simon's learning what to do with the polo thread

[simon k]

thanks Sam... need to see how much money falls out of the honda

cutting the domes off the strut tops isn't an issue, it almost happened one day just to see what was under them and what the tops actually look like

[Sydneykid]

For a car that is going to see track time I wouldn't bother with an off the shelf road car oriented "kit" (springs and shocks) because they are never right, especially in a FWD car. They always have drastically insufficient rear spring rates which generally means that they have insufficient damping to control those more appropriate spring rates. Especially when coupled with the substantial rear swaybar upgrades also required (damping is also required to control the swaybar). Oxymoronically they also often have too high a front spring rate and possibly too high damper rates. Unfortunately in shock absorbers we get what we pay for, if we pay twice as much then they are generally close to twice as good.

On a car with strut based front suspension, I would always use an inverted shock. Having the shock body control the front end geometry gives a far better result than a shock shaft, especially a hollow shaft with an adjuster rod inside.

It is very budget dependant, but I would always suggest choosing a superior quality damper with no adjustment than an inferior one with adjustment. Keeping in mind that being a hydraulic transfer device (oil moves from one side of the piston to the over) they are velocity sensitive and hence "self adjusting". Of course that's within the capacity of the valving on the piston. So a good quality piston with sufficient valves and porting gives a much broader range of "self adjustment" than one with simplistic valving and piston with holes drilled in it.

As anyone with high level motorsport experience will tell you, damper tuning is more of an "art" than a "science" and an inexperienced tuner playing with dampers will more often than not make it worse rather than better.


Cheers
Gary

[simon k]

hmmm, so trying to read your meaning ..

I won't be happy with the MCA blues - they're street oriented and I just noticed that they even say "if high performance/motorsport applications are an important priority for your car/setup, we highly suggest stepping up to the X-R Series", so I'll drop them off the shopping list

Sounds like I should be buying the best dampers I can afford and building the rest of the suspension around that - are Bilsteins really the best? is there something else that is as good but better value?

Assuming Bilsteins - they either come as a kit with springs or on their own. I have Sam's H&R springs, so maybe I only need to buy dampers. Are B8's the top line as far as Bilstein go?

Bilstein VW Polo (9N) 1.8 GTI B8 Sprint Shock Absorber, Bilstein-Shop.com

inexperienced tuner playing with dampers will more often than not make it worse rather than better.

I'm definitely inexperienced, so don't want to to throw money away by making it worse or putting in something that I'll grow out of

[Sydneykid]

There are a lot of options. You could get a set of B8's front struts, stick them in the lathe and machine off the spring seats and fit a "coil over conversion kit (around $120 each). Basically a threaded sleeve with a bottom spring seat and a locking ring. That gives height adjustment and the ability to use any "race style" parallel spring and choose whatever spring rate desired. A cheap hot wound spring for ~$100 a pair, H&R cold wound springs for ~$150 a pair, or a pair of Eibachs for ~$200 a pair.

The B8's struts have an an inverted shock, so tick that box, and they have a more than decent piston. I haven't had a set on the dyno but I'd be surprised if they didn't handle the spring rates you would want to use.

For the rear, not strut based, so doesn't need to be inverted, a pair of B8's would be OK. But would almost certainly need revalving as the spring and swaybar rates you are likely to use are going to be outside their "self adjusting" range. That's not a big deal (or cost), less than $300 typically (for the pair).

If the funds become available later on you can add a single adjuster (combined bump and rebound), that's just a shock shaft change and re uses the same valves but with a different piston. Retains the same shock body, strut etc. Might be able to do a double adjuster (separate bump and rebound) which means another change of piston and shaft. Possibly better to turn it into a triple adjuster, with high speed and low speed bump on a remote canister whilst retaining the rebound adjustment on the shaft.


As long as there is the budget you will never "grow out of it".

If H&R make a kit for the Polo that might be worth exploring, they are basically a Bilstein shock which means all of the above applies. In my experience the Germans (Bilstein, Boge, Sach) Dutch (Koni) and British (Dynamic, Protech, Nitron) have the best damper science. The Swedes (Ohlins), Aussie (SupaShock) and Yanks (Penske) are good too but expensive.


None of the above should be taken as knocking MCA's offerings. But excluding the Gold remote canister adjusters (I have a set on my Skyline) they are built/spec'd to a target price. As per previous post, we get what we pay for.


Cheers
Gary

[sambb]

Nice post Gary - very good stuff. Looks like B8's could be the answer Simon. Especially if paired with some method to get some camber (k-mac tops or at the bottom with subframe/front LCA bushes/TT ball joints) I'll be pulling out 180mm long 7kg/mm fronts (60mm I.D). If you get B8's and do the adjusting collar conversion to the fronts I'll donate those springs to your cause. I run that front rate but with the 22mm front bar, so with the stock bar you'd be in a very good spot. Gary, Simons rear ARB is a bit of a beast - could he get away with soft 25N/mm H&R rears or even the same rate but 20 mm taller stock rears if he had B8's in the back - just with most of the anti roll coming from the bar? Maybe run the lower H&R's in the wet or on fast tracks and the taller stockers when you want it to rotate more??

[simon k]

yes, that was very very informative Gary - I did some reading about revalving the dampers, and converting to coilovers like you said sounds like it would be easy, I could probably do it on my little lathe at home...

I won't be doing another sprint until August so there is a bit of time to fiddle around

I really appreciate all of the information you guys are sharing with me, it's awesome

[Sydneykid]

Nice post Gary - very good stuff.

Always welcome. I'm just passing on what information I can, that I think might be useful.

Gary, Simons rear ARB is a bit of a beast - could he get away with soft 25N/mm H&R rears or even the same rate but 20 mm taller stock rears if he had B8's in the back - just with most of the anti roll coming from the bar? Maybe run the lower H&R's in the wet or on fast tracks and the taller stockers when you want it to rotate more??

As well as diagonal weight transfer there is longitudinal weight transfer to consider. Turbo FWD cars have a lot of torque capability and the amount of weight transfer is directly proportional to that torque (geometry not withstanding). The rear swaybar is only going to help the front wheel traction when there is steering angle and/or lateral G. Keeping in mind that what we are trying to achieve is the ability to wind the steering lock off as early as possible in the corner so that we can accelerate harder/earlier (make the straight longer). Big upgrades in the rear spring rate are necessary to achieve that. Plus a step up in bump valving doesn't hurt either.

Increasing the rear ride height is one way to increase the weight transfer onto the front outside wheel, which helps on turn in. But softening the spring rate has detrimental effects in mid corner and exit speeds. One step forward, 2 steps back. I raise the ride height, with the same spring rate. Either by winding up the spring seat or, if that's not available, then I stick a spacer between the spring and the spring seat (top or bottom it doesn't matter).


Cheers
Gary

[sambb]

more good stuff. Takes a bit more back and forth with us I'm guessing Gary before before it sinks in compared to your usual audience, but your a good communicator and I think we're all learning plenty and having light bulb moments when we think back to why the car was doing this or that when set up a certain way.
Do you think 6 or 7kg/mm of front spring would be too much for stock B8 front valving? Just thinking would it be cheaper to go B14's
if they don't need coilover collar modding and are valved for stiffer fronts to begin with, and then he might only have to revalve the rear dampers?
I found these numbers out about some of the main coilover contenders a while back (I posted it ages ago):

"........

While researching it though, I found out some info on some of these coilvers that may help someone else make a decision on them in the future:

Bilstein B14 (PSS) front spring rate - progressive 38-61N/mm (220-350lb/in) emailed response from bilstein.de
rear spring rate - 45N/mm (257lb/in)

H&R (#29325-2. 2935-1 has been discontinued) emailed response from H&R.de
front spring rate - helper spring 20N/mm, main spring 70N/mm (400lb/in)
rear spring rate - 40N/mm 230lb/in)

Eibach pro street -S front spring rate - 36N/mm (205lb/in) Eibach sydney
rear spring rate - 23-30N/mm (130-170lb/in)

The bilsteins run a much squarer spring rate with the H&R's being more front biased with the roll stiffness. Either of them are a lot more focused than the Eibach's that are not far off strut style street springrates. Eibach make the springs for KW apparently so you could maybe assume that KW V1's have similar springrates to the pro street - S but their damper valving might be different......"


Looks like they all need stiffer springs thrown at them.

[Sydneykid]

The front B8's should be able to handle 6 kgs/mm (330 lbs) or 7 kgs/mm (390 lbs) springs, of course I'd have to confirm that with Bilstein. With around 800 kgs on the front wheels and hence 400 kgs each of spring load to hold that up, it's not hard to see why they should be OK. No chance with the rear B8's though, with the lower weight plus being too far away from the spring rates we'd want to run.

The spring rate tuning in the kits is interesting, 400 front & 230 rear = 64% front & 36% rear, which is about the weight distribution. It's obvious to see what they were aiming for, tuning for equal response front and rear over bumps, humps, pot holes etc. Road car suspension frequency tuning 101, but not good for track use.

Cheers
Gary

[sambb]

I had a feeling that's what they might be going for. The frequency thing to stop uncomfortable oscillating/porpoising and/or working on the assumption that the end user will most likely buy one of their rear bars too. And also the fact that the nanny state world doesn't want to kit form sell anything that pushes the envelope a bit for fear of litigation.
I came very very close to getting the B14's/H&R's but for the very reason that they are so rear soft I went the way I did because I thought their rear dampers wouldn't be up to it if I threw stiffer springs in. I didn't know what I know now (mostly cos of you) but I did know from mucking around on the B8's that I needed at least square spring rates minimum and I wasn't going to get that with those kits. BUT had I known that the B14's can be revalved etc it might have changed things.
I'd driven B14's at the Huntley in my mates Clio and it was awesome. But his car was understeering when we were at wakefield even with a big rear bar set to max so after that we put some 6kg/mm rears that came out of my car into the the back of his and he sid the car just came alive when he was at the Southern Loop. Probably his B14 kit was biased the same way which is why the stiffer rears really helped him. He has square spring rates now (rears nearly 40% stiffer than bilstein spec) but I'll have to tell him he can get the rear B14's revalved cos he'd likey be underdamped now yeah?. Do you do the re valving Gary or is that just a Bilstein Sydney service?? The Clio RS has a mutant front bar too so I reckon he should track down a normal Clio and downgrade that. Hopwfully I'll get to drive his at the VW Nats it'll be good to compare his to mine - same weight distribution (except for CoG), similar suspension design, similar suspension setup/quality, same tyres for a good comparo.

[simon k]

Interesting... So 64% front / 36% rear on the H&R springs (400 / 400+230 = 0.635 ?)- I was curious about the weight distribution and found an old post from Sean that agrees...

08 Polo GTI - Stock in terms of weight, no weight loss attempt whatsoever: stock wheels, brakes, interior, near full tank of fuel, tow bar, roof racks and sub woofer, and some chassis bracing mine weighed in at 1240kg without driver.

Front Left - 384kg Front Right - 396kg
Rear Left - 232kg Rear Right - 228.5kg

ie. 62% front weighting and ~50% left/right

so if they've attempted to make the car respond to bumps the same from front to rear? IE the same bump going under the left front wheel will effect the car the same amount as it would for the left rear... However, I think what you're saying about being able to accelerate earlier in the corner, we want more weight on the front wheels, therefore don't want the car to squat, therefore want harder springs at the back? However, making the rear springs harder means that when they do deflect, we need dampers with more resistance to movement to control them? is that the right way to think about it?

this one "Bilstein B14 (PSS) front spring rate - progressive 38-61N/mm (220-350lb/in) emailed response from bilstein.de
rear spring rate - 45N/mm (257lb/in)" with progressive fronts would be in the region of 46% to 58% - is that right? Progressive like this means they're initially soft, but firm up. Initially soft means the front will dive under braking, getting more weight on to the front wheels, but needs more front anti-roll bar to stop it from leaning over?

maybe?

Just to muddy the waters a bit, for dirt motorkhanas in my mini, I want the back of the car to slide more so I'm adding rear toe-out, and I think I need to stiffen the rear to reduce the amount of suspension travel that needs to happen before the tyres can break traction. The mini is hydrolastic (fluid damping linked front to rear on each side), so I'm wondering if it's worth adding a tap in-line to isolate each corner, and maybe strapping the rear down on to the (competition/progressive) bump stops.

[simon k]

I had a feeling that's what they might be going for. The frequency thing to stop uncomfortable oscillating/porpoising and/or working on the assumption that the end user will most likely buy one of their rear bars too. And also the fact that the nanny state world doesn't want to kit form sell anything that pushes the envelope a bit for fear of litigation.
I came very very close to getting the B14's/H&R's but for the very reason that they are so rear soft I went the way I did because I thought their rear dampers wouldn't be up to it if I threw stiffer springs in. I didn't know what I know now (mostly cos of you) but I did know from mucking around on the B8's that I needed at least square spring rates minimum and I wasn't going to get that with those kits. BUT had I known that the B14's can be revalved etc it might have changed things.
I'd driven B14's at the Huntley in my mates Clio and it was awesome. But his car was understeering when we were at wakefield even with a big rear bar set to max so after that we put some 6kg/mm rears that came out of my car into the the back of his and he sid the car just came alive when he was at the Southern Loop. Probably his B14 kit was biased the same way which is why the stiffer rears really helped him. He has square spring rates now (rears nearly 40% stiffer than bilstein spec) but I'll have to tell him he can get the rear B14's revalved cos he'd likey be underdamped now yeah?. Do you do the re valving Gary or is that just a Bilstein Sydney service?? The Clio RS has a mutant front bar too so I reckon he should track down a normal Clio and downgrade that. Hopwfully I'll get to drive his at the VW Nats it'll be good to compare his to mine - same weight distribution (except for CoG), similar suspension design, similar suspension setup/quality, same tyres for a good comparo.

ha - it took me nearly an hour to write my last response in between working and whatever else I was doing... you got your reply in under mine. Revalving looks simple to do, but I assume testing the response afterwards and ensuring that they're identical from side to side would be where the money is.

[Sydneykid]

I can do the revalving if I have time, then run them up on the dyno to make sure that they are at the targeted spec and most importantly exactly the same. There's a few parts involved, a couple of seals, the valve stack has to be rebuilt, 10 or so shims, I'd also use different oil (the non foaming, high temp, competition level) assembled and then regased with nitrogen (I just bought a new bottle). I might have the right tool for regasing (there are a number of different configurations), if not I can borrow one. I always keep the shock dyno sheets (hard and soft copy), that way it easy to retest and compare.

There has probably been 20 or so FWD cars where I have had to revalve the rear shocks, but only a handful of fronts. So it's not at all unusual.

Cheers
Gary

[Sydneykid]

Interesting... So 64% front / 36% rear on the H&R springs (400 / 400+230 = 0.635 ?)- I was curious about the weight distribution and found an old post from Sean that agrees. so if they've attempted to make the car respond to bumps the same from front to rear? IE the same bump going under the left front wheel will effect the car the same amount as it would for the left rear...

It's not quite that black and white, there are movement and leverage ratios to consider, plus anti dive and anti squat geometry. But that's the overall philosophy.

However, I think what you're saying about being able to accelerate earlier in the corner, we want more weight on the front wheels, therefore don't want the car to squat, therefore want harder springs at the back? However, making the rear springs harder means that when they do deflect, we need dampers with more resistance to movement to control them? is that the right way to think about it?

You got it, the rebound damping controls the recoil of the spring, without sufficient rebound damping the car would go along the road like a pogo stick, or a 60's American car. Because we can't have a solid spring (or a piece of 4 x 2) the bump damping has to be enough to slow down the weight transfer (off the front onto the rear). Also we are going to put, say a 2 x 400 lbs springs in the rear of the car that only weighs about 800 lbs, so without enough damping to control it, it would bounce from one tiny bump to the next, the wheels hardly ever in contact with the track.

this one "Bilstein B14 (PSS) front spring rate - progressive 38-61N/mm (220-350lb/in) emailed response from bilstein.de rear spring rate - 45N/mm (257lb/in)" with progressive fronts would be in the region of 46% to 58% - is that right? Progressive like this means they're initially soft, but firm up. Initially soft means the front will dive under braking, getting more weight on to the front wheels, but needs more front anti-roll bar to stop it from leaning over?

Most times progressive springs aren't there to actually give progressive spring rates, they are just there to take up space so the coils don't fall out on full droop. They might have a tiny bit of progression, maybe 10 to 15 mm's, which soaks up the ripples in the road, or the course gravel rumble. I use helper/tender springs in some race cars but they are totally sacrificial. Progression gives a false feeling to the driver that the suspension is going to continue to move until it runs out of "soft" rate, then it stops or slows down on the "high" rate. Without any change in driver input, that doesn't inspire confidence.

Cheers
Gary

[Sydneykid]

Just to muddy the waters a bit, for dirt motorkhanas in my mini, I want the back of the car to slide more so I'm adding rear toe-out, and I think I need to stiffen the rear to reduce the amount of suspension travel that needs to happen before the tyres can break traction. The mini is hydrolastic (fluid damping linked front to rear on each side), so I'm wondering if it's worth adding a tap in-line to isolate each corner, and maybe strapping the rear down on to the (competition/progressive) bump stops.

I have avoided working on Minis for a long time and I'd like to keep it that way, sorry. If I can give you one tip from watching the Mini guys, they used bumpstops, many different ones, different densities and different heights to tune the suspension. I assume you already have a rear swaybar on it? If not there's your number 1 step.


Cheers
Gary