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I'm not sure if this is on topic, but I'd like to know the answer before it comes a repair question.

I have a Y2K Triumph Speed Triple - great bike. First gear comfortably takes to 90km/h. Needless to say, in city riding I have to short-shift out of first but there seems no point in going to second so I go straight to third by double clicking the changer.

Is there any mechanical downside to doing this?

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up vote 6 down vote accepted

nope, not at all. I have a z06 vette and the engine has so much torque that I can easily go from 1st to 5th. Under normal driving I skip gears all the time. Generally transmissions don't really care about which gear you want to use next.

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2  
But does the a sequential gear box of a motorcycle work differently to the gearbox of a car? Unfortunately, my car is a piece of crap so skipping gears just brings frustration. – dave May 30 '11 at 21:39
    
I don't know if motorcycle transmissions have something special, but I think all manual gearboxes generally operate on the same principle. All the gears are engaged at all times but one gear rotates independently of the shaft its on. Then there's external mechanism (like synchros) that lock a specific gear with the shaft using splines. Here's a yamaha gearbox: boats.net/parts/search/Yamaha/Motorcycle/1988/FZR750RU/…, and this is one that I rebuilt few years back: allstategear.com/T56Interior-ExteriorBreakdown.htm. Idea seems to be the same – DXM May 30 '11 at 23:01
    
The car I learned to drive in (Pontiac Sunbird) was so weak that skipping gears was normal operation. You had to wind it out to get up to speed, then skip directly to the tallest gear it could cruise in. 2-4 and 3-5 were real common patterns... :-) – Brian Knoblauch Feb 22 '12 at 19:39
1  
@DXM: there are some key differences between a motorcycle transmission and a typcial manual automobile transmission. For one thing, motorcycle tranmissions have no synchronizers, but more importantly, motorcycle transmissions are sequenital. There's no way to shift straight from first to third, you must go through second on the way. Even if you never release the clutch in second gear, the transmission engaged second gear on the way. To dave: there should be no mechanical downside to shifting as you suggest. – mac Jul 17 '12 at 15:14

It depends on how you do the skipping

If, when you do it, you hear loud clunks, that means you are not matching the RPM's to the road speed, to the transmission.

Motorcycles have a synchronous transmission with with relatively fragile shift forks operated by a shift drum. The forks move the gears side to side to engage. if you are hearing a loud 'clack' when you do this. Stop doing it. You dogs and slots on the gears will get worn and eventually the bike will fall out of gear while your driving, hit a 'false neutral' and then clack and clack as it's trying to get back in gear. When this happens you run a higher likelyhood of getting bent shift fork, which means a total tear down for most MC engines.

Image of a damaged Gear

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Here's a damaged shift fork

enter image description here

I don't recommend this type of shifting unless you are seasoned and can do it silently. If you can speed shift, you can probably do this as speed shifting is all throttle control and timing.

MC transmissions are fragile. They aren't corvettes, corvettes (most manual cars) have a completely different mechanism for shifting. They are not synchronous transmissions. Be nice to your speed triple, it's beautiful, but it's a teacup of a transmission, just like my Aprilia or Suzuki's.

Watch this video of a transmission shifting. You will understand my paranoia more. I've had to split too many cases fixing the results of poor shifting practices. I don't want you to have to deal with that issue.

Motorcycle Transmission Shifting in Action

Here's another one with a different view.

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My understanding is that as long as you know the gear you're switching into will provide you the torque you need to continue accelerating, you should be fine. In fact, it makes sense to me that you'd actually cause more wear by letting out the clutch, catching the gears, and then pulling it back in. You'd also cause less smooth acceleration due to very slight engine braking (or I just suck at manual).

I'm a computer programmer, not a mechanic (ergo, you should not take any advice from me and probably do the exact opposite!), but on my bike I usually start out in first, shift to third around 20mph depending on how fast I need to accelerate (traffic around here is full of "those" people), and then fifth or sixth.

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I am not a driving expert, but I think it has to do with RPM. If you want to skip gears, make sure the RPM are at the right level or you damage your gears. Again, I am no expert, but I think it is related to RPMs.

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2  
No problems there, it's a close ratio box with a tall first gear. 60km/h in first would be about 7000 rpm. Double clicking the gear changer takes that down to about 3500 rpm - still within the sweet spot. – dave May 31 '11 at 18:34

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