LSD in a FWD?

"zeontestpilot" (zeontestpilot) 05/25/2016 at 13:03 • Filed to: None

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This is how I understand it, a limited-slip differential helps ensure both wheels get power, instead of one wheel on a slippery surface running at high rpms. It’s also ideal for rwd cars, namely for drifting and again, ensuring both wheels have powers. But what about a fwd car like my Grand Prix? What would the advantages and disadvantages be? I'm genuinely curious.

TheHondaBro > zeontestpilot 05/25/2016 at 13:08

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Decreased understeer. The Integra Type-R has an LSD.

Supreme Chancellor and Glorious Leader SaveTheIntegras > zeontestpilot 05/25/2016 at 13:08

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“Civic Si: Limited Slip Front Differential

The helical type limited slip differential (LSD) in the Civic Si improves acceleration and cornering performance by insuring that both front wheels receive an optimum level of torque at all times. In a straight line, both wheels are better utilized to put the engine’s power to the ground with minimal wheel spin. During hard cornering, the LSD transmits more torque toward the outside wheel to bias more power to the tire with the most grip. This also facilitates the outside wheels longer travel distance relative to the inner wheel. Primary benefits include the ability to accelerate harder exiting corners and enhances the vehicle’s responsiveness to throttle inputs in corners. Helical means the differential’s gear teeth are cut at an angle to the gear’s shaft.”

itschrome > zeontestpilot 05/25/2016 at 13:09

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you can buy a LSD for those! what they mostly do is help with launching and destroy handling. people like them for tuned up L^& cars they take to the track, drag that is. I’ve heard they make daily driving a bit of a pain in the ass.

RamblinRover Luxury-Yacht > zeontestpilot 05/25/2016 at 13:09

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Reduced torque steer and improved resistance to one-wheel spins on launch. Probably some other points, like resistance to lift-off oversteer.

for Michigan > zeontestpilot 05/25/2016 at 13:10

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Mazdaspeed3 has a LSD to help put all that turbo power down. I’m sure other performance FWD cars have them too, but that’s the only one I’m familiar with.

zeontestpilot > TheHondaBro 05/25/2016 at 13:11

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Nice! but with my 200 hp and 230 lbs of torque, I doubt I even get any understeer to correct it.

zeontestpilot > TheHondaBro 05/25/2016 at 13:13

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Nice! but with my 200 hp and 230 lbs of torque, I doubt I even get any understeer to correct it.

LongbowMkII > itschrome 05/25/2016 at 13:13

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I don’t see how. Unless the differential lockup is set extremely low causing it to lock with only a bit of torque making parking lots a pain.

My speed3 is happy > for Michigan 05/25/2016 at 13:15

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Yep

themanwithsauce - has as many vehicles as job titles > zeontestpilot 05/25/2016 at 13:16

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Reduced torque and udnersteer, better control through the turns, and no more one wheel peels.

RallyWrench > zeontestpilot 05/25/2016 at 13:17

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Instead of one tire fire, you’ll get two. LSDs are equally effective in FWD cars, you’ll have much less tendency to spin up the inside tire exiting corners, and if you drive in wet weather or snow you’ll be much less likely to lose traction. The disadvantage in hard driving, depending on the type of diff, is it can effect turn in and pull the car wide of the apex when you get on the power. You’ll have to relearn how to drive it, that’s all.

Berang > zeontestpilot 05/25/2016 at 13:19

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I know they are used a lot in rallying, but that’s on loose surfaces. I think it may result in “interesting” handling on the road, although it should perform better despite this.

Little Black Coupe Turned Silver > zeontestpilot 05/25/2016 at 13:21

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LSD is fantastic in a performance-orientated FWD car! For your average daily driver, it probably isn’t needed...

My Cobalt SS has it, it was part of an optional package that included Recaro seats. It’s needed, because it does exactly the same thing you said. When you’re getting on it on a road course, it kicks in to help, especially on corner exit. FWD needs all the help it can get to put the power down, and a LSD is great for that job.

Klaus Schmoll > zeontestpilot 05/25/2016 at 13:23

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You’d probably get a lot of torque steer. I remember Clarkson joking about the MK2 ST:

Q: Where do you work?

ST owner: Wherever the car takes me in the morning.

zeontestpilot > RallyWrench 05/25/2016 at 13:23

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Curious...can you further explain what you mean by ‘pull wide’ though? Would the rear swing out or something?

zeontestpilot > themanwithsauce - has as many vehicles as job titles 05/25/2016 at 13:24

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Ha, no more wheel peels would be nice!

zeontestpilot > RamblinRover Luxury-Yacht 05/25/2016 at 13:26

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What's lift-off oversteer?

zeontestpilot > itschrome 05/25/2016 at 13:27

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How does it destroy the handling?

zeontestpilot > Supreme Chancellor and Glorious Leader SaveTheIntegras 05/25/2016 at 13:28

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Is that only for the civic si though?

ESSSIX GmbH - Accountant/Wagon Thumper > zeontestpilot 05/25/2016 at 13:28

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It over steers when you lift off.

zeontestpilot > Berang 05/25/2016 at 13:31

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How would it be interesting? :)

Little Black Coupe Turned Silver > zeontestpilot 05/25/2016 at 13:31

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It doesn't, people in here don't understand what they are talking about...

MultiplaOrgasms > zeontestpilot 05/25/2016 at 13:31

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For realz? FWD cars usually have ~65% of their weight on the front axle. If one lifts off the throttle weight shifting science happens and the rear tires get unloaded and lose traction.

zeontestpilot > Little Black Coupe Turned Silver 05/25/2016 at 13:32

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That’s what I figured. Especially in the corners, since I love them so much...

ADabOfOppo; Gone Plaid (Instructables Can Be Confusable) > zeontestpilot 05/25/2016 at 13:33

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My GTI has one. I like it. Handles just fine.

Little Black Coupe Turned Silver > MultiplaOrgasms 05/25/2016 at 13:33

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For realz? Not everyone knows terms like that, especially when starting out.

Supreme Chancellor and Glorious Leader SaveTheIntegras > zeontestpilot 05/25/2016 at 13:34

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Nope.

MultiplaOrgasms > Little Black Coupe Turned Silver 05/25/2016 at 13:35

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For dealz

interstate366, now In The Industry > zeontestpilot 05/25/2016 at 13:36

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In Japan, the 4th and 5th generation Prelude had available LSDs, as did performance-oriented versions of their 6th and 7th generation Accord.

RallyWrench > zeontestpilot 05/25/2016 at 13:37

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No, the rear would stay put. Theoretically, if you’re on the right line you’re on the power at or before the apex of a corner. With an LSD up front, the car will try to pull to the outside of the corner on the power, basically trying to straighten the wheels. Power understeer. Every FWD and most AWD cars do this naturally anyway to a certain degree, but it can be exacerbated by a diff and the increased grip it provides, instead of just lighting the inside tire on fire and carrying on as it would stock. It’s a “problem” you can use to your advantage though, since with most FWD cars you late apex anyway. Some diffs behave differently, too. Quaifes and Peloquins can both still spin up the inside tire if there’s very low or no grip, whereas Wavetracs don’t. The Peloquin and Quaife can be more aggressive assuming equal traction though. If the diff is a 1.5 or “two way”, it can create slightly harder turn-in as well, but this can also be compensated for with deeper trail braking, rotating the rear.

itschrome > LongbowMkII 05/25/2016 at 13:37

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yes, this. remember this is an aftermarket add-on. it’s not exactly tuned for daily use.

RamblinRover Luxury-Yacht > zeontestpilot 05/25/2016 at 13:40

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You lift off the gas - engine braking (and only engine braking) sets in, which on FWD means front wheels only. 60%+ of weight plus a dynamic shift of maybe another 20-30%, then add in that the engine/driveline braking will not be symmetrical. Like torque steer in reverse, only worse. Lift off the gas sharply, and you turn the car into a Segway with a tendency to pull to one side. An LSD makes driveline braking more symmetrical left to right - so, you’re just dealing with a normal, un-broken Segway.

zeontestpilot > MultiplaOrgasms 05/25/2016 at 13:41

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It’s better to ask and look like an idiot, then to pretend to know when you really don’t, :).

Berang > zeontestpilot 05/25/2016 at 13:44

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Two things: Because the steering wheels are also the driving wheels, the LSD will be trying to power both wheels when going around corners. The first thing that happens is the steering would tighten up because all of the CV joints will be under power. With modern power steering this may not be too noticeable though. The second is that cornering may just feel “weird” or the steering less responsive under power.

MultiplaOrgasms > zeontestpilot 05/25/2016 at 13:45

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Good thing I am not one of those people.

zeontestpilot > interstate366, now In The Industry 05/25/2016 at 13:47

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It would be interesting to drive both a lsd and a non-lsd version to feel the difference.

zeontestpilot > RallyWrench 05/25/2016 at 13:48

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Awesome explanation, thank you!

Probenja > zeontestpilot 05/25/2016 at 13:50

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Off topic but this one even has a lockable front differential.

Party-vi > zeontestpilot 05/25/2016 at 13:52

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Can someone confirm that an LSD in a FWD would tend to have the front understeer more?

nafsucof > zeontestpilot 05/25/2016 at 13:57

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II installed an LSD my focus ST it helps dramatically. Acceleration it keeps power transmitted through both wheels evenly. Around corners it powers the outside wheel and pulls the nose under helping cars that have understeer. Coming out of corners and set of the inside will spend equal power sent to both wheels. My differential is no more than 60% of power to either side unless one wheel is off the ground, it acts like it’s an open differtial. Under breaking it helps prevent one wheel from locking up so the ABS doesn’t need to work as hard. I was able to make my car feel very neutral with the LSd installed

zeontestpilot > RamblinRover Luxury-Yacht 05/25/2016 at 13:58

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Thanks for the explanation!

nafsucof > zeontestpilot 05/25/2016 at 14:04

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A non torque biasing diff like a viscous fluid diff, one that tries to stay 50:50 will send the power to both front wheels and since they are spinning at the same rate you go wider than the wheel is pointed. With Torsen it is like 60:40-40:60 so depending on which what your wheel is pointed it changes mechanically overpowering the outside wheel speeding up that side pulling you in vs out. Open diff would be 0:100-100:0 so coming out of turn the inside wheel goes to 100% power and spins/smokes!

zeontestpilot > Probenja 05/25/2016 at 14:07

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It's on topic for me. Is that a fiat?

zeontestpilot > Berang 05/25/2016 at 14:09

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You're right, that is interesting, :).

RamblinRover Luxury-Yacht > zeontestpilot 05/25/2016 at 14:16

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This would be why FWD aggressive driving is often best with a straight switch from gas to braking. You can get away with a little liftoff in RWD, because then you’re just deploying the anchor (pulling with the rear wheels), and until you brake, you’re just risking understeer or some rear wheel slide - not your steering wheels - and this is where “throttle steering” comes in. Off the gas for more understeer, push on the gas for more oversteer, find a happy medium between the steering of your front wheels and the push/pull from the rear.

If you’re in a FWD and lifting off, however, your rear wheels will be totally fine with a high slip angle as they continue to roll, and they’re not going to resist coming around much at all - they’re not braking, after all.

Before you know it, that relatively easy oversteer has snowballed, because the rear wheels weren’t allowed to do their job. If you get on the brakes, the rear wheels *are* helping to slow the car.

Tatanko > interstate366, now In The Industry 05/25/2016 at 14:18

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My ‘03 Maxima had a fairly rare helical LSD in its 6-speed manual too, and I’m positive that it was an option on the Maxima for several years leading up to ‘03 (though it was a viscous LSD on the previous 5-speed transmission).

DrJohannVegas > Berang 05/25/2016 at 14:20

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First, your two things, as described, are essentially the same thing. Second, the “tightening up” you may feel when under power has nothing to do with the CV joints. It has to do with the scrub radius, and thus the effective moment of the force around the steering axis. Since the centerline of the tire (and thus the effective vector of the force) does not intersect the steering axis, there is a rotational force on the steering. The “tightening up” comes from geometry, not joints.

Also, “open” differentials transfer equal torque/force to both wheels, and “differentiate” on speed. Limited slip diffs bias torque to equalize speed differences. So, both wheels are powered in both cases. The “weirdness” which some folks describe is actually the change in the force acting on the steering axis as the differential biases torque to equalize speeds.

Berang > DrJohannVegas 05/25/2016 at 14:21

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Well I didn’t want to look like a huge dork explaining that open diff powers both wheels anyway, but whatevs.

CB > Berang 05/25/2016 at 14:24

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Wait, an explanation was asked for and you didn’t want to sound like a dork by explaining? What?

Berang > CB 05/25/2016 at 14:25

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They wanted to know about handling, not how differentials work. I’ll leave that convo to whoever feels like having it.

mattc993 > Berang 05/25/2016 at 14:25

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DrJohannVegas > Berang 05/25/2016 at 14:29

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Aight. I mostly get worked up about scrub radius because part of the reason so many HELLAFLUSH cars drive like absolute dogshit is because wide rims that poke to look super cool also tend to move the centerline of the tire outward from the car’s centerline.

This has the unfortunate consequence of changing the (usually) small negative scrub radius on most FWD cars into a moderately large positive scrub radius. If you do that, all of the stability designed into the steering and suspension geometry is tossed out the window and things start to get...twitchy.

Edit: I should note that my obsession with this particular aspect of steering geometry comes from the inimitable Dave Coleman (of SCC). http://www.superstreetonline.com/features/news/…

bob and john > DrJohannVegas 05/25/2016 at 14:30

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rrrriiiiiiiggghhtttt up until the point where one wheel comes off the ground, then SPIN BABY SPIN

Berang > DrJohannVegas 05/25/2016 at 14:33

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You will, BTW, feel a tightening effect on cars with 0 scrub radius, which old car mags always (perhaps incorrectly) attributed to the CV joints. That may be a different effect though, but is what I was thinking of. Putting wheels with the wrong offset and changing the scrub radius kind of results in shit steering feel at any speed.

DrJohannVegas > bob and john 05/25/2016 at 14:35

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In an open diff, both wheels are getting equal torque: zero.

With a clutch type diff, the speed equalization shuffles forces around.

With a Torsen-type, because you only get torque bias, not speed equalization, things get funny. If you have a T1 diff with a 4:1 bias ratio, for instance, and one wheel is in the air (thus making max transferrable torque zero), your other wheel gets 4 * 0 = 0. WOMP WOMP.

Little Black Coupe Turned Silver > Party-vi 05/25/2016 at 14:37

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Nope. Because it doesn’t.

DrJohannVegas > Berang 05/25/2016 at 14:41

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I don’t have the data at hand, but I’d conjecture that few, if any, production vehicles (especially FWD ones) are designed with 0 scrub. It’s what gives steering a self-centering feel, and it’s part of the geometry which makes a street car “streetable”. It also does a lot of other fun things with weight jacking under steering, depending on other geometry. But, I digress...

I’d bet that, whatever force is claimed to come from the CVs is acting on the steering because the CV joint itself (where the shaft bends) is not in the same plane as the steering axis. So, that may be part of the game, but it’s not the main cause.

interstate366, now In The Industry > zeontestpilot 05/25/2016 at 14:52

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A pair of JDM 4th gen Preludes would be ideal for that. The presence of the LSD was the only difference. The LSD 5th gen had a hotter engine, and to my knowledge the LSD was standard on the Accord trims that had it.

Berang > DrJohannVegas 05/25/2016 at 14:53

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A few early FF cars did, Citroen, SAAB, etc.

This was the only way to get “light” steering before power steering.

RallyWrench > DrJohannVegas 05/25/2016 at 14:54

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I miss Dave Coleman’s writing, SCC used to be a bible to me.

DrJohannVegas > Berang 05/25/2016 at 14:56

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Is that from the Zapletal articles in RCE? I haven’t seen those in years!

Berang > DrJohannVegas 05/25/2016 at 14:58

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No idea. Just googled citroen scrub radius to find a pic.

nafsucof > Party-vi 05/25/2016 at 15:03

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Depends on the type and the action it's designed for some increase and some decrease but the ones that increase understeer, are better for straight lines as they try to be 50:50 power bias.

Probenja > zeontestpilot 05/25/2016 at 15:34

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Yes, Fiat do Brasil made a “Locker” version of most of it’s “Adventure” lineup. Here is a Strada doing a test of the system:

Rusty Vandura - www.tinyurl.com/keepoppo > DrJohannVegas 05/25/2016 at 15:44

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So for us old guys with dried-out brains, are you saying that putting big, stupid rims on a car makes the car drive poorly?

DrJohannVegas > Rusty Vandura - www.tinyurl.com/keepoppo 05/25/2016 at 15:57

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Pretty much.

Edit: You can do it “right” and it may not have such deleterious effects.

Wrong Wheel Drive (41%) > Little Black Coupe Turned Silver 05/25/2016 at 16:13

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Well for daily driving, FWD or RWD, a limited slip is not going to be necessary. And really, the LSD actually makes driving more difficult with RWD and limited skills lol. It just makes the car more likely to throw the rear end out if traction is lost. But it is incredibly helpful in the winter time and can be useful for racing once you know what you are doing.

Xyl0c41n3 > Wrong Wheel Drive (41%) 05/25/2016 at 16:21

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“...can be useful for racing once you know what you are doing.”

You DO know that LBC has raced for years, right? I think she just MIGHT know wtf she's talking about.

Little Black Coupe Turned Silver > Wrong Wheel Drive (41%) 05/25/2016 at 16:25

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...I said pretty much exactly the same thing, so, ok...

Diesel Panda > zeontestpilot 05/25/2016 at 16:43

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http://www.vw.com/models/golf-gt…

go drive the new GTI with and without the performance package, report back with results :)

interstate366, now In The Industry > Tatanko 05/25/2016 at 18:08

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The LSD on the JDM 4th gen Prelude was viscous. The 5th gen Prelude SiR S-Spec and 6th gen Accord Euro-R both had Torsens. I’m not sure what type of LSD the Accord SiR-T had.

Rusty Vandura - www.tinyurl.com/keepoppo > DrJohannVegas 05/25/2016 at 18:56

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+1 if you buy the tires and rims on credit and +2 if they wear out before they’re paid for.

Danger > DrJohannVegas 05/25/2016 at 20:20

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That is a great article.

DrJohannVegas > Danger 05/25/2016 at 20:23

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At the Jalopnik karting event this year, Patrick George joked about Jalopnik trying to get a Kickstarter going to buy the back archives for Sport Compact Car. The very thought made me giggle with glee.

zeontestpilot > Diesel Panda 05/25/2016 at 20:31

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Ha. Apparently the closest be dealership is an hour away.

Wrong Wheel Drive (41%) > Little Black Coupe Turned Silver 05/25/2016 at 22:31

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Reading comprehension is not my strong suit lol

Wrong Wheel Drive (41%) > Xyl0c41n3 05/25/2016 at 22:31

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Oh yeah I know that, I was generalizing. Sorry, I was basically agreeing with the comment but me and words don't get along!