Publishing my Autocross Secrets

[jtmcinder]

The Bilsteins that matter are monotube. That's why they can have remotes added to them. If you're thinking of getting twin-tubes, get Konis, which can be revalved if necessary.

- Jtoby

 

[DSMunknown]

So DG, how much different (or in what way) is the info you are providing different from what some of the books in the link below offer?:




http://www.wincom.net/trog/autocross/books.html




EDIT: Nevermind, you're one-in-the-same. BTW did you ever sell your beloved Talon?




http://sports.groups.yahoo.com/group/stu/message/14296

 

[eclipsh]

It would be very helpful if you could suggest a specific strut/spring combination for 1g or 2g DSMs and then break down WHY they are the right combo for our cars. I'm sure many on this site aren't up for (or capable of) doing complex math for their suspensions.

Also, a diagram or photos of how to rig up those Bilsteins would be awesome. What gas are you using to adjust the pressure in them?

EDIT: just noticed you can't get monotube Bilsteins for a 1g

 

[jtmcinder]

Elsewhere, Dennis has suggested 900/400 for a 2G, which is about 2.5/2.6 in terms of natural frequencies. This also places the weight-transfer balance and roll-resistance balance approximately equal to the static-weight balance (assuming RM bars, front and rear), give or take a point or two. I haven't seen any discussion of setting race cars up in terms of natural frequency (but am open to this idea); I've seen lots of discussion of matching the weight-transfer balance to the static-weight balance. Since, in this case, the two forms of logic agree, maybe it doesn't matter which logic you use.

If someone posts the motion ratios for a 1G, along with typical corner-weights, it would easy to repeat the math.

- Jtoby

 

[eclipsh]

In case anyone else went WTF when motion ratios were mentioned above:

http://www.shock-shop.com/Critical Damping/Taking CDA Measurements.pdf

 

[90AWDTalon]

If someone posts the motion ratios for a 1G, along with typical corner-weights, it would easy to repeat the math.

- Jtoby

I haven't measured for myself but I read on this forum a long time ago that the motion ratios are front .92 and rear .84. I have no clue what the typical corner weights are though.

 

[jtmcinder]

If those are correct, then 600/500 would be the suggested starting point, assuming that the front/rear corner-weights are 900/600. It also suggests that the "default" suggestion of 350/350 is a bit too biased to the rear.

- Jtoby

 

[mavisky]

I haven't measured for myself but I read on this forum a long time ago that the motion ratios are front .92 and rear .84. I have no clue what the typical corner weights are though.

I'm guessing that's for a 1g awd?

 

[mavisky]

If those are correct, then 600/500 would be the suggested starting point, assuming that the front/rear corner-weights are 900/600. It also suggests that the "default" suggestion of 350/350 is a bit too biased to the rear.

- Jtoby

That sounds seriously stiff compared to the 450 lb front 350 lb rear that I was looking at.

 

[jtmcinder]

My current set-up is 650/425, which is 2.11/2.67. My car is seriously loose at speed and I'll probably have 850s in the front next summer, if I don't try the massive wing trick, instead.

If those are the correct motion ratios for your car, then 450/350 is 2.18/2.21. I can empathize with your reaction to the idea of 600 fronts on a 1G, since the idea of going above 650 in the front of my own car seems crazy, but both the math and experience says my fronts are too soft.

Keep in mind, however, that all the math concerning optimal spring-rates is predicated on a huge and probably unwarranted assumption: that you have the shocks to match. Neither of us do, so this is mostly masturbation.

- Jtoby

 

[mavisky]

Good point on the shock factor.

 

[90AWDTalon]

I'm guessing that's for a 1g awd?

Yep.

I think that the front is probably the same, but I suspect the rear is probably different unless they used the same rear suspention setup on your fwd.

 

[90AWDTalon]

Good point on the shock factor.

Shocks are a huge factor, my miata is 500/335 and rides better than stock, and thats on a car a 1000 pounds less than a dsm. But I have shocks that are matched, one of the sets DG doesn't like.

 

[90AWDTalon]

My current set-up is 650/425, which is 2.11/2.67.

Just out of curiosity, what are the 2g motion ratios?

 

[mavisky]

Yea, AGX's blow, and so does the rear suspension design on 1g fwd dsm's.

 

[90AWDTalon]

Yea, AGX's blow, and so does the rear suspension design on 1g fwd dsm's.

I dought it blows as bad as the awd rear suspension. And yes I agree agx's blow, I hate mine.

 

[jtmcinder]

Just out of curiosity, what are the 2g motion ratios?

They are .76/.91, which should help explain why 2Gs need very high front springrates. (Remember, you square the motion ratio before multiplying by the springrate to get the wheelrate.)

- Jtoby

 

[mavisky]

I dought it blows as bad as the awd rear suspension. And yes I agree agx's blow, I hate mine.

I dunno, live axle, single panhard rod.

 

[90AWDTalon]

I dunno, live axle, single panhard rod.

AWD's have the rear subframe from the all wheel steer gvr4. But when they put them in the dsm's they removed the steering rack, but they didn't do anything to keep the wheels from self steering, which they do and turn the opposite of what would be benificial. There used to be a good write up of what the rear wheels do under different circumstandes on taboospeedshop.com but that site is gone. If I remember correctly the wheels toe in under braking, toe out under excelleration, and when turning the turn the same as the front wheels.
/ /
/ /

Found an old copy of the write up unfortunately no pics.
http://web.archive.org/web/20041216041339/www.taboospeedshop.com/atil.htm

 

[mavisky]

Yea, I remember reading that. I was under the impression that there was some sort of active toe eliminator that existed to keep all that bs under control.

 

[logic]

Here are the pictures from that page, in order of appearance, if it helps.

 

[logic]

1G AWD active rear toe control link

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The 1G AWD T/E/L and active rear toe control link is a part of the stock double wishbone suspension one our cars came with. Although the Galant VR4 is eqipped with rear wheel steering as we see on the picture on the left, it does not suffer from the rear toe change under heavy acceleration or braking due to the fact that its rear control arms are tied together by the hydraulic steering rack preventing the trailing arms from moving in and out independently (under acceleration or braking) while being able to move them in and out at the same time and thus steer the rear wheels. Once the rear steering rack is removed, the functionality of the suspension becomes identical to 1G AWD with the "benefits" of the active rear toe link.

Since the 1G AWD T/E/L trailing arms are fully identical to those of Galant VR4 (including the holes for the tie-rods of the hydraulic rack), it's quite possible that the 1G AWD T/E/L active toe control link is just simply a left-over of the VR4 rear steering that was not removed in attempt to lower manufacturing costs.

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The active rear toe link was designed to increase toe-out under heavy acceleration and toe-in under heavy braking to improve safety of the vehicle when operated by unexperienced drivers. While increasing the toe-in will produce understeer, toe-out increase makes the car numb and unresponsive.

The trailing arms are not actually connected to the rear subframe in any solid manner but rubber-covered links inserted in the hollow trailing arms that pivot around the ball-joints of the lower control arms. The toe links are further connected to the trailing arms by bolts preventing the trailing arms from twisting and front-to-rear movement while allowing them to move from side to side.

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This is the normal state of the trailing arms while the toe links are being centered during normal cruising conditions.

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The trailing arms move in while increasing the toe-in during heavy breaking.

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The trailing arms move out while increasing the toe-out during a launch and hard acceleration.

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Both wheels are steering in the same direction during cornering - which results in understeer.

Now, picture what the active rear toe link does when negotiating a corner and you'll see why it's really not a good feature for rally, drag, road corse or autocross car.

If you decide to eliminate the unecessary understeer and improve the handling of the car, instructions regarding the active toe link elimination can be found here.

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Mitsubishi Galant VR4 rear steering controlled by hydraulic rack.

 

[eclipsh]

For those seeking to eliminate that problem but who don't want to fab their own parts DSS sells this little gem:

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89-94 AWD Rear-Toe Eliminator


OR... You can do like Pagosa DSM did (and will be doing to mine this spring)

<img src="http://www.dsmtuners.com/gallery/files/5/0/6/5/5/DSCN0213.jpg" alt="control arm heim joint" />

 

[mavisky]

Ahh, see I was sure there was an elimination kit out ther for it. See I have no adjustable toe or camber in the rear at all, and as the suspension compresses it actually moves the wheels to the driver's side.

 

[bjones18]

Carsickness has nothing to do with anything.

...Milikens ... NF turned out to be a very useful tool ...sprung mass more or less level over bumpy ...driven faster ...A slight rearward NF bias ..goes faster....

DG

NF is the way to compare between vehicles. If you are concerned about sta-bar effects you can use the one-wheel bump rate (which includes stabar twist) as opposed to the two-wheel bump (stabar rotates), in the NF calculations.

Spring rate is force/displacement (statics). NF allows vibration theory in suspension design/development. Without NF how do you know how close you are to critical damping?

It is all about evenly loading the contact patches through transient maneuvers and being robust to road imperfections.