teoh2005

From what I understand, with the IS-F now there is some electronic system that prevents the inner wheel from spinning when going around a corner when maximum traction is reaced. A Torsen Diff aka a Torque Biasing Differential only works on the outer wheel allowing more power to be put down only under throttle application. So what this would theoretically mean is that the TBD or Torsen diff will allow the outer wheel to put down more power/spin more and not affect the inner wheel and not trigger the VDIM.

I have a Quaife TBD in my Cayman S and issues never rise. Occasionally the PSM (traction) light will go off but I usually switch it off anyway.

-Kevin

lobuxracer

iTrader: (2)

Might want to read this and re-think your position.

A TBR diff splits torque and sends a greater proportion to the slower wheel. That would not be the outside wheel in any turn. Your hope is the inside wheel is lifting and slipping excessively for the best possible outcome, but this may not be true.

A TBR diff works on a multiplication basis, so if the inside wheel is in the air, you multiply torque by zero and you get the same effect as an open diff. Definitely one of the downsides of a TBR diff.

The electronic LSD applies the brake to the wheel spinning faster which essentially locks up an open differential. So the spinning wheel stops spinning, and drive is achieved by the opposite wheel. It's simple, and can be effective, but apparently is not as good as the mechanical solution since the TBR diff has been rumored to make a significant drop in lap times.

The issue most of us are concerned about is the electronic LSD interfering with the TBR diff. We're hoping (in a big way) the TBR unit will prevent the electronic control from applying the brakes because the wheel speed sensors won't indicate slippage sufficient to engage the electronic control. If we were to lift an inside wheel, then it would be very beneficial to leave the electronic control in place for this specific circumstance, but if the electronic control interferes with the TBR diff's function, then all of us retrofitting the TBR diff will be unhappy.

teoh2005

First if you have driven on a track and have an open diff you will know that the INNER wheel WILL spin more and the outer wheel will be slower. For instance if you are entering a right hand corner, you turn right, all the weight transfers to the left putting more traction to the outer/drivers/left wheel and less to the inner/passengers/right wheel. This results with inner tire smoke. The "electronic lsd" will try and prevent the inner tire smoke by applying the brakes to the inner wheel.

With a TBD, once the inner/passengers/right wheel begins to loose traction and spin more, the TBD takes the torque from that wheel and applies to the outer/drivers/right wheel. Because this is happening the "electronic lsd" should not be triggered. But honestly if you are driving at the track, most people switch off the VDIM/traction control, I do.

For the TBD to work, the inner wheel must have resistance meaning it must be touching the ground. A TBD will not work if you get wheel lift and the inner wheel is not contacting the ground. For this to happen, you really need to be attacking a corner. I have had the experience in my Cayman when going from a fast right-left corner. There is a brief moment where there is wheel lift and the TBD is not working. Its not a huge issue, but to correct that a true LSD with clutches would be needed. The big plus with the TBD is that is has gears as opposed to clutches in an LSD so its virtually maintenance free.

More information can be found here:
http://www.torsen.com/general/genera...hat%20is%20TBR

-Kevin

IceIridium

iTrader: (2)

Thanks for the pics Joe.

Hmm... that blue bottom steering wheel doesn't go with the Alpine interior at ALL. It's odd enough (but doesn't bother me too much) that we Alpiners have black/white stitching on the seats but blue stitching on the doors and armrest. Adding that would be excessive. I can see how it would go with a black interior though.

Which brings up a question I've been meaning to ask... I swear I've seen a picture of an F steering wheel just like that but with Alpine leather bottom, but I can't find a pic of it. If it exists, was it a rewrap or oem? And no, it wasn't white CF like Cathy's, I mean white leather. I'd like to get that one instead.

Joe Z

iTrader: (10)

2008 Neiman Marcus Edition IS-F (only 50 made)

Whire Leather & White Stiching Steering Wheel




Joe Z

duboseq

They went from Ninja Blades to Throwing Stars!

lobuxracer

iTrader: (2)

I have driven the IS-F on a track and didn't have a problem that I could attribute to the open diff. I've read the entire Torsen site more than once, starting in 1998 when I decided to learn more about the diff in my Supra. I've also been either racing or around racing for the last 40 years or so. IME autocrossers have the biggest problems with inside wheel lift.

I've spent enough time with FWD to know exactly what happens with an open diff when one wheel has zero traction and while you say it isn't a big deal with your Cayman (a car originally delivered without an LSD) during transitions, I can tell you it is a huge deal in a FWD because your acceleration drops to zero and the guy behind you with an LSD suddenly becomes the guy in front of you pulling away.

If you read the documentation from Lexus, you'd also know that the electronic LSD does not ever turn off, just like ABS, EBFD, and brake assist never turn off. So push on the button all you like, you'll never turn off the electronic LSD.

Key to all of this - the torque goes to the wheel that is not spinning. The TBR does not care which wheel it is, it only cares that one is spinning faster than the other. Again, the hope is this is the inside wheel, and, if the Torsen diff is installed, that it will respond to spinning better than the electronic device and preclude the electronic LSD from engaging. The only instance where the electronic LSD has an advantage is when a wheel is off the ground (again, we would hope it is the inside wheel since it would really suck to have the inside wheel getting more torque than the outside wheel and forcing the car to go straight instead of turn, but since a TBR device and the electronic LSD do not know which wheel is inside or outside, they will apply more torque to the wheel with traction.)

teoh2005

I've read your post several times now and I still do not understand what you are getting at.


I have driven the IS-F on a track and didn't have a problem that I could attribute to the open diff. I've read the entire Torsen site more than once, starting in 1998 when I decided to learn more about the diff in my Supra. I've also been either racing or around racing for the last 40 years or so. IME autocrossers have the biggest problems with inside wheel lift.
-If you do not notice you cannot put power down efficiently with the open diff, then you are not applying much throttle as you are going through the apex. Of course if you drive more conversatively the open diff will not be an issue. If you are tracking aggressively you will notice this open diff or any open diff will be holding you back.


I've spent enough time with FWD to know exactly what happens with an open diff when one wheel has zero traction and while you say it isn't a big deal with your Cayman (a car originally delivered without an LSD) during transitions, I can tell you it is a huge deal in a FWD because your acceleration drops to zero and the guy behind you with an LSD suddenly becomes the guy in front of you pulling away.
-First off why are we talking about FWD? IS-Fs are RWD and my Cayman S is Mid Engine/RWD. Also my Cayman S has a Quaife TBD that I added 2 years ago. There are instances on the track where I have rear inner wheel lift an the TBD does not engage. Its only momentary but once the car settles and when inner wheel touches the ground again, the TBD rengages.



If you read the documentation from Lexus, you'd also know that the electronic LSD does not ever turn off, just like ABS, EBFD, and brake assist never turn off. So push on the button all you like, you'll never turn off the electronic LSD.
- I am aware of that if you push the VDIM button on the dash it simply comes back on. From my understanding once you do the "pedal sequence" the entire VDIM is shut off and since the VDIM acts as the "electronic lsd" it will not become an issue

Key to all of this - the torque goes to the wheel that is not spinning. The TBR does not care which wheel it is, it only cares that one is spinning faster than the other. Again, the hope is this is the inside wheel, and, if the Torsen diff is installed, that it will respond to spinning better than the electronic device and preclude the electronic LSD from engaging. The only instance where the electronic LSD has an advantage is when a wheel is off the ground (again, we would hope it is the inside wheel since it would really suck to have the inside wheel getting more torque than the outside wheel and forcing the car to go straight instead of turn, but since a TBR device and the electronic LSD do not know which wheel is inside or outside, they will apply more torque to the wheel with traction
-I really don't know what you mean here. The diff is on the rear axle. The inner wheel on any car will always have less traction and want to spin more when going around any corner. The point of the TBD is to prevent inner wheel slippage and transfer the torque to the outer wheel allowing more power to be put down. So by having a TBD, it allows more torque to applied to the outer wheel and less to the inner wheel thus replacing the task of the "electronic lsd." I know the main issue here is whether the TBD will interfere with the VDIM's function of an "electronic lsd." I would have to say no. The TBD will do its job and also function as an "electronic lsd" and should not trigger any VDIM lights. Its the same with Porsche's PSM. I have the Quaife TBD on my Cayman S and there are no issues.
You also keep talking about the electronic LSD having an advantage when a wheel is off the ground. How often does that ever happen? It may happen at the track depending on driver skill but even if it does its only for a brief moment. Finally you mention something about a TBD affecting steering (making a car go straight instead of a turn). I don't see how it would as the diff is on the rear axle not the front where the steering is being done.

-Kevin

encore888

Interesting updates and thx for the pics, the dual-tone NM edition, Terra cotta etc. are unique approaches that suit the -F line well.

n0th1ng

iTrader: (9)

I dont like the wheels personally. But w/e it does feel diff then other stock wheels...
Thanks for the updates on other things too

CrazyMPG

iTrader: (4)

I actually want some Euro or Jap spec IS-F BBS wheels...the 08-09 ones...haha used tho in good condition...not new...lol

Rash

iTrader: (1)

In japan there's a light grey wood option.

Joe Z

iTrader: (10)

They have had this special order option since the IS-F was first released...

Nothing new, the USA Spec never got that option on the IS-F


Joe Z

lobuxracer

iTrader: (2)

OK, let's make it simple: you're wrong. VDIM NEVER turns off completely no matter what you do with the buttons - see below for what the switches do.




As for what I'm getting at - there's a whole lot of chassis set up that determines how much your inside wheel will spin. IME, the F set up isn't problematic until you are trying to squeeze out the last tiny bit of performance, and the car doesn't have an inside wheel lift issue - see below:



It also does not wear the rear brakes heavily (a dead giveaway the electronic LSD is working hard). However, if it does lift the electronic LSD would help by doing what the Torsen can't because the Torsen is multiplying by zero. I'm far LESS concerned the Torsen will interfere with the electronic and a lot MORE concerned the electronic will interfere with the Torsen simply because I'd rather have torque transfer than braking any day.

You said you don't understand how the rear wheels steer the car. It would seem you've not done much work with chassis set up. Rear wheels affect turning pretty dramatically - in karting, the inside wheel is intentionally raised off the surface because they run solid axles and if the inside rear wheel is on the ground, the kart will go straight under power. You really want the outside wheel to have more drive and in a car with independent rear suspension, you'll add toe in to the rear wheels to help the car turn under power. I've done a bit of work on both dirt and asphalt chassis to make cars go faster. There's a lot to it that isn't intuitive or obvious.

Joe Z

iTrader: (10)

Hi Kevin,

You guys are making this a Great read!!

Quick pointer, if you press the Trac button once quickly, the "Traction Control" System remains off till approx 20-25mph. Then it turns back ON.

Now if you press and hold the Trac button for 3 seconds, the TRAC & VSC Systems are turned & remain OFF, until turned back ON via button or engine shut down/restart..

"Pedal Dance" is the long way of tunring OFF the trac & vsc system. Which is how it can only be done on some of the 2006 Lexus models.

Regards,

Joe Z


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