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0 pointsUnklejoe8y ago0 comments

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...

https://c.slashgear.com/wp-content/uploads/2015/11/cobra-jet...

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

0 comments

8 comments · 3 top-level

killjoywashere8y ago· 3 in thread

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_moon8y 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.

clarkmoody8y 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

2 more replies

UnklejoeOP8y 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.

grkvlt8y ago· 2 in thread

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.

UnklejoeOP8y 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.

grkvlt8y ago

So the tires are acting like torsion springs then?

1 more reply

jdunck8y ago

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

j / k navigate · click thread line to collapse

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8 comments · 3 top-level

killjoywashere8y ago· 3 in thread

burger_moon8y ago

clarkmoody8y 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

2 more replies

UnklejoeOP8y ago

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.

grkvlt8y ago· 2 in thread

UnklejoeOP8y 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.

grkvlt8y ago

So the tires are acting like torsion springs then?

1 more reply

jdunck8y ago

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

j / k navigate · click thread line to collapse