Just purchased my sti, wanted to learn more about the driver control differential can any one tell me the advantages of using manual settings?
chris sparks
the dccd when put in manual lets the driver adjust the power to eitha the front or rear wheels....for example 40% up front and 60% to the rear or vice versa
geez, there is WAY too much confusion about the DCCD.
it will not affect mileage in any way, unless you lock it and drive in circles.
the big myth:
"you can adjust power distribution front and rear."
this is NOT true. the differential gearing physically sends 65% of the power to the rear, and 35% of the power to the front. this cannot be changed without replacing the whole diff unit, period.
truth:
"you can adjust the limited slip of the center diff."
the limited slip is adjustable. you adjust how much of an effect it has between the front and rear drive axles. this is how it works:
auto:
it stays "open" until the front wheels or the rear wheels slip. the front or rear drive axles will spin at different speeds, and immediately the limited slip effect tightens. before you notice, you get the magic traction the STi is known for. this happens WAY faster than a human can react, so for 99% of driving, LEAVE IT IN AUTO!
manual: full rear: (open)
the diff operates normally without any additional effect from the limited slip. if the front or rear wheels break loose the diff is working WAY overtime, and thus, is overheating, this isn't good either.
manual: partial rear:
the diff operates normally but with an adjustable effect from the limited slip. if the front or rear drive axles begin to spin at different speeds, the limites slip begins to "grab". the amount if "grab" is what is adjustable, and it will hold at that amount no matter what the circumstances.
manual: full forward: (50/50 or lock)
this is called a 50/50 or lock, because both drive shafts are locked to gether. (its not literally locked, but the diff is "grabbing" as hard as it can no matter what the situation. so, if the diff is set to full forward, or "locked," then its obviously sending 100% of the power to both the front, and to the rear, because the two drive shafts can't spin at different speeds. so they call it 50/50 or locked.
the easiest way to explain how the DCCD works, is imagine you're holding up a heavy object by two ropes, one is tied to each end, and both ropes are in the same hand. a large rops is holding 65% of the weight, and a smaller rope is holding 35% of the weight. if one begins to slip, your grip tightens. thats it!
if you go to a manual setting, you hold the ropes at a given force no matter what the circumstances are.
this can be bad, because if the front and rear drive shafts are being held open or at a set force, the diff may spin too quickly, which will cause it to overheat. this is also bad because when you sharply at low speeds, you're not letting the diff do its job. the front driveshaft will need to spin faster because its turning arc is larger. if its set to manual, and is at any setting other than full rear (open), the diff itself is trying to fight what it was designed to do, and the driveshafts and wheels are getting the rigid after effects. they will clunk and bind because they are trying to fight back.
so again, just leave it in auto, unless you're drag racing, then full lock but ONLY for the run down the straight. if you try to turn, the car will clunk, bind up, and buck.
it will not affect mileage in any way, unless you lock it and drive in circles.
the big myth:
"you can adjust power distribution front and rear."
this is NOT true. the differential gearing physically sends 65% of the power to the rear, and 35% of the power to the front. this cannot be changed without replacing the whole diff unit, period.
truth:
"you can adjust the limited slip of the center diff."
the limited slip is adjustable. you adjust how much of an effect it has between the front and rear drive axles. this is how it works:
auto:
it stays "open" until the front wheels or the rear wheels slip. the front or rear drive axles will spin at different speeds, and immediately the limited slip effect tightens. before you notice, you get the magic traction the STi is known for. this happens WAY faster than a human can react, so for 99% of driving, LEAVE IT IN AUTO!
manual: full rear: (open)
the diff operates normally without any additional effect from the limited slip. if the front or rear wheels break loose the diff is working WAY overtime, and thus, is overheating, this isn't good either.
manual: partial rear:
the diff operates normally but with an adjustable effect from the limited slip. if the front or rear drive axles begin to spin at different speeds, the limites slip begins to "grab". the amount if "grab" is what is adjustable, and it will hold at that amount no matter what the circumstances.
manual: full forward: (50/50 or lock)
this is called a 50/50 or lock, because both drive shafts are locked to gether. (its not literally locked, but the diff is "grabbing" as hard as it can no matter what the situation. so, if the diff is set to full forward, or "locked," then its obviously sending 100% of the power to both the front, and to the rear, because the two drive shafts can't spin at different speeds. so they call it 50/50 or locked.
the easiest way to explain how the DCCD works, is imagine you're holding up a heavy object by two ropes, one is tied to each end, and both ropes are in the same hand. a large rops is holding 65% of the weight, and a smaller rope is holding 35% of the weight. if one begins to slip, your grip tightens. thats it!
if you go to a manual setting, you hold the ropes at a given force no matter what the circumstances are.
this can be bad, because if the front and rear drive shafts are being held open or at a set force, the diff may spin too quickly, which will cause it to overheat. this is also bad because when you sharply at low speeds, you're not letting the diff do its job. the front driveshaft will need to spin faster because its turning arc is larger. if its set to manual, and is at any setting other than full rear (open), the diff itself is trying to fight what it was designed to do, and the driveshafts and wheels are getting the rigid after effects. they will clunk and bind because they are trying to fight back.
so again, just leave it in auto, unless you're drag racing, then full lock but ONLY for the run down the straight. if you try to turn, the car will clunk, bind up, and buck.
Nice write-up, thanks. I was also under the myth school of thought since that is how my dealer explained it to me.
Question: Everything I have read about the DCCD (forums, mags, etc.) concludes that the car performs at its best when left in Auto mode and should be left there 99% of the time even as you suggested. Why then do we even have it if its best to let the computer do its thing? Some on the forums have suggested that the different modes are suited for autoX use but the numbers still suggest otherwise (ie. auto mode is still better, even for autoX). Is it just a selling gimmick or an option to brag about?
Question: Everything I have read about the DCCD (forums, mags, etc.) concludes that the car performs at its best when left in Auto mode and should be left there 99% of the time even as you suggested. Why then do we even have it if its best to let the computer do its thing? Some on the forums have suggested that the different modes are suited for autoX use but the numbers still suggest otherwise (ie. auto mode is still better, even for autoX). Is it just a selling gimmick or an option to brag about?
remember the impreza's heritage. its a rally car. rally cars typically drive on unfavorable surfaces (read: slippery). under these conditions it is possible to alter the car's handling more noticably by altering the slip factor of the center diff.. so, for the average joe that doesn't compete in the WRC, traction during snow driving can be improved because the center diff is already clamped tighter than normal open operation, and it will help resist only the rear wheels spinning. you'll have to apply enough power to break all 4 wheels loose instead of just 2 where then the system suddenly fights to regain lost traction. with the adjustability, its a known and controlled difference.
does that help?
does that help?
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