simon's learning what to do with the polo thread

[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

[sambb]

you're going to have to give us your bank account details Gary for the open ended consult that's been happening here on the 9N3 forum. Appreciated.

[simon k]

yes, bank account, or at least an address to get some booze delivered to, perhaps on a weekly basis!

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

lol, fair enough - but I bet if you worked on one now you'd love how simple it all is compared to modern stuff.... and no, I don't have a rear swaybar on it yet, there is an one sitting in the corner of the garage, was almost ready to fit a few weeks ago but life got in the way. Working on it now...

[sambb]

simon these Ground Control adjustable tops are for sale in the parts section. Probably wouldn't fit but is a good parts breakdown iin case you were to make something. I do know that Greg (Kaanage) fitted some to his Tdi that he tracks. He runs at Phillip Island a fair bit. He might be worth contacting re some advice for tops.

[Sydneykid]

you're going to have to give us your bank account details Gary for the open ended consult that's been happening here on the 9N3 forum. Appreciated.

yes, bank account, or at least an address to get some booze delivered to, perhaps on a weekly basis!

No problem guys, glad to be of some help and I'm sure that we will be in the same place, at the same time, sometime and then I'll let you buy the Jack Daniels

Cheers
Gary

[Sydneykid]

lol, fair enough - but I bet if you worked on one now you'd love how simple it all is compared to modern stuff....

The electronics are simpler but the suspension is multiple times harder to get to do what I want it to do. Try getting a Mini to have greater than 1 to 1 camber change to roll ratio, or heaven forbid a sub terrainian rear roll centre

and no, I don't have a rear swaybar on it yet, there is an one sitting in the corner of the garage, was almost ready to fit a few weeks ago but life got in the way. Working on it now...

Right now would be good


Cheers
Gary