Wheel spinning

[Anonymous]

sureley it makes a difference when pulling away in the wet?

[Anonymous]

If you've got a turbo'd 2 then pulling away in the wet is a wheel spin frenzy. Doesn't matter if you've got LSD or spikes in your tyres. If you think the LSD is your answers then i'm afraid your going to be dissapointed. It takes no time time at all to get used to the different conditions and it can actually be quite amusing to floor the throttle in 3rd and feel the wheels spinning trying to gain traction. But basically it's in your control, you just need to try it to appreciate it.

This Sunday is a good time to try it, i believe, if you can make it to MK.

Juansolo your proving to be quite a guru in the mechanical workings, i like reading your posts cause they actually talk sense. I take my hat off to you.  s:wink: :wink: s:wink:

[Anonymous]

It will be more useful on a turbo'd car yes.  Won't make much, if any difference in getting off the line though.  Unless one of your wheels is on a patch of oil and the other isn't that is.

figured... featherweight foot around the city will be!  s:) s:)
or I will look like some kid in '89 blacked-out (and peeled off) 3 series, doing slides from the traffic lights

[juansolo]

sureley it makes a difference when pulling away in the wet?

If you think about it you are feeding the same drive to both wheels.  If the weight on both wheels is the same and the surface under the wheels is the same (thus having the same traction properties), then there is no reason that one of the wheels will spin faster than the other, which is what an LSD is there to combat.

Now imagine you are on a track and going around a tight corner.  All of the weight of the car is on the outside of the vehicle.  With a standard open diff (and a lot of power), flooring the throttle on exit with the car loaded up this way will cause the torque to go to the place of least resistance, which is the unloaded wheel.  Once that starts spining you'll just spin all the torque away.

What an ATB diff does (see here: http://auto.howstuffworks.com/differential.htm and here for an the Torsen (ATB) white paper:  http://www.sonic.net/garyg/zonc/TechnicalInformation/TorsenDifferential.html) in this situation is direct the torque to the outside wheel that has the traction, allowing you to power out of the corner more effectively.  It can only do this to a point though.  Most are a ratio of 5:1.  But in reality once you exceed that both wheels are spinning anyhow and your already catching an armfull of oversteer.

This is also why it's more difficult to donut a car without an LSD.  The priciple is the same.  You need to get both wheels spinning but as you're essentially trying to turn a very tight corner, the inside one instantly unloads and spins up.  What the ATB does is exactly what's mentioned above and gets both wheels spining.

However as I've mentioned before, ATB's don't work in extremely low traction situations.  You try driving on ice and you'll find that the ratio is exceeded instantly, the diff goes open and one wheel will spin up.  This is why in the days before electronic diffs, rally cars all used plate differentials as an ATB would be useless on the loose surfaces.  

A plate LSD is far more brutal than most diff's that you'll find on a road car.  It's a proper LSD for a start.  What they do is allow a certain amount of slip (set up when it is built) before essentially locking the diff.  Drive is then directed 50/50 to both driven wheels regardless of traction.  One of them could be in the air for all it would care.

The problem with plate diffs is that they are incredibly noisy.  I have one in the Westy and the looks I get sometimes are comical as it sounds like the back of the car is about to fall off at any time when trundling around the paddock as even the slightest amound of steering lock starts the diff 'winding up'.  Basically they bang and clunk in a very loud way.  They also need new oil every year and require rebuilding when they wear out.

There are others;  Viscous diffs work (very simply speaking) on the resistance of special oil within it.  Worm diffs just freak me out and I don't understand them at all.

The main rule of thumb is that if it's a road car or a road / occasional track day car: fit an ATB/Torsen.  If it's a pure track vehicle, fit a plate.

[juansolo]

Juansolo your proving to be quite a guru in the mechanical workings, i like reading your posts cause they actually talk sense. I take my hat off to you.  s:wink: :wink: s:wink:

  s:oops: :oops: s:oops:  Why thank you.  s:oops: :oops: s:oops:   It all comes from buying a kit car that was utterly unsuitable for the purpose I wanted it for and the resulting very expensive rebuild after I blew the engine and decided to sort it all out in one fell swoop.

It also helps to know people who really know there stuff.  I have a friend up the road who prepares race and sprint cars for a living (and re-built a lot of mine).  My mate who stores my car used to restore classic vehicles (almost scratch built one!).  Finally I have my rallying friend who lives and breathes very silly cars.  Their knowledge and help has been invaluable.  

Before the kit I had little real knowledge of how any of this stuff worked.  I just had to pick up a lot of this stuff really rapidly as there was little that didn't need sorting in the car.

FWIW, when I get around to it, I'll be doing write ups on both the kits on my site.  I used to have a running diary for both on Pistonheads but the spiraling costs depressed me so I deleted them.  I will get around to it as both are insights into the reality of preparing a strong enough kit for track use.  Which is not as straight forward as you might think.

[Anonymous]

sureley it makes a difference when pulling away in the wet?

If you think about it you are feeding the same drive to both wheels.  If the weight on both wheels is the same and the surface under the wheels is the same (thus having the same traction properties), then there is no reason that one of the wheels will spin faster than the other, which is what an LSD is there to combat.

my mate has a celica (old shape - jap ST202) and he did a stationary burnout infront of me once, and when he pulled away there was only tire marks from one wheel? now for this car to do this, it most definately wont have an LSD, BUT the traction on both wheels and suface was the same so how come only one wheel spun??

So surely an LSD would get you off the line quicker if both wheels are spinning (as you have twice the grip)

[juansolo]

So surely an LSD would get you off the line quicker if both wheels are spinning (as you have twice the grip)

You'll get off the line quicker if neither of your wheels are spinning   s:wink: :wink: s:wink:  

Also you don't have twice the grip, the grip level is the same regardless of whether you have an LSD or not.  All an LSD does is redirect torque either proportional to grip (Torsen/ATB) or by locking drive to both wheels (plate).  

For one wheel to spin up and not the other there is a difference in traction for some reason.  Maybe, being FWD, he had a little bit of lock on (doesn't need to be much), or the tyre pressures were different, or many other factors that can effect this.

[filcee]

sureley it makes a difference when pulling away in the wet?

If you think about it you are feeding the same drive to both wheels.  If the weight on both wheels is the same and the surface under the wheels is the same (thus having the same traction properties), then there is no reason that one of the wheels will spin faster than the other, which is what an LSD is there to combat.

Sorry to be picky .. . but won't unequal length drive shafts have some effect on this?  I think a longer drive shaft will 'absorb' the energy destined for the wheel by twisting more than a shorter one.  Therefore everything at each wheel is not quite the same - the wheel at the end of the longer shaft will have less energy sent to it because the longer shaft used some up (less torque?).  The '2 has different length shafts 'cos it's a cheap ex-FWD engine stuffed in the back.

I believe that Honda did a lot of work on their engine bays to make drive shaft lengths as equal as possible to reduce torque steer for the FWD cars - ISTR the old CRXs had equal length drive shafts.  Not sure if this was carried forward to the mental Integra-R, as that had a worm LSD fitted.    Now why doesn't MrT do some of that?

[Tem]

If you think about it you are feeding the same drive to both wheels.

May I disagree?  s:oops: :oops: s:oops:

In basic theory, you are...but once you go deeper into it (and real life is as deep as it gets), I don't think you are. The right side wheel gets more torque than the left side wheel. It's not a major difference, but it is there. And I'm afraid I don't have enough knowledge to specifically explain the reason...it's a weird mixture of differential internals and axle movements. I'm still working on understanding it  s:oops: :oops: s:oops:

You can easily try it with non-LSD car that has enough power to spin the wheels on given surface. Major power easily spins both wheels, but if you try to balance on the limit between traction/spin, you'll just spin the right wheel. And it's always the right wheel, never the left one (assuming they have the same grip).

It was a real issue with my Mk1 MR2, which didn't have LSD  s:? :? s:?  It wasn't an issue with stock engine on dry roads though, there's plenty of grip for both wheels once you're moving. I did notice it in tight corners though, but nothing I couldn't live with. It was an issue on winter though, nothing that would make normal driving too hard, but an issue when you really wanted to go fast. With some extra power and wider tires, it became on issue on summer as well...again, nothing that would stop me getting the groceries though  s:twisted: :twisted: s:twisted:

[juansolo]

May I disagree?  s:oops: :oops: s:oops:

By all means   s:wink: :wink: s:wink:  

FWIW traction is always going to be more of an issue with a FWD car than a RWD one.   As you don't need a whole lot of power to require an LSD (Honda ITR/Focus RS), or traction control via ABS (pretty much everything else) to try and keep this in check.

As for an LSD getting you quicker of the line; it doesn't.  If you are spinning your wheels you are already not getting off the line as quickly as you could and are wasting fractions of a second as your tyres scrabble for grip.  If however you're doing it properly the wheels are not spinning and there is therefore no work for the LSD to do in the fist place.

You youself mentioned that you didn't have an issue with the standard car and it was only when you increased the power that the problems started.  That was my point exactly.  It's when the power starts to more easily overcome the grip available that an LSD really starts to make it's presence felt.  The turbo people in particular with their non-linear power delivery will appreciate it more than most.

[Tem]

As for an LSD getting you quicker of the line; it doesn't.  If you are spinning your wheels you are already not getting off the line as quickly as you could and are wasting fractions of a second as your tyres scrabble for grip.

This is splitting hair, but I think it does help.  s8) s8)  Let's say the torque is distributed 51% to right and 49% to left. That means you can only use 98% of grip that is theoretically available, or you will lose traction and end up spinning one wheel. Not really a major difference and surely nothing to worry about in real life (unless you're racing).

Then again, when you go above that and spin the wheel, first you'll lose major power on the spinning wheel and only some end up to the wheel with grip (=less acceleration). Also, you'll have to raise the throttle a lot without LSD go gain grip on the spinning wheel again, while with LSD you can get away with a lot smaller throttle decrease. And this is what actually makes it help in real life, cause no human can make a perfect launch again and again. It's easy to make a non-spin launch every time, but then you're not trying enough  s:lol: :lol: s:lol:

Also, the fastest acceleration comes when you're spinning the rear wheels at about 107% (meaning 7% faster than fronts/real speed). More or less impossible to do with driver controlling the throttle, but that's why God invented electronics for us  s:twisted: :twisted: s:twisted:  Obviously you can't do that without LSD.

But you're right that the stock '2 doesn't really need that in real life  s8) s8)

[juansolo]

This is splitting hair, but I think it does help.  s8) s8)  Let's say the torque is distributed 51% to right and 49% to left. That means you can only use 98% of grip that is theoretically available, or you will lose traction and end up spinning one wheel. Not really a major difference and surely nothing to worry about in real life (unless you're racing).

When both wheels are driving the car then 100% of the grip is being utilised.  Only when a wheel(s) is spinning does this reduce.  Grip is down to the tyres and road surface, not the LSD.  When it comes to torque distribution, again as long as both wheels are not spining, 100% of the available torque is being utilised.

Diffs vary where torque goes all the time, an ATB certainly.  Other than welding a diff up or fitting a plate LSD, you'll never get a true 50/50 split.  But then that's not always desireable as the ATB (up to 5:1 or whatever) will actually make better use of the available torque out of corners than a plate diff given that it can give more than 50% of the torque to the loaded wheel.

It's all swings and roundabouts and there is no right or wrong answer.

[Anonymous]

May I join in? I think the issue now is whether or not we are getting a 50/50 torque split between both rear wheels, which ideally we should be. If we are not, as TEM is saying, then an LSD will help because it will in effect redistribute the torque to both wheels.

If there is already an equal torque split then juansolo is right because as long as there is equal traction on both tyres then the perfect start will be acheived when the tyres are on the verge of spinning and the torque is divided equally between the two.

The only exception is if there is differeing levels of traction across the rear axle, in which case the LSD will help to juggle the torque between both sides of the axle to avoid spinning it away.

Hope that lot makes sense

[Tem]

I think the issue now is whether or not we are getting a 50/50 torque split between both rear wheels, which ideally we should be.

Like I said above, I'm afraid I can't explain it nor provide any proof  s:oops: :oops: s:oops:
Still trying to understand this stuff myself, it's pretty dman complex  s:? :? s:?

But I'm sure everyone has access to a car without any kind of LSD...make the wheel(s) spin and note how it's always the right side wheel that spins (or both). You just can't make the left wheel spin alone, assuming you're going straight and have even grip for both wheels.

[Anonymous]

Just to throw a couple of ideas in:

Unequal length driveshafts - I seem to remember other cars I've owned (don't know about the '2) used different diameter shafts and made use of both hollow and solid shafts to try and match the distortion properties and weights of both shafts.  I'm sure it's not ideal, but I bet they get pretty close.

Right wheel always spinning - is this going to be down to weight distribution? All things being equal, I would expect RHD cars to spin up the left wheel first due to the weight of the driver.

[Tem]

Right wheel always spinning - is this going to be down to weight distribution?

Well, try it on RHD cars. I'll still bet for the right wheel  s8) s8)

Most RWD cars have equal lenght shafts for rear wheels, the '2 is just an exception to that, so it can't be that.