Front suspension design input needed

[358Mustang]

I just don't know what baseline numbers to shoot for, camber gain, roll center height etc.

[Ron Sutton]

Originally Posted by 358Mustang

I just don't know what baseline numbers to shoot for, camber gain, roll center height etc.

Gotcha.

Have you decided if you're going the conventional suspension strategy route with low front travel & high roll angle (stiff springs & moderate sway bar) or to the modern high front travel & low roll angle strategy (soft springs & big bars)?

I ask because the optimum roll centers are very different.

Brian, if you have an idea of what you're going to do spring & bar wise, share that, and that will help clarify things. Thanx !

[358Mustang]

Originally Posted by Ron Sutton

Gotcha.

Have you decided if you're going the conventional suspension strategy route with low front travel & high roll angle (stiff springs & moderate sway bar) or to the modern high front travel & low roll angle strategy (soft springs & big bars)?

I ask because the optimum roll centers are very different.

Brian, if you have an idea of what you're going to do spring & bar wise, share that, and that will help clarify things. Thanx !

So in order to couple with the rear setup I have got.. I am running a home made 3 link in the rear, roll center is about 8". coilover shock behind the axle, with a 300# spring. It needs more roll stiffness in the rear I feel, maybe due to the angle I have my shocks kicked in at... So my plan was to add a rear sway bar to that.

I just mention the rear because obviously I need them to work together. I am thinking I probly want to go with a little stiffer of a spring up front to limit front travel. I am trying to get the CG down and planned on having the motor fairly low. SO I guess that would fall towards the stiffer spring, softer bar category unless you can say why the other way is better..

I am unsure exactly on spring rate, I would thinkg of starting in the 450-500# range... Coilover mounted as far towards the tire as I can within reason

[Mike Maier]

Ok' I'm gonna through my two cents in. Long as you can on the lower arms. This is dictated by the width of the steering / center link you are using. upper arms will be as long as possible while still achieving the camber gain you are striving for. Roughly .7 pr. inch will be pretty good. Roll center should be lower than 2", no lower than groundish. Yes I said groundish. Your front springs combo's look good but the rear is too low. Do not confuse spring with bar, two different tools.

Just saying

[358Mustang]

Originally Posted by Mike Maier

Ok' I'm gonna through my two cents in. Long as you can on the lower arms. This is dictated by the width of the steering / center link you are using.

So the rack I am using, the tie rod mount points are 18" center to center, so I would want my lowers to mount close to or on the same horizontal spacing as that to minimize bump steer, right?


upper arms will be as long as possible while still achieving the camber gain you are striving for. Roughly .7 pr. inch will be pretty good. Roll center should be lower than 2", no lower than groundish. Yes I said groundish. Your front springs combo's look good but the rear is too low.

When I was talking about bar, I was thinking about adding a rear sway bar.. I got to the point where I was un sure if I should keep adding spring (coil spring) rate, or add a sway bar to help control roll.

Do not confuse spring with bar, two different tools.


Just saying


Thanks for the input Mike.

.....

[Ron Sutton]

Originally Posted by 358Mustang

So in order to couple with the rear setup I have got.. I am running a home made 3 link in the rear, roll center is about 8". coilover shock behind the axle, with a 300# spring. It needs more roll stiffness in the rear I feel, maybe due to the angle I have my shocks kicked in at... So my plan was to add a rear sway bar to that.

I just mention the rear because obviously I need them to work together. I am thinking I probly want to go with a little stiffer of a spring up front to limit front travel. I am trying to get the CG down and planned on having the motor fairly low. SO I guess that would fall towards the stiffer spring, softer bar category unless you can say why the other way is better..

I am unsure exactly on spring rate, I would thinkg of starting in the 450-500# range... Coilover mounted as far towards the tire as I can within reason

Gotcha. You're going the conventional route.
Based on what you said, it looks like you're looking to travel the front end in the 3/4" to 1-1/2" range (at the crossmember). I should have asked this earlier ... will you be autocrossing, running track days at full size road courses or both?

Regardless, for a low travel/high roll suspension set up …
• If your priority is autocross or the low speed corners of road courses, your target RC should be around 1” in full dive.
• If your priority is the mid-speed corners of road courses, your target RC should be between 1.5” to 2.5” in full dive.
• Of course, you can set it for anything in-between.
• The higher the RC is within the range 1” to 2.5” favors the mid-range corners. Lower favors the low speed corners.
• If optimum lap times matter to you, the answer of what is the optimum roll center will come through testing.
• If you're not that hardcore & just want to have fun running the track hard & fast, pick what makes sense to you & go run it.

P.S. I concur with Mike's tips above. He & I both favor high travel/low roll set-ups, so that influences our designs & geometry settings, including lower roll centers ... and long control arms which tame the geometry changes. The farther you travel the front suspension ... the more the longer control arms help.

I attached an illustration of my Track-Star front suspension which we travel in the 4" to 4.5" range at the crossmember (more at the outer front wheel). I design these custom for each client's particular car, but the LCA's end up in the 23" to 25.5" range & UCA's in the 11.75" to 13" range. This allows us to travel the front end that 4-4.5" and have the optimum geometry throughout the travel.

If you're traveling the front end only a little, then control arm length is less of an issue.

[Ron in SoCal]

^ Secret Sauce.

[358Mustang]

Originally Posted by Ron Sutton

Gotcha. You're going the conventional route.
Based on what you said, it looks like you're looking to travel the front end in the 3/4" to 1-1/2" range (at the crossmember). I should have asked this earlier ... will you be autocrossing, running track days at full size road courses or both?

Regardless, for a low travel/high roll suspension set up …
• If your priority is autocross or the low speed corners of road courses, your target RC should be around 1” in full dive.
• If your priority is the mid-speed corners of road courses, your target RC should be between 1.5” to 2.5” in full dive.
• Of course, you can set it for anything in-between.
• The higher the RC is within the range 1” to 2.5” favors the mid-range corners. Lower favors the low speed corners.
• If optimum lap times matter to you, the answer of what is the optimum roll center will come through testing.
• If you're not that hardcore & just want to have fun running the track hard & fast, pick what makes sense to you & go run it.

P.S. I concur with Mike's tips above. He & I both favor high travel/low roll set-ups, so that influences our designs & geometry settings, including lower roll centers ... and long control arms which tame the geometry changes. The farther you travel the front suspension ... the more the longer control arms help.

I attached an illustration of my Track-Star front suspension which we travel in the 4" to 4.5" range at the crossmember (more at the outer front wheel). I design these custom for each client's particular car, but the LCA's end up in the 23" to 25.5" range & UCA's in the 11.75" to 13" range. This allows us to travel the front end that 4-4.5" and have the optimum geometry throughout the travel.

If you're traveling the front end only a little, then control arm length is less of an issue.

Thanks a lot for the diagram of your suspension. That helps me a lot to visualize things... This is a strict road race car, that I am trying to build it to be as fast as possible (isn't that the point? )

Here is a picture of my car and what I have mocked up, which is basically an engine and the start of some frame work, so like I have said I more or less have a clean sheet. I wanted to go with high backspace wheels to keep the scrub radius down. I plan on using an 18" wheel, will obviously be custom due to the bolt pattern...

[Ron Sutton]

Originally Posted by 358Mustang

Thanks a lot for the diagram of your suspension. That helps me a lot to visualize things... This is a strict road race car, that I am trying to build it to be as fast as possible (isn't that the point?

You're welcome.

I don't think you should pull ideas from my design if you're building a suspension for a conventional set-up. Mine is optimized for a high-travel/low-roll setup and would not be optimum for a low-travel/high-roll set-up. It's not that it can't be run that way, but the geometry is not correct for a low travel/high roll set-up. For example, in a high travel set-up like mine, I have the geometry designed to be optimum for 4.5" of dive at the crossmember and a roll angle of 0.8°. Everything is different for low travel.

You will need different:
A. Anti-dive percentage
B. Roll Center location (static & dynamic)
C. Camber gain
D. Caster Gain
E. Bump Steer

If you build yours like mine & travel the front end 1-1/4" and roll it 3.0° ... the camber gain is too small, the caster gain is too small, the roll center is not optimum, etc. I suggest looking at examples in road race suspension design books printed before 2005.

Best wishes & don't hesitate to share or ask for help. Lots of good guys on this site.

[GregWeld]

Brian ---


Just get it over with --- sell your stuff and buy one of Ron's custom track cars with a Mustang body.

When I get done with my '40 Ford Pickup project.... that's what I'm going to do.