Limited Slip Diffs?

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jcochrane
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Limited Slip Diffs?

Postby jcochrane » Fri Nov 17, 2017 11:29 am

More cars these days come with LSD either standard or as an option. I have driven a few cars with one but I am not entirely convinced that they are of great value for many cars for "Road Driving". On track is another matter, though. What do others think of their use specifically for road driving?

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akirk
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Re: Limited Slip Diffs?

Postby akirk » Fri Nov 17, 2017 1:20 pm

I think that some of the comments we are seeing on places like Pistonheads suggest that drivers are so comfortable in their modern cars that they are taking them closer and closer to limits as the cars disguise the move away from safety - this then brings on an arms race - the more you do that, the more tech you need to protect the driver...

so, are they needed - probably not, on a track you are aiming to keep beating the time, so you should be on the edge, on a road, you should not! Having said that my z3 has one - and apparently without they are more twitchy (I haven't driven another to know) - the M5 has one, no idea without - and the RR no doubt has several diffs :) I have to look back probably to my MG to find a car without - but there is a much greater purity of driving with a car like that which possibly means that actually you would be missing the point in adding one - so perhaps modern cars need them, older don't?

Alasdair

devonutopia
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Re: Limited Slip Diffs?

Postby devonutopia » Fri Nov 17, 2017 1:49 pm

I have a limited slip diff (Peloquin) in my road car - Fabia diesel.... :D

Whilst I appreciate I did it for trackdays there's definitely a benefit on the road, primarily the pull out of corners. However, under most advanced driving situations I can't see it being hugely useful. Perhaps it aids traction for an overtake in that both wheels grip on acceleration, rather than an open diff, where one wheel might spin - affecting the manouvere.

I wouldn't say it was good value for money, but my car is highly tuned, so to me it was worth doing. Probably cost me £750 for the diff and fittings, then the labour and time to build the gearbox (spare one I got) and then swap over which was probably 4 hours or so of garage rates.

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jcochrane
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Re: Limited Slip Diffs?

Postby jcochrane » Fri Nov 17, 2017 1:59 pm

Thanks for the answers so far. Interesting. My question was prompted by having recently driven a front wheel car that could be purchased with or without a LSD. The model I drove was without. On a 30mph left hand bend which part way through flowed into a long 10pc uphill I tried to provoke a negative reaction by dropping to 2nd gear and useing maximum throttle on turn in. As expected with the weight of the car well over the back axle, just after exiting torque steer moved the car slightly left then traction control pulled it back on line without any drama. It was all so quick, undramatic and I doubt I lost much acceleration. So would a LSD have made a significant difference?

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GTR1400MAN
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Re: Limited Slip Diffs?

Postby GTR1400MAN » Fri Nov 17, 2017 2:07 pm

My Renaultsport Clio has an electronic LSD (so software vs mechanical). It applies braking to the inside spinning wheel (a bit like ESC - Electronic Stability Control). Can't say I've noticed any problems exiting side roads in the wet, so I assume it is doing its job well. The Honda Civic used scrabble at the slightest provocation. Having said all that the Clio also has traction control, so which bit of software is doing the work, or if they are really one and the same function, I don't know.
Mike Roberts

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exportmanuk
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Re: Limited Slip Diffs?

Postby exportmanuk » Fri Nov 17, 2017 2:40 pm

Someone pulled out in front of me in a big Hyundai this morning. Spinning up the inner front wheel which then resulted in the TRC cutting the power dramatically and leaving himt stranded in the middle of the road. No drama for me, I had anticipated his emergence and was slowing anyway but the look of horror on his face was quite amusing. I guess he could have used a LSD.
Andrew Melton
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sussex2
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Re: Limited Slip Diffs?

Postby sussex2 » Fri Nov 17, 2017 5:33 pm

Memories of a Saab 99 turbo, one of the first, and massive amounts of wheel spin; even the later Saab's had the same problem (I had a disastrous 9-3).
I've an MX5 (1.6 110bhp) with no LSD and I recently drove another with LSD. I think my, less powerful but unadulterated car, is much sharper and more pure.
The lack of such things as ABS/ESC etc keep you a bit more sharp as well, because you feel more vulnerable.

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jont-
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Re: Limited Slip Diffs?

Postby jont- » Fri Nov 17, 2017 6:40 pm

sussex2 wrote:I've an MX5 (1.6 110bhp) with no LSD and I recently drove another with LSD. I think my, less powerful but unadulterated car, is much sharper and more pure.
The lack of such things as ABS/ESC etc keep you a bit more sharp as well, because you feel more vulnerable.

I'm not sure that's got much to do with the LSD though.

I have two front engine, rear-drive cars. Neither is particularly powerful, one is open diff and the other has a torque biasing LSD. My observation is that pulling out of tight junctions in low grip conditions, the open diff car will tend to spin a wheel up. The LSD equipped car will grip better initially, but then try and go sideways (until the electronics restricts it).

When I had an MR2 turbo, forum thought was that giving these cars an LSD contributed to more car/scenery interface problems than would have happened with an open diff.

My understanding is that in power-on limit conditions, cars equipped with LSDs tend to be more willing to continue going sideways (or spin), while open diff cars send the power to one wheel, "spinning" it away, so any sideways momentum is quickly lost. I guess where this may feel like twitchiness is over a short patch of low grip surface when the faster wheel then tries to grip again and send the car the other way.

For rear wheel drive cars, I suspect much of the "need" for the LSD comes from marketing, brought on by pictures of the Stig or Chris Harris going sideways on the lock-stops with smoke pouring off the tyres (which can only be achieved in a car with an LSD). Much like cars are being ruined by chasing nurburgring lap times. For FWD cars, with the quest for ever more power there's arguably more need to cope with sending too much power to the wrong wheels.

As for which on a road car - TBH, if you're driving within the law and to roadcraft, there should be naff all difference.

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jcochrane
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Re: Limited Slip Diffs?

Postby jcochrane » Fri Nov 17, 2017 7:14 pm

Hi Jon, that was very helpful and confirms what I suspected. I am going ahead with purchasing the non LSD version.

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akirk
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Re: Limited Slip Diffs?

Postby akirk » Fri Nov 17, 2017 8:32 pm

jcochrane wrote:Hi Jon, that was very helpful and confirms what I suspected. I am going ahead with purchasing the non LSD version.


check also the resale value - on some cars such as some of the more powerful BMW 1 series cars, I believe they hold a higher resale value with LSD
Alasdair


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