Rebound and bump for idiots

[daniel_csl]

Hi,

There appears to be a lot of experience with KW suspension on this forum so I thought I would pose the question... how does bump and rebound affect my ride quality.

I have read the pdf on thorney website but am having trouble relating to real world and my setup. For example, the pdf suggest rebound impacts dive and roll, whereas I thought softening off my compression (bump) would result in a great weight transfer, and ultimately grip?

Which setting has the greatest impact on ride comfort? ie help soaking up bumps and ridges while just cruising?

Thanks

[shimmy]

Hi,

There appears to be a lot of experience with KW suspension on this forum so I thought I would pose the question... how does bump and rebound affect my ride quality.

I have read the pdf on thorney website but am having trouble relating to real world and my setup. For example, the pdf suggest rebound impacts dive and roll, whereas I thought softening off my compression (bump) would result in a great weight transfer, and ultimately grip?

Which setting has the greatest impact on ride comfort? ie help soaking up bumps and ridges while just cruising?

Thanks

Most effective way of improving ride quality is by......










Going back to OEM as KW has a poor range for road settings

[Thorney]

lol.

I'm writing an article for a magazine about car set up so the full detail will have a wait (its a 5 page article) but in essence:

Spring - holds the car up and combined with ARB controls some aspects of the cars roll, stiffer spring means car will roll less but means it will take more of a bump to get it to compress (I wont go into progressive rates etc).

Compression (bump) damping - controls the speed at which the shock compresses when hitting a bump in the road, on 3 way suspension this is split between high speed and slow speed. High speed means high speed compression, ie hitting a kerb, slow speed is more transissional; undulations in the road. So, if you have a ride where the car feels too crashy over bumps then its likely your bump is too hard and needs to be softer. However if you go too soft the chances are the spring is too hard for your needs and you're better off changing a spring rather than running damping on full soft.

Rebound damping - this controls the speed the shock extends after compression, rebound tends to control the speed at which the car retains its balance, if the car feels bouncy the chances are the rebound is too soft and is reacting too quickly so you need to stiffen it up.

Add in tyres, wheels, ARB's, ride height, camber, castor, trail, toe, mono tube/twin tube, aero and driver style and you can see why it takes some time to really develop suspension for road or track. In development we tend to use three way adjustable (4 way sometimes buts its hard work) to set up damper settings which are then used on the less adjustable shocks for the road. Takes me 2 full days to set up a race car from scratch on three ways for example and assumes about three spring rate changes.

[Thorney]

There is also no 'right' answer, I tend to prefer very stiff springs and very soft damping as (IMO) it allows greater adjustment of grip over a wide range of applications, but other people prefer a very soft spring and very hard damping, its a case of whatever works for you.

Generally soft = grip but it comes at the expense of overall speed.

[glendog74]

Most effective way of improving ride quality is by......

Going back to OEM as KW has a poor range for road settings

Rubbish...

And you have had first hand experience of KW Shim? :smt012

[Curly]

he's pulling yer chain snoopdog

[shimmy]

And you have had first hand experience of KW Shim? :smt012

yep

[glendog74]

he's pulling yer chain snoopdog

Most probably - as Shimmy always does... :clown:

yep

Go on then, tell me all about your personal experience of KW V3's or Clubsports as fitted to your M3 CSL & why there isn't enough adjustment... :whistle:

[daniel_csl]

Thanks for the help:thumbs:

So bump will infact control things like rear end squat and diving under braking.

Based on no experience at all I would have thought that a soft to moderate bump and harder rebound would suit our roads?

[shimmy]

Most probably - as Shimmy always does... :clown:



Go on then, tell me all about your personal experience of KW V3's or Clubsports as fitted to your M3 CSL & why there isn't enough adjustment... :whistle:

not my CSL but the M3 i drove with KWV3, the only criticism i found was there didnt seem to be enough adjustment to get it compliant enough for the road anywhere near OEM or as much as Intrax. It seemed to still be a bit lumpy and thumpy which i was not used to

Now i know the springs might have been different but that was my experience:smokin:

[glendog74]

not my CSL but the M3 i drove with KWV3

Hardly a long term test impression then? :whistle:

I have to admit, when i first got my KW Clubsport kit, i had it fitted by a reputable garage but one, who by their own admission, were not familiar with KW and it's setup. It was fitted in a bit of a rush during a hectic day and without particular reference to the fitting/setup instructions... Needless to say, my initial impressions were of no obvious improvement over OEM on the road, but comfort was similar.

I then had a helpful mechanic stiffen the setup better for my recent track day at Donny and it seemed to help a little - but again; not very impressive. This unfortunately made the ride stiff and very crashy - particularly at high speed on the Autobahn (>120mph...)

To make things worse, i then had the driver's side front lower wishbone replaced under warranty by BMW which cocked the whole camber/toe settings right up!

So, i had a car with decent suspension that was simply not right...

To illustrate quite how badly the car was now setup, i recently had the car setup by a 'KW specialist' somewhere on the Continent... They found the front camber was -2.5deg left side, -1.0 right (thanks BMW...), the ride height had been set too low and was at risk of becoming coil-bound, and the rear toe was in on one side - out on the other! I had wondered why the car was pulling to the left... :banghead:

Well, the 'KW specialist' returned all settings to the ones that they recommend and straight away the car felt a lot better on road and much more composed at high speed. Ride was a little firmer than OEM but not uncomfortably so.

However, it was on track that the settings have really transformed the car - the best setup i have experienced yet. I had the chance to drive the Ring last week over 4 days and had both wet, dry, and damp conditions to experiment on. Having been shown how to adjust the car bump and rebound settings (which is a lot easier to do than some 'nay sayers' will claim) i was able to dial out a little understeer skip in wet conditions by softening rebound. In the dry the car is absolutely fucking awesome - and that was on PS2 tyres! :supz:

So what i'm trying to say is, there are several top brands of suspension out there and we have knowledge and good things to say of some more than others. The key really is in the setup and how well this has been done. I will now soften the car out a little for UK road winter driving and it will be fine.

What i do know is that my KW Clubsport kit is now setup superbly and i also have the knowledge to fine tune it to suit. It really does engender huge confidence in the car around a track and is very liveable with day to day on road - i'm now very very happy! :thumbs: :thumbs: :thumbs:

[northernjim]

I did wonder what the flock you were doing at the factory rob.....


I can vouch for how different a few 'twiddles'technical term I know! of the knobs can transform a car



now you can put up all the pictures of their RS! and how it drove???

[daniel_csl]

Glendog74 - with a statement like that you are going to have to share your ride height and camber/toe settings:thumbs:

[shimmy]

there didnt seem to be enough adjustment to get it compliant enough for the road anywhere near OEM or as much as Intrax. It seemed to still be a bit lumpy and thumpy which i was not used to

Hardly a long term test impression then? :whistle:

but it seems pretty accurate though

no obvious improvement over OEM on the road, but comfort was similar.

This unfortunately made the ride stiff and very crashy - particularly at high speed on the Autobahn (>120mph...)

Well, the 'KW specialist' returned all settings to the ones that they recommend and straight away the car felt a lot better on road and much more composed at high speed. Ride was a little firmer than OEM but not uncomfortably so.

so on road it was no better than oem, then rubbish and CRASHY, then finally firmer but not uncomfortably so :whistle:.

i am not arguing about track set up at all, but just that KWV3 seemed to not have a soft a setting for road as OEM:supz:

[glendog74]

i am not arguing about track set up at all, but just that KWV3 seemed to not have a soft a setting for road as OEM:supz:

And herein lies a flaw in that point: OEM suspensions are built with compromise always in mind between sporty handling characteristics and ride comfort...

I didn't fit KW Clubsports to emulate OEM road ride comfort after all! But if i'm honest they really aren't that indifferent to that now anyway when set up for road.