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July 3, 2012
September 20, 2011
ANSWER: 2001 996 Cup
Let’s break you question into 3 segments: 1. springs which is easy, 2. vehicle setting that give indications of handling characteristic, and 3. shock settings which is the most difficult to answer based on the existing information.
Lets establish some of the baseline first. The GT3 Cup you have will weigh approximately 2850 with a 175lb driver and 5 gallons of fuel. Roughly 61% of the weight is to the rear. The vehicle came with front( 10 position) and rear(8 position) adjustable sway bars. Not cockpit adjustable. The original shocks would likely have been non-adjustable Bilstein or Sachs. Springs would have been H & R 220 NM front and 240NM rears.
Beginning with the springs, which as you know, establishes the platform on your setup. 800 lb/in springs in the front will give you a front frequency around 230 cmp (cycles per minute) and 1000 lb/in springs in the rear frequency of about 115 cpm. What this translates to in engineering and driver terms is: the vehicle will not neutral and will require substantial alignment, shock, and sway bar adjustment to overcome. The vehicle will have an under-steer characteristic but large amounts of rear mechanical grip.
Running large amounts of camber is more conducive to a vehicle running very stiff, on very smooth tracks, using the berms to turn the vehicle, ie. European tracks. The ojective is to have the largest contact patch possible when cornering for optimum speed. This is affected by: vehicle weight, tire construction and type, tire pressures, track conditions, etc. Excessive amounts of camber is detrimental to acceleration and braking and cornering. One would use a tire pyrometer (not infra-red) to assist in the determination of how much camber. On DOT tires, that is properly sprung, I would not expect more than 2.1 degrees of negative front or rear.
With respect to the toe settings, vehicles are the fastest on the straights with 0 dynamic toe. Toe is introduced to compensate for dynamic wheel loading at speed resultant from contact patch rolling resistance. “Some” toe in the rear allows more predictability at “turn-in” and “steady state turning”. Too much toe-in causes rear instability under braking; too much toe-out causes and oversteer at turn entry and transition. Front toe can speed up or slow the RATE of turn in. Vehicles with more toe in feel like the steering wheel is pushing the front of the vehicle into the turn where vehicles with toe out feel like the tires are pulling the nose into the turn. Actually, this IS what is happening. Running front toe out on a vehicle that is over-sprung will allow better turn-in... at the expense of straight line speed and stable braking.
On the topic of the shocks: 200 reservoir pressure is within the acceptable range(150-200) for these shocks. Manufacture recommendation is 175 lbs; more pressure causes the graph to move up without appreciably altering the profile; substantially higher pressures causes undue wear on the seals and o rings. Lower pressure could allow oil cavitation thus causing the shock to become “spongy.”
On the subject of the shock setting, the numbers are relative with lower numbers indicating a softer setting. Unfortunately, the numbers on the shocks are more specific to the individual shocks you have. The low speed knobs can become loose and rotate independent of the adjusting shaft; when this occurs, you lose the coordination between left and right on the same axle. Basically, the numbers mean very little until the shocks are dyno-ed and actual resistance numbers can be assigned to the clicks and numbers on your shocks. Without the actual numbers, you are making relative adjustments (3 is more than 2) as opposed to knowing that you are adding 50 lbs of damping.
In our process, we start with all the settings soft (most mechanical grip) and add damping based on driver preference.
Hope this helps!
Glenn
Lets establish some of the baseline first. The GT3 Cup you have will weigh approximately 2850 with a 175lb driver and 5 gallons of fuel. Roughly 61% of the weight is to the rear. The vehicle came with front( 10 position) and rear(8 position) adjustable sway bars. Not cockpit adjustable. The original shocks would likely have been non-adjustable Bilstein or Sachs. Springs would have been H & R 220 NM front and 240NM rears.
Beginning with the springs, which as you know, establishes the platform on your setup. 800 lb/in springs in the front will give you a front frequency around 230 cmp (cycles per minute) and 1000 lb/in springs in the rear frequency of about 115 cpm. What this translates to in engineering and driver terms is: the vehicle will not neutral and will require substantial alignment, shock, and sway bar adjustment to overcome. The vehicle will have an under-steer characteristic but large amounts of rear mechanical grip.
Running large amounts of camber is more conducive to a vehicle running very stiff, on very smooth tracks, using the berms to turn the vehicle, ie. European tracks. The ojective is to have the largest contact patch possible when cornering for optimum speed. This is affected by: vehicle weight, tire construction and type, tire pressures, track conditions, etc. Excessive amounts of camber is detrimental to acceleration and braking and cornering. One would use a tire pyrometer (not infra-red) to assist in the determination of how much camber. On DOT tires, that is properly sprung, I would not expect more than 2.1 degrees of negative front or rear.
With respect to the toe settings, vehicles are the fastest on the straights with 0 dynamic toe. Toe is introduced to compensate for dynamic wheel loading at speed resultant from contact patch rolling resistance. “Some” toe in the rear allows more predictability at “turn-in” and “steady state turning”. Too much toe-in causes rear instability under braking; too much toe-out causes and oversteer at turn entry and transition. Front toe can speed up or slow the RATE of turn in. Vehicles with more toe in feel like the steering wheel is pushing the front of the vehicle into the turn where vehicles with toe out feel like the tires are pulling the nose into the turn. Actually, this IS what is happening. Running front toe out on a vehicle that is over-sprung will allow better turn-in... at the expense of straight line speed and stable braking.
On the topic of the shocks: 200 reservoir pressure is within the acceptable range(150-200) for these shocks. Manufacture recommendation is 175 lbs; more pressure causes the graph to move up without appreciably altering the profile; substantially higher pressures causes undue wear on the seals and o rings. Lower pressure could allow oil cavitation thus causing the shock to become “spongy.”
On the subject of the shock setting, the numbers are relative with lower numbers indicating a softer setting. Unfortunately, the numbers on the shocks are more specific to the individual shocks you have. The low speed knobs can become loose and rotate independent of the adjusting shaft; when this occurs, you lose the coordination between left and right on the same axle. Basically, the numbers mean very little until the shocks are dyno-ed and actual resistance numbers can be assigned to the clicks and numbers on your shocks. Without the actual numbers, you are making relative adjustments (3 is more than 2) as opposed to knowing that you are adding 50 lbs of damping.
In our process, we start with all the settings soft (most mechanical grip) and add damping based on driver preference.
Hope this helps!
Glenn
Question: 2001 996 Cup
I'm working with a friend on a car he just purchased - 2001 996 Cup Car and was wondering if you can help determine if his set-up is good.
Here is his setup -
JRZ Triple adjustables. 200psi
Initially set at:
Low Speed Bump - 2 (of 4)
High Speed Bump - 7 (of 12)
Rebound 3 (of 4)
1000# springs.
20.7mm solid ARB
-3.0 degree camber
3mm toe in
295/40-18 tires (likely to change to 275/35-18)
110mm ride height (measure from factory point per tech manual)
Front -
JRZ Triple adjustables. 200psi
Low Speed Bump - 3 (of 4)
High Speed Bump - 11 (of 12)
Rebound 3 (of 4)
800# springs.
20.7mm solid ARB
-3.3 degree camber
2mm toe out
255/40-18 tires (likely to change to 245/35-18)
88mm ride height (measure from factory point per tech manual)
Let me know what you think..
Thanks Glen!!
Here is his setup -
JRZ Triple adjustables. 200psi
Initially set at:
Low Speed Bump - 2 (of 4)
High Speed Bump - 7 (of 12)
Rebound 3 (of 4)
1000# springs.
20.7mm solid ARB
-3.0 degree camber
3mm toe in
295/40-18 tires (likely to change to 275/35-18)
110mm ride height (measure from factory point per tech manual)
Front -
JRZ Triple adjustables. 200psi
Low Speed Bump - 3 (of 4)
High Speed Bump - 11 (of 12)
Rebound 3 (of 4)
800# springs.
20.7mm solid ARB
-3.3 degree camber
2mm toe out
255/40-18 tires (likely to change to 245/35-18)
88mm ride height (measure from factory point per tech manual)
Let me know what you think..
Thanks Glen!!
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