Understanding Weight Transfer
Discussion
victormeldrew said:
ABS would have to be REALLY good to actually help, good enough to rewrite the laws of physics I suspect. For absolute max braking you need to get to the point of locking up without actually getting there. ABS works by modulating brake pressure as we all know, but once you have broken traction other variables come into play. It's not easy to get grip back once its broken. Can ABS match a really talented human on the brakes in the dry? My gut feel is that is can't, as it relies on grip being lost first and braking being momentarily suspended until it recovers. Someone who can get the brakes to the point of locking and hold it there without ever actually locking has to outperform ABS. That said, anyone trying to do so on a real road rather than a glass smooth racetrack will end up in the scenery.
When you refer to wheels locking it sounds as if you're thinking about the wheel stopping rotating. A good ABS shouldn't do that, it should just the braking to keep the percentage slip within a range. If it keeps the slip reasonably close to the optimum, it is doing basically the same job as the expert driver who is threshold braking. From what I've seen, if ABS systems have a fault it is that they tend to be too conservative and not allow the tyre to generate enough slip under high grip conditions. And that's understandable given the need to provide lateral stability under slippery conditions.
victormeldrew said:
A big difference between race drivers mere mortals is in the way they brake. Where road drivers will gradually increase brake pressure as the slow, race drivers do the exact opposite. Maxiumum braking as soon as is possible, then taper off as the car slows. The faster the speed, the harder it is to lock the wheels...
It's worth considering that some race drivers drive cars that benefit from downforce, which totally skews the comparison...
GreenV8S said:
victormeldrew said:
ABS would have to be REALLY good to actually help, good enough to rewrite the laws of physics I suspect. For absolute max braking you need to get to the point of locking up without actually getting there. ABS works by modulating brake pressure as we all know, but once you have broken traction other variables come into play. It's not easy to get grip back once its broken. Can ABS match a really talented human on the brakes in the dry? My gut feel is that is can't, as it relies on grip being lost first and braking being momentarily suspended until it recovers. Someone who can get the brakes to the point of locking and hold it there without ever actually locking has to outperform ABS. That said, anyone trying to do so on a real road rather than a glass smooth racetrack will end up in the scenery.
When you refer to wheels locking it sounds as if you're thinking about the wheel stopping rotating. A good ABS shouldn't do that, it should just the braking to keep the percentage slip within a range. If it keeps the slip reasonably close to the optimum, it is doing basically the same job as the expert driver who is threshold braking. From what I've seen, if ABS systems have a fault it is that they tend to be too conservative and not allow the tyre to generate enough slip under high grip conditions. And that's understandable given the need to provide lateral stability under slippery conditions.
It's also fair to say that even and average ABS will probably be able to maintain more grip that all but a handful of the most skilled and practiced individuals. Personaly I'd prefer to develop my own skills rather than rely on some silicon and copper wiring to do my thinking for me, but that's a whole other argument.
willibetz said:
victormeldrew said:
A big difference between race drivers mere mortals is in the way they brake. Where road drivers will gradually increase brake pressure as the slow, race drivers do the exact opposite. Maxiumum braking as soon as is possible, then taper off as the car slows. The faster the speed, the harder it is to lock the wheels...
It's worth considering that some race drivers drive cars that benefit from downforce, which totally skews the comparison...
Downforce of course is a different ballgame, as are slick tyres. The basic physics remain the same though.
Incidentally, the drive with Tim Harvey when he calmly talked about the differences in braking technique whilst driving a Cerbera at unbelievable speeds made me appreciate the huge gulf between enthusiastic drivers and professional racers. Truly humbling.
victormeldrew said:
Someone who can get the brakes to the point of locking and hold it there without ever actually locking has to outperform ABS.
This is nicely illustrated in the Car Limits 'bending the rules' DVD for anyone who wants to see it in action. An ABS equipped car is shown to stop in a shorter distance by not allowing the ABS do all the work.
willibetz said:
victormeldrew said:
A big difference between race drivers mere mortals is in the way they brake. Where road drivers will gradually increase brake pressure as the slow, race drivers do the exact opposite. Maxiumum braking as soon as is possible, then taper off as the car slows. The faster the speed, the harder it is to lock the wheels...
It's worth considering that some race drivers drive cars that benefit from downforce, which totally skews the comparison...
i was just about to mention this - downforce (or rather downforce / lift characteristics front / rear at different speeds, which you *will* have to whatever degree in whatever car) will also play a part in how best to brake
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