My experience with LSD is mostly limited to older BMW and Mercedes models with clutch-type diffs. I’ve driven examples of the same car with and without LSD. The rear rend definitely moves around more with an LSD, especially in slippery conditions. Not a problem for guys like us GRM’ers who live for this stuff. But I can see it causing trouble for typical, non-enthusiast drivers.
In reply to alfadriver :
Having driven a lot of LSD equipped FWD cars in Canadian winters and autocross, I can tell you that you are wrong in your assumptions. I have driven a viscous LSD in a Maxima, a HLSD in a B15 Sentra Spec-V and a HLSD in a MS3 in winter. I have also driven the comparable models (base manual Maxima, normal B15 Sentra and my Mazda5), and I can tell you that an LSD is a nice addition in all of these models in winter. Even when equipped with winter tires (mandatory here), the LSD helps with traction and does not introduce any understeer. In fact, the viscous type can introduce a little oversteer because it acts in deceleration as well as acceleration.
And in performance driving, like others have said, if the front tires are loaded, the LSD can reduce the understeer at corner exit. The LSD acutally pulls the car out of corners. I loved that about my Spec-V in autocross.
And the E-LSD are in no way comparable because it is impossible to calibrate for all situations. For example, in winter, they tend to react too slowly and then over-react. (As tested in a Focus ST).
I think the absence of LSD in cars has more to do with people being clueless and misinformation.
In reply to fanfoy :
Nice to hear that someone has done the work to set one up. But that does not excuse the basic physics of the point of an LSD. While many here can deal with oversteer on decelerations, most drivers can't, so I would not exactly think that's a feature.
And it's a whole lot cheaper to do a traction control system that deals with the same problem than an LSD. Cars are not designed for autocrosses, track days, and certain snow situations. They are made for nominal drivers in nominal situations and sub 1% of the driving has to deal with the compromise.
Snrub said:I don't get it. People want AWD for traction, but no one will pay for a LSD? Yes traction control has improved, but I still think a LSD is better. I remember about a decade ago it cost ~$150 to option a LSD on a F150. That's a complete no brainer anywhere with snow. FWD cars could really benefit from it.
Limited slip diffs hurt traction in low grip situations. When (not if) one tire loses grip, both tires spin, and you slide off the road.
This is why ABS type traction control (E-diffs) are way better, they brake the wheel that is spinning while still allowing the other wheel to maintain grip. As long as it is done right.
alfadriver said:FWD cars understeer really badly if you have a LSD in it.
So do rear wheel drive cars, and it only gets worse the closer the wheelbase is to the track width.
Sonic said:Adding a helical LSD to our Civic race car made a nice difference, the car is well balanced. If anything, when understeering under throttle and hard cornering, if you go for full throttle the car tends to tighten its line up and understeer less than with part throttle.
Helicals are not LSDs! They are torque biasing differentials. They don't limit slip at all. That is why they drive so nice.
I'm guessing the base-model Camaro gets an LSD because Camaro owners are the type of people who are into doing burnouts and one-wheel peels are lame.
I think the LSDs can help in winter when one tire is on ice and the other isn't. One wheel peel is certainly a thing, and it is happening at such low speeds (usually) that it isn't dangerous.
In all fairness to the "low traction" scenario, I absolutely got the back end a bit loose in my RX-7 a few times on wet pavement by getting too happy on the go pedal too soon when I first got it.. It was never out of hand, but it does get your attention when you're not meaning for it to happen. It never happened in my E30, but the LSD on that seems to be much more gentle with the lock up. The E30 also didn't have a turbo spooling up to dump some extra power into the equation mid corner.
Thanks for the great discussion so far. It seems the answer is (currently) Modern traction systems (where they exist) are more cost efficient and possibly safer.
I still prefer mechanical aids. I'm debating refreshing/replacing the rear LSD in my Subaru.
In reply to Brett_Murphy :
I drove my first RX-7, an '80, through three winters no problem.
My second RX-7 had a limited slip. It was undrivable in the winter. You could not turn around in a parking lot because the car would just crab in the direction you had the steering turned, instead of turning around. Gas stations were especially a treat. And WHEN the car lost traction on the road, it would go sideways because when one tire lost traction, both did, so no more directional stability.
The only time I had my third RX-7 on snowy roads, I called a tow truck because it was actually dangerous. Driving on city streets, I hit the curb with the rear wheels multiple times. Not enough grip to put down enough thrust to push the front tires over the snow, so when the tires spun, sideways and bang into the curb. If I had an open diff, it would not have been nearly so bad. I figured it was cheaper to spend the $65 to have the car towed to where my other car was than the extreme risk of wrecking.
In reply to Knurled. :
I've never had that experience with LSDs in snow. In the Jeep, you'll slide the rear end around more with an LSD than without, but you have to put down more power before any wheelspin / sliding starts to happen. And the rear end behaves much more predictably when you do get it loose (and doesn't snap back in as violently if you let off the throttle).
Brett_Murphy said:
I still prefer mechanical aids. I'm debating refreshing/replacing the rear LSD in my Subaru.
So here's a good opportunity to point out some odd thinking when it comes to using an LSD over a braking TC system- how much is it going to cost you to refresh the diff in your Subaru?
For my Alfa- a new set of clutches is $65, and I have to add in the time that it takes to remove the axle, take it apart, do the refresh, and then repeat in reverse. Vs. just changing the pads plus the rotors on the axle. I know my Alfa is cheaper and easier to work on than most modern stuff (and I don't have the option of a TC system- so it's more a cost & time reference).
I'm not sure why people obsess over the work on the braking system and prefer to work on the diff.
Back in HS, a friend of mine told me that he would rather downshift and use more clutch to slow down vs. the brakes. Ignoring the issue that BOTH systems wear out, and that one is massively easier to maintain.
rslifkin said:In reply to Knurled. :
I've never had that experience with LSDs in snow. In the Jeep, you'll slide the rear end around more with an LSD than without, but you have to put down more power before any wheelspin / sliding starts to happen. And the rear end behaves much more predictably when you do get it loose (and doesn't snap back in as violently if you let off the throttle).
I kind of have. After 14 winters in my Miata, I really questioned the need for the LSD. Nice to have, sometimes, and the Miata is at least set up to gently oversteer in a fun way. But I don't think it was required like conventional thinking wants us to believe.
rslifkin said:In reply to Knurled. :
I've never had that experience with LSDs in snow. In the Jeep, you'll slide the rear end around more with an LSD than without, but you have to put down more power before any wheelspin / sliding starts to happen. And the rear end behaves much more predictably when you do get it loose (and doesn't snap back in as violently if you let off the throttle).
Jeeps are also pig-heavy enough that they crush the snow instead of floating on top. This weight helps you get moving but it means that the thing is unwieldy when you're trying to drive at 75-80 on hardpack.
Best winter car I ever had was a 2200lb Golf. With an open diff. I want to get to where I am going, not putz around driving at 50mph scared of the white stuff all over the place. The only reason I cruised at 75-80 on hardpack was because it did not have enough power to go faster than that. Needed WOT in 3rd gear.
alfadriver said:ack in HS, a friend of mine told me that he would rather downshift and use more clutch to slow down vs. the brakes. Ignoring the issue that BOTH systems wear out, and that one is massively easier to maintain.
If you use the CLUTCH to slow down and not the engine, you deserve everything bad that happens to you, just like the people with DCT transmissions who stop a car length early and creep forward every five seconds at traffic lights.
IMO, Ford should not have issued a reflash on the dual clutch transmissions in the Focus and Fiesta. They should have just issued a letter that said if they had shudder and shifting problems, it was because they were horrible drivers and the car was simply punishing them for how much they failed at life. Of course, this is "bad optics" or whatever.
In reply to alfadriver :
The car I was discussing above doesn't have a breaking TC system. I have a viscous LSD in the rear, and it's old and barely there anymore. If it was a Torsen, I wouldn't be worrying about it at all.
I get what you're saying, though. I'll also admit the only real braking TC system I had experience with was in an early 2000s BMW 325ix and it just felt weird, like it was doing something different every time- probably because it was doing what the engineers programed as "best" for those given circumstances. The inconsistency kind of threw me off a bit, but I probably could've gotten used to it, especially for something that would be street driven. So, to be fair, I've not given brake based TC systems much of a chance, and they've probably gotten a ton better than that E46 I drove. I'd love to put a new system to the test, but they're not something you can test safely on the street or during a test drive, so unless somebody hands me their keys at a rallycross, it's unlikely I'll get a chance anytime soon.
In reply to Knurled. :
It's heavy, but if you start comparing to a lot of modern cars, it stops sounding nearly as heavy. It weighs about the same as a modern Challenger / Charger as a comparison point. It'll do 55 - 60 comfortably on hardpack (on 235 width Hakka R2s), but generally somewhere around that speed, most hardpack is rough enough that going faster starts to get kinda sketchy (in terms of fighting to keep it going where you want more than actually sliding around or anything).
I've driven plenty of lighter, FWD cars in snow and hated every single one. Open diff FWD in snow is miserable to me. Heck, a friend recently bought a new Civic and commented on how he missed his (open diff RWD) E46 in the snow on one particular hill on his commute. Both had snow tires. The Civic would get up the hill, but it was a fight to not break traction (it's a long, steep, curvy hill). The E46 would break traction and kick the tail out in the worst spots on the hill, but it would just keep going even if you had the tail out a good bit. Then again, that E46 was one of the most impressive things I've seen in the snow. I watched it go through snow deep enough to be plowing a lot with the front bumper and it still moved along more easily and with less wheelspin than the Jeep in 2wd in the same snow.
A bit of a practical digression:
I drove a GTI with the performance package. It uses a Haldex type system to act as an LSD for the front wheels. I really liked the way it drove compared to one without the performance package. The difference was subtle, but I think it wasn't just my imagination. Granted, this was on roads, during a test drive, but there was a traffic circle involved on the route.
Finding a base 2016 or a 2017 Sport model, which has the performance package and no sunroof, is a bit of a chore. I've seen a few, but they are still sparse on the ground. The later ones all have a sunroof if they have the performance package, and I don't want a sunroof.
Buying a base model and putting an LSD in it with a tune would give me the setup I want, but I'd be voiding any kind of warranty on it at that point.
However, when it comes down to reality, I'm probably not a good enough driver on an autocross course to have the LSD make that much of a difference. Learning to drive a car without it through the warranty period then swapping in an LSD later on might be the path to developing the the skillset in the car where it wouldn't cover for mistakes at the start.
Or, I could just pick up a Mazda3 with the trick new traction thing they're using, save some money, have better reliability and enjoy that.
Seems I have another test drive to do.
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