Schnelletrecker
Member
Hi,
in this thread http://www.a2oc.net/forum/showthread.php?t=6066 the question emerged why to pay so much for a set of aftermarket shocks to get rid of bouncing ride behaviour (and ride harshness).
Sure, the price tag of the recommended Koni FSD shocks has a deterrent effect at first glance. But let’s go a little more into detail.
IMHO a well done suspension upgrade is one of the most effective mods to realise on A2s. However there are several A2 typical given facts that cannot be changed but should be considered during a suspension upgrade:
A) An aluminium body is considerable stiffer both in torsion and bending than regular steel designs of similar shape (same effect with mountain bikes, i.e. rather “soft“ classic chrome-moly steel frame versus „stiff“ oversized aluminium frame).
B) The relatively high A2 centre of gravity.
C) The relatively short wheelbase (short moment arms promote sway motions especially in conjunction with point B.
D) The very differring load between front and rear axle.
As we know the A2 stock suspension setup featuring linear springs (with only little initial sensitivity thus rough initial response) and very weak damping forces does not match the above listed A2 "handicaps“ properly.
---------------------------------------------------------------
A possible sophisticated (but expensive) A2 supension solution could be a set of custom made springs that features distinctive progressive characteristics. On the one hand this progressive setting would allow
- nice smooth compensation of small to mid size road surface irregularities and
- on the other hand also would prevent bottom out tendencies effectively.
However, because such progressive springs cannot be used safely on A2s without strong damping forces, two features have to be incorporated:
I. a wide-range adjustability of powerful rebound damping with preferably multi-stage performance to match the varying progressive spring rates and
II. a custom fine-tuned compression damping valve.
That special compression valve should be able to mobilise sensitive low- to midspeed response characteristics adressing mainly small road surface imperfections for comfort reasons. At the same time these rather moderate low/mid speed compression (and also rebound) damping forces must still provide enough strength for controlling the comparable small initial spring rate(s) of the progressive springs with authority. So handling capabilities and also roll/pitch motion control must not be affected negatively.
But I suspect this proposed “ideal” custom suspension setup would be very hard to realise
for our cars since nice handling performance, sound roll/pitch compensation and comfortable/smooth initial response are very difficult to reconcile.
---------------------------------------------------------------
Because of these above described custom damping/spring tuning related difficulties the mentioned Koni FSD dampers come into play again. Their damping setup turns out to be a compromise between nice balance and comfort especially on less than perfect roads:
1. The FSD compression damping characteristics have been optimised for dealing even with wicked road conditions (no bottom out, no bounce), however at the expense of lowspeed sensitivity. Positive side effects of such rather high compression forces are good handling abilities and reduced pitch and roll motions. So with respect to the compression valving, the FSDs are well suited for progressive type springs up to 35 mm of lowering.
2. The FSD rebound damping, being uniquely triggered mainly by frequency, thus is multi-staged in a special way. In particular with progressive springs unwanted low frequency car body motions (roll/pitch) can develop. The FSDs should have no problem to automatically minimise these 1 Hz body motions by the now stiffened rebound damping force mode. However I presume too weak rebound damping force in combination with progressive springs at certain situations [for example if the high frequency damping mode(= low amplitude rebound force) is activated and the springs at the same time got more or less packed coincidentally]. Then those packed progressive springs, now holding high spring rates, can expand very quickly.
So to fill this FSD-“gap” of lowspeed compression sensitivity depicted in point 1, especially a 15“ wheel solution is indicated. Using that rim size combined with high profile tyres will nicely absorb small road surface irregularities but will not solve bouncing tendencies being mainly based on non-harmonising damping force/spring rate setups.
Finally a list of A2 suitable 15“ wheel sizes with corresponding comfort factors and unsprung mass comments can be found here:
http://www.a2oc.net/forum/showpost.php?p=47169&postcount=19
Cheers
in this thread http://www.a2oc.net/forum/showthread.php?t=6066 the question emerged why to pay so much for a set of aftermarket shocks to get rid of bouncing ride behaviour (and ride harshness).
Sure, the price tag of the recommended Koni FSD shocks has a deterrent effect at first glance. But let’s go a little more into detail.
IMHO a well done suspension upgrade is one of the most effective mods to realise on A2s. However there are several A2 typical given facts that cannot be changed but should be considered during a suspension upgrade:
A) An aluminium body is considerable stiffer both in torsion and bending than regular steel designs of similar shape (same effect with mountain bikes, i.e. rather “soft“ classic chrome-moly steel frame versus „stiff“ oversized aluminium frame).
B) The relatively high A2 centre of gravity.
C) The relatively short wheelbase (short moment arms promote sway motions especially in conjunction with point B.
D) The very differring load between front and rear axle.
As we know the A2 stock suspension setup featuring linear springs (with only little initial sensitivity thus rough initial response) and very weak damping forces does not match the above listed A2 "handicaps“ properly.
---------------------------------------------------------------
A possible sophisticated (but expensive) A2 supension solution could be a set of custom made springs that features distinctive progressive characteristics. On the one hand this progressive setting would allow
- nice smooth compensation of small to mid size road surface irregularities and
- on the other hand also would prevent bottom out tendencies effectively.
However, because such progressive springs cannot be used safely on A2s without strong damping forces, two features have to be incorporated:
I. a wide-range adjustability of powerful rebound damping with preferably multi-stage performance to match the varying progressive spring rates and
II. a custom fine-tuned compression damping valve.
That special compression valve should be able to mobilise sensitive low- to midspeed response characteristics adressing mainly small road surface imperfections for comfort reasons. At the same time these rather moderate low/mid speed compression (and also rebound) damping forces must still provide enough strength for controlling the comparable small initial spring rate(s) of the progressive springs with authority. So handling capabilities and also roll/pitch motion control must not be affected negatively.
But I suspect this proposed “ideal” custom suspension setup would be very hard to realise
for our cars since nice handling performance, sound roll/pitch compensation and comfortable/smooth initial response are very difficult to reconcile.---------------------------------------------------------------
Because of these above described custom damping/spring tuning related difficulties the mentioned Koni FSD dampers come into play again. Their damping setup turns out to be a compromise between nice balance and comfort especially on less than perfect roads:
1. The FSD compression damping characteristics have been optimised for dealing even with wicked road conditions (no bottom out, no bounce), however at the expense of lowspeed sensitivity. Positive side effects of such rather high compression forces are good handling abilities and reduced pitch and roll motions. So with respect to the compression valving, the FSDs are well suited for progressive type springs up to 35 mm of lowering.
2. The FSD rebound damping, being uniquely triggered mainly by frequency, thus is multi-staged in a special way. In particular with progressive springs unwanted low frequency car body motions (roll/pitch) can develop. The FSDs should have no problem to automatically minimise these 1 Hz body motions by the now stiffened rebound damping force mode. However I presume too weak rebound damping force in combination with progressive springs at certain situations [for example if the high frequency damping mode(= low amplitude rebound force) is activated and the springs at the same time got more or less packed coincidentally]. Then those packed progressive springs, now holding high spring rates, can expand very quickly.
So to fill this FSD-“gap” of lowspeed compression sensitivity depicted in point 1, especially a 15“ wheel solution is indicated. Using that rim size combined with high profile tyres will nicely absorb small road surface irregularities but will not solve bouncing tendencies being mainly based on non-harmonising damping force/spring rate setups.
Finally a list of A2 suitable 15“ wheel sizes with corresponding comfort factors and unsprung mass comments can be found here:
http://www.a2oc.net/forum/showpost.php?p=47169&postcount=19
Cheers
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