Suspension Geometry

[Cattrax]

Does anyone have the suspension geometry that they would care to share? I have Win Geo 3 and would like to enter the geometry to check roll center, scrub, bump steer, camber gain, etc, etc. I used it on my current kit car and with a few modifications beyond basic alignment track results were much better. Hopefully I will have a partially completed kit bought in a few weeks to measure but I would like to start playing with the program sooner. As I recall, all that is required is the X,Y, and Z locations of the ball joints, the control arm bushings, and the tie rod ends. If the suspension is symmetrical, only measurements from one side are required. I will post any results.
Ken

[The Stig]

Does anyone have the suspension geometry that they would care to share? Hopefully I will have a partially completed kit bought in a few weeks to measure but I would like to start playing with the program sooner. As I recall, all that is required is the X,Y, and Z locations of the ball joints, the control arm bushings, and the tie rod ends. If the suspension is symmetrical, only measurements from one side are required. I will post any results.
Ken

Good morning Ken,

"If the suspension is symmetrical, only measurements from one side are required. I will post any results."

You may want to make sure that you have accurate measurements for all corners.


Ted Harrison (LS Man) here on the forum would be a very good point of contact for Suspension points, alignment requirements, and weight balance.

Do A search on "LS Man", and look for his posts in regard to suspension set up.

There have been other posts as well, but Ted documented his with videos, fairly detailed explanation.


David Borden (David) is another that can help you with the GTM Geometry and shock settings and what-not. You will find him on the Mk-IV forum these days. ("David's Mk-IV build"), I think.


Now... once you get the suspension in the right place(s), you will need to make sure that you test fit the body, for (body-alignment) purposes in order to make certain that your wheels are in the center of the wheel openings. There has been quite a lot posted about this as well. Search "Body Alignment".

You can take a cruise through Gene's (fastthings) videos that he has posted throughout his build. Very comprehensive in terms of detail and just plain fun to watch.

Have fun.

Mike

[Cattrax]

Thanks Mike. I have done several searches for suspension words but I will try some author searches. I was hoping to find the measurements needed for modeling the geometry but I have not. Measuring does not take too long, just tedious to get it accurate enough for good results. Plus the pivot point of a ball joint is a bit of an estimate anyway.
From the photos of the GTM that I am buying, it appears that the unpainted body has been mounted sans doors. Assuming that I do not like the geometry, I will check the wheels in the openings before I remove the body and chop off any suspension mounting points. I am not too much on body work. Should I mount the doors first to see that the body was correctly mounted to the frame?
Do many owners track or race their GTM's? At trackdays I see Radicals, Panoz, Novels, Sevens, and lots of Cobras but I do not recall seeing a GTM.
Thanks again for some direction.
Ken

[kabacj]

Should I mount the doors first to see that the body was correctly mounted to the frame?
Do many owners track or race their GTM's? At trackdays I see Radicals, Panoz, Novels, Sevens, and lots of Cobras but I do not recall seeing a GTM.
Thanks again for some direction.
Ken

Hi Ken

I race my GTM. Check out my build thread. "GTM roll cage modifications" for what I did to get the GTM race prepped

If you have a gen one frame you probably will want to add more caster. The gen 2 frame is fine out of the box
In my opinion I only added power steering.

The alignment, spring / damping rates and downforce balance are what I would focus on first.

You are going to love the GTM on the track I do.

John

[crash]

There are only two GTMs that are frame numbered for sanctioned events that I know of. The PDG car and John's car. You can see a bunch of the PDG stuff at http://www.prototypedevelopmentgroup.com/. I believe someone has taken the suspension point measurements that works for PDG, but I also don't think they are readily available. Probably your best bet is to wait until you actually get the car in your garage. Rim and tire size SIGNIFICANTLY change the suspension geometry.

[Fred Brewer]

You might try reaching out to Joel,, aka JCHRACER. If I remember correcctly he had some type of cad file. I know there was a spreadsheet David Borden did as well. I dont know if all of that info is on this forum,,, might want to check the other one.

http://www.ffcars.com/forums/42-fact...gtm-frame.html

http://www.ffcars.com/forums/42-fact...-redesign.html

http://www.corvetteforum.com/forums/...-geometry.html

[Fred Brewer]

Turns out I must of saved some .stp files back in 2009,, text says from a gentleman named Doug Clark. Can't remember the specifics,,, but if you give me your email I'll forward a copy along.


STep.PNG

[Cattrax]

Thanks All. I meant to reply sooner but was out of town for a while. The links look like great sources of info. I will do some reading and measuring.
Ken

[Taz Rules]

I'd take a copy of those STP files if you are offering them, Fred. [email protected]

BTW, Cattrax, I have some stuff I fiddled with in Autodesk Inventor. Might be useful to you. Measured with a tape measure (I didn't have calipers), so the accuracy might not be to the standard that you need. (Also, I got the engine and brake from other sources.) But nonetheless...
6 piston brake assy.jpgCHEVY LS3 ENGINE.jpgGM 7470569 Front Wheel Hub.jpgGM 10332529-RH Steering Knuckle Front PS.jpgGM 10333409-RH Control Arm Front Upper PS.jpgSuspension Rear DS.jpg

I can't assemble the front suspension, like I did the back, because I don't believe I have a copy of a lower A arm.
I also don't have the bracket that mounts the rear shock.

Let me know if this can help, you see my email above.

[Cattrax]

Thanks Taz. I PM'd Fred for a copy too.
Tape measure accuracy seemed to work on my last project. The vertical center of rotation of ball joints are a bit of a guess anyway unless one knows the radius of the ball. If you have a loose one, you can swing the stud back and forth to estimate a center of rotation. IIRC mine were just above the top of the joint.
Ken

[Fred Brewer]

I'll get those out to you guys in the AM,,, it's all on my home PC.

[Cattrax]

Thanks Fred. Received them fine. I think a drafter in the office could pull measurements off of them but unless I missed something, what I was looking for was all pivot points relative to the ground below the centerline of the frame. They need to be in X (fore-aft), Y (left-right), and Z (vertical) format. All steering pivot points and shock mounts are needed too. The program then will calculate all sorts of data, bump steer, scrub, camber gain in roll, bump, and droop, roll center, motion ratio, Ackerman, etc etc. On my last kit, installing some taller ball joints and shimming the steering tie rod down gave me some camber gain and eliminated the bump steer. On the Gen 1 it sounds like it is common to lower the front upper control arm mounts to improve that end of the car. I have not seen much on the rear.
Crash is probably correct in that I just need to wait and measure an actual car. Hopefully I will get to pick it up next weekend.
Thanks again for any help.

[Cattrax]

Okay, I finally completed measuring suspension points the best I could estimating pivot points etc. I entered the data in a program that calculates A arm lengths and they do not agree exactly with what I measured. I will try to sort out and adjust but the attached is what I have for now. If someone has more accurate measurements please post. It says my MS Excel file is invalid. Suggestions?
Ken

[Cattrax]

Trying again.

[Cattrax]

I could only attach as non-Excel files. Let me know if another format would be better.

[Cattrax]

0412151640.jpgPS all fore and aft dimension are from an arbitrary point in front of the front wheels.
I have been reading about some of you checking bump steer. I took a couple pics of my cheap bumpsteeer gauge. One was too large. Basically it is two pieces of plywood or 1xwides, a piano hinge and a economy dial indicator. Take the springs loose (both) as with any other gauge, lean this against the wheel/tire and with a floor jack under the frame, cycle the suspension through the movement range desired. You really don't even need a dial indicator to see if you have a problem. You can probably see 1/32" of movement when compared to 1/8" toe in is probably close enough. The dial indicator just makes it easy to zero in when adding shims with a bump steer kit.