[akira]

Blip/downshift

1. Disengage clutch
2. Blip throttle for rev match
3. Downshift
4. Release clutch

I've been doing steps 1, 3, 2, then 4, meaning
1. Disengage clutch
3. Downshift
2. Blip throttle for rev match
4. Release clutch


but I guess that i've heard that doing it 1,2,3,4 is better for the synchros... Obviously this is all done in a split second, but i'm still a newbie and not mechanically inclined, so if someone could explain what's actually going on internally that would be great! I've gone to howstuffworks.com to read up on this which has also been helpful..

 

[Matty]

anything wrong with doing

1
then
2 and 3
then
4

?

 

[akira]

Since it all takes place within a split second, i assume it's ok, i'm just trying to understand exactly what's going on with the input/output shaft, tranmission, synchros, etc during 2 and 3 and if it's better to do 2 or 3 first and why (again understanding why and what's going on)...

anything wrong with doing

1
then
2 and 3
then
4

?

 

[lee]

Blipping the throttle raises the rpm's of the gears and shifter dogs and helps them to mesh alot smoother. It also has the effect of raising the eng rpm so when you let the clutch out the rpm is better matched to the lower gear selected. There is a school of thought that promotes "clutchless" shifting but I believe that is better suited to up and not down shifting. I also do not practice that technique. I'm sure you'll hear from others before this thread runs out.

 

[silentbob]

Motorcycle transmissions do not have synchros like a car. Blipping the throttle after pulling in the clutch and before shifting really won't do anything. What you need to do is to blip the throttle before letting the clutch out to prevent rear wheel lockup on aggressive downshifting.

 

[akira]

great, thanks for clarifying. so it sounds like 2 and 3 are interchangeable with no negative effects. thanks.

Motorcycle transmissions do not have synchros like a car. Blipping the throttle after pulling in the clutch and before shifting really won't do anything. What you need to do is to blip the throttle before letting the clutch out to prevent rear wheel lockup on aggressive downshifting.

 

[Ten-6]

"Bliping" and down shifting should happen simultaneously for a smooth shift, it just takes practice.

 

[Accord]

It's the same thing as a heel/toe downshift on a car.

 

[Yossarian]

I just blip the throttle at the same time I downshift.

To me, it's only three steps.

1. disengage clutch
2. blip throttle while downshifting
3. reengage clutch

4. hang on while the rear wheel hops if you've gone from 2 to 1 at too high a speed.

Okay, four steps.

 

[lee]

Motorcycle transmissions do not have synchros like a car. Blipping the throttle after pulling in the clutch and before shifting really won't do anything. What you need to do is to blip the throttle before letting the clutch out to prevent rear wheel lockup on aggressive downshifting.

Really? Then why do I have two bikes sitting down there that do?

 

[brettc63]

A good question

This is a good question in the sense that it makes us/me actually think about what it is we do unconsciously and why do we do it 'that way'.

Originally Posted by silentbob
Motorcycle transmissions do not have synchros like a car. .

Really? Then why do I have two bikes sitting down there that do?

I've always assumed that motorcycles didn't have syncro and never really gave it much thought after that.
So cloudrider - are you saying you have motorcycles with syncro? If YES: then you 'learn something new everyday', what makes and models?? I'm assuming that they are some sort of 'cruiser' and maybe not sports bikes as such. Yes/no ??
(Syncromesh, as I understand it, is yet another mini-clutch(cone type) inside the gearbox between the dog gear and the rest of the gears although I'm not sure how this works in a constant mesh bike gearbox)

Originally Posted by silentbob
......... Blipping the throttle after pulling in the clutch and before shifting really won't do anything.

At first I thought I disagreed but now I think you are right, and in the end it is all for the benefit of the clutch by matching the 'new' rpm of the engine for the lower gear when the clutch is let out.
Originally Posted by silentbob
What you need to do is to blip the throttle before letting the clutch
out to prevent rear wheel lockup on aggressive downshifting.
Basically - So yeh Matty, Yossarian and Ten-6 - 2 & 3 are (in my mind) happening at the same time.

Cloudrider mentioned clutchless shifting which is yet another facet of this whole question. Akira, if you still haven't satisfied your thirst for knowledge - Link: http://www.ducatispot.com/forum/showthread.php?t=277&highlight=clutchless

 

[lee]

I'm afraid I misled you when I said I have two that do. They're HD five speeds which I modified to bring the rpm of the shifter dogs and gear up to that of the gear the dogs/gear are about to engage. Gets rid of that awful "clunking" HD's have when changing gears. Silentbob's right. Bikes don't have syncros. Stupid response on my part.

 

[brettc63]

OK - no worries. Thanks.

 

[akira]

thanks, brettc63,

check this link out. i think it'll help visualize the synchros i've learned a lot from this website!

http://auto.howstuffworks.com/transmission3.htm

(Syncromesh, as I understand it, is yet another mini-clutch(cone type) inside the gearbox between the dog gear and the rest of the gears although I'm not sure how this works in a constant mesh bike gearbox)

 

[FlyerLen]

I just blip the throttle at the same time I downshift.

To me, it's only three steps.

1. disengage clutch
2. blip throttle while downshifting
3. reengage clutch

4. hang on while the rear wheel hops if you've gone from 2 to 1 at too high a speed.

Okay, four steps.

I agree, I think the blip and letting the clutch out have to happen almost simultaneously; if you separate them 1-2-3-4, you will drop too many revs by the time you let the clutch out and it’s all a wasted effort. I could be wrong, though (I’m MUCH better at it in a car than on my bike…)

 

[akira]

well, i guess i knew this was all taking place within a matter of a split second. just was curious about the mechanics of what's actually happening internally, and if there's a difference between doing 2->3 or 3->2 within the split second. in other words, when you say 'almost simultaneously', what's the difference (mechanically) between this period of time.
thanks, flyerlen!

I agree, I think the blip and letting the clutch out have to happen almost simultaneously; if you separate them 1-2-3-4, you will drop too many revs by the time you let the clutch out and it’s all a wasted effort. I could be wrong, though (I’m MUCH better at it in a car than on my bike…)

 

[akira]

another great link with transmission on a motorcycle (original link is for auto)

http://auto.howstuffworks.com/framed.htm?parent=transmission.htm&url=http://www.dansmc.com/gearbox.htm

thanks, brettc63,

check this link out. i think it'll help visualize the synchros i've learned a lot from this website!

http://auto.howstuffworks.com/transmission3.htm

 

[CW AF 03]

You don't necessarily need to blip the throttle if you feed the clutch out smoothly and keep the time between pulling it in and letting it out to a minimum. I usually make my first downshift into a corner before I even roll off the gas. Seems to work out ok and the bike doesn't get upset in the process.

 

[duckster]

with a constant mesh gearbox, you have 5 gears spinning on the countershaft at different speeds and only one at a time engaged by a shifter dog actually transmitting power.

Its important to blip the throttle before actually shifting gears so that the shifter dog and gear are at similar speeds as the dog engages. Otherwise you get a bigger "clunk"
as the gear and the input shaft locks up to countershaft speed. In practice the blip and shift are nearly simultaneous.
If you shift first and then blip, you still get the gear clunk but you avoid the engine overrun when the clutch is released. Its much smoother to avoid both by shifting after the blip.

Upshifting with no clutch can be done very smoothly by applying a little upshifting pressure on the gearshift and then rolling off the throttle briefly. As long as the throttle is on, the shifter dog won't move because it is under load. when the throttle is relaxed, the input shaft slows momentarily allowing the engaged dog to slip out and the next gear dog to slip into the next higher gear as the shaft speed matches the gearspeed.
As soon as the shifter pedal moves, indicating the shift has happened, you get back on the gas again smooth as silk.

 

[ahastings]

......
Its important to blip the throttle before actually shifting gears so that the shifter dog and gear are at similar speeds as the dog engages. Otherwise you get a bigger "clunk"
as the gear and the input shaft locks up to countershaft speed. In practice the blip and shift are nearly simultaneous.
If you shift first and then blip, you still get the gear clunk but you avoid the engine overrun when the clutch is released. Its much smoother to avoid both by shifting after the blip.

This doesn't make sense, because the transmission is disconnected from the engine when you blip because the clutch is pulled in. I think you are confused about how a sportbike trans. works. The "shifter dogs" as you called them are just protrusions on the side of the gears that engage with each other as the gears are slid side to side by the shift forks when you change gears. That is why it is called a constant mesh gearbox as the gears on the input and output shafts are always meshed with each other.
The purpose of blipping on downshifts has nothing to do with how the gear dogs mesh, it is solely to match rpms so when you let the clutch back out you don't get wheel hop or a sudden spike in RPM. In racing blipping and downshifting is done in one motion because you are doing everything as quickly as possible.
I don't use that technique anymore when I am racing. I just feed the clutch out slowly after downshifts effectively creating a manual slipper clutch. This is when riding a bike without a slipper clutch.
If you have a slipper clutch than the whole blipping thing is a moot point.