Suspension design for Locost with Vsusp

[horizenjob]

This thread is for folks to work on suspension designs for their Locost or Seven style car.The design data can be shared using links to the Vsusp web page which puts all the data in the link.

Please make your links readable with a description. You can use http://tinyurl.com for this.

It is also a big help to name your project and provide a version number on the first dialog box in Vsusp. THis goes into the URL data. Otherwise it's just a pile of numbers and can't be distinguished from any other Vsusp drawing. If you change a diagram add your initials or something.

Thanks to Rob7 for creating this tool and thanks to SkinnyG and anyone else providing data from their car.

As time goes on I will try to provide a table of contents here to help make this information more available.

SkinnyG's more Lethalerer Seven: (changed to include the project name)
Lotus S2, Chevette front spindles, Toyota Corolla GT-5 rear narrowed 2 inches
http://tinyurl.com/SkinnyGLethalerer2V01

OptimusGlen's with Volvo front spindles
http://tinyurl.com/OptimusGlenVolvoV07

CheapRacer's Lotus Elan
modified to Locost track width (Front only)
http://tinyurl.com/CheapRacerLotusElanStyleV04

[SkinnyG]

Playing with Lethal Locost #2

Lotus S2 chassis
Chevette spindles
Corolla GT-S track width narrowed 2"
6" ground clearance (to clear Duratec oil pan)
Low front roll center is a priority - Lethal Locost #1 didn't turn in so well without it

I like how the RC moves inside on turns - reduces jacking.

Rear suspension is not done - I'm running a Solid Axle.

http://tinyurl.com/8sepshh

[horizenjob]

I played a bit with these numbers, so thank you for posting them SkinnyG. Also thanks for the perspective on turn-in and your roll center.

Your setup may be showing the issues with stock geometry spindles and the high lower wishbone they tend to use. Here is a small change to produce more camber correction in roll, the upper pivot point is dropped by 1.2". Now when the car rolls 2 degrees the outer wheel has 0 degrees of camber instead of 0.6 degrees positive. The roll center has jumped to 4" though, a dramatic change.

I'm not recommending these changes so much as trying to discuss what's going on. Does your front suspension have Ackermann and/or toe-out? Also could you bolt a spacer to the bottom of your Chevette spindle to lower the lower wishbone?

http://tinyurl.com/Lethalator

[horizenjob]

I like how the RC moves inside on turns - reduces jacking.

I am not completely comfortable really using the roll center numbers because I am not sure what they really are saying. In particular I am dis regarding the horizontal location information. I do look at the angle of the line of force from the contact patch to the instant center. I think that's a direct indication of the jacking forces. The roll center stuff produces results that are not sensible in some cases, so the fact that they are sometimes sensible does not really make up for this...

Actually I think it would be nice if Vsusp could plot that angle. Either directly or as a percent of cornering force showing up as jacking. Does that make sense?

[horizenjob]

SkinnyG, I'm running some more numbers here is some progress. I am trying to get more camber correction and also a low RC.

In this case the lower wishbone inner pivot has been dropped from 1.8" to 1". This is in addition to the change above. This slightly lowers the roll center by about 1/4" and it improves the camber correction with 2 degrees of roll from 0.4 degrees to 0.9 degrees.

http://tinyurl.com/Lethalator-V-001

Do folks mind if I create a thread for suspension discussion using Vsusp and move this discussion there? Then we can discuss Vsusp here and suspension design using Vsusp in the new thread. That should help Rob keep track of our feedback better.

[SkinnyG]

The lower a-arm inner pivots are kind of stuck on the Lotus chassis - I can't easily move them.

The high-mountedness of the lower arms is not a problem, because there will be QUITE A BIT of the Duratec hanging below the S2 chassis - I need the ground clearance.

I can change the inner pivot of the upper arms to anything.

I autocrossed Lethal1 for a couple years (and still do off and on), and tried all manner of things to make it turn. Dropping the front roll center to the ground (well, as low as I could go - it looks like it's on the ground) made a significant difference. A contributing issue may have been a very low panhard in the rear (sits even with chassis bottom). However, it is ~very~easy~ to drive at the limit.

Lethal2 will get the steering rack moved closer to axle center to try and get some dynamic Ackerman. At a full-lock turning circle, Lethal1 "scrubs" or "walks" like an old Chevy Blazer (short wheel base truck with long wheelbase knuckles).

I'm more than happy to have y'all play with my setup. It would be interesting to see what "the collective" can do with it.

[SkinnyG]

Aggressive angle geometry of Lethal1:

[SkinnyG]

Caterham R500 w/Duratec:

[horizenjob]

SkinnyG do you have any numbers on that R500? I downloaded a very detailed 3D model but it didn't seem to be correct for things like suspension pickup points.

[SkinnyG]

I do not have any (x,y,z) placement numbers, only alleged alignment specs.

Pouring over every photograph I can find, the control arms appear to be close to parallel. This gives a nice low roll center, but probably compromises camber curve.

[L8 apexr]

Arms may be close to parallel but as long as the upper is shorter you'll still get the camber gain,if its stiff enough to resist much roll than camber gain isn't all that critical I'm guessing.Look at how much static camber the F1 guys run,you'd think that would be comprimising braking grip but they have some very clever dudes finding the fastest way around so.....
In other words,perhaps simply running more static camber once up and running will be just fine compared to stressing over what camber curve to go with.

[SkinnyG]

Maximizing the roll center location is a greater priority to me than maximizing camber gain. You can have all the optimizing of camber curve that you want, but if it doesn't turn in properly....

In everything, there is compromise. And ultimately it will be dictated by packaging.

[L8 apexr]

Thats kinda what I was getting at,but reading it now I think I failed to convey it.Shifting the priority to roll center location/stabilization over camber gain makes sense to me but for sure take that with a grain of salt.

[horizenjob]

I think you should have it all. I wouldn't give up without a fight anyway. AutoX requires a car that can change direction quickly and also turn tightly. So Ackermann would help more then it would on a big oval. I find toe out helps my car turn in, but that's on a road course and you need even more turn in. Still I would try a little over 1/8" toe out.

The roll center affects weight transfer as soon as the car generates sideways force, before it starts to roll and the anti-roll bars come into play.

Can you mount the lower wishbone under the chassis or is that impossible or too unlike a Lotus?

[SkinnyG]

Because I am trying to appear as "original" as possible on #2, I am bound by packaging.

I tried toe out from 1/16" all the way up to 3/4" and it did not help turn-in. Toe helps "fake" a bit more Ackerman.

I tried raising the rear, but just ended up with a bunch of pre-load (also not good).

I ended up progressively dropping the front lower and lower and lower until it felt right. Had to relocate the lower shock mounts because I ran out of travel.