Dynamo hubs, how much drag?

ugo.santalucia

I have built a few dynamo hubs into wheels (SON, Shimano and Supernova) but always for others. Spinning the wheel in the jig, there appears to be a huge amount of drag... is this really annoying?

I am considering building myself one for the winter, given my LED light only has 2 hours worth of battery and it requires me to remember to charge it every day, but > 50% of the time the light will be off... is it worth it?

arthur_scrimshaw

I don't know about drag but in my mind the main criteria for using a dynamo set up is for extended rides (touring and some Audax rides) where the ability to re-charge batteries is not available. I'd have thought the cost of the setup (SON hub plus decent front light) would at least as much as say an Exposure Strada, which would last years and give 10 to 12 hours at a time at good levels of illumination?
I like the idea of dynamo, just not convinced I need it. But then that's not stopped me trying other things.

kayakerchris

Yes
The drag is totally unnoticeable when riding. I think that commuting is the perfect place for a dynamo hub. never worry about charging, batteries whatever. Simply climb on the bike and the lights start working. They stay on for traffic lights and turn off themselves at work or home.

meanredspider

C'mon, Ugo, you should know better than that. What load are you going to apply to the dynamo?

veronese68

My colleague with the heaviest wheels in the world, I won't say who built them, insists he doesn't notice the drag in a dynamo.

ugo.santalucia

Veronese68 wrote:

My colleague with the heaviest wheels in the world, I won't say who built them, insists he doesn't notice the drag in a dynamo.

5 Kg... still holds the record... I think it was Alfine rear and dynamo front on some Rigida Taurus rims... almost a shame I used double butted spokes

meanredspider

I used to notice it on my Brompton - but then it was an old skool dynamo against a very little wheel/tyre.

veronese68

ugo.santalucia wrote:

Veronese68 wrote:

My colleague with the heaviest wheels in the world, I won't say who built them, insists he doesn't notice the drag in a dynamo.

5 Kg... still holds the record... I think it was Alfine rear and dynamo front on some Rigida Taurus rims... almost a shame I used double butted spokes

That sounds right, haven't seen that bike for a long time. He decided he had to sell some bikes a while ago so set up an Ebay account. He's bought 3 frames and a couple of wheelsets since then and not sold anything.

ugo.santalucia

meanredspider wrote:

C'mon, Ugo, you should know better than that. What load are you going to apply to the dynamo?

I can't quite work out how many watts it will suck to produce a given amount of current. Bear in mind 10 Watts is like going from suppa duppa tyres to a pair of cheap nasty ones

Bobbinogs

Huge amount of drag?? When running unpowered I think the stats are something like less than ONE mechanical watt going to waste...and even when actually powering a decent light the mechnical watts required are typically 5-10. If you wear your natty new helmet in Flanders colours at the same time then I reckon you will come out all square!

meanredspider

If you know the current and voltage, Watts is easy. The bit I don't know is the efficiency of a dynamo - but 50% would probably put you in the right ballpark.

marcusjb

A Schmidt SON is around 65% efficient.

With no load, the drag is 0.5W ish.

So, during the day (see below) you're giving away next to nothing, less than if there is a zip undone on your jersey.

Powering a light (or a USB charger during the day) and you are going to put 5-10W into it - yes, it's a chunk, but it's all fit and forget, no worrying about batteries, keep your phone/GPS charged for days on end.

Unless you're racing, the drag is not going to make a jot of difference. I wouldn't use one on a 24hr TT for example (partly for drag, partly so I can remove the unaero light at daybreak). I have a mix of SON28s and SONdeluxes.

SON are gold standard, the Shimano units are not far off in efficiency and are about 25% of the price (the are not very serviceable though, whereas a SON is not user servicable, but should return to the factory every 50000km).

I was hoping to link to the CTC article where they tested a load of dynohubs and so on - but they appear to have mucked up their PDF archive during the whole change to CUK.

smoggysteve

ugo.santalucia wrote:

I have built a few dynamo hubs into wheels (SON, Shimano and Supernova) but always for others. Spinning the wheel in the jig, there appears to be a huge amount of drag... is this really annoying?

I am considering building myself one for the winter, given my LED light only has 2 hours worth of battery and it requires me to remember to charge it every day, but > 50% of the time the light will be off... is it worth it?

Alternatively if it's just for extra lighting, I used to have a set of lights that were fitted onto the axles and were held on by the QR . They charged by having a magnet pass like and old school Garmin speed sensor. They would flash pretty fast and be solid for about s minute while stationary. Made by Sigma and they were available in German bike shops. I'll root around and find a pic if you like

smoggysteve

http://www.ridewill.it/p/en/ventura-221235-led-light-set-dynamo-magnet-induction-front-and-rear/111218/

Like this but different

sungod

there's a lot of info here...

http://www.peterwhitecycles.com/schmidt.php

...towards the end of the page there's a chart comparing a few types to a normal hub, on/off, at speeds up to 30kmph

ugo.santalucia

Bobbinogs wrote:

Huge amount of drag?? When running unpowered I think the stats are something like less than ONE mechanical watt going to waste...and even when actually powering a decent light the mechnical watts required are typically 5-10. If you wear your natty new helmet in Flanders colours at the same time then I reckon you will come out all square!

Deal

ugo.santalucia

marcusjb wrote:

A Schmidt SON is around 65% efficient.

With no load, the drag is 0.5W ish.

So, during the day (see below) you're giving away next to nothing, less than if there is a zip undone on your jersey.

Powering a light (or a USB charger during the day) and you are going to put 5-10W into it - yes, it's a chunk, but it's all fit and forget, no worrying about batteries, keep your phone/GPS charged for days on end.

Unless you're racing, the drag is not going to make a jot of difference. I wouldn't use one on a 24hr TT for example (partly for drag, partly so I can remove the unaero light at daybreak). I have a mix of SON28s and SONdeluxes.

SON are gold standard, the Shimano units are not far off in efficiency and are about 25% of the price (the are not very serviceable though, whereas a SON is not user servicable, but should return to the factory every 50000km).

I was hoping to link to the CTC article where they tested a load of dynohubs and so on - but they appear to have mucked up their PDF archive during the whole change to CUK.

thanks... all this arguing with you has put me in the mood for PBP 2019...

ugo.santalucia

SmoggySteve wrote:

http://www.ridewill.it/p/en/ventura-221235-led-light-set-dynamo-magnet-induction-front-and-rear/111218/

Like this but different

KInd of be seen more than seeing though... could be good for a rear

marcusjb

ugo.santalucia wrote:

thanks... all this arguing with you has put me in the mood for PBP 2019...

See you there! There's not many rides I would do multiple times, but PBP is a whole different league of fun. I can not imagine not doing it (whereas this year is the world's second largest 1000km+ brevet in the form of LEL and whilst I will feel pangs of jealousy for those riding it, I can handle not riding it this time I think!).

The route is not outstandingly interesting, or challenging in terms of terrain - however, well, the people! All the people cheering you on for 4 days is just incredible. Coming into a control town and there being huge crowds at all hours of the day - nothing quite like it.

Dynamos are definitely handy in that style of riding, both for lighting and for keeping electronics charged up (though a medium sized USB battery pack is enough to keep GPS going for the duration and phone if you're careful). I did PBP the luxurious way in 2015 and spent two nights in hotel rooms, so charged stuff at wall sockets!

ugo.santalucia

marcusjb wrote:

ugo.santalucia wrote:

thanks... all this arguing with you has put me in the mood for PBP 2019...

See you there! There's not many rides I would do multiple times, but PBP is a whole different league of fun. I can not imagine not doing it (whereas this year is the world's second largest 1000km+ brevet in the form of LEL and whilst I will feel pangs of jealousy for those riding it, I can handle not riding it this time I think!).

The route is not outstandingly interesting, or challenging in terms of terrain - however, well, the people! All the people cheering you on for 4 days is just incredible. Coming into a control town and there being huge crowds at all hours of the day - nothing quite like it.

Dynamos are definitely handy in that style of riding, both for lighting and for keeping electronics charged up (though a medium sized USB battery pack is enough to keep GPS going for the duration and phone if you're careful). I did PBP the luxurious way in 2015 and spent two nights in hotel rooms!

Not challenging is ideal, given the distance... and I was thinking single speed anyway. Much like the Paris-Roubaix cyclo, I would expect to be the people at the side of the road to make the event!

I guess GPS is the other bit of kit I'll need... plenty of time... what do you use?

Provided I qualify, is there a draw or everybody is automatically accepted?

marcusjb

I've ridden it geared and fixed - it's a great fixed/single speed route as the climbs are not ever so steep (can be long though). Some tough (long) descending on fixed caused me a bit of arse ache last time.

You do not need GPS at all - it's 100% sign posted with volunteers at many key junctions.

I believe the last two times, any one who has qualified (i.e. ridden an Super Randonneur series in the months of January to June in the time leading up to PBP) has got a place no problem. They do run a pre-registration scheme where those with the longest brevets in the season before can pre-register first (think it went something like 1000km+, 600km, 400km and then 300km) - but that really doesn't do ever so much, you get a bit more flexibility on your start time, but you still have to qualify.

Here's my guide to the registration process in 2015:

http://www.marcusjb.com/blog/2013/11/05 ... -2015-then

As I have said elsewhere, if you want it enough, riding a long way at a moderate pace isn't actually ever so hard. Until it is - it's usually the stuff that is outside of your control like weather, mechanicals etc. that will start to gnaw away at your resolve. But the head will almost always give up before the body - the body can and will keep going, there will be awful times where everything hurts, but as Churchill (may have) said "When you’re going through hell, keep on going" - it will get better.

ugo.santalucia

My bugbear to long distance was riding in the dark, but over the past year I have commuted all winter and actually really enjoyed riding in the dark... it's very relaxing.

Good to know there is work to do in 2018... although I am not sure I want to ride a 1000 km one year before, kind of makes PBP into less of a challenge... maybe a 600 km

Brakeless

I find riding in the dark one of the most enjoyable parts of long distance cycling. You're in a little world of you own, the roads are really quiet if not empty. As long as you are well lit I find nearly all traffic gives you more room than they might in the day. I think half the time they are quite bemused to see a cyclist lit up like a christmas tree in the middle of nowhere at 2 in the morning. Riding in the countryside as the sun comes uo and the world start to rise is also pretty special.
You also tend to cycle a bi slower and steadier at night so any issues with Dynamo 'drag' are really not relevant/noticeable at all.

alan_sherman

I have a SON delux, honestly don't notice it is there. i even commute in daylight with the lights on now as I've become too lazy to switch the switch. I used that wheel on all winter club runs too. I doubt I'll ever get a non-dynamo front wheel again.

The shutter precision ones are about the same efficiency but cheaper.

My only regret was not getting a disc one (for flexibility)

ugo.santalucia

alan sherman wrote:

I have a SON delux, honestly don't notice it is there. i even commute in daylight with the lights on now as I've become too lazy to switch the switch. I used that wheel on all winter club runs too. I doubt I'll ever get a non-dynamo front wheel again.

The shutter precision ones are about the same efficiency but cheaper.

My only regret was not getting a disc one (for flexibility)

I'd have to get a disc one. The SON flange geometry for disc is not ideal, but it would go on a "mainly for flat" single speed bike, so it shouldn't be a massive issue.

Shutter precision? Noted

alan_sherman

http://www.spacycles.co.uk/m2b0s170p0/P ... ilt-Wheels

You may have your own sources, and preferences for rims, but the SP d8 wheel from spa seems a great deal. My delux hub cost more about 8 years ago.

term1te

I use an SP8 hub on my commuting bike with a nice set of Philips lights. Its a great set up and I wouldn't go back to battery lights. Its a bike built for utility not speed, so I don't care about the tiny drag from the dynamo when the lights aren't on. When I turn the lights off I can feel a slight reduction in the resistance, but it's mostly psychological as even with a 50% efficiency it can't be more than 6W difference. When I built the dynamo wheel the intention was to swap it out in the summer, but I've left it on for the last few years as it didn't seem worth it.

bernithebiker

Free tea and biscuits if you want to deviate to Quimper....

dennisn

ugo.santalucia wrote:

I have built a few dynamo hubs into wheels (SON, Shimano and Supernova) but always for others. Spinning the wheel in the jig, there appears to be a huge amount of drag... is this really annoying?

I am considering building myself one for the winter, given my LED light only has 2 hours worth of battery and it requires me to remember to charge it every day, but > 50% of the time the light will be off... is it worth it?

Well, a little drag is no big deal. However, getting run over by a truck because of poor lighting would be a really big drag.

ugo.santalucia

dennisn wrote:

ugo.santalucia wrote:

I have built a few dynamo hubs into wheels (SON, Shimano and Supernova) but always for others. Spinning the wheel in the jig, there appears to be a huge amount of drag... is this really annoying?

I am considering building myself one for the winter, given my LED light only has 2 hours worth of battery and it requires me to remember to charge it every day, but > 50% of the time the light will be off... is it worth it?

Well, a little drag is no big deal. However, getting run over by a truck because of poor lighting would be a really big drag.

Always good advice Dennis... :twisted: the alternative is a battery light, as I am currently using, trying to always remember to charge it

roger_merriman

ugo.santalucia wrote:

dennisn wrote:

ugo.santalucia wrote:

I have built a few dynamo hubs into wheels (SON, Shimano and Supernova) but always for others. Spinning the wheel in the jig, there appears to be a huge amount of drag... is this really annoying?

I am considering building myself one for the winter, given my LED light only has 2 hours worth of battery and it requires me to remember to charge it every day, but > 50% of the time the light will be off... is it worth it?

Well, a little drag is no big deal. However, getting run over by a truck because of poor lighting would be a really big drag.

Always good advice Dennis... :twisted: the alternative is a battery light, as I am currently using, trying to always remember to charge it

Or one with a longer run time, I agree though powerful a lot of modern lights are power hungry and need charging frequently which is tedious. Or you get ones with battery packs which though longer lasting mean you have to fit to bike etc.