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Advanced Suspension Geometry and Design

Posted by Cosworth 
buerckner
Andrew Buerckner
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Re: Advanced Suspension Geometry and Design
February 06, 2014 05:48PM
Quote
john vanlandingham
For those numbers to mean hannything we need to know vehicle weight, and travel.

Yeah but I'm flat our remembering what I had for breakfast, let alone that stuff! spinning smiley sticking its tongue out
But I'll have a go,(rough figures which are probably worse than none) it had 190mm travel fr, ~250mm rear. 840kg total. Didn't ever get that one on the cornerweights but the old similar car was ligher at 790kg and 59:41, againg that's pretty meaningless as it was 3 door 3-cyl turbo, as opposed to 4 door, 4 cyl. So who knows.

Also anyone that takes our blabbering on the net as more than a rough guide would have to have rocks in their head.smileys with beer
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Re: Advanced Suspension Geometry and Design
February 06, 2014 06:27PM
Quote
john vanlandingham
Quote
Reamer
If I were to throw a test set up on a fwd car looking for more traction I would add tons of rebound in front struts soften front springs and stiffen rear springs.

My thinking would be get the wieght on the front tires under braking. Then hold it there with the front rebound. And have the rear stiffer to not let the weight get to the back of the car. This should make about as much bight as you could in a fwd car.

Now if this would be drivable in rough conditions I dont know?

ACK! I maybe should phrase it clearer...OK then ACK!!!!

Uhm er, we have BUMPs here and there. And when we brake---those that bother too anyway, we hit a bump, suspension moved in, the another, it moveds in more and add braking and a bump it moves in MORE---no in left.
Then we hit another bump..while on the bump stops...

¿ǝnןɔ ɐ ɐʎ ǝʌıƃ sıɥʇ sǝop ¿uǝɥʇ suǝddɐɥ ʇɐɥʍ ʍouʞ noʎ


˙ɟooɹ ǝɥʇ uo uıɐd ǝɥʇ sǝɥɔʇɐɹɔs uǝʇɟo ʇı 'ɹǝʍoןs ʇsnɾ ʇou sı sıɥʇ ǝʞıן punoɹɐ ƃuıʌıɹp ǝsnɐɔǝq ˙uo sǝʞɐɹq ǝɥʇ dǝǝʞ ¿ǝɹǝɥʇ ʇı dǝǝʞ oʇ ʇuɐʍ puɐ pɹɐʍɹoɟ ʇɥƃıǝʍ ʇuɐʍ
˙˙sʎɐʍǝpıs ƃuıoƃ ʎq ɹo ƃuıɹǝǝʇs puɐ sǝʞɐɹq ɥʇıʍ ʎןןɐuoısɐɔɔo puɐ ʎןuıɐɯ sǝʞɐɹq ɥʇıʍ ʇɥƃıǝʍ ǝɥʇ ǝʌoɯ ǝʍ puɐ 'sʎɐʍ ɥʇoq ƃuıɹds ǝɥʇ ƃuıןןoɹʇuoɔ ɹoɟ ƃuıdɯɐp ɥƃnouǝ ʇsnɾ ɥʇıʍ dn uoısuǝdsns ǝɥʇ ʇǝs ǝʍ ʎɐs ı os ˙ɹǝʇsɐɯ oʇ ɯǝʇsʎs ןɐɔıʇıɹɔ puɐ ןɐɹʇuǝɔ ǝɥʇ ǝɹɐ sǝʞɐɹq ǝɥʇ ʇǝɥʇ ʎןǝʇǝɹɐdǝs puɐ 'ǝʌoɯ oʇ spǝǝu uoısuǝdsns ʇɐɥʇ uoısuǝɥǝɹdɐsıɯ ǝɥʇ ɹǝpun ɹoqɐן ı

Dammit John! I just threw my neck out!



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Pete
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Re: Advanced Suspension Geometry and Design
February 06, 2014 06:48PM
Quote
Mad Matt F
John,

Didn't you do some offset stuff for Volvo's to use ears instead of plug-in's...

Couldn't you go one step further?

So with the rear steer upright (like the justy, wink, wink) you could move the strut forward as seen in my CAD drawing below. Now you have 2013 WRC travel for the cost of a RWD front strut cartridge leaned back a bit...

That looks weak as hell IMO. Note that the guys who ARE doing this kind of setup don't seem to be using ears, they've got something that looks like a big fat clamp holding the strut tube on.

On the other hand if you started out with something like what Ford started doing in 1977...



then you'd only be stuck with a ball joint position that is way too high up on the upright at a minimum, and an easily bent spindle if you use stuff from before 1994... And the rest of the suspension sucked as well for lots of reasons (poor steering geometry so the inside tire dragged through turns, crap suspension geometry, they put the spring on the control arm so everything was 3x heavier than it needed to be...)

I was really considering Fox uprights for the RX-7 (I'd give it some caster, too, I think Ford was afraid of caster) but I could never get over how HIGH the ball joint is on the upright. It's almost at spindle height. That makes your roll center down in the weeds unless you also mount the control arms high up on the body and use tiny little tires.



Pete Remner
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1978
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Edited 1 time(s). Last edit at 02/06/2014 06:52PM by Pete.
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john vanlandingham
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Re: Advanced Suspension Geometry and Design
February 06, 2014 09:31PM
Quote
Creech
Quote
john vanlandingham
Quote
Reamer
If I were to throw a test set up on a fwd car looking for more traction I would add tons of rebound in front struts soften front springs and stiffen rear springs.

My thinking would be get the wieght on the front tires under braking. Then hold it there with the front rebound. And have the rear stiffer to not let the weight get to the back of the car. This should make about as much bight as you could in a fwd car.

Now if this would be drivable in rough conditions I dont know?

ACK! I maybe should phrase it clearer...OK then ACK!!!!

Uhm er, we have BUMPs here and there. And when we brake---those that bother too anyway, we hit a bump, suspension moved in, the another, it moveds in more and add braking and a bump it moves in MORE---no in left.
Then we hit another bump..while on the bump stops...

¿ǝnןɔ ɐ ɐʎ ǝʌıƃ sıɥʇ sǝop ¿uǝɥʇ suǝddɐɥ ʇɐɥʍ ʍouʞ noʎ


˙ɟooɹ ǝɥʇ uo uıɐd ǝɥʇ sǝɥɔʇɐɹɔs uǝʇɟo ʇı 'ɹǝʍoןs ʇsnɾ ʇou sı sıɥʇ ǝʞıן punoɹɐ ƃuıʌıɹp ǝsnɐɔǝq ˙uo sǝʞɐɹq ǝɥʇ dǝǝʞ ¿ǝɹǝɥʇ ʇı dǝǝʞ oʇ ʇuɐʍ puɐ pɹɐʍɹoɟ ʇɥƃıǝʍ ʇuɐʍ
˙˙sʎɐʍǝpıs ƃuıoƃ ʎq ɹo ƃuıɹǝǝʇs puɐ sǝʞɐɹq ɥʇıʍ ʎןןɐuoısɐɔɔo puɐ ʎןuıɐɯ sǝʞɐɹq ɥʇıʍ ʇɥƃıǝʍ ǝɥʇ ǝʌoɯ ǝʍ puɐ 'sʎɐʍ ɥʇoq ƃuıɹds ǝɥʇ ƃuıןןoɹʇuoɔ ɹoɟ ƃuıdɯɐp ɥƃnouǝ ʇsnɾ ɥʇıʍ dn uoısuǝdsns ǝɥʇ ʇǝs ǝʍ ʎɐs ı os ˙ɹǝʇsɐɯ oʇ ɯǝʇsʎs ןɐɔıʇıɹɔ puɐ ןɐɹʇuǝɔ ǝɥʇ ǝɹɐ sǝʞɐɹq ǝɥʇ ʇǝɥʇ ʎןǝʇǝɹɐdǝs puɐ 'ǝʌoɯ oʇ spǝǝu uoısuǝdsns ʇɐɥʇ uoısuǝɥǝɹdɐsıɯ ǝɥʇ ɹǝpun ɹoqɐן ı

Dammit John! I just threw my neck out!

teee heee maybe try this.
http://textmechanic.com/Reverse-Text-Generator.html



John Vanlandingham
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Reamer
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Re: Advanced Suspension Geometry and Design
February 07, 2014 07:51AM
Looks like my dislexia works good in these cases!

So more rebound in a bike helps smooth the big bumps but more rebound in a car will put you on your roof. Or is it the stiff rear springs will put you on your roof?

Thats the set up I would try for MOST faward bite in a FWD.

Also when I say tons I mean lots more then compression stroke. So say 140lb compression and maybe 700lb rebound. Also my oval car is more in the 1600 lb rebound range.


Thats why I threw it out there to see what guys thought.



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danster
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Re: Advanced Suspension Geometry and Design
February 07, 2014 09:46AM
Is there really an optimum geometry? I don't think so. Only a best compromise depending on a multitude of constantly varying factors.

In my experience most FWD production shopping cars are designed to inherently under steer for safety. Lift off the throttle when it starts to slide in a corner and generally grip returns.
That is a fine way of keeping the weekly shopping of eggs, ketchup and beer safely in the bags in the trunk instead of it being thrown all over the interior when the car lands on it's roof in a ditch if the car were to have more "edgy" or "nervous" handling characteristics.
Exception being some French stuff with torsion beam rear axles that can suffer from lift off over steer. But the froggies only eat bread and cheese so no great clean up problem for them if the car rolls.

So I guess depending on driver preference (which is also a huge factor) of how you wish the car to handle, you could tweak the geometry to move away from the OEM original designed in tendencies, and induce a characteristic of what you want, whatever that may be.

I understand that depending on their construction, radial tyres can also cope with a fair amount of camber change and still keep their footprint.
So how radical does the geometry really need to be? Presumably it must keep the tyres within their operating window.
Every time I go to watch the cars in the woods, I see mk2 Escorts humping most things. Live rear axle and very short TCAs on the front.

Modern off-road bikes have amazingly capable suspension with multiple adjustments, it is incredible what they can do if set up correctly, but that can involve subtle spring rate changes and re-valving the forks / shock to fine tune for rider weight and whatever discipline they are used for, motocross and woods riding are very different. So I guess that confirms my suspicions that a best compromise is going to be as good as it gets.... Well until Honda come out with Vtec geometry with moving pivots points.



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john vanlandingham
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Re: Advanced Suspension Geometry and Design
February 07, 2014 11:16AM
Quote
danster
Is there really an optimum geometry? I don't think so. Only a best compromise depending on a multitude of constantly varying factors.

In my experience most FWD production shopping cars are designed to inherently under steer for safety. Lift off the throttle when it starts to slide in a corner and generally grip returns.
That is a fine way of keeping the weekly shopping of eggs, ketchup and beer safely in the bags in the trunk instead of it being thrown all over the interior when the car lands on it's roof in a ditch if the car were to have more "edgy" or "nervous" handling characteristics.
Exception being some French stuff with torsion beam rear axles that can suffer from lift off over steer. But the froggies only eat bread and cheese so no great clean up problem for them if the car rolls.

So I guess depending on driver preference (which is also a huge factor) of how you wish the car to handle, you could tweak the geometry to move away from the OEM original designed in tendencies, and induce a characteristic of what you want, whatever that may be.

I understand that depending on their construction, radial tyres can also cope with a fair amount of camber change and still keep their footprint.
So how radical does the geometry really need to be? Presumably it must keep the tyres within their operating window.
Every time I go to watch the cars in the woods, I see mk2 Escorts humping most things. Live rear axle and very short TCAs on the front.

Modern off-road bikes have amazingly capable suspension with multiple adjustments, it is incredible what they can do if set up correctly, but that can involve subtle spring rate changes and re-valving the forks / shock to fine tune for rider weight and whatever discipline they are used for, motocross and woods riding are very different. So I guess that confirms my suspicions that a best compromise is going to be as good as it gets.... Well until Honda come out with Vtec geometry with moving pivots points.

Danny. I lurv you. best post by far--and best connected to reality.
Ta.



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Reamer
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Re: Advanced Suspension Geometry and Design
February 07, 2014 07:12PM
Yes thats a good post for real world rally. And im sure we all agree.

Then again we also are gear heads who like to learn how and why things are the way they are. A good handling car makes the driver look good. The same goes for an ill handling car makes a driver look bad.

I still would like to know what to throw at the rear of my car to get the feel im looking for. It needs to feel more confortable to push harder.



First rally 2013
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Re: Advanced Suspension Geometry and Design
February 09, 2014 02:26PM
Quote
john vanlandingham
Danny. I lurv you. best post by far--and best connected to reality.
Ta.

Pfft, It was a risky post tbh. Ya know that posting anything near reality on t'internet can always backfire when one gets shredded by the hypothetical, theorizing, computer aided design engineers, with a bazillion hours of online philosophising, backed up with little practical experience whatsoever to know what the feck they are trying to accomplish.

Did you know the shear volume of bullshit posted on the internet actually has a measurable effect on our vehicle's handling?
Well, in an ironic twist of fate, our metallic cars are now susceptible to the magnetic forces caused by the electro-magnetic fields emitted from the excessive abundance of servers required to store the terabytes of all the utter gibberish wafflings on how to improve car handling...
Think about it, why else would the top teams be using composites.....

NB> The above is to be taken in a humorous fashion. But bench racing will only get you so far.



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danster
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Re: Advanced Suspension Geometry and Design
February 09, 2014 02:51PM
Quote
Reamer
I still would like to know what to throw at the rear of my car to get the feel im looking for. It needs to feel more comfortable to push harder.

Have you had your vehicle put through a full 4 wheel alignment geometry check to see what is actually happening? Springs removed and checking from full droop to full compression.

If you had the baseline figures for your car, and also what a standard car has, it may be interesting to see the comparison and see whether something stand out or odd is occurring.



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john vanlandingham
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Re: Advanced Suspension Geometry and Design
February 09, 2014 03:02PM
Quote
danster
Quote
Reamer
I still would like to know what to throw at the rear of my car to get the feel im looking for. It needs to feel more comfortable to push harder.

Have you had your vehicle put through a full 4 wheel alignment geometry check to see what is actually happening? Springs removed and checking from full droop to full compression.

If you had the baseline figures for your car, and also what a standard car has, it may be interesting to see the comparison and see whether something stand out or odd is occurring.

Jus a weee bit of emphasis.
Compare and contrast is what I call that.. Do the both and stare at it for a ciggie or two before THINKING.

Like this:


Empty the mind and look at the 2 columns...



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MattP
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Re: Advanced Suspension Geometry and Design
February 09, 2014 08:51PM
I loved my various Frenchie cars for their 3 legged handling skills. Worst FWD was the Opel Corsa/Vauxhall Nova, 1.6l in a car that was 146" long not wheel base that was 92" used to swap ends.



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alkun
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Re: Advanced Suspension Geometry and Design
February 09, 2014 09:58PM
I'll contribute my 2 cents:

Its not really advanced design, in fact its about as simple as possible.

As I are caveman, my tastes are biased towards the trusty volvo 240. Longish wheelbase, solid rear axle and generous suspension travel make for a , predictable, forgiving, easy to drive rally car.

definitly agree with Matt above, wheelbase is going to play a primary role in handling. When I have driven shorter cars close to the limit I have found myself frowning more than smiling.

As for specific changes to geometery, while redoing to front strut to knuckle clamps on my 240, Tim bumped the negative camber to about 2.5 degrees. This was added at the same time as changing to the 50mm struts with huge increase in rebound damping and structural stiffness,so one can't isolate the results, but compared to the stock car there is a world of difference in cornering. tendency to understeer in all conditions is greatly reduced, and the front end generally feels more stable and gripped up. There is a feeling of pivotting around the inside front wheel in very sharp corners that I find especially nice. Sean has mentioned building A-arms for the volvo that could dial in more castor as well in order to add a bit more to the bite of the front wheels. This would certainly be fun to play with.
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Reamer
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Re: Advanced Suspension Geometry and Design
February 10, 2014 12:10PM
Ive done begginer test. Ive had springs out and traveled many times. Thats how I found the front issues. At 7" ride hieght I had 1 3/4" up travel before the strut was fully compressed. I raised the strut tower so the strut at 7" ride is mid travel. 6 degrees caster.

I have not yet put the bump steer guage on the rear to check to see what toe is doing with bump.

I didnt change upper or lower control arm angles to change rear roll center.

I changed the forward mounting arm and the tierod. There maybe some unwanted toe change with travel causing problems. a quick measure shows 1/16" toe in fully compressed per side so 1/8" total toe in. iT may go crazy mid travel I didnt measure threw travel just ride hieght and compressed.

I think I may try to raise rear roll center if it isnt to complicated.Was thinking about adding forester spacers to rear cradle then lower it back down to ride hieght and try it. This will add a few degrees angle to all the rear susp control arms. Seems most pics I find of 08 up sp cars are way lower in the rear then the front.



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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Do It Sidewayz
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Re: Advanced Suspension Geometry and Design
February 11, 2014 10:30PM
I like where this thread is going.

I will admit to playing with some of the concepts mentioned here, with some success on my impreza, and what most of you are saying here agrees with the theories I followed.


Currently racking my brain trying to figure out how to get more straight line grip on Ice with my Ice Racer Impreza. It's bone stock with regards to suspension, except removed sway bars. The car turns and sets ok, but lacks serious forward bite. It will get roasted off the corners by RWD and FWD cars!



Chris
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