What is the point of 6 gears?
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  1. #1
    1000+ Posts U Turn's Avatar
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    Default What is the point of 6 gears?

    I've posted this thread as I have noticed in some previous posts, what I believe to be a lack of understanding of the purpose of having an extra gear, for example 6 instead of 5.

    My understanding is that depending on the configuration of ratios, there are two distinctly different purposes in having the extra gear. One configuration is having the 6th gear ratio high enough to enable relaxed low-rev crusing on highways etc. Take for example the commodore, offered in both 5-speed and 6-speed variants. With similar final drives, the first 5 ratios of both variants are very similar. However, in the latter variant the 6th gear ratio is significantly high for improved fuel economy at high speeds. Hence it's completely useless in enhancing performance.

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    The second configuration is when the 6th gear in the 6-speed variant is similar in ratio to 5th gear in the 5-speed variant. In this configuration, the 6th gear is not going to do anything to improve fuel economy over its 5-speed variant. However, it will allow the rest of the ratios to be closer spaced therefore making more use of the powerband of the engine. The 6-speed box in the gti6 is similar to this configuration, though it's 6th gear ratio is very slightly taller than on the 5-speed variant to give a good compromise between performance and economy.

    Further comments appreciated.
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  2. #2
    who? when? huh? GTI124's Avatar
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    I'm not confused.

  3. #3
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    i completely understand and yes i agree there is a lot of confusion as to the point of a 6

  4. #4
    Budding Architect ???? pugrambo's Avatar
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    not only does it make the GTi-6 delight to drive but what also is good is that there was basically nothing else on the market at the time that had a 6spd box

    the other thing is that i find the torque of the J4RS engine is still very good for pulling away in 6th but you also have the fun of dropping 2 gears and really giving the car a bootful

    there may have been the holden very shortly afterwards but what other 4pots had a 6spd ???

    this makes the GTi-6 also a very unique thing for it's day

    and those who own and drive one realise that this "problem" of lack of turning circle is really a blessing (you get to drive further )

    but seriously it really isn't a drama anyway
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  5. #5
    Gone Fishin' Ray Bell's Avatar
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    The Honda S2000 had a six speed from the beginning, and it's a 4-cylinder...

    Of course the Dodge Viper was also so equipped some years before.

    FWIW, I think the major advantage of the highly over-driven top gear (whether it be a fifth or a sixth gear) is reduced engine wear rather than improved fuel consumption.

  6. #6
    1000+ Posts brenno's Avatar
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    Even the Porsche 968 had a 6 speed box from the early, as did various Commodores.

    The GTi6 was the first FWD NA sold in Australia with a 6 speed box though.

  7. #7
    Gone Fishin' Ray Bell's Avatar
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    And let's not forget that Fiat have a people mover that runs an 1100cc engine and a seven-speed box...

  8. #8
    Fellow Frogger! seesully's Avatar
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    Let's not forget that having the extra gear is not necessarily about the final drive ratio... It's about having so much more fun throwing around through the gears in these sporting varients.
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  9. #9
    pur-john, not pew-john! peujohn's Avatar
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    What about the Triumph Dolomite Sprint? It had a four speed gearbox, with electric overdrive on 3rd and 4th, giving six forward ratios. I'm not sure in what order the six ratios were used... I guess 1, 2, 3, 3 OD, 4, 4 OD. Perhaps 3 OD would often be skipped. I think some versions of the Triumph 2500 used the same 'box. This was in the seventies.

    Also the mid eighties Mitsubishi Colt Supershift with 8 forward ratios. A four speed plus another two speed gearbox operated with a separate lever. I don't know how effective this was, but the updated model used a conventional five speed gearbox.
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  10. #10
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    Quote Originally Posted by peujohn
    Also the mid eighties Mitsubishi Colt Supershift with 8 forward ratios. A four speed plus another two speed gearbox operated with a separate lever. I don't know how effective this was, but the updated model used a conventional five speed gearbox.
    My neighbour had one of these. It was certainly effective for spinning the front wheels in the "low range" first gear The two "ranges" in the gearbox were called "Performance" and "Economy" which I seem to remember was a bit of a laugh!

    Derek

  11. #11
    1000+ Posts brenno's Avatar
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    Quote Originally Posted by peujohn
    Also the mid eighties Mitsubishi Colt Supershift with 8 forward ratios. A four speed plus another two speed gearbox operated with a separate lever. I don't know how effective this was, but the updated model used a conventional five speed gearbox.
    I had one of these for a week or so, it was hilarious! We worked out how to use all the gears sequentially and would take off from the lights and go through the first 4 gears quite quickly. We got the strangest looks in it.

  12. #12
    Gone Fishin' Ray Bell's Avatar
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    There are overdrives and there are overdrives...

    The Laycock-style units sap power like an automatic, because they have to pump oil to keep the clutches engaged. But they give quick clutchless changes into the overdrive.

    Triumph used these in various cars like the TRs and the 2000 variants and the Stags (ugh!) and the Dollymites. They could be changed to be available on all four gears, but probably suffered somewhat if overused in the lower rations.

    On the other hand, the Borg-Warner style of overdrive as used on Chryslers, Studebakers and some Austins... and improved upon slightly for use in Toyota Crowns... was intended for use with a three speed box and came into play in whatever gear was engaged when you reached 23mph.

    I had mine rigged quite differently to the standard arrangement, where the 23mph minimum applied and it was a more or less automatic engagement, brought about when you lifted your foot and dropping out when you gave it a footfull as with an automatic's kickdown. Hard on the diff...

    So I was able to use mine from zero, taking off in first, going to first overdrive merely by backing off... then switch off the overdrive and make a clutchless change to second, switch on ready for the backoff when revved out in second and the same procedure into third... a six speed clutchless gearbox.

    But there was no engine braking when not in overdrive... unless the overdrive was locked out. It had a ball-ramp style freewheel. This also meant that you could stop on an uphill slope and not roll back, as the ball ramp would engage and the direct gear would try to overtake the overdrive... it just sat there.

  13. #13
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    Quote Originally Posted by Ray Bell
    And let's not forget that Fiat have a people mover that runs an 1100cc engine and a seven-speed box...
    ...so too does the BMW M5.


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  14. #14
    Fellow Frogger!
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    A friends Chevrolet Corvette had a 350 Mated to a 4 speed up front which drives a 2 speed & diff in one unit at the rear. Like mentioned previously 1, 2, 3, 3OD, 4, 4OD. But it didnt matter because you were well over 200 kph before you had to worry about such things I had a drive and if i remember rightly you still had to change into 5th and 6th ??? hmmm.

    How does the trans in your ST170 work Linc ?

    Is it something like the Corvette ? Oh, no i just read something about a dual layshaft transaxle design...hmm different again.

    Oh well, what will they come up with next ?

  15. #15
    Gone Fishin' Ray Bell's Avatar
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    Certainly nothing new...

    Pre-war German luxury cars often had a Maybach gearbox called the 'Doppelschnellgang'... I don't know how many ratios it delivered, but the name seems to indicate a lot of them!

  16. #16
    1000+ Posts Poo-Go's Avatar
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    Quote Originally Posted by jester_fu
    It's obviously the reason they use so many gears in Trucks. And yes, i do already fully understand that a preselector is used, so you don't use all of the available gears. But, they are there so you can use them if the load requirement justifies it.
    Another reason there are so many gears in trucks is to cover the reduced rev range of a low-revving diesel engine. In a car, idle covers from (say) 850rpm at idle to (say) 6800rpm at redline. That's a factor of 8 times that any gear can cover. A diesel engine typically in any truck might idle from 500rpm to 2500rpm. That's only 5 times, so it needs more gears if it wants the same speed range as a car.
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  17. #17
    Gone Fishin' Ray Bell's Avatar
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    But it's the real power range they're trying to get to use...

    500rpm to 2500rpm would mean they would need only two gears... in fact, the lower the rev limit the fewer gears you really need, as there is generally greater flexibility.

    But the torque and horsepower are better in a certain range... perhaps 1650 to 2250rpm, so that's where you need to keep the engine for performance and fuel consumption.s

  18. #18
    Fellow Frogger!
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    I think the Holden Calibra also had a 6 speed box, but i think it was in the ill fated AWD they released, which from what I have heard had reliability problems.
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  19. #19
    1000+ Posts Poo-Go's Avatar
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    Quote Originally Posted by jester_fu
    Not necessarily.
    I never said necessarily, I said another reason. The points you make are all valid, but that doesn't make mine not so.
    Last edited by LookingforMi16; 10th November 2004 at 10:09 PM. Reason: spelling and grammar
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  20. #20
    Gone Fishin' Ray Bell's Avatar
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    Maybe not the points he made, but the ones I made did...

    Read my second paragraph.

  21. #21
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    Quote Originally Posted by Ray Bell
    Maybe not the points he made, but the ones I made did...

    Read my second paragraph.
    Yep, and I agree.
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  22. #22
    Fellow Frogger! matt205's Avatar
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    Lexus IS200 has a 6sp, and it's a cracker.
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  23. #23
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    anyway gears are sooooo 20th century. Those Continually Variable Transmissions are absolutely brilliant when engineered properly. Using conical drive systems those cars fly. -Oh and bikes- Apparently they put a helluva lot of stress on the engine though as they spend about 95% of their time sitting in the peak torque range.

  24. #24
    Gone Fishin' Ray Bell's Avatar
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    Oh give me the twentieth century...

  25. #25
    1000+ Posts Fordman's Avatar
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    Default More on truck gears

    A little off-topic, but I think quite interesting:
    A few years ago I did quite a bit of heavy truck re-engineering (ie, optimising a trucks performance with different gearboxes & axles, etc) and at first I wondered why the Europeans with mountains to climb only had 5 or 6 speed boxes, and we were replacing them with 12 & 15 speed boxes for our relatively level roads - it seemed back-to-front.
    The answer is that on a very steep climb you haven't got time to change down to a close ratio gear, you need to let the engine lug down as far as possible then whack it down a big gear and bring the engine back to its highest rpm before the momentum is lost.
    On Australian roads (similar USA) you may have a long gradual climb over 20-30 kms and you want to be able to select a suitable gear for that gradient without lugging or over-revving the engine.
    I guess the same logic applies to cars - a grunty engine with a wide torque range only needs 4 or 5 gears, a highly tuned small capacity engine needs a few more or you can't find a suitable gear for the speed & load.
    (It's really a bit sad that I find this interesting - where has my life gone??!!)

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