Understanding LSD specs and their impact on handling.

[fuzzy-hair-man]

I've been doing a bit of research into LSDs for my CG13DE mini as I wanted to know a bit more what the specs mean and their impact on handling. I thought I'd share some of the results in the hope others might chime in and let me know where I got it wrong or their experiences.

The main diff for the micra seems to be the gripper (clutch plate), there's also a Cusco (clutch plate) and the Nissan viscous coupling diff that came with the 31V gearbox. I'm not sure the Cusco is available any longer, good luck finding the appropriate 31V gearbox and diff and then I doubt it'd go in the mini, so that leaves the Gripper. I have seen reference to another diff but I can't find the source anymore.

here's a couple of sources of info:
http://www.cuscousainc.com/downloads/dl/file/id/190/cusco_lsd_guide.pdf
https://taylor-race.com/sites/default/files/understanding_differentials.pdf
As a result I'll concentrate on the clutch plate design:

There seems to be three specs:

• ramp angles
• preload
• number of clutch plates

Preload
Preload expresses how much force is pushing the clutch plates together before any difference in wheel torque is detected, it's the base or minimum locking action the diff has. A diff with low preload should feel similar to an open diff to drive until a difference in torque / slip is detected, then how the diff reacts comes down to the ramp angles (below). A high preload would be tighter, it's locking early and more so the effect will be more immediate and initially stronger, MAY? cause initial understeer on corner entry as it has to overcome preload?

Ramp angles
These are the ramps that the diff cross pin climbs to add additional (above preload) locking to the diff there are 2 numbers, the first specifies the ramp on acceleration the second ramp for deceleration.
The ramp angle sets two things;

1. how effective the ramp is a steeper ramp will be harder for the cross pin to climb and so it won't lock as hard as a shallower ramp if both diffs have the same number of clutch plates.
2. How quickly the diff reacts to slip or torque differences, a steeper angle will get to 100% lock earlier especially if the number of plates is increased to allow it.

Typical might look like 35/60 which would be a 1.5 way diff offering locking on acceleration (35) and less effective locking on deceleration (60) keep in mind the steeper ramp will need more clutch packs to be as effective as a shallow ramp, these will use the same amount of packs (same diff).
A 45/45 is a 2 way diff this might be paired with a greater number of clutch packs to make the 45 ramp effective.
A 35/90, 35/0 or 35/80 might??? be classed as a 1 way diff a 90 degree ramp offers nothing for the pin to climb (the 0 is expressing an ineffective ramp... I think confusing).

Clutch packs
The more clutch packs the more friction is available to lock the diff, you don't need more than 100% locked so more clutch packs might be used with steeper ramps or could limit the overall locking available to say 60% or 80%.

 

[fuzzy-hair-man]

Whew!

So now to how that effects handling, this is where my research helps me less... Please let me know if I got it wrong.

If I were after a road car I might typically look at:

• a low initial preload to reduce chattering and wear for urban driving and allowing a predictable 'no slip' behaviour.
• shallow ramp angles so the diff acts progressively and locking is slower so I don't get unpredictable behaviour.
• A 1 way diff, with less locking under deceleration to limit lift off oversteer.

A fast road / track might look at:

• Higher initial preload so the diff is loaded up and active but not so much intersections and parking are excessively painful.
• more aggressive / higher ramp angles so full locking comes in earlier with more clutch packs to help make these effective.
• A 1.5 way diff some action under deceleration.

A race or rally:

• high initial preload, as they want the diff active, expect less sharp turns or if rallying have gravel and can slip?
• Same higher ramp angles up to about 45 - 55 for aggressive more immediate locking.
• 2 way diff, although this seems to depend on the car and the driver's preference etc

Particularly ramp angles seems to variable with driver's preference, so it seems important to understand the implications.

To my application; mine is in a mini with a CG13DE, the car is on 10" wheels, and will have 165/70/10 A008 yokohama tyres (currently old hard 145s which is probably why I'm struggling for traction!).
Weighs about 630kg
About 90hp dyno tuned (59.1kW @ wheels) new engine hoping to raise that to 100 - 110hp @ fw.
Going to lighten that flywheel as much as possible.
Will be a fast road car, it might see a track but nothing certain.
I'd prioritise nice, predictable handling and good manners over all out speed.

I was on a wet slipperly road the other day and still spinning wheels as I changed into 4th! so even with better tyres the diff should still be useful!
On the same drive (wet / slippery) as I lifted off I could just start to feel the back wanting to step out (I think) so I don't want that to be any more pronounced if possible, the back of a mini is pretty light.
The only other K11 gripper LSD in a mini I know of is Matt's lightweight race mini aiming at 150hp it's specs are 40/60, 80nm preload, and 8 plates (not sure how many the k11 gripper normally has).

 

[pollyp]

Hi fuzzy, here's what I experienced with my LSD.

Firstly application: I run a turbocharged CG13 K11, 162hp 150ftlb.
Driven as both a daily commute & abused on long high speed trackday circuits.

https://www.micra.org.uk/threads/pollymobile-ii-specification.65262/

 

[pollyp]

LSD Clutch pack configuration

2-sided LSD:
This is usually how the Gripper mechanical LSD arrives, configured with clutch packs on each side of the spider pinion gear.
Gives equal left/right behaviour, reliable & stronger.

1-sided LSD:
For people who need to retain the speedometer gear, Gripper makes a special configuration that sacrifices one side of the clutch pack to fit the speedo gear.
This layout tends to stutter only during RH turns and less reliable or durable.

 

[pollyp]

LSD Plates

Smooth finish - very loud & aggressive chatter, enough to loosen drive shaft nuts.

Grooved finish - the newer design feature these spiral grooves to retain oil across the surface and provide a very smooth engagement with less chatter.

Configuring more plates to contact each other will increase surface area, which gives a similar result as increasing preload force and/or ramp angles, making the locking action more sensitive to torque input.

Wheel speed difference affects the chatter freqency.
Torque affects chatter intensity.

 

[pollyp]

LSD Preload

Stiff preload - harder steering centering, both wheels coupled stronger, sharing more available traction, reduce wheel spin/locking, more tendency to understeer, LSD ramp engagement more sensitive to torque input.

Loose preload - softer steering centering, less understeer, more wheel spin/lockup under low loads, LSD ramp engages more progressively & over a broader torque range.

Wear rate - A fresh LSD begins at 110/85nm Accelerate/Decelerate preload but soon after bedding-in it stabilises at 80/65nm and wears away as graph shown.

Reliability - Running 150ftlb through a 1-sided LSD with a single preload washer kept overloading & crushing it till it fractures into pieces many times.

Stacking two preload washers would 1/2 the deflection for a given preload force and stopped it cracking again.

 

[pollyp]

LSD Ramp Angle

2 way (45/45deg) -

An aggressive & sensitive on/off engagement.

It will suddenly disengage and re-engage if driver slowly lifts throttle from accelerate > coast > decelerate during mid-corner, which upsets the balance.
LSD tip is to commit to the corner, you're either on power or decelerating, do not hesitate or change mind mid-corner.

Aggressive decel ramp makes it understeer more under braking & turn-in.

1.5 way (80/45deg) -

Very forgiving & progressive engagement.
Less aggressive decel ramp helps reduce wheel locking under braking but still allows the car to change direction, I often trail-brake to help turn-in.

 

[pollyp]

LSD engagement behaviour through corner

Unsufficient throttle - zero torque through LSD, diff is open & slipping, slight understeer.

Balanced light throttle - LSD locks just enough to reduce wheel spin, giving fastest exit and allow both turned wheels to 'pull' the front towards the apex.

Too much throttle - LSD locks 100%, torque exceeds traction of both wheels, power understeer badly.

 

[Low Rider]

Although Gripper have stepped up their game over the years, I'd take other options over buying another.

The AP Suretrac I have in my current CGA3 coilpack gearbox is a much nicer drive and is more than capable of dealing with 238bhp and 230lb/ft of torque.

Thankfully the RS5F70a gearbox, which is what the next engine will use, takes a Quaife ATB.

 

[SuperUno]

I really rate the Suretrac diff we have in the rally car, effective enough to stop wheelspin but not too intrusive. Th Ugh as stated above you need to learn to commit to corners, basically you have to believe the diff will pull you round the corner which it will.

 

[fuzzy-hair-man]

Thanks Paul, Matt and LowRider, Paul you're responses are always well thought out and complete... Thanks Again.

I've slowly been reading through your build thread again Paul and the troubles you've had with the Gripper have had me somewhat worried, I can appreciate that it's the one sided version and that the design will improve over time but shattering preload springs and wear on plates is more maintenance and stuffing around that I'd hope for...

Because the mini's engine bay is tiny and the design of my subframe (I won't go into details) it's not possible to remove the gearbox without the engine indeed it would be better to remove the entire front suspension to get the engine out. I am also half a world away from the supplier so if it were a set and forget solution or had local support this might be OK this doesn't seem to be the case with the Gripper... or other clutch plate designs such as the Cusco.

That's the first I've heard of the SureTrac, can you provide a link where I can find some more info, closest I could find was this:
http://www.eaton.com/Eaton/ProductsServices/Vehicle/Differentials/Suretrac/index.htm#tabs-4
But the applications listed are all heavy machinery and it's a Suretrac GA.

Something like the Quaife ATB seems preferable for my application as they seem more progressive and consistent with a daily drive, install and forget application.

More looking and I've found these:
http://www.calverst.com/technical-info/gearbox-limited-slip-diffs-what-s-available/

http://www.mycaterham.com/66828/117416.html

Are yours the pawl type as described in the links? Where do you get them? Looking at I think they might be a better option.

I'd looked at Quaife but as you say LowRider they only seem to do the larger gearboxes (presumably Pulsar /Almera).

 

[SuperUno]

I got my Suretrac second hand, and I am not sure they make them anymore.

 

[pollyp]

I believe my 1-sided LSD with 1 preload ring kept breaking due to the 150ftlb along with the shock loading of shifting up quickly during trackdays. when I drove it normal purely on the road, it stayed intact.
so if your's is bout 110hp, it'll handle that ok.

all mechanical LSD will eventually wear out & perform less and they all have their pros cons, depends what ur after and which one best suits ur needs & sacrifices.

hmm random thought of the day, I wonder if anyone's retro-fitted electronic traction control?

 

[fuzzy-hair-man]

Thanks again for the feedback,

Yeah no luck finding suretrac anywhere so far, I'd really rather more of a set and forget and something that is as you say unobtrusive, if it picks up wheelspin a bit later that's ok.
Was AP linked with Lockheed? (as in brakes) I've seen references to AP Lockheed with suretrac and AP Racing but the Aussie supplier says they aren't the same company as has the diff but did use to be Lockheed...
Other references reckon the design was sold to eaton, used in a Subaru and some ATVs and eaton discontinued them but kept the name, which explains why it's a clutch plate design on thier website.

LowRider you don't want to sell yours once you get your quaife do you?

 

[Low Rider]

Thanks again for the feedback,

Yeah no luck finding suretrac anywhere so far, I'd really rather more of a set and forget and something that is as you say unobtrusive, if it picks up wheelspin a bit later that's ok.
Was AP linked with Lockheed? (as in brakes) I've seen references to AP Lockheed with suretrac and AP Racing but the Aussie supplier says they aren't the same company as has the diff but did use to be Lockheed...
Other references reckon the design was sold to eaton, used in a Subaru and some ATVs and eaton discontinued them but kept the name, which explains why it's a clutch plate design on thier website.

LowRider you don't want to sell yours once you get your quaife do you?

The box will be surplus to requirements once I've dropped the engine and box out of the car sometime in Q1 of next year. So, I'd certainly consider selling it on

 

[fuzzy-hair-man]

The box will be surplus to requirements once I've dropped the engine and box out of the car sometime in Q1 of next year. So, I'd certainly consider selling it on

Thanks that'd be awesome! I'm building up a spare motor for the mini but there's no rush on it so that timing is perfect! Stoked!