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Advanced Suspension Geometry and Design

Posted by Cosworth 
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Grant Hughes
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Re: Advanced Suspension Geometry and Design
March 21, 2014 12:33PM
So you have 1/8 static toe, 1/8 more under compression. Sounds about right, maybe go zero static and see how that feels.



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Reamer
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Re: Advanced Suspension Geometry and Design
March 21, 2014 01:18PM
I had 1/8" static then it went to zero then to in 1/8". Not good. John im talking what the toe does in travel not staic at ride hieght. I agree when tires are light they dont do much. This is also when the issue im having creeps up the most. The tire was moving crazy amounts in the wrong direction. I was just posting a article on bump and what most car builder want there bump to be at. Nothing about static toe in or out.

I reset my toe to zero at 7" ride hieght then I moved the outer tie rod down 3/8" and got the numbers Vermont sports car told me I should be looking for. Its crazy how much 3/8" shim changes the hole charictoristic of how the wheel travels. The wheel now is going from 1/8" in at full droop to about .40 out at full compression. It barely moves the guage from 7" to full compression.



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Re: Advanced Suspension Geometry and Design
March 21, 2014 05:07PM
I believe the toe-out mantra in the cone crushing crowd is derived from the theory that they're almost always turning and hardly ever going in a straight line (and never at speed). So toe-out on a loaded rear wheel actually means that you're asking that rear wheel to do a little steering for you.



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Reamer
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Re: Advanced Suspension Geometry and Design
March 21, 2014 06:11PM
Im sure it is in cone crushing also. These numbers I got came straight from an engineer who developed the rear susp on Higgins 2013 car. I finaly talked to some body there that was willing to tell a few secrets. I guess seeing there now working on the 2015 car they dont care so much about there old stuff. They even got some used susp at a not so bad price considering there so much new.



First rally 2013
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Total rallies as driver 6
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Cosworth
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Re: Advanced Suspension Geometry and Design
March 21, 2014 08:40PM
Quote
simoniac
I believe the toe-out mantra in the cone crushing crowd is derived from the theory that they're almost always turning and hardly ever going in a straight line (and never at speed). So toe-out on a loaded rear wheel actually means that you're asking that rear wheel to do a little steering for you.
You're right Simon, this idiocy of doing toe out is specifically related to the lower speeds they run at. Less speed means less weight transfer for turn in rotation.

As for rally, I have some Citroen setup sheets that calls for 5mm toe in at the back of the C2 R2Max and DS3 R3T.
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Re: Advanced Suspension Geometry and Design
March 21, 2014 09:56PM
Quote
Cosworth
Quote
simoniac
I believe the toe-out mantra in the cone crushing crowd is derived from the theory that they're almost always turning and hardly ever going in a straight line (and never at speed). So toe-out on a loaded rear wheel actually means that you're asking that rear wheel to do a little steering for you.
You're right Simon, this idiocy of doing toe out is specifically related to the lower speeds they run at. Less speed means less weight transfer for turn in rotation.

As for rally, I have some Citroen setup sheets that calls for 5mm toe in at the back of the C2 R2Max and DS3 R3T.

The idiocy is unfortunately multiplied by the fact that those type of guys write endlessly of it and like a disease it has spread and infected a Continent, and they are too full of themselves and their 32 classes so everybody is a wiener sport that they forget that it is not something that Moses brought down from the mountain carved in stone tablets....

Paulino mio, do you know what bushes or what those car listed had in their links?



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Re: Advanced Suspension Geometry and Design
March 22, 2014 11:29AM
You guys just dont get what im typing. Thats fine. I did say I set my toe at zero at 7" ride hieght.This was to sort the brain while watching bump guage. I dont know where I will end up setting static toe I will figure that after some testing.

Im sure the toe on a wrc could be 5mm in at ride height. Chances are its near zero or zero at full bump witch means its ganging TOE OUT. Im also sure there figuring where there toe is at insane full droop. Im not saying my car should have zero or what static toe.

Im saying what car builders want the toe to do during travel. You know what its doing ALL the time while driving. Im sure me and all the other articles could be wrong just dont keep mixing static toe with what the tire does in travel. The articles I was searching were for baja trucks. I figure they will have there shit sorted better then the zero info you can find on rallycars. Paul could post some Citron set up sheets so maybe we could learn soemthing. Im sure there for the machanic not the engineers that designed the susp.

This is what this is for to sort out the shit so we can all go faster.



First rally 2013
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Re: Advanced Suspension Geometry and Design
March 22, 2014 12:07PM
Quote
Reamer
You guys just dont get what im typing. Thats fine. I did say I set my toe at zero at 7" ride hieght.This was to sort the brain while watching bump guage. I dont know where I will end up setting static toe I will figure that after some testing.

Im sure the toe on a wrc could be 5mm in at ride height. Chances are its near zero or zero at full bump witch means its ganging TOE OUT. Im also sure there figuring where there toe is at insane full droop. Im not saying my car should have zero or what static toe.

Im saying what car builders want the toe to do during travel. You know what its doing ALL the time while driving. Im sure me and all the other articles could be wrong just dont keep mixing static toe with what the tire does in travel. The articles I was searching were for baja trucks. I figure they will have there shit sorted better then the zero info you can find on rallycars. Paul could post some Citron set up sheets so maybe we could learn soemthing. Im sure there for the machanic not the engineers that designed the susp.

This is what this is for to sort out the shit so we can all go faster.

OK, and that is what Paulino had in mind when he started the thread: Look at what way cool stuff is, compare what we have and then look at the numbers and designs..compare and contrast..

And I know he's as frustrated as I am with all the auto-cross bullshit where the idiots spring their cars so stiffly that vey likely the only compliance they get is from bodyshell torsional twist (bearing in mind that many of the fools have stock bodyshells with no cage, or a bolt in junk Auto-powerz shit that does nothing to stiffen the shell) So those fools can set the non-moving suspension and then wank forever about it.
Our suspension moves a whole lot constantly, and as you show, some stuff moves around a shock about..
I'll post up a whole slew of old Ford Group A stuff...cause some of that is close to production---unlike cars built under the World rally Car rules where everything is purpose built and perfected.
First I have some cleaning to do.



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Iowa999
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Re: Advanced Suspension Geometry and Design
March 22, 2014 12:59PM
Quote
Reamer
You guys just dont get what im typing.

I do.

One of the best designs that I've seen has a flat (at zero) bump-toe curve in the front, with the suggested starting value of zero toe. In the rear, the curve was nearly linear, with toe-out in bump and toe-in in rebound. At static ride-height, toe was set to about .04 in (on each side). At full squat, toe was zero; at full droop, it was about .08 in (on each side).

The logic is simple. You want rear toe-in when the butt of the car rises under braking. You want near-zero rear toe when the butt sink under power. You always want the front near zero so the car is predictable.
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Re: Advanced Suspension Geometry and Design
March 22, 2014 03:07PM
Yes. Thats what ive read also. Paul is saying 4mm in at ride hieght. That makes sense to me to make the rear more stable entering.

The stock 08 is junk for this and this very well could be the issue me and other with 08 are seeing. The rear bump steer at snodrift on my car was going the opposite direction. In on compression and out on droop. Lots out on droop. So my theory is when you get hard on brakes and get the ass light the car will step out in the rear super easy. This was shown in Osullivan's test crash. His may have been cold brakes. I feel he is more talented then that and could of corrected if it were just brakes. because of piss poor rear susp design 2 things cought him out and he couldnt save it.

It looks like Subaru wanted a bolt in rear susp. Where all the arms will bolt onto one cradle and they can take that cradle and fit it into any chassis they want. Makes sense for production line but horrible for the racer.

What vsc and I coppied was get rid of the short front trailing arm. Make a longer tie rod to correct bump steer. A stock rear tie rod is 10" long mine is now 14.5" long. My bump is super close now. I cant even guess how far off stock is over 4" shorter and way off from where it needs to be located to get zero bump. The stock trailing arm is so much shorter the tire pulls foward so much on droop the tire almost hits the front of the wheel well. Jack the back of an 08 up and watch the tire swing foward a mile. That has to be inconsistant feeling to drive.

I am super impressed with how SP teams have figured out how to make these cars fast. Then again Cline runs within 1/2 sec mile speeds with a bone stock sti, stock ecu stock diffs and diff controller from a 100k 05. with miss matched front rear susp. Running against vsc built sp cars with anti lag and trick diffs. Wonder how fast Van way or Roberts would be if they were in an 07. My guess is way faster.



First rally 2013
Rally car type AWD subaru
Total rallies as driver 6
Total rally cars built 2
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Total rally cars repaired from offs 4
Total years racing exp other then rally 19 yrs
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Cosworth
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Re: Advanced Suspension Geometry and Design
March 22, 2014 03:26PM
You boys are over thinking this, these are FWD cars with trailing arm rear suspension setups that have nearly zero travel, and there's no rear bump steer. So a static 5mm toe in, is a dynamic 5mm tow in. Now this doesn't mean it will work well for your cars.

As for the SP cars, they don't have trick diffs, its all stock. And the newer ones with the handicapped rear suspension, its been long fixed with shock valving. The cars handle just as well as the previous. Just not as light. They are actually pretty good, because in Group N they have put the evo out of business.

I cant attach those setup sheets I have, they're PDF's and this board wants images. Anyone know how can I upload these things here. I have Citroen and Peugeot stuff.
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Cosworth
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Re: Advanced Suspension Geometry and Design
March 22, 2014 03:28PM
Quote
john vanlandingham
Paulino mio, do you know what bushes or what those car listed had in their links?
Aluminum bushes inserted into the OEM arms on cars like R2's and Heims on the more Group Aish type of cars.
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Iowa999
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Re: Advanced Suspension Geometry and Design
March 22, 2014 03:46PM
Trailing arms make the system a tad more difficult to model on a napkin, but they also make it more important to do so, because of how the trailing arm shifts the entire wheel back during bump. What you often find is that the slight difference in the lengths of the so-called camber arm and toe arm causes most of the toe change to be due to the rearward shift of the wheel due to the trailing arm, instead of mere non-parallelness of the two lower arms.

In any event, the solution is often as simple as swamping to a taller-stalk ball-joint on one of the two lower arms. By making the two lower arms (more) non-parallel, you can swap a car from having a negative to a positive bump-toe curve. The only issue is whether the off-the-shelf versions of said long-stalk ball-joints will stand up to the beating of rally.
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Re: Advanced Suspension Geometry and Design
March 22, 2014 03:57PM
I mean $1800 Trick diff controller married to a $3500 ecu. T/C kickin it dirt style! My bad.

I was told it was corrected in the shock package. Do you have any thing on what they actually did for valving to fix this? I can buy there rear shocks for a small fee. But would rather revalve what I have if I could find out what it needs.

Over thinking is prolly correct but if someone fast ever gets behind the wheel of my ride they should be happy with how it drives. Plus my next rally isnt until STPR so what else should I do except Test at my compound that I dont have, tinker with susp crap and car diets! The cars down to 3130lb need to lose another 250lbs! I could prolly drop 50 off myself but the car still needs to weigh 2900lb with out me.

It is lighter then sp rules so im in the ball park if the car had a driver it could prolly run up towards the front of RA rallies.



First rally 2013
Rally car type AWD subaru
Total rallies as driver 6
Total rally cars built 2
Total rally cars caged 3
Total rally cars repaired from offs 4
Total years racing exp other then rally 19 yrs
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Re: Advanced Suspension Geometry and Design
March 22, 2014 04:00PM
I believe I got my rear susp sorted out bump wise ive moved things around and it seems to do what paper says it should do. I need to sort out the rear shock and spring combo and I think it is ready to throw dirt.



First rally 2013
Rally car type AWD subaru
Total rallies as driver 6
Total rally cars built 2
Total rally cars caged 3
Total rally cars repaired from offs 4
Total years racing exp other then rally 19 yrs
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