some logic in the mechanics of it too? Any views?
The Dax suspension is (pardon the pun) very lateral thinking! I was thinking along a similar lines the other day actualy! D a m n it!!!! Someone else always seems to have my ideas done before I think of them!!!! It all seems very clever in practise though! Do you think this would work on a single seater? From a theory/dynamic point of view ignoring the packaging headache. Is the roll centre high because it has been designed that way or can it not be any lower?
The radical website has plenty of decent pictures of the NIK link suspension on their website for those interested. Couple those with Sam's descriptions and it will all make more sense.
Not really that unusual compared to the above however recent F1 front suspension designs seem to have moved towards short upper and lower wishbonbes both tilting upwards. This seems contrary to all the "classic" suspension theory I have been reading about and I can't see why? Surely there will be side ways scrub out with bump movements. Is an increase in front track adavantageous with suspension travel? I know most reasons behind F1 suspension will be driven by aerodynamics but there must be some logic in the mechanics of it too? Any views?
FrazM said:
Do you think this would work on a single seater? From a theory/dynamic point of view ignoring the packaging headache. Is the roll centre high because it has been designed that way or can it not be any lower?
I'm not sure how well the Dax Camber Compensation system would be suited to a modern single seater, because they need a very stable platform for aero. The Dax system works so well on non-downforce cars because it allows fairly compliant springing without upsetting the camber, but if you watch the video clips, the dive/squat under acceleration and braking are (relatively) massive. For smooth circuits, it would probably just be easier to stick with the traditional approach of fitting very stiff springs to limit all suspension movement (camber change as well as squat/dive/roll) to an acceptable degree. It might be interesting on a hillclimb single-seater, perhaps used in conjunction with dive/squat limiting 3rd springs, but it would be quite a complex solution.
As far as I understand it, the fact that the upper wishbones are 'floating' (albeit cross linked) means that the roll centre is defined geometrically in pretty much the same way as a swing axle, so it's always going to be on the centre line, at the height of the bottom suspension pick-ups.
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