Reply With QuoteNice job. Looks like a similar design to the Ultra Racing (UR) ones but looks like it'd be a fair bit lighter. I'd be interested to see what it weighed. Stiffening the rear just transforms the Polo. It'll be a different car.
Volkswagen Enthusiast
My mate Jason was getting very keen to stiffen up the back of my car - Sam had sent me a set of K&R springs and we went to put them in and found that they weren't any stiffer the stock springs. We went to the workshop and Jason found the springs from the front of a Civic that they've been mucking around with. They were much stiffer, and about 5" too long - I cut them down and we stuck them in. Turn in was a lot better, much less understeer - my usual corners on the way to work give me a good back-to-back test. On Easter Monday my wife and I took it for a run around north-east vic for lunch through lots of winding roads - a little choppy at the back, but good
The picture below shows the springs - left to right are K&R, standard, Honda, and the piece I cut off. The plastic thing inside the Honda spring is a locator to keep it in the centre at the bottom
Next was to put a rear bar on it, Jason had decided that the idea of putting a pipe inside the hollow bit of the existing bar was a dud - first because it'd mean drilling holes which would make stress points, and second because he reckons the whole thing was too flexy anyway - we were both shocked at how far we could lift one wheel before the other would leave the ground - something like 20cm on the stock springs - so anyway, he bent up a big piece of pipe and told me to draw up a plate to go under the rear spring hanger.
I had to go away for work this week so left the car with him. The 2nd and 3rd pictures show the bar - I took it off and painted it today, can't really see it in the 3rd picture, but it's the black thing
I only took it to get some petrol, but it really turns in - it should be a very different animal at the sprint tomorrow. I still have the same tyres as last time - I should be able to pick up a few seconds
Volkswagenist
Nice job. Looks like a similar design to the Ultra Racing (UR) ones but looks like it'd be a fair bit lighter. I'd be interested to see what it weighed. Stiffening the rear just transforms the Polo. It'll be a different car.
Volkswagen Enthusiast
I did think about weighing it - I wouldn't call it light, maybe 8kg?Originally Posted by sambb
Volkswagen Enthusiast
I was 2 seconds faster with the new springs and rear bar - much more driveable... I'm told the car spent most of it's time on 3 wheels though, but I haven't seen any photos
front caster camber are next on the list - I might need to spend money to achieve them...
...and desperately need tyres... Bridgestone have a 4 for 3 deal going which includes RE003s
Volkswagenist
look around the big tyre stores that do online stuff/ebay - in 205/50/15 you can get 'street' semis like federal RS-RR's (treadwear 200) for more or less the same money and they kill RE003's on the track. Did you end up on 15's?
3 wheeling will be good for motorkhana if you do it in the Polo. Its amazing how fast a car rotates with the handbrake when its only got one rear on the deck! Did you try the H&R rears?
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I really need to replace the road tyres, so the 15"s might be on the backburner for a bit. I don't think I can swing buying wheels plus tyres
Sliding around on 3 wheels can get a bit scary in a motorkhana - there's a lot of weight on that one wheel.... my mini 'hops' sometimes where the outside back tyre grips and lets go and grips and lets go and the whole back of the car bounces, not a nice feeling
I completely forgot about changing the springs, didn't even take them with me... next round is at Winton, maybe I'll do it there
Volkswagenist
Yeah the 3 wheeling might not be as pronounced with the softer H&R rears. I know what you mean re the hopping. Mine was doing that a little through Griffins at Panorama this year. Other tyre option is Nankang Ar-1's - proper dirt cheap R specs. I'm getting a set to replace my A050's if a mates Clio goes comparably well on them after doing a similar swap at the south circuit. He'll be my guinea pig.
Volkswagen Enthusiast
Those front K&R springs are progressive, when the 6 closely wound coils touch it only leaves the 5 widely wound coils as the spring rate. If you tell me the coil ID, no of coils and the wire diameter I can calculate the soft and hard spring rates. The 3 wheeling is generally a sign of insufficient front spring rate, insufficient rear spring rate, comparatively too much rear anti roll and too little front anti roll. If there is insufficient rear rebound damping to control the swaybar then that can contribute to the 3 wheeling.
A 2 second lap time improvement is not to be sneezed at, but with a little more tuning there is plenty more to come.
The hopping is almost certainly insufficient rebound damping, all round.
Cheers
Gary
Golf Mk7.5 R, Volvo S60 Polestar, Skyline R32GTST
Volkswagenist
If you aren't washing out the front from all the weight transfer, the 3 wheeling from your solid rear axle conversion kit is OK.
Get decent track tyres (semi-slicks like Yoko A048R/A50 or Hankook Z221) on 15" rims and you won't believe the difference.
Resident grumpy old fart
VW - Metallic Paint, Radial Tyres, Laminated Windscreen, Electric Windows, VW Alloy Wheels, Variable Geometry Exhaust Driven Supercharger, Direct Unit Fuel Injection, Adiabatic Ignition, MacPherson Struts front, Torsion Beam rear, Coil Springs, Hydraulic Dampers, Front Anti-Roll Bar, Disc Brakes, Bosch ECU, ABS
Volkswagen Enthusiast
correction - 2.6 secondsThose front K&R springs are progressive, when the 6 closely wound coils touch it only leaves the 5 widely wound coils as the spring rate. If you tell me the coil ID, no of coils and the wire diameter I can calculate the soft and hard spring rates. The 3 wheeling is generally a sign of insufficient front spring rate, insufficient rear spring rate, comparatively too much rear anti roll and too little front anti roll. If there is insufficient rear rebound damping to control the swaybar then that can contribute to the 3 wheeling.
A 2 second lap time improvement is not to be sneezed at, but with a little more tuning there is plenty more to come.
The hopping is almost certainly insufficient rebound damping, all round.
Cheers
Gary- I'd jumped into the final session with another group when it had 3 laps to go and pulled out a 1:04.5 - I forgot to check the times for that session but they're up on natsoft now
I spent a fair amount of time reading about 3 wheeling last night and one thing I picked up on was that the front springs may be too soft. I did go back to your priority list however and front springs are at the bottom - maybe they need to be bumped up.
I'd be pretty confident that the ratio between rear anti roll v's front would be a long way from whatever is optimal. The front-end is completely stock and you can see how stiff the back is - that pipe is 2.25" OD and 5mm wall. Is there a way to measure roll stiffness of my rear bar without measuring the bar itself? The bar is solidly made and welded properly, but quantifying the material spec etc. might be difficult.
The blue spring in the previous photo is a H&R rear spring, I have the fronts also. Sam said they are 27N/mm, stocks are 25N/mm, but I haven't had them in the car
Rebound damping is something Jason was talking about, he reckons I should try to find some dampers from a heavy 4wd because they have good rebound control - I don't know whether that's a wise thing to do, but there are plenty of Landrovers around the workshop that I can steal parts off.
nah, it's not from washing out the front, it's all about turn-in.... it's working really well. I'd love some proper track tyres for this car, but the family budget just doesn't allow it. Road tyres need to go on this month, there is a set of audi 15" wheels on offer for beer money I could go and pick up, but at 6" they're probably only wide enough for a 195
I think my right-rear wheel might have lifted and turned off my cruise control on the way home from work tonight. There is a lovely progressively increasing cambered right-hand corner on the usual route I take. It's a 100 zone and I don't slow down for it - but today the traction control light flashed and the cruise turned off - there wasn't any movement from the front-end so I reckon the back might have just had a little sniff of air-gap between it and the road... though you wouldn't think it would slow down enough to make that much difference to the wheel speed... dunno, will see if it does the same on the way home tomorrow...
here's a picture from yesterday too
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