DashKid

iTrader: (2)

There are theories on this. Some people say it is o.k to skip gears when down shifting long as you get the rev matching right. For example you don't want to go from 6th to 3rd at 70 mph without rev matching.

Some people say its bad in general to skip gears period.

crazjayz

Skipping gears is fine, but rev-match is much harder. If you're doing 2k in 5th doing about 60mph, do you know what rpm you have to be at in 3rd? It's not just a blip of the throttle anymore, but rather revving to something like 6-6.5k rpm. That's what makes it harder.

mastorian

rev match ftw!

kieranlavin

nah, automatic transmissions ftw

Mike

iTrader: (1)

The ones who tell you it is fine are the ones who do not understand how the drivetrain really works. Basically it boils down to this

Engine ->clutch<- Midshaft ->transmission<- wheels

Your clutch connects the midshaft and engine together, and your trans connects the midshaft and wheels together. This way, if the Clutch is disengaged, or the trans is in neutral, there is a break in the "train" and you cannot put power down to the ground through the wheels.

The Clutch allows for a difference between the engine and midshaft speed to be "scrubbed off". E.g. when you start from a dead stop, you clutch in, disconnecting the engine and midshaft, go into gear, connecting the midshaft and wheels. Remember, the midshaft was spinning at the same speed as the engine before you clutched in, so the synchros are bringing down midshaft speed to the appropriate speed by slipping to match a ratio with the wheels, Zero in this case since you're stopped. Then you start slipping the clutch to allow power to go down to the wheels until you're going fast enough that you can stop slipping.

Now, lets start with clutch load. If you do a redline start, slipping the clutch, it's obviously going to put much more load (and consequently wear) on the clutch, right? Going to that 6th gear synchro, if you did a redline shift from 5th gear, you'll get roughly a 1800 RPM drop. The 6th gear synchro was designed specifically with that load in mind; during normal driving conditions, the synchro should never match up more than that, and usually much less.

When you skip from say.. a redline 3rd gear shift to 6th, you're now putting a ~4000 RPM load on the synchros. This energy works in powers; you're putting not a ~2.3x load, but a ~2.3² amount in load, so in reality, close to 5x the load the synchros were designed for.

Instead, what you can do is Clutch in, move the shifter into 4th, then 5th, then 6th, and then clutch out. This breaks up that load into smaller increments. Yes, the engine is not connected, but the midshaft and trans are connecting every time you go into gear, and the synchros for each gear are doing a smaller portion of the work. Most importantly, the load each gear is taking on is one that the synchro is designed to handle.

Rev-matching and skipping gears are related, but have no direct effect on each other unless you're double clutching. You can rev-match, but it only brings the engine speed up to where it should be for that lower gear. The midshaft is still spinning at the lower RPM, and will be brought up by the synchros under an abnormally high load.

When I'm downshifting multiple gears, I still don't skip gears. The only REAL reason anyone would skip gears downshifting is if you're street racing; I doubt you'd ever need ALL 330 horses for an emergency maneuver. On the track, you can heel-toe downshift multiple times during braking with absolutely no affect on performance if you can do it well. If you're not doing some serious racing, you'll have ABS anyways.

DashKid

iTrader: (2)

Mike: I was talking about down shifting. Yes you should never skip a gear while shifting up to a gear that is bad in general but in down shifting if you can rev match down shift to a gear it won't do a lot of damage. On the other hand if you mess up on the rev matching than it does a world amount of damage depending the gear and rpm.

CrazyJayZ: It's called knowing your car. Actually, at 60 you can rev match to 2nd at 7k get that extra power and upshift to 3rd but like you said if you want to go to 3rd it should be about 6k-6.5k

Mike

iTrader: (1)

Downshifting and upshifting put the same type of load on the synchros, but downshifting a gear rarely creates as large of a RPM gap.

Revmatching does nothing to bring the midshaft speed up, which is what the synchros are doing. It only brings the engine speed up. Ever try to go into 1st at 30 mph? You can, if you gently push up long enough on the shift ****. You'll hear a whine that gets higher pitched. That's the synchros spinning up the midshaft up fast enough so that your trans can get into gear. Do you think revmatching a 2->1 shift will make it any easier to move your shift lever?

kRAM

iTrader: (1)

Thanks for some very helpful information.