Diff and Gear ratios

[GeoffBob]

I've occasionally seen questions in this section with regard to ideal differential and gear ratios, and the operation and setting up of a limited slip differential on a track car.

Thus, for those interested in this topic, Cartechbooks at http://www.cartechbooks.com have recently published "High Performance Differentials, Axles and Drivetrains" by Joe Palazzolo. At $25 I personally think it's a bargain. Read this book and you'll understand why the BMW ZF clutch type LSD is better suited to slow driving on an icy or wet road than it is for racing through a chicane or hairpin.

'Hope this is of interest to someone.

[oldbimmer]

Hmmmmmmmm... That's certainly of interest. I've never quite got my ahead around the different types of LDSs.

Thanks for posting.. Might have to get a copy

[GeoffBob]

If anyone is interested in how an automatic torque biasing (ATB) LSD works I have a PDF of Michael John Quaife's 2003 patent document that you can download. Right click here and select "Save Target As..."

His design makes use of helical pinion gears in place of the usual tapered planet gears found in an open diff or clutch type LSD. These helical pinion gears experience a lateral force proportional to the difference in the tractive force between the two output shafts which cause the two sun gears (and thus the output shafts) to progressively lock together, unlike the clutch type LSD which locks suddenly, and thus tends to upset the balance of a track car at speed.

As simply as I can put it, with a Quaife ATB LSD, the greater the loss of traction at one wheel - the more that wheel will progressively lock to the other wheel (delivering torque to the wheel with traction). This is the basic reason why this type of LSD is termed "automatic torque biasing". The clutch type LSD, on the other hand, tends to rapidly snap together the two output shafts (via the clutch discs) when the difference in the tractive force between the two wheels exceeds a certain value.

[GeoffBob]

I have also added this book to my collection:



Personally I find that the gearbox and final-drive (diff) are the most misunderstood parts of any car, with both as important to the performance of a track-car as the engine, suspension and tyres. With the two books listed above you shouldn't have any trouble understanding both items. The two are unfortunately aimed at the American audience, but the principles are the same regardless of whether you call it a gearbox or transmission.

I have found the first book above particularly useful as it includes understandable explanations and detailed pictures of most types of limited slip differential, including the plate/clutch type, the helical geared type (Quaife, Eaton, Torsen), the viscous type (GKN Viscolok), the Detroit Locker, and even a brief explanation of electronically controlled "torque vectoring" diffs.

And if you have in mind to modify your gear ratios and install spur (straight-cut) gears in order to setup an ideal gearbox for your trackcar, then get your hands on a copy of High Performance Manual Transmissions, as above. See http://www.cartechbooks.com for details.

[e301988325i]

Gearing calculator

http://www.unixnerd.demon.co.uk/revs.html