Ralphy - camber thrust is one thing but not really a component of steering induced by suspension geometry relative to body roll.

Rear suspensions are often designed to induce a certain steering effect with body roll.  For instance, a semi-elliptic leafspring suspension will typically have the springs mounted such that the axle moves forward under bump, which in a corner causes the outside wheel to steer into the turn producing roll understeer.

...Hence the need for a simplified explanation.

Wow.  That looks like of of my engineering books from college.  If I have another nightmare about missing my final exam, it's all your fault!

Characteristic                           how to address                                           comments

Body role                                   Sway bar                                                 
                                                      rigged mounting of sub frame           
                                                      Poley bushings instead of rubber   

Squat                                           build it in linearly                                   
                                                      Built in reaction                                     

Rear Steer                                 adjustable reactive toe                         

Wheel hop                                  upper watts link

Roll steer

Lateral stability                        rigged mounting of differential

Control arm stability               trailing arm                                                       doesn’t need to be watts to get the job done

Hub torque                               trailing arm and upper watts

I had levels of importance but I removed them because it all depends on what a person is trying to do.  What my be of a high level of importance for one application may not matter on another.

OK, so here is my $64 question. If you build a suspension with toe-steer, Can you alter rear toe and camber settings to zero? What I have seen, typical IRS settings include negative camber and toe-in. If you were able to compensate the negative effects in cornering with toe-steer, allowing the rear wheels to track dead straight and flat would increase speed performance in straight line driving, no?

Duane where are you! LOL!

I have been reading on roll-steer, I think some confusion has been posted by many at other sites. The best way I think to explain what I comprehend is. If you took a chassis steering in a straight line it would steer straight. Now add 500lbs. to the right rear. What this does is cone the right rear tire, smaller to the out side. This cone shape will want too make the right rear tire track right, outward. In turn the rear would go right and the chassis would go left causing over-steer.

Being that most cars have a double wishbone in front and a solid axle in the rear. The front can be tuned to remove roll-steer but the rear cannot. The solid axle can be moved fore and aft to compensate however removing this coning of the loaded tire can't be improved. An IRS does camber so the effect would be less than a solid axle chassis no mater.

Last edited by Ralphy (11/15/2011 8:43 am)

hey 37ford I like the revised spread sheet much better "area of importance" is much better than level of importance.  Couple things I would change. first  make an "area of  importance" for each "how to address" solution. 

second change up the classifications  of "area of importance"  and define them:

Driver-Cruiser                 Daily driver or other application where Ride quality is the primary goal
Street-Track                    Driven regularly and ride quality is important but not to the exclusion of performance
Track-Autocross            Only sees race time handling is paramount ride quality is irrelevant

third I would add another category, "should be avoid for this application"

Example:

Body role                Sway bar                                                     Driver-Cruiser/Street-Track/Track-Autocross            N/A   
                                   rigged mounting of sub frame               Track-Autocross                                                                       Driver-Cruiser/Street-Track         
                                   Polly bushings instead of rubber        Street-Track/Track-Autocross                                           Driver-Cruiser


As to the "squat solutions"  there are really only 3 ways to do it:
1.  build in linear squat.  angle the movement of the suspension so that as the suspension travels up it also travels back slightly.
2. run an IRS system EXACTLY as designed and utilize any anti-squat built in to the system.  In some cases its linear and some cases it is reactive.  for instance the newer Jag units are set up with the wishbnes angled slightly to create linear squat, but on the older Jag set up the bushings on the cage and the position of the trailing arms were designed to induce a little squat during suspension compression.
3.  Design a squat inducing link (similar to what Jag did) problem here is to do that you either need TONS of trial and error, a degree in engineering, modeling software so you can put it all in to a computer to see exactly what is happening, or better yet ALL three.  Option three is out of my league but may be an option for some.

OK, I got an answer from Stroker427, he built his own toe-steer IRS. His car is pictured here, here are his thoughts on toe-steer from experience. Stroker is in Italy.

I "totally agree with Pappy!
Rear bump steer can be very usefull is specific conditions... even at the beginning or at the end of the corner.... but is very critical to be adjusted.
Furthermore any different track or condition needs a specific design.

For example I did a test with my car setting a good quantity of bump toe-in and rebound toe-out. This was helping a lot in a very tight autocross.... braking the toe-out helps the insetion in the corner and toe-in during acceleretion coming out from the corner was avoiding oversteer.

Anyway was very difficult to set the proper amount of toe changing.

A neutral condition is the best compromize for predictability!"

Stroker (Pier) havin a little fun.
http://www.youtube.com/watch?v=LX6JvEyT__Q&feature=player_embedded

Last edited by Ralphy (11/15/2011 5:58 pm)

I realized there were a couple more things I wanted to add, and deleted it.  Then, I couldn't get it to repost.

About the *,  I added a "level of difficulty" column to hopfully serve as a way to distingush the "How to address" options so that, if it's your desire, you can pick the easiest options to accomplish your area of importance.  Of course, level of difficulty will vary from vehicle to vehicle and IRS to IRS, but I think we can ballpark it.


Still unsure if a lower watts link can be considered an effective wheel hop solution.

Spreadsheet sent.

We should be careful trying to create all these masterful spreasheets.  We might just eliminate the need for the forum.

No, I'm all for making another.  How do you want to approach it?  Would these be "feature preferences"?

Here's how I look at the process:

1. Deciding to use an IRS.
2. Deciding your area of importance.
3. Deciding how you want to address the problem characteristics that match your area.
4. Determining what additional measures you want to take to make it perfect for you.

The last step would include things deciding where to place the brakes.  Would you rather hae the ease of maintenance or reduced unsprung weight for perfomance?  It would also inclide any further upgrades like lightening the half shafts, bushing choices, beefing up the LCAs, etc.

Does this sound like a locigal approach?  Is this anything like what you are thinking?

The latest -

Let me know if there is something you disagree with or something I need to add.