BMW M135i: PH Fleet

Oh what a difference a diff makes...

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.

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

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Scottie - NW

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