customizing suspesion.
05-09-2010, 05:22 PM
#1
Nordschleife Master
Thread Starter
customizing suspesion.
I am wondering if anyone has thought about, or even started to make any changes to the suspsension (front or rear) for a pushrod activated shock setup?
Or better yet a pushrod activated torsional (radial) damper mono shock setup for the 928?
Or are those types of changes simply not allowed for most sanctioning bodies?
I am curious as one could really cut down on unsprung weight doing this.
The other benefit to the latter setup would be the complete elimination of the swaybars to a much more adjustable setup.
Or better yet a pushrod activated torsional (radial) damper mono shock setup for the 928?
Or are those types of changes simply not allowed for most sanctioning bodies?
I am curious as one could really cut down on unsprung weight doing this.
The other benefit to the latter setup would be the complete elimination of the swaybars to a much more adjustable setup.
05-09-2010, 05:32 PM
#2
Race Director
Colin
Do you have any pictures of this type of setup....it sounds like the Carrera GT to me...
Not sure about sanctioning bodies "allowing" it...but many groups tend to sort things based...
I do understand that the motion ratios of stock 928 suspension are a bit odd....but it does work very well on track.....even running far from ideal springs-shocks I have found the Estate to handle on par with Spec Miatas....which is considered among the best handling touring racers out there.....
Do you have any pictures of this type of setup....it sounds like the Carrera GT to me...
Not sure about sanctioning bodies "allowing" it...but many groups tend to sort things based...
I do understand that the motion ratios of stock 928 suspension are a bit odd....but it does work very well on track.....even running far from ideal springs-shocks I have found the Estate to handle on par with Spec Miatas....which is considered among the best handling touring racers out there.....
05-09-2010, 05:41 PM
#3
Nordschleife Master
Thread Starter
Brian,
The CGT uses a pushrod activated shock design. Yes.
It does not use the monoshock design with a torsional damper though.
I would really like to do this as one could use the pushrod and mount the pivot to the pivot bar of the upper a-arm and then position the shock/spring to the firewall where on the other side would be a pad and a roll-cage attachment. This would pull a ton of flex out of the front end without having to reinforce the shock towers. Plus as previously mentioned this would drop a fair number of pounds of unsprung weight off each corner.
The CGT uses a pushrod activated shock design. Yes.
It does not use the monoshock design with a torsional damper though.
I would really like to do this as one could use the pushrod and mount the pivot to the pivot bar of the upper a-arm and then position the shock/spring to the firewall where on the other side would be a pad and a roll-cage attachment. This would pull a ton of flex out of the front end without having to reinforce the shock towers. Plus as previously mentioned this would drop a fair number of pounds of unsprung weight off each corner.
05-09-2010, 06:38 PM
#4
I have thought about this a bit, Ill start with my thoughts on the rear of the car.
As far as push rod based shocks an easy setup would be to have bell cranks mounted in the hatch area right next to the holes for the top mount of the coilovers and have a pushrod go from the stock location on the control arm up through the floor to the cranks and mount the shocks in the hatch on a brace of sorts that would ideally tie in with the roll cage. This would make it really easy to adjust and allow for clever alternatives to swaybars if it was found to be needed.
Don't forget about pull rods, I didnt see a clear path for these though. The most likely place for them is to mount the pull rod next to the upper control arm as long as this didn't create any strange compliance effects. This would require a new subframe that could mount them or a very solidly mounted drivetrain to build brackets off of. The axle is in the way if you don't direct the pull rod downward and aft considerably if I remember correctly.
As far as modern radial dampers go I remember them being first used in F1 on a Ferrari I beleive, probably incredibly expensive. Citroen 2cv used radial friction dampers that were really cheap, but probably not ideal. This car also had a suspension that was linked front to rear not side to side. This had a number of benefits that suited that car. A 90's two seater Alfa also had a front to rear linked suspension, but it was all hydraulic. Worked well, but it was very complicated. The radial dampers may have trickled down to something more reasonable, I havent checked in a while.
As far as up front, I have noticed the really odd motion ratio. Seems like the arm that acts on the coilover goes from the axis of the lower control arm mounting points and up at a 30 degree angle or so, compared to the control arm, to where the shock mounts on the bracket with the swaybar. If that arm makes a smaller than 90 degree angle with the top coilover mount in the instantaneous direction of its motion then it is progressive, if it is a larger angle than 90 it is digressive. Seems like it is digressive from my eye balling it, I would bet the stock springs are progressive if anyone ever measured them.
I think space restricts the appropriate use of a push or pull rod here without drastic changes. Although a pull rod would likely be more feasable if a mounting could be made to the crossmember (or a new crossmember that would accept a lowered engine with a dry sump) for coil overs where the rack plate mounts. Ground clearance would suck though. A pull rod coming from a custom upper control arm to a bell crank on the lower frame rail, acting through the inside of the A on a custom lower control arm, which acts on the horizontal coilover connected to the crossmember.
Would be interesting to see, but a total redesign would give the best results with a push/pull rod setup as opposed to using stock stuff.
As far as push rod based shocks an easy setup would be to have bell cranks mounted in the hatch area right next to the holes for the top mount of the coilovers and have a pushrod go from the stock location on the control arm up through the floor to the cranks and mount the shocks in the hatch on a brace of sorts that would ideally tie in with the roll cage. This would make it really easy to adjust and allow for clever alternatives to swaybars if it was found to be needed.
Don't forget about pull rods, I didnt see a clear path for these though. The most likely place for them is to mount the pull rod next to the upper control arm as long as this didn't create any strange compliance effects. This would require a new subframe that could mount them or a very solidly mounted drivetrain to build brackets off of. The axle is in the way if you don't direct the pull rod downward and aft considerably if I remember correctly.
As far as modern radial dampers go I remember them being first used in F1 on a Ferrari I beleive, probably incredibly expensive. Citroen 2cv used radial friction dampers that were really cheap, but probably not ideal. This car also had a suspension that was linked front to rear not side to side. This had a number of benefits that suited that car. A 90's two seater Alfa also had a front to rear linked suspension, but it was all hydraulic. Worked well, but it was very complicated. The radial dampers may have trickled down to something more reasonable, I havent checked in a while.
As far as up front, I have noticed the really odd motion ratio. Seems like the arm that acts on the coilover goes from the axis of the lower control arm mounting points and up at a 30 degree angle or so, compared to the control arm, to where the shock mounts on the bracket with the swaybar. If that arm makes a smaller than 90 degree angle with the top coilover mount in the instantaneous direction of its motion then it is progressive, if it is a larger angle than 90 it is digressive. Seems like it is digressive from my eye balling it, I would bet the stock springs are progressive if anyone ever measured them.
I think space restricts the appropriate use of a push or pull rod here without drastic changes. Although a pull rod would likely be more feasable if a mounting could be made to the crossmember (or a new crossmember that would accept a lowered engine with a dry sump) for coil overs where the rack plate mounts. Ground clearance would suck though. A pull rod coming from a custom upper control arm to a bell crank on the lower frame rail, acting through the inside of the A on a custom lower control arm, which acts on the horizontal coilover connected to the crossmember.
Would be interesting to see, but a total redesign would give the best results with a push/pull rod setup as opposed to using stock stuff.
05-09-2010, 06:45 PM
#5
I forgot, monoshocks are great, but you still need a second shock unless you are willing to give up damping in pitch or damping in roll.
Not clear on your description of the idea you proposed in the last post... Can you clarify? I might just be reading it wrong, I can't tell.
edit: Nevermind I get what you are saying. There would still be inward flexing forces, they would just be acting in a differnt place, the base of the bell crank pivot.
Not clear on your description of the idea you proposed in the last post... Can you clarify? I might just be reading it wrong, I can't tell.
edit: Nevermind I get what you are saying. There would still be inward flexing forces, they would just be acting in a differnt place, the base of the bell crank pivot.
05-09-2010, 08:07 PM
#6
Nordschleife Master
Thread Starter
Chris,
Nice post and thanks for sharing your thoughts.
Ideally I would love to tie them in and use 1 shock, with the torsional bar in the middle acting as the swaybar. However the space constraints would I think require too much work.
However for the rear, I thought about going in through the original shock mounts and tying it into the roll cage.
But for the rear if one was to use a pull rod setup (like formula fords) then one could mount the shock under the car. Say modifying the aluminum cross brace for the anchor. It is very strong and the rest of the suspension bolts to it. I do agree putting the shocks inside the car would make a very nice and easy time to adjust ride height etc. though.
Nice post and thanks for sharing your thoughts.
Ideally I would love to tie them in and use 1 shock, with the torsional bar in the middle acting as the swaybar. However the space constraints would I think require too much work.
However for the rear, I thought about going in through the original shock mounts and tying it into the roll cage.
But for the rear if one was to use a pull rod setup (like formula fords) then one could mount the shock under the car. Say modifying the aluminum cross brace for the anchor. It is very strong and the rest of the suspension bolts to it. I do agree putting the shocks inside the car would make a very nice and easy time to adjust ride height etc. though.
05-09-2010, 08:22 PM
#7
Rennlist Member
See the front end of Rover P6 here....bellcranked to have spring against the firewall, but still has the shock vertical and direct...In a 928 you might fit the shock in there if there is more space.
http://www.britishv8.org/Articles/Rover-P6-Design.htm
jp 83 Euro S AT 52k
http://www.britishv8.org/Articles/Rover-P6-Design.htm
jp 83 Euro S AT 52k
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05-09-2010, 08:50 PM
#8
Colin think about the nett gain when you compare the weight of alloy shocks. With springs 600/400 my sprung weight is approx 9 kgs for all 4 shocks. It wouldn't be 9 kgs but I am being conservative. Now you can take it further and run the rear shocks I have upside down and do what Adrain did and have Ti pins made for the rear suspension. I suppose it would do down to 7 kgs or a bit less as I am counting the whole shock weight, ( that is not counting the 1 Kg gain from Ti pins) where I should be deducting the sprung part. Is it really worth it when that weight is so low?
Put in further context, look at the weight of the wheel, I think a magnesium wheel would be a better benefit as it is on the end of a lever effectively. A mag wheel weighs 8 kgs for the front and 9.5 for the rear and a fellow has a set here in Oz made by OZ (for sale too) Also the brake weight, lots of gains there, my Ferrari F50 set up is very light, kilos lighter than the GTS setup.
Or just have a look at what Mike Simard has done, all is very nice.
Cheers Greg
Put in further context, look at the weight of the wheel, I think a magnesium wheel would be a better benefit as it is on the end of a lever effectively. A mag wheel weighs 8 kgs for the front and 9.5 for the rear and a fellow has a set here in Oz made by OZ (for sale too) Also the brake weight, lots of gains there, my Ferrari F50 set up is very light, kilos lighter than the GTS setup.
Or just have a look at what Mike Simard has done, all is very nice.
Cheers Greg
05-09-2010, 10:41 PM
#10
Nordschleife Master
Thread Starter
I am already doing a 2 piece floating brake rotor design (380mm) for the front and rear to shave some unsprung weight. I am not however interested in doing ceramic brakes, the main reason is the cost. I checked it out and it would be around $15-20k to do it right with ceramic brakes. And that is JUST the brakes.
As to the rims, I have 18x11" rims which weight a tick over 14 lbs a piece (6.4kg) So I have already shaved another 1.5-2kg off each corner from your setup Greg. However these rims are track only rims, if I were to go over a bit pothole the shells would bend.
I am going with much stiffer than 600/400 setup. And I will be doing an invert shock mount if I stay normal. But sometimes it is fun to do it just cause you can. The weight savings is just one more benefit.
Down the road I will build my own car from scratch, and I will do the pushrod style shock setup on it. But got to thinking about doing it on the 928 too.
As to the rims, I have 18x11" rims which weight a tick over 14 lbs a piece (6.4kg) So I have already shaved another 1.5-2kg off each corner from your setup Greg. However these rims are track only rims, if I were to go over a bit pothole the shells would bend.
I am going with much stiffer than 600/400 setup. And I will be doing an invert shock mount if I stay normal. But sometimes it is fun to do it just cause you can. The weight savings is just one more benefit.
Down the road I will build my own car from scratch, and I will do the pushrod style shock setup on it. But got to thinking about doing it on the 928 too.
05-09-2010, 11:29 PM
#11
Ceramic brakes are not that light when compared to the two piece discs, it just depends on which discs you are comparing. If you want and apples to oranges comparison, the Ferrari front discs I was offered weigh 6.5 kgs, with lots of reserve in stopping power, by that I mean heat dispersion ability. My front discs weigh around 7 kgs. (355 mm) will stop just as quick but don't have the same capacity. The setup that Colin refers to would have about the same heat capacity as the Ferrari stuff but will be closer to 9 kgs.
I passed on the Ferrari stuff, not because of the price, they were only $2K all up but because I wanted to avoid 19" wheels, they use a 394 mm disc on the front same as the ZR1 , I thought about buying them for the calipers only but they are a complex braking system with their anti friction system and I thought it would be more enjoyable just to give myself an upper cut than install them. They are beautifully made and have very nice pistons. Porsche btw went a different route with ceramic pistons.
As you probably know my track wheels I am very happy with are 18" with 9" fronts with a great offset. I will never do enough laps to need that much heat capacity and the ceramics don't last on the track anyway.
I don't know if I will run the rear shock upside down just because it make the job to fit them literally doubly difficult.
Greg
I passed on the Ferrari stuff, not because of the price, they were only $2K all up but because I wanted to avoid 19" wheels, they use a 394 mm disc on the front same as the ZR1 , I thought about buying them for the calipers only but they are a complex braking system with their anti friction system and I thought it would be more enjoyable just to give myself an upper cut than install them. They are beautifully made and have very nice pistons. Porsche btw went a different route with ceramic pistons.
As you probably know my track wheels I am very happy with are 18" with 9" fronts with a great offset. I will never do enough laps to need that much heat capacity and the ceramics don't last on the track anyway.
I don't know if I will run the rear shock upside down just because it make the job to fit them literally doubly difficult.
Greg