dmkozak

I guess I just assumed that Lexus felt the IS350 just didn't need it (even as part of the Sport Package). But, with the IS-F not having one, and the competitors all pretty much having lsd (except notably BMW, but it is a matter of time for BMW), I am wondering why Lexus has an aversion to putting a lsd in the IS.

wushuboy

what is LSD? sorry if this is a stupid question

joonsta

The dictionary defines LSD as "a powerful psychedelic drug that produces temporary hallucinations and a schizophrenic psychotic state."

lobuxracer

iTrader: (2)

Limited slip differential. They didn't put one in because they have an electronic system using the brakes that does the same thing.

al503

Kinda surprised at this answer... A true LSD will actually lock up the differential so that both tires are putting the power down. The brakes will only slow down the tire that is spinning. You can imagine which one is preferable to the enthusiast.

I didn't know the F wasn't coming with an LSD. Big mistake if this is so and makes me wonder how serious Lexus really is to building a competitor to the M3.

ba-b4

how can they build the IS-F without lsd?! crazy even the G35 has one and lots of sport economy cars!

RocketGuy3

iTrader: (1)

How do you know the IS-F doesn't have one? That information is already released?

That would be a pretty big let down... Haven't the cars they're trying to compete with had an LSD standard for years?

dmkozak

Yes, Lexus put out a press release and Lexus executives gave info to Club Lexus people at the Detroit show. The execs specifically said no manual transmission variant and no mechanical limited slip differential. See "F marks the Lexus spot" under Club Lexus Industry News.


Those are my points, leading to my question of why Lexus does not want to use a "real" lsd in the IS. I don't know and I don't understand it. I am hoping someone can shed some light on this.


P.S. For the poster who thought electronic brake distribution was the same thing and others who want a simple explanation, listen to Marisa Tomei's explanation near the end of My Cousin Vinny.

lobuxracer

iTrader: (2)

Thanks for playing the game. Might want to try again. This is how they do it.

lobuxracer

iTrader: (2)

Not really. A true LSD comes in two different styles. One is uses a torque bias ratio (Quaife, Torsen, et. al.), the other uses wet clutches inside the spool to "lock" the axles but still allow them to turn independently when the force applied to the wheels is sufficient to overcome the clamping force in the clutches.

The Quaife and Torsen units depend entirely on both tires having some traction since the torque is multiplied by the torque bias ratio and delivered to the wheel with traction. If the inside wheel has no traction, you are multiplying by zero, and we all know what happens next - inside wheel spins mercilessly and outside wheel has zero torque, just like an open spool.

The clutch-type LSD will not fail to transfer torque under any conditions, however, the unit is subject to wear (sometimes very significant and rapid wear), and they tend to chatter unless you have exactly the right amount of additive in the differential lube. Tuning the clutches is a bit of an art, and because the clutches can be worn out very quickly on a road course, they are not preferred for circuit racing.

In defense of Toyota's methodology - applying the brakes is identical to a clutch-type LSD without the downside. Since the brakes are not constantly applied, there is no chatter when turning, and the only time the brakes are engaged is when VDIM senses one wheel accelerating at a much greater rate than expected. Because VDIM is yaw aware and wheel speed aware, it has all the information it needs to do this intelligently. Whether it actually executes this properly is another question, but one that few drivers will ever test under ordinary driving conditions.

There are preload washers in the differential that act like a very weak clutch-type LSD, and their function is mechanically identical to the Phantom Grip. Apply resistance to the pinion gears, and they will tend to deliver torque when they would ordinarily just spin freely and allow the "free" wheel to rotate with complete abandon. Please note that Torsen differentials are often tuned in this same fashion using different thickness washers to preload the worm gears, despite Torsen's instructions to the contrary.

Maybe you haven't tried this. Maybe you didn't grow up in the snow belt when FWD was only found on a Cadillac. I did. I learned that the best trick to solve a single spinning wheel is to apply the parking brake 2 or 3 clicks to prevent the spinning wheel from getting all the power. I have used this technique on snow and in sand to get a car out of a bad situation. It works. Toyota is just applying a technology solution to something that used to be only possible with gears and mechanical devices. You may argue with the execution, but you have no argument with the principles behind the technique. They are irrefutable.

dmkozak

I still don't understand how this applies "more" power to the wheel with more grip. Or, are you saying applying more power to the wheel with more grip is irrelevant, possibly because reducing power to the less grip wheel accomplishes the same thing when either you have more than enough power going naturally to the more grip wheel (and applying still more power to the more grip wheel would be a waste) or simply reducing the less grip wheel's power still "shifts the balance of power" by reducing the less grip wheel's slippage? Or, is it a combination of both?

y2ks2k

Lexus needs to buy the Sti DCCD and drop it in the IS250 AWD

al503

I saw a marketing vid of the new 335 taking off from a standstill. The rev'd it up and dropped the clutch. The right rear wheel started spinning and there wasn't that much forward progress for a good second or so. You could see the brakes modulating that spin and it eventually took off. Even with that brake modulation, the left rear didn't look like it was doing anything.

I can't say with certainty that we're comparing apples to apples but both the 335 and the IS have open differentials and both seem to use their brakes to control excessive wheelspin.

One of the guys on the g35 forum has a highly modded coupe 750+ bhp on built internals. There are nice vids of him passing vipers, z06's, lambos, etc., on the straights of various tracks. He has over 40+ track days on the same pumpkin. Maybe he got one made out of unobtanium but he hasn't had any issues with that much power, running 315mm R compounds in the rear. I actually haven't read of one clutch type LSD g/z owner wearing their's out...

If this is truly the case, I guess all those Vette, Viper, M3... (actually, I can't think of any high performance sports car with an open differential, can you?) owners have to deal with the downside of having an LSD when they could have the same performance without it...

Sorry for the sarcasm but there is a reason all of the sports cars that I can think of off the top of my head have a true LSD and don't rely simple braking to accomplish the same thing.

lobuxracer

iTrader: (2)

Many of them have a Torsen. What happens when a Torsen lifts the inside wheel? It spins. Mercilessly. It transfers ZERO torque to the outside wheel. AMHIK, my Supra has one. It's only better than an open diff if both wheels are on the ground.

Who sells a clutch-type differential on a street car today? I haven't seen one in a long, long, time unless it was a club racer package not intended for street use.

And apparently, you're not clear on concept. Applying the brake is identical in function to having a clutch-type limited slip.

lobuxracer

iTrader: (2)

Any open differential will apply 100% torque to the opposite wheel if you apply the brake on one of the wheels and lock it up. You don't want to do that in service, but at the extreme, that's what happens. If you measure the wheel speed and modulate the brake, you will reduce the torque going to the slipping wheel and increase the torque going to the wheel with traction based on the amount of slip.

In a clutch-type LSD, the ratios are fixed by the amount of slip the clutch pack allows. You can adjust it mechanically or you can adjust it with additives in the differential fluid (within a small range).

The electronic system is actually better suited to managing the torque because it uses feedback. None of the mechanical methods do this, although the gear types are much closer to this function than the clutch types.