Schirmer Kinematics

[72dan]

I have seen a bunch of posts with opinions on what Team Schirmer’s axle Kinematics is if anything at all.
Schirmer is a full pro race team with extensive experience with the E92 M3. It is amazing they run sub 7 minutes times at the ring in an M3, then normally aspirated and not much aero.
Here is an online article on kinematics
https://e31wiki.org/wiki/Active_Rear_Axle_Kinematics
It is described as a BMW invented 4-wheel steering system for stability improvements through rear steering, adjusting anti-dive, anti-squat properties and more.
I have AST 3-way coil overs and all the SPL control arms and Schirmer may use the same but there is a lot more to setting up a car. For example, now that all arms are adjustable I can set camber and caster from the arms below or from the front strut towers. Doing it from below will change front track and wheelbase slightly.
Ackerman Steering – that is the inside tire, especially in a tighter radius corner is traveling around a smaller diameter circle so the inner wheel needs more steering angle than the outer wheel, how much, 20%, 40%.
Bump steer, roll centers front and rear, anti-dive, anti-squat, etc.
They have done a lot of racing at the ring and I am sure they have tried at least a hundred different combos to get below 7 minutes.
Then look at their builds. They fully gut the car and their roll cage is joined to the body at all the pillars with webbed metal. I am sure their spring rates are higher than most have on their coil overs here, the frame needs to be stiff, so it doesn’t flex for the suspension to work correctly.

It isn't a low cost setup but it seems to work really well. I don't know if anyone here in the USA has a car with their full setup. It would be interesting to see lap times at our popular tracks here with their full setup.

[dparm]

There was a lot of discussion on the Schirmer stuff in the track forum recently. You may want to go look through there, but the consensus was a lot of their work is a closely-guarded secret.

[dmitriyo]

When they say kinematics, what they mean is a study on OE vehicle setup and then adjustment of that geometry for better track fit, adding flexibility where needed via bespoke parts.

Looks like they have monoball upgrades all around along with added adjustment to tweak roll centers, ackerman perhaps as well. These are things that are not adjustable via factory or even some aftermarket components.

Having studied bump steer and geometry on these platforms there is definitely a lot on the plate. Addressing those issues goes a long way for handling and dynamics.

Its just not all straight forward measurements and the needed adjustment are not always easily achievable.

[roastbeef]

some of the parts they use are unique and not available to us. for example, i asked them if they sold a rear lower control arm that they use for a true rear coilover setup and their response was, "no chance." lol

this is just a guess, but i have a feeling their recipe is correcting for bump steer, lightening what they can, and widening without jacking up track width.

[amrazM]

Yeah the schrimer cars are black magic, they are extremely fast around the ring for NA cars, there’s a lot of other tuning garages in Germany, france etc but none seem to be as well known as Schrimer and the xx31 car. To date I havent Seen a photo from the bottom of a Schrimer car. I know A couple of the cars are 4.4L

[roastbeef]

They get down and dirty. Very impressive stuff.

[amrazM]

The execution of their builds is also impressive

[slicer]

Those pics are making me aroused. Especially the rear suspension.

[roastbeef]

i'm pretty sure that cage is the same one that motorsport24 sells. i dig it, but i'd crack my head on the diagonal roof crossbar.

they also use intrax suspension... intrax throws around terms like "anti roll control" and "adjustable hydraulic bump stops" as features. the anti roll control could be something that other dampeners have, but this is the first i've heard of an adjustable hydraulic bumpstop. pretty neat stuff.

[slicer]

The Schirmer Cages are fabricated and welded in place by Schirmer. At least that's what I have gathered by their videos and images. They have TUV approval as a builder of cars. Their builds are re-titled as Schirmer cars (no longer BMW).

[roastbeef]

thats awesome. are there any known schirmer cars in the US?

[72dan]

Originally Posted by roastbeef

i'm pretty sure that cage is the same one that motorsport24 sells. i dig it, but i'd crack my head on the diagonal roof crossbar.

they also use intrax suspension... intrax throws around terms like "anti roll control" and "adjustable hydraulic bump stops" as features. the anti roll control could be something that other dampeners have, but this is the first i've heard of an adjustable hydraulic bumpstop. pretty neat stuff.

I have to agree with the previous response that isn’t based on any off the shelf bolt in cage.
I don’t think intrax has anything to do with it, roll control is likely low speed compression adjustment.
The rear suspension pic that is in the thread now, that’s where I think the magic is. I think there is rear steering where the outside rear wheel turns slightly the same direction as the car is cornering among other things.
Their work is spectacular.

[roastbeef]

i'm more saying the designs look similar... m24 could have just produced a similar cage.

when you mention rear steering, are you talking about them setting it up to properly deal with changing toe under compression? i'm not 100% sure i'm looking at a "steering" rear end in the traditional sense.

[72dan]

Originally Posted by roastbeef

i'm more saying the designs look similar... m24 could have just produced a similar cage.

when you mention rear steering, are you talking about them setting it up to properly deal with changing toe under compression? i'm not 100% sure i'm looking at a "steering" rear end in the traditional sense.

Intentionally changing rear toe under compression to toe in more on the outside tire. The inside tire then would toe out.
The article that I linked to discusses it in depth. If the rear tires steer into the corner it reduces scrub. If you think about it if you want to turn right and you turn the front and rear tires to the right the car can move to the right without loading g forces. Only the rears are only turning a fraction of what the fronts turn.
Rear steer confuses me a bit. I know the newer 911s use it and other cars. At low speeds the rears turn the opposite direction like in a parking lot, that decreases turn radius and at high speeds the rears turn the same way as the fronts.

[roastbeef]

Originally Posted by 72dan

Intentionally changing rear toe under compression to toe in more on the outside tire. The inside tire then would toe out.

so how do you setup the car to do this? if you have adjustable links, the toe angle has to be fixed at some point, but what else do you set to cause the outside to toe-out and the inside to toe-in under load? do the upper links have to be parallel at ride height or something? (this isn't something i'm familiar with at all)

by the way, how do you like your ast three ways? how often do you find yourself adjusting the high and low speed bump from track to track?

[Richbot]

If they're building to FIA rules there's a reason the cages end up looking similar

Building passive rear-steer into a 5-link means you're playing within a narrow range of bump travel to get the 5 links, which all influence wheel alignment to some degree, to all tug just the right amount in just the right direction at just the right amount of displacement...the amount of testing time in those cars must be colossal. I'm sure active setups are no less time consuming to tune but at least you have something you can change with a laptop and mapping to the steering angle and yaw and so on instead of just spinning heim joints...curious if that suspension has anything like that installed on it, everything looks like it's in its normal spot and I don't see any actuator boxes or etc. on either end of any of the links

Odds are good they have found a setup that works, found a way to make it bolt-in and repeatable, and have branded it as their proprietary kinematics to add a secret sauce feeling to what you're getting.

[roastbeef]

If you set everything up without springs or dampeners, would you be able to cycle the suspension and see the toe change? Or does it require load to create intended deflection?

[slicer]

Originally Posted by roastbeef

If you set everything up without springs or dampeners, would you be able to cycle the suspension and see the toe change? Or does it require load to create intended deflection?

You need dampers in place otherwise the suspension will not be fixed. The shock is one of the pickup points for the suspension. It would be the equivalent of removing one of the arms. That's how you check bump steer. Remove the springs only.

[Richbot]

Yah that's how people build models for their actual suspension on their actual cars. Take springs out, stroke suspension along its whole travel, sometimes with frickin lasers involved. I'm not sure you need the shock in the rear to locate anything, once the bushings are gone it can't be doing any location of anything as it is just along for the ride when the main LCA moves it does nothing but move with it, but up front on the strut yeah duh that's the entire vertical load path

[72dan]

Originally Posted by roastbeef

so how do you setup the car to do this? if you have adjustable links, the toe angle has to be fixed at some point, but what else do you set to cause the outside to toe-out and the inside to toe-in under load? do the upper links have to be parallel at ride height or something? (this isn't something i'm familiar with at all)

by the way, how do you like your ast three ways? how often do you find yourself adjusting the high and low speed bump from track to track?

I like the AST 5300 setup. They are a true coilover conversion for the rear. The spring rate I chose is similar to the 700/1000 setups you see on the traditional separate rear setup, I forget the number but whatever the conversion was for the rear. If I were driving daily I would use a softer spring.

I had them at 175 psi. I just built my own nitrogen setup for filling shocks and tires. I put them at 225 psi, it is quite a bit stiffer but also it speeds up rebound. I have found that settings somewhere in the middle are best, too stiff on the compression and the tires don't follow the road well. Now with 225 psi I think I am going to soften my sway bars. I have the Hotchkiss adjustable bars front and rear both on the second from softest setting. The coilovers are pretty stiff don't know that I need all that much sway bar now. I don't drive my car daily. I love the feel all monoball, I have all SPL control arms front and rear, 5300's, solid subframe connectors, etc. It is awesome in the corners but today I was on the 405 from the valley to LAX and every ridge in the freeway I feel and hear. I put nitrogen in the tires as well, put them at 32 psi F/R. It has been so cold at night they were around 28 cold to get 32 warm with regular air.

[72dan]

Originally Posted by Richbot

If they're building to FIA rules there's a reason the cages end up looking similar

Building passive rear-steer into a 5-link means you're playing within a narrow range of bump travel to get the 5 links, which all influence wheel alignment to some degree, to all tug just the right amount in just the right direction at just the right amount of displacement...the amount of testing time in those cars must be colossal. I'm sure active setups are no less time consuming to tune but at least you have something you can change with a laptop and mapping to the steering angle and yaw and so on instead of just spinning heim joints...curious if that suspension has anything like that installed on it, everything looks like it's in its normal spot and I don't see any actuator boxes or etc. on either end of any of the links

Odds are good they have found a setup that works, found a way to make it bolt-in and repeatable, and have branded it as their proprietary kinematics to add a secret sauce feeling to what you're getting.

All cars have steering angle change under suspension travel. Back in the day we would go through a lot to bumpsteer a car, moving steering tie rod connections up or down so they are the same length and angle as the lower control arm. And yes it was a ton of work, moving the suspension through full travel with no spring and taking measurements. But I am old and back in the day it was Datsun 240Z or 280Z and there was a lower control arm and a strut, not 5 links. So stiffer springs, shocks, sway bars, suspension bushings and bump steer was the hot setup back then.

I think subtle adjustments can be made with the length of arms giving stock mounting points.
There are two ways to make significant changes, either change pickup points on the chassis or use a different spindle/upright with different connection locations.
Suspension technology has advanced so much in the last 10-20 years it is really amazing to me. Look at the Nurburgring lap times for the last 10-20 years, new 911's 10 or more second a lap faster than the previous generation chassis with basically the same tires, same weight, all geometry, track width, etc.

What seems to make sense is on the rear suspension if the bushings were softer that controlled the leading edge of the rear tire versus the trailing edge of the rear tire, in a corner the outside tire is loaded so the front bushing would compress more allowing the tire to turn into the corner slightly. At the same time the inside tire with the same softer bushing controlling the leading edge the inside leading edge would flex more allowing for slight toe out on the inside rear tire.
I have no idea how much rear steer is ideal.

[M3 Number 86]

72dan who are you? you are in los angeles - do you hit the track a lot?