Team-BHP - Limited Slip Differential on a 2WD to improve rough road ability?

One the biggest issues with owning a 4WD SUV is that 4x4 gear is fitted only to the top-most variant. Add the Rs. 1 Lac extra for the 4x4 gear, and you know why 90 to 95% customers opt for 2WD variants (even if that particular model has 4WD option). Plus, there is the additional 100 kilo weight of 4x4 gear, which affects performance and fuel economy.

Now, we have a number of motorsports companies in India that modify cars for rallying. And that includes retro-fitting Limited Slip Differential. Eg:
http://www.redroosterperformance.com...roller=product

Quote:

We've all felt the loss of control or traction due to differential wheel motion at some point or the other. It happens when one wheel slips, causing a difference that results in loss of performance. Wheel spin may look spectacular, but such losses of traction waste time either from a standing start or exiting a bend, whether driving on the road, rally stage or even a drag strip!

Fortunately, QUAIFE's patented Automatic Torque Biasing (ATB) Helical LSD differential is an effective, well-proven, low-cost solution. The QUAIFE ATB differential is designed to compensate for the loss of drive that occurs with a conventional differential when one wheel slips. Whilst requiring some torque in the slipping wheel, the QUAIFE unit is progressive in action but never locks; controlled power is transmitted to all the driving wheels! Ideally suited to high powered front wheel drive systems, QUAIFE ATB differentials are also used in rear and four wheel drive vehicles where optimum traction is required

And here is a video of how adding LSD helps a vehicle perform better off-road.

https://www.youtube.com/watch?v=OoEO8DpWGUI

From what I understand, LSD costs around $500.

Questions:

1) How much of an improvement in off-roadability can one expect from a Limited Slip Differential? From what I understand, Tata Xenon 4x2 has LSD. How good is it off-road?

2) Any idea about safety & long term reliability of retro-fitting LSD? Quiafe seems to be very popular.

3)Are there likely to be braking issues (increase in braking distance, for example) or issues with tyre wear?

Yeah, definitely FWD has an advantage over RWD, in many conditions - because of placement of engine (weight) on the driven wheels.

I'm particularly interested in advantages of adding LSD to FWD vehicles - because all cars in compact SUV segment are FWDs . They already have decent ground clearance, to handle the rough stuff. People are already trying crazy stuff with their FWD Compact SUVs. Here is an example -

https://www.youtube.com/watch?v=2CXh8YjWHNQ

Essentially, I'm interested in relative advantages/disadvantages of (LSD + FWD) Vs part-time 4WD (without LSD) when it comes to off-roadability

Note to purists: I'm using the word "off-roadability", instead of "OFF ROAD". I basically mean handling a little bit of slush on what used to be roads. ;)

Hi Smartcat,

Yes, an LSD or a Manually Selectable Locker will do wonders to a 2WD. I wouldnt say it would equal a 4WD, but, yes, in some situations a 2WD with a locked rear diff will perform as good as a 4WD with open diffs. And, in some rare cases (articulation pits), a 2WD with a locked diff just might outperform a 4WD.

However, the main advantage of a 4WD is the low ratio gearbox. You wouldnt get that in a 2WD.

As for Front wheel drive LSD's or lockers: Front wheels are turning wheels. So, a differential wheel speed is not avoidable and the LSD's or lockers prevent that. So, in less traction turns you might face directional issues with the car - It will tend to steer straight. Also, a front LSD will reduce the tyre life by quite a bit.

I would suggest an LSD or a Manual Locker for a road use rear wheel drive vehicle, not a front wheel drive vehicle. Though front LSD's give good launch control to drive wheels, hence, if the vehicle is used for drags, lsd will work in favor. Not for normal family use.

Here's a video done for a friend illustrating the use of a locker in a rear wheel drive (in 2WD) : https://www.youtube.com/watch?v=VYr2cr5DnUc

Quote:

Originally Posted by dhanushs (Post 4056268)

Yes, an LSD or a Manually Selectable Locker will do wonders to a 2WD. I wouldnt say it would equal a 4WD, but, yes, in some situations a 2WD with a locked rear diff will perform as good as a 4WD with open diffs. And, in some rare cases (articulation pits), a 2WD with a locked diff just might outperform a 4WD. I would suggest an LSD or a Manual Locker for a road use rear wheel drive vehicle,

Useful info, thanks!

Quote:

Though front LSD's give good launch control to drive wheels, hence, if the vehicle is used for drags, lsd will work in favor. Not for normal family use.

Even Quaife's website talks about performance/lap time improvement in FWD cars. This is something I'm NOT interested in as such.

Quote:

So, in less traction turns you might face directional issues with the car - It will tend to steer straight. Also, a front LSD will reduce the tyre life by quite a bit.

OK now that is quite scary. I guess this is one of those things one needs to fully understand before experimenting. However, a company like Quaife designs LSDs specifically for FWD cars. I'm pretty sure they would have taken care of the above issue. From their UK website -

http://quaife.co.uk/quaife-products/...-differential/

Quote:

- Safe, progressive and seamless in action, the Quaife ATB differential never ‘locks’
- Fitment greatly reduces unwanted torque steer and understeer
- Improves braking performance on front wheel drive cars by reducing lock up and minimising ABS intrusion due to torque transfer action
- Reduces tyre wear, especially on front wheel drive cars
- Gear operated with no service components to replace – ever
- Direct replacement for factory standard ‘open’ differential unit
- Retains normal axle lubrication systems and maintenance schedule
- Over 100,000 units sold worldwide since the 1980’s
- Backed by a Quaife lifetime warranty for both motorsport and road use

Quote:

Originally Posted by smartcat (Post 4056135)

And here is a video of how adding LSD helps a vehicle perform better off-road

Ever since i decided to pick up the Innova it was on my mind to put a LSD in the rear differential. Actually the wish precedes the Innova purchase because I was thinking of picking up the refreshed Scorpio before I bought the Polo GT and the Eaton autolocker was on my mind as seen in 1100D's marengo .

I am looking for a compatible LSD for the Crysta and hope to put one in someday. I am not too sure about autolocker in the Innova because i don't know how it will behave on the street as its mainly an on-road vehicle.

And thus my interest in Crysta's rear axle ;)
http://www.team-bhp.com/forum/offici...ml#post4057177

Quote:

Originally Posted by i_see (Post 4058591)

A silly doubt from my side
Just like a limited slip differential, Will an ESP ( electronic stability program as in vehicles sold in EU) also bail out a 2WD vehicle in the same tricky situations mentioned in the above posts ?

In a 2WD atleast, I think both ESP and traction control reduces the vehicle's ability of handle slush/snow. Because these systems either brake individual wheels or cut engine power when it detects wheel slip.

Quote:

Originally Posted by Guna (Post 4058597)

Fitting LSD on the front wheels, I wonder if it comes in the way of normal functioning of the differential and has adverse effect while driving on the Tarmac.

Quaife says it actually improves on-tarmac performance -> shaving couple of seconds off lap times, reducing understeer and increasing tyre life. But if it really improves performance as claimed, why don't car manufacturers fit LSD in performance oriented FWD cars like Octavia RS, Focus RS, Civic Type R etc?