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Question For Mech Engineers

Discussion in 'Technical and Troubleshooting Torque' at netrider.net.au started by 2wheelsagain, Feb 23, 2008.

  1. Why are motorcycle gearboxes (most) configured as 1 down, others up?
    They are sequential boxes so why not build them with netural at the bottom or top?
    I know the 1 down etc can be reversed for racing but netural is still between 1 & 2.
    Is there an engineering reason why this is so :eek:


     
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  2. Everything you wanted to know about motorcycle gearboxes:

    http://www.wootbike.com/articles.php?article_id=3&page=1

    Page two has a little about the 1-N-2-3-4-5 pattern... to do with sequential gearbox, fork selectors and dogs... but probably not enough to answer your question fully.... but my guess is having nuetral between 1 & 2 makes the gearbox just that fraction smaller.


    Of course, no discussion about mc mechanicals is complete without a trip to Dans MC pages: http://www.dansmc.com/gearbox.htm
     
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  3. A couple of bikes have put neutral at the end. The Honda C90 Step-Thru and its siblings are all N-1-2-3, and I seem to remember that the early Kwak triples were similarly configured.
     
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  4. *wades into battle with his mighty Mechanical Engineer hat on*

    Actually, I'd probably look towards 'safety' and useability more than technical reasons for placing Neutral as a half-shift between 1 and 2.

    Firstly,
    Keeping it either above or below 1st gear makes sense because if you're in Neutral you'll want First, first. If you're looking for Neutral, you're probably already in First and not Fifth.

    Second,
    If you're clicking down gears as you approach traffic lights and lose count (or don't know what gear you're in), you go 2, 1, and suddenly you're in Neutral... Which could be totally disastrous if you need to power away quickly. Particularly if you geared down to get a bit more acceleration for evasive action - suddenly you have nothing!

    By hiding the Neutral as a precise half-shift between 1 and 2, there's a reduced chance you'll "find it" accidentally as you bang down the gears towards First.


    As an aside, a sequential gearbox isn't anything special - It just has a clever rotary gear selector instead of an H pattern. (Of course, motorbikes use fancy constant-mesh gearboxes with huge dogs and no syncromesh, but that's not related to the "sequential" part).

    Instead of having a H pattern which lets you move the gearbox's selector forks around randomly you've got a rotating cam of sorts which pushes the selector forks into different positions every time it's indexed one gear higher or lower.

    http://auto.howstuffworks.com/sequential-gearbox1.htm

    With that in mind, Neutral could be pretty much anywhere you want on the gear selector. But "next to" 1st makes the most sense.
     
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  5. Bingo, we have a winner! :grin: +1
     
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  6. its where the gremlin likes to live, its too cold below first and two hot above 2nd, when he gets upset he changes into Angle gear for you
     
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  7. There are apparently some bikes that don't stop at either end - ie clicking down from first goes to 5th and up from 5th goes to 1st.
    I've been told this can make riding very interesting :shock:.
     
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  8. Thanks for most replys and links.
    The jury is still out :shock: Plenty of bikes have 5 neturals :grin: and I often dont remember what gear I'm in but I bl@@dy well know when its first :p
    I'm not saying netural should be anywhere else, just asking the question :LOL:
     
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  9. Were.

    That's the rotary shift pattern mentioned earlier.

    It was used by J manufacturers in the 60s. Almost everyone except Honda had one, but only with 4 speeds.

    These included Bridgestone, Yamaha, Kawasaki, Lilac and Suzuki. (And before robsavv :wink: has a go at me, all these were sold here, too!) The big danger is lifting up from 4th and getting neutral, then forgetting that one more up shift puts you into first, with consequent astronomical over-revving.

    Had they built in a limit to prevent this action while in motion the idea would have been useful for those lazy guys who cannot be bothered changing down at the lights, before they get there.

    At least one bike, the Bridgestone 175 Dual Sports (a trailie) had a selector switch to give you either 4 speed rotary shift or 5 speed sequential with N at the bottom.

    Back in the 80s Mitsubishi had a Colt with (driver selectable) either 4 or 5 speed box with different ratios. That was the forerunner to sport or economy mode shift patterns.

    Cheers

    Trevor G
     
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  10. :LOL: That would not have been fun and I can see why that idea was binned :)
     
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  11. Not just the triples, PatB ;-)

    The A1 and A7 rotary valve twins (250 and 350) and every other model except the W650 BSA A10 clone, until the Z1 four and the F11 (250 trailie), had N at the bottom. I am quite sure...but might have forgotten one.

    They were solving a problem that wasn't really.

    Cheers

    Trevor G
     
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  12. http://www.timberwoof.com/motorcycle/faq/riding.html



    From Wikipedia:



    I'm inclined to go with the 'discouraging riders from coasting in N then causing accidental lockups by shifting into the wrong gear' reason.
     
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  13. Don't know who this robsavv guy is, but I see nothing to "have a go" at you Trev. I think you have me pegged all wrong.


    Anyway, I like the standardizing of safety reason. Makes a whole lotta sense!
     
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  14. All the dog teeth are on the inside of the gears this way.
     
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  15. My various CZs/Jawas all had a neutral between every gear. I originally thought it was because the gearboxes were so crude. Eventually I twigged that it was to allow easy coasting down hills in neutral so the premix lubed two-stroke wouldn't nip up due to high revs on a closed throttle.

    Gotta say, although the sequential change on a bike may not be anything that clever, it still makes me smile when I remember the hype associated with sequential boxes on performance cars. Bikes had had 'em for something like 60 years at that point :grin: .
     
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  16. ahhh but you could rebuild them with fencing wire.
     
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  17. A gross oversimplification. You needed beer cans and condoms too, tucked into the toolbox next to the Mole grips and 4 pound hammer :grin: .
     
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  18. Can you imagine operating a H-pattern with your foot on the bike? :LOL: :grin:

    To be fair, the fancy-schmancy manual-sequential gearboxes on road-going sportscars are a bit more complex than the bike setup - With a computer to automagically operate the clutch, change gears, match revs, release the clutch.

    You are right, though. :) Sequential is very much the 'in thing' right now, whether it's a legitimate manual-sequential box on a sportscar or a gimmicky family car option having you tell the power-inefficient torque-converter what gear it should be in because having to change gears is considered "sporty".

    (Not to poo-poo torque converters - they have their advantages over a conventional clutch, particularly their ability to transfer 100% of the applied torque while slipping, and I respect that).
     
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