Information Suspension overview: sport springs, sport dampers, coilovers and airride

Schnelletrecker said:
Hello humps,

don't hesitate to post your new ride "feelings" here ;)
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I hope you have caught my 'feelings' in the other thread http://www.a2oc.net/forum/showthread.php?t=4807 specific to FSDs.

Anyway, something just came to me after a bit more driving with the FSDs. It is still a firm ride but much more controlled and subdued over the bumps. The handling has actually improved a lot, especially cornering, it is so flat now! I'm thinking if I installed FSDs with Polo 9N springs, will that combination make it a high comfort softer ride but still maintain safety against rolling because the FSDs are so good at that?

P.S. I'm actually enjoying more of the handling improvement than the extra comfort I got from these dampers!
 
humps said:
I'm thinking if I installed FSDs with Polo 9N springs, will that combination make it a high comfort softer ride but still maintain safety against rolling because the FSDs are so good at that?
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That’s fine seeing you satisfied with the Koni FSDs.

Well in Germany there are no experiences with A2’s modified with Polo 9N springs (this isn’t allowed here). If these Polo springs in fact are softer than the standard A2 springs I would not recommend this modification for safety reasons. The main reason is still the pretty high CG of our cars versus a Polo.
 
humps,

if your search/desire for comfort is “stronger“ than the overall-appearance you really should switch to 15“ wheels plus “balloony“ tyres. That would be an awesome combination with your current FSDs in terms of ultra smooth setting (for A2 relations). There are many nice 15“ rims designs out there.

Recommendable sizes would be:

6x15ET38 to ET25
6.5x15 ET35 to ET25
7x15 ET35 to ET30

and

195/55R15 tyres (195/60 would already be too large)

You will notice a very soft and pleasant ride using this combo without losing safety reserves!
 
Very good thread. Just to Add - my first A2 had H&R springs fitted and it was horrid, the ride was dire, and eventually went to Eibach - much better.
 
I can't imagine having the body kit and 15" wheels although the kit is nowhere near being installed at the moment. I'll stick to my standard SE rims for a while, but I think my next set of rubber will be 195/50. It should be much easier to find, cheaper and have a little more cushion so hopefully the ride will become even better!
 
195/50 on 16" rims

Hi Humps,

Just had a pair of Toyo 195/50 fitted to rear wheels. Still got 185/50 on front. There is a small improvement in ride quality at the rear. I wanted the fitter to put the new on the front, but was advised that it really was not a good idea as it can cause handling problems. When the fronts wear out I will be fitting 195/50 there too.

I notice the difference most on speed cushions and on those red squares at speed limit changes that vibrate the car. Noticably less vibration from the rear.

Nice tread pattern on the Toyo. Ride height up by 5mm and rims have an extra 5mm protection from kerbs.

John.
 
In one of the first reply, there is told you should stay away from H&R springs, but what about their coilovers???
any info 'bout that?
thank u
Sam
 
AudiA2Belgium said:
In one of the first reply, there is told you should stay away from H&R springs, but what about their coilovers???
any info 'bout that?
thank u
Sam
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Well there are no coilovers by H&R available for A2 vehicles. However, there is a complete sport suspension unit called H&R CUP-KIT featuring 40/35 mm lowering. The sport dampers used here are not adjustable. Anyway I would stay away from H&R due to the way too firm springs...
 
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Schnelletrecker said:
Well there are no coilovers by H&R available for A2 vehicles. However, there is a complete sport suspension unit called H&R CUP-KIT featuring 40/35 mm lowering. The sport dampers used here are not adjustable. Anyway I would stay away from H&R due to the way too firm springs...
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oke thanks
i heard a lot of good things 'bout H&R for other cars
now i've heared this i'll think to buy KW var 1
thanks guy's
 
Update:

Meantime I carried out an upgrade of my stainless FK Silverline-X coilovers, after 1 year of usage without any probs.

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It turned out that these yellow Koni sport dampers equipped coilovers provide quite comfortable ride quality (for sport suspension relations), definitely qualified for long-range routes. That is also based on the relatively low compression damping setup, supplying speedy response especially on wicked roads. So these characteristics will match most A2 drivers IMHO. However this was too smooth for me.
 
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Compression damping:

To increase the dynamic feedback at the steering wheel and also to reduce the distinctive annoying understeer-tendencies of any A2 (especially the diesels) I decided to modify the front dampers’ compression setting, In addition a relative high degree of rebound damping should be selected.

Unfortunately the good Koni sports dampers don’t feature a hand operated device to alter compression strength - so one must change internals.

For that the Koni experts of POOHL POWER (Germany) adjusted a new compression setting according to my specifications by using

1. a different bottom valve matching both the high front axle load and the actual FK spring characteristics

2. high-viscosity oil

A compression damping test was made pre- and post-mod. The stock setting reached 45 kilograms vs the new remarkable 105 kg “mark“. So compression damping now is more than twice as strong as intended by FK.
 
Rebound damping:

In additioon to the compression damping adaption the rebound setting was re-adjusted for harmonic ride reasons.

Although the rebound adjustability feature of the Koni dampers primarily is intended for resetting the stock rebound strength (after many many thousands of miles), they can be “misused” for more sporty ride purposes very efficiently. For instance by tuning very high rates of rebound damping all around, a car can almost fully lose its pitch and roll movements.

Next to the FK Koenigsport coilovers only the Silverline-X does offer a continuous rebound damping adjustment for A2 at both axes. However due to the very lightweight rear of the A2 it is highly recommended to change rebound cautiously at the rear. After having consulted POOHL POWER I turned the rear axle rebound 50% off full soft, i.e. 360 degrees. That is the maximum recommended rear rebound setup for A2s.

Applying more than that at the rear can result in tricky handling performance (abrupt oversteering) during dynamic load changes!

Based on last years driving experiences with different front rebound settings I finally set it at 30% off full soft, that is 360 degrees by operating the white Koni adjusting knob.

Front axle rebound damping generally can be adjusted even stronger than that. But too much front rebound damping sadly results in a quite rough ride, due to the incapability of absorbing potholes etc (depending on the amount of negative spring travel and the spring rate). Moreover the “hated” understeer-tendency would be intensified then.
 
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So both measures, i.e. the noticeable increase of compression damping at the front and the subsequent re-adjustment of rebound damping all around, changed the car’s handling significantly.

The A2 now behaves very neutrally and super-balanced on most surfaces, not only in dynamic situations. Body pitch and roll motions have been minimised, the increased compression damping in fact acts like a sturdy anti-roll bar.
Now virtually no understeer is left and no more “softish” feedback at the steering wheel. Although the dynamic reserves of the stock FK coilovers already were outstanding they have been extended once more. The significant front/rear axle load discrepancy (a concession to the A2 aluminium lightweight concept) seems to be “compensated”.



Finally two graphs depicting the actual (perfect IMHO) setting of the Koni damper chararcteristics in combination with FK coilovers for A2 diesels.
 
Last not least I would like to add another advantage of the above described compression damping modification. In consequence of the more “potent” bottom-valve, combined with high viscosity damper oil, a high static piston counterpressure is established, similar to high quality nitrogen gas sport dampers.

That “new” pressure does lift the A2 front axle about 20 mm statically – providing additional 20 mm of valuable residual spring travel!

To accommodate the car’s appearance the front spring seats have been lowered correspondingly. There’s no prob with insufficient main spring pre-load because of the auxiliary pre-load spring feature per strut.





P.S. I recommend using a dust cap for protecting the piston rod at the front suspension. These are not delivered for FK coilovers sadly. So I took a CV boot made by BMW (part# 32111118688) - cheap and well working contra water and dirt!
 
Schnelletrecker, this is mind blowing stuff for me!! It sounds very interesting, do you have a few photos of the different valves? Wow, I'm already happy with FSD and stock springs, dunno what I would do with a full set of coil overs!
 
Below shown are the three main types of dampers used for cars:

- mono tube high pressure gas
- twin tube hydraulic
- twin tube low pressure gas



There are only few disadvantages of a twin-tube hydraulic design versus a mono-tube nitrogen gas-type:

- High pressurised monotubes tend to respond more sensitively at low piston speeds than twin-tube designs. This quicker initial response characteristics is very welcome especially for track racing, However on public streets - being less than perfect - a more delayed/inertial (less agile) initial low speed response can be perceived more comfortable subjectively.

- Unlike monotube high pressure gas dampers the mounting orientation of hydraulic twin tube dampers is vertically primarily (up to maximum of about 40 degrees from vertical). That prevents generating an oil/gas emulsion.

- High pressure gas dampers are less prone to temperature changes than hydraulic oil dampers. So at low temps the damping oil – while becoming more viscous - can harden the damping. Meanwhile there are (high-tech) dampers available featuring an automated temperature compensation, meaning they automatically readjust the damping force depending on the oil temperature.

- Pressure-less hydraulic twin tubes can be internally modified or overhauled for relatively little money.
 
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humps said:
...do you have a few photos of the different valves? Wow, I'm already happy with FSD and stock springs, dunno what I would do with a full set of coil overs!
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Hello humps, I don’t have pics of a bottom valve because I was not allowed to enter the factory workshop - for KONI factory staff only. The Poohl-Power folks are former Koni employees. Anyhow a dynamic “test drive“ (also over very rough roads) with my A2 was included right after the upgrade.

Such bottom valves consist of a defined number of so called shims. These shims of different thickness’ and/or diameter are made of steel and can elastically bend at high oil pressures enabling pre-defined oil-flow. They can also feature thoroughly defined small slots and/or bores acting as oil passages.

By carefully selecting the number and the type of shims it is possible to realise any wanted damping characteristic - perfectly matching that specific car setup (axle loads, spring rates and also driving style if required). In addition small coils can be integrated into such bottom valves to accurately trigger damping force by fluid velocity.

For the rebound damping valve unit at the piston also needle valves can be applied in addition to shims.

The usage of a special damping oil does reduce heat accumulation, even if highly viscous.




So in general twin-tube-hydraulic dampers are well suited for tuning measures to custom match your specific car requirements. Both the piston-valve and the bottom-valve are accessible easily (with the right tools) and can be modded or exchanged. Same applies to the damper oil fluid.

Illustration of a bottom valve shims package:
 
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A brief introduction to compression damping modes​

The before shown two load/velocity diagrams are results of dynometer damper tests. In contrary to springs damping force is mostly triggered by velocity. So damping force does change depending on how fast the piston/rod moves.

Modern damper setups usually feature non-linear characteristics. Mostly a degressive damping mode is desired. Degressive means that the damping force remains more or less constant above a certain (high) fluid velocity. That eliminates too harsh damping effects over very rough roads while still mobilising best handling.

Progressively working dampers seem to be only made for some (slow) 4WD offroad cars. They do benefit from extra comfort but handling suffers clearly.



We have to differentiate between compression low-speed and compression high-speed damping.


1. Low speed compression damping addresses mainly the comfort reserves on less bumpy roads. Typically a rather soft damping force is applied in this case.

A relatively high compression damping force at low piston velocities basically promotes handling behaviour (e.g. high speed turns) and reduces body roll and pitch movements. Also nose diving tendencies at hard braking can be reduced considerably applying strong low compression forces. Typically good sport dampers feature sophisticated low speed compression abilities (best handling without being too harsh).

Low speed characteristics can be altered effectively by changing the oil viscosity for instance. If traction suffers or the ride quality tends to be too harsh especially over short-waved surface, the low speed rate is too strong and should be reduced.



2. High speed compression damping on the other hand deals with the ability to optimally handle bad road surface such like cobblestone, manhole covers or unclean expansion joints. So if you encounter bottom-out tendencies, the high speed compression damping capabilities can be too weak and should be increased.



Mostly changing the damping characteristics (setup) both in compression and rebound does have a considerable higher impact on ride comfort and ride performance than changing the spring rate!
 
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Talking FSD (Frequency Selective Damping):​

Koni FSDs are twin tube low pressure gas dampers. While checking out this new technology, the rebound damping force is no longer triggered by velocity only (like Koni red and yellow), but also by impulse frequencies activating a special oil-bypass-valve device.

The below pictured force/velocity diagram shows how selective this damping technology works.

Car body motions usually create a natural frequency of about plus/minus 1 HZ. A wheel (unsprung mass) on the other hand generates a frequency of about plus/minus 10 HZ as a rule.



To minimise the 1 HZ body roll and pitch motions a quite high rebound damping force is required.

To minimise the 10 HZ typical wheel frequency already low rebound damping force provides best comfort results.



So low frequency motions, for example in fast turns or during hard braking, will automatically stiffen up the damping (high amplitude rebound damping due to closed bypass valve) – thus increasing dynamic stability and safety noticeably. The blue 1HZ-curve is degressively (bi-linear) shaped and will therefore support handling excellently.

High frequency motions however initiated by rough cobblestone, deep-seated manhole covers or unclean expansion joints at bridges for instance are softened for comfort reasons – using relative low amplitude rebound damping based upon the now opened bypass valve. The red 10HZ- curve is progressively (bi-linear) shaped and does rather assist comfort than handling.

The main downside (for most folks maybe the only) of the FSD technology is that there are limitations when it comes to “serious” lowering. For most cars, up to a maximum degree of lowering of about 35 mm, the FSD dampers can still make use of their intelligent frequency selective damping. Below that amount of lowering, the predefined FSD effectiveness obviously is narrowed or disabled. Maybe then the residual spring travel is insufficient to properly activate the bypass valve (FSDs don’t like bump stops!). Or perhaps the body and wheel frequencies are “shifted“ too drastically because of too high spring rates...
 
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