How does a torsion bar suspension work?

just guessing here, but I wonder if the relativities between Monroe and Bilstein would have (not) appreciably changed over the period?

Honestly, the Monroes were shite from day 1. Way too much rebound, specifically in the rear. It was just the valving.

Side note, I'm presently working on a car that has a ton of front anti-dive, of which I've never been a fan. It's brilliant. Live/learn. I still don't like anti-squat.

Edited by Fat Boy, 08 July 2019 - 23:37.

I don't, and I'd have thought Tim would be much more helpful than me on the track stuff, but as a first question what exactly can you adjust? Did they include graphs? Once upon a time John Miles measured the front shocks on a whole bunch of B class cars (Fiesta etc). He then overlaid the graphs after scaling them for motion ratio. If you crudely linearise the curve as a low speed bit and then a high speed compression and high speed rebound, he found that the ratio of the two high speed parts varied wildly from about equal, to 4 times as much rebound as compression. His private conclusion was that nobody in the 90s really knew what they were doing, in the paper he wrote he just said that shock tuning is a difficult compromise, assuming that all the development engineers were competent.

 

Milliken includes a brief section on dampers for racecars, I don't have it to hand but I can dig that out.

The compression/rebound split is a big deal in terms of feel and grip. Rebound is often used because it's easy to feel. Moderate changes have meaninful ride, response and handling. Because of this fact, it's almost always overused in my opinion. Designating a spring, then winding in the rebound bleeds until you're happy is a lot easier than holding rebound damping constant while testing the trade-offs between compression damping and spring rate. Really nailing the trade-offs between grip/response on the compression side is difficult to do well, but makes for a much better overall product. I've never had success with a heavily rebound-stiff car unless it was a spec damper with little/no adjustability.

That conclusion rests on the assumption that Bilstein shocks from 15 years ago were as good as they are now, AND that the 15 year old Monroes didn't degrade over time. Neither is likely.

As if I've never tested a bloody damper. C'mon. Even if we give the Monroes every benefit of the doubt, I'm talking about how they're valved, not the build quality or technology inside. The Monroes felt very similar to the stock damper (which I didn't like and was getting away from so many years ago in the first place). It turns out they probably just reproduced the same basic force curve as stock.

Bilstein seemed to actually try to produce a better than stock valving...and they did.

I was discussing a new suspension geometry with a drift racer, and he asked me if I thought antidive would help, and in what way. He'd dug up an old post of mine where I was moaning about it. So Fat Boy, what has changed? Is it that the antidive keeps your aero rake constant even with softer springs? That was my guess.

I was discussing a new suspension geometry with a drift racer, and he asked me if I thought antidive would help, and in what way. He'd dug up an old post of mine where I was moaning about it. So Fat Boy, what has changed? Is it that the antidive keeps your aero rake constant even with softer springs? That was my guess.

I would think that anti dive would be of no use to a drift racer.... they hardly use front brakes in anger..

Aye, but with a clean sheet design there is no reason not to think about it.

I was discussing a new suspension geometry with a drift racer, and he asked me if I thought antidive would help, and in what way. He'd dug up an old post of mine where I was moaning about it. So Fat Boy, what has changed? Is it that the antidive keeps your aero rake constant even with softer springs? That was my guess.

I'm not exactly sure. All I know is this car doesn't seem to have any of the issues you might suspect with a lot of 'anti's'. The suspension manual claims 66.3% front anti-dive and 91.6% rear anti-lift. It does a hell of a good job of controlling the aero platform (an aero-dominant car). The car has no provisions to change suspension geometry and I have no wish to. It's nice when the factory can get that bit right.

Also, I'm not running this car particularly soft. It's 4-4.5 Hz on the front without bump rubbers or the 3rd engaged.

Bumpy!

Road car shocks are so totally diverse as to be rediculous.

Once put some Bilstien gas shocks into the rear of a Commodore,, it was undriveable as the gas pressure was obviously way too much. On other vehicles gas pressure shocks lifted and firmed the ride which was excellent. 

I have fitted 'off road shocks' to 4wds and some are excellent and others useless, either to stiff or soft and floaty. And again  both good brands as well as cheapies too

Back at the start of HQ Racing they used Bilstiens  as the contro shock which obviously had a problem as when the rear got sideways the wheels danced big time. The Pedders used now do not do that.

Using Gabriel shocks in my Ford Galaxie they were stuffed in 10000km. Now the thing has some used Pedders gas shocks in the rear from the Falcon racecar and some 7 rate basic AFCO steel body street stock shocks. All of which are a vast improvement.

And the racecar has got some 'Pro Shocks' built by Wayne Randall for the car and while hardly ideal they are a LOT more supple than the stiff road car shocks previously installed. And a LOT cheaper than many so called race shocks.

Had a Gabriel 'top out' in the Super Mod, that was junked also. Now I use all proper speedway shocks though had one give up and it had the wheels really dancing while going quite slowly. The track was poor. Though that shock probably leaked the oil out. It had sat for quite a while.

 I now before every meeting disconnect the top of the shock and feel them to make sure they are ok.

I was discussing a new suspension geometry with a drift racer, and he asked me if I thought antidive would help, and in what way. He'd dug up an old post of mine where I was moaning about it. So Fat Boy, what has changed? Is it that the antidive keeps your aero rake constant even with softer springs? That was my guess.

Drifters do not need aero. They want the car unhooked, especially in the rear. The wings are to look fast and nothing else.

They still need shock control though ofcourse, the last thing they want is the wheels either end dancing when driving sideways with the tyres smoking.

Success in the sport of "Drifting" requires tyre smoke and cornering speed. Anything that improves grip (including aero) is a benefit.

Success in the sport of "Drifting" requires tyre smoke and cornering speed. Anything that improves grip (including aero) is a benefit.

The ones I'm familiar with have plenty of smoke. Some of it's even from the tires.

When I've watched them, they seem to have quite a bit of legitimate understeer, but massive HP and a hand brake to put the car sideways. They also have a _ton_ of steering lock available.

Road car shocks are so totally diverse as to be ridiculous.

I took my son to a monster truck show. I wanted to go to the back and do a couple re-valves for some of the guys just to make it fair. Gravedigger might as well been driving on a feather bed.

I just find it funny how I missed the blatantly bloody obvious about my own truck.

70 degree lock angle, 700 hp+, various arguments about wheelbase and MoI .

No mention of aero, so far. I'll toss it into the conversation this week.

70 degree lock angle, 700 hp+, various arguments about wheelbase and MoI .

 

No mention of aero, so far. I'll toss it into the conversation this week.

I think CG placement/ballasting could be a big variable to investigate. On the aero side, I would look more at a large rudder piece to straighten the car (like an LMP car). Downforce in general will make the car less linear to drive, but I think increasing the inherent stability(not necessarily more understeer) in the car would allow the driver to induce more instability without getting in trouble.

^^^

To clarify that aero comment: I meant that adding drag, as opposed to downforce, might increase the yaw stability of the car like feathers on an arrow. It could do this without being overly yaw sensitive.

Getting the car straightened out again is a big deal, but I'm wondering how much grip he'll want to squander while drifting, fighting the aero. Maybe active aero?

I recently had the pleasure of being driven in a top drift car (HGK e92 eurofighter, basically a bmw e92 shell, with all Kevlar panels, big honking dart V8 LS with almost 8 liters and samsonas sequential dogbox.... uses US made quick change rear end with spool) and what amazed me was the sheer amount of cornering "grip" that is the result of those rear tires being spun around... They just get it sideways as much as they need and gun the throttle..... uses up a set of tires in 3 km...

Yep. You only get points for smoke and angle but if you don't have enough grip and the other guy drives past you its all over.

If you are ever bored draw a free body diagram of a drifting car. There's a reason why every serious vehicle dynamics book kicks off with a chapter on coordinate systems, which i doubt anyone reads unless they have to.

Time to dust off my Miliken...

I am always wonderin about Ackerman angle and drift cars...Thinking aboutits influence on handling.. Having said that, I think that in order to has as much angle as possible, considerations on ackerman angle are thrown out..

Yep. You only get points for smoke and angle but if you don't have enough grip and the other guy drives past you its all over.

Angle and proximity to specified apex points.. Thing is, you need to be able to follow the car in front, as close as possible, and follow its angle and speed... not easy always.. especially if the cars are not matched..

Time to dust off my Miliken...

I am always wonderin about Ackerman angle and drift cars...Thinking aboutits influence on handling.. Having said that, I think that in order to has as much angle as possible, considerations on ackerman angle are thrown out..

I have always taken the (simple) view that for vehicles that must operate in modes ranging from 4 wheel drift through to opposite lock 2 wheel drift, the easy solution is zero Ackerman.

I took my son to a monster truck show.

One of the better motorsport events I've been to. 

It was in a basketball arena in Milwaukee, bit cramped. 

No kidding, huh? This was in Angel Stadium in Anaheim. It was pretty awesome.

Love them or hate them, they had a bunch of 8 year old boys literally jumping up and down cheering. They're doing something right.

I recently had the pleasure of being driven in a top drift car (HGK e92 eurofighter, basically a bmw e92 shell, with all Kevlar panels, big honking dart V8 LS with almost 8 liters and samsonas sequential dogbox.... uses US made quick change rear end with spool) and what amazed me was the sheer amount of cornering "grip" that is the result of those rear tires being spun around... They just get it sideways as much as they need and gun the throttle..... uses up a set of tires in 3 km...

The spool comment is interesting. It just shows that, at the end of the day, they must want the thing to be inherently stable (and reliable).

I have always taken the (simple) view that for vehicles that must operate in modes ranging from 4 wheel drift through to opposite lock 2 wheel drift, the easy solution is zero Ackerman.

I'd drill a couple holes and let the car tell me what it wants. The weight jacking due to steer angle would be meaningful one way or another. You can engineer it all you want, but the racetrack will always have its say.

The spool comment is interesting. It just shows that, at the end of the day, they must want the thing to be inherently stable (and reliable).

I think there are several reasons for having a spool in there. First it is, as you say, a stable and reliable and predictable solution. It just works one way and there is zero maintenance.

Second, the way these cars are driven now..... There is so much power they just aim the car with the handbrake and stomp on the throttle... Fancy diffs might have been the thing in the old days when they drove a street/race toyota 1600 cc....

I'd drill a couple holes and let the car tell me what it wants. The weight jacking due to steer angle would be meaningful one way or another. You can engineer it all you want, but the racetrack will always have its say.

Of all the things in the car I find the ackerman most interesting... normal road cars tend to have lots of ackerman built in. Theory on slip angles dictates that track cars should have negative ackerman because of the different slip angles of front wheels... I dove a westfield (seven clone) some years ago that had anti ackerman. It might have worked for fast tracks but was just horrible on short tight track we tested on as it just wouldnt turn in. Plus, you couldnt push the damn thing around the pit. We found a quick solution in running lots of toe out. Also I remember Carol Shelby saying that the more ackerman they put in, the faster the car was...

Hot tip, irrelevant for racing cars. To minimise the turning circle, for a given inner wheel steer angle (which is the usual package limitation on lock), the optimum 'Ackerman' including toe, or steering error as I think it is sometimes called (difference between what you'd expect for a given radius and what you actually get), is not what you get from the drawing board solution. For some cars at least it is about 70% of the difference between perfect Ackerman and parallel steer. It is somewhat dependent on tires, camber, kpi and castor. I've never bothered exploring why

Is that 70% Ackerman or 30%?

30% shy of the theoretical Ackerman angle.

Thanks Greg.

Of all the things in the car I find the ackerman most interesting... normal road cars tend to have lots of ackerman built in. Theory on slip angles dictates that track cars should have negative ackerman because of the different slip angles of front wheels...

Any design choice is a compromise. The question is whether or not that compromise works well with respect to the whole.

Hi Nathan

Some engineering drawing of anti-roll bar parts and suspension systems with anti-roll bars can be seen on this website:

https://engineeringart.uk.com/

https://engineeringa..._poster_quality

That March rear suspension is Captain CrazyPants. All that effort to get an inboard disc, and then still ending up with a huge scrub radius. However, the first rule of looking at somebody else's design is to assume they had a good reason for doing what they did. Maybe they didn't like having the outboard ball joints too close together. Quite reasonably the purist might wonder what harm scrub radius does at the rear. I can't see the arm that reacts longitudinal forces, is that the weird bent tube at the top in the photo?

The other thing I was looking at was the stub axle/CV joint.They've carefully placed the CV joint on the kingpin axis, perhaps that was a weak point at the time.

Edited by Greg Locock, 23 August 2019 - 11:41.

Hi Greg

Links go from the top and bottom of the upright, forward to chassis mountings, to react longitudinal forces. The top bent tube is the adjustable anti-roll bar.

Greg the drawing I am looking at is a rear (non-steered) wheel.

Yup.

Quite reasonably the purist might wonder what harm scrub radius does at the rear. I can't see the arm that reacts longitudinal forces, is that the weird bent tube at the top in the photo?

 

The other thing I was looking at was the stub axle/CV joint.They've carefully placed the CV joint on the kingpin axis, perhaps that was a weak point at the time.

1. A large rear scrub radius does put a heavy load into the toe link. It's likely to have a lot of deflection-based toe change due to any force traveling through the contact patch.

2. The bent tube is the anti-roll bar. There is a straight trailing link which addresses the longitudinal forces.

OK, the suspension architecture, 2 body mounts with trailing arms and a torsion/bending element linking them, is a twist beam. Whether the torsion element is beam or a bar depends on the manufacturer (some use both in the same suspension). The torsion element operates as an ARB not as a road spring. 

Nope, the french hatches all had ARBs separate to the torsion bar inside the beam. The torsion bar acts as a spring.

Got a diagram? I just get spaghetti when i try to figure out how to terminate two torsion springs to the body past trailing arms.

Got it

http://tech-racingca...-i-alpine-turbo

Assymetrical of course.

And in the case of the Renault 14 and several other models, the design used an asymmetric wheelbase too.

Renault 3, Renault 4, Renault 5, Renault 6, Renault 7, Renault 16.  Also: Peugeot 205, 405, 306 (but their wheelbases are even).  Not to forget the Citroën Traction Avant, which had the same layout as the Renaults in the mid-1930s.

Got it

 

http://tech-racingca...-i-alpine-turbo

 

Assymetrical of course.

On later renault 5s it was symetrical with torsion bars ending half way across.... however that one had some elements of twist beam too... Peugeots had a design that was more like real independant trailing arms..