996 ieal spring stiffness calculation
#31
Originally Posted by analogmike
I believe the street GT3 LSD is not up to autocross or track use, they last barely a year.... the motorsports units are BEEFY, no comparison.
#32
Rennlist Member
Thread Starter
The LSD is a 2004 cup one, in stock form (as is the gearbox).
Yes, no monoball anywhere in the suspension. I do not have the ride heights at hand, but they are between road car and cup ones. It will be set as low as possible.
What I guess is that the ABS needs a lot of weight transfer on the front tyres. By comparaison to stock cars of friends, with stock (busted) LSD, and stock springs, also on MPSC2, they tend to dive more under braking, with the ABS not engaging so frequently.
I will try several springs configurations. Having had exchanges with pkm consulting and optimumg (really great people there !), trying to do the math(even if I do not understand everything), and having had a look at several track dedicated gt3, ohlins suspension options and spring proposal, and so on, I am going to use a set of 996 cup 2 ways dampers I have to be able to adjust (a bit !) to several spring rates, starting on the very soft side (70 & 160), and see if it feels better for me (and lap times ;-)). I will also take a set of 110 for the front, and will let you know.
I wonder if the technology of the shocks is a big factor too...
We have a new serie here, with dedicated 718 caymans on MPSC2. I have talked with the Ohlins guy that developped the suspension, and they really are on the soft side (not the same car, I admit ! And without the motion ratio it does not make a lot of sense to compare...), but no more than 90 at the front, if I remember correctly.
I will let you know... Many thanks for all advices.
Any geo recommandation for these tyres ?
Yes, no monoball anywhere in the suspension. I do not have the ride heights at hand, but they are between road car and cup ones. It will be set as low as possible.
What I guess is that the ABS needs a lot of weight transfer on the front tyres. By comparaison to stock cars of friends, with stock (busted) LSD, and stock springs, also on MPSC2, they tend to dive more under braking, with the ABS not engaging so frequently.
I will try several springs configurations. Having had exchanges with pkm consulting and optimumg (really great people there !), trying to do the math(even if I do not understand everything), and having had a look at several track dedicated gt3, ohlins suspension options and spring proposal, and so on, I am going to use a set of 996 cup 2 ways dampers I have to be able to adjust (a bit !) to several spring rates, starting on the very soft side (70 & 160), and see if it feels better for me (and lap times ;-)). I will also take a set of 110 for the front, and will let you know.
I wonder if the technology of the shocks is a big factor too...
We have a new serie here, with dedicated 718 caymans on MPSC2. I have talked with the Ohlins guy that developped the suspension, and they really are on the soft side (not the same car, I admit ! And without the motion ratio it does not make a lot of sense to compare...), but no more than 90 at the front, if I remember correctly.
I will let you know... Many thanks for all advices.
Any geo recommandation for these tyres ?
#33
Originally Posted by cid042
The LSD is a 2004 cup one, in stock form (as is the gearbox).
Yes, no monoball anywhere in the suspension. I do not have the ride heights at hand, but they are between road car and cup ones. It will be set as low as possible.
What I guess is that the ABS needs a lot of weight transfer on the front tyres. By comparaison to stock cars of friends, with stock (busted) LSD, and stock springs, also on MPSC2, they tend to dive more under braking, with the ABS not engaging so frequently.
I will try several springs configurations. Having had exchanges with pkm consulting and optimumg (really great people there !), trying to do the math(even if I do not understand everything), and having had a look at several track dedicated gt3, ohlins suspension options and spring proposal, and so on, I am going to use a set of 996 cup 2 ways dampers I have to be able to adjust (a bit !) to several spring rates, starting on the very soft side (70 & 160), and see if it feels better for me (and lap times ;-)). I will also take a set of 110 for the front, and will let you know.
I wonder if the technology of the shocks is a big factor too...
We have a new serie here, with dedicated 718 caymans on MPSC2. I have talked with the Ohlins guy that developped the suspension, and they really are on the soft side (not the same car, I admit ! And without the motion ratio it does not make a lot of sense to compare...), but no more than 90 at the front, if I remember correctly.
I will let you know... Many thanks for all advices.
Any geo recommandation for these tyres ?
Yes, no monoball anywhere in the suspension. I do not have the ride heights at hand, but they are between road car and cup ones. It will be set as low as possible.
What I guess is that the ABS needs a lot of weight transfer on the front tyres. By comparaison to stock cars of friends, with stock (busted) LSD, and stock springs, also on MPSC2, they tend to dive more under braking, with the ABS not engaging so frequently.
I will try several springs configurations. Having had exchanges with pkm consulting and optimumg (really great people there !), trying to do the math(even if I do not understand everything), and having had a look at several track dedicated gt3, ohlins suspension options and spring proposal, and so on, I am going to use a set of 996 cup 2 ways dampers I have to be able to adjust (a bit !) to several spring rates, starting on the very soft side (70 & 160), and see if it feels better for me (and lap times ;-)). I will also take a set of 110 for the front, and will let you know.
I wonder if the technology of the shocks is a big factor too...
We have a new serie here, with dedicated 718 caymans on MPSC2. I have talked with the Ohlins guy that developped the suspension, and they really are on the soft side (not the same car, I admit ! And without the motion ratio it does not make a lot of sense to compare...), but no more than 90 at the front, if I remember correctly.
I will let you know... Many thanks for all advices.
Any geo recommandation for these tyres ?
#34
Rennlist Member
Thread Starter
What annoys me is that I have to brake earlier than a stock 996 gt3 that is heavier, let alone that feeling that it does not really brake. The former issue may be (IMHO) caused by to few load transfer. The second one is, I guess, due to being more accustomated to slicks than semi.
Could you please elaborate on 996 gt3 Vs cup main differences, relevant in my case ? (suspension wise)
Rear tyres sizes, obviously damper and spring rates...
many thanks for all the replies
Could you please elaborate on 996 gt3 Vs cup main differences, relevant in my case ? (suspension wise)
Rear tyres sizes, obviously damper and spring rates...
many thanks for all the replies
#35
Originally Posted by cid042
What annoys me is that I have to brake earlier than a stock 996 gt3 that is heavier, let alone that feeling that it does not really brake. The former issue may be (IMHO) caused by to few load transfer. The second one is, I guess, due to being more accustomated to slicks than semi.
Could you please elaborate on 996 gt3 Vs cup main differences, relevant in my case ? (suspension wise)
Rear tyres sizes, obviously damper and spring rates...
many thanks for all the replies
Could you please elaborate on 996 gt3 Vs cup main differences, relevant in my case ? (suspension wise)
Rear tyres sizes, obviously damper and spring rates...
many thanks for all the replies
Sounds you have some of the items sorted on your car. But monoball upper rear mounts, adjustable front and rear control arms. Adjustable toe links. And of course the spring rates, dampers, camber, ride height and toe that all make a pretty big difference on handling on the track. The early cups(if I recall correctly) did not have monoball rear control arms or solid caster pucks. But seems like most guys installed them latter. So if you have cup seat time it highly possible yours had rear monoball arms and solid pucks. Monoballs in the rear makes an incredible difference with all the rear weight. My car got the latter monoball 997 cup dogbones which none of the 996cups came with that I am aware.
#36
Rennlist Member
Thread Starter
Okay, so the car is now ready for its first test at Dijon, on Friday, with its new springs. Unfortunately, we have not been able to put the 2 way dampers I would have liked to, so we revalved a set of early 996 cup ones.
Springs are 70 Nm/mm front & 160 Nm/mm rear, for the first try. The first goal is to see if it can brake correctly with more weight shift leading to less ABS usage. Coming from 240/260 Nm/mm, the difference should be obvious, and I think that I will have to go back, at least a little bit.
I will let you know how it goes, handling/feeling/braking wise and if it does something to the lap times...To be continued...Cedric
Springs are 70 Nm/mm front & 160 Nm/mm rear, for the first try. The first goal is to see if it can brake correctly with more weight shift leading to less ABS usage. Coming from 240/260 Nm/mm, the difference should be obvious, and I think that I will have to go back, at least a little bit.
I will let you know how it goes, handling/feeling/braking wise and if it does something to the lap times...To be continued...Cedric
#37
Rennlist Member
Thread Starter
Quick feedback from last race weekend at Dijon with the new setup :
- The braking is far better, and I can, now, modulate the brakes without the ABS engaging every time I touch them (also I have removed the brake assistance)
- I can feel the car loading its front wheels far better
- I really lack rear end grip/handling.
* I do not know if its by comparison with the Cup S I drove the same day which had too much rear (or too few front :-P)
* Or if it is the rear spring that are too hard versus fronts (or vice-versa). ARB were full soft rear, full stiff front.
* I do not think it has much to do with aero, as these cars do not seem to have much of it…
Lap time Wise : A full 3 sec better than last year, BUT on fresh tyres (sport cup 2) Vs old and tired ones last year. On a 1'30-1'33 lap.
RAce 1 : DNF ; Race 2 : 1st (in the last turn, Vs a Manthey modded 991 GT3 RS :-))
- The braking is far better, and I can, now, modulate the brakes without the ABS engaging every time I touch them (also I have removed the brake assistance)
- I can feel the car loading its front wheels far better
- I really lack rear end grip/handling.
* I do not know if its by comparison with the Cup S I drove the same day which had too much rear (or too few front :-P)
* Or if it is the rear spring that are too hard versus fronts (or vice-versa). ARB were full soft rear, full stiff front.
* I do not think it has much to do with aero, as these cars do not seem to have much of it…
Lap time Wise : A full 3 sec better than last year, BUT on fresh tyres (sport cup 2) Vs old and tired ones last year. On a 1'30-1'33 lap.
RAce 1 : DNF ; Race 2 : 1st (in the last turn, Vs a Manthey modded 991 GT3 RS :-))
Last edited by cid042; 06-27-2018 at 05:01 AM. Reason: Forgot something
#38
Originally Posted by cid042
Quick feedback from last race weekend at Dijon with the new setup :
- The braking is far better, and I can, now, modulate the brakes without the ABS engaging every time I touch them (also I have removed the brake assistance)
- I can feel the car loading its front wheels far better
- I really lack rear end grip/handling.
* I do not know if its by comparison with the Cup S I drove the same day which had too much rear (or too few front :-P)
* Or if it is the rear spring that are too hard versus fronts (or vice-versa). ARB were full soft rear, full stiff front.
* I do not think it has much to do with aero, as these cars do not seem to have much of it…
Lap time Wise : A full 3 sec better than last year, BUT on fresh tyres (sport cup 2) Vs old and tired ones last year. On a 1'30-1'33 lap.
RAce 1 : DNF ; Race 2 : 1st (in the last turn, Vs a Manthey modded 991 GT3 RS :-))
- The braking is far better, and I can, now, modulate the brakes without the ABS engaging every time I touch them (also I have removed the brake assistance)
- I can feel the car loading its front wheels far better
- I really lack rear end grip/handling.
* I do not know if its by comparison with the Cup S I drove the same day which had too much rear (or too few front :-P)
* Or if it is the rear spring that are too hard versus fronts (or vice-versa). ARB were full soft rear, full stiff front.
* I do not think it has much to do with aero, as these cars do not seem to have much of it…
Lap time Wise : A full 3 sec better than last year, BUT on fresh tyres (sport cup 2) Vs old and tired ones last year. On a 1'30-1'33 lap.
RAce 1 : DNF ; Race 2 : 1st (in the last turn, Vs a Manthey modded 991 GT3 RS :-))
#39
Rennlist Member
Thread Starter
The diff seems good, no problem feeling it dealing with the frequent power oversteers.
The rear end is stable under braking, may be touchy in turn-in, and completely loose in the exit (acceleration) of the turn.
The are no really slow corners in Dijon, but it is the same in high and medium speed corners.
The rear end is stable under braking, may be touchy in turn-in, and completely loose in the exit (acceleration) of the turn.
The are no really slow corners in Dijon, but it is the same in high and medium speed corners.
#40
Originally Posted by cid042
The diff seems good, no problem feeling it dealing with the frequent power oversteers.
The rear end is stable under braking, may be touchy in turn-in, and completely loose in the exit (acceleration) of the turn.
The are no really slow corners in Dijon, but it is the same in high and medium speed corners.
The rear end is stable under braking, may be touchy in turn-in, and completely loose in the exit (acceleration) of the turn.
The are no really slow corners in Dijon, but it is the same in high and medium speed corners.
#42
Originally Posted by cid042
Unfortunately not, it is full soft, and full stiff front.
#43
Rennlist Member
Thread Starter
Thanks for the advice. I will try to follow this way. The ability to adjust the alignment at the track, and limited track time will be the challenges ;-)
#44
Race Car
70nm front and 160nm rear are the springs in the car right now? That's a huge split front to rear and likely causing the imbalance issue you're seeing. I run a 30nm split front to rear on my car and like the balance of it and can fine tune with wing and shocks to get the car comfortable on any track I run including bumpy surfaces. if you like the way the front is working now I'd go down to a spring in the 110nm range in the rear.