Advanced Suspension Geometry and Design

Which FWD trailing arms are we talking about? I can think of a few designs that are far from static in their toe or camber curve.

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Pete Remner
Cleveland, Ohio

1984 RX-7 (rallycross thing)
1978
Silence is golden, but duct tape is silver.

Hmmm

Google kills another hour...

http://www.google.com/patents/US4105222

I won't post the whole text... you can go to the link

but tid bit from a 1978 patent... looks like "modern" Dubya Arrr Seee, cept behind instead of in front of the driveshaft...

Abstract
An independent strut-type suspension system for a front wheel drive vehicle, wherein the shock absorber is secured at the lower end thereof to the steering knuckle at an angle such that it extends rearwardly of the drive shaft and below the center line thereof, providing a low overall height profile, coupled with anti-dive and anti-lift characteristics, with a coil spring mounted eccentrically around the shock absorber to diminish bending moments on the shock absorber.

Bla bla bla



Edited 1 time(s). Last edit at 03/29/2014 02:40PM by Mad Matt F.

Isn't that the opposite of Dubya Are See? They're angling the shock behind the axle to get anti-dive and anti-squat, while WRC fronts have the shock in front the axle for pre-dive and, therefore, compliance under braking.

Or did I miss the point?

Oui. re the angle. as I so eloquently tried to say something to that effect.

my point was the long travel in a short space.

but in the case of angled ahead, does the brake torque not cause a moment that pulls the spring/shock apart in effect causing anti dive with a compliant spring for bump?



Edited 1 time(s). Last edit at 03/29/2014 10:12PM by Mad Matt F.

Oops. Yeah. You'd get anti-dive from the shock's angle. I was thinking of the typical LCA angle.

Here's another issue that might motivate the angling of the shock across the top of the axle, as on WRC cars (besides anti-dive from torque on the hub and getting more room for long-travel shocks): by having the shock not be a perfect radius from the axle, there will be much less side-force on the shock during braking. This force becomes the force that tries to extend the shock, instead, when the shock comes across on top of the axle.

Maybe fancy rally shocks (lubricated by male reproductive juice, in some cases) don't suffer from "stiction" when side-forces are applied, so maybe this is a useless point. But I thought I'd bring it up since I found it on a napkin at lunch.



Edited 1 time(s). Last edit at 03/31/2014 04:52PM by Iowa999.

So I'm resurrecting this thread. Some interesting stuff, some great links (ordered some books last night) and some good discussion.

As some of you know, my leggy shell is done for, and starting to look into building up a car. Got a lead on a clean GD shell for cheap, most all my stuff will bolt up to it (only 1/4 of the leggy is ruined) and I plan on building up the car in accordance of the new National Limited Open rules. Which basically puts restrictions the majority of the suspension components. Things like subframes must remain stock, stock hubs must be used, stock mounting points must be retained, the rear strut mounting can be raised up to 3" for those GR subie guys.

My question here is, what could be done to maximize or improve the subaru geometry? I plan on buying the bilstein tubes and doing my own ears and turning. I can design up and fabricate custom control arms, as well as strut mounts. Would adding a lot of caster through a custom control arm and mount amount to anything? Any geometry that could be corrected through well designed lateral links and trailing links in the rear?

I got to spend a lot of time under SRTUSA's 06-07 car last week and was really surprised to see how much of it was stock. Truly was a group N car that just had some nice engine bits and a dogbox trans. Off the shelf parts everywhere. Cusco trailing arms, stock STI front arms, stock hubs, etc. compared to the 2016 car that is basically an entirely new car from the firewall forward. In talking with Pastrana how his new 2016 car compared to the 06 car, he mentioned that besides the obvious power increase, the biggest change was just how incredible the straight line braking was compared to the 06 car. That the sideways grip was still similar, but the braking was where a lot of time was gained. What part of the geometry could be changed to improve that?

Still learning more and more about the suspension geometry and how things play together with an eye to try and improve a new shell to the limit of the rules.

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MConte05
So I'm resurrecting this thread. Some interesting stuff, some great links (ordered some books last night) and some good discussion.

As some of you know, my leggy shell is done for, and starting to look into building up a car. Got a lead on a clean GD shell for cheap, most all my stuff will bolt up to it (only 1/4 of the leggy is ruined) and I plan on building up the car in accordance of the new National Limited Open rules. Which basically puts restrictions the majority of the suspension components. Things like subframes must remain stock, stock hubs must be used, stock mounting points must be retained, the rear strut mounting can be raised up to 3" for those GR subie guys.

My question here is, what could be done to maximize or improve the subaru geometry? I plan on buying the bilstein tubes and doing my own ears and turning. I can design up and fabricate custom control arms, as well as strut mounts. Would adding a lot of caster through a custom control arm and mount amount to anything? Any geometry that could be corrected through well designed lateral links and trailing links in the rear?

I got to spend a lot of time under SRTUSA's 06-07 car last week and was really surprised to see how much of it was stock. Truly was a group N car that just had some nice engine bits and a dogbox trans. Off the shelf parts everywhere. Cusco trailing arms, stock STI front arms, stock hubs, etc. compared to the 2016 car that is basically an entirely new car from the firewall forward. In talking with Pastrana how his new 2016 car compared to the 06 car, he mentioned that besides the obvious power increase, the biggest change was just how incredible the straight line braking was compared to the 06 car. That the sideways grip was still similar, but the braking was where a lot of time was gained. What part of the geometry could be changed to improve that?

Still learning more and more about the suspension geometry and how things play together with an eye to try and improve a new shell to the limit of the rules.

Its a shame about the Le-gassy..
Those GD are more or less the same as any other Subie, just seems like a LOT heavier and slightly different execution of the rear top mount...just to annoy people...

Who knows really what can be done regarding actual geometry...Not much..More casyer would be nice to a point, but you retain the stock knuckles--especially in the rear and you're kinda locked in..
One thing I did for Colin Bombara out East to try and mitigate some of the bad bending load on the rear ears was I made him a spherical bearing top mount, a nice strong one...BIG bearing..
The idea was as the suspension goes up and the arc of the knuckle/hub begins to "go over the top of the arc" with a bearing, the bearing can rotate and no bind up like a solid rubber thing will..
It stopped the bending which was pretty bad...Of course this is more of an issue with struts with 210 travel cause the knuckle/hub moves higher in the arc...

Now as for you getting some of the Bilsteins, I am assuming you are meaning their so called universal 50s, yes?

You better do some planning because as far as I know as of maybe 5 minutes ago they have only a few obscure parts and unfortunately for some, no lower tubes....
And I think I just cleaned them out of the last of the fronts and rears which they had remaining which would be the thing for a GD and that's only because I have so many tubes......Evidently I have moved 90% of what they have sold of these....

So some hurdles ahead..

I am negotiating with them about some design changes and just how they are marketing them--as well as their fixed valving choices some of which they will never sell cause they're flat ODD>

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John Vanlandingham
Sleezattle, WA, USA

Vive le Prole-le-ralliat

www.rallyrace.net/jvab
CALL +1 206 431-9696
Remember! Pacific Standard Time
is 3 hours behind Eastern Standard Time.

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MConte05
...the biggest change was just how incredible the straight line braking was compared to the 06 car ... but the braking was where a lot of time was gained. What part of the geometry could be changed to improve that?

Nothing to do with suspension geometry, in 2006 they were still running the old shitty Ferodo DS3000, then in 2009 I introduced them to PFC, and I know in 2012 they were still using them while I was in UK cause I'd get calls sometimes, but now I think they went to Endless pads.

All the antidives and prodive geometries are great but do very little to inline -G.

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Cosworth

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MConte05
...the biggest change was just how incredible the straight line braking was compared to the 06 car ... but the braking was where a lot of time was gained. What part of the geometry could be changed to improve that?

Nothing to do with suspension geometry, in 2006 they were still running the old shitty Ferodo DS3000, then in 2009 I introduced them to PFC, and I know in 2012 they were still using them while I was in UK cause I'd get calls sometimes, but now I think they went to Endless pads.

All the antidives and prodive geometries are great but do very little to inline -G.

Call me stupid, but why would that make a difference? All the braking force is generated through the tires right? If they were using Michilens back in 2006 vs DMACK DMG2+, but the same size tire as in 2016 (215 width) then shouldn't be too much of a difference? Pastrana seemed to be suggesting it was the way the new 2016 car was designed from the ground up, not so much a better brake pad or tire.

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MConte05
Call me stupid, but why would that make a difference? All the braking force is generated through the tires right? If they were using Michilens back in 2006 vs DMACK DMG2+, but the same size tire as in 2016 (215 width) then shouldn't be too much of a difference? Pastrana seemed to be suggesting it was the way the new 2016 car was designed from the ground up, not so much a better brake pad or tire.

Because a higher bite pad will always give the impression of better brake setup because less pedal force is required. And for a driver that immediately says better car, even if the distances are the same. Doesnt really matter what Pastrana suggests, of course he's going to talk wonders of the new car. But back then they had a GrN setup with stock m/c and GrN spacer, which is incredibly hard brake pedal, along with DS3000 pads, its nearly impossible to get brake look up. Now with a pedal box and better pads, its much easier to extract more out of the brakes.

The only thing suspension wise that can help is the fact that they have more wheel travel and can afford to run softer springs than before and therefore more grip. Otherwise its all brakes.

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Cosworth
The only thing suspension wise that can help is the fact that they have more wheel travel and can afford to run softer springs than before and therefore more grip. Otherwise its all brakes.

So is this a benefit of progressive springs/dampers as well?

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Grant Hughes

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NoCoast
So is this a benefit of progressive springs/dampers as well?

No, you can achieve that with any kind of shock valving, progressive, digressive, linear or regressive (penke's lol). Progressive springs have no business in racing otherwise WRC/WTCC/F3/etc. wouldnt still be running linear stuff. I have them in my DMS and they're shite... the "soft" part gets compressed right away from the preload or weight of the car, and my Reigers have a longer but softer spring.