I think with the VW setup you would get toe-in in the front from deflection of the rear bush under braking. Probably more movement in that bushing than any toe that is induced through the tie-rod & control arm geometry interplay....

I have seen a guy on Vortex model the camber & toe curves throughout the range of travel but that assumed no bush deflection due to braking. Of course bearings would solve that problem but only a couple of people run them due to the hassle & expense.


Turning the fron subframe around in the rear also induces a toe-in situation under braking due to deflection of the large bush now at the front of the control arm.

Not sure you would want toe-out in the rear under compression if you could get it---car gets double squirelly on the landings from the biggest jumps---no thanks.

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____________________________________________________________-

One. Class -- 2WD

www.quantumrallysport.com

http://www.facebook.com/home.php?#/pages/Quantum-Rally-Sport/281129179600?ref=nf

john vanlandingham Wrote:
-------------------------------------------------------
> eyesoreracing Wrote:
> --------------------------------------------------
> -----
> > Excellent point about the tie rods in
> tension!
> >
> > -Dave
>
> Seems just a point of view, and the yield should
> be the same in straight compression,
> or straight tension, as far as I know.
> Maybe some Gen-you-whine mechanical Injur-near
> like Tim Taylor could elucidate a bit for use. I
> could see something in severe compression buckling
> when a side load would be put to it, but other
> than that can't see a difference.

Tain't no such thing as pure forces in a rally car. You can hang a --insert heavy object here-- on a wee little stick of welding rod, but I challenge you to balance the same --heavy object-- on the same size stick. If the rod were perfectly uniform, the loads placed perfectly square on the ends, and there were no side loads induced from your attempts to balance it, MAYBE you could keep it from buckling. But not in a rally...

Those side loads can easily come from the tie rod end design. Way too many tie rod ends have the ball joint not perfectly in line with the centerline of the tie rod. Usually there's some packaging thing going on when the wheels are at full lock that necessitates this. It doesn't take much side load when you're compressing a rod to make it wanna go all bendy.

I suspect on a front-steer car, your more common failure mode is probably a tensile failure of the inner ball joint, but I'm just guessing.

> And Dave are you smoking some spliff
> here?:

No, but I could use some...

Quote:Good packaging argument for going
> backwards. I think there might be good geometry
> arguments too. Most front suspensions are designed
> to toe out slightly under compression, and by
> reversing it, you're making it toe-in. That's a
> better thing to have in the back...
>
> First, 'splain why rubber bushed cars tow out
> slightly (a simple drawing of a box and two arms
> sticking out and force vector draw would answer
> this---force ^ arms with tires resist going that
> way, bush complies and arms boing rearward, and
> the say 2mm toe in becomes say 0,5mm in.)
> Why does that same thing, rearward deflection this
> away V result when the same rubber in in back, and
> the car drives forward?

Bushings have nothing at all to do with it in this case. Remember, there's a ball joint between the control arm and the wheel, so even if bushing deflection did move the end of the control arm fore and aft, the ball joint would prevent that from becoming toe. It would just be fore-aft movement.

The toe change should be apparent if you just scroll up and look at the picture of the lower control arm and the tie rod. The arm and rod appear to be approximately the same length, but the arm is hanging down and the rod is nearly horizontal. As you compress the suspension, both the arm and the rod will swing through an arc, which will cause them to pull their ball joints in toward the center of the car slightly. Because it's angled upward more, the tie rod will always be slightly ahead on the arc, and thus pulling in faster than the control arm.

In the front suspension, the tie rod is behind the wheel, so pulling in faster toes the wheel out. In the rear suspension, the tie rod is in front, so it pulls the toe in.

If you don't want to trust the picture, just trust common sense steering geometry. When the driver turns the wheel, the outside suspension will compress. If the wheel were to toe in, you'd have a car that that dynamically added steering angle to the loaded wheel as the body rolled. Roll oversteer is spooky shit! Toeing out just a little adds a nice, controllable roll understeer that you take for granted.

You obviously don't want roll-induced toe out at the back, but you don't want too much toe in either. It makes the car all understeery. On the bright side, dropping off the throttle makes the rear lift, which toes you back out, so some dynamic toe can sometimes add additional throttle steerability. 510 has a bunch of toe change with suspension travel. Sucks on the track, bitchin in the dirt.

If those tie rods really are exactly the same length as the control arm, you could move the rear rack up until they're parallel if you want to get rid of the rear toe.

>
> I would suggest if a person were doing this they
> would assure themselves that the bush compliance
> doesn't become toe out, unless of course they're
> into drifting and want snap oversteer at 20 mph.

Again, it's suspension travel, not bushing compliance in this case. That rear toe-in under compression will be toe out under braking because of the rear suspension droop. That's the side effect of this kind of geometry. In a rally car, I'd argue it's a very good side effect. In an RX-8, not so much. That's why we changed the toe curve on the rear of the RX-8 last year. Less toe in under compression means more neutral cornering attitude and better high speed braking stability.


-Dave

That's a good explanation Dave.

I guess turning it around has worked out for the best

---

-Jason

Luck and smarts both perform equally well...

For the record, I didn't think of the toe change thing until I had seen it finished. Had I been building it, I probably would have put it in facing forward and then had to move the rack to fix the roll oversteer...

-Dave

>>>Bushings have nothing at all to do with it in this case. Remember, there's a ball joint between the control arm and the wheel, so even if bushing deflection did move the end of the control arm fore and aft, the ball joint would prevent that from becoming toe. It would just be fore-aft movement. <<<<<


The statement above is problematic. THe toe in does not come from the knuckle being fixed relative to the control arm (duh) but from the geometry of the tie-rods.

The deflection of the big rear bushing allows fore-aft movement (actually an arc about the front pivot) moving the end of the control arm backward and in. The tie-rods are swept slightly forward therefore this type of rearward deflection will cause toe-in.

---

____________________________________________________________-

One. Class -- 2WD

www.quantumrallysport.com

http://www.facebook.com/home.php?#/pages/Quantum-Rally-Sport/281129179600?ref=nf

Excellent point. I should have said it had nothing to do with what I was specifically smoking. Clearly there are plenty of other things going on that I couldn't spot in the photos. I don't even see that geometry in this one, which should show that. They seem kinda parallel, but it isn't the best angle. I think your toe change also falls under the general common sense steering geometry.



I can see a tie rod end that isn't perfectly in line with the tie rod axis, though. Bendy bendy...

-Dve

eyesoreracing Wrote:
-------------------------------------------------------
> I can see a tie rod end that isn't perfectly in
> line with the tie rod axis, though. Bendy
> bendy...
>
> -Dve


This is true. That's why a set of these (scirocco tie rod ends are straight) are sitting in the garage. It's cheaper to buy the whole damn tie rod assembly than just the tie rod themselves ....

Although I am considering ditching the stock tie rods all together and put in some heim joint/rod ends to beef it up. Then I could also build a couple attachment points on the inside to play with how much toe-in I want...... hum

---

-Jason

OK Dave I see whatcher talking with the tie rod included. Since I think the whole idea is kinda chancey thing I haven't paid a lot of attention, and didn't think of the tie rods position relative to control arm.

Wonder what sort of actual suspension element is going to be used?
All kinds of work and it's be a shame to throw some shit insert or strut in there.

---

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.

mack73 Wrote:
-------------------------------------------------------
>
>
> Although I am considering ditching the stock tie
> rods all together and put in some heim joint/rod
> ends to beef it up. Then I could also build a
> couple attachment points on the inside to play
> with how much toe-in I want...... hum
>

Hmmmmmmm who has some CrMo arms all set up for being links?
Who who? WHO?
>
>
> 94 Golf
> www.Mack73.com

---

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.

john vanlandingham Wrote:
-------------------------------------------------------
> OK Dave I see whatcher talking with the tie rod
> included. Since I think the whole idea is kinda
> chancey thing I haven't paid a lot of attention,
> and didn't think of the tie rods position relative
> to control arm.

And if it all goes pear shapped, I cut the mounts off and bolt in the stock beam again. No harm no foul.


> Wonder what sort of actual suspension element is
> going to be used?
> All kinds of work and it's be a shame to throw
> some shit insert or strut in there.
>
> John Vanlandingham
> Sleezattle, WA, USA
>
> Vive le Prole-le-ralliat
>
> www.jvab.f4.ca

Patience John, yes I will be using your suspenders. I just accepted a job on monday so now the funds can begin flowing. Being laid off sucks.

---

-Jason

mack73 Wrote:
-------------------------------------------------------
>
> Patience John, yes I will be using your
> suspenders. I just accepted a job on monday so now
> the funds can begin flowing. Being laid off sucks.

It does give ya time to work on labor intensive things tho!
>
>
>
> 94 Golf
> www.Mack73.com

---

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.

Jason,

Not to get you too off track but wanted to congratulate you on finding another job.

---

Name: Dawud Jackson (DJ)
Age: 30
Location: Seattle, WA
Occupation: Computer dude.

DJackson Wrote:
-------------------------------------------------------
> Jason,
>
> Not to get you too off track but wanted to
> congratulate you on finding another job.
>
>
>
> Name: Dawud Jackson (DJ)
> Age: 26
> Location: Seattle, WA
> Occupation: Computer dude.
>

Thanks DJ. New title is IT & Product Manager. Company makes video cameras for Police Officers. It's an interesting mix between managing the support dept. with a bit of product development thrown in.

---

-Jason

Nice! do you get free incar setups to test?

---

Welcome to the cult of JVL drink the koolaid or be banned.

Dazed_Driver Wrote:
-------------------------------------------------------
> Nice! do you get free incar setups to test?
>
> Feisty Peacock?
>
> My noodle I doodled was ate by a poodle

Actually yes. They said they wanted to throw one in when I told them I'm working on a rally car

---

-Jason