Best Shocks for Autocross
10-24-2006, 01:26 PM
#31
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Originally Posted by Orthonormal,Oct 24 2006, 01:19 PM
As for the shaft diameter, I don't think I understand either. In my mind, the shaft diameter is related to compression of the gas charge, resulting in a static force and a weak spring response. The piston head diameter would be what determines the volume of oil that must be displaced.
10-24-2006, 03:50 PM
#32
Registered User
No, I meant shaft diameter. Shaft diameter determines how much fluid is displaced through the low speed valving for compression control. The shaft enters the shock body, and displaces fluid to the remote reservoir, where it is metered through a shim stack with adjustable preload (in the case of Moton, JRZ, Penske 8660 & 8760, and probably others).
Moton went to a large shaft diameter, as I understand it, because cars with aero downforce are very pitch sensitive, and as a result use extremely high spring rates. High spring rates lead to very small shock displacements, so to increase the compression sensitivity, Moton went to a large shaft diameter.
The down side for stock class autocross is that large shaft area leads to increased lifting force due to the shock gas pressure (lifting force per corner=pressure * shock shaft area). The result is an increase in ride height, which you cannot compensate for because the spring perch location must be at the stock location. You can try to run lower gas pressure, but then you risk cavitation and the resulting inconsistent shock response.
**Warning, advanced tech geek content**
One last thing: be weary of large ranges of adjustment. It isn't everything its hyped up to be. You can achieve large ranges, but it comes at the expense of hysteresis and a resulting loss of mechanical grip. (reference) If you approach the extremes of compression adjustment, and the car doesn't seem to respond as expected, it is probably due to this phenomenon. For best results, you really need to have the main compression valve stack (the shims on the piston) matched to the reservoir adjustment.
Steve
Moton went to a large shaft diameter, as I understand it, because cars with aero downforce are very pitch sensitive, and as a result use extremely high spring rates. High spring rates lead to very small shock displacements, so to increase the compression sensitivity, Moton went to a large shaft diameter.
The down side for stock class autocross is that large shaft area leads to increased lifting force due to the shock gas pressure (lifting force per corner=pressure * shock shaft area). The result is an increase in ride height, which you cannot compensate for because the spring perch location must be at the stock location. You can try to run lower gas pressure, but then you risk cavitation and the resulting inconsistent shock response.
**Warning, advanced tech geek content**
One last thing: be weary of large ranges of adjustment. It isn't everything its hyped up to be. You can achieve large ranges, but it comes at the expense of hysteresis and a resulting loss of mechanical grip. (reference) If you approach the extremes of compression adjustment, and the car doesn't seem to respond as expected, it is probably due to this phenomenon. For best results, you really need to have the main compression valve stack (the shims on the piston) matched to the reservoir adjustment.
Steve
10-25-2006, 06:37 AM
#34
Registered User
Back to the original poster: why are you convinced that you need high-end shocks? People have won national-level events on Konis and even the stock shocks. Sure, properly-tuned shocks will make you go a little faster, but not nearly as fast as a new set of V710s or A6s will.
10-25-2006, 06:43 AM
#35
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Originally Posted by Windscreen,Oct 24 2006, 06:50 PM
The result is an increase in ride height, which you cannot compensate for because the spring perch location must be at the stock location.
Is that the reason why you went with Penske and not Moton?
10-25-2006, 09:21 AM
#36
Originally Posted by Naka,Oct 24 2006, 09:47 AM
I didn't know Jason Saini sold Motons. How do I get a hold of him? Does he have a shop? He's from Chicago, right?
https://www.s2ki.com/forums/index.php?showtopic=329395
10-25-2006, 09:59 AM
#37
Registered User
In stock class, ride height changes due to legal modifications are permitted. Spring perch height must be per the stock dimensions.
Honestly, I went with Penske because I got a decent deal on them when I bought them used from Jason Saini. At the time I really didn't know much about shocks, but knew I wanted to buy some high end ones because of my autocross aspirations. If I started all over again and had to buy something new, I'd go with Penske or Ohlins.
And, BTW, Jason's Motons are sold and long gone. They now reside on Jarrad Rahal's car (yes, son of Bobby).
Steve
Honestly, I went with Penske because I got a decent deal on them when I bought them used from Jason Saini. At the time I really didn't know much about shocks, but knew I wanted to buy some high end ones because of my autocross aspirations. If I started all over again and had to buy something new, I'd go with Penske or Ohlins.
And, BTW, Jason's Motons are sold and long gone. They now reside on Jarrad Rahal's car (yes, son of Bobby).
Steve
10-25-2006, 04:00 PM
#40
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Originally Posted by PedalFaster,Oct 25 2006, 09:37 AM
Sure, properly-tuned shocks will make you go a little faster, but not nearly as fast as a new set of V710s or A6s will.
Tires = seconds
Shocks = tenths of seconds.
Stick with buying tires. bag them and keep them indoors, they will last a long time.