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.
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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.