RE: Rota rims and Nitto tires
ZenBoy said:
Sands said:
Open diffs don't do this, which is 99% of all RWD cars out there.
My RWD car sure doesn't do this, and it's got Positraction.
My 2000 2.5RS didn't do this, and it had a limited-slip rear differential.
The difference between those cars and my STi, at first glance at least, is that the STi has a limited-slip front differential as well.
The rate of lock up totaly depends on the ramp angles of the plates in the diff. So just because a car has a LSD doesn't mean it will behave just like another car with an LSD.
If you have a car wtih a posi rear end, which if I'm not mistaken is a locker, I'll bet it's a muscle car. Without any other info, I'll bet it will understeer like a pig with or without the posi rear end. (Does the posi need to be locked manually?) Provided you don't power oversteer that is. :lol:
ZenBoy said:
mccullpl said:
I figured it was the front diff starting to lock under power (or unlock when letting off the gas)., forcing the front wheels to try to turn at the same speed...I'm certainly not an ME, but it kinda makes sense to me. It would also explain why nobody notices it on a rear drive car, or a WRX. (no front diff).
I think
mccullpl has spelled out what I've been thinking as well - it's the limited-slip front diff. Under throttle, the diff is starting to lock up when it has enough torque distributed to it. This would also explain why adjusting the torque bias to the rear of the car helps the problem so much.
Zen
Try going through the same corner at the about same speed (say 45 mph or so) a few times with the following conditions (needs to be a fairly aggressive corner and DCCD in auto):
1. gearbox in neutral, just coasting
2. gearbox in gear, foot off the clutch and trailing throttle
3. gearbox in gear, foot off the clutch and neutral throttle (just enough to not slow down, but not loading up the gearbox)
4. in gear, really hard on the gas
What you should feel:
1. Should be totaly transparent and shouldn't feel the diffs at all
2. Front diff should start to stiffen up a little since the engine brake will put a load on the front lsd. Should start to push and you'll feel the center diff move torque around.
3. Line should be tight and car should rotate, but you'll feel the center diff move torque around
4. Get ready to counter steer! Power totaly overcomes the front diffs tendency to lock - but since you're under power, all the wheels are pulling, not slowing the car down.
(I found a pdf file with a more technical description of the DCCD action, but I can't track it down right now - which is what I'm basing the info on above)
From my track experience (all on a e39 bmw) the hardest thing I've had to learn was to get on the gas sooner and harder then I thought the car could do. The rear end will dig down and get more grip then you thought, all without making the car push. In fact it rotates better. You get the right amount of lateral slip in the rear tires to rotate the car, even though the front end it unloaded (which normally will make it loose grip)
The sti is the same, but the car expects you to drive in a certain way. The computer needs to have a certain progression of brake, transition and power.
The best way to describe it is to drive the car like a FWD car on entry and a RWD car on exit - but you have the FWD half to pully you out of an oversteer on exit. [edit] the difference to a non-lsd fwd car to the STI is the trailing throttle will tend to stiffen up the front LSD, which promote push, so you need at least a neutral throttle to free it up (or out of gear, which is stupid if you're on the track) [/edit]