daniel mason
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| posted on 7/10/11 at 04:49 PM |
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Can someone please explain re-valving shocks
As above really. Can someone please tell me what's involved in re-valving suspension shocks? Why it's needed? And why aren't they
valves to suit when purchased as the manufacturers know the install? Cheers
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snakebelly
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| posted on 7/10/11 at 05:55 PM |
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im sure Matt (Procomp) will be along shortly, they will be doing ours in the next couple of weeks......
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greggors84
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| posted on 7/10/11 at 10:19 PM |
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Basically its changing the shims that limit the flow of oil from one side of the damper to the other.
Changing the shims will give you a different range of adjustment when you move the dial. I guess manufacturers fit a standard shim to all their
dampers its its too much work to set them all up individually. For most people as long as they have the right spring rate they will be happy.
If you know what you are doing its not hard to re valve dampers (not sure about all dampers as I only really have experience with koni and ohlins) but
you need the equipment to dyno them and re gas.
Chris
The Magnificent 7!
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austin man
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| posted on 7/10/11 at 10:41 PM |
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I think its only needed if you are looking at maximising the handling characteristics on the track I wouldnt see that use on the road would require
this or give any real noticeable differences
Life is like a bowl of fruit, funny how all the weird looking ones are left alone
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Sam_68
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| posted on 8/10/11 at 06:21 AM |
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As a VERY MUCH simplified answer to your question of why it is needed:
What you're actually trying to achieve is something related to 'critical damping' (note that I say 'related to' -
typically, it's 25-50% of critical damping coefficient, for road cars).
Critical damping is where the damper would stop the wheel/spring deflection exactly at the point of physical deflection, without it
overshooting and oscillating at all.
The mathematical formula for calculating critical damping coefficient is:
Coefficient of damping = square root(4xspring rate/sprung mass).
Pretty obviously, therefore, the amount of damping you're trying to achieve is related to both the spring rate and the corner weight... both of
which will vary from car to car (and spring rates and wheel rates will be different at each end of a car, even).
Cheap, single-adjustable shock absorbers allow you to very coarsely adjust the damping to suit the particular spring rate/corner weight, but on
most the range is far too stiff for very lightweight cars like Locaterfields (so you end up having a choice of only two or three adjustment settings
at the bottom end of the range), and in any case manufacturing tolerances mean that they are pretty inconsistent too... you'll find differences
between the response on 4 'identical' dampers if you put them on a dyno, so the most basic task is to create matching pairs of dampers,
almost like 'blueprinting' them, with valving giving an adjustment range that is well-related to your spring rates and sprung mass.
Then you get into the subject of high- and low- velocity damping:
Again as a VERY MUCH simplified explanation, high velocity damping (rapid deflection of the damper) deals mainly with the spring deflections caused by
imperfections in the road surface, whereas low velocity damping deals mainly with roll and pitch movements of the chassis caused by acceleration,
braking and cornering.
On more sophisticated dampers, you can modify the high- and low- speed damping characteristics independently of each other, to some degree, so (for
example) you can stiffen the low speed damping so that it temporarily 'props up' one corner of the car as it turns into a bend, affecting
the tyre load at that corner and hence modifying transientundersteer/oversteer characteristics without affecting the ride quality too much.
This is getting into the realms of black art, though, where you need to know what you're doing to achieve the optimum solution.
I'd strongly disagree with Austin Man - particularly on light cars, proper damping makes a massive difference to both ride quality and
handling on road use (arguably more important than on track, 'cos you've got more ruts, potholes and manhole covers to deal with on the
typical British B-road than you have at Silverstone  ). If you don't believe me, try driving an S1 Lotus Elise on its original Koni dampers
(which were heavily compromised by Lotus' development and manufacturing budget when the car was first introduced) back-to-back with one that has
been retrofitted with the Bisltein dampers from the Series 2 Elise.
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