Why you need a LSD if you like cornering!

[CSG Mike]

So a brief explanation of what is going on here

Top graph = throttle position
2nd graph = Front left wheel speed
3rd graph = Front right wheel speed
4th graph = Rear left wheel speed
5th graph = Rear right wheel speed
6th graph = steering angle (negative = left, positive = right)

Blue/purple thin boxes - compare the left and right wheels, and you can see momentary lockups under braking. Decreasing wheel speeds mean I'm braking the car, and the little sudden dips are the wheels on the verge of locking up, but recovering before they actually do. The wheel speed would go to 0 if it actually locked up. This is shown to demonstrate the accuracy of the equipment we are using, and validity of this test.

Red box #1 - under acceleration and turning, notice the wheel speed differences between the rear left and rear right wheels. The rear left wheel is the "inner" wheel in this case, and you can see spikes where it speeds up, and then slows back down as I modulate the throttle. With a mechanical LSD, I would be able to give the car more throttle without the rear wheels going at different speeds or spinning altogether. Spikes on the left rear wheel here indicate that the inside wheel is spinning, rather than gripping. The inside wheel travels a lesser distance than the outer wheel, and should be travelling at a lower speed, not a higher speed.

Red box #2 - Notice the dips and peaks of the rear right wheel, compared to the rear left wheel. The spikes up and down are a result of throttle modulation, but I am unable to put down any power, because when I do get on the throttle, I'm spinning the inside (rear right) wheel instead of accelerating.

Red box #4 - Note the spikes in the rear left wheel. Same thing; I'm modulating the throttle (top graph) to accommodate the car's inability to put all the power down. If the inside rear wheel were not slipping, I'd be able to corner faster, and put down more power.

Red box # - I manage to spin BOTH wheels for once, and need to countersteer....


TL;DR: mechanical LSDs help you power out of corners, and corner faster, regardless of power output levels (note that all the times where I cannot power out are at partial throttle) and driving experience.




*edit*

Some highlights from others.

Originally Posted by ja1217

It's quite possible that what happened to me was just a case of me kicking up a bunch of dirt, temporarily messing with the wheel speed sensors and throwing, but if that's the case I don't see anything like that in my wheel speed data. I only see a lot of inside wheel spin (clutch type LSD is planned for next year) in that turn:

{Green=Front Left, Brown=Front Right, Blue=Rear Left, Orange=Rear Right}

Turn 2 is right around the 1500ft mark and then you can see the fronts lock up going into turn 5 around 4100ft

Originally Posted by Captain Snooze

This is not a very scientific review. Firstly my lap times are......mmmm....well....ahhh......variable. Secondly, I have had a tune along with the fitment of the diff since my previous track day.

BUT even so today I bettered my best time by 0.6 of a second!! This is significant (2.2 kilometer track) but the more interesting thing is the way the rear now feels.
Have a look at this pic. This was my second lap out, still getting the tyres up to temperature.



I was a little enthusiastic and the rear went a bit sideways. I was doing 110 km/h when I started to apply corrective lock. OMG!! The creaminess of the slip was just freakin' awesome and most impressive there was no vicious snap back. That is , previously I would find the break away nice but then the rear would tend to snap back. No more. Previously a slip of this magnitude at that sort of speed would result in a bit of heart rate increase. Today it was like meh. Loved it. I also seemed to be getting on the power sooner (I haven't looked over prevoius data as yet) with less drama. I'm not really sure what is going under trail braking (my trail braking is not great) but there were certainly no adverse reactions there.

Worth it for track use? Definitely yes!! I'm thinking that if it makes a difference at my level then the difference it must make for someone who knows what they're doing must be huge.

Originally Posted by Captain Snooze

The benefits of some mods are..... well... debatable. And some people have claimed benefit for some mods where I have found none. This is not one of them. I was sceptical but f**k me, I wish I had installed a Giken earlier*.

*In my opinion this mod is kinda pointless for street use but your mileage/kilometerage may differ.

[whataboutbob]

Thanks Mike, nice writeup.

[7thgear]

hey mike, as an aside, did you pull the wheel position sensor using the Solo DL or a more advanced unit?


did AiM release a new FRS/BRZ file

[neilr]

Originally Posted by CSG Mike

With a mechanical LSD, I would be able to give the car more throttle without the rear wheels going at different speeds or spinning altogether.

For my own clarification...

I'm reading this as: you can't do this because the car doesn't have a mechanical LSD.

I thought the FR-S & BRZ came standard with a Torsen LSD. Isn't that a mechanical diff? Please clarify if I've missed something obvious.

Src:
[ame="http://www.youtube.com/watch?v=u0EOrzn7-Qc"]http://www.youtube.com/watch?v=u0EOrzn7-Qc[/ame]

[CSG Mike]

Originally Posted by 7thgear

hey mike, as an aside, did you pull the wheel position sensor using the Solo DL or a more advanced unit?


did AiM release a new FRS/BRZ file

This is from the latest AIM Solo DL firmware.

Given that the AIM Solo DL now reads Oil Temp and Wheel Speed sensors, we're thinking about doing a group buy if there is enough interest.

[CSG Mike]

Originally Posted by neilr

For my own clarification...

I'm reading this as: you can't do this because the car doesn't have a mechanical LSD.

I thought the FR-S & BRZ came standard with a Torsen LSD. Isn't that a mechanical diff? Please clarify if I've missed something obvious.

Src:

The car comes with a Torsen, but if you lose traction with one of the wheels, then the differential effectively becomes open. Loss of traction can be lifting a wheel, or spinning a wheel. In this case, the inner wheel is spinning.

[7thgear]

Originally Posted by CSG Mike

This is from the latest AIM Solo DL firmware.

Given that the AIM Solo DL now reads Oil Temp and Wheel Speed sensors, we're thinking about doing a group buy if there is enough interest.

I just updated! (didn't realize I was on xx.53 and not xx.54)


now I have all these fun things too!

[dp1]

@CSG Mike, you're doing this only to torture me until my OSGiken gets installed...jk

[CSG David]

Originally Posted by dp1

@CSG Mike, you're doing this only to torture me until my OSGiken gets installed...jk

@RehabJeff86 is also in the same boat. LOOOL

[stugray]

Originally Posted by CSG Mike

The car comes with a Torsen, but if you lose traction with one of the wheels, then the differential effectively becomes open. Loss of traction can be lifting a wheel, or spinning a wheel. In this case, the inner wheel is spinning.

BUt I thought that if we lifted a wheel the ECU would use the VSC to apply brakes to the spinning wheel.

[CSG Mike]

Originally Posted by stugray

BUt I thought that if we lifted a wheel the ECU would use the VSC to apply brakes to the spinning wheel.

In theory, but that's really, really intrusive, and you don't want that to happen on track. I've seen guys get sideways at 120+ because of that.

Also, that functions by slowing you down; the goal is to go faster

[stugray]

Originally Posted by CSG Mike

In theory, but that's really, really intrusive, and you don't want that to happen on track. I've seen guys get sideways at 120+ because of that.

So did you pull the fuse so that the VSC would not respond?

Originally Posted by CSG Mike

Also, that functions by slowing you down; the goal is to go faster

Ummm... SO slowing the spinning wheel would slow you down??
I thought that was the whole concept of a LSD.

[troek]

its applying brakes do regain traction is why it slows you down.

[7thgear]

Originally Posted by stugray

So did you pull the fuse so that the VSC would not respond?



Ummm... SO slowing the spinning wheel would slow you down??
I thought that was the whole concept of a LSD.

it's slowing down the spinning wheel so the LSD kicks in and gives power to the one that's not spinning


but because this is achieved through electronics and well.. brake actuation, it's really just a hack