Curious Ponder

[DrZoom]

First of all hows it going everyone, quasi new here. I have a 1g DSM Talon TSI Fwd. I'm looking at some suspension upgrades to auto x my car. I was curious if anyone made or has thought about making a conversion kit to turn the fwd eclispe's rear suspension into intedependent suspension???? I know that the awd ones have it, but I was told that their suspension relies on the existance of the rear driveshaft???? Is there anyway around it? (eg. custom fab a rear crossmember?) would a 2g fwd suspension do it if it were independent???? I would have bought an awd but ive always loved driving fwd. grew up on it.

Thanx

 

[Amar1995]

It would be alot of work, but you could just buy a complete subframe with everthing brake lines, hubs, ect. From a 1g GSX/TSI and bolt it under your car without the differential and drive shafts. It would weigh more and I don't know how much you gain from it

 

[Defiant]

I don't know that FWD much cares what it's dragging around.

DSMs are fairly nose-heavy.

 

[RamenPride]

so basically this is a FWD to AWD conversion, but without the swapping the drivetrain

 

[bjones18]

First of all hows it going everyone, quasi new here. I have a 1g DSM Talon TSI Fwd. ....intedependent suspension???? I know that the awd ones have it, but I was told that their suspension relies on the existance of the rear driveshaft???? Is there anyway around it? (eg. custom fab a rear crossmember?) would a 2g fwd suspension do it if it were independent???? I would have bought an awd but ive always loved driving fwd. grew up on it.

Thanx

Look under the rear of your car, I would be suprised if it were a solid axle.

 

[pneumo]

Look under the rear of your car, I would be suprised if it were a solid axle.

Suprise! The 1G FWD has a solid trailing beam rear axle.

 

[bjones18]

Suprise! The 1G FWD has a solid trailing beam rear axle.

Is it a twist beam? Some twist beams perform well.

 

[pneumo]

Yes it is a twist beam, and yes it does perform quite well. I have a 90 FWd and a 92 AWD, so I've compared their handling. The FWD rear end has a lively, tossable feel when driven fast through the twisties. The AWD rear end feels squishy and dead by comparison. IMHO converting to an AWD IRS would be a bad move. Why? First off, it's a lot of work to do. Second, there are too many rubber mounts in the AWD rear end for good feedback and consistent handling. The suspension is mounted on a subframe, which is mounted to the body with large rubber bushings.

The AWD IRS can work without a driveshaft, but it can't work without the rear diff, since the control arms bolt to the diff case.

 

[jtmcinder]

This is getting interesting.

How much of the extra "tossability" of the FWD rear do you think is due to the more solid connection to the unibody and how much do you think is due to the flat bymp-camber curve? My experience driving RWD live axle cars is that they are tossable and catchable because you can use the lousy camber to get the tail free and then use power and weight transfer to get it back. Cars with IRS are much harder to break and then catch because the better camber curve forces you to really over-do it to get it to break free. And by then you just ain't gunna catch it.

- Jtoby <- 540* spin at Devons in 2001

 

[pneumo]

How much of the extra "tossability" of the FWD rear do you think is due to the more solid connection to the unibody and how much do you think is due to the flat bump-camber curve?

It's hard for me to separate the two. I can feel the back end of the AWD car take a set during turn in, while the FWD car doesn't have that delay. Some of that might also be due to the active toe link.

I've noticed something similar now that I'm playing around with front camber. The front end felt responsive and consistent with stock camber. Now that I've added more negative camber to the front end I can feel it settle into the corner. The cornering power is improved now, but turn in seems to suffer slightly. Is this normal or have I fouled up somewhere?

My experience driving RWD live axle cars is that they are tossable and catchable because you can use the lousy camber to get the tail free and then use power and weight transfer to get it back.

I've used the same technique in my FWD when I'm feeling brave; enter the corner a little hot, trail brake to get the back end out, and modulate the throttle to keep the back end in line. I haven't been able to do that with the AWD car, although it's getting closer now that I have a ST rear sway bar.

Cars with IRS are much harder to break and then catch because the better camber curve forces you to really over-do it to get it to break free. And by then you just ain't gunna catch it.

It sounds like IRS/AWD cars need to be driven with a different technique.

- Jtoby <- 540* spin at Devons in 2001

^ Whee! dizzy? ^

 

[jtmcinder]

I can't say that I noticed turn-in getting worse with more front camber, but I can say this: even a touch of front toe-out does wonders. If you are dreadfully serious about autocrossing, you must run some front toe-out and tire-wear be damned.

The 540* spin was hilarious. I was about a half-second behind ACM with one run in hand. With nothing to lose, I went into serious attack mode and nailed the opening section of the course. Problem is, that put me about 5 or more mph faster into a 180* turn around and the next thing I knew I was 50' off course in the weeds.

- Jtoby

 

[bjones18]

Yes it is a twist beam, and yes it does perform quite well. ..... The suspension is mounted on a subframe, which is mounted to the body with large rubber bushings.

The AWD IRS can work without a driveshaft, but it can't work without the rear diff, since the control arms bolt to the diff case.

Are you saying the 1G lateral IRS control arms are "bushed" to the Diff-case....Diff-case bushed to the subframe...subframe bushed to body?

 

[bjones18]

This is getting interesting.

How much of the extra "tossability" of the FWD rear do you think is due to the more solid connection to the unibody and how much do you think is due to the flat bymp-camber curve? .......Cars with IRS are much harder to break and then catch because the better camber curve forces you to really over-do it to get it to break free. And by then you just ain't gunna catch it.

- Jtoby <- 540* spin at Devons in 2001

There are about zero production independent suspensions with 1degree of camber gain per degree of body roll....leaving less than optimum camber in cornering..hence the negative static camber setting for racing/auto-x. The twist beam (ignoring structural deflections) keeps the wheel perpendicular to the road surface (take a look at a strut in cornering )

I am not voting for twistbeams. I am saying....how well you understand...and tune your suspension is more important than the architecture itself. Trading one suspension for another can be like trading one engine for another....swapping a v-6 in place of a 4 cylinder...maybe you should "build" your 4 cyliner

 

[bjones18]

It's hard for me to separate the two. I can feel the back end of the AWD car take a set during turn in, while the FWD car doesn't have that delay. I've noticed something similar now that I'm playing around with front camber. The front end felt responsive and consistent with stock camber. Now that I've added more negative camber to the front end I can feel it settle into the corner. The cornering power is improved now, but turn in seems to suffer slightly. Is this normal or have I fouled up somewhere?

I've used the same technique in my FWD when I'm feeling brave; enter the corner a little hot, trail brake to get the back end out, and modulate the throttle to keep the back end in line. I haven't been able to do that with the AWD car, although it's getting closer now that I have a ST rear sway bar.

It sounds like IRS/AWD cars need to be driven with a different technique.

You are on the learing curve. Sometimes changes to the rear feel like changes to the front. Common to suspension design/tuning is that when you change one thing...you in-advertently change two others. Sorting it out is why people get paid to do this.

Many "racers" prefer RWD for the separation of throttle and steering to balance the car in cornering. AWD has the added complexity of throttle forces creating steering forces (torque steer).

Comparing a FWD with twistbeam rear and AWD/IRS is pointless. weights, sta-bars, roll centers, shock valving, wheel rates, compliances, tires, maybe ride heights, are all different.

"feeling" the before-after part change differences is the basis for learning. read a couple books. Make sure your speeds are consistent run2run and your steering inputs are consistent run2run (or notice the difference in angle/torque input)

 

[jtmcinder]

bjones -

You are seriously underestimating the knowledge level of the people with whom you are talking. Please adjust your attitude and level of detail accordingly. Thanks.

- Jtoby

 

[pneumo]

Are you saying the 1G lateral IRS control arms are "bushed" to the Diff-case....Diff-case bushed to the subframe...subframe bushed to body?

The control arms are bushed to the diff case, the diff case is bolted solidly to the subframe, the subframe is bushed to the body.

In addition, the mounting brackets for the rear swaybar are mounted to the subframe, so it won't control the little bit of body roll happening between the body and the subframe.

 

[DrZoom]

Sorry I'm still learning about suspension, and I dont know half the terms you guys are mentioning, is the common accepted idea that I should tune the suspension how it sits and try that? does that mean the stocker suspension ,with some work can handle nicely because its "twisted"???

Thank for all the info

 

[pneumo]

Ha! Sorry, looks like the tech talk got a little deep.

Here's a pic of the 1G FWD rear suspension: www.dsmtuners.com/forums/showpost.php?p=1414901&postcount=4 There's a beam that connects the left and right wheels together. When you go around a corner one side compresses and the other side extends, which twists the beam slightly, so we call it a twist beam. That twist works the same as an anti-roll bar.

What to do? Basically, start with stiffer shocks and springs. How stiff depends on how much speed you want, and how much comfort you're willing to give up. There's a nice Tech Guide at the top of this page to get you started in choosing shocks and springs.

I also recomend adding some negative camber to the front suspension. Neg. camber is when the top of the wheels tilt in more than the bottom. It helps keep the bottom of the outside tire flat on the road when cornering, adding grip. Stock alignment has slightly positive camber, which is why your car feels like it pushes around every corner. While you at it, have the front toe set to 1mm toe-out. This will improve steering feel and add a slight bit of traction up front, too.

You can do the alignment tricks before or after you get shocks and springs. It will help either way.

 

[DrZoom]

THANK YOU SIMPLE EASY ADVICE!!!!! I am a little curious about camber what do you mean the top of the wheel tilting down more than the bottom??? I thought a wheel cant be tilted cuz its round or m i not thinking correctly.

Matt

 

[pneumo]

Hmmm OK how about this? Negative camber is when the top of the wheel leans toward the center (or midline) of the car.

The Tire Rack (tirerack.com) has front camber bolts for about $25. It's cheap and easy. Just make sure to have it aligned at a shop that will set it to your specs, not the factory specs.