Allroad suspension - Arnott bags, Bilstein shocks
04-24-2012, 06:25 AM
#21
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Ride, particularly in L1 is hard. Mexchanic know says shocks are bad (OEM's with 150k).
In light of the discussion on this thread, should I replace shocks with Arnot Bilstein kit or OEM Audi shocks?
How hard a DIY project is this?
Thank you.
04-24-2012, 06:49 AM
#22
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Thread Starter
Taking the shocks/springs off is not hard at all.
Disconnecting the shocks from the springs, and replacing one or the other not difficult either.
OEM shocks are around $500 each. Arnott/Bilstein 2 for $700 or so.
I have the Arnott springs/bags (Gen 2) in the front (firmer, but not harsh by all means), but a bit under dammpened with the (old) stock shocks; I plan to replace with Bilstein shocks hoping they match the higher spring rate of the Arnott bags better (may even sent them to Bilstein for custom valving)
I replaced the rear shocks with Arnott/Bilstein shocks (old OEM were worn). Works well even in conjunction with the stock airbags. Long term: will replace stock bags with Gen 2 Arnotts.
Note: the stock rear shocks have the 'trailer' feature (a valving system that helps when heaving loads are detected in the rear). This feature is NOT available on the Arnott/Bilstein shocks. I currently don't tow (looking for a lower cost solution for Class IV hitch than is currently available from Bosal or the reverse engineered solution available from forum member here or other forum).
Disconnecting the shocks from the springs, and replacing one or the other not difficult either.
OEM shocks are around $500 each. Arnott/Bilstein 2 for $700 or so.
I have the Arnott springs/bags (Gen 2) in the front (firmer, but not harsh by all means), but a bit under dammpened with the (old) stock shocks; I plan to replace with Bilstein shocks hoping they match the higher spring rate of the Arnott bags better (may even sent them to Bilstein for custom valving)
I replaced the rear shocks with Arnott/Bilstein shocks (old OEM were worn). Works well even in conjunction with the stock airbags. Long term: will replace stock bags with Gen 2 Arnotts.
Note: the stock rear shocks have the 'trailer' feature (a valving system that helps when heaving loads are detected in the rear). This feature is NOT available on the Arnott/Bilstein shocks. I currently don't tow (looking for a lower cost solution for Class IV hitch than is currently available from Bosal or the reverse engineered solution available from forum member here or other forum).
I replaced all 4 bags with Gen I Arnots.
Ride, particularly in L1 is hard. Mexchanic know says shocks are bad (OEM's with 150k).
In light of the discussion on this thread, should I replace shocks with Arnot Bilstein kit or OEM Audi shocks?
How hard a DIY project is this?
Thank you.
Ride, particularly in L1 is hard. Mexchanic know says shocks are bad (OEM's with 150k).
In light of the discussion on this thread, should I replace shocks with Arnot Bilstein kit or OEM Audi shocks?
How hard a DIY project is this?
Thank you.
04-25-2012, 01:41 PM
#23
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I replaced all 4 bags with Gen I Arnots.
Ride, particularly in L1 is hard. Mexchanic know says shocks are bad (OEM's with 150k).
In light of the discussion on this thread, should I replace shocks with Arnot Bilstein kit or OEM Audi shocks?
How hard a DIY project is this?
Thank you.
Ride, particularly in L1 is hard. Mexchanic know says shocks are bad (OEM's with 150k).
In light of the discussion on this thread, should I replace shocks with Arnot Bilstein kit or OEM Audi shocks?
How hard a DIY project is this?
Thank you.
05-12-2012, 04:36 AM
#26
AudiWorld Senior Member
Thread Starter
Confirmed that Bilstein offers custom revalving for Bilstein shocks.
NO answer from Arnott: asked them if I can order the revalving from them (all they have to do is tell Bilstein to ship them the revalved version).
Here is a thought: I could take my rear Arnott/Bilstein out and ship to Bilstein for revalving; alternative: I will need front Arnott/Bilstein soon. Have Arnott ship them to Bilstein for revalving (at least one time shipping saved). Prefer this one. Will post when I am ready to go that way.
05-12-2012, 04:43 AM
#27
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Thread Starter
I am sure they have considered it. If the shocks could NOT handle the entire range (wheel travel AND setpoint change), it would immediately destroy the shocks (no shock is mechanically designed to bottom out and the take entire dynamic force of car/wheel).
Since Bilstein supplies the shocks, they surely will have run the calculation.
05-30-2012, 07:19 PM
#28
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Hey this is a great thread! I've been trying in vain to get answers to these questions since buying my C5 a few months ago, and am tearing my hair out.
Now I've learned more in the last five minutes than the previous five months!
I've done the 402 mod, and find - like others in the thread - that it makes the ride completely horrible at L1. At L2, it's bearable but wallowy, bouncy and definitely not conducive to sports driving. More like an allweather ocean racer in choppy seas perhaps.
I'm in Australia btw and was lucky enough to find a 2001 2.7TT with 6-sp MT in showroom condition, under 80,000 km (50,000 miles) on the clock. Atlas Grey if you're interested.
I also have a 1.8T with much happening under the hood and lowered springs, revalved Bilsteins etc. More of that later.
My diagnosis of the stock AR suspension is that, first, it is hopelessly under-damped (but could this be worn shocks at only 50,000 miles?). And second, while the damping rate presumably remains the same as you raise or lower the suspension, spring rates do not. In fact, as you get lower you're taking air pressure out of the bags so you are making the springs SOFTER. This is the opposite of what you want if you're trying to achieve sports handling. You need more control by making everything harder.
It's this latter aspect which I think causes both Arnotts and Bilstein to lose interest. Too hard, as the changing spring rates upset the balance between spring and damping rates.
The best you can hope for is to get the damping rates right at one ride level and accept that at any other level it will be less than perfect, and may be really terrible. But this needn't be a disadvantage if you want to ride at L1 all the time and only use the higher levels if you're on rough ground or trying to climb a high kerb or driveway.
Another confound of course is that damping rates (and possibly spring rates) may change as the suspension ages and deteriorates, as well as in summer and winter, so the calculations are likely to be a bit rubbery. Not to mention the need for different settings for compression and rebound and possibly for high and low velocity movements.
Bilstein can of course revalve their shocks (I assume all of them, certainly the sports range), but the question is what would they revalve them to? My A4 has Eibach lowering springs fitted, but the Bilsteins were still going to make them too high. So in order to give myself some control over ride height, I had Bilsteins machine a range of grooves in the body for the spring perch (can only be adjusted off-car, natch). Ride height is now perfect for my needs, but can they get the damping rates right? I've had them back twice and they are close, but still not right. The fronts lack control on low-velocity rebound which means when you hit a gentle bump (eg different heights in road surfaces after road repairs), she pitches up and takes a couple of bounces to come under control. Not enough to go through the hassle of removing them yet again and waiting two weeks for them to come back from Bilstein, but an irritation nonetheless.
So for our purposes, the trick would be to find out what the spring rate is at a particular ride height (different of course with OEM, Arnotts Gen I and Gen II) and try and work out with Bilstein what an appopriate damping rate would be for this spring rate.
If someone can hit on the correct formula, this would be fantastic for the rest of us.
My apologies if none of this is new to you. Also for the verbal incontinence:-)
Now I've learned more in the last five minutes than the previous five months!
I've done the 402 mod, and find - like others in the thread - that it makes the ride completely horrible at L1. At L2, it's bearable but wallowy, bouncy and definitely not conducive to sports driving. More like an allweather ocean racer in choppy seas perhaps.
I'm in Australia btw and was lucky enough to find a 2001 2.7TT with 6-sp MT in showroom condition, under 80,000 km (50,000 miles) on the clock. Atlas Grey if you're interested.
I also have a 1.8T with much happening under the hood and lowered springs, revalved Bilsteins etc. More of that later.
My diagnosis of the stock AR suspension is that, first, it is hopelessly under-damped (but could this be worn shocks at only 50,000 miles?). And second, while the damping rate presumably remains the same as you raise or lower the suspension, spring rates do not. In fact, as you get lower you're taking air pressure out of the bags so you are making the springs SOFTER. This is the opposite of what you want if you're trying to achieve sports handling. You need more control by making everything harder.
It's this latter aspect which I think causes both Arnotts and Bilstein to lose interest. Too hard, as the changing spring rates upset the balance between spring and damping rates.
The best you can hope for is to get the damping rates right at one ride level and accept that at any other level it will be less than perfect, and may be really terrible. But this needn't be a disadvantage if you want to ride at L1 all the time and only use the higher levels if you're on rough ground or trying to climb a high kerb or driveway.
Another confound of course is that damping rates (and possibly spring rates) may change as the suspension ages and deteriorates, as well as in summer and winter, so the calculations are likely to be a bit rubbery. Not to mention the need for different settings for compression and rebound and possibly for high and low velocity movements.
Bilstein can of course revalve their shocks (I assume all of them, certainly the sports range), but the question is what would they revalve them to? My A4 has Eibach lowering springs fitted, but the Bilsteins were still going to make them too high. So in order to give myself some control over ride height, I had Bilsteins machine a range of grooves in the body for the spring perch (can only be adjusted off-car, natch). Ride height is now perfect for my needs, but can they get the damping rates right? I've had them back twice and they are close, but still not right. The fronts lack control on low-velocity rebound which means when you hit a gentle bump (eg different heights in road surfaces after road repairs), she pitches up and takes a couple of bounces to come under control. Not enough to go through the hassle of removing them yet again and waiting two weeks for them to come back from Bilstein, but an irritation nonetheless.
So for our purposes, the trick would be to find out what the spring rate is at a particular ride height (different of course with OEM, Arnotts Gen I and Gen II) and try and work out with Bilstein what an appopriate damping rate would be for this spring rate.
If someone can hit on the correct formula, this would be fantastic for the rest of us.
My apologies if none of this is new to you. Also for the verbal incontinence:-)
05-30-2012, 07:50 PM
#29
AudiWorld Senior Member
Thread Starter
Kermac:
Couple of comments.
a) the spring rate is NOT changing a lot with height/level.
I have a graph somewhere, but it is VERY flat. If the bags where perfect cylinders, only the WEIGHT would cause the spring rate to go up (=increase the pressure).
b) I am still fantasizing about a means to artificially increase 'weight'. Thinking along the lines of finding a rubber rope and connect to chassis and axle. Even if tensioned with only 250 lbs, that still amounts to a 25% or so more 'weight' (=higher air pressure = higher spring rate).
c) don't forget the increased spring rate caused by the Hotchkis most AR ethusiast have (at least in single wheel spring action)
d) getting valving right? Well, its under dampened (in my front case: new Gen 2 (stiffer), Hotchkis, LOTS of 407, plus worn stock shocks. 18x8 wheels with 245/45x18 tires (bit heavier than stock). Result: terrible.
So Bilstein plus 35% higher damping rate should help. Unless I find a way to further increase the pressure/spring rate in the bags.
e) Goofy idea: fill air bag with high viscosity fluid. Less compressible media in there = higher spring rate.
f) Goofier idea: instead of air (very compressible), fill air bag with other, less compressible media
To all those tinkerers out there: pick up the challenge on hand.
Couple of comments.
a) the spring rate is NOT changing a lot with height/level.
I have a graph somewhere, but it is VERY flat. If the bags where perfect cylinders, only the WEIGHT would cause the spring rate to go up (=increase the pressure).
b) I am still fantasizing about a means to artificially increase 'weight'. Thinking along the lines of finding a rubber rope and connect to chassis and axle. Even if tensioned with only 250 lbs, that still amounts to a 25% or so more 'weight' (=higher air pressure = higher spring rate).
c) don't forget the increased spring rate caused by the Hotchkis most AR ethusiast have (at least in single wheel spring action)
d) getting valving right? Well, its under dampened (in my front case: new Gen 2 (stiffer), Hotchkis, LOTS of 407, plus worn stock shocks. 18x8 wheels with 245/45x18 tires (bit heavier than stock). Result: terrible.
So Bilstein plus 35% higher damping rate should help. Unless I find a way to further increase the pressure/spring rate in the bags.
e) Goofy idea: fill air bag with high viscosity fluid. Less compressible media in there = higher spring rate.
f) Goofier idea: instead of air (very compressible), fill air bag with other, less compressible media
To all those tinkerers out there: pick up the challenge on hand.
05-31-2012, 03:03 AM
#30
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Gee - another great post! Thanks vtraudt - I'm learning heaps from you guys.
I've obviously been going down the wrong path with the assumption that they drop the ride height by reducing the pressure in the bags. So what's the mechanism? I did read the primer a couple of times, but didn't find a lot of answers in it.
Love your idea of the rubber rope. Let us know how you go - you could be onto a world first (be sure and patent it...)
I know a lot of AR enthusiasts put on stiffer roll bars, but I don't see the point in that until you've got your spring and damping rates right. As you say, the bar only acts on one wheel at a time, having the opposite effect on the other.
Likewise, I won't be putting on anything bigger in the way of wheels and tyres until this is sorted, nor increasing power output beyond the basic St I flash (240 kW /320 hp). This provides more power than the suspension can safely cope with IMHO. But the factory brakes are so bad I think an upgrade may be the next thing. How come Audi made so many errors in the design of what is basically a fangtastic car?
What's the 407 you have lots of?? What is 407 exactly?
Do you think I'm correct in identifying damping rates as contributing more to the problem than spring rates? Most owners of course fit Arnotts bags when the OEM ones expire and leave the stock shocks in place. From the enthusiast's point of view, you'd probably be better with the stock bags and Bilsteins all round.
However, I guess the combination of Arnotts Gen IIs AND Bilsteins would be better although as I said I don't know how much stiffer it would end up. You probably don't need a whole lot more stiffness on compression but heaps more on rebound to bring the initial bounce under control.
If Bilstein were just prepared to put a bit of development work into it, I'm sure revalving would be a simple formula. There might be enough performance ARs on the roads in the US to justify the development cost. Here you could count them on one hand.
I've obviously been going down the wrong path with the assumption that they drop the ride height by reducing the pressure in the bags. So what's the mechanism? I did read the primer a couple of times, but didn't find a lot of answers in it.
Love your idea of the rubber rope. Let us know how you go - you could be onto a world first (be sure and patent it...)
I know a lot of AR enthusiasts put on stiffer roll bars, but I don't see the point in that until you've got your spring and damping rates right. As you say, the bar only acts on one wheel at a time, having the opposite effect on the other.
Likewise, I won't be putting on anything bigger in the way of wheels and tyres until this is sorted, nor increasing power output beyond the basic St I flash (240 kW /320 hp). This provides more power than the suspension can safely cope with IMHO. But the factory brakes are so bad I think an upgrade may be the next thing. How come Audi made so many errors in the design of what is basically a fangtastic car?
What's the 407 you have lots of?? What is 407 exactly?
Do you think I'm correct in identifying damping rates as contributing more to the problem than spring rates? Most owners of course fit Arnotts bags when the OEM ones expire and leave the stock shocks in place. From the enthusiast's point of view, you'd probably be better with the stock bags and Bilsteins all round.
However, I guess the combination of Arnotts Gen IIs AND Bilsteins would be better although as I said I don't know how much stiffer it would end up. You probably don't need a whole lot more stiffness on compression but heaps more on rebound to bring the initial bounce under control.
If Bilstein were just prepared to put a bit of development work into it, I'm sure revalving would be a simple formula. There might be enough performance ARs on the roads in the US to justify the development cost. Here you could count them on one hand.