Why is is that Ford specifically, and alot of other WRC/S2000 cars as well seem to run soo much castor in the front?



Thinking it seems to make some sense, as the car is moving forward, and hitting bumps, the forces would be more linear with the strut assembly instead of at right type angles.

Ideas? thoughts?

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Chris

(FWIW)

I just asked 'Logic' the same question.

The answer I got was "turn in is paramount!"

Cool question Chris,

Looking at the photo there, it looks like the strut bottom is well ahead of the axel (same in the rear). Would that not reduce the effect of the sloped strut on the caster, as the actual pivot point is not that far from vertical. Interesting how the strut top now lines up with the bottom of the A piller. It certainly would transfer more of the impact shocks up into the body, rather then ripping off control arms.

Hmmm I wonder what that does for bump steer???

Matt



Edited 1 time(s). Last edit at 12/03/2009 09:30AM by Mad Matt F.

Subaru's already run something similar in the rear, with the strut mounting being infront of the axle...not as wild, but still same type of idea.

Heres the question now.

If i go and get some camber/castor plates, and dump the top of the front strut back as far as i could in the tower. What results am i going to get?

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Chris

Good question! Also an interesting picture. It must have been a fun test day. Tarmac set up in the snow!

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Robert.

"You are way too normal to be on Rally Anarchy." Eddie Fiorelli.

Chris Chris Chris... Dontcha have all this stuff memorized

Increased castor will help turn in and add dynamic camber without the need to run over-aggressive static camber. The spec C rear a arm bush adds castor as well as the somewhat cheezy whiteline ALK garbage. I know you're plenty capable of making some bad-ass camber castor plates so why not do that? Make me a set while you're at it!

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Gone fishing

dave,

i know the theories...and all that, but just wonder about the extremes.

i'm already running the Alloy arms, and flipped the rear pin for the free castor mod (look it up on nasioc).

I do think going to an extreme like this will change bump steer forsure, as it'll change the tie rods and control arms from being parallel... Dump the strut top back, and the steering arm on the knucle will go up.


Maybe this is Ford way of packaging a SUPER long travel strut into the space. I know the Focii WRC cars run wicked amount of wheel travel, possible that this is how they are getting it in there, without extending the towers through the hood?

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Chris

It's about packaging.

How could you accommodate a super long strut?
We know they have around 12" or 300mm travel since we can see the huge gaps when in the air tween tire and fender lip is about half the tire diameter and we know the max diameter is 65cm or 25.4", so we know the overall length of the strut for min 12" travel is 12" of upper part, 12" in the tube + min 4-6" over overlap so a total of between 28-30".
Where would you put that 30" if it all was above the CV like a Subie or Xratty? That thing has to go somewhere.
Well we're back in what we faced on bikes in 76-78....


This is what we used up to about 1976:


You can see the increase in overall length in just a few years and the same principle: spindle in line with damper x is as far as you could make it (about 200-210mm travel---about the same as I can do for rwd guys.
Put the damper ahead or behind, you can have an much longer over length and have about 300-310mm travel.




Place it ahead of the CV in the knuckle and you just burned up maybe some of the length, tilt it back and burn up some more length AND have the strut top and tower closer to the junction of firewall, inner wheel well and A pillar which has a nice tube backing it up and that is way stronger than having a tower out in the middle of a thin steel wheel arch stamping.

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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.

So I gues the question would be; is there an easy way of increasing the articulation of the tie rods and ball joints?

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Gone fishing

And, what would you do about the conflicting geometry of the control arm vs the strut? As now the strut is moving up and back, and the control arm was just going up and down. Is the control now angled to account for this?

Chris, I think that would be the problem of your thought of just making up camber plates. I guess if the control arm bushing were soft enough to accommodate the misalignment you might get away with it, but at the limits of travel there might be quite the bind.

Matt

Oops,

I recant my statement! If the upper strut mount had enough articulation such as a spherical joint, I don't think there would be any binding. (at least that's what a terrible sketch and poor math skills told me!). But I think it would maginally increase effective spring rate (again poor math skills, vectors and stuff still confuse)

Matt



Edited 1 time(s). Last edit at 12/04/2009 03:27PM by Mad Matt F.

The angle reduces the spring rate and could possibly give it a slightly falling rate through the travel depending on the mounting. Looks like it's mostly for packaging purposes to me but it would also have the benefit of reducing the bending load on the strut bushings. Are there any close up pictures of the knuckle interface?

-Tim

Damn,

Right reduces rate... bloddy math!

Matt

Daniel Buehler Wrote:
-------------------------------------------------------
> (FWIW)
>
> I just asked 'Logic' the same question.
>
> The answer I got was "turn in is paramount!"


Wouldn't that depend on the scrub radius?

- Pete (Probably missing something from the larger picture)

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Pete Remner
Cleveland, Ohio

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

Tim Taylor Wrote:
-------------------------------------------------------
> The angle reduces the spring rate and could
> possibly give it a slightly falling rate through
> the travel depending on the mounting.
>

Something I just thought of - having the strut at an angle like that will give you a pretty hefty antidive, so they can get it that way instead of through the control arms.

Antidive strictly through the control arms (front pivot low/rear high) doesn't follow the road so well because the wheel needs to move forward as it goes up. Now they can get their antidive while also having the spindle move back as it goes up instead of forward.

About 10-15 years ago some bike company came out with a neat suspension fork, instead of being telescopic, it was on a linkage, and the wheel's travel was J-shaped. It was supposed to work extremely well, as long as all those pivots weren't loose.

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Pete Remner
Cleveland, Ohio

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