A brief return to Heavy Rear Bars
peter pyce said:
There are situations at which it will actually over steer and quite badly and quite suddenly! It depends what you do with that car. and no matter how good you are, there are panic situations which you can not predict, neither prevent, at which the car is asked to perform at its limits (or beyond) and that is where it gets really scary with heavy rear bar and novice enthusiast driver. Driving a car with heavy rear bar requires very good training and reflexes, especially if the road conditions are not optimal (read: rain, snow, not smooth surface on mountain roads, etc).
It is easy to "upgrade" the car, but how many are up to the task to drive an "upgraded" car?
This post is just so whoever reads here, thinks about the other side of the story. And in case your car surprises you one day, you can't say "Hey, nobody told me so!".....
Hello Everyone
Peter sent me a link to this very interesting thread, and although it's been a year since I last visited the TDIclub forums, it's very nice to see that the supportive and helpful atmosphere here is still alive and well (and IndigoBlue, it's always nice to read your comments!).
Anyway, if you'll forgive me for returning to a point made a few thread pages ago, I wanted to add something to Peter's warning about a "Heavy Rear Bar" setup being a potential handful on slick roads. Many people, when they hear such warnings, make the (entirely reasonable) assumption that if they can learn to handle this setup at high speeds on a dry road (or on an autocross course), then they'll be ok at lower speeds on more slippery surfaces. Others similarly put great stock (again, for entirely understandable reasons) on assurances from racers and fast drivers that the big-rear-bar setup is so benign and easily handled on the track that it should cause no problems at ordinary street speeds. But, unfortunately, things are not so straightforward as that.
If a car's handling balance at high speeds is fundamentally similar to its balance at lower speeds, then yes, you can assume that a setup that's benign and controllable on a dry, high-speed track will be similarly benign on a slippery-but-lower-speed road surface; indeed, the slippery-road situation might even prove easier to handle, as things will be happening that much more slowly. But if the handling balance at low speeds is fundamentally different from that at high speeds, then all bets are off. And that unfortunately is the case with a Heavy Rear Bar setup on a VW Golf or Jetta (especially on an A4 or earlier chassis).
To grossly oversimplify things: an A4 Golf/Jetta derives its high-speed dry-road stability by preferentially rolling its front wheels into adverse camber; in plain English, at high cornering loads the front wheels on an A4 are leaning away from the corner much more strongly than are the rear wheels. This leaning reduces the grip on the front end, and the resulting understeer makes it relatively difficult to spin the car (you can still spin, but you have to work at it!). Surprisingly, when you add a Heavy Rear Bar to the A4 chassis, you don't really change things at the high-speed, dry-road limit: at the fastest cornering speeds, even the stock A4 has lifted its inside rear wheel, and all a Heavy Rear Bar does in this situation is to raise it a bit higher; since both the stock car and the HRB car thus have an identical 100% rear lateral weight transfer, the handling balance is roughly the same between the two vehicles, and the HRB car still strongly understeers (at the dry-road limit).
It's for this reason that people report an HRB setup as feeling benign on a high-speed track (it ought to -- at the highest cornering loads, they're essentially driving a stock vehicle). Indeed, it can be a very flattering setup: the HRB allows for a fair bit of oversteer at initial cornering loads (when the stock-car wheels would still be 4-square on the ground), which allows one to flick the tail out into a slide; once the cornering loads really build up, stock-levels of understeer set in to stabilize everything, allowing one to bring the tail smoothly back in an impressive looking drift.
The problem with an HRB setup is when you take the car away from the dry, sticky, high-speed track, and place it instead on a slick public road (e.g., one that's wet, greasy, or icy/snowy). On such a road, the car hits its cornering limits at much lower g-loadings, and the tires begin to let go while the front tires are still relatively upright. Because the front tires are still upright, breakaway happens before there's an awful lot of understeer, and even a stock A4 can readily swap ends (at least on ice) if the driver isn't careful. Add a Heavy Rear Bar (which increases the oversteer at low cornering loads), and you can get into a snap spin situation, where the terminal oversteer is so sudden and unexpected that very few drivers can correct in time.
(Note: ask Peter about the time he came around a fast, dry corner in his HRB-fitted Jetta, and unexpectedly drove across some rain runoff -- having now driven with and behind Peter on some winding mountain roads, I can vouch for his being a very skilled and experienced driver (and a great guy!)...and the resulting oversteer gave even him some heart-in-mouth moments.)
Anyway, those who've waded through the huge Vortex handling thread will have seen that Peter and I aren't huge fans of the HRB setup. When a Heavy Rear Bar is fitted as part of balanced package to an intelligently modified car, it can make a lot of sense (please note that Shine themselves say that their bar should be added to a car only after their spring kit has been fitted). But on its own, an HRB turns the benign A4 chassis into something that's benign in the dry and decidedly less so on slippery roads, and this Jekyll and Hyde transformation is NOT what one wants on an all-weather passenger vehicle driven on public roads.
As always, thank you very much for allowing me to be a guest on your wonderful forum. Best wishes to everyone for the coming spring, and may all your VW adventures be pleasant ones.
Cheers,
Ceilidh