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Why Do People Short Shift


aslcbr600
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I was just watching some youtube videos of the level 1 class and granted it's the level 1 class so it's not the more veteran CSS students. However I see this on other on bike videos too during races. Why do people short shift 3-4k rpms before redline? I also see them bringing in the power but then shifting at say 13k rpms out of 16k from 3rd to 4th then go up another 1-2k rpms and then shift again to 5th just to downshift 2 gears before the next turn......seems like a whole lot of wasted movement and time.

 

I also see GP guys shift mid corner but even pros make mistakes or have to adjust something on the spot mid turn to get the drive they need coming out of the exit. Although GP guys don't shift up 2 gears and waste 6k-7k rpms in the process either.

 

 

 

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There could be several reasons for short-shifting. For instance, if you already have more power than you can use in 4th gear, there is no reason to drop down into 3rd even if you have revs to spare. You can see that even in MotoGP racing. Also, at times they may use one gear too high - or even too low in the 2-stroke days - to save a shift or two.

 

 

For the bloke that does a few trackdays a year, short-shifting make sence for other reasons. Since doubling the rpm increase the stress on the engine by 8 times, you can see that pulling 16k rpm cause alot more wear than 13k rpm does. Fuel consumption also get up considerably when pulling those final rpm. The change in rpm is also less between gears the lower the rpm (although it's the same measured in per cent) making it easier to be smooth, good for control as well as life of tyres and drive train. It could also be that the rider shifts by ear and that his ears tell him that the engine is reving high enough.

 

I do not know what bike that is in the video, but even a rather peaky engine like theCBR600RR peak around13000 and power start to drop off past 15k rpm. Pulling to 16k would make for slower progress than shifting at 15k, and the difference between 13k and 15k rpm upshifts would not be worth much unless you're looking for a tenth or two per lap.

 

 

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Personally, I almost never short shift on the track, but my bike redlines at 9000 and the power peak extends from about 7000 to 9000, so I keep it up there and almost never drop below 6000 except in very slow corners. A lot of inline 4s peak well below redline so the top 2000 rpm or so are just there as "overrun" for convenience - sometimes you can use it to avoid having to shift, but you will have less power (and acceleration) if you run it up that high on the straights.

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I agree with the points made above; mainly that the peak power is around 13,500 rpm and you can feel the engine start to "fall off" somewhat after that, so it makes a lot of sense to keep the bike in the 10k - 13k range, because you get terrific power in that range. Some bikes (not the BMW) "nose over" sharply once you exceed peak power - I have a little 50cc two stroke that has a very narrow power band and drops off dramatically past a certain rpm.

 

Speaking specifically about Level 1 at the school, most riders are on the BMW for the first time, and often whatever they ride at home does not rev as high, have as much power, or go as fast in each gear as the 1000cc BMW. So, if they shift by the sound of the engine, they may shift early because it sounds over revved to them, or if they do it by sense of speed they might think that if they are going 70 mph they should be in 5th not 3rd! Also the BMW has incredible acceleration, so sometimes by the time it hits around 9,000rpm it is pulling hard enought that the rider either assumes that IS peak power or gets intimidated and doesn't want to go any higher. Also... the shift light is set pretty low on the school bikes, I think it comes on around 9-10,000 rpm. That is adjustable but the factory setting is somewhat low, presumably to reduce the wear and tear on the engine.

 

On my MD250, I sometimes short shift intentionally (on race starts, for example) to make SURE I don't hit the rev limiter, because on that bike if you hit the limiter you lose a TON of momentum. It is much better to shift a little too early than to hit that limiter.

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I understand the power band aspect of it, I guess my question is this. In a racing application is it better to waste time shifting up 2 gears when you have RPM left just to downshift back down 2 maybe 3 gears before the turn or even with the lack of upper RPM having to spend less time downshifting and still more time on the throttle before the turn.

 

Just seems to me like if you are spending more time on the shifting when you could be on the throttle longer would outweigh say the 10hp drop in peak RPM. In other words wouldn't I be faster if I spent 3 more seconds on the throttle and 1 second on the downshift before the turn rather then 3 seconds on the downshift and then hitting your turn in point, lean angle set, back on the throttle.

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I understand the power band aspect of it, I guess my question is this. In a racing application is it better to waste time shifting up 2 gears when you have RPM left just to downshift back down 2 maybe 3 gears before the turn or even with the lack of upper RPM having to spend less time downshifting and still more time on the throttle before the turn.

 

Just seems to me like if you are spending more time on the shifting when you could be on the throttle longer would outweigh say the 10hp drop in peak RPM. In other words wouldn't I be faster if I spent 3 more seconds on the throttle and 1 second on the downshift before the turn rather then 3 seconds on the downshift and then hitting your turn in point, lean angle set, back on the throttle.

 

There are so many variables in this, like the type of bike you ride, the characteristics of the power band, what sort of bikes you are racing against, etc., that there's probably no pat answer - you'd just have to use your judgement and/or an electronic timer to decide which ends up faster.

 

A very big issue, though, would be your own comfort level with shifting - how long does it take you, how reliably can you get the downshifts, how certain are you about which gear you ARE in and which gear you WANT to be in, are you comfortable with being leaned over and downshifting, does being on the brakes affect your downshift, etc.. If there is any hesitation at all on shifting, or if it is consuming attention you need for other things like judging entry speed, you might be better off NOT shifting to get that extra horsepower..

 

As as personal example, I am faced with this decision on one track where I race - I run out of 3rd gear in a short chute between a turn and a chicane. I can either go a little softer on my drive and stay in third, or pick up 4th but then almost immediately downshift going into a quick chicane. In that spot, I was feeling very rushed and sometimes missing the downshift (I use all clutchless downshifting and was not blipping the throttle consistently due to hard braking) so I decided I was better off just staying in third. That is, UNTIL a coach from the school showed me a better way to get the downshift. Once the uncertainty and rushed feeling of the downshift was gone, it became absolutely worth it to go up to 4th even though there wasn't much room. It made a difference in my laptime, and an even bigger difference in my race results because it is a great place to pass if you can get enough of a drive.

 

There is a braking/downshifting drill you can do off-track at the school. It can REALLY reduce the time and attention spent on shifting. You might try watching a video of Will (check the school website for the on board videos showing the tracks) and compare the time spent on a downshift to what you see in most riders' on board video, and you can see how much time it takes some riders to shift compared to pro racers.

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To add to this thread (not sure if it's been covered), I often use short shift if I'd otherwise have to shift mid turn when the bikes at big lean angles. Whilst it's ok to do this with moderate lean angles, at high lean, long turns where you're still winding the throttle on, I'd always short shift to remove that instability. It's rare, but at Jerez, turn two into 3 is a short shift because of this and also because you turn quickly from the right to the left hand side.

 

 

Bullet

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Those were pretty quick downshifts, what exactly is the drill or method? I am comfortable upshifting mid turn but I haven't done much downshifting mid turn because I feel there is a greater risk in upsetting the handling on a downshift rather then an upshift.

 

This has been covered pretty well in other threads, you might try searching "clutchless downshifting". Basically you want to blip the throttle to match RPMs and if you can go to clutchless downshifts, most riders find they can do them a lot faster than using the clutch. Once you get used to it, it's very fast and not having to mess with the clutch lever means one less thing to coordinate.

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There could be several reasons for short-shifting. For instance, if you already have more power than you can use in 4th gear, there is no reason to drop down into 3rd even if you have revs to spare. You can see that even in MotoGP racing. Also, at times they may use one gear too high - or even too low in the 2-stroke days - to save a shift or two.

 

 

For the bloke that does a few trackdays a year, short-shifting make sence for other reasons. Since doubling the rpm increase the stress on the engine by 8 times, you can see that pulling 16k rpm cause alot more wear than 13k rpm does. Fuel consumption also get up considerably when pulling those final rpm. The change in rpm is also less between gears the lower the rpm (although it's the same measured in per cent) making it easier to be smooth, good for control as well as life of tyres and drive train. It could also be that the rider shifts by ear and that his ears tell him that the engine is reving high enough.

 

I do not know what bike that is in the video, but even a rather peaky engine like theCBR600RR peak around13000 and power start to drop off past 15k rpm. Pulling to 16k would make for slower progress than shifting at 15k, and the difference between 13k and 15k rpm upshifts would not be worth much unless you're looking for a tenth or two per lap.

 

 

11ss_hon.jpg

 

 

 

http://images.motorc...ge/11ss_hon.jpg

 

 

 

 

Interested in where you get that data as my (abet outdated )SAE paper says piston/ring wear essentially doubles at top torque VS top horsepower.

 

looking at Triumpg'ws new inline 3's , i'd say its native to engine tune and design and not really a broad spectrum. :)

 

 

 

 

I'd concur with fuel consumption thou,

 

 

 

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Interested in where you get that data as my (abet outdated )SAE paper says piston/ring wear essentially doubles at top torque VS top horsepower.

 

 

 

 

 

 

 

That could be because BMEP or whatever they call it is at its peak at max torque, hence cylinder pressure is at its highest. Just speculating here.

 

 

However, the load I talked about was the mechanical load on the crank/conrod. That's not the same as wear rate going up 8 times, just that the physical forces acting on the moving parts increase by that amount. However, I do not have the personal knowledge to back this up - I read it in an articel written by Kevin Cameron. So it could be wrong for all I know :unsure:

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The only thing I can add are a couple of situations where I short shift, may help you understand where & why it may be used. And I don't usually run above 12,000rpm anyway (redline is 13,500rpm), but I put that down to mechanical sympathy. First situation I can think of is if I'm approaching a corner at the end of the straight and I rev it out a bit, I will run out of revs before my turn point, so that would mean shifting up a gear for only a short period on the throttle, followed very quickly by downshift/braking and turning. Putting all those actions so close together gets a bit too busy for me, so I began short shifting about mid way down the straight so I approach the corner with less distractions and more attention.

 

One other situation for me is on corner exit. In particular there is one slower 1st gear corner on my regular track that if taken in first gear the revs run out very soon on exit, and revving out first gear also tends to remove traction at the front wheel. wink.gif (Especially if the bike is not yet fully out of the corner and settled.) So I usually enter that corner in 2nd gear and focus on opening the throttle earlier and getting better drive that way.

 

I think the important thing in all of this is to recognise that just because a person is riding around hitting the limiter before each gear change, does not necessarily mean they're making best use of the throttle and rev range. Speaking personally I know that when I used to ride that way, it did feel much more "busy", but I was using so much of my attention looking at the tacho, watching for when to shift that I would arrive at the corner without much free attention. I am riding a whole lot faster now that I use my gear shifts to create free attention rather than trying to rev out each gear, and also short shifting for those other reasons mentioned. My speed improvement came from having more attention and using it on improving corner entry (and midcorner, exit) speed, not from necessarily twisting the throttle more on the straights. Something to think about. smile.gif

 

Just reading back that last paragraph, I keep coming back to that part about using gear shifts to create free attention... I like it! biggrin.gif

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First situation I can think of is if I'm approaching a corner at the end of the straight and I rev it out a bit, I will run out of revs before my turn point, so that would mean shifting up a gear for only a short period on the throttle, followed very quickly by downshift/braking and turning. Putting all those actions so close together gets a bit too busy for me, so I began short shifting about mid way down the straight so I approach the corner with less distractions and more attention.

 

Yes, exactly - perfect explanation. I do exactly that every lap of my home track, between T5 and T6. I'd suggest that this is one of the most common scenarios where short shifting helps the rider make time.

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The only thing I can add are a couple of situations where I short shift, may help you understand where & why it may be used. And I don't usually run above 12,000rpm anyway (redline is 13,500rpm), but I put that down to mechanical sympathy. First situation I can think of is if I'm approaching a corner at the end of the straight and I rev it out a bit, I will run out of revs before my turn point, so that would mean shifting up a gear for only a short period on the throttle, followed very quickly by downshift/braking and turning. Putting all those actions so close together gets a bit too busy for me, so I began short shifting about mid way down the straight so I approach the corner with less distractions and more attention.

 

One other situation for me is on corner exit. In particular there is one slower 1st gear corner on my regular track that if taken in first gear the revs run out very soon on exit, and revving out first gear also tends to remove traction at the front wheel. wink.gif (Especially if the bike is not yet fully out of the corner and settled.) So I usually enter that corner in 2nd gear and focus on opening the throttle earlier and getting better drive that way.

 

I think the important thing in all of this is to recognise that just because a person is riding around hitting the limiter before each gear change, does not necessarily mean they're making best use of the throttle and rev range. Speaking personally I know that when I used to ride that way, it did feel much more "busy", but I was using so much of my attention looking at the tacho, watching for when to shift that I would arrive at the corner without much free attention. I am riding a whole lot faster now that I use my gear shifts to create free attention rather than trying to rev out each gear, and also short shifting for those other reasons mentioned. My speed improvement came from having more attention and using it on improving corner entry (and midcorner, exit) speed, not from necessarily twisting the throttle more on the straights. Something to think about. smile.gif

 

Just reading back that last paragraph, I keep coming back to that part about using gear shifts to create free attention... I like it! biggrin.gif

 

 

 

 

Now that makes perfect sense, it's better to sacrifice a little bit of each gear to get yourself setup before the turn point faster and get back to the throttle faster for better drive out of the corner! Thanks for the explanation that put it into perspective for me.

 

 

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