CVT vs Centrifugal clutch vs Manual

[Crazymanneil]

Hey people.

At the risk of starting a flame war, what are peoples favourite transmission and why?

For myself I like manual boxes, but have never ridden a bike with CVT or crentrifugal clutch so not much to base it on. I do know that go-karting over here tends to use centrifugal clutch and they seem to be pretty slow to get moving from a standstill.

For my own diesel bike ideas I've always tended to a manual box, but reading other peoples posts I've started to open my mind to other possibilities, not least because of availability. I've done some reading on CVT's etc but some real world opinions anyone? I'm thinking around 40 to 50 horsepower if it makes any difference.

Neil

[Erik "EVA Products]

Hallo Neil,
Only the CVT word should be enough to make up your mind.

It means that the constant variation is related to the enginespeed and roadspeed and to match these 2 as good as possible.

this is not the case with a normal gearbox. There is allways a range of rpm that gives pour power transfer.

Go to your local yamaha dealer and ask a testdrive on the T-max.
I am 100% sure you will not have to think it over and take the CVT system.

However there are many cvt systems with different ratios and different setups. Sometimes the clutch is stick/slip on the beld. sometimes it is a centrifugal clutch and sometimes with a fluid clutch .the correct version of the syste should be calculated.

That is why we overhere have chosen 3 types of cvt that match different drive possiblities and service intervals. (2x rubber and 1xsteel beld )

Erik

[Byrdman]

I personaly like manual transmissions. I like shifting and enjoy being part of the driving process. CVT just feels too automatic to me.

I do however think that CVT's are the wave of the future, especially in motive types of applications. Running an engine (Gasoline or diesel) at it's most efficient RPM and controlling vehicle speed with the transmission is already used in mass automotive applications. Motorcycles are the next logical step.

[Anorak_ian]

I'm getting to the point where I'm thinking of junking the Enfield gearbox and using a cvt. I can't get an extended shaft for my box in the UK unless I part with £120 and the Indians say they are hard to find now. Plus £100+ for trials gears to make it work the way I want. The second hand box was £60 and £120 for the clutch, I may as well sell them and get a cvt.

Anyone know where I could get one in the uk?

Ian

[Fiddler]

I would much prefer a manual transmission for that feeling of rider input that others have mentioned. However with an engine that starts making usable power around 1600rpm and only revs cleanly to about 3600rpm, cvt is in my opinion a sensible engineering solution.
I sourced mine in the UK from Combidrive in Carmarthenshire. Phone 01588 823757 or fax 01588 823056. They seem a small outfit and im not sure what their core buisness is but they were very happy spending time discussing requirements and offering technical advice when i used them. Highly recommended.

Cheers, mark

[andrewaust]

Yeah, even though I feel a CVT might be better to hold the engine in a better power band for a longer time etc, I just like the old clunky gearbox

I've never been able to get a ride on a M/C with a CVT, but scooted around on a mates Honda 4 wheeler, breaking a belt in the middle of nowhere

Availability is also a personal problem for me, just lucky enough to get the extended shaft for the Enfield. CVT's etc would have to come from the states, meaning $$$$$ that means Customs taking an interest.

Then theres the homework to set a CVT up, order the wrong stuff, more time. So guess you guy's get the picture why I just kept to the old clunky box.

One other thing ....... If you need to brake really quick, like a 8 foot Kangaroo decides to take an interest in you - a manual gearbox is good for shifting real quick for some aided compression braking, and yes it did happen to me once, then there was a Horse another time and of course heaps of loose nuts behind the wheel

Time to take out some more life insurance I guess



PS: What about Diesel Electric - could be the next step in technology!



It's all fun hay!



Cheers guy's


Andrew

[Crazymanneil]

Interesting posts guys. Jury is still out for me although I guess it would depend on stuff like availability. Going for a test ride on a T-Max sounds like a good idea so I will look into that (provided they are in the UK?)

Neil

[gilburton]

you are obviously not in to scootering as there are available anything from 50cc-650cc scooters with CVT transmission in the UK so you will just have to find local dealers.Another option is to get a copy of T&G magazine(formerly twist and go) or Scootering to get some idea of availability but most main makes have scooters in the lineup these days so it shouldn't be a problem.I used to run a Daf 66 with CVT and it's a bit strange as you just put your foot down and the revs stay constant but the road speed quickens to match the revs rather than the other way round and the sensation is a bit deceptive as initially you don't seem to be moving as fast as the revs but you are and you will probably find this out if you try an automatic scooter.I should think CVT for an industrial diesel would be the best as these engines are made for constant revs although it is not quite as economical as manual gearing as you can't drift along in a high gear with the engine on a light load as the CVT will keep the revs constantly higher.Hope this helps,cheers

[oilburner]

I'l go CVT when there is a compact steel push belt CVT or a standalone version of Honda's hydraulic (beltless) CVT which is scheduled to appear in the Honda DN-01 motorcycle this year or next. The current rubber belt CVTs are too bulky for inline applications. Until then, it's a BMW manual gearbox and dry clutch for me.

My $0.02CDN

Avery

[balboa_71]

The scooter cvt's are a bit different from Comet types. Most scooter cvts clutch after the cvt, allowing the cvt drive unit to always be engaged with the belt. The driven unit is on a shaft that is input to a centrifical clutch. The clutch has to be larger to handle to added torque (from primary reduction) but the trade off is lower full engagement speed (from roughly 3 to 1 primary reduction) which lowers friction and heat when engaging. While as Avery stated, the cvt's are bulky, they are light weight and trouble free for the most part (belts breaking and misc. worn items), and quite plentiful here in the states. If we could get an affordable gearbox here in the states, we would go that route, I'm sure.

Cris

[Throttlepansy]

My only experience with CVT is the "Rusty Justy", an old Scooby. But I love the CVT..Way better than slush-boxes! Acceleration is deceptive 'til you get used to the engine note. Another brill invention is the Torotrak IVT (http://www.torotrak.co.uk)... Theyve just started making these for lawn tractors, so they're compact... Might be interesting... [/url]

[roverthetop]

just finished making my first diesel bike. will continue working on it for biodiesel and svo. wanted to let you all know that i ship cars to and from the states and the uk in containers, so throwing in some spares for you wouldnt be difficult. may take a bit longer than you want, but free! if you need anything from the states, i would be happy to help. i am working on my 2d go at a diesel bike using a comet cvt.
cheers
b

[Diesel Dave]

Hmmmm

Both systems have their benefits, if converting an Enfield I'd keep the gearbox. If scratchbuilding I'd choose a CVT. I have both a geared Enfield diesel and a CVT equipped chopper still under construction.

My diesel Enfield has the later 5 speed box and this is a boon with such few HP on tap, it allows me to overgear for the flat and downhill bits and it's easy to drop a gear for any inclines.

4 Speeders are more of a challenge as in std trim there is a huge gap between 3 & 4, this means you will be well out of the power band before being able to downchange for a hill. I'd choose a close ratio gearset over the trials gears - you need then close together to make the best of the power available.

The use of the Taurus input shaft is flawed when considering more than 10Hp, this was originally intended for a 6Hp motor and has a large unsupported element - don't expect bearings to last very long is asking to transmit a lot of power; but they are easy and cheap to replace.

Diesels - especially stationary engines have fixed injection timing and therefore a narrow usefull power band - 2000 to 3600 rpm. To take advantage of this you need LOTS of gears - even the new generation of diesel vans have 6 speed boxes and these rev through to 4500 rpm.

CVT's require carefull setting up to work properly, variator weights, spring tensions and even ramp profiles all need to be tuned to work properly in a motorcycle application. Out of the box a Comet will work but essentially it's a compromise setup and most need the heaviest weight possible in the driver clutch to work properly.

I've raced both 50cc geared bikes with 7 gears and 70cc scooters with CVT's and although there was a good 15 years between the two the CVT's would win hands down today. Racing auto scooters have the ability to hold a very narrow power band way up in the range (14000 rpm) whilst the CVT takes care of the gearing needs. I've seen them pitted against one another in practice sessions and the geared bikes visibly loose ground when changing gear.

BTW my missus 70cc scooter leaves my diesel Enfield for dead - even it's top speed is better, I win at the fuel pump though.

There is a market for both systems - CVT's are gaining ground and acceptability in the motorcycle and scooter world, as materials technology improves (kevlar belts have made a huge difference) CVT's will get better and better.

One other consideration - you will need a HUGE primary case to enclose a CVT the Comet 44 magnum driven pulley is 8.5" in diameter and this will end up approx where your ankle will end up unless you are considering either a sportsbike or chopper seating position. Choosing a narrow motor helps; the Yanma & clones are better than the Lombardini or Hatz motors in this respect.

There are a lot fewer parts to a CVT and so long as you carry a spare belt there is little else to go wrong, compare this to a primary chain, clutch (especially the cable) and the gearbox there are far more parts to go wrong. In aircraft manufacturing and design analysis the number of components is used as a factor in assessing risk of failure.

Hope this helps
Dave

[oilburner]

Perhaps one of the most compact CVT setups is the one used on the mid seventies American made Rokon ST340 and RT340. The bike had a claimed 18hp at 6000 rpm.

The first link below shows the CVT; notice how close the pulleys are. The second link shows the bike with cover installed. It doesn't take up much if any more room than most primary cases.

http://www.dansmc.com/rokon340.jpg (cvt setup)

http://www.bradsbikes.net/image_collect ... 195525.jpg

FYI

Avery

[gilburton]

In the UK try Tecumseh dealers as they apparantely handle Comet drives