Are there any disadvantages to installing a LSD to a Micra~?

[men-at-arm]

Hi All,

A friend and I were debating about the advantages of limited slip differentials. Since I live in a canyon and must drive in and out daily to get anywhere, I clearly saw the advantage of having LSD installed for spirited driving since my 5 door K11 is already fully modified suspension-wise with BC adjustable height coils with lowering springs and Nismo 24mm front sway bar, SB (Taiwanese brand) 20mm rear sway bar, OMP strut brace. My friend, playing the devil's advocate I assume, said I ought to reconsider .. because .. there are certain disadvantages of FWD with LSD. I asked such as what ? The reply was basically that the front end may push (understeer) under power.

After some quick searching, I could not surface any article myself on the internet which could tell me definitively whether there are any disadvantages. Moreover, there was at least one article which said it would definitely help having a LSD with a FWD car, particularly if it has plenty of power.

My K11 is not a monster car (as yet), but it is running a IHI #3 turbo pulling about 140ps at the wheel with a Sentra 331 5 speed, 750kg metallic hydraulic clutch. Wheels are 15 inch BBS clone alloys with Taiwanese 15/45/195 VR tires.

Your thoughts and opinions would be greatly appreciated~!

Cheers, Steve Lin in Taipei

An example of a JDM LSD available locally ..
http://goods.ruten.com.tw/item/show?21201186818637

 

[pollyp]

hi
i'm using a Gripper 1.5way clutch LSD on my turbo 1.3 SLX with 160bhp 160ftlb used daily and occasional trackday.
its made in coventry and i brought it from matt humphris in oxford who sells it.

check my blog for details
-page 18 post 856 i received the non-speedo version of the 2-way lsd
-page 19 post 943 i received the speedo version of the 2-way lsd
-page 50 post 2453 the preload ring had shattered for awhile (was an old design) giving no preload
-page 51 post 2502 recently replaced preload with an updated tougher design and less preload for daily use, changed to 1.5-way ramps

http://micra.org.uk/threads/pollymobiles-rebuild.35251/page-51

the lsd is a traction aid, such as during straight launches and exiting track corners, by sharing torque between the two wheels at all times.
its especially beneficial for high torque fwd setups where its more likely for one wheel to spin in an open-diff and lose half the traction & front grip.

all fwd will power understeer by design at a point where the excessive torque overcomes the available traction & grip of the front wheels causing understeer.

during cornering in an open diff, when the driver requests more torque than the available traction that any one driven wheel has, it will spin with most of the torque, loseing all its traction and grip, but the other front wheel would retain most of its traction & grip cos it'd receive minimal torque, although at this point the grip of the 2 undriven rear wheels would be higher than the 1 front wheel that hasn't spun, therefore it power understeers.

an lsd on the other hand would raise the amount of torque required before overcoming the traction of one or both the driven wheels, essentially moving the point of power understeering to a higher torque amount so more of it can be used to drive the car forward to where the wheels are pointing through the available traction between both tyres.
if the driver requests even more torque through the limited available traction of both wheels (simply flooring an overpowered engine mid corner), it will of course power understeer.

there's many setting parameters of a clutch lsd such as
ramp angles - ratio of how much pressure on the lsd clutch for a given torque input
preload - how much diff lock to start with from zero torque input
lsd force - how much locking force from a given pressure on the plates

too much locking force and/or preload could cause understeer on or off power

when using the clutch lsd on a daily car, three things to notice:
- the steering will be heavier especially during low speed turning. the higher the preload and/or more aggressive the ramp angles, the harder it will wanna straighten up. i have PAS which really helps.
- the more torque you apply when launching and turning from a t-junction, the stronger it will wanna turn in towards the apex
- if u slowly ease off the power mid-corner, the behavior of the lsd ramps & plates have a tendency to suddenly unlock when going between accelerate/coast/decelerate modes, changing the balance of the car.

so ur entering the corner, turn the wheel certain angle, with certain amount of throttle load which loads up the ramp & lsd plates and applies a level of diff lock.
when u back off the throttle slowly till the torque input is almost zero, it reaches a threshold where there's not enough ramp load to lock the diff.
the lsd ramp retains abit of pressure on the plates briefly cos the sliding splines tends to jam but then the sliding ramp un-jams loose and suddenly becomes open-diff and the car will surprisingly want to turn-in more with the same steering angle.

so the trick in cornering on normal roads with a clutch lsd is to either maintain a steady throttle throughout the turn or back off the power while applying less steering angle quickly as the diff unlocks

 

[men-at-arm]

Thanks for your reply.

Not an expert on this .. so question: is the Nismo LSD in the Taiwanese auction I provided in the link -- a Torsen type~? Does it differ from your clutch type LSD~?

Thanks in advance~!

 

[men-at-arm]

May have found evidence that Nismo LSD is the same as your 1.5.

 

[men-at-arm]

http://www.nengun.com/nismo/gt-lsd-pro

 

[pollyp]

yeah its the same clutch lsd type.
note if u wanna use the stock speedo pinion, it'd prob need to be a one-sided clutch-pack type like mine to allow room to fit the speedo ring gear, so check they can do such versions.
if you have other means to measure road speed, the normal full 2-sided clutchpack lsd u see in the nismo pic or the first gripper lsd i received, would work better, more balanced lsd effect turning left/right & longer lasting

 

[pollyp]

oh wow just checked bout the nismo gt lsd pro and u can just alter between 3 initial preload settings by simply draining the oil, pop one of the shafts out and turn the pinion gear plate thing with a ratchet. real handy without taking the gearbox out and apart

http://www.nismo.co.jp/en/products/competition/lsd/gt_lsdpro.html