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Old 05-13-2011, 02:41 PM   #1
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Default front diff on mi4lp

guys, bit confused!!!

been out of the game for the last few years, since i came back everyone is using a spool!

i've gotta say, im mot there biggest fan!! i dont like the way the car feels, makes it feel like the car is front wheel drive and to be honest, i dont think it suits my style of driving!

i can understand people saying the are the quickest round a track, but what confuses me is why on carpet with foams do people run a diff in the front, especially in the states?

i've heard that ball diffs cant handle the power that the new brushless systems kick out, but surely if this was the case, foams on a grippy carpet track with a 4.5t motor will be the worst case scenario? yet as i mentioned above, a diff is whats used in this circumstance.

why would a diff work ok with foams, but not with rubbers on a grippy carpet track? again, i can understand if traction isnt there in the first place, but with the mi4 i find people trying to lose grip as the car generates so much.

i'll be interested to hear the thoughts from the guys in the states to see what they've got to say. a spool just seems to go against any engineering practices!!,

mark
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Old 05-13-2011, 02:55 PM   #2
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it has mainly to do with the traction (slip) curve of foam versus rubber tires, rather than durability. if you can get the steering out of a front diff on rubber tires, then by all means run it. diffs are easier on the transmission and reduce the front end chatter brought about by the cvd joint at extreme steering angles. however, most guys find it difficult to be fast (truly fast) with a standard front diff in the car.

a good compromise, right now, is running a front gear diff packed with between 100 and 500K oil. this will allow for the steering that most need, but offers some of the characteristics of a front diff. it's softer on center, but will roll more over the front end than a locked front axle (spool).

before you hock the spool, try getting a better setup with it. when the setup is good, the car will no longer feel like the front axle is pulling the rest of it around. doing this will give you a better feel for how a (gear) diff changes the car when you decide to go that way.

like anything, it's a matter of tradeoffs. rarely will you find a tuning aid that is all positive. set your car up around whichever you choose, and if the steering is there, the lap times should be as well.
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Old 05-13-2011, 03:26 PM   #3
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man that reply was quick!!

funnily enough, i've just got myself a gear diff with the intention of trying to fit it in the front.......not as easy as it sounds!

the main problem i have with a spool is waaaayyy too much steering, then the back end losing traction out of the corner until the front finally pulls it straight.

ive got a testing session in a couple of weeks at an indoor carpet track that is known for having loads of traction, last time i went i couldnt get rid of enough steering until i turned my steering rates down to 70%!

the idea of a gear diff with really heavy oil sounds like a solution, as like you said it potentially will give the best of both worlds!

have you seen a gear diff i the front? if so, how did it go?
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Old 05-13-2011, 03:59 PM   #4
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the heavy gear diff is the rage in the states right now, as we run on a lot of tight carpet tracks. that might be where it shines the most. i've recently gone back/forth so the qualities of each are still pretty fresh .. (not that we should at any point allow ourselves to forget what we've tested/learned).

thing is, it's not as simple as one versus the other since you can effectively dampen the 'diff' action from zero (locked) to full (freewheeling). personally, i didn't find the 300/500K front diff to solve any real problems or induce them either. it's subtle for the casual driver. and to me it wasn't just "how much" but "how" the car changed. the slight diff action actually allows the car to turn a bit tighter off power and on, in my experience. while the spool pulls the car forward a bit more during cornering, causing a bit of a larger turning radius.

honestly, before you play with the gear diff (which, incidentally might be tough to cram into the narrow bulkhead spacing of an mi4 if you don't have a purpose built unit), i would advise you to solve the problem you're having with the spool in. not that you're asking, but to me, the on-power rotation sounds like a rear end issue. too little toe, too tight a diff (or it's roached), or too large a rear piston hole. there are a multitude of other alignments you can tweak, but these three are what i would call the 'game changers' if they are out of whack.

i guess a simple analysis can be performed by observing how much off-power steering you have. anything other than a spool is going to increase your off-power steering or cause the rear to lose some grip (synonymous to me). if your car can't afford that, then swapping the spool is likely to give you another set of problems to solve ...
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