Advanced Suspension Geometry and Design

This is a topic that is rarely discussed but should be at least fairly understood.

Lets have a discussion and see if we can compile some good information on theories of suspension geometries and design. What works best for a FWD or for a RWD car.

We all know the basic Caster, Camber, and Steering Axis Inclination type stuff, BUT as the title says, lets talk more advanced stuff, like things engineers spend time testing for and makes a car totally different. Lets talk design features like Anti dive, pro dive, anti squat, pro squat, or the effects of raising the Instant Center closer to the CG to reduce roll.

All of these are taken into account when proper development is put into a car, for example the Fiesta R2's they handle so well why? Its not just the Reiger dampers, I'm sure the Msport control arm bushes are offset to reduce anti dive in the front. Fixed bumpsteer? What else would they have done to put the power down.

SO with all of this in mind, if someone was to completely change their suspension what design features and why?

Examples:

Lets just say that a Civic gokart like suspension was to be changed from dual control arm setup to front struts and something swing arm like in the rear.

Or converting a RWD car to a proper 4 link setup and adding compression or tension struts to the front TCA's. Must put the power down and lift the inside wheel off the ground in tight corners.

Lets drink some beer over this.

i have some questions then related to my Rx-7 project. Using the picture as reference (my daily driver) which i should note is the same as my rally car in setup.


Can i have too much caster? To where the motion of the damper is effected. Can the motion be adjusted by change the angle at which the control arm sits?

Also, any good reads on bumpsteer and what it is exactly?

---

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

The real question you want to ask is what slip angle the car will be in during the average corner and what driving technique should be used to quickly change that slip angle.

Or go back a little further and start with an existing chassis and ask "what will it not do like I want it to do" and start improving from there.

---

Jason McDaniel

Paulino, good topic--always ignored..
Now you know I'm a compare and contrast type guy usually saying "this works good on this, howzit same or different from zat thing there"

Problem is we have very little ANYTHING to start the modelling from..
Now if we had lotsa data and could begin doing some simple CAD models some things might jump out at us immediately..

Alas we don't but this could become a multi-year epic thread like "OH the Next Big Thing that's Going Save Rally"

So who do we know that WILL---not can, but will make some simple drawings?

---

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.

Quote
modernbeat
The real question you want to ask is what slip angle the car will be in during the average corner and what driving technique should be used to quickly change that slip angle.

Or go back a little further and start with an existing chassis and ask "what will it not do like I want it to do" and start improving from there.

You know we're talking rally right? Slip angles on an average corner in rally? Lets keep this real and to the point. And the driving technique is flatout!

Quote
Cosworth

Quote
modernbeat
The real question you want to ask is what slip angle the car will be in during the average corner and what driving technique should be used to quickly change that slip angle.

Or go back a little further and start with an existing chassis and ask "what will it not do like I want it to do" and start improving from there.

You know we're talking rally right? Slip angles on an average corner in rally? Lets keep this real and to the point. And the driving technique is flatout!

Hardware, mm and degrees, right?
Plus Juan.

---

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.

Quote
john vanlandingham
Paulino, good topic--always ignored..
Now you know I'm a compare and contrast type guy usually saying "this works good on this, howzit same or different from zat thing there"

Problem is we have very little ANYTHING to start the modelling from..
Now if we had lotsa data and could begin doing some simple CAD models some things might jump out at us immediately..

Alas we don't but this could become a multi-year epic thread like "OH the Next Big Thing that's Going Save Rally"

So who do we know that WILL---not can, but will make some simple drawings?

John, no need to get all that complicated. We both started from the times where CAD was a series of strings on a board using thumb tacks and a protractor to measure the angles. Or we can just make a regular paint drawings, we dont need to build a car from scratch here just talking theory. But to apply these geometry changes it would be even simpler than that, just use a level a measure the angle on the current suspension setups and maybe modify from there. For example shimming the mounts or re-drilling the bolt hole for control arms, just enough to adjust the geometries.

Remember back in Group A, rules only allowed mounting points to be changed by a max of 20mm. So if 20mm(.810) was enough to make those cars behave night and day differently it will be enough for us mortals.



Edited 1 time(s). Last edit at 01/30/2014 08:39PM by Cosworth.

Quote
Cosworth

Quote
modernbeat
The real question you want to ask is what slip angle the car will be in during the average corner and what driving technique should be used to quickly change that slip angle.

Or go back a little further and start with an existing chassis and ask "what will it not do like I want it to do" and start improving from there.

You know we're talking rally right? Slip angles on an average corner in rally? Lets keep this real and to the point. And the driving technique is flatout!

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?

And FWIW, this is what I do at my day job.

---

Jason McDaniel

Quote
Cosworth

Quote
john vanlandingham
Paulino, good topic--always ignored..
Now you know I'm a compare and contrast type guy usually saying "this works good on this, howzit same or different from zat thing there"

Problem is we have very little ANYTHING to start the modelling from..
Now if we had lotsa data and could begin doing some simple CAD models some things might jump out at us immediately..

Alas we don't but this could become a multi-year epic thread like "OH the Next Big Thing that's Going Save Rally"

So who do we know that WILL---not can, but will make some simple drawings?

John, no need to get all that complicated. We both started from the times where CAD was a series of strings on a board using thumb tacks and a protractor to measure the angles. Or we can just make a regular paint drawings, we dont need to build a car from scratch here just talking theory. But to apply these geometry changes it would be even simpler than that, just use a level a measure the angle on the current suspension setups and maybe modify from there. For example shimming the mounts or re-drilling the bolt hole for control arms, just enough to adjust the geometries.

Remember back in Group A, rules only allowed mounting points to be changed by a max of 20mm. So if 20mm(.810) was enough to make those cars behave night and day differently it will be enough for us mortals.

CAD: Cardboard And Drawing...
Was it +-20? I thought it was 15 but long time. And not relevant here since nobody ever knew anything about Group A...

Well really the reason I thought of it is so many kids now probably will have their eyes roll up and fall into a coma like state if the drawing isn't interactive and beautiful, and preferably some big gasoline explosions, ya know?

---

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.

Quote
Gravity Fed
Also, any good reads on bumpsteer and what it is exactly?

Yes plenty of reads on it. Bumpsteer is the change in toe with suspension travel. There's also roll steer. Similar syndrome. Lots of good illustrations.

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?

And FWIW, this is what I do at my day job.

In that case quit being a joker and give straight answers. BUT only if you know what you're talking about. Like a few others on here, we also pay the mortgage from working in the racing industry. So talking about slip angles is not what we're asking here. And wouldn't the slip angle change depending on speed, CG, centre of rotation, tyre construction, and most important drive style? Lets keep it on subject eh... Geometries.



Edited 1 time(s). Last edit at 01/30/2014 10:53PM by Cosworth.

Quote
john vanlandingham
CAD: Cardboard And Drawing...
Was it +-20? I thought it was 15 but long time. And not relevant here since nobody ever knew anything about Group A...

Well really the reason I thought of it is so many kids now probably will have their eyes roll up and fall into a coma like state if the drawing isn't interactive and beautiful, and preferably some big gasoline explosions, ya know?

The allowed stuff was:
Full suspension geometry and layout. The original mounting points must be preserved within a 20mm radius

Quote
Cosworth

Quote
john vanlandingham
CAD: Cardboard And Drawing...
Was it +-20? I thought it was 15 but long time. And not relevant here since nobody ever knew anything about Group A...

Well really the reason I thought of it is so many kids now probably will have their eyes roll up and fall into a coma like state if the drawing isn't interactive and beautiful, and preferably some big gasoline explosions, ya know?

The allowed stuff was:
Full suspension geometry and layout. The original mounting points must be preserved within a 20mm radius

Yeah and pretty amazing what guys could drive with that limit.

Alex bump---or droop steer is when the arc thesay balljoint does is different than the arc the tie rod end does so the one pushes the other and the knuckle toes in or out when the suspension moves up and or down.
I find droop a pain.

---

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.

i need to measure and make angles for the 7 and report back

---

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

Quote
Cosworth
In that case quit being a joker and give straight answers. BUT only if you know what you're talking about. Like a few others on here, we also pay the mortgage from working in the racing industry. So talking about slip angles is not what we're asking here. And wouldn't the slip angle change depending on speed, CG, centre of rotation, tyre construction, and most important drive style? Lets keep it on subject eh... Geometries.

I am keeping it on subject.

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.

---

Jason McDaniel

How does one determine slip angle without investing in additional sensors and gps?