Suspension and spring rates

ccannx

Goblin Guru
I'm starting this thread as a place ask questions and share general knowledge about suspension. I have heard a lot of varying information about shock and spring setup and feel almost as if i'm more confused than when I started.

I'm currently sitting on 300in/lb 9ht300 springs on all four corners and last autocross the car felt good but did not hold grip well in sweepers or transitioning through slaloms. I'm sure some or a substantial amount of my issue is very poor power delivery due to the on off throttle i'm having on my untuned motor.

There is science to spring setup involving things I'm not in complete understanding of like motion ratio, angle correction factor and wheel rate vs spring rate. Some are running 400lbs/in f and 300lb/in R , 600lb/in front 125lb/in rear and 125lb/inF 300lb/in rear with varying success. I have ran 300lb/in F 500Lb/in R and the car felt good but just too loose over bumps and throttle steer was excessive. I have corner weighted the car and measured the spring compression with the 300lb/in springs on all four corners and was surprised to find that the 9 inch springs were only compressing to 8" and that puts somewhere in the ballpark of 300lbs on each corner which I guess is where motion ratio is coming into play.

For example : front right FR269lbs 7 7/8 spring height, front left FL242lbs 8"spring height, RR432lbs 8",RL486lbs 7 3/4 spring height. The Rear Left wheel of 486lbs actual corner weight is only having an impact of 375lbs of compression on the spring not sure if this is whats called wheel rate? The measured spring angle is only 5.4 degrees according to my angle finder.

The second problem which goes along with what some are doing is there is only 1 inch of droop. If I wanted 2 inches of spring compression on that corner it would seem going to a to a 150lb/in spring would solve that problem 2+150=300lb resistance. I still have not measured the shock travel so do not know what the middle of the spring travel would be. This video does a good job of explaining why softer springs create more grip :
. After watching the video its easy to understand why sprung suspension travel is so important to maintaining grip.

The Goblin has great suspension geometry up front compared to the rear and I have to keep taking camber out trying to get even wear distribution on the front. The car just doesn't seem to roll onto the outside edges of the front tires and this is a good thing. It easily accepts huge spring rates and rewards with less body roll. Huge spring rates in the front of the car effects the spring frequency. When going into a corner the outside front high spring rate should hold up that corner of the car pushing the inside rear down creating more grip on the inside rear. The other way to control roll is a sway bar. We have provisions to put a swaybar on the rear but the most used method of controlling roll in autocross is to put the swaybar on the opposite end of the drive wheels.

This is a good read about car setup and also has a small section on suspension Frequency : http://farnorthracing.com/autocross_secrets.html
If I understand it correctly the Idea is the frequency the spring oscillates at syncs up with the rear frequency so setting up the rear just slightly higher creates a catch up type scenario when you first hit a bump with the front of the car and then rear cancelling out imbalance.

So far the numbers are pointing me toward softer than expected "variable rate springs", bumpstops and the need of a front swaybar for next season.

Please feel free to add on or correct anything that I don't understand which is alot at this point, I will try to update this thread the more I find out.
 
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Desert Sasqwatch

Goblin Guru
Wheel rate calculations:
MR = WT/ST (Motion Ratio = Wheel Travel divided by Spring Travel)
WR = SR/(MR X 2) (Wheel Rate = Spring Rate divided by Motion Ratio squared)
 

George

Goblin Guru
Been running my Goblin in autocross last two seasons. Still have not got it to work as I would like. I am not a good driver so I have a couple of younger more aggressive divers run the car.
My best setup to date is 500# front springs, front sway bar with 154# per inch wheel rate. rear springs at 150#.
Car will push when accelerating in the turn and loose if you let off. Tires for autocross a Hoosiers 9.5x15x23 r35
and rears are 13.75x15x24.5 r35.
What I think my issue is not enough weight on outside rear tire when cornering. I an going to lower the rear roll
center and see if it will produce more weight transfer. On lowering the rear roll center you have to lower the car which will reduce camber gain on current rear suspension.
A couple of other things that are different on my car are. The rear hubs have been extended so the ball joint is 1.3 lower
which allows me to lower the rear of the car, current rear ride height is 5". Had to put driveshaft shop axles in because of axle angle was pulling them apart. The engine is modified with cams, head ported, intake ported and forged piston and rods. It will turn 8100rpm so I never had to shift out of 2nd gear when autocrossing. Throttle is set a 60% for better drivability.

Brad
 

George

Goblin Guru
A couple of other mods that need to be added to the list. All of my tie rod ends are heim joints. It has been modified
so that there is no bump steer front or rear (sometimes called roll steer). Made new steering arm with 0 ackerman and 1" shorter to quicken steering. Have found when scaling car getting both front weight close to each other and the same in the rear is better.

Brad
 
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Desert Sasqwatch

Goblin Guru
QA1 has a good FAQ site that has some good information that may help to understand setting up the suspension for shocks, springs, etc.

 

ccannx

Goblin Guru
EDITED 12-18-2020 : Spring rates on that calculator are 161f 167r thats really low ! I have come to find the Goblin works best on a similar setup that comes with the kit or at least when I got my kit with the BC coil overs. The recommendation is to run the 400lb springs up front and the 300lb springs in the rear. For autocross I am currently running a 500lb spring up front and 200 in the rear. Somewhere around 350lbs front spring rate my Goblin likes to bottom out on our bumpy lots.

It’s a lot of info to plug in and measure so It may be a wildly inaccurate result. The unsprung weight is only a guess but spring angles and a/b dimensions should be close.
 

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Ross

Goblin Guru
Total weight will be close to: 1100 pounds in the rear axle, 600 pounds in the front, with a 200 pound driver in the goblin.
 

ccannx

Goblin Guru
Total weight will be close to: 1100 pounds in the rear axle, 600 pounds in the front, with a 200 pound driver in the goblin.
This is with me in the car I am 200lbs. If it’s possible to get the rear a little more balanced and shoot for close to 500 on each rear corner. I will try to get the car as close to balanced I can with parts/equipment placing. After that Cross weight will be focused on. Setting cross weight at 50/50 will should give repeatable handling predictability while turning left or right.
 

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George

Goblin Guru
On the rear the wheel rate is about 89% of spring rate. I use 50% when guessing front wheel rate.
If you use a 500# spring your rear spring will hanging loose on the inside wheel of a turn.

Brad
 

ccannx

Goblin Guru
Yes it rotated a bit to well with 500lb springs in the rear. Have you measured the piston travel with the rear BC coilovers ?

I have the spring off the front and measured 4" of travel in the shock. I measured 5 inches on the rear with the spring compressed 1 inch so assuming 6 inches of travel and 500lbs static load would put a spring somewhere at 150-175 for a 45-50% spring compression at ride height.
 
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Ross

Goblin Guru
I met Dale and his wife at the 2019 Midwest Spring Meet, he was driving the black Brunton Stalker. He has been a great help, and I am looking forward to setting up my Goblin with his help. He has a list of videos for me to learn, and I wanted to share it here.

HI Ross

Let's talk basic set-up. Playing with springs and associated costs will not necessarily get your Goblin to handle properly. What works for one will maybe not work for another. Each owner has a feel they will be comfortable with and that driver skill figures into the overall outcome.

Remember, too, that a lot of folks are driving a car configured differently than they have experienced before. Sure you know how a rear wheel drive or a front wheel drive feels and acts. A mid-engine Goblin is different and needs to be driven differently. Each configuration has its own issues. You can take a bad handling car with a good driver and they will beat you in your good handling not as well experienced driver.

Goblin owners who are cruisers will want a soft ride, autocross will want a different package than the track racer.

Different folks have different driving skills. Some are smooth drivers, some are aggressive drivers. I have one son with each skill. The smooth one is as fast as the aggressive one at autocross in the StalkerV6.
My 48 year old Lotus Europa (mid engine) would hang with the StalkerV6 if it had more than 80 horsepower. It handles very well with the factory springs - 110-115 front and 75 rear. I remind my boys to tighten the nut behind the wheel.

So, first the basic set-up has to be right. And second, the driver has to learn the car. Then can we make it the beast it has potential of becoming.

I'm going to bore and overload you with videos, now. Hopefully you can gain some tips to help you progress in your Goblin build.

I told Jeremy that I would attempt to make it down to one of your autocross events this year.

Dale

Front:

Rear:

Springs stuff:

Suspension setup stuff:
(bear in mind that this information probably is in context with a front engine car)


Ackerman: https://www.youtube.com/watch?v=YVisLuiU-Oo
 

JERMzSS

Well-Known Member
Yes it rotated a bit to well with 500lb springs in the rear. Have you measured the piston travel with the rear BC coilovers ?

I have the spring off the front and will measure the travel this evening. I measured 5 inches on the rear with the spring compressed 1 inch so assuming 6 inches of travel and 500lbs static load would put a spring somewhere at 150-175 for a 45-50% spring compression at ride height.
I was looking real hard into 500lb spings in the rear of mine. I still have a ton to learn about this crap. I know my A7s help alot but my current set up is pretty much what Lonny and Adam recommend and its working very well so far. The only change I've made is the 2.5 degrees of negative camber in the rear.

Where I autocross is an old asphalt/rock road that has very different levels of grip depending on what part of the track you are on. The front stretch has a lot of grip for accelerating and turning but the opposite side has alot less. The rocks are more rounded and you can't brake nearly as hard there without locking them up.
 

ccannx

Goblin Guru
A7’s are magical. They are fantastic for about 5-6 events and then seem to lose their spirit. I don’t think high rates are the way to go contrary to what I’ve been told by more experienced mod car folk.

Ive seen data that softer is faster at least in the bumpy lots that we autocross in.

Im really slow in the goblin and I didn’t think that would be the case. I need to get it to a tuning guru and also get this suspension sorted. We do have a good bit of top level people that run in our events a fast chap in an nd Miata ran a scratch time 4 seconds faster than me raw at the last event.
 

George

Goblin Guru
The Goblin has a lot going for it but I too am having trouble getting it to hold in the turns. It has the power and the braking but it lateral g's are low.

Brad
 

JERMzSS

Well-Known Member
Are you guys trail braking? I find left foot braking and trail braking keeps the front planted very well for me.
 

ccannx

Goblin Guru
Are you guys trail braking? I find left foot braking and trail braking keeps the front planted very well for me.
Are you driving on the track ? I have only autocrossed the Goblin. I have never had the capacity to trail brake at an autocross there is just to much going on to fast for me. My goblin also needs a tune and is also way to tail happy to attempt it at this point. I tried trail braking at our Lemons races and I found the Porssat /a mid engine 911 doesn't respond well to trail braking but the miata does. Maybe when i get a good tune and finish getting the suspension worked out I can give it a shot in the Goblin.
 
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