2BWise

Drive train. Everything from the clutch back.

mark kibort

depends on if its on acceleration or deceleration.

decel would be the inertial of what is being reflected to the driveline after the transmission toward the engine.
accel would be the engine and the driveline before the transmission.

mark kibort

Ironic, because that technique usually makes cars end up on the track, LOOKING like your Avitar picture!!! all bent out of shape, and "upset"

erioshi

... naw, never mind ... the gulf between reality, perceptions, prejudices and pixel driven perfection feels like it is just too great to overcome here ... Corner-carvers seems to have nothing over this sub-forum when it comes to swinging ones pixielated "bravado".

I'm glad you so carefully clarified your perception of what is actually happening in the car before jumping in. As you know all car, track and driving combinations are universal and interchangeable, right?

It's also a good thing there are never any differences in what we perceive someone to be saying and what they may actually be trying to communicate. English is infallibly precise. That's why the practice of law is completely free of conflict, misunderstandings, the need for clarifications, etc.

Based on your RennPoints history of a 47% podium finish .. but only scoring podiums where there were 3 cars or less in your field .. I will from now on consider you the absolute, de-facto, un-argument-able, expert on all things racing and race track related.

RennPoints link:
http://www.rennpoints.com/driverhistory/?racer=2840

Yes, you are a driving instructor. So what .. BTDT too.

Wow .. I really seem to have jumped in with booth feet here. Guess I'm having a "grumpy" morning. Looks like I need to keep myself out of here. Sorry if I offended.

KaiB

Not a thing bent out of shape there at all my boy...did that 5 times in a row and never spilled a drop of beer.

mark kibort

That was a cliche' for "out of control".... or better said, you were controlling your car that was bent out of shape.

Anyway, I'm sure you did. after the 5th time, i would have you brought in for a little discussion about car control.

Please, take your drifting to the hip hop events at a parking lot near you!
its nothing to be proud of. It means, in racer lingo.... you blew it!

Hey "my boy", I love to get sideways and actually pour my passenger one while doing so.... but i save that for the snow covered roads!

sbelles

LOL. As long as we got that straight.

sbelles

Now you know I was just yanking your chain right Mark?

2BWise

No. It's a resultant of the driveline inertia; having to spin the entire driveline to match the engine speed. That is what produces the force that breaks the driveline. This makes it more probable that failure occurs in the lower gears than the higher as the inertial force from the speed mismatch is higher at the lower speeds.

mark kibort

well, i the end, there has to be two equal forces. the driveline spinning up isnt what creates any noteworty force, its the spinning up of the engine to meet driveline speed in a downshift. That happens just by moving the shift lever to the lower gear. then the clutch is released. how fast that happens, dictates the force. its the rate of change of KE. Its the force that the tires are going to act on the road because the inertial forces of the engine have to be brought up to a speed, much higher than it is at currently. (i.e. too low an RPM to match the downshifted driveline speed in the lower gear).

Clearly, the car moving at the higher rate of speed, is imparting a force to the tires and the road has provided an equal and opposite force, and now the engine has to try and match this equal and opposite force, and it cant, so the driveline snaps at the crank, clutch, short shaft, driveline, or input shaft to the transmission.

thats why as you downshift into an even lower gear, the forces are much less. and you dont have the chance to break drivelines is the same situation happens in 2nd or 1st. the rate of KE change is less, so the engine inertia being the same, is accelerated to a lower speed, and at a lower rate because there is less force on the driveline to accelerate the engine to the matching RPM.

example....

you missmatch 2nd to 1st downshift, and pop the clutch out..
what happens?

thats a 8:1 reduction coming from a 11:1 reduction in the gear box. the force starts at the rear tires and their Cf. (mu) if it takes 4000lbs to make a tire break free, thats the force at which its spinning up the engine's inertia.... that force would be 4000ft-lbs / 8:1 or near 500ft-lbs.

if you measured how fast the engine spun up, the torque would be 500ft-lbs. the driveline could survive. more than likely.

now, do the same in 4th to 3rd. get a chirp at 3rd gear by dumping the clutch and the REFLEcTED inertial of the entire car is at the tire on the road. even though the break away force is still 4000lbs, you are going much faster! (much higher KE). the gear ratio is less, but the reflected torque to the driveline is 4000lbs / 5:1. now you are talking 800ft-lbs. this force is what breaks the driveline components. the CV joiints, half shafts are not seeing anything higher than what they see when breaking the wheels free under acceleration.

Yes, the engine is applying an equall and opposite force, or trying to and it cant, because the the rate of acceleration is so great, the torque exceeds the twisting limits of the driveline and then it breaks!

so, i think you are thinking about it a little backward.

accelerating, you are right. you speed shift into 2nd or 3rd, and the engine being brought down so quickly, is the inertial force that generates stress on the driveline, and CV joint and axles. more the axles, as thats why they bust at the drag strip. all that engine inertia dumps through high gear ratios to the tires. the weak link then becomes the axles, not the driveline, although both are subjected to higher than normal forces.

jdistefa

Easy fella. Given what you posted about your preferred driving technique I suspect you could learn a thing or two from Scott.

erioshi

Have a nice day.

I walk gears in a sequential .. with a traditional box it's just wasted time & energy. At least if the car has real brakes & tires and can use truly use them. If I can't find the right rev match from neutral in any appropriate gear to the matching speed .. immediately and at will .. without upsetting the chassis .. I haven't spent enough time the car yet.

I have no interest in playing row, row, row my boat.

KaiB

Wow!

Do you work at being a jerk, or does it come naturally.

You must be quite the shoe.

erioshi

I have excellent help here.

Another possibility occurs to me. There could be a car set-up problem.

If a car is gaining a benefit from engine braking, assuming the driver is making maximum use of all the braking force available through the brake pedal, then the braking system of the car is not at its optimal configuration.

I'd look to brake bias, pads & rotors (sizes, compounds), wheel & tire set-up, springs & dampers, etc.

In any braking event, 100% of the time at effective maximum braking capacity should be more efficient then maximum effective braking capacity interrupted when where's no engine braking (during downshifts). Phiziks, right?

jdistefa

Somebody kill me. Do it quickly. Please.