My 'intro' thread - 'Steep Learning Curve in the Peak District' went into some sort of runaway condition and embraced several different subjects which, in view of the thread's title and location, were less likely to be seen and be of any benefit to other people new to this subject so I thought I would start one or two new threads with more specific titles.
In my intro thread trex came in with some interesting information on these 'auto' gearbox hubs and I copy some of the correspondence here.
JimB asked David at Electrifying Cycles "....However, I think the NuVinci CVT is going to feature in my final list of wants (rather than needs, again) and I have been trying to find more details of the KTM Macina NuVinci stepthru other than those on the German language pdf that I downloaded.
I notice that they appear to claim a max possible range of 180 kms although I don't speak German but find the prospect of a possible 112 miles range rather unlikely given the battery size indicated.
On any given bike is one likely to get better or worse 'fuel consumption' with a NuVinci compared to a standard 8 gear hub (not derailleur)? I would have thought the auto would be worse, if only slightly so.
EDIT Does the NuVinci CVT hub have more drag when not powered compared to a standard manual set of gears? My Suzuki Burgman 650E (with CVT) is virtually impossible to move without power."
David answered "...I have not ridden this type of system before but am aware of people noticing drag. Range depends very much on how you use the bike. I normally half the range quoted but it is largely dependant on assistance level used and terrain as well as rider weight and weather (longer range in warm, sunny weather)........"
trex said "Nuvinci is a bad idea.
The new model has a freewheel, so the rear wheel spins like on a normal bike but the transmission loss is still around 18%. If you ride unpowered, it's hard work."
then came back with this information;
"Derailleurs don't lose much power through friction, hub gears and the Nuvinci do.
In the case of the Nuvinci, progress in reducing friction loss depends on oil chemistry.
At the contact point, you have two oil surfaces coming into near contact, one surface is the ball and the other the input (or output) disc. The two surfaces are still separated by a little oil. This oil gap is pulled apart by the two sides, cavitation forces line up oil molecules in the gap, thus the oil behaves like a solid rod connecting ball and disc (a solid is no more than molecules that got lined up and can't move out of position). This 'rod' changes immediately back into liquid form a millimeter or so away from the contact point. When a liquid solidifies, it releases heat, widh radiates into the surrounding. This heat loss explains why friction loss of CVT is higher than mechanical (eg Shimano) hub gears.
This loss is only incurred when you ride on the flat or going uphill. Going downhill uses the freewheel.
NuVinci Continuously Variable Transmission - Wikipedia, the free encyclopedia
http://www.fallbrooktech.com/sites/default/files/videos/N360_Datasheet_English_Web.pdf
http://forum.ctc.org.uk/viewtopic.ph...38578&start=30 "
In addition, I have seen a few comments that this gearbox is 'draggy' and that that is noticed when riding without electrical assistance. But the jury may still be out on that at least as far as the most recent incarnations of the technology is concerned......
JimB
In my intro thread trex came in with some interesting information on these 'auto' gearbox hubs and I copy some of the correspondence here.
JimB asked David at Electrifying Cycles "....However, I think the NuVinci CVT is going to feature in my final list of wants (rather than needs, again) and I have been trying to find more details of the KTM Macina NuVinci stepthru other than those on the German language pdf that I downloaded.
I notice that they appear to claim a max possible range of 180 kms although I don't speak German but find the prospect of a possible 112 miles range rather unlikely given the battery size indicated.
On any given bike is one likely to get better or worse 'fuel consumption' with a NuVinci compared to a standard 8 gear hub (not derailleur)? I would have thought the auto would be worse, if only slightly so.
EDIT Does the NuVinci CVT hub have more drag when not powered compared to a standard manual set of gears? My Suzuki Burgman 650E (with CVT) is virtually impossible to move without power."
David answered "...I have not ridden this type of system before but am aware of people noticing drag. Range depends very much on how you use the bike. I normally half the range quoted but it is largely dependant on assistance level used and terrain as well as rider weight and weather (longer range in warm, sunny weather)........"
trex said "Nuvinci is a bad idea.
The new model has a freewheel, so the rear wheel spins like on a normal bike but the transmission loss is still around 18%. If you ride unpowered, it's hard work."
then came back with this information;
"Derailleurs don't lose much power through friction, hub gears and the Nuvinci do.
In the case of the Nuvinci, progress in reducing friction loss depends on oil chemistry.
At the contact point, you have two oil surfaces coming into near contact, one surface is the ball and the other the input (or output) disc. The two surfaces are still separated by a little oil. This oil gap is pulled apart by the two sides, cavitation forces line up oil molecules in the gap, thus the oil behaves like a solid rod connecting ball and disc (a solid is no more than molecules that got lined up and can't move out of position). This 'rod' changes immediately back into liquid form a millimeter or so away from the contact point. When a liquid solidifies, it releases heat, widh radiates into the surrounding. This heat loss explains why friction loss of CVT is higher than mechanical (eg Shimano) hub gears.
This loss is only incurred when you ride on the flat or going uphill. Going downhill uses the freewheel.
NuVinci Continuously Variable Transmission - Wikipedia, the free encyclopedia
http://www.fallbrooktech.com/sites/default/files/videos/N360_Datasheet_English_Web.pdf
http://forum.ctc.org.uk/viewtopic.ph...38578&start=30 "
In addition, I have seen a few comments that this gearbox is 'draggy' and that that is noticed when riding without electrical assistance. But the jury may still be out on that at least as far as the most recent incarnations of the technology is concerned......
JimB
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