Advanced Suspension Geometry and Design

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modernbeat
THE most important part of rally car geometry that you start with is the ideal slip angle for the type of car you are driving. That is THE base for everything else that you will build on. And I don't make my mortgage from the "racing industry" like so many other fabricators, tire busters, vacuum bag composite artists, sales people, marketeers or event masters. I make it in suspension technology, geometry, longevity, and tuning.

But thanks for the insult anyway.

And no, the "ideal" slip angle does not change except for surface conditions (available grip). Tires (the proper spelling, even for people from North Carolina) change it a very small amount, not enough to change geometry. And we're talking about changing geometry, not CG or rotational inertia, so unless you plan to make those radicaly adjustable while driving, you have to assume they are fixed and work around them.

Didn't mean to sound like an insult in what I wrote and after reading again still don't see it as an insult, but apologies anyways. On the other hand your halfass attempt on insulting me only shows that you were so bent out of shape in proving your self worth that you proceeded to insult half of the people that make the racing industry go around. You don't know me or what I do or have done in professional motorsports world wide, and I dont feel the need to back it up anyways . But I'm not from NC but thanks for thinking so, I like it here and that's why I came back from UK, but as far as tire/tyre the rest of English speaking world spells tyre and not tire, . But enough of this before we go down in a JVL style

The reason I was trying to stay away from slip angles is because its something that its going to be irrelevant for someone trying to just fine tune his current setup. You were talking about slip angles around the order of 45 degrees. That's too much for rally. 45° degrees is something that would work for a sprint race car or a dirt late model, but in rally I think 25° is probably as much as you can go without until it starts costing you time. In fact last year I was talking with Dick Cormack (Mr DMACK) in Ireland at the Rally Donegal and we were talking about exactly the slip angles on his tyres. Tarmac tires have a max of 8-10° depensing on wet/dry and the gravels I think it was 20° or 25° cant remember now. So I'm sure the ideal slip angles of the car cant be more than what the rubber can withstand.

Anyways, going back to suspension geometry my old boss in Banbury used to be one of the engineering managers at Prodrive from 1986 to 2008, and he used to say that anything anti dive/anti squat are ALL anti suspension and that you would want to keep things a linear as possible. Obviously things change when you're fine tuning a chassis to work with all sorts of other components, aerodynamic, active diffs, etc.

Thanks for the headsup on the locost softwares, will look into them.

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john vanlandingham

Famous and been around forever rally engineer Christian Larioux


said in a long LONG interview in Racecar Engineering (which showed an amazing amount of unintentional arrogance) put the problem very simply and clearly "on asphalt were are searching for handling, on gravel we are searching for grip".

he said on asphalt in testing it was very easy to put sensors everywhere and measure everything you desire and can imagine. On gravel it was very difficult to get reliable information not the least of which because as he put it "a good driver will "drive around' all kinds of problems" and the drivers---he said again in so many words---are monkeys that don't have a clue how anything in any area of the cars work "because they are so complicated" and so their feedback is suspect and again said several times in "so many words" and their observations must be ignored...

Despite his shocking arrogance it did zero in on the essence of the dichotomy: asphalt its engineers and equipment that is primary because it is so consistent and simplistic, gravel is difficult, and the driver's perception and skill is central.

That is nice words for what I've been saying for 40 years ----the difficulty and unpredictable nature of the surface---different often left to right, different turn by turn, different lap by lap, different during the day...------makes doing the job far more challenging---and the challenge to one's flexibility and adaptability is the main attraction on loose surfaces.
It's hard to do it well. And the more powerful the vehicle , the more challenging finding grip is. (hence why I personally look at 2wd cars as the more desirable because its more challenging) and thus more satisfying.

Remove the difficulty in finding grip and any schmuck and drive fast as long as they can afford the equipment and tires.

That said it doesn't mean we can't think of ways----within reason----to optimise the vehicle which I believe was Paulinho's original intention rather than a fap fest of theoretical posturing.

Its true John, drivers are an engineers nightmare, because they're the worst and most inconsistent source of data. I've have a driver by the name of Mathias Lauda tell me the setup was shit on morning practice and he couldn't drive like that at the 24hours of Spa in 2012, when he was going out for the 2pm test I had told him we fixed this that and the other, and didn't do anything but put new tires and test with more fuel load. When he came back he was happy with the setup and to leave it like that for the race. Yes that was Nikki Lauda's son... We have the telemetry and know what works and what doesn't, so in this situation the placebo effect did wonders!

after alignment, the rx-7 has 5.9 degrees of caster.

thoughts?

---

First Rally: 2010 First RallyX: 2004 (a bunch)
Driver (0), Co-Driver (7)
Organizer (3), Volunteer (3)
Cars Built (2.5), Engines Blown (2) Cages Built (0) # of rotations (3.5)
Last Updated, Apr 9, 2023

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john vanlandingham
Remove the difficulty in finding grip and any schmuck and drive fast as long as they can afford the equipment and tires.

That said it doesn't mean we can't think of ways----within reason----to optimise the vehicle which I believe was Paulinho's original intention rather than a fap fest of theoretical posturing.

Exactly muchacho, no one is going to plot their car in CAD and butcher up the whole car. But redrilling a coupld of holes or making offset bushes to adjust some geometry features to help find grip is what would be most beneficial in a post like this. And yes, GRIP is the numero uno in gravel, and tarmac is handling. So in a 2wd car putting the power down is what makes the car fast even if its sliding wide. Ever notice the FWD rally cars have ALL the weight up front? None of the weight distribution fab that roadracers get horny over. All in the name of grip.

Greek



Edited 1 time(s). Last edit at 02/05/2014 08:22AM by Iowa999.

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john vanlandingham
That said it doesn't mean we can't think of ways----within reason----to optimise the vehicle which I believe was Paulinho's original intention rather than a fap fest of theoretical posturing.

My whole point too actually. There's useful stuff to be talked about but it's easy to just get to wankery if you don't even start with what you want the thing to do. I figger, find grip and not have the car do stupid things suddenly to make the driver's job even worse. The bit with instant center I mentioned is one thing that came to mind - adjustments that are relatively easy to do that might make softer springs work better. Make any sense, or should I just butt out?

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Reamer
I was thinking about bumpsteer recently. I added pins and converted my tie rods to hiems to adjust bump. I havent set it yet wasnt sure where I should set it.

I was thinking of going from ride hieght to full compression because thats where the tire sees the most weight? I am planning on max .20 out all positive If I can get it that close. Rally cars have a lot more travel then what ive worked with in the past.

I've driven two nearly identical rallycars (FWD).
One we bought years ago and have tuned it from a pig to drive that wanted to kill you every change it got to something halfway good. Small changes step by step till we got there. Still plenty to go yet.
In the class we run you can't change suspension type or layout and can only move pivot points but ~15mm sphere(provided the bolt up to the original body mount points)

The other was built from scratch and had half the power and an extra 80KG but was faster in any non-power type stages.
Why? Started with what we had learnt with the other car and used that as base setting.
The biggest change was a much quicker steering ratio, more castor ~6 deg, more antidive, more travel +50mm and
fixing the BUMP STEER! It went from 12mm total toe change throughout the 220mm travel to under 1 mm total from full droop to 20mm before full conpression then only moved another 1mm right into the bumpstops.

Anyway my 2c worth is to measure what you have, see what can be changed realistically with you skills/budget/time. Make small steps and TEST TEST TEST.

The theory is out there, shit you may even have to TALK to people in the service park and spend some actual time and money testing, maybe even stick a good driver in the car, but it always has been worth sec/km and a car that handles will make all your rallies more enjoyable.

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mekilljoydammit

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john vanlandingham
That said it doesn't mean we can't think of ways----within reason----to optimise the vehicle which I believe was Paulinho's original intention rather than a fap fest of theoretical posturing.

My whole point too actually. There's useful stuff to be talked about but it's easy to just get to wankery if you don't even start with what you want the thing to do. I figger, find grip and not have the car do stupid things suddenly to make the driver's job even worse. The bit with instant center I mentioned is one thing that came to mind - adjustments that are relatively easy to do that might make softer springs work better. Make any sense, or should I just butt out?

No no your comments are good and thoughtful and in the right spirit...
Let's keep this going. I want to learn more. Always more to learn....

But----not directed at you---I think one can learn more about "our" problems by looking at gravel specific things and blabbering about formula cars is waaaaaaaaaaaaaaaay off the deep end of fappery...
Hopefully we can just ignore the fappists.

---

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.

Hokay, tone's hard on the internet sometimes, and god knows I really don't have much experience even driving street shit on gravel.

I know this is a kinda highfalutin solution, but I really do kinda wish that someone could take a nice precise measuring thingy to some cars - late Group A, early WRC era since there weren't too many tricks that the works cars were playing with valving yet - and just figger out what they were doing. I mean, guessing what's desirable is all well and good, but being able to check is nicer. Even just like "oh, the struts are angled like so, the ball joint's at this height, the two inner pivots are at that height, and the length between 'em all is such and such" would be beautiful. Maybe the Ford books for the later stuff had that kind of stuff, but I don't recall it.

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mekilljoydammit
Hokay, tone's hard on the internet sometimes, and god knows I really don't have much experience even driving street shit on gravel.

I know this is a kinda highfalutin solution, but I really do kinda wish that someone could take a nice precise measuring thingy to some cars - late Group A, early WRC era since there weren't too many tricks that the works cars were playing with valving yet - and just figger out what they were doing. I mean, guessing what's desirable is all well and good, but being able to check is nicer. Even just like "oh, the struts are angled like so, the ball joint's at this height, the two inner pivots are at that height, and the length between 'em all is such and such" would be beautiful. Maybe the Ford books for the later stuff had that kind of stuff, but I don't recall it.

Tell me about the tone thing.. I have said often enough that if I ain't being straight---and even that is never 100% , then imagine the character John Lithgow played in that great TV show "Third Rock from the Sun".....that's the perfect tone that he did when I want to be silly.

And yeah my idea i---being a very simple minded type of guy--and very visual biased---is we make like 2 maybe 3 columns, and so we see "what's really bitchin and optimised" and of course the base-line "What dey started from" and maybe "where dey went".

Then I think the difference will jump out of the page, and THEN we can ask questions about THOSE Obvious things---and THEN we can see if we can understand what those difference DO..
and finally: "can we do dat on this pile in the garage?"

I believe this can be more fruitful than jabbering about bullshit as if it was between runs in some fuckin parking lot and you have to impress the other guys who don't know what your day job is.

---

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.

boyfriend



Edited 2 time(s). Last edit at 02/05/2014 08:22AM by Iowa999.

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Iowa999
Would you do this by blind trial and error or would you think about basic suspension design to choose the locations of said new holes?

Yawn.

Ok, you CAN try the blind way, but unless you're a very good driver and know what you're doing chances are you'll end up with a worse setup. SO, knowing a bit about the basics and what the behaviours will be with each change will get you going in the right direction. That's the whole point of this thread, getting some tribal knowledge so that we know what small changes to make.

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mekilljoydammit
The bit with instant center I mentioned is one thing that came to mind - adjustments that are relatively easy to do that might make softer springs work better. Make any sense, or should I just butt out?

Its perfect, lets keep at it.



Edited 1 time(s). Last edit at 02/02/2014 12:39PM by Cosworth.

ate



Edited 1 time(s). Last edit at 02/05/2014 08:22AM by Iowa999.

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Iowa999
The point about bump-steer sent me back to my napkins and pencils. Assuming a single, L-shaped lower control arm, if you lower the rear inboard pivot (to alter the anti-dive), then you're pretty much guaranteed to change the bump-steer. Same goes for moving the top of the strut back for more caster. So what is the suggested order of things with regard to tweaking and testing?

My guess is that you do whatever you have in mind with regard to both the lower LCA and the top of the strut, and then do what needs to be done to zero the bump-steer. If nothing else, my napkin suggests that lowering the rear inboard pivot of the LCA and moving the top of the strut back at the same time will make the job of zeroing the bump-steer easier than doing just one of these changes; that's what suggested to me that you'd deal with the bump-steer last. The only problem I see if that testing the changes to the LCA and strut-mount wouldn't provide accurate information unless you fix the bump-steer every time.

I'm not sure the napkin is giving you correct results. I'm a bit blurry still front last night but I'm not sure how moving the strut back would affect bump steer, moving it inwards will definitely change because its changes the inboard "line" that connects the lower arm inner point, the inner joint on the tie rod , and the upper arm inner joint or in this case the strut mount. And then the intersecting points from a planar view towards the center of the chassis. Well its better posting a pic.

it



Edited 1 time(s). Last edit at 02/05/2014 08:23AM by Iowa999.