Diff' confusion

[Cloggy Saint]

Just been looking at the wiki diff' page and could use some answers! It looks as if some of the diffs for M20s came in both open and lsd form, yes? What would be the best open diff' for a 2.5 touring, and just what is the benefit of an lsd?

[Silverfang]

Considering ratio alone for the touring, a 3.64:1 ratio would be the most ideal (medium case) since this gives a balanced setup for both acceleration and cruising speed.

The point of having a limited slip differential is to reduce the amount of single wheel spin, say when coming off a tight corner or such, and having the inside wheel spinning up, sometimes causing the car to slide round, or 'lurch about'.

The limited locks up beyond a certain torque value and makes the rear axle lock up like a kart's. This in turn makes the back end slide out a bit, but makes it far more predictable when doing so.

In wet / snowy / low grip situations, having a limited slip in the back can make life a lot easier as the car is more consistent and easier to control if the back end does step out.

I've driven both Mantas and E30's with and without LSD's in my time and believe me, I'd rather have one with than without!

[Grrrmachine]

All BMW diffs follow a standard ratio pattern, and pretty much every ratio was available in Open or Limited Slip form. All LSDs are rare, but some are rarer than others.

I've got a 3.64 Open on my 325i Touring, but I'm also running a 320i gearbox which gives better acceleration gears in second and third. If you use a 3.64 with your 325i box you might find it quite blunt. A 3.73 is considered a better compromise between acceleration and motorway speeds, while a 3.91 is for storming away from the traffic lights but can be tiring at motorway speeds.

[Brianmoooore]

All LSDs are rare

Unfortunately so, considering they were a relatively cheap option!

[Cloggy Saint]

Thanks for the replies, I've the chance to get a 3.73, which sounds like the best option.