Shifting gears in a Megabusa

[NiteLite]

I have been looking around on different forums, trying to find one that had a few Megabusa owners, and it seems that this forum does

 

I got my Megabusa only a few days ago, so I am still learning to drive it and I was wondering about shifting gears. As you all know, the Megabusa has a sequential gear box from the Hayabusa. I was wondering how you (other owners) prefer to do upshifts and downshifts ? Do you release throttle, clutch and then push the gear lever or do you do clutch-less shifting by putting load on the gear shifter and then just lifting off the throttle a little bit to let the dogs engage in the new gear ? Or maybe you do it in a completely different manner ?

 

One of the articles that made me wonder was this, which tells me I might be doing it wrong with my "standard-car synchromesh-shifting style": http://www.hewland.com/svga/help.htm

 

Anyway, I would love you hear from guys who have driven the car for a while and has some experience in what seems to be the most "reliable" way / best way to shift

Edited April 12, 2010 by NiteLite

[Birkin42]

I have never driven a BEC but have a ton of miles on sport bikes. I never use the clutch on an upshift and just breath the trottle, and breifly use the clutch on the downshift. The transmission dogs have always looked fine when serviced. I quickly abandoned clutched upshifts once I got into bikes since the shifts never seemed smooth, and like the article said, leads to clutch problems.

[Hank]

I shift each gear with the lever as quick as possible, but I let off the gas and I use the clutch. If that helps.

 

Once I put the Flatshifter Max + Pro paddle shift system on my car I will only use the clutch to take off and stop.

[bsimon]

Motorbikes are simple dog boxes. Dog boxes respond better to clutchless shifts by matching RPMs. In racecars, motorbikes, or big trucks with close ratio transmissions, this means you just lift the footfeed a tad to unload the dogs and switch gears. If your gearbox has a sequential shift drum, it makes the switch faster and more precise 'cause you don't have to stir the 'box between the gates.

:driving:(I finally found an appropriate thread for this smilie!)

 

Here's a good synopsis of the various procedures from the man himself, Bill Hewland.

http://www.hewland.com/svga/help.htm

[NiteLite]

Ok, Being a "car engine"-guy for many years, shifting without clutching just felt a bit scary, but it sounds like I should try it, hehe.

 

Thanks for all the response so far.

:driving:(I think you are right, this smilie does in fact seem very appropriate )

[bsimon]

If you have a synchronized gearbox, you probably shouldn't be shifting without the clutch. The balk rings and tiny syncro teeth will take lots of wear unless you take a good amount of time to match rpm between gears. The clutchless technique really only works well with face type dog engagement gearboxes. ie; motorbikes, Quaife, Hewland, Webster, etc.

 

Truck transmissions are the exception. Although they are synchronized, the ratios are so close together (sometimes less than 450 RPM on the auxiliary box) that there is very little time needed to match the rpms. Tagging the clutch twixt gears becomes a bother and causes more clutch wear than it's worth.

[NiteLite]

I have a Westfield Megabusa with a Hayabusa engine and Hayabusa 6 speed sequential gear box

[Hyper]

With a dog box you need to either float shift or double clutch. The company I work for has automated heavy duty transmissions where we float shift by controlling the engine.

 

The input shaft needs to slow down (for up shifts) which a normal synchronized transmission is accomplished by the synchro. If you double clutch you've got to de-clutch to break torque and get of gear, re-clutch at the new synchronous engine speed (to slow down the input shaft), then again de-clutch select the gear and resume. I've double clutched for Semis which is all well and good (the engine inertia is huge so you've got plenty of time), but most good drivers float shift.

 

To float shift you've got to break torque (lifting off the accelerator), select neutral, slow the input shaft (let engine speed drop), then select your gear. Of course, it's much easier to explain than to to actually do, but my suspicion is that motorcycle gear boxes are designed for float shifting.

[DeanG]

On much lighter motorcycles I follow the Keith Code's Cal Superbike school approach. Up shift - load the transmission lever quickly back off the throttle then back on. Once the revs match the shift happens automatically. Down shift - clutch in, bump the throttle to increase match revs, push the shift lever down, clutch out, throttle to desired setting.

[Mondo]

I think all us old sportbike guys agree on using the clutch to take off and downshift.

 

For a while now, there's been electronic kits that let you keep the throttle pinned and cut the spark for a split second while upshifting... recently saw one that even allows downshifting without the clutch (revs up the motor to match lower gear automatically).

That might be what Hank is talking about.

[andrew7]

Nitelight, I'm happy to hear of another BEC. The tranny is the weak point of our cars and I recommend shifting like a standard car. I agree with the guys here about motorcycle shifting, I started at 7yrs old. I shift up and sometimes down clutchless. When I tried shifting the 7 like a bike only a few shifts where smooth the rest happened with a traumatic bang and the car lurching back and forth. Many times I thought I lost my tranny. Now when I shift, I preload the shifter, ease up on the throttle, (drop the rpms from 14000 to 13000) and put foot pressure on the clutch pedal and its enough for the clutches to slip and engage the next gear seamlessly.

 

I have three reasons why I think clutchless shifting does not work well in cars.

One is weight, if a bike is 400# and now its moving 1200# this adds more strain to our trannies. Second is control, I can control my hand movement on a bar throttle far more precisely than my foot, but I don't race and my last name is not Schumacher so it could be debatable. Third is drive line slack and cushion. Our cars are locked from the engines to the tires while a motorcycle normally has some chain slack and a rubber crush drive in the rear hub to take up shock load during an imprecise shift. I believe all these factors contribute to more stress and less enduring engines. If you have sponsors and a pit crew bang away, but if you don't and you blow a dog or fork you'll have to do this picture.

 

Happy BECing.

[DeanG]

I think Andrew7 makes very good points. I would expect BEC's to require more maintenance intensive than Sevens with car engines. The weight of a Se7en is high in comparison to sport bikes (500 lbs, even a Goldwing is only 800 lbs). Another factor is that Se7ens have much more traction. Shock loads would be much greater.

[Hyper]

Another big consideration is transmission design. A bike transmission has straight cut gears and sliding clutch (dogs), while a car transmission has helical cut gears and synchronizers. Single clutching with a dog box can be problematic because the input shaft won't slow down to match the new engine speed without the clutch engaged. That means when you try to force it into gear with the clutch fully open you're slowing down the input shaft you're using metal/metal contact which slowly wears the sliding clutch.

 

What Andrew is suggesting is basically synchronizing with the clutch disk itself, which probably works quite well. As soon as he breaks torque the sliding clutch can disengage, the drag on the flywheel from the clutch slows the input shaft and then the sliding clutch can re-engage. I also agree shock loading is probably much higher, but I'd be interested to see what a BEC transmission failure really looks like.

[Mondo]

I wonder if a slipper clutch (more and more sportbikes are coming with them) would work... that would make downshifting a no brainer.

[TheDingo8MyBaby]

http://www.apexspeed.com/forums/showthread.php?t=39735

 

Thougth this may be of interest to you guys... especially after tax returns.

[NiteLite]

Geartronics also sell a kit that looks rather good, even has a few videos on their site explaining and showing how stuff works.

 

http://www.geartronics.co.uk/paddleshift.htm

 

Nice to hear all of the different opinions Sounds like using the clutch is the way to go maybe, but with more of a manual sync then you might be used to from a car.

[NeilW]

For first hand experience of the Geartronics kit, speak to Nicholas Belling at Firman West Cars - http://www.firmanwestcars.com They are the North American agents. They use the Geartronics system on their F1000 race cars.

 

Regardless of whether the engine is in a bike or a car, there is no need to use the clutch, up or down - so long as the engine cut and throttle blip are timed correctly. That's where the Geartronics system scores over its rivals. Most aftermarket shifters are pretty crude bits of kit which work on fixed timers for the shift actuator & engine cut etc. Unfortunately, a gear shift is never consistent, and the shift times vary dramatically, thus rendering the cheap systems next to useless. The Geartronics system differs in that it uses a highly intelligent controller that monitors the gearbox position, engine speed and throttle position. This enables it to alter it's behaviour depending upon the prevailing conditions and how the shift is progressing. So, for example, it will only cut the engine for as long as is necessary to engage the next gear - this means there is no danger of turning the engine back on prematurely and damaging the box. Also you're not killing the engine for longer than necessary and slowing the vehicle.

 

Regarding matching revs and shock loadings -on the upshift, if you cut the ignition while on a full throttle, the engine speed drops very very rapidly, something in the order of 1000-1500 RPM over the period of just 10 engine revolutions. This rate of fall works out quite nicely with superbike gear ratios and pneumatic shift systems because the revs will be a pretty good match for the next gear by the time the dogs start to engage.

 

Downshifting is a bit more complex though. Contrary to what most people think, the throttle blip isn't just to match the revs, it's to unload the box to enable the dogs to disengage the current gear. There is less of a requirement to use engine control to match the revs because the vehicle should be braking hard during downshifts anyway. So, you don't need to increase the RPM during downshifts as much as you need to reduce RPM during upshifts.

 

To make fast and non-damaging downshifts you need to use quite a large throttle blip in order that you can increase the engine speed sufficiently once the dogs do disengage. This then causes other knock-on effects that must be dealt with by the electronics. The crude solenoid shifters don't have any strategy to deal with this, and as a result the downshifts are often inconsistent, agressive and potentially damaging to the box.

 

Things are happening so fast during a shift that it's impossible to guess or predict what timings are required. The only way to ensure consistent and non-damaging shifts is to use a sophisticated gearbox control unit. Unfortunately they tend to be more expensive than the crude timer devices (which usually come with the solenoid based systems), but you have to balance the initial extra purchase price against the cost of a transmission repair...

 

Neil.

[graham]

Take a look at flatshifters website at http://www.quickshifters.com some great onboard footage of their cluchless up and down gearshifts at work .

graz

[Hank]

Graham, I promise I'll get around to installing your Flatshifter Max + Paddle Shifted Pro system on my Megabusa eventually. I sold my house and don't have room to take the car apart to install the kit. The rollcage and scuttle need to come off, and there is a bit of machining required for the electric actuator pivot block.

[tex]

i change very similar to driving a normal road car - only you can do it a lot faster with less clutch travel

 

i wouldnt recommend clutchless - just gonna crash the gears and damage them. the 1st gear is the trickiest - just feeeeeel it engage then the rest are a cinch