Quote:
Originally Posted by OhondaU
Ok, provided the clutch is completely released and you are currently in 3rd gear...
There is no input from the engine, so the output shaft will be driven by the rolling wheels. At this point this is your only source of incoming force into the transmission. The output shaft will be driving the input shaft, which is spinning close to whatever RPM the engine was at when you released the clutch. At this point whenever you upshift, the synchros have the wonderful job of slowing all the rotating mass of the input shaft and all the gears riding on it to the speed dictated by the new gear ratio. So if you are at say 60 mph in 3rd and shift to 6th the input shaft will have to slow from ~6000rpm to ~2700rpm. Now if you were in 5th gear at 60mph and shifted into 6th the drop would only be from ~3600rpm to ~2700rpm, quite a bit less energy to dissipate. So the skip-shifting means more energy dissipation which is more heat generated which is more wear created. Seeing as the equation for rotational kinetic energy is: (1/2)*I*omega^2, where omega is your angular velocity (RPMs). It would seem going from the 5th-6th shift of 900rpm drop to a 3rd-6th shift with a drop of 3300rpms would result in having to dissipate 7 times the amount of energy as a normal shift! So instead of your 6th gear synchro lasting, oh say 210,000 miles, it would only last 30,000 miles!
Now that is entirely a theoretical discussion and real life is infinitely more complex than what is represented above, your shifting habits, the type of MTF your run, and even the speed at which you skip-shift among many others will all affect the mileage you get from your transmission.
The safest bet, double clutch your upshift if you are going to be skipping that many gears. And if you don't, as long as these aren't redline skip shifts under high load, you should be ok.
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with double clutch upshifting, alls you have to do is release the clutch in neutral for a second right? so this would be much easier than double clutch downshifting.. i can easily do this since im coasting anyways and ready to put it into 6th.. so clutch in > neutral > clutch out for 1 second > clutch in > 6th > clutch out.. basically your are engine braking the transmission, but since its in neutral.. right?
Quote:
Originally Posted by bangmonsta
Great explanations, you seem to understand this stuff. I'm still a bit confused though. Could you explain the synchros in more detail? I've never quiet understood what happens to them during shifting. I only know they help the dog teeth in the collar connect to the gears, but I dont see what exactly happens when you shift.
So far all I know about the engine is that it's connected to the transmission via the clutch. Transmission picks the gear by using selectors, then there is a differential connected to the transmission. To put it short, here's what I know on why/how a car moves.
Engine -> crankshaft -> flywheel -> clutch -> transmission -> differential -> ????? ->wheels. I have no clue where that differential go or what it does, howstuffworks.com. Got any good reading material? I'd like to complete my little arrow diagram and understand it all lol. I think the input shaft comes from the engine, and output shaft goes to the differential?
I know rev matching helps keep the clutch healthy by matching the flywheel's speed to the speed the clutch should be spinning at and reducing friction wear, but I've always thought that rev matching would also save the synchros
Also, when you say clutch is "released", as mentioned on top. Are you saying that clutch pedal is down, meaning we're free to shift? Or gear is engaged?
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99% of the time "clutch released" means your foot is off the pedal, this guy just used that 1% to confuse everybody
Quote:
Originally Posted by OhondaU
Ok, here's a short article on transmission on howstuffworks.com
Howstuffworks "How Manual Transmissions Work"
You will probably be most interested in part 4.
Getting more in depth and answering your other questions probably deserves a thread on its own, especially the part on differentials (a subject that is misunderstood by most).
And when I said the clutch is "released" I meant the pedal is all the way down and the clutch is disconnected from the flywheel. |
like i said above, 99% of the time your talking about the clutch, you are referring to the pedal; its probably best not to refer to the clutch itself, as this gets confusing.. clutch in / clutch depressed / clutch down = pedal to the floor; clutch out / clutch released / clutch up = foot off pedal.. when we talk about steering, we refer to the steering wheel, when we talk about gas, we refer to the gas pedal, etc