5 ms·

Modern high-end aftermarket EFI systems (such as MoTeC) do have traction control, but it's not as effective as one would expect. The main issue I found is that

Modern high-end aftermarket EFI systems (such as MoTeC) do have traction control, but it's not as effective as one would expect. The main issue I found is that street tires often just don't have the traction required, even under ideal conditions. The result is that traction control has to cut power so much that it ends up hurting the quarter mile times. It does help tremendously on consistency and safety though. Things start to pucker when all four wheels start hazing in a 1000 HP AWD car. You seem familiar, but for others, here's what a typical 8 second car looks like leaving the line: http://www.speednik.com/files/2015/01/screen-shot-2015-01-26-at-9.51.04-am.jpg http://www.speednik.com/files/2015/01/screen-shot-2015-01-26... https://c.slashgear.com/wp-content/uploads/2015/11/cobra-jet-16-900x420.jpg https://c.slashgear.com/wp-content/uploads/2015/11/cobra-jet... http://cdn.dragzine.com/wp-content/blogs.dir/2/files/2011/11/mtsmall3.jpg http://cdn.dragzine.com/wp-content/blogs.dir/2/files/2011/11... Notice how massive the rear tires are. EDIT: Added picture of an 8 second all wheel drive car (GTR). The interesting thing here is the clear bias of traction towards the rear. When launching a car with that much power, the weight shifts towards the rear enough to render the front wheels almost useless (unless the suspension is extremely stiff). https://i.ytimg.com/vi/Nf4pJZaK7P4/maxresdefault.jpg https://i.ytimg.com/vi/Nf4pJZaK7P4/maxresdefault.jpg

killjoywashere 9y ago
I suspect Tesla's advantage is in linear acceleration. Those internal combustion cars need a gearbox so the initial acceleration is very high in that first gear. This the same reason the Navy wants to go from steam to electric catapults: you get the plane to the same speed off the cat, but the acceleration curve is straight, so there's lower peak load on the airframe, so your planes last longer. Similarly, the Tesla can keep linear acceleration with gear shifts.
- burger_moon 9y ago
  Right but to hit an 8 second 1/4 you're trap speed is 170-190 depending on how fast your 1/8 mile was. There simply isn't even distance to accelerate linearly in 1/4 to hit 8 seconds without leaving the line like a bat out hell. The suspension on most of these cars is also far from normal. There's very few cars in the world which make an8 second pass on independent rear suspension. Most of these cars have straight axles and 4 link suspension. I really want to see a Tesla Roadster make an 8 second pass with whatever tires it needs because tires alone won't get you there. They got some serious engineering in that thing to make it hit 8 seconds with a suspension that doesn't make you hate life.
  - Unklejoe 9y ago
    There are some IRS cars capable of going 8's. The ones I've seen the most are GTRs, Supras, and the occasional 2JZ/LSx swapped 240sx (I think they swap a Nissan/Infiniti Q45 rear into it or something). Now that the 2015+ Mustang has IRS, I expect to see more of them as well. I think there's already one in the 8's. But yeah, IRS is a major pain at that power level. Most (all?) of the performance cars today have IRS, so I expect improvements to come.
  - clarkmoody 9y ago
    Accelerating at 1.28g (41.25 ft/s2) for 8 seconds will get you to exactly a quarter mile. x = 0.5*a*t^2 = 0.5 * 41.25 ft/s2 * (8s)^2 = 1320 ft = 1/4 mi Under that acceleration, your final speed is 225 mph v = a*t = 41.25 ft/s2 * 8s = 330 ft/s = 225 mph
    - ska 9y ago
      Accelerating at > 1g off the line has its own set of issues - without extra downforce from somewhere you have traction problems regardless of tires, street tires just make it worse. This is why you see so many approx 2.9s 0-60 times in higher end sports cars, it's hard for aerodynamics to affect it much over the first couple of seconds.
      - killjoywashere 9y ago
        Correct me if I'm wrong, but isn't downforce an aerodynamic issue? There are no aerodynamics at 0 mph. You do have a torque problem, but the Tesla is actually a fairly heavy car, is it not? Also, isn't Tesla's center of mass pretty near the same height as the axles? So it's not like the rear end is going to get under the front end.
        ska 9y ago
        Sorry, i just worded it badly. The point is that without downforce, you can't overcome the traction issue. To a first approximation at 1g accel from a standing start, your resulting force vector is at 45 degrees (mass at 1g down, accel at 1g forward). Accelerating harder just makes the problem worse. At speed, the answer to this is downforce (e.g. how F1 cars can corner as fast as they can). But for the first couple of seconds, you can't generate much downforce from aerodynamics because you aren't going fast enough. And there are limits to what a spoiler, etc. can generate. For a lot of street legal sports cars, this all evens out about the same way, and they end up with very similar 0-60 times. If you try and systematically knock down all of these problems, you'll end up with a top fuel car. In that case you may get ~1000lb of downforce from exhaust alone, which gets you past the first bit while you are going too slow for the big wing to be really effective.
grkvlt 9y ago
Wow, the buckling of the tire wall in the last two pictures is crazy. I guess that happens because there is enough friction to stop the wheel moving, and the axle is trying to turn it faster, causing a shear force. With normal tires, I assume they would just slip at that point and spin because they don't have enough friction in the contact patch touching the road.
- Unklejoe 9y ago
  Yep! The tires are actually designed to do that. It really helps to prevent things from snapping by absorbing some of the shock when the cars drop the clutch or let go of the trans brake.
  - grkvlt 9y ago
    So the tires are acting like torsion springs then?
    - andyjsong 9y ago
      It increases the footprint of the tire at the start, giving the car more grip. Here is a video: https://youtu.be/-VF0JwxQqcA?t=10m42s https://youtu.be/-VF0JwxQqcA?t=10m42s
      - grkvlt 9y ago
        Thanks, that's really interesting - there's some amazing technology going into what I had previously assumed was a fairly boring static (modulo the rotation, of course) component of these vehicles.
jdunck 9y ago
And what if the battery weight is nearer axle centerline than an ICE?

killjoywashere 9y ago

I suspect Tesla's advantage is in linear acceleration. Those internal combustion cars need a gearbox so the initial acceleration is very high in that first gear. This the same reason the Navy wants to go from steam to electric catapults: you get the plane to the same speed off the cat, but the acceleration curve is straight, so there's lower peak load on the airframe, so your planes last longer. Similarly, the Tesla can keep linear acceleration with gear shifts.

burger_moon 9y ago
Right but to hit an 8 second 1/4 you're trap speed is 170-190 depending on how fast your 1/8 mile was. There simply isn't even distance to accelerate linearly in 1/4 to hit 8 seconds without leaving the line like a bat out hell. The suspension on most of these cars is also far from normal. There's very few cars in the world which make an8 second pass on independent rear suspension. Most of these cars have straight axles and 4 link suspension. I really want to see a Tesla Roadster make an 8 second pass with whatever tires it needs because tires alone won't get you there. They got some serious engineering in that thing to make it hit 8 seconds with a suspension that doesn't make you hate life.
- Unklejoe 9y ago
  There are some IRS cars capable of going 8's. The ones I've seen the most are GTRs, Supras, and the occasional 2JZ/LSx swapped 240sx (I think they swap a Nissan/Infiniti Q45 rear into it or something). Now that the 2015+ Mustang has IRS, I expect to see more of them as well. I think there's already one in the 8's. But yeah, IRS is a major pain at that power level. Most (all?) of the performance cars today have IRS, so I expect improvements to come.
- clarkmoody 9y ago
  Accelerating at 1.28g (41.25 ft/s2) for 8 seconds will get you to exactly a quarter mile. x = 0.5*a*t^2 = 0.5 * 41.25 ft/s2 * (8s)^2 = 1320 ft = 1/4 mi Under that acceleration, your final speed is 225 mph v = a*t = 41.25 ft/s2 * 8s = 330 ft/s = 225 mph
  - ska 9y ago
    Accelerating at > 1g off the line has its own set of issues - without extra downforce from somewhere you have traction problems regardless of tires, street tires just make it worse. This is why you see so many approx 2.9s 0-60 times in higher end sports cars, it's hard for aerodynamics to affect it much over the first couple of seconds.
    - killjoywashere 9y ago
      Correct me if I'm wrong, but isn't downforce an aerodynamic issue? There are no aerodynamics at 0 mph. You do have a torque problem, but the Tesla is actually a fairly heavy car, is it not? Also, isn't Tesla's center of mass pretty near the same height as the axles? So it's not like the rear end is going to get under the front end.
      - ska 9y ago
        Sorry, i just worded it badly. The point is that without downforce, you can't overcome the traction issue. To a first approximation at 1g accel from a standing start, your resulting force vector is at 45 degrees (mass at 1g down, accel at 1g forward). Accelerating harder just makes the problem worse. At speed, the answer to this is downforce (e.g. how F1 cars can corner as fast as they can). But for the first couple of seconds, you can't generate much downforce from aerodynamics because you aren't going fast enough. And there are limits to what a spoiler, etc. can generate. For a lot of street legal sports cars, this all evens out about the same way, and they end up with very similar 0-60 times. If you try and systematically knock down all of these problems, you'll end up with a top fuel car. In that case you may get ~1000lb of downforce from exhaust alone, which gets you past the first bit while you are going too slow for the big wing to be really effective.

grkvlt 9y ago

Wow, the buckling of the tire wall in the last two pictures is crazy. I guess that happens because there is enough friction to stop the wheel moving, and the axle is trying to turn it faster, causing a shear force. With normal tires, I assume they would just slip at that point and spin because they don't have enough friction in the contact patch touching the road.

Unklejoe 9y ago
Yep! The tires are actually designed to do that. It really helps to prevent things from snapping by absorbing some of the shock when the cars drop the clutch or let go of the trans brake.
- grkvlt 9y ago
  So the tires are acting like torsion springs then?
  - andyjsong 9y ago
    It increases the footprint of the tire at the start, giving the car more grip. Here is a video: https://youtu.be/-VF0JwxQqcA?t=10m42s https://youtu.be/-VF0JwxQqcA?t=10m42s
    - grkvlt 9y ago
      Thanks, that's really interesting - there's some amazing technology going into what I had previously assumed was a fairly boring static (modulo the rotation, of course) component of these vehicles.

jdunck 9y ago

And what if the battery weight is nearer axle centerline than an ICE?