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BMW 3-Series (E90 E92) Forum > BMW E90/E92/E93 3-series General Forums > General E90 Sedan / E91 Wagon / E92 Coupe / E93 Cabrio > DST/DTC and grippier tires= more power to the wheels?



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      01-04-2013, 08:49 PM   #1
thenewrick
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DST/DTC and grippier tires= more power to the wheels?

So if the traction control reduces power output and applies the brakes if it encounters wheel spin would it makes sense then that if you put grippier tires on and give it the same amount of power you'll experience less wheel spin thusly putting more power to the ground in DST/DTC mode?
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      01-04-2013, 08:56 PM   #2
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Yes stickier tires mean more power delivered to the ground.

It also means better control and braking distances.

All of that is irrelevant to the DTC / DSC. If your tires are spinning, it's a nanny that kicks in when it thinks the driver is out of control.

Turn those off if the tire spinning is intentional.
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      01-04-2013, 08:57 PM   #3
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      01-04-2013, 08:58 PM   #4
thenewrick
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I think you missed my point entirely. The traction control kicks in and reduces power output when it senses the wheels spinning. So the idea is that if you aren't spinning the tires then the traction control systems won't initiate and thusly will not be reducing power and braking the car autonomously.
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      01-04-2013, 09:00 PM   #5
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^ Duh. Why would a car limit the power if none of the tires are over spinning...
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      01-04-2013, 09:03 PM   #6
thenewrick
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That's just the point I was making. I think it's kind of interesting at least. Essentially gaining big whp numbers just from stickier tires. My last car was AWD and worked quite a bit differently. AWD burnouts are a whole nother beast from the BMW traction control systems.
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      01-04-2013, 09:15 PM   #7
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Quote:
Originally Posted by thenewrick View Post
I think you missed my point entirely. The traction control kicks in and reduces power output when it senses the wheels spinning. So the idea is that if you aren't spinning the tires then the traction control systems won't initiate and thusly will not be reducing power and braking the car autonomously.
The problem is that your point is correct, but backwards in logic.

Traction control never reduces power to the ground. It DOES reduce engine output and apply the brakes, but that's in order to arrest the wheel spin. The fact that the wheels are spinning at that point implies that power isn't efficiently being translated into kinetic energy in the car via force on the ground in the first place.

Basically, there are two places engine output can go - if your wheels are spinning and the car isn't moving at all, your engine power is getting converted to heat in the tires due to the kinetic friction of the tire against the ground. If your wheels are static on the ground (not spinning with respect to it, as is the typical and desired case for a car) that same energy is instead being moved into the kinetic energy of the car moving forward, and drag, and rolling resistance, etc (all of which provide a force impeding the car's motion, and thus a power removal from the system, since F*D=W).

Basically, traction control serves to reduce power output from the engine if that power isn't being used properly. The traction control isn't at all your enemy here.

Let's take the case that you had a perfect traction control system and motor. The motor would be throttled NEVER higher than the point at which it'd break the tires free. The tires wouldn't ever spin, but there's still a cap on the amount of power you can apply from the engine and still be putting that power into the car moving forward. With the traction control off, you'd suddenly break the tires free at that point, and since the coefficient of kinetic friction is much, much lower than that of static friction, the force you'd be applying on the ground would all of a sudden be much less, and you'd be converting a LITTLE power to motion, but a LOT of power to tire heat.

tl;dr: there is a cap on power you can apply to the wheels, past which that power is no longer completely being converted to motion. Additionally, if you operate anywhere PAST that cap, you all of a sudden rapidly drop the amount of power you were previously converting to motion. Traction control serves to keep you hovering right around that cap, so that you can maximize power to the ground in a wide variety of rode conditions.

That cap, however, is dictated by the friction between tire and ground. It will be lowered by ice or sand, and similarly, increased by grippier tires.

In terms of max acceleration, grippier tires are better until they're so grippy your engine doesn't have the torque to break them free. But of course, grippier tires implies higher rolling resistance as well, which will do bad things to fuel economy. Hence the need for balance on a consumer car.
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      01-04-2013, 09:26 PM   #8
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I'd like to drag race my car with my old wheels and tires and new wheels and tires and see how much more power I can get to the ground with traction control on.
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      01-04-2013, 09:30 PM   #9
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Quote:
Originally Posted by thenewrick View Post
That's just the point I was making. I think it's kind of interesting at least. Essentially gaining big whp numbers just from stickier tires. My last car was AWD and worked quite a bit differently. AWD burnouts are a whole nother beast from the BMW traction control systems.
You're not gaining "big" whp from stickier tires. Power out of your engine is the same regardless of your tires. You're just realizing more of it as a result of stickier tires.

AWD drive systems are of course different. Audi / BMW / Subaru / Mitsubishi use different designs with different methods of transfer of power from loss traction and ratio of front / rear power delivery.

A RWD system will of course be very different...

I'm not seeing your point.
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      01-04-2013, 09:33 PM   #10
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Quote:
Originally Posted by thenewrick View Post
I'd like to drag race my car with my old wheels and tires and new wheels and tires and see how much more power I can get to the ground with traction control on.
How exactly will you quantify more said power?

You're not going to gain more power regardless of tires or traction control.

If you're associating "power" to acceleration times, then you need to rethink your wordings.
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      01-04-2013, 09:35 PM   #11
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Quote:
Originally Posted by thenewrick View Post
The traction control kicks in and reduces power output when it senses the wheels spinning. So the idea is that if you aren't spinning the tires then the traction control systems won't initiate and thusly will not be reducing power and braking the car autonomously.
That is absolutely correct. In situations when the available traction is the limiting factor (i.e. powerful engine and/or slippery surface), increasing the traction will result in more power being successfully used to accelerate the car. In DTS/DTC mode it means that DTS/DTC will kick in later (or not kick in at all). However, it also works in non-DTS/DTC mode, since it allows you to successfully deliver more power without breaking the traction (i.e. without causing useless wheel spin).

The same principle works with braking. The grippier your tires are, the more braking power you get, i.e. the harder you can press your brake pedal without causing the ABS to kick in.

Of course, in situations when traction is not a limiting factor for acceleration (i.e. the engine is too weak to break the traction) installing grippier tires will not improve acceleration (although it still makes perfect sense in braking context).

Last edited by AndreyT; 01-04-2013 at 09:43 PM.
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