Which wheel spins first?

[briandee]

He must be prying something with that 6"!! That is a mechanical leverage!

You have got to be kidding me. It's all about the size of the handle and how you grip it when using a screwdriver. Absolutely nothing to do w/ the length of the screwdriver shaft. Do some research on the interwebs before spouting stuff like this. Please...it'll make you sound way more intelligent. If you can't figure it out lemme know and I'll provide some links to the formula.

ETA: The shaft of the screwdrive is not a 'lever' in this type of work.

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[FiestaAlex]

The (transmission) output shaft drives the differential ring gear.
The power flows through the side and pinion gears to the halfshafts.

There are so many things that can then alter traction at any given time or place.
It stands to reason that the tire with the least traction at that instant would be the one to spin first.



Dave

This

 

[FiestaAlex]

But his photos clearly show both tires smoking. And so does that video I posted. LOL

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Video: one tire is clearly going 10x faster than the other

Photo: are they your cars? Do you know for a fact there's no LSD?

Also we're talking about a launch, not a standing burnout. A wheel can only spin so fast, especially when essentially melting - some torque will still go to the other side. When launching, one side will slip first. You are wrong. If you were right, open diffs would be best in all cases and LSDs/lockers would not exist.

Tell me why they exist and what they do, if both wheels always spin together with an open diff

 

[FiestaAlex]

In a straight line, the passenger side will spin first because the axle is longer. Basic physics. The longer the lever, the higher the torque.

Unequal length half shafts DO make a difference in torque steer but it's not because of lever length, it's because the longer one acts as a torsion bar to a greater extent.

ST shafts are pretty thick, and not very long, but technically it does impact which wheel breaks loose first. As does tire pressure, corner loading/weight, surface conditions, etc.



And before the other guy tries to argue I'll leave this here:

https://en.wikipedia.org/wiki/Torque_steer

Asymmetric driveshaft angles due to any combination of
Unequal driveshaft length or diameter

The problems associated with unequal length driveshafts is endemic to the transverse engine layout

Where unequal length driveshafts are used, their torsional stiffness must be made equal. This can be accomplished by making the shorter shaft hollow, and the longer shaft solid.

 

[D1JL]

OK, my question is, why does this make any difference anyway?
It is a proven fact that a car is quicker if you don't spin the tires.
If you are popping the clutch just to hear/see the tires spin you are promoting breakage of other parts.
These little cars today aren't built like the ground pounders of yesteryear.

If the right axel does provide some snap torque as some suggest (although I am not convinced) it would be very insignificant.
Why not just lower the air pressure in the right tire by a pound or two to compensate.

I am not an automotive engineer or a master of physics.
These are just my observations and opinions.



Dave

 

[cxwrench]

Unequal length half shafts DO make a difference in torque steer but it's not because of lever length, it's because the longer one acts as a torsion bar to a greater extent.

ST shafts are pretty thick, and not very long, but technically it does impact which wheel breaks loose first. As does tire pressure, corner loading/weight, surface conditions, etc.



And before the other guy tries to argue I'll leave this here:

https://en.wikipedia.org/wiki/Torque_steer

That all sounds pretty solid, definitely a lot different from what [MENTION=1668]haste[/MENTION] was talking about. Good info for sure.

 

[FiestaAlex]

OK, my question is, why does this make any difference anyway?
It is a proven fact that a car is quicker if you don't spin the tires.
If you are popping the clutch just to hear/see the tires spin you are promoting breakage of other parts.
These little cars today aren't built like the ground pounders of yesteryear.

If the right axel does provide some snap torque as some suggest (although I am not convinced) it would be very insignificant.
Why not just lower the air pressure in the right tire by a pound or two to compensate.

I am not an automotive engineer or a master of physics.
These are just my observations and opinions.



Dave

I think we've certainly gotten off topic. The question was "which wheel spins first"

The answer is "the one with the least traction" because it's an open diff. I really didn't expect this to be a controversial answer. This is not wrong, but neither is saying that an open diff CAN spin both wheels.

Under perfect conditions, you will spin both wheels with an open diff. The amount of traction has to be the same, or at least very close. So flat ground, same amount of weight on each corner, etc.

Why bother discussing it? Well, it's a forum, and it's what people do. As long as we can keep it civilized and nobody gets too upset, i don't see an issue.

For anyone that cares, you can read the science behind open and locked diffs:

https://en.wikipedia.org/wiki/Locking_differential

https://en.wikipedia.org/wiki/Differential_(mechanical_device)#Loss_of_traction

The gist is that an open diff applies equal torque but allows different rotational speeds. Locked is the opposite - rotational speeds are equal, but the wheel with more grip is getting more torque. In off-road applications this is very pronounced, where both wheels are VERY unlikely to have equal traction at any given time, and the amount of traction in general is lower compared to asphalt. You won't get far in an open 2wd in mud for example.

On a paved road this matters less, but still does:

It is a proven fact that a car is quicker if you don't spin the tires.

100% correct. Which is why you want an LSD - you will spin less with the same amount of power. It is also a proven fact that a car is quicker if you launch hard instead of leaving from idle. But you can only apply as much power as your traction allows. It's easier to overcome the traction of one wheel than both together. Hence, a car with an LSD will usually launch harder than one with an open diff, all other things being equal.

This is one sore point for me, is that STs didn't come with an LSD and other than FWD, it's probably the biggest detractor in an otherwise great little car.

Ps. it grabs the brakes on whichever side is spinning instead Ughh

 

[alexrex20]

You are wrong. If you were right, open diffs would be best in all cases and LSDs/lockers would not exist.

Tell me why they exist and what they do, if both wheels always spin together with an open diff

Are you retarded?

 

[alexrex20]

The gist is that an open diff applies equal torque but allows different rotational speeds. Locked is the opposite - rotational speeds are equal, but the wheel with more grip is getting more torque. In off-road applications this is very pronounced, where both wheels are VERY unlikely to have equal traction at any given time, and the amount of traction in general is lower compared to asphalt. You won't get far in an open 2wd in mud for example.

[video=youtube;ux5QD7gtczg]https://www.youtube.com/watch?v=ux5QD7gtczg[/video]

Would ya look at that... Open diff, 2wd, off road. and it's spinning both tires.


Btw, please quote me where I said "both wheels always spin together with an open diff." I'll wait.

 

[cxwrench]

Are you retarded?

You really do try to piss people off, don't you? His post is correct. A limited slip will put the available power down more effectively than an open diff. There is no question about this, that's why limited slip differentials exist. At the extreme consider a 4x4 w/ lockers on both axles. With good traction and looooow gears there is virtually no slip on crazy off road terrain.

ETA:

[video=youtube;ecCCmC0RByY]https://www.youtube.com/watch?v=ecCCmC0RByY[/video]

or:

[video=youtube;1T5H0PU8USQ]https://www.youtube.com/watch?v=1T5H0PU8USQ[/video]

 

[alexrex20]

Video: one tire is clearly going 10x faster than the other

Yes, you ARE retarded. I guess someone needs to introduce you to this phenomenon called WIND. I'm honestly surprised you've never heard of or seen wind before, considering you can tell exactly how quickly a tire is spinning without even being able to see it. Are we watching the same video? Because the one I linked only shows the passenger tire. Yet you know one tire is spinning 10x faster than the other? How are you calculating 10x? I'd love to hear your explanation.

 

[alexrex20]

You really do try to piss people off, don't you? His post is correct. A limited slip will put the available power down more effectively than an open diff. There is no question about this, that's why limited slip differentials exist. At the extreme consider a 4x4 w/ lockers on both axles. With good traction and looooow gears there is virtually no slip on crazy off road terrain.

And? Where did I say otherwise?

Some people seem to think that an open diff is extremely unlikely to ever spin both tires. That is incorrect. It's actually quite easy and common for an open diff to spin both tires. But I'm sure he'll come up with some excuse as to why the 2nd video I just posted is not relevant.

 

[jmrtsus]

Try loosening a screw with a 3" long screwdriver compared to a 6" screwdriver and tell me which is easier to turn.




Clearly more smoke from the right front.

The only way a longer screwdriver has more torque is if you use it sideways! Basic physics.