Some interesting power calculations (discussion fodder)

[Steve Ciccarelli]

Hi everyone,

I enjoy seeing the various bikes and equipment folks use during the rides and the engineer in me got curious about the tradeoffs in the various technologies.  Back in the day, there was a member of DC Randonneurs who (literally) strapped a lead-acid boat battery to his rear rack and used that to power his electronics.  There were those among us who thought this was a bit nuts, but the man was a machine. Still, I don't recommend this! 

Clearly battery technology has improved since then, but I also see folks using tried-and-true dynamo technology for their power needs.  My curiosity had me asking:

which takes more effort away from propelling the bike forward - a battery of X weight providing power vs a dynamo system (of weight Y) doing the same.

For the calculations, I took my worst case.  On the 400k, I carried a 50k mah battery weighing 610g.  Mind you, I used only 42% of its charge (which is the data I was looking to collect) so I could have cut that battery in half for the 400k, bringing the weight cost down to around 300g. Even less if I stopped running my iPhone screen and listening to music while riding - probably around 200g.  The screen is the power drain. But that's not realistic - I need the screen at times, and that's that.

I also had 2x 1000 lumen battery headlights at 200g each with 8hr run time per light.  Overkill, but again, I was collecting runtime data. Built in 6000 mah batteries each.

Shutter Precision, Schmidt SON29 and SON 28 dynamos are all around 400-450g, so let's call the weight a wash.  A 40k mah battery (lasting around 400mi) weighs the same as a dynamo.  A 25k battery (lasting 400k) would be around 2/3.  

So, configured for a 24hr ride (8 hr at night), the weight is a wash: power bank + battery headlights vs dynamo.  And it turns out, weight doesn't really matter all that much.

Magnetic drag does. For the battery, there is none.  Continual power, period.  For the dynamo, drag is 1-3w when off, 6-ish watts when the electronics is on (50% efficiency avg).  Passing that into some complex calculations, it turns out this is FAR more of an issue than weight.  The dynamo's drag is essentially to a sustained 0.2-0.5% grade with the peak drain at night when the rider is most tired (and the lights are on). This is based on me, as a 180 pound cyclist. The numbers are less favorable if you're lighter.

Worse, the dynamo powers a 70 lumen light, max. For the same weight, I'm running 2000 lumens and riding at 20mph without coming anywhere near overdriving the beam.  This from experience. And I can get another 8 hours of runtime by popping them into a charger block during a 30 minute power nap.

I'll be honest, I didn't expect the numbers to work out this way.  I was wincing when I loaded that beefy little battery into my top tube bento, and I was delighted to see I'd only used around 19mah at the 200 mile mark.  10k mah/100mi is about what I've been experiencing on my permanents. That's 800k before I drain that 50mah and significantly better than that if (like on Charmed Clover) I run smaller batteries and recharge or get fresh ones after each loop.  

Bottom line:  I'm pretty spoiled by 2000 lumens at night. I hated riding in the dark before. Now it's no big deal because I can see (literally) 200m ahead of me at all times. That's 20 seconds of ride time at 20mph. Even if the weight and drag calculations worked out differently, I'd be loathe to give this up.  The drag numbers working out in favor of the batteries (no constant 0.3% grade penalty) is gravy.  

Thoughts?

Steve

[Jeff Loomis]

I am sure that modern battery lights are superior to dynamo from a performance standpoint.  I will continue to choose dynamo and pay the several watt penalty because I don't need another thing (battery state, swapping and charging) to deal with on a long ride.  I am happy with the light output and beam pattern of the eDelux II.  There are much brighter lights available now and if I wanted more light on the road I might make a different choice.  Tires are another area where people may sacrifice speed for other attributes.  Your choice of tire can cost you a few or even tens of watts in the worst case.  Many randonneurs still choose chunky, slow-rolling tires because they don't want to deal with flat fixing.  If you are quick at fixing a flat the efficiency difference is probably more valuable but we all know a flat at a mental low point can kill your ride and might even prompt you to DNF.

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[Roberts, Mark]

Battery lights.

 

Long climbs are hard enough without having to think about the additional drag of a dynamo hub all the way up.

 

 

 

Mark W. Roberts

K&L GATES LLP
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[don person]

I have 7 wheels with SP hubs and 4 bikes with dynamo lights. 

Built my first in 2017(-ish) and loved never needing to worry about charging lights. 

I do carry a basic battery light for backup. 

I run the lights any and every time I’m on the bikes. Never noticed or cared about the extra effort that may be needed. 

shiggy Don Person
Dead Center WA

[Steve Ciccarelli]

I'm 100% with you on the tires.  I run beefy tires with slime tubes in them.  I detest, despise and abhor flats.  I'll gladly pay the weight cost there to avoid ever having to fix one on the road and since moving to this setup a few years back, I've not flatted since.  I religiously change the tubes yearly and the tires every other. I should probably shift to changing the tires yearly as well now that I'm doing considerably more mileage.

Watch me flat and eat those words on the next long ride.

Steve

[Geoff Hazel]

I’m of two minds on tires.  Back when I was commuting between Bellevue and Seattle I got occasional flats and found them quite inconvenient. 

I picked up a pair of Schwabe marathons which were rated very good for puncture resistance. I suppose they were but I never found out because I could easily feel 2 to 3 miles an hour going off my average speed. Felt like I was riding through a headwind all the time . 

I don’t know what I switched back to, but it was something more prone to flats, but better rolling.  And it didn’t take long to switch back. 

On the other hand, I tried some ultralight tires for city permanents in the winter  around Seattle and wind up getting a flat almost every ride. Any increase in speed was negated by the flats.  Now I’ve switched back to Continental four seasons and so far so good.

I don’t ride enough any more  to stay in good enough fitness to be able to ignore small losses in efficiency. So I need to try to find the sweet spot between flat resistance and rolling resistance. 

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[Kole Kantner]

Does anyone have ideas for measuring or obtaining relative rolling resistance of tires? I know my Continental Grand Prix 5000 tires feel a bit faster than the Schwalbe Marathon tires, but it would be nice to have a % number to factor against tire cost and flat resistance. I have seen some watt charts, but not many tires are on there, and I also know the results can be significantly skewed by tire pressure and surface roughness (chipseal).

What about finding a flat section, calibrating a power meter, and riding it both ways at a similar average speed? 

Unfortunately, my new Coros Dura does not directly display kilojoules like all Garmin units do, but it is relatively easy to calculate with average power and ride time. I still love the Coros Dura for the phenomenal battery life. I have used mine for about 100 hours and it is still at 75% charge. I think mine must recharge during the day when I am not using it. The GPX track display is good for seeing the course, but I have not found out how to display distance to next turn that I used to appreciate with Garmin navigation.

Kole

From: seattl...@googlegroups.com <seattl...@googlegroups.com> on behalf of Jeff Loomis <je...@loomisclan.com>
Date: Tuesday, May 12, 2026 at 3:19 PM
To: ciccp...@gmail.com <ciccp...@gmail.com>
Cc: Seattle International Randonneurs <seattl...@googlegroups.com>
Subject: Re: [SIR] Some interesting power calculations (discussion fodder)

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[Ken Lanteigne]

I've watched battery and LED technology improve, with an eye toward moving away from the dynamo eventually. Over that same 15 year time period, I've gone from switching my lights off during daylight, to running lights day and night. So I've effectively raised the bar for my required battery life. And like someone else said, another charging requirement is the last thing I want at an overnight. I'm keep waiting. 

Regarding weight, had to chuckle since I was just prepping my fixie for the fleche. My nice light fixie is now a tank, and I have not yet added water bottles. In addition to the dynamo lighting, I have a rather heavy Fenix backup headlight that likely will not get turned on. Thinking about a spare tire. Looks like cold and rain, so that'll add poundage of clothing. 

I did read somewhere that rolling resistance is lower on wet roads, so there is that. 

Ken

[Kole Kantner]

+++ for the convenience of dynamo lights. I have run always-on dynamo lights for safety for decades. It is also helpful to always have light whenever I need it. A few years ago, I noticed one of my Shutter Precision hubs was really dragging when on and I switched back to SON hubs for dramatically reduced drag. Now I can barely tell the difference between lights on or off and I just leave them on for better training and safety. I would like to try the new SON Ladelux, but for now the eDelux II with SON 28 hub still meets all my needs. It would also be fun to measure power differences with lights on or off, but that might be even harder to measure than tire rolling resistance differences.

Kole

From: seattl...@googlegroups.com <seattl...@googlegroups.com> on behalf of Jeff Loomis <je...@loomisclan.com>
Date: Tuesday, May 12, 2026 at 3:19 PM
To: ciccp...@gmail.com <ciccp...@gmail.com>
Cc: Seattle International Randonneurs <seattl...@googlegroups.com>
Subject: Re: [SIR] Some interesting power calculations (discussion fodder)

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[Kole Kantner]

Does anyone get flats with tubeless road tires? Does the sealant seal up most flats like a slime inner tube? Is it very troublesome to repair a flat on tubeless tires? I have heard tubeless may also roll a bit easier, but I am mostly concerned about reducing flats while maintaining good rolling resistance and increasing tire longevity.

Kole

From: seattl...@googlegroups.com <seattl...@googlegroups.com> on behalf of Steve Ciccarelli <ciccp...@gmail.com>
Date: Tuesday, May 12, 2026 at 3:41 PM
To: Jeff Loomis <je...@loomisclan.com>
Cc: Seattle International Randonneurs <seattl...@googlegroups.com>
Subject: Re: [SIR] Some interesting power calculations (discussion fodder)

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[Bill Gobie]

For rolling resistance you could look through Wim Schermer's tire tests. (And critique AI-translated Dutch.) He has tested lots and lots and lots of tires for his velomobile. I think his methodology is pretty good, although missing a dissipative element. 26" tires are going to be close to 700c in RR. 

Bill

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[don person]

Kole, look up the Chung Method. It can be used for aero and/or rolling resistance testing.

Then there is this: 

https://escapecollective.com/introducing-escape-tyre-testing-get-ready-to-rethink-accepted-wisdom/

shiggy Don Person
Dead Center WA

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[Bill Gobie]

The crust of sealant and dirt inside my fenders says I have had a number of punctures that went unnoticed.

I have had a cut that required plugging the hole, which then sealed up with more sealant.

I had to put a tube in when I hit a pothole too hard and the tire burped. Must have been a spectacular spray of sealant because the driver behind me stopped to ask if I was ok. Could not reseat the tire with a hand pump so I had to put a tube in. It was messy.

Bill

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[Bill Gobie]

Seems to me RR should increase on wet roads because the tires pick up and fling water, which takes energy.

Bill

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[don person]

My road tires are 38-42mm wide, and I almost always run them tubeless with Orange Seal or Panaracer Seal Smart. I don’t know how many flats I didn’t have because punctures were sealed quickly. But after a few years the inside of my fenders look like I sprayed them with undercoating. If anything the latex sealants are much better than traditional Slime. 

I can only think of one flat that required a tube. Cut the tire hitting a square edged rock on a soft dirt road. A 6-8mm hole .

shiggy Don Person
Dead Center WA

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[Kole Kantner]

Thanks for the link to the escape collective article. It was looking very interesting, but then wanted $112 to read the rest of the article. Have you seen the rest of the article? I see it does allude to dramatic differences dues to tire temperature. I see that in automobile gas mileage as well, either from tires or air resistance, or something else.

Kole

[don person]

This this link

Here's a gift article for you from Escape Collective: https://escapecollective.com/introducing-escape-tyre-testing-get-ready-to-rethink-accepted-wisdom/?gift-token=vOqB7Awl

shiggy Don Person
Dead Center WA

[sh...@ivory.org]

I have been following this site for years.  It probably doesn’t simulate real world conditions very well, but at least it is a level playing field.

 

https://www.bicyclerollingresistance.com/

 

I use Schwalbe Marathon Plus tires on my touring bikes.  They’re ridiculously slow, but I haven’t ever had a flat tire while touring.  I carry tweezers and flip the bike over every couple days to pick out bits of wire, glass, rocks and other sharp objects before they get through the extra layer.

 

I use Continental GP 5000 TR S 32mm tires on all my road bikes, and I run them tubeless with regular Orange Seal.  I almost never get flat tires that don’t seal themselves and carry plugs to fix the ones that don’t.  I carry a whole extra tire and 2x tubes for really bad luck, and I’ve used it maybe four times in well over 100,000 miles.

 

I realize dynamos and dynamo-powered lights are gradually falling out of favor as battery technology improves, but the new Ladelux light and charger is just amazing.  When paired with a SON 28, It will keep three devices (Samsung S25 Ultra, Garmin 1050, Garmin inReach Mini) fully charged indefinitely, at 10 or 11 mph, with the headlight on, on a loaded touring bike.  I am sure it is slowing me down, and I simply don’t care.  It’s luxurious and absurdly satisfying not to have to plug in every night. 

 

I just built a wheel with the new SON 29 S, which has even higher output at slower speeds, but I haven’t finished building the bike it will go on.  I just wish it didn’t only come in black (this goes for the Ladelux too).

 

I resisted weighing in on this topic, because I am sure “real” randonneurs have different concerns than I do, but I love dynamos and dynamo-powered chargers!

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[Evil Jim]

WRT rolling resistance questions, BRR is the largest collection of data that I know of...but I've not dug into the dataset much, myself.  I have simply seen it regularly referenced in discussions.

Due to my inexperience, IDK how their testing compares to IRL riding, but it would still be a great comparison tool, I would think.

For tubeless and flats...I have had great success on my bikes, though I am no longer doing rando/brevet distances.  That said, aside from plenty of road rides, I have done some very Cascade gravel riding (on 'cross tires) and still been fine.  At this point, I most commonly change out tires for wear, over any other reasons.

If a slice doesn't seal, or as is more common for me, I'm low on sealant, it is a mess to deal with a flat.  Such incidents have been very uncommon, but I simply put in a tube and deal with it all once I am home again...whether that's peeling the tube out, or replacing the tire.
There's always enough sealant, once compressed between tube and tire, to adhere the tube into the casing. =)

I do need to get around to buying/including a plug kit in my saddle bag.  IME so far, this has not been a failure mode on paved roads...so I continue to push it off.

Jim

Puget Sound roads and gravel (both trails and roads)

Clydesdale weight (200+ lbs)

32 mm road tires

33-35mm 'cross tires

big, fat, chunky MTB tires

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[Steve Ciccarelli]

Yeah, that makes sense to me too.  Lower resistance on wet roads?  Water has some nonzero amount of viscosity, this doesn't make sense to me.  Energy is needed to lift that water off the road which isn't necessary when dry.  *scratching my head*

[don person]

AFAIK BRR testing is all done on a small diameter metal drum with the wheel is a fixed position (can only move vertically). Allows comparisons between tires, but may or may not be relevant to real world conditions. 

shiggy Don Person
Dead Center WA

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[Bill Gobie]

Lithium batteries require some care. It is not good to always charge them to 100%, nor to leave them charged at 100% for long periods. Ditto leaving them discharged below ~20%. Do not charge them below about 40°F, and absolutely not below freezing, including powering your gps from a power bank or dynohub. The batteries inevitably decay over time, which guarantees devices with non-replaceable batteries have limited lifetime$. (Looks at gasping iPad.)

Bill

[sh...@ivory.org]

The batteries in the devices I carry on my bicycle last longer than the devices themselves are likely to.   I’ve simply never had a problem with noticeable battery life degradation in over 160,000 miles of charging with a dynamo hub charger.

 

A bigger concern is water resistance.  The USB-C port on my previous phone got damaged, so I had it replaced by a factory-authorized repair company.  However, the phone died due to water ingress on a rainy ride this winter, and I learned that the water resistance is no longer assured (let alone warrantied) after the case has been opened.

 

Bottom line: if your phone is ever serviced (e.g. to replace a battery), it is probably no longer water resistant.

 

From: seattl...@googlegroups.com <seattl...@googlegroups.com> On Behalf Of Bill Gobie
Sent: Wednesday, May 13, 2026 11:48 AM
To: don person <don.p...@gmail.com>
Cc: ciccp...@gmail.com; k.lan...@gmail.com; Seattle International Randonneurs <seattl...@googlegroups.com>
Subject: Re: [SIR] Some interesting power calculations (discussion fodder)

 

Lithium batteries require some care. It is not good to always charge them to 100%, nor to leave them charged at 100% for long periods. Ditto leaving them discharged below ~20%. Do not charge them below about 40°F, and absolutely not below freezing, including powering your gps from a power bank or dynohub. The batteries inevitably decay over time, which guarantees devices with non-replaceable batteries have limited lifetime$. (Looks at gasping iPad.)

 

Bill

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[Steve Ciccarelli]

Bill,

All very true!  However, despite that, I still charge everything to 100% for the bike because, well, my 50k mah battery only costs $30. Sure, in 3 years, it'll decay and lose 10% of its holding capacity but then it'll get recycled and I'll buy one that weighs 2/3 as much and holds 30% more power. If Toyota's solid state batteries make it to the market, these things will be featherweight and last forever. Current technology 10k mah packs are down under $10 and last me 100 miles of ride time.  In a word, disposable. 

This being said, you've got a great point on storage.  I ought to burn down the built in 6k mah batteries on my headlights to 50% for storage when I don't use them for weeks at a time, then top them back off the day before an event.  Makes sense.  Tail lights, I use all the time, so they get deep cycled (pardon the pun) almost daily.

Steve

[Steve Ciccarelli]

Shaun,

Good info! Thankfully my iPhone hasn't ever been opened.

I used to run into problems in the rain where the phone would tell me "liquid detected" and refuse to charge from the power bank.  Now, ror rain rides, I put my phone in a ziplock bag (complete with charger cable and quadlock case) and mount that on the bike. I lose a lot of touch screen response when I do that, but the phone stays bone dry.  For lights, not an issue as the battery's integrated into the headlight.

Steve

[Bill Gobie]

My previous GPS's battery life suddenly cratered. Best explanation is I ran it off a dynohub in freezing weather.

Bill

On Wed, May 13, 2026 at 11:58 AM sh...@ivory.org <sh...@ivory.org> wrote:

[Kole Kantner]

Hi Shaun,

Thanks for the helpful information. The SON 29 S and Ladelux look really nice, although a bit expensive. Which model SON 29 S did you get and why?

 I am inclined to get the regular width 6-bolt in 32-hole since I am used to that, but perhaps so many spokes are now over building.  I have never broken a spoke in 40 years of riding, but I always value durability over cutting too many corners. If 24 spokes leads to more issues I will take the small additional weight and drag of 32. After all, a dynamo hub will probably have more drag impact than the number of spokes.

Kole

From: sh...@ivory.org <sh...@ivory.org>
Date: Wednesday, May 13, 2026 at 11:03 AM
To: Kole Kantner <ko...@uw.edu>; don person <don.p...@gmail.com>
Cc: je...@loomisclan.com <je...@loomisclan.com>; ciccp...@gmail.com <ciccp...@gmail.com>; Seattle International Randonneurs <seattl...@googlegroups.com>

Subject: RE: [SIR] Some interesting power calculations (discussion fodder)

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[sh...@ivory.org]

I have the 32-spoke center lock version. 

 

I am not quite a “Clydesdale” (yet?), but I hover close to it, and I carry way too much stuff on my bikes, so the combined weight is considerable.

 

I’ve only broken spokes on a 26” Rohloff wheel that was improperly built with the wrong rim AND wrong spokes.  Rohloff specifies both for 26” wheels and will – allegedly – not honor warranties if you deviate from these instructions.  This experience is why I decided to start building my own wheels.

 

I got used to using the 6-bolt dynamo hubs because SON doesn’t make a shiny polished aluminum version of the SON 28 center lock hub, but I actually prefer the center lock versions.

 

• Shaun

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[Roberts, Mark]

I generally don’t weigh in on these things, but would like to voice the modernist view since most of the voices seem to be more traditionalist.

 

I’ve used both generator powered lights and battery powered lights and I prefer the latter for several reasons.

 

As an anecdote, in my view generator hubs are not a foolproof, no worry solution.  On one Paris Brest Paris, my generator hub failed in the rain.  I managed to borrow a battery light, and then bought a small battery light and fortunately was able to finish.  Another time, a friend (who will go nameless) crashed and broke his front generator wheel on PBP – fortunately it was the last day so he could borrow a regular wheel to get to the finish, but that would have been a problem had it happened a day earlier.

 

For the last 10-15 years I have used battery lights, and the technology is quite good and always improving.  For super long brevets of longer than 1200, I don’t ride 5 days straight anyway, but stop every night and have a chance to recharge my lights, bike computer, phone, etc.  Devices charge faster than they used to, so for me, everything is topped off after 3 or 3-1/2 hours.  I really don’t need a light that will last 80 hours, as I hope to ride in the daylight, too.

 

Regarding wheels, using battery lights not only avoids the generator-drag issue (whether real or just psychological), but it also opens up more wheel choices.  I prefer lighter carbon wheels, frequently 35-45mm in depth. That generally means no generator hub, as there are increasingly fewer choices for purchasing standalone carbon rims to build up with a generator hub.  Wheel manufacturers are also moving towards wider internal rim diameters for wheels, to better fit wider tires, and there also is a lot more choice in that regard in modern carbon wheelsets.  That set up can also address the rolling resistance issue.  Of course, it’s true that it may be easier to fix a spoke on an aluminum wheel, but spokes on carbon wheels don’t tend to break as often in my experience, maybe because the rims flex less.  I’ve broken spokes on aluminum wheels but not carbon wheels.  My general rule of thumb is to make sure my bike is in good repair before I ride, at home, rather than overpack and carry solutions for every possible emergency.

 

In less than three weeks, I will ride a hilly 1000km brevet on the island of Sicily.  There will be night riding.  My primary light will be a Fenix BC26R, which gives me 9.5 hrs at 600 lumens, with a turbo feature of 1600 lumens for 3.5 hrs.  It is very solid construction.  I will carry at least one spare battery, which weighs little, and is easy to swap out on this light.  Maybe one more spare battery in a drop bag. 

 

For a second light, I will either pack my second Fenix light, or else an Exposure Joystick or Leyzne 1200 lite drive, both of which give up to 1200 lumens (Exposure lights are solid but pricey).

 

All my devices are now USB C to simplify and improve charging; I don’t find it a huge hassle to charge the lights, as they easily detach from their mounts; it is just part of the routine.  I carry a small charging block that can fit 3 charging cables so I can re- charge everything at once from a single outlet.  I also carry on the bike a small, lightweight portable battery (Nitecore 5000 or 10000ah) if I need to top anything off while riding.  I can even through-charge with that battery, so on overnights I can re-charge the portable battery itself and another device at the same time using only one USB port on my charger.

 

This gives me the ability to have bright lights for descending and for the flats. I’ve used this or similar set ups in the past with success, including the same event in Sicily two years ago.

 

I’m not trying to dissuade anyone from using generator lights for randonneuring.  I just want to say that there are in fact excellent battery light solutions out there that will work.  It doesn’t require a special purpose wheel.

 

 

 

 

 

 

 

 

Mark W. Roberts

K&L GATES LLP
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From: seattl...@googlegroups.com <seattl...@googlegroups.com> On Behalf Of Kole Kantner

Sent: Wednesday, May 13, 2026 2:17 PM

To: sh...@ivory.org; don person <don.p...@gmail.com>
Cc: je...@loomisclan.com; ciccp...@gmail.com; Seattle International Randonneurs <seattl...@googlegroups.com>
Subject: Re: [SIR] Some interesting power calculations (discussion fodder)

 

Hi Shaun, Thanks for the helpful information. The SON 29 S and Ladelux look really nice, although a bit expensive. Which model SON 29 S did you get and why? I am inclined to get the regular width 6-bolt in 32-hole since I am used to that, but

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[David Litt]

"If Toyota's solid state batteries make it to the market" ... indeed! 

I think they were targeting having them in the market for the 2020 Tokyo Olympics ... but still no sign of them actually being in EVs anytime soon, if ever, and it will take far longer before they are in bicycle lights. Otherwise, battery tech does continue to raise the bar. My latest iPhone (16e) and latest Garmin (1040) last 2x or more as long as the corresponding products would have a decade ago, and my "spare" battery-powered front light doubles as a battery bank to charge those devices in a pinch.

But seriously, my vote goes for dynamos. I don't want to worry about using up my battery and I don't need something else to charge on a long ride. I don't want to worry about rain ingress issues -- which I had the last time I used a battery powered light on a long ride. Last year, I built up one of the new DT Swiss dynamo hubs (with SP dynamo components inside) and it has been great so far. Maybe it adds a few hundred grams vs a regular front hub (which you need to add to your comparison(), but it works no matter how long the ride, no matter how much rain.  A Busch & Mueller IQ-XS provides plenty of light for riding on the road at night. Set and forget ... and use 24x7 when you want daytime lights as well. The dynamo light weights a lot less than a battery powered light too. 

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[Andrew LaMarche]

I've noticed a fair number of folks seem bothered by charging batteries, which is fair - it would annoy me. But the world of lights accepting swappable 18650 and 21700 lithium cells is now quite large, and the cells themselves are quite cheap. I basically have a few torches powered by 18650 cells that I printed helmet and handlebar mounts for, and I just pop cells in and out as the batteries die. Since all the batteries are fully charged before I depart, I also don't have to worry about the charging inefficiencies from recharging an on-board, non-swappable light battery.

I did a 600k with considerable bouts of night riding last year, and didn't come close to using up the 4 batteries I brought with me.

That said, I'm still interested in dynamo lights. If you want to nerd out, this link has some interesting circuits for dynamo lights and provides some interesting insights into how the dynamo being a constant current source (at a given speed) can allow you to really crank light out with the right circuit design.

-Andrew

[David Litt]

Which lights (torches) do you use with the swappable Li-Ion cells? I have a Fenix one that I gave to a friend to use at LEL together with a few spare cells … it was well-built (and heavy as a brick for its size) and I did not particularly like the beam shape — if I recall it was not driver-friendly for oncoming cars.  I cannot find many others that actually allow you to swap out the battery like an old flashlight and are designed with a beam cutoff. Lumintop B01?  Other?  Any that have a nice beam pattern — plenty of light down the road, even illumination, decent width, cutoff to avoid angry drivers flashing their bright lights) as my Busch Mueller IQ-SX?

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[Andrew LaMarche]

I use a Sofirn HS20 (click for technical review). It does not have any cutoff features, since it's really designed to be a headlamp. I haven't had any issues with cars, but I also don't live in area with a ton of traffic (NH/VT). You can get a sense for what the beam for the throw LED looks like on high here.

On a 600k last fall, I used an Energizer X1000, which also worked just as well. Similarly, no cutoff.

Both of these headlamps are pretty cheap - they don't have any voltage regulation features, so the light output decreases with battery voltage as the battery depletes. If you want that, you'll probably want something like the newer Sofirn HS22 (click for technical review)

Some of the lights are designed to accept button-top 18650s rather than flat-top (slightly smaller length). When I run into this issue, I just slap a couple neodymium magnets on one end - it works well for low current draw applications like lamps.

I've heard the Lumintop B01 is a nice light, but if you ride in tough terrain the battery holder springs are susceptible to breaking.

-Andrew

[Bill Gobie]

I have a Fenix BC22R which Fenix advertises as having a cutoff beam pattern. Compared to a round beam, I suppose it does. The cutoff is nowhere near as sharp as a Schmidt Edelux II has. The Fenix on its higher power settings is far brighter than an Edelux II. Its run times seem in line with what Fenix claims. It uses a swappable battery. I got it as a daytime running light and nighttime descending light. I have not used it seriously at night yet.

On a nostalgic note, when I began randonneuring the ne plus ultra was a Schmidt SON hub driving twin halogen Schmidt E3 headlights. You could feel the 10W drag when both lights were on. The beams were narrow and rather dim, and the potential need to replace burned out bulbs was ever present. The lights had some attractive features, however. The halogen filaments produced a warm continuous-spectrum light that many considered provided better illumination than the nominally brighter early generation LEDs. I still find light from LEDs somewhat unsettling. The dim halogens allowed very good night vision adaptation. I could look up and see the stars and Milky Way overhead. One splendid night on a 600 many of us were able to turn our headlights off and ride by the light of the full moon over the North Cascades.

Bill

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[Hahn Rossman]

They have changed the course some for PBP2027 to address the problem of riding at night with other riders blinding you with their round beams. Remember the oncoming vehicle might be another cyclist, not just cars!

Hahn Rossman

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