CVT and hills- a no go?

[coachgeo]

I used a CM400 Honda that worked well... We used a Comet variable belt drive. If you have hills do NOT use a variable belt drive. You can't keep speed up hills. ....

Did you try different tunes to the CVT? Curious to why you could not get that to work. Granted this is a different topic and should be started in the proper forum so not to hi-jack this fellows thread

[phoenix827]

I used a CM400 Honda that worked well... We used a Comet variable belt drive. If you have hills do NOT use a variable belt drive. You can't keep speed up hills. ....

Did you try different tunes to the CVT? Curious to why you could not get that to work. Granted this is a different topic and should be started in the proper forum so not to hi-jack this fellows thread

Tried everything, no luck. Moving on. Got better gear range with the five speed anyway.

[coachgeo]

Tried everything, no luck. Moving on. Got better gear range with the five speed anyway.

Read your old thread on this but there was little info.

What size engine?
What model of comet?

[phoenix827]

We have a 10hp Sterling engine which is a Yanmar clone and used a 40 series Comet. We tried several different gear ratios and the 40 series Comet is not adjustable. The real problem is that the drive acts as a direct link to the Comet. If speed changes in the slightest the drive changes. So as you start up a hill it automatically drops ratio and speed. If I'm running 50 it will be 35 by the top of the hill, no matter what we tried. If you have very level terrain where you are it is great. Where I live, it sucks. Dropping speed up a hill can get you killed by the idiot cagers doing 70 in a 50 zone. The five speed has a lower first and an overdrive. This is a much better gear range than the Comet as well. People on this board have stated, and I have seen evidence, that the Variable drives loose as much as 30 percent in heat. I can tell a huge difference in the drive at different temperatures. It pulls faster and smoother on a cool day, on a hot day it feels like it's stuck in molasses. I got the five speed for free and I have time and the skills to adapt it. I will post on the improvement.

[coachgeo]

We have a 10hp Sterling engine which is a Yanmar clone and used a 40 series Comet. We tried several different gear ratios and the 40 series Comet is not adjustable. ....

Thank you. What was your combination of Driver Clutch unit and Driven Pully unit? According to the below from GoCart's USA there are two ratio bands available according to which driven pully one uses.

[phoenix827]

My drive is the top in the diagram. Interesting thing to note is it only shifts the range. It does not increase it. It moves the entire range 0.24. This can be altered by changing the final drive. We tried that. Utterly useless change. The five speed having a overdrive gives me much more gear spread. This is very useful with a limited rpm range. This should work very well.

[coachgeo]

Don't know how much affect tenths make on ratio range. My math may be off but it appears the spread of the range increased with the larger pully. Higher range went up 0.24 and lower range changed by 0.40.

What is RPM range of your engine?

Would love others thoughts on his hill climbing issues being a inherient CVT issue orrr???

[phoenix827]

The diagram you posted shows the ranges for both sizes. The range increase is negligible. The one drive never makes a true one to one ratio, basically an under-drive.luckily that is not the one I have. I believe it would be worse than it is. I have been in contact with many others, all report the same problem. The problem lies in the fact that there is no way to hold it in the top range. As soon as the rear wheel changes speed, the drive reacts. Its nice to have an auto trans, but there is still the issue of parasitic loss. Some have told me it is as high as 30 percent. That could mean as much as 30 miles to a gallon more for me. My new trans will be finished by the end of this week, then I'll begin the install.

[coachgeo]

just disecting this as a learning experience. Don't care; for the sake of this discussion, the plan to convert to mechanical 5-speed except comparision of speed data on hills between the two.

Just trying to learn myself and hopefully some other readers where downfalls lie for CVT. So far few have used CVT so their is not much to go by. Heiko and the Track Bike seems to be having very good success with them but those are much larger engines. The Scooter industy seems to pretty much all gone to CVT. But your bike is heavier than those I supose.

Searched the net the other day for info about CVT parasitic loss and came up with talk but only one reference to a percent value. It too said up to 30%, then again several others coupled loss discussion with the idea that gains of keeping engine in best powerband out weighed the losses. So with that simple search it does not show anything conclusive.

Thanks for participating so far. Honestly was expecting more folk to chime in than just us two.

[sbrumby]

WhenI see them at the I. O .M TT, then I might take some interest. Raceing is generally a good test. You need minimal losses and maximum control. I dont think CVT does it.

[coachgeo]

WhenI see them at the I. O .M TT, then I might take some interest. Raceing is generally a good test. You need minimal losses and maximum control. I dont think CVT does it.

your point is good. Now question is..... were CVT's the gear boxes used on the quads that did the Dakar earlier this year.... hmmmmm.

[coachgeo]

.... were CVT's the gear boxes used on the quads that did the Dakar earlier this year.... hmmmmm.

first search shows that at lease one of the Buggy's did. See

http://www.marathonrally.com/news/sa_da ... 983.0.html

Further research looks like all the snowmobiles raced are CVT too.


BUTTTTTTTT on second thought... this avenue of racing discussion is irrelevant to this thread. Goal is to disect why this fellows CVT sucked on hills. Was it combination of small engine w/low rpm mated to a CVT.... or was it a complete different CVT setup would theoretically better matched to his set up..... orrrr??? Answers learned from this disection will help everyone understand better when to use / not to use CVT tranny on their bikes.

[BoxerOtto]

hey george, the thing about most cvt's which make them constantly variable and always in the right gear is also their downfall for constant speed. they are load sensing which means the more load applied eg "hill" the more it shifts to keep the engine at the same rpm and a loss of rpm to the wheel or track or whatever your turning. if your engine cannot produce enough power to overcome the extra load it shifts. even small snowmobiles produce a lot more power than these diesels. google some hillclimb racing yamaha's @ 450hp. now i say most cvt's because i belive the style that automakers use are not quite like comet style in the sense that a computer controls load sensing therefore can be tailored to shift a variety of ways and actually hold speed. again this technology is not really new other then adding computers. if you really want to dig and look for variable transmissions look at farm combines from the 1940's to the 1970's specificaly "massy harris" model 82 or super 92. there are many others. they used a variable transmission which was a mvt. manually variable where the secondary pulley was not affected by load because a small hydraulic cylinder controlled the pulley not a spring ,and it only moved from input from the operator of the combine. the other thing they did was have a three speed manual transmission with a clutch attached to it to give variable ranges plus three range gears. also mtd lawn tractors use a similar mvt transmission on some of their units which gives many ratio's but is not load sensing and needs input from the driver to change speeds. i belive these have been out scince the 1960's.

[coachgeo]

Thankx BoxerO

When comparing a 3cyl diesel ATV/RTV or Bike (Heiko's and the TRACK for example) to this 10hp bike.... by what Im gathering your saying.... its an HP issue. If the bike has HP to carry the weight of rider and bike up hill with out needing downshift much even if it was manual then..... your good to go with CVT?

Heiko's and the TRACK have not reported problems on grades.... or their being quiet about that?

[BoxerOtto]

yes and no. yes the more hp you can throw at it the less it will need to downshift, so it solves that problem , but i'm still not a big believer in them for a few reasons. one is heat generated and the constant tuning and servicing these clutches need to keep them at their optimum. there are better quality clutches but when you look at sleds and quads they usually need maintenence and belts after very short periods of time in miles compared to what you would be asking from them for a motorcycle. the other thing i don't like is the huge extra mass spinning off the end of the crankshaft which the bearing surfaces were not designed for. have a good look at a sled engine crank bearing area and you will see what i mean. also if the secondary clutch is not alignned properly and not allowed to float it can cause tremendous thrust load on the crankshaft. the larger engines obviously deal with this better. i'm not saying it doesn't work but for me a regular gearbox solves these problems and will be way less maintenece and more cost effective in the long run. you should talk to dieselfly about this his seems to be working for him but he is running a punsun v-twin, so more power.

[Sphere]

Car CVTs have nice control loops to influence the "gear selection". You can make the drive for snow, mountains, fuel efficiency, or performance. Youtube for BOSCH CVT.

[coachgeo]

yes and no. yes the more hp you can throw at it the less it will need to downshift, so it solves that problem,

. Intersting. Will have to keep an eye closer on racing ATV's and who goes with CVT and who goes with Geared. They certainly have hill climbs in the courses.

added info beyond the topic of bike in question

but i'm still not a big believer in them for a few reasons. one is heat generated

hmm... add cooling fins?

constant tuning and servicing these clutches need to keep them at their optimum. there are better quality clutches but when you look at sleds and quads they usually need maintenence and belts after very short periods of time in miles compared to what you would be asking from them for a motorcycle.

have no knowledge about sleds. Im in TX lol. Will have to listen to you folk living in cold country for more knowledge on this. Thinking about it though these sleds also run at twice to two and half times the rpm's of the diesels. So question is will this lower wear and tear on the CVT components. Lots of RTV's running around on the ranches out here and huge lawn cutting industry with big mowers and all with CVT's. Have not heard a wiff about maintance issues.... but then again they dont do speeds (or rpms) of sleds.

the other thing i don't like is the huge extra mass spinning off the end of the crankshaft which the bearing surfaces were not designed for. have a good look at a sled engine crank bearing area and you will see what i mean.

Got any pics? Know nothing about sleds. You say HUGE.... but is it really? Engines like say a 3cyl diesel have heavy clutch etc. mounted their normally. Also much larger heavy flywheels and their industrial purposed. Maybe trim flywheel to an amount equivulant to the CVT's weight ? All 2 and 1cyl diesels are typically used for industrial purpose too .... what all do they end up having attached to their flywheels crank, does those items really put less strains on the engines than a CVT? They might.... I certainly don't know.

also if the secondary clutch is not alignned properly and not allowed to float it can cause tremendous thrust load on the crankshaft. the larger engines obviously deal with this better.

Would assume a bike builder aligns the tranny gears, sprockets, jackshafts etc. as close to perfect as they can too. So not sure how this is any different a neccessity.

i'm not saying it doesn't work but for me a regular gearbox solves these problems and will be way less maintenece and more cost effective in the long run.

Time will tell ... there is no specifict data yet to support they are more or less expensive, time consuming, require more maintanace etc. on bikes.

you should talk to dieselfly about this his seems to be working for him but he is running a punsun v-twin, so more power.

Hopefully he will chime in here

[roodesign]

Hi there, I have a Kubota Z482 (13hp) engine with a comet 94c/90d set up...I also have the problem with slowing down on hills...but I think that is because I have the drive pully set up with extra weight to engage at a lower rpm which causes the centrifical portion of the drive to have more force relitive to the torque reactive driven pully. On a hill, the drive shifts to about the engine's torque peak (+,- 2500rpm) and just chugges up the hill...the drive should allow the engine to (just) reach it's top rpm (and max hp) on the 90d drivin, there are several adjustments that can be done to control the force that the torque reaction produces for overpowering the driver pulley's centrifical forces...I will be doing this shortly, and report back.

if you would like to see the Vehicle, go to http://www.roopod.com as far as durabilty, I have 2000 miles on my first belt, and I can see that it has worn, but there is yet very little if any change in the way that the cvt behaves...

[skoleskibe]

Im using a comet 40 with a 7,5" driven.
Its slightly tuneable, try shifting or omitting the springs in the driver, and you'll have a max out at app 2200 rpm instead of 32-3400 rpm, and a clutching piont of app 1000 rpm in stead of 1800rpm. You coupe also try moving the fix point of the torquesensing spring, simply by drilling one or more holes for it to Mount in to. This affects the Dow shifting quite a bit.
Im using a Yanmar l100 engine in my bike, and so far my normal flat road no wind speed is ajour 80 kph. The aboslute max according to gps is 103kph.
Climbing hills often slows the bike down to about 60-65 kph. If you lock the cvt at top end, you Will still loose speed uphill A's the engine simply does not have the Oomph to dó the job.

Regards

[DieselFly]

I have been playing with the weights and springs in my CVTech CVT for a over a year now. for those that say there is not enought ratio in a CVT mine has a total of 6.97 with a .45 overdrive. If I put the set up the shift out point around 2200-2400rpm (max torque) the clutch will engage around 1200rpm and the engine will never see over about 2900 rpm and will dog a little on hills and the top speed is about 65 mph. The next setup that I used on the driven clutch (heavier spring light weights) results in the engagement going up to 1400rpm and a shift out speed of 3200rpm. The bike will cruise at 3000rpm at 60mph indicated and it under reads by about 4mph do to an oversize front tire. If you hit a hill the bike wiil shift up to 3200 and climb with no lose of speed. The max rpm I have seen with this setup is 3400 so there is still about 1hp left but why run the sh*t out of the engine. All of that said it does lose 5mpg with the second setup but the top speed also goes to 75mph. I have almost 3000 miles on my first belt and about 1mm of wear. If you are finding your belt is not lasting its is either not aligned properly or the driven clutch spring does not have enought tension and allows the belt to slip. The CVT that I have is not a perfect match for the size of rear tire as it is ment for ATVs with a smaller tires (but it was cheap). There is a lose of energy with any transmission but the lower weight and less complex to install CVT can be made to work very well. If you can't get up the hill put a bigger engine in

Sean

[Rhynri]

I realize this is an old thread, but it is a rather important topic. To the best of my knowledge, nearly all snowmobiles use CVTs, almost all of these are belt CVTs. It's a thick belt too, almost two inches wide. My sled would engage forward motion at about 3k solidly. The sled, which is a '92 polaris INDY 650 XLT EFI (3cyl fuel injected cast iron block 650cc engine) you had three RPMs the engine would operate at. 5200 (for slow speeds (min seemed to be about 20mph-ish)) 7200 (this maintained your current speed usually) and WOT which was 9400rpm. Cracking it wide open from a stop would get the sled to about 80mph in a little over 3 seconds if you could hook the long track up. It had hydraulic power disc brakes and was quite heavy. They had quite the sound too. This is a bone stock sled similar to mine. Clicky for Youtube! They had some issues with ethanol freezing water into the injector lines and people burning out the cylinders because they didn't wait for the engine to warm (it warms the cylinders from left to right and drops idle speed when finished).

With the high RPMs, when you hit a hill one of two things would happen. Either the track would pop loose (not a big issue on a sled, you rarely ever completely hook up) or the engine would absorb the slight decrease in gear ratio with ridiculous power. On the hill for our diesels, a little drop in speed translates to a bigger shift in gear ratio and the ratios are then shrinking before the engine is even able to counteract the shrink. I think most CVTs are suitable for higher RPM applications, and our belts in the CVTs we are seeing are somewhat small and thin for the torque being appied, which leads to reliability issues. The belt in my sled is the stock belt, the sled itself has 5.6k miles (which is more than it sounds like on snow, a 200 mile ride is a day's work because the trails are all offroad).

[DieselFly]

Golf carts CVT, Quads CVT, Side by sides CVT, The clutch sets are tuned for the applications. They are very tunable and you need to start with a setup that has a working range suited for your use. My CVTech set came with two sets of weights, Three drive springs and two driven springs. I'm still playing with springs and weights. I had it the way I liked but the Turbo has changed the torque and HP enought that I'm at it again. I'm playing mostly with shift out RPM and back shift. And yes it climbs hills with ease and normally only picks up 200 rpm on the steepest grade I can fine around here and will accelerate up hills with little problem.