"Stock" Suspension Ride and Roll Rates

Sebnuts

Member
Here is an analysis of the “stock” Goblin suspension ride and roll rates, meant to be a baseline resource for anyone interested.

General:
Weight - 1640lbs
Wheelbase – 97.25in
Tires – Stock LNF SS 225/40R18
Front Weight Distribution - 36%
CG Height – 20.5in
Roll Stiffness - 2.7°/G

Front Setup:
Track Width – 59.4in
Roll Center Height - 3.8in
ARB - None
Spring Rate - 400lbs/in
Motion Ratio - 0.62
Wheel Rate - 155lbs/in
Frequency - 2.60Hz/156cpm
Front Roll Rate - 332ft-lbs/°
Front Roll Rate Distribution - 36.5%
Front Total Lateral Load Transfer Distribution (TLLTD) - 38.5%

Rear Setup:
Track Width – 58.3in
Roll Center Height - 1.6in
ARB - None
Spring Rate - 300lb/in
Motion Ratio - 0.97
Wheel Rate - 281lbs/in
Frequency - 2.56Hz/154cpm
Rear Roll Rate - 579ft-lbs/°

Steady State Weight Transfer:
38082

The image above is a graphical representation of the steady state lateral load transfer in a corner with a lateral acceleration of 1G. The red circles represent the vertical load on the tires.
The green line represents the front TLLTD. If the front TLLTD is greater than the front weight distribution, it will contribute to understeer/push. If the front TLLTD is less than the front weight distribution, it will contribute to oversteer/spin. There are many factors that contribute to the overall balance of the car, and this is just one of them.
The Goblin's front TLLTD is 2.5% higher than it's front weight distribution, which contributes a small amount of understeer/push.

Ride Rate Notes:
The Goblin's ride frequencies are quite high. For reference, typical non-aero cars range from 1.6 to 2.0Hz and aero cars range from 3 to 5Hz.

Roll Notes:
The Goblin's 2.7°/G roll stiffness is in the typical range for high performance road and track cars.
At approximately 1G lateral acceleration, the front inside wheel will be at full droop. Higher accelerations will result in the tire coming off the ground.

If there are any questions or other graphs of interest let me know and I’ll get them added.
 
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JBINTX

Goblin Guru
Seb: Interesting analysis.
Curious - what is your background?
What software are you using to do the analysis?
I think some pics we have taken (in general) visually support your conclusions.

IMG_7583.jpgIMG_7584.jpg
 

Sebnuts

Member
Professionally, I'm a mechanical engineer. I've been doing heavy equipment type machine design for the last 10 years.
I have no prior experience in suspension design, or even performance driving. When I placed the order for the car, I knew I was going to upgrade the rear suspension, so I ordered up some textbooks to get the basics and theory down. My primary reference has been "Race Car Vehicle Dynamics" by Milliken. I still have a lot to learn from experience, but that will come after the car is done.

As far as software goes, Solidworks is my 3D modeler of choice. For the suspension analysis, I've been using Susprog3D and Excel.
 

TravMac

Well-Known Member
RCVD - the go to for a lot of suspension folks. I've got a copy as well looking for the setup of my car this year with a bit more thought behind it. Glad to see some more data and curious where it goes from here as you get the car in your own hands.
 

Chubbs

Well-Known Member
When I placed the order for the car, I knew I was going to upgrade the rear suspension,
Curious about this...care to elaborate? Are you just planning to do coilovers? Or are you talking about a complete redesign?

My goblin has been a handful driving at the limit. I'm hoping staggered wheels/tires will help keep it in line. If not, more drastic measures may be necessary.
 

Sebnuts

Member
An almost complete redesign. Originally I was thinking just a custom lower control arm and repositioning the upper strut mount along with a proper spherical bearing, but now I've shifted to SLA with a custom lower control arm and 2 link upper. Upright will remain stock and I'll be utilizing the BC Racing coilovers since I already purchased them with the kit. I'm hoping to have the design portion wrapped up in the next week or so and will be posting that info on my build thread.
 

Chubbs

Well-Known Member
I can't wait to see what you come up with. The DF guys teased an updated rear suspension, but it seems like the project stalled out. Probably not enough demand. For most people, the Goblin has more performance than they can/will ever use.

I'm fascinated with suspension tuning. But after all my research and trial and error, I now know enough to know I don't know anything. It's half science, and half black magic.
 
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