Advanced Suspension Geometry and Design

I'm going to place these here:
This is a good starting point, and is free. MotoIQ, Suspension Guide
Here is a good article published my Michelin on tires. Michelin, Grip - The Tyre
This book is pretty inexpensive and goes a little bit more in depth. Geared more towards road racing, but much of the same theory applies. Carroll Smith, Tune to Win
Now if you eat all of those up and now you want to make your brain explode, here's a really good way of doing that. Milliken and Milliken, Race Car Vehicle Dynamics

Jason is correct in stating that you always need to start with slip angle. Those four little contact patches are the only thing in contact with the ground, and everything you and your car do is transmitted through that area. So understand what they are doing, and then build and tune your suspension around that.

As for measuring slip angle, to my knowledge at any rate, several VERY expensive sensors on-car or a test rig to get accurate measurements. Rough approximations can be made fairly easily in a flat, level, empty parking lot with some cones though using an accelerometer found in any smartphone, measuring your cars ackerman steering wrt steering wheel input, and knowing corner radius. Drive in circles around your cone at different speeds (keep speed constant per each full circumference driven) and take note of steering angle and corner radius for each speed (a track app like RaceChrono can be used to measure actual corner radius). Then compare G to steering angle to actual corner radius. The difference between steering angle and corner radius is your slip angle. The slip angle generating the highest G force is (more or less) the optimum slip angle of your tires for your car in it's current set-up.
**Note, I would set your car up the way you have it set up for race day. Cooling your tires between runs would also be recommended. Sweeping your testing area prior to testing to maintain approximately the same road surface wouldn't be the worst idea in the world either.

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"The more I learn, the more I realize I don't know and have so much more to learn." - Claude Rouelle, Optimum G lecture June, 2011

Didn't this game already get played out over and over?


Here is the latest that I remember
http://www.specialstage.com/forums/showthread.php?52489-Edumacate-me-on-WRC-level-Rally-Suspensions

John, you working on that secret long travel project you alluded to? My golf could use 300mm of travel :-)

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____________________________________________________________-

One. Class -- 2WD

www.quantumrallysport.com

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

Mary



Edited 1 time(s). Last edit at 02/05/2014 08:18AM by Iowa999.

Except for the Milliken text book, those are fairly dated. And the good books out there don't address the pertinent issues with gravel/grass/sand surface racing. They all want to stick to formula cars on circuits.

But three books I ask all my guys to start with are these:

The Racing & High-Performance Tire, Paul Haney
http://www.amazon.com/The-Racing-High-Performance-Tire-Balance/dp/0768012414

Vehicle Dynamics and Damping, Jan Zuijdijk
http://www.amazon.com/Vehicle-Dynamics-Damping-First-Revised/dp/147724736X

Think Fast: The Racer's Why-To Guide to Winning, Neil Roberts
http://www.amazon.com/Think-Fast-Racers-Why--Winning/dp/1451558759

None of these books have "answers". Haney's book even comes out and says so. But it's description of the tire and what is going on within it will help anyone trying to make the most of theirs either by diagnosing issues or setting up the suspension. Zuidijk's book is horrible. I think it must have originally been written in Dutch and translated by a government textbook translator. Some of the illustrations are missing and some are miss-referenced. It's difficult to read, but Jan writes about damping concepts, some of which are old and dated, some of which have been discarded by the community, and some of which are still being used. Neil's book is easy to read and is an excelent book on how to budget your modifications and prep budget so you spend time and money in the places that will actually make the car faster (or more long lived) and not in the minutiae that some internet experts like to argue about (why argue about roll center placement in a car that allows it to move six feet?).

I suggest that anyone that wants to enjoy a hobby involving modified cars read and understand all three books. Neal's first, Paul's second, and Jan's if you can get through it.

There are lots of software simulators, so you don't have to use the string and cardboard that Staniforth and Valkenburgh used. Many are free or low cost. The Lotus 7 replica guys (LoCost 7) seem to keep abreast of them and even have a subforum dedicated to design software.

http://locostusa.com/forums/index.php

But the best I've found is still SusProg3D. It's a little expensive, but does everything I want. http://www.susprog.com/

The issue then is - what do you want? What are the targets? To win! Well, sure. But what wins? AWD wins, usually. Then what? Cars that don't break, duh. Then start removing gross flaws. Anyone in roadracing will tell you how bad trailing arm rear suspension is. Yet in low-grip situations the E30, FC-RX7, VW Beetle and XR4ti seem to do OK. Hell, it's THE favorite IRS suspension in desert racing. So what's better? Multilink? Beam axle? Rear strut? Twin A-arm? The easy way out is to copy what others do that works, but why does it work?

---

Jason McDaniel

Oh well off into the land of Fappery.

---

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.

Simple question looking for a simple answer:

You have a FWD vehicle with strut-type suspension on the front and lets call it twist-beam on the back (VW). You raise the front and lower the back slightly:
Does that change the anti-dive characteristics of the front end?

-Grant

Sure outdated and focusing on tarmac racing, but some key aspects to a winning "formula" are overarching between on and off-circuit racing. You said so yourself when you brought up slip angles(for one example)-

Quote
modernbeat
Serious. Yes. In rally. Not all cars or drivers take average corners at 45 degrees, or 180 degrees like crazy rally videos. I doubt most take them at 15 degrees. And is sliding though at 45 degrees really the fast way in a FWD or AWD car?

You do have a point for looking at the big picture and figuring out how to achieve it.

John, often times useful information can be found in the land of Fappery. You've been in this scene for a while, and are a walking encyclopedia of rally-related information and experience. Care to shed some light?
P.S. I know you're not a fan of CAD, so let's leave that aspect out of this for now.

---

"The more I learn, the more I realize I don't know and have so much more to learn." - Claude Rouelle, Optimum G lecture June, 2011

had



Edited 3 time(s). Last edit at 02/05/2014 08:19AM by Iowa999.

Quote
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.

Do you mean the slip angle relative to the road or the slip angle relative to the ground that is constantly rolling out from underneath the car?

Big difference in spirit but I've a strong suspicion that the best effective slip angle, "best" meaning highest lateral grip, and "slip angle" meaning the tire relative to what the tire is contacting, is the same for asphalt and gravel and dirt. The difference is, gravel and dirt are constantly rolling out from under the tire so the car has a greater angle of attack.

I haven't read any papers to confirm or deny, this is just gut feeling.

The next thing is, every tire is loaded differently, and the best slip angle may be different for different loadings, so why should the tires all be assuming the same slip angle for a theoretical arc? (This is one of the strongest arguments I'd heard *against* having perfect Ackerman geometry)

---

Pete Remner
Cleveland, Ohio

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

Quote
Pete
Do you mean the slip angle relative to the road or the slip angle relative to the ground that is constantly rolling out from underneath the car?

Big difference in spirit but I've a strong suspicion that the best effective slip angle, "best" meaning highest lateral grip, and "slip angle" meaning the tire relative to what the tire is contacting, is the same for asphalt and gravel and dirt. The difference is, gravel and dirt are constantly rolling out from under the tire so the car has a greater angle of attack.

I haven't read any papers to confirm or deny, this is just gut feeling.

That's an interesting point actually. There is a ton of info out there on slip angles and slip ratios within the traction circle, but traveling beyond the traction circle is not examined nearly as in depth. I know that lateral load being generated by the tire drops off gradually as slip angle increases beyond max FY, but comparing it to the loss of road surface is something that I haven't found much on.

Quote
Pete
The next thing is, every tire is loaded differently, and the best slip angle may be different for different loadings, so why should the tires all be assuming the same slip angle for a theoretical arc? (This is one of the strongest arguments I'd heard *against* having perfect Ackerman geometry)

This is 100% accurate. The amount of lateral load the tire is able to produce per unit slip angle changes based on tire pressure, temperature, inclination, normal force acting on it, etc. Though when limitations prevent the use many data acquisition gadgets, assumptions and approximations can be made. Back of the napkin math on slip angles and tire performance if you will.

By the way, I'm recently relocated to the state of Ohio. Working in Columbus. Are you going to be rallycrossing your RX7 with OVR this year? I'm working on getting mine up and running and hope to be pitting it against you. We should meet up sometime and talk about dirt, beer, and silly spinning triangle things sometime.

---

"The more I learn, the more I realize I don't know and have so much more to learn." - Claude Rouelle, Optimum G lecture June, 2011

a



Edited 1 time(s). Last edit at 02/05/2014 08:19AM by Iowa999.

Quote
MeCalledEvan
Sure outdated and focusing on tarmac racing, but some key aspects to a winning "formula" are overarching between on and off-circuit racing. You said so yourself when you brought up slip angles(for one example)-

Quote
modernbeat
Serious. Yes. In rally. Not all cars or drivers take average corners at 45 degrees, or 180 degrees like crazy rally videos. I doubt most take them at 15 degrees. And is sliding though at 45 degrees really the fast way in a FWD or AWD car?

You do have a point for looking at the big picture and figuring out how to achieve it.

John, often times useful information can be found in the land of Fappery. You've been in this scene for a while, and are a walking encyclopedia of rally-related information and experience. Care to shed some light?
P.S. I know you're not a fan of CAD, so let's leave that aspect out of this for now.

Yes I agree but I always stress ----more lately as I understand more about my rather well developed Doaist and Chan Buddhist leanings that that which brings us closer to what we want to do is good--and I say for 99.9999% of us ---me included---that the GOAL is the have this overwhelming transcendent experience which in the West is sometimes called "being in the zone" which we interpret as "FUN!"...

In Buddhism they have this thing I have been posting called "The Noble 8 Fold Path" which is nicely broken down here---nicely because in discussion we often are talking about "everything all at once and not keeping clear the differences between "who, what, when, where, how---and why"


When they talk of "right" its natural to ask "what is right? How do I know I am on the right path?"
And they say "That which brings you nearer to you goal is the right path, and that which takes you away is not"

So if I believe that the goal is this "sudden enlightenment" we may experience when we're "in da zone, doood"-- then maybe spending hundreds of dollars on some books about tube frame cars with fully adjustable suspension parameters and poring over them for months to the point you think you understand ........we'll maybe there might be some interesting junk-n-stuff but we don't drive cars with complete design freedom and fully adjustable suspension parameters... so it seem to me this is taking us away from our goal--of self enlightenment....

Paulinho might agree that starting narrower, ie looking at one REAL example of a car that we know works REAL GOOD---, then looking at THAT examining what is known to work, then looking at what we actually HAVE might help us see similarities and differences and then we might see how those similarities and differences affect how 'your' car works....
I hope he does, that's I believe called "empirical" reasoning..
Don't know if you're into all this philosophical brou ha ha (hey I'm old you get philosphical when you're old, m'kay?) but here's what wiki says:

Quote

Empirical evidence (also empirical data, sense experience, empirical knowledge, or the a posteriori) is a source of knowledge acquired by means of observation or experimentation.[1] Empirical evidence is information that justifies a belief in the truth or falsity of an empirical claim. In the empiricist view, one can only claim to have knowledge when one has a true belief based on empirical evidence. This stands in contrast to the rationalist view under which reason or reflection alone is considered to be evidence for the truth or falsity of some propositions.[2] The senses are the primary source of empirical evidence. Although other sources of evidence, such as memory, and the testimony of others ultimately trace back to some sensory experience, they are considered to be secondary, or indirect.[2]

Regarding CAD, well I absolutely heart the results as much as I don't lurv the process and slap my forehead in best Jewish Mama form when kids think they need some super spiffy graphix or a movie provided to them or they can't even try to understand something.. I can make a simple sketch and I know the drawing---like words---are referring to a "thing" something in the real word so the drawing can be rather cursory---because it is the thing and the "concept" that is primary...
But if a person doesn't know the point of the drawing is to refer to something, then they need pretty drawings or videos..
In fact my dear friend Kevin Hawkinson and I sat down and did a whole series of dimesnsion notes both underneath and inside of a 240 Volvo so he could bang out a beautiful CAD model so we could see---directly experience---the motions of the rear axle, links and so tweak the 4 link boxes (made them tapering) and the shock towers BEFORE chacking away with tools..And it went boing boing, it was definitely a Soooper Bitchin model..

So I believe it actually can help and as Paulinho said maybe help is see simple things we have the means to pull off--and predict beforehand improvements--and that give foundation for judging if the effort is RIGHT--as in bringing us nearer 'enlightenment' we get when we're driving down a gravel road laughing our heads off.

Hope this is clear.. It is, but I hope people can follow.

---

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.

little



Edited 4 time(s). Last edit at 02/05/2014 08:20AM by Iowa999.

Quote
john vanlandingham
Hope this is clear.. It is, but I hope people can follow.

Definitely. That was great. I like it.

So back to talking about sproingy things and geometries? I also would like getting more input from people who have done more racing on gravel than I have.

---

"The more I learn, the more I realize I don't know and have so much more to learn." - Claude Rouelle, Optimum G lecture June, 2011

Quote
Iowa999
Ignoring your spelling of Taoist, I got this funny image of Lao Tse, before riding off into the sunset on his water buffalo (or whatever), being asked by the gatekeeper for a model of his buffalo's legs, rather than a book of his own wisdom. Better yet, the gatekeeper suggesting that having his buffalo squat down a little would increase his anti-dive geometry.

But keep in mind that I sometimes cough really hard after lunch and this can release chemicals better left stored in globs of phlegm for some other time.

[wow ... it's typo day or what?]

I spell it Gung fu and Guomindang (the bad guys)
And as for my ol buddy Lao Tzu and his sidekick is it 莊子 Zhuangzi
莊周 Zhuang Zhou?

I'm afraid there are no 'one way" answers to transliteration of even common and easy Putonghua words, much less stuff 2300 years old, and since my foot in the door is 粵語/粤语 which you might call 'Cantonese' and there we see consistant t/d changes which don't mean diddly. or tiddly.

---

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.