Quaife ATB Diff ?

[billgatese30]

the torsen, but I'm not sure if it just because with the quick rack you end up catching it faster, making it feel easier to control and less snappy, although it is nice and predictable on the track.

[bss325i]

I need a better diff and rack!

[billgatese30]

I know, every time I get out teh S50 and back in to the sport it just feels different becuase of that rack

[GeoffBob]

From when the ATB first came out and up untill he purchased his (under my reccomendation) everything i had read about it was that it was more suited to FWD application than RWD. Why, i cant remember.

Most likely because the "progressive" action of the ATB diff (adjusting the torque according to the needs of each wheel) is ideally suited to curing the problem of torque steer. Another one of the ATB diff's party tricks.

I seem to recall this was something Quaife pushed in their marketing efforts. It's not to say that it isn't suited to a RWD car, I just think they were using the whole "ATB cure for torque steer" as a means to make inroads into the FWD market. For road going cars I would think that Quaife have hit the nail on the head, but whether the Quaife ATB is ideal for FWD track cars I wouldn't know, could be that it responds exactly as Jon has described.

Jon, I was thinking about what you said about your friends car last night. Did he buy that Quaife new or second hand? If he had excessive spin on the inside wheel it sounds to me as if the friction discs and bellville springs between the two sun gears, and/or the friction discs and bellville springs between the pinion gears and gear housing could be shot. Either that or he has way too much torque in 2nd or 3rd gear for his tyres to handle. But then if that were the case and the Quaife were working I would expect both wheels to spin (assuming there isn't a ridiculous amount of body roll and wheel launching going on).

I would say that some slip on the inside wheel is possible. As the ATB mechanism takes torque away from the inside wheel (and gives it to the outside) its not to say that there isn't still enough torque left at the inside wheel to still cause some slip - but excessive wheel spin (slowing his exit speed) sounds to me as if there is something wrong with that unit?

Just a thought.

Please keep more of the above coming gents! This is interesting reading for someone like myself who is still learning about diffs. The technical books and patent documents are filled with explanations as to how they work, but forums like the zone are the only place find people who have a "feel" for how they perform on the track

[Jon_Bmw]

Definately an interesting topic, is it a bit sad to get excited by diffs? I think I must be doubly sad, a FWD 'diff'

My friend is a cheque book racer, but in an unusual stance. He does all the work himself, but with no expense (within reason) spared. It will have been a new diff, but there is a chance he will have worn it out after a lot of hard grafting. For road cars they are very much 'fit and forget' but tarmac rallys are going to give it a punishing and increase wear rates massively(10/15 times? on a mileage/wear rate)!

The engine probably is too powerful for the chassis which isn't helping, but you try telling a racing driver that he has too much power! >210bhp btw. I suspect some decent foot modulation would partially solve his issues, but when the red mist sets in...well you probably know what it is like. I have passengered in it once, and I never will again....we crashed after about 5 minutes! Slicks and progressively heavier rain don't match.

Looking forward to the report of how you get on. Get that car finished!

[N00b]

This has been very interesting reading so far.

[ShakeyC]

Im only familiar with the early type ATB diffs which the following is based upon.

The problem i found is the feeling of no drive when a driven wheel lifts with ATB, and the varying rate of biasing is little unnerving and unpredictable compared to typical plated LSD. On a track or road without much adverse camber ATB traction is very good at getting drive out the corners or powering harder into a long bends the back end does feel more sticky.

On rallies, hill climbs and rough, wet muddy rutted roads ATB is better than plated LSD ONLY because of traction control. Rallying an mk2 escort through the wintery woods of north east rally few years ago in my mind confirmed that without electronics ATB is not much better than open diff for such applications. With TC when a wheel looses traction the brakes or slump in power helps the ATB work in favour in such condition transfering drive across smoother hence less flashing lights on the dash

FWD car ATB does wonders for traction but same problem applies on roads with lots camber changes and textures the ATB magnifies torque steer as its constantly varying the lockup in opposition of where you may want to steer. On every day driving or track its much more forgiving definately more traction and stability. On a reasonable surface road pressing on the ATB works with you pulling you round bends harder because of similar camber and traction on both driven wheels the diff isnt fighting against the steering. When it does fight the steering trust me your arms know about it!

My personal preferance is plated LSD on basis of predictable and consistant confidence it gives me on the throttle and braking points. With ATB is more difficult to steer on the throttle I found for example chicanes ATB is faster on entry and exit but middle of the esses is slower (slower apex's), wheras with plated LSD on same car entry is slower but middle (apex's) and exits are faster but both can give similar overall times if you adjust your style to suit the technology.

[ShakeyC]

I forgot to add another similar diff to ATB is a Torsen Diff which employs a similar plantery arrangement but the difference is it has preloaded friction plates which lock together with when biasing reaches below a spec amount of torque bias such as lifting a wheel or on ice, mud too. But nowhere near as widely available commercially.

[GeoffBob]

Fantastic review Shakey, thanks for that. Great to hear from someone who has actually driven both and can objectively compare how they feel during competition usuage.

I am in complete agreement with you with regard to the combined use of the Quaife and traction control. As I understand it, the locking mechanism on the Quaife operates entirely as a function of the torque difference between the two output shafts. In the event that a wheel is lifted or encounters a very low traction surface, the torque distribution returns to 50/50, and thus the locking mechanism will fail to engage. The intelligent application of brakes to the slipping wheel thus ensures that the locking mechanism continues to function.

BTW, the diff described in John Quaifes 2003 patent includes sprung-loaded friction discs between each pinion gear and the diff cage to achieve an effect similar to the Torsen. I have since found out, however, that Quaife have never gone into commercial production of this unit, so all Quaife ATB diffs produced today are still based on the original patent from the 1960's.

I, for one, will be operating my Quaife ATB diff with my Bosch 5.1 ABS/TC system (still to be programmed) to ensure that I get the most out of the ATB mechanism. I fully understand, however, that the Quaife is not ideally suited to eveyone's application.

[jaistanley]

The ZMRoadster and ZMCoupe diffs aren't Torsen type. Only a few Z cars got one.. I beleive it was the 2.8 Coupe's (from europe) and all non ZM's after 1999 that had the 'LSD' option ticked on purchase. I got quite excited when I thought my ZMRoadster donor car had the Torsen type, but then found out and saw for myself they don't. Apparently the ramp angles are revised on them (or they have an extra plate - I can't remember which).

Incidentally though my S50 is VERY sideways in the wet (I still haven't had the bloody thing aligned!!!), it is very easily controlled. In the dry it seems very progressive and controllable. I personally think this is a combination of having to use 215 tyres and the relatively linear power delivery of the S50 engines.