Thursday 2nd November 2017

BMW M135i: PH Fleet

Oh what a difference a diff makes...

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Twice in one week I found myself making use of the M135i's newly-fitted limited-slip differential, but each time the circumstances were very different. On the Thursday I was at Bruntingthorpe - the vast airfield in Leicestershire that's effectively now an enormous storage facility for new cars and old planes, with a bit of a test track attached to it. I was there to drive a Nissan GT-R for an Autocar feature, but the photographer was knocking about in my M135i and it would have been daft not to have a squirt in the tricked-up BMW.

I've driven enough non-LSD equipped M135is on track to know how frustrating they can be. Get on the throttle mid-corner and you might bonfire the inside rear tyre, or you might get good drive towards the exit, or it might slide neatly and progressively. No way of knowing which. With the Quaife diff in place, however, you can make the car behave exactly how you want it to, be that neat and positive drive to the exit, or the full yeehah dorifto with both tyres on fire and the throttle wide open. It really is a vast improvement.

The other occasion, the following Saturday, was somewhat less exciting. I had reason to abandon the car on a muddy grass verge - the things you do when chasing Wales Rally GB... - and had it not had its LSD I'm certain the M135i would have spun one of its rear wheels uselessly until it had buried itself in the gloop.

In fact, the truth of it is you don't need to be on a test track or in the boonies to feel the benefit of the LSD. On the road you appreciate how little the car now relies on its traction control system and how, when nobody's looking, you can play with the balance of the car on the throttle. I don't mean the big hero slides that might cost you your licence, but those cheeky little tail wiggles on a roundabout or in a tight bend that make you giggle to yourself.

Birds charges £2,033 for the LSD, with fitting taking just a couple of hours - and while the diff was going in they also fitted a short shift kit. Whereas before the gearshift was a touch ponderous, it's super direct and mechanical now. I think it suits the nature of the car. The guys also modified the clutch pedal to add a little heft to it, which I don't mind when I'm having a bit of a blast but could do without in stop-start traffic. The short shift kit costs £532, the clutch pedal mod £113.

Chasing the world's best rally drivers around Snowdonia was a stern test for the M135i, not least because it was loaded up with the better part of 400kg of people and stuff. Rear seat passengers did want for legroom on the four-hour return motorway journey, but on Snowdonia's stunning mountain roads the car was still great fun to do drive. For those of us sat up front it was relaxing and comfortable on the M5, too. Following a gravel rally really is a mucky past time, though. Mud everywhere. The M135i will need a proper wash soon.

So the chassis is sorted, thanks to the Bilstein dampers and Eibach springs, and the Quaife LSD is doing its thing. One last trip to Birds beckons, when we'll see about getting more power out of that turbocharged six-cylinder. I reckon 385hp should do the trick.

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FACT SHEET
Car: BMW M135i
Run by: Dan Prosser
Bought: July 2017
Mileage: 33,300 total, 2,300 this month
Purchase price: £17,500
Last month at a glance: Dan gets a dose of LSD and loves the effects

Previous reports:
'You could get an M135i for that' - so we have!
Shockingly good improvement with new suspension fitted

[Scottie - NW]

Fairly amazing really that it came without a LSD as standard.

Even 20 years ago rwd cars with decent power came with them standard.

What type of LSD is fitted, viscous/helical etc?

[Scottie - NW]

MustardCutter said:

Scottie - NW said:

What type of LSD is fitted, viscous/helical etc?

Birds fit the Quaife ATB.

I know it's Quaife, the article says that, but that is the manufacturer as opposed to the type of LSD?

[Scottie - NW]

s m said:

Scottie - NW said:

MustardCutter said:

Scottie - NW said:

What type of LSD is fitted, viscous/helical etc?

Birds fit the Quaife ATB.

I know it's Quaife, the article says that, but that is the manufacturer as opposed to the type of LSD?

It's a helical gear torque apportioning diff

Thanks, am trying to learn more about diffs as the viscous LSD I have is not great.

[Scottie - NW]

MustardCutter said:

Scottie - NW said:

MustardCutter said:

Scottie - NW said:

What type of LSD is fitted, viscous/helical etc?

Birds fit the Quaife ATB.

I know it's Quaife, the article says that, but that is the manufacturer as opposed to the type of LSD?

If you know it's a Quaife then you should know it's an automatic torque biasing (ATB) helical gear based diff like all Quaife diffs. Apologies for trying to help.

fido said:

cerb4.5lee said:

That's always baffled me too, my old 200sx couldn't even manage 200bhp as standard...yet it still came with a LSD from the factory.

Traction control helps to some extent - if it can brake individual wheels then you have an electronic locking diff - though it sounds like the M135 doesn't do this or cuts power when what you want is power to both wheels.

It does use the rear brakes to mimic an LSD, but it can be quite intrusive and unpredictable as the article eludes to. It's certainly a frustration I have with mine.

Edited by MustardCutter on Thursday 2nd November 13:52

Mustardcutter, was not trying to be rude sorry if it appeared that way, was trying to understand the type of LSD as opposed to the make as I am looking to upgrade one.

I have a similar problem to cerb4.5lee in that I have a s14a 200sx, which is a light rwd car, putting out 398bhp and 378 lbft and the viscous LSD is not good, so I am considering upgrading to the Helical one from the later S15 model, I am told helical is better than viscous?

A complication is the car only has 3 channel ABS, two on the front and the rear sensor is in the diff. I've fitted race logic traction control myself, use GTR wheels with wide semi slicks, have full alignment kits and so on, and the power goes down lots better, but I have been advised switching to the helical will also yield improvements.

I do also realise that 400bhp in a light rwd car will always mean some traction limitations but I am trying to minimise them as I've done a little hill climbing and sprinting, albeit a bit rubbish, but even 0.3s improvement would put me up a few places

Edited by Scottie - NW on Thursday 2nd November 15:23

[Scottie - NW]

s m said:

Scottie - NW said:

s m said:

Scottie - NW said:

MustardCutter said:

Scottie - NW said:

What type of LSD is fitted, viscous/helical etc?

Birds fit the Quaife ATB.

I know it's Quaife, the article says that, but that is the manufacturer as opposed to the type of LSD?

It's a helical gear torque apportioning diff

Thanks, am trying to learn more about diffs as the viscous LSD I have is not great.

The coupling is probably knackered if it's the original - after time and many heat/duty cycles they will 'revert' to open. You can get them recon'd and rerated but people seldom do, usually the same with plated diffs.
Advantage with Torsen diff such as the S15 runs is it basically fit and forget

Thanks am keeping my eye out for a S15 helical diff to upgrade to. I did look at rebuilding an after market diff into the original casing, some good manufacturers do kits, I was warned a 2 way is track only really and you have to alter your driving style to suit, whereas a 1.5 way is much better.

At my level though I think a S15 helical is a nice upgrade.

[Scottie - NW]

Would this Quaife Helical ATB diff be a 1.5 way?

[Scottie - NW]

s m said:

Scottie - NW said:

Would this Quaife Helical ATB diff be a 1.5 way?

A Quaife diff doesn't lock like a plate diff so this wouldn't apply.
A Quaife diff is just apportioning the drive torque between the drive wheels dependent on the bias ratio rather than locking them together.
That's why in a Quaife diff if you have zero torque at one wheel ( airborne wheel or no friction say on sheet ice then it can only send or bias the equivalent torque to the other wheel multiplied by that ratio - as zero times anything is zero then that's how much torque is sent to the other wheel .....I.e. Zero )

Well explained thank you, getting my head around this a bit better now.