Rear roll center question

[SSLance]

Nice work Rob... **polite golf clap** :D

Appreciate the time you put in to make the illustrations, it really helps.

[Peter Mc Mahon]

I like where you’re going with this! How would you offset the front roll center? Just built right in from the original design?

[cornfedbill]

I like where you’re going with this! How would you offset the front roll center? Just built right in from the original design?

Yes, it would need to be built into the front suspension. Circle track chassis builders do it all the time. Often they use different height spindles right and left.

It seems to be interesting in theory for a road course, street or autocross car. I'm not sure I would be gutsy enough to try it except in a left-turn-only car.

[j-rho]

Wait, so it's safe to come back in the water?

An accessible entry-level text I really like is Herb Adams' Chassis Engineering- https://www.amazon.com/Chassis-Engin...7548882&sr=8-1

To me, the most important concept in understanding handling is tire load sensitivity, and Herb's book got it to "click" for me. Once you've grokked that, and have developed the driving and testing chops to know how tune a car to make it handle better, the rest kinda falls in to place. There are other entry-level books that explain these things (a lot like the Fred Puhn book), then the more advanced texts like Milliken. Even when everybody has the purest intentions, forums maybe aren't the best way to learn the basics.

To the OP's thoughts - the way I think about it, is each wheel can move in six possible directions (some call these "degrees of freedom") - up/down, forwards/backwards, in/out. We want to allow for the up/down but not the other four. If you had a live rear with nothing to constrain it laterally, when you turned into a corner, the front of the car would turn but the rear axle would keep going straight, which is an undesired outcome.

In suspension geometry, most of the stuff that constrains wheels can be looked at as circles, where the center of the circle is where the thing mounts to the chassis, and the point on the circle, where the arm/link connects to the axle/knuckle/whatever. In allowing for the up/down motion of the wheel/tire, since you're dealing with circles, it's tough to make the path perfectly up/down, and it's not always what you want (e.g. camber gain).

It can be neat to examine the forces going through all these links under various dynamic conditions (trail braking-on entry, powering at corner exit, etc.) to see how changing the geometric relationships would affect how loads/forces get distributed and moved around. It all comes back to tire load sensitivity. In general nobody's paper design is perfect in practice without real-world testing and iteration. So it's best to design in adjustability so you can tune things like anti-squat later, just as you'd tune spring rates, sway bars, shock settings, tire pressures, etc.

p.s. I'm flattered to be thought of as in the same league as Norm Peterson - he knows way more than I do!

[cornfedbill]

Wait, so it's safe to come back in the water?

An accessible entry-level text I really like is Herb Adams' Chassis Engineering- https://www.amazon.com/Chassis-Engin...7548882&sr=8-1

Yes, a very good book.

[dontlifttoshift]

Wait, so it's safe to come back in the water?
......bunch of stuff.....!

Good to see you back posting.

[raustinss]

I'd say this is a Ron Sutton question.....but anyone with half a clue knows what hes up to right now lmfao in a sad way

[Peter Mc Mahon]

Wait, so it's safe to come back in the water?

An accessible entry-level text I really like is Herb Adams' Chassis Engineering- https://www.amazon.com/Chassis-Engin...7548882&sr=8-1

To me, the most important concept in understanding handling is tire load sensitivity, and Herb's book got it to "click" for me. Once you've grokked that, and have developed the driving and testing chops to know how tune a car to make it handle better, the rest kinda falls in to place. There are other entry-level books that explain these things (a lot like the Fred Puhn book), then the more advanced texts like Milliken. Even when everybody has the purest intentions, forums maybe aren't the best way to learn the basics.

To the OP's thoughts - the way I think about it, is each wheel can move in six possible directions (some call these "degrees of freedom") - up/down, forwards/backwards, in/out. We want to allow for the up/down but not the other four. If you had a live rear with nothing to constrain it laterally, when you turned into a corner, the front of the car would turn but the rear axle would keep going straight, which is an undesired outcome.

In suspension geometry, most of the stuff that constrains wheels can be looked at as circles, where the center of the circle is where the thing mounts to the chassis, and the point on the circle, where the arm/link connects to the axle/knuckle/whatever. In allowing for the up/down motion of the wheel/tire, since you're dealing with circles, it's tough to make the path perfectly up/down, and it's not always what you want (e.g. camber gain).



It can be neat to examine the forces going through all these links under various dynamic conditions (trail braking-on entry, powering at corner exit, etc.) to see how changing the geometric relationships would affect how loads/forces get distributed and moved around. It all comes back to tire load sensitivity. In general nobody's paper design is perfect in practice without real-world testing and iteration. So it's best to design in adjustability so you can tune things like anti-squat later, just as you'd tune spring rates, sway bars, shock settings, tire pressures, etc.

p.s. I'm flattered to be thought of as in the same league as Norm Peterson - he knows way more than I do!

Does that book have a picture of the way to measure the rear roll center showing the geometry behind it?
Jaws is my favourite movie!