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Limited slip diff!

59K views 204 replies 61 participants last post by  SenderPiggins 
#1 ·
Is there speculation ford performance is coming with a mechanical limited slip diff for the front?

I really need this upgrade! How About mountune?

I can also order a quaife myself but i need to know if it fits and works in a focus rs 2016.


Anybody have more info!
 
#128 · (Edited)
holy ****. there is a lot of misinformation in this thread. idk what the deal is here.

front LSD will be faster. there are a lot of different types of LSDs, but you guys are all talking as if all front LSDs are super aggressive, practically locked diffs. that is not how modern diffs work - with clutch types, there is such a thing as 1 way & 1.5 ways diffs...

for instance, the 1 way clutch diff, which is IMO the ideal solution for any front driven axle, will be OPEN on decel, and lock on accel. The understeer most people seem to be referring to here, I'm assuming must be in regards to corner ENTRY/turn-in. 1 way diffs do NOT impact that. Then, on corner exit, clutch types will send torque to the outside wheel. if you are arguing about LSDs creating corner EXIT understeer, you're beyond help.

I didn't read about which exact differential (incl. how it is set up - 1.5 way clutch diffs can often be set up as 2 ways, or 1 ways, or use springs to adjust clamping force or engagement) is going into the '18 FORS but in regardless, in aggregate the car will be faster, all else held equal. will it be immensely faster? no. but will it make enough difference if you are autocrossing and looking for tenths? yes, particularly if you are getting corner exit wheel spin, if some people do.

I think the real issue is people are upset/worried/trying to justify that their 16s and 17s are going to be worse than the 18. get over it.

PS, understeer is not the devil. it seems to me the car could use a little more front end stability. on top of that, how the car behaves (understeer, oversteer, whatever), is completely set-up dependent, including how the drivetrain operates. maybe, depending on how they set up the front LSD, the car WILL push more (on corner entry) - if you don't like that, adjust tire pressures. adjust shocks. adjust springs. adjust weight. or do nothing at all, and the car will likely still turn in great. and then enjoy the front of the car clawing itself out on corner exit. some of you guys really sound like it's just a front axle locker and the car will just completely scrub whole way through. also saw some earlier chatter about how it takes away traction or something - no, just no.

Better than a braking "e-lsd" that overuses the brakes and is hardly effective to begin with.

--

one more post-script - it doesn't really make sense to compare open, active diffs in some of the modern awd cars to traditional mechanicals. for instance, take the evo's center diff. it is open," BUT it uses hydraulic pressure to clamp the front & rear wheels together on and off. you could replace it with a limited slip, but that isn't going to be as good as the ACD, which can also be programmed to behave in whichever manner you like. so again, open on corner entry, lock on corner exit - no understeer on entry then, with pure traction pulling the car out on exit.

that is the same reason the rear drive in the RS is a beauty. not because of over driven rear wheels or anything like that, but pure independent control of each wheel by the car's ECU. they can't "lock" together which is probably part of why the car is so loose, but on corner exit it will do exactly what a limited slip does, which is prioritize power to the outside wheel.

I really love awd cars, awd tech, mechanical lsds, active lsds, etc. - but some of you guys are really bungling it up. that's not unusual when a car is new, people are still confusing what ACDs do in Evos. hopefully I clarified the discussion a little. I started the rear diff and acd tuning threads on evom in doing all this research, but that prob doesn't mean anything to most of you.
 
#129 ·
holy ****. there is a lot of misinformation in this thread. idk what the deal is here.

front LSD will be faster. there are a lot of different types of LSDs, but you guys are all talking as if all front LSDs are super aggressive, practically locked diffs. that is not how modern diffs work - with clutch types, there is such a thing as 1 way & 1.5 ways diffs...

for instance, the 1 way clutch diff, which is IMO the ideal solution for any front driven axle, will be OPEN on decel, and lock on accel. The understeer most people seem to be referring to here, I'm assuming must be in regards to corner ENTRY/turn-in. 1 way diffs do NOT impact that. Then, on corner exit, clutch types will send torque to the outside wheel. if you are arguing about LSDs creating corner EXIT understeer, you're beyond help.

I didn't read about which exact differential (incl. how it is set up - 1.5 way clutch diffs can often be set up as 2 ways, or 1 ways, or use springs to adjust clamping force or engagement) is going into the '18 FORS but in regardless, in aggregate the car will be faster, all else held equal. will it be immensely faster? no. but will it make enough difference if you are autocrossing and looking for tenths? yes, particularly if you are getting corner exit wheel spin, if some people do.

I think the real issue is people are upset/worried/trying to justify that their 16s and 17s are going to be worse than the 18. get over it.

PS, understeer is not the devil. it seems to me the car could use a little more front end stability. on top of that, how the car behaves (understeer, oversteer, whatever), is completely set-up dependent, including how the drivetrain operates. maybe, depending on how they set up the front LSD, the car WILL push more (on corner entry) - if you don't like that, adjust tire pressures. adjust shocks. adjust springs. adjust weight. or do nothing at all, and the car will likely still turn in great. and then enjoy the front of the car clawing itself out on corner exit. some of you guys really sound like it's just a front axle locker and the car will just completely scrub whole way through. also saw some earlier chatter about how it takes away traction or something - no, just no.

Better than a braking "e-lsd" that overuses the brakes and is hardly effective to begin with.

--

one more post-script - it doesn't really make sense to compare open, active diffs in some of the modern awd cars to traditional mechanicals. for instance, take the evo's center diff. it is open," BUT it uses hydraulic pressure to clamp the front & rear wheels together on and off. you could replace it with a limited slip, but that isn't going to be as good as the ACD, which can also be programmed to behave in whichever manner you like. so again, open on corner entry, lock on corner exit - no understeer on entry then, with pure traction pulling the car out on exit.

that is the same reason the rear drive in the RS is a beauty. not because of over driven rear wheels or anything like that, but pure independent control of each wheel by the car's ECU. they can't "lock" together which is probably part of why the car is so loose, but on corner exit it will do exactly what a limited slip does, which is prioritize power to the outside wheel.
Agreed on all counts. As if grabbing the inside brake so that you can transfer more torque outward is better than actively transferring torque through the LSD. It's not. Tim O'Neil has said the car is more predictable and consistent with the LSD and he drives on loose surfaces where push is more noticeable. Sure with a LSD you will be able to push harder in the corner and more easily reach the limits of grip but that's because you are more effectively laying power down at high cornering loads. The LSD works in harmony with the e-dif probably making it more effective it doing its own job while assisting the mechanical dif
 
#130 ·
I'm not worried about justifying my older car, I'm interested in knowing if this mod is worthwhile to me. Does the car feel vastly better with the Quaife or not? I put a Quaife in my SRT8 and loved it. I'm am still on the fence on if this would provide nearly as much of a benefit in the RS. At this point I'm leaning towards not getting one. I have yet to hear any rave reviews.

I don't really care about the tenths of a second, I'm more concerned with how the car feels and if it is more fun. My days of competing in autox or on the track are behind me. The Team O'Neal comment that the car is more predictable is the only good data point to me at this point. I do wonder if that is on or off road though based on what they do.


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#131 ·
again, this is for tenths, not "feel" per se. not competing, not necessary. especially when the RDU is already so great, that it takes care of most of the cars oomph.

really though, I was just trying to clarify the rampant misinformation in the thread. I don't understand the pushback on what is hands-down an improvement.
 
#132 ·
My pushback is this- that video of the GNK engineer in England saying that a front LSD will cause more understeer with the Twinster.

I don't consider myself uneducated. I'm an ex-pro racer. I ran a Porsche race/mod shop (almost all were RWD Porsches), etc. I'd really love an in-depth discussion with an engineer where we could talk physics and the mechanics of it. I'm confident the Quaife will offer benefits, but will likely cause some issues as well.

I'd also like to know if the Twinster tuning is different in 2018 because of the Quaife, or if it exactly the same settings as the prior cars.




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#133 ·
I'd also like to know if the Twinster tuning is different in 2018 because of the Quaife, or if it exactly the same settings as the prior cars.
So far, this is a question Ford is not answering. The "answer" given when asked was a side step, and see if the statement can be misinterpreted as an answer.
 
#134 ·
I think the push back is coming from how well the front works right now. It may not be crazy efficient, but it really works when combined with the rdu.

I like to think I understand front dif stuff. Fwd or awd. And you're right about 1 way, 2 way, etc. and all the diffences between various designs.

But food for thought.

If you're already using 100% of the outside front tires grip(maybe past that into scrub), and you transfer into corner exit(mash the gas), if the dif applys any more force to the outside front, you're going to exceed the tires ability.


I know I know. Tons of variables.

The biggest one being that the RDU/PTU overdrives the rear relative to the front.

Imagine a situation where the rdu trys to lock the outside rear on exit, And an LSD tries to lock the outside front. Now the outside front is going slower than the rear.

I'm thinking out loud. Definitely not arguing, but interested in spitballing about this.
 
#142 ·
Oh agreed. No my envy here though. I'm just curious.

All I can make now are assumptions. Fun to noodle about though.
 
#148 · (Edited)
I don't think Kuczera (GKN engineer) gave his rationale for why a LSD will cause understeer on an AWD car. But his comments were specifically addressing a front LSD on the RS, so it is interesting. And your point about what specific set of circumstances in the whole range of dynamic handling situations needs to be made clear. As you said, you can't simply say an "LSD on the front of an AWD vehicle causes understeer". You have too many handling variables to support such a broad statement. E.g., throttle on, trailing throttle, corner entry, mid corner, corner exit, etc., etc. etc. But, as a general rule, and he was speaking specifically about our car, the LSD causes throttle on understeer; and trailing throttle oversteer. And contrary to assertions that the LSD was "more predictable", he said just the opposite.

I think the important takeaway from your comments are that folks need to be careful not to make generalizations across an almost infinite number of possible dynamic handling situations.

That being said, I find it difficult to imagine that a front LSD on our car is going to result in anything more than a slight incremental advantage in some extreme situations. And I bet a lot of us "Sunday Pilots" are going to prefer the setup without a front LSD.

But as you alluded, let's wait and see. If somebody starts knockin' 2 seconds a lap off their times at Willow...I'll take notice.
 
#149 · (Edited)
I don't think Kuczera (GKN engineer) gave his rationale for why a LSD will cause understeer on an AWD car. But his comments were specifically addressing a front LSD on the RS, so it is interesting. And your point about what specific set of circumstances in the whole range of dynamic handling situations needs to be made clear. As you said, you can't simply say an "LSD on the front of an AWD vehicle causes understeer". You have too many handling variables to support such a broad statement. E.g., throttle on, trailing throttle, corner entry, mid corner, corner exit, etc., etc. etc. But, as a general rule, and he was speaking specifically about our car, the LSD causes throttle on understeer; and trailing throttle oversteer. And contrary to assertions that the LSD was "more predictable", he said just the opposite.

I think the important takeaway from your comments are that folks need to be careful not to make generalizations across an almost infinite number of possible dynamic handling situations.

That being said, I find it difficult to imagine that a front LSD on our car is going to result in anything more than a slight incremental advantage in some extreme situations. And I bet a lot of us "Sunday Pilots" are going to prefer the setup without a front LSD.

But as you alluded, let's wait and see. If somebody starts knockin' 2 seconds a lap off their times at Willow...I'll take notice.
can i see the video where he says an LSD in the front of an AWD car would cause throttle ON understeer? I have never heard of this. in fact, this sounds completely backwards. completely backwards. if such is the case, why would anyone add an LSD in the front of an awd car??? you guys are really hanging onto this guy's word like it's gospel, so i'd at least like to see where he talks about it and the context. as a general rule, an LSD provides more torque to the outside wheel. i've never experienced a car with an added LSD in front that increases power-on understeer. honestly the whole thing sounds backwards.

i've already said repeatedly that it will be an incremental advantage. maybe more than incremental once power is added. there is no way it is going to give the car 2 seconds in a same day scenario on any given track without something else going on.

finally, this is ford's baby (wrt to the 2018). you think they're gonna just willy-nilly throw on a front LSD, and turn their pride & joy drift baby into an understeering pig? you think they're gonna do this AND make the car slower for it? hopefully a decent rag & C&D or R&T will actually do some same-day testing with the '18 and '17 and see what kind of difference in handling it makes. like i said, maybe the way they have it set up will create some understeer (again, not the devil) - but would be very surprised if it results in the car being slower.

if people are reading this to determine if they should add an LSD, i would honestly be very wary of people saying it will make the car worse. a 1 way clutch type, as i've said, is still OPEN in an off-throttle situation. then, as you feed power back, it will simply add more torque to the outside wheel instead of giving both wheels the same amount.



::
i hope to god this is not the interview you were referring to, where the product technology director of GKN in the UK also 100% contradicts what your other guy has been claimed to have said:

When you accelerate out of a bend you typically understeer because the front axle becomes light. If you add additional torque to the outside via an LSD (it doesn't matter whether it's on the front or the rear), that pulls the vehicle in and gives less understeer.

Another advantage is the opposite. Every LSD reduces throttle-off [lift-off] oversteer in a bend to a quite significant extent. Same goes for lane changing manoeuvres. If the vehicle becomes unstable the LSD more or less automatically reduces torque to stabilise and that's yaw damping.
https://www.pistonheads.com/feature...py-all-about-limited-slip-differentials/25275

goodness. hope we can put to bed this idea of a front LSD creating additional power on understeer. note he mentions the stability re: corner entry. this is what i was referring to as far as perhaps adding corner ENTRY understeer (not power-on, corner exit). as i've mentioned, some LSDs will do this if they're engaged on decel as well as accel. however, not ALL LSDs do this (which is why I'm assuming he means his, and he only talks about torsen & viscous type diffs in this article), re: 1 way clutch type. Again though, increased stability in corner entry (and braking) is never a bad thing. Clutch type diffs can also be tuned to vary how much they engage on decel (very little 1-way, in the middle 1.5-way, a lot 2-way), which is a beautiful thing but not worth the TNT unless you're racing.
 
#151 ·
So I've caught up on all 8 pages of this thread now. First, I think there is really a lot of good information here. Also, what appears to be some guesses, and apparently some hurt feelings too.

What I've been able to gather from all this is:

1) Seems like at stock HP levels, no one seems to have an issue with the car as is.
2) With increased HP the LSD seems to tame down the torque steer. (Mentioned by the only person here who actually has it installed. And on the Other LSD discussion thread from a member with it installed, but also increased HP.)
3) Theoretically, this may introduce some understeer, which may or may not be detrimental, depending on your intended use. But yet to be verified how much and if at all detrimental.

So, with all that said, is there any way to objectively test this?

So far I know of only 2 members who have done this and reported their experiences, and both seem very happy.

I'm kind of ignorant to how this will "help" or "hurt" the cars performance. In the FoSt platform, it was a no brainer, if you upped the HP/Tq, you needed it to put power down, period. Seems much grayer here. I'd be interested to see some sort of objective measure, if that's even possible.


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#152 ·
A magazine with someone like Randy Pobst comparing a '17 to and '18 would be exactly what I'd want, but it's not going to happen. The RS just isn't big enough in the USA to have them do this. If we were talking about this on a Mustang, we might get it.


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#154 ·
I said I wouldn't engage in any more bickering on this subject and won't. I'm only posting to confirm that there has been no recalibration of the AWD system, and won't. Ford have said this, the same GKN engineer has said this. So we'll have to wait on independent testing. Someone out there will test them back to back
 
#155 ·
for further clarification, you are referring to their comments on the brake torque vectoring in the front, correct? this makes sense, and there's really no need. the brake torque vectoring simply has to do much less with an LSD in the front. Better for the brakes over many laps as well.

i wouldn't really call this bickering. more like educating people on what mechanical diffs actually do and debunking misinformation that keeps spreading around.
 
#169 ·
The P1 can get tire spin without issue, even at triple digit speeds.


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#171 ·
yea i'm not sure w.r.t. to the p1. here's a little more color on their system:

The video notes that if the P1’s brakes get too hot, the effect is limited or shut down. However, you’re probably going to be below the heat threshold of this car’s carbon ceramic brakes the entire time you own it. Unless you actually use the thing for its intended purpose and put it on a race track.
As to why McLaren opts for this brake-based traction system over a mechanical limited slip differential, a representative from the company spelled it out pretty simply: “the current system works with less components and complexity. It’s not just unique to the P1- our whole lineup has the same setup.”
deadspin-quote-carrot-aligned-w-bgr-2

obviously, it's worth noting also that differential setups on the rear axle of a car can be very different from the front, based on power, weight distribution etc. so while a 1-way (in general a diff that doesn't lock on decel) may be recommended in the front axle of a nose heavy awd car, commonly a 1.5-way is employed in the rear.

perhaps also they don't believe p1 purchasers will really make use of it, lol
 
#173 ·
Randy Pobst on the P1,

“I was so busy I never felt like hitting that little DRS button. It can spin these very sticky Pirelli Trofeo R tires violently through second and third, a wonderful feeling, frankly.”

It's also why he posted faster laps in the 918 on Laguna.


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#180 ·
another question mark with this open diff + brake torque vectoring system - besides the overheating/overuse of the front brakes - change the brake set up, change the response of vectoring? hell, even change the heat, change the response - esp for those of you who are going full blown track racing with real track pads that require heat to have any sort of bite, and then ramp up quickly as the heat builds - very inconsistent run after run, brake zone after brake zone. not what you want in this car. looking forward to how the 18 does
 
#181 ·
While that is true with the Focus ST, which has much less brake capacity, the RS does not have this issue, even on stock pads.

Change the fluid to prevent boiling and you are golden for basic HPDE work. In time, you may need better pads. The system is adaptive, if you put stronger brakes on the car, it will use them less to achieve the same result.
 
#182 ·
u have documentation on the adaptive part? i'm hearing of RS's spin the front wheels coming out of tight corners so is the adaptive part purposely allowing spin or does it not have enough brake force stock? and if upgrade the pads, is it still going to allow spin (not overwhelmed with OE brakes) or will it work better (stock pads overwhelmed)?
 
#185 ·
You guys can roast me on this..but since 2018 has front LSD, does it also have rear already? If it doesn’t have rear, why not?
 
#190 · (Edited)
The only proper limited slip differential (ZF-style) available for the RS MMT6 is from Drexler Motorsport.

All the other mentioned are not really limiting slip, just biasing torque and will behave just like open diffs when overwhelmed by a large torque input, or on snow, or when a wheel is in the air (curbs on track etc), thus the mixed reviews ranging from “transforming the car” to “not doing much, if anything at all” - it all depends on expectations :)

What is needed is a clutch pack like in the RDU, and some preload so the clutch can bite and balance torque even when a wheel has absolutely zero traction.

The Drexler model I have on my car is this one:Limited slip differential Ford. It fits like a glove but be prepared to redo the bearing preload which implies sourcing shims, and (maybe) to deal with the bolt kit as the one that came with the diff had heads a tad bit too large and I got some interferences. Nothing that cannot be solved by using new Ford bolts though so not an actual problem.

345470


345471


You just get the diff, the other parts on that pic were sourced separately.

The setup I asked them to build for me includes 45/60 ramps and 40N preload. Happy to discuss if anyone is interested to know what that means.

The diff was a tad harsh at first but I forgot it was there after a bit of running-in. What I mean by that is no special effects in the steering or anything crazy. I used the recommended oil (Ravenol Racing Gear Oil) and the diff is doing what it’s supposed to do, and quite brilliantly. Not much noise, just the humming under torque while cornering (the clutch’s noise) and the typical tik tik tik at high steering angles that basically just says the diff is doing it’s thing.

Now I’m battling with RDU tunes to find something that complements it perfectly but overall is a good improvement.

As a side note I have used Quaife ATB front and rear on another (comparable) car, an Escort Cosworth with 400hp. Both removed after the first winter and replaced by Titan TractionMaster plates diffs and never looked back. I also competed in an Escort Maxi Gr. A (F2, 2.0 N/A FWD) with a Quaife MkII 6-speed sequential and their “race” ATB with friction washers and the only thing I want to say is: never again. I’ve also competed with ZF (FWD) and SADEV (4WD) diffs so I think I can say from direct experience the Drexler is legit 😁
 
#192 ·
Unless you drive on snow or any surface with vastly uneven traction and lots of power. This is why you don’t see helical diffs on any race car.

Don’t get me wrong, helicals are great to even out slight differences in traction, like when a wheel is on the dry and another on a humid patch. They even out nicely and do improve traction in mild, everyday cases. I’d recommend them for taxis and ambulances, even fire trucks.

For an RS with a tune or worse, they don’t do much and with enough power and/or uneven enough surface the traction can swing left to right completely randomly as open diffs do. Just try a launch in a 90° corner on any surface and tell me how it feels.
 
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