Help With Shock Rates
03-27-2012, 02:15 PM
#1
Melting Slicks
Thread Starter
Help With Shock Rates
I’m looking for some thoughts and or recommendations for shock rates for my GTM and figured the group here collectively knows more than any other place I hang out as you guys are real racers. Also, as much research as I try to do it all seems like black magic with very little in the way of specific recommendations. I hoping that since my GTM uses a C5 suspension I might be able to correlate what you guys run to an appropriate setup for the GTM.
As I said, the GTM runs a Coil over C5 suspension, weighs about 2700 lbs. give or take, I would think the wheel rates would be the same as a C5 as well as unsprung weight. I will be running a front sway bar but no rear bar for now.
The spring rates that the GTM guys use do vary a bit. The factory gives a 450 for the front (no sway bar) and a 750 rear. A number of guys are running 650’s in the rear. I’m thinking I’ll start with a 350 up front as I have the sway bar and the 750 in the rear. I wouldn’t be surprised if the rear spring got lessened though.
As for the shocks supplied,,, there were two versions of the Koni’s. The first set was a single (rebound) adjustable and the second set had no adjustments. I got them dynoed and here are the charts:
This is the earlier shock that was adjustable
The later shock,,, a bit stiffer
Some of the guys are going to much stiffer shocks in both compression and rebound although there is not a lot of info available on the shock rates . I'm wondering what your thoughts may be on the shock rates posted? A little on the soft side or a lot? For you guys that have dyno plots of your shocks,,, taking any differences in spring rates into consideration,, how much shock are you running and how does it compare?
Thanks guys!
As I said, the GTM runs a Coil over C5 suspension, weighs about 2700 lbs. give or take, I would think the wheel rates would be the same as a C5 as well as unsprung weight. I will be running a front sway bar but no rear bar for now.
The spring rates that the GTM guys use do vary a bit. The factory gives a 450 for the front (no sway bar) and a 750 rear. A number of guys are running 650’s in the rear. I’m thinking I’ll start with a 350 up front as I have the sway bar and the 750 in the rear. I wouldn’t be surprised if the rear spring got lessened though.
As for the shocks supplied,,, there were two versions of the Koni’s. The first set was a single (rebound) adjustable and the second set had no adjustments. I got them dynoed and here are the charts:
This is the earlier shock that was adjustable
The later shock,,, a bit stiffer
Some of the guys are going to much stiffer shocks in both compression and rebound although there is not a lot of info available on the shock rates . I'm wondering what your thoughts may be on the shock rates posted? A little on the soft side or a lot? For you guys that have dyno plots of your shocks,,, taking any differences in spring rates into consideration,, how much shock are you running and how does it compare?
Thanks guys!
03-28-2012, 10:56 AM
#2
Tech Contributor
In general, and for heavy cars, Koni adjustables are hard to beat!
If we already had a set of the single adjustables, we would first try them, especially since you are planning on running lower rate springs in the front. From there, we would make changes as necessary.
Of course, the correct procedure for doing this is to first decide upon your spring rates, and then (assuming the dampers need changing) have Koni custom valve your singles based upon the car weight, spring rate, and type of track surfaces you run. Koni racing knows how to calculate all that stuff.
And, to go a step further, Koni can transform your single adjustables into double adjustables, custom valved, although this gets expensive.
Now showing my ignorance for all the world to see, what is a GTM?
Ed
If we already had a set of the single adjustables, we would first try them, especially since you are planning on running lower rate springs in the front. From there, we would make changes as necessary.
Of course, the correct procedure for doing this is to first decide upon your spring rates, and then (assuming the dampers need changing) have Koni custom valve your singles based upon the car weight, spring rate, and type of track surfaces you run. Koni racing knows how to calculate all that stuff.
And, to go a step further, Koni can transform your single adjustables into double adjustables, custom valved, although this gets expensive.
Now showing my ignorance for all the world to see, what is a GTM?
Ed
03-28-2012, 11:11 AM
#3
Safety Car
In general, and for heavy cars, Koni adjustables are hard to beat!
If we already had a set of the single adjustables, we would first try them, especially since you are planning on running lower rate springs in the front. From there, we would make changes as necessary.
Of course, the correct procedure for doing this is to first decide upon your spring rates, and then (assuming the dampers need changing) have Koni custom valve your singles based upon the car weight, spring rate, and type of track surfaces you run. Koni racing knows how to calculate all that stuff.
And, to go a step further, Koni can transform your single adjustables into double adjustables, custom valved, although this gets expensive.
Now showing my ignorance for all the world to see, what is a GTM?
Ed
If we already had a set of the single adjustables, we would first try them, especially since you are planning on running lower rate springs in the front. From there, we would make changes as necessary.
Of course, the correct procedure for doing this is to first decide upon your spring rates, and then (assuming the dampers need changing) have Koni custom valve your singles based upon the car weight, spring rate, and type of track surfaces you run. Koni racing knows how to calculate all that stuff.
And, to go a step further, Koni can transform your single adjustables into double adjustables, custom valved, although this gets expensive.
Now showing my ignorance for all the world to see, what is a GTM?
Ed
03-28-2012, 11:12 AM
#4
Melting Slicks
Thread Starter
In general, and for heavy cars, Koni adjustables are hard to beat!
If we already had a set of the single adjustables, we would first try them, especially since you are planning on running lower rate springs in the front. From there, we would make changes as necessary.
Of course, the correct procedure for doing this is to first decide upon your spring rates, and then (assuming the dampers need changing) have Koni custom valve your singles based upon the car weight, spring rate, and type of track surfaces you run. Koni racing knows how to calculate all that stuff.
And, to go a step further, Koni can transform your single adjustables into double adjustables, custom valved, although this gets expensive.
Now showing my ignorance for all the world to see, what is a GTM?
Ed
If we already had a set of the single adjustables, we would first try them, especially since you are planning on running lower rate springs in the front. From there, we would make changes as necessary.
Of course, the correct procedure for doing this is to first decide upon your spring rates, and then (assuming the dampers need changing) have Koni custom valve your singles based upon the car weight, spring rate, and type of track surfaces you run. Koni racing knows how to calculate all that stuff.
And, to go a step further, Koni can transform your single adjustables into double adjustables, custom valved, although this gets expensive.
Now showing my ignorance for all the world to see, what is a GTM?
Ed
As for what a GTM is,,, it's a kit put out by Factory five,,, think C5 Corvette based (motor, suspension, tanks etc) GT40.
On the street
Road America
03-28-2012, 12:56 PM
#5
thanks!
03-28-2012, 11:40 PM
#6
gtpvette,
If you really want to understand your set up, find a suspensen calculator that will allow you to input the suspension geometry, spring rates, weights and output a % critical damping. The values on the graph cant be understood without knowing what critical damping that translates to on your car.
The shape of the cure is more linear than what is typical with vettes. They usually have a more digressive curve on rebound around 2-3 ips.
el es tu,
Here is a quote from the .pdf you posted:
“This means that when the
damper is moving slowly, such as
during cornering, the damper
forces are high. But when the
damper is moving fast, for
example over potholes, the
damper forces are low.”
This basically means it is a digressive curve. In F1 this is taken to an extreme. Penske has the same technology on their pistons and they call it a "velocity dependant piston, VDP". This acts like a blow off valve when the F1 cars hit the curbs.
Just my 2 cents,
Chris Shay
If you really want to understand your set up, find a suspensen calculator that will allow you to input the suspension geometry, spring rates, weights and output a % critical damping. The values on the graph cant be understood without knowing what critical damping that translates to on your car.
The shape of the cure is more linear than what is typical with vettes. They usually have a more digressive curve on rebound around 2-3 ips.
el es tu,
Here is a quote from the .pdf you posted:
“This means that when the
damper is moving slowly, such as
during cornering, the damper
forces are high. But when the
damper is moving fast, for
example over potholes, the
damper forces are low.”
This basically means it is a digressive curve. In F1 this is taken to an extreme. Penske has the same technology on their pistons and they call it a "velocity dependant piston, VDP". This acts like a blow off valve when the F1 cars hit the curbs.
Just my 2 cents,
Chris Shay
03-29-2012, 08:32 AM
#7
Drifting
Member Since: Dec 2005
Location: Dayton, OH
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Just as a side note: The curves you posted are basically worthless as far as determining how your setup will perform on the track.
You need curves from various travel rates and all a bunch slower than 12"/sec. anything over 3 - 4 inches per second is fast and should have some sort of a digressive curve.
Below 3 - 4 inches per second is where the story of how things will perform/handle is told.
These rules of thumb apply to our type of racing. The key rates vary for NASCAR and F1.
You need curves from various travel rates and all a bunch slower than 12"/sec. anything over 3 - 4 inches per second is fast and should have some sort of a digressive curve.
Below 3 - 4 inches per second is where the story of how things will perform/handle is told.
These rules of thumb apply to our type of racing. The key rates vary for NASCAR and F1.
03-29-2012, 09:55 AM
#8
Just as a side note: The curves you posted are basically worthless as far as determining how your setup will perform on the track.
You need curves from various travel rates and all a bunch slower than 12"/sec. anything over 3 - 4 inches per second is fast and should have some sort of a digressive curve.
Below 3 - 4 inches per second is where the story of how things will perform/handle is told.
These rules of thumb apply to our type of racing. The key rates vary for NASCAR and F1.
You need curves from various travel rates and all a bunch slower than 12"/sec. anything over 3 - 4 inches per second is fast and should have some sort of a digressive curve.
Below 3 - 4 inches per second is where the story of how things will perform/handle is told.
These rules of thumb apply to our type of racing. The key rates vary for NASCAR and F1.
03-29-2012, 10:08 AM
#9
Melting Slicks
Thread Starter
gtpvette,
If you really want to understand your set up, find a suspensen calculator that will allow you to input the suspension geometry, spring rates, weights and output a % critical damping. The values on the graph cant be understood without knowing what critical damping that translates to on your car.
The shape of the cure is more linear than what is typical with vettes. They usually have a more digressive curve on rebound around 2-3 ips.
If you really want to understand your set up, find a suspensen calculator that will allow you to input the suspension geometry, spring rates, weights and output a % critical damping. The values on the graph cant be understood without knowing what critical damping that translates to on your car.
The shape of the cure is more linear than what is typical with vettes. They usually have a more digressive curve on rebound around 2-3 ips.
Thanks for your thoughts. Let me list all of the information I’ve gathered. Weights have been done, note the rear should be close to a C5 for both total an unsprung, front is lighter in total equal in unsprung. Motion ratios should be close to C5 with Coil overs.
Mr Hoffmans numbers on shock motion ratios :
http://forums.corvetteforum.com/auto...the-wheel.html
Unsprung Weight info – Highly unscientific and done on my Bathroom scale. I only weighed the front as the rear wasn’t off the car but I assume to be close.
Upright/Hub 16 lbs
Front Caliper & Rotor 29 lbs
Front Upper & lower A-Arm & Shock/Spring 18 lbs
Stock C5 Corvette Rims & bald tires
front 17 x 245 - 39 lbs.
Rear 18 x 295 - 49 Lbs
C6 Z06 Replica Rims & new Nitto Invos
Front 18 x 275 - 52 lbs
Rear 19 x 345 - 69 lbs
Another gentleman ( a guy way smarter than me) took that and came up with:
Front
Wheel/tire/hub/rotor/caliper/etc. = 84 to 97 lbs. so let’s call it 90 lbs. unsprung
Control arms/shocks/springs = 18 lbs. so let’s call it ½ times 18 = 9 lbs. unsprung
Total unsprung front corner weight = 99 lbs.
Total front corner weight = 2600 (car with driver) times 41% divided by 2 = 533 lbs.
Sprung front corner weight = 533 – 99 = 434 lbs.
Rear
Wheel/tire/hub/rotor/caliper/etc. = 94 to 114 lbs. so let’s call it 104 lbs. unsprung
Control arms/shocks/springs (assume same as front) = 18 lbs. so let’s call it ½ times 18 = 9 lbs. unsprung
Axle = 8.2 lbs so let’s call it ½ times 8.2 = 4.1 lbs. unsprung
Outer CV = 5.2 lbs unsprung
Total unsprung rear corner weight = 122.3 lbs.
Total front corner weight = 2600 (car with driver) times 59% divided by 2 = 767 lbs.
Sprung front corner weight = 767 – 122.3 = 644.7 lbs.
Front
Motion Ratio = 1.39 (0.72)
Rear
Motion Ratio = 1.46 (0.68)
I will add that I think my total weight will be a bit different,, that is heavier. I’m expecting 570 or so total on each front and 800 or so on each rear for around 2750 total.
Let me also add this. Another gentleman (another guy way smarter than me) put this spreadsheet together. It allows us to plug in the required information to come up with recommendations based on % of critical damping. Real slick.
The problem becomes how much dampening do we really want? With a digressive curve do you build in way more than 100% in the first 1-3 IPS then bleed it off? I’ve read another theory that 65% or critical dampening should be plenty. Does that imply a straight (linear) curve?
So my thought remains (maybe incorrectly) that a well set up C5 running coil overs in the rear with a 600-700 lb spring should have a shock setup that I might like to look at.
Am I incorrect in this?
03-29-2012, 10:31 AM
#10
gtpvette,
If you really want to understand your set up, find a suspensen calculator that will allow you to input the suspension geometry, spring rates, weights and output a % critical damping. The values on the graph cant be understood without knowing what critical damping that translates to on your car.
The shape of the cure is more linear than what is typical with vettes. They usually have a more digressive curve on rebound around 2-3 ips.
el es tu,
Here is a quote from the .pdf you posted:
“This means that when the
damper is moving slowly, such as
during cornering, the damper
forces are high. But when the
damper is moving fast, for
example over potholes, the
damper forces are low.”
This basically means it is a digressive curve. In F1 this is taken to an extreme. Penske has the same technology on their pistons and they call it a "velocity dependant piston, VDP". This acts like a blow off valve when the F1 cars hit the curbs.
Just my 2 cents,
Chris Shay
If you really want to understand your set up, find a suspensen calculator that will allow you to input the suspension geometry, spring rates, weights and output a % critical damping. The values on the graph cant be understood without knowing what critical damping that translates to on your car.
The shape of the cure is more linear than what is typical with vettes. They usually have a more digressive curve on rebound around 2-3 ips.
el es tu,
Here is a quote from the .pdf you posted:
“This means that when the
damper is moving slowly, such as
during cornering, the damper
forces are high. But when the
damper is moving fast, for
example over potholes, the
damper forces are low.”
This basically means it is a digressive curve. In F1 this is taken to an extreme. Penske has the same technology on their pistons and they call it a "velocity dependant piston, VDP". This acts like a blow off valve when the F1 cars hit the curbs.
Just my 2 cents,
Chris Shay
My driving is over rough tarmac and I also tend to get airborne at times, so the idea of nicer shocks that can maintain more control is very tempting as a future modification
btw is this available in all their racing shocks such as the ones offered by hardbar?
03-29-2012, 12:26 PM
#11
Drifting
Member Since: Dec 2005
Location: Dayton, OH
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I dont see anything wrong with the posted CVP graph that would make me call it worthless. It covers 0 - 12 ips so you can see what is happening at the low speeds. A PVP graph would be nice but they are more costly to run, and a PVP is nothing more than several CVP graphs put together with peak values from each CVP run.
and jumped on the forum for a distraction, probably should not have posted until I felt better
