I am looking at 2 different rear dynamo lights,
- Busch & muller Secula Plus, it weighs about 70g, and gets mounted the rear fenders.
- Busch & muller Toplight line brake plus, gets mounted to the back of the rack.

Is the added weight of the rear light on the fenders, going to cause issues going down bouncy gravel roads, bouncing left and right? I will probably run with SKS longboard fenders

The rack mounted light is my 2nd choice, but it takes up a lot of space on the rear of the rack and may interfere with me lashing things to the sides. If any, what would the pros and cons be for mounting it on the rear rack? all I can think of is it will give me the option of going rackless and still have a rear light.

On a side note, how close should you fenders be mounted to the tyres? I have mine 2-5mm from the tyre, but I read today that for 700x37 I should get 45mm fenders and mount them 20mm from the tyres.

Just a side note on lights. I use battery powered taillights instead of dynamo for several reasons. When I flip the switch on the light to power the USB charger instead of the light, my taillight would be off, but on overcast days I like to run taillight during the day. Thus, if I want to use my USB charger and taillight at the same time, it has to be battery powered. Most of my touring is in places where flashing taillights are legal, thus I usually use flashing mode when I use the taillight during daytime. But, the dynamo powered lights I have looked at are only available in constant on mode, not flash mode. And the last reason is unique to me, not you, I have an S&S bike and I do not want to deal with the wiring issues when I disassemble and reassemble the bike. But, if you would rather go with the convenience of no batteries to worry about, get one of the lights you are looking at.

I try to get at least 10mm of clearance between fenders and tire, more if frame allows. Front is more critical than rear, if you get something stuck in the front, you could go over the bars. But the rear, you would likely just put a flat spot on your tire tread. Knobby tires are more likely to pick up something that could jam between the fender and tire, but I assume you are not using knobby tires on your bike.

Also Is the Schmidt SON Taillight small and in an aluminum housing that bolts to the Rear rack*

SON Rear Light..

Flashing bike lights are Verboten in Germany , so they are steady on.

* Again they work with B&M on the Fresnel Lens technology making a single light source wider,
and B&M offers its own mini dynamo taillight . (though the mount may not be Metal) it costs Less.


When I mounted a taillight on an SKS mudguard I drilled where the Metal Strut bracket was on the rear . For reliable rigidity .

If too far up for the angle you want, adding a strip of stainless steel (rack mount strut) bolting to that hole

then Mounting the light to the plastic Mudguard backed up by the metal reinforcement on the inside , proved itself durable .


Since wheel spew slings off the center of the tire I had less wide Mudguards an Inch above the tire .

so any sticks and crap fall away rather than Jam against the mudguard struts as It May if you set the gap as small as You describe ..

Back of helmet. Battery powered.

I own the Secula Plus and I love it. Very visible light. But there is also a version that mounts to the rear triangle. Check Oceanaircycles for some pics.

Lightskin puts an LED array and a Battery Inside the seatpost SEATPOST ? LightSKIN

It hardly takes up any space and shouldn't interfere with anything (my line plus lacks the brake option, but they're the same size)

Sigmasport Cuberider II mounted on the seat stay. Have these on my fat bike and my Surly Troll. Horizontally adjustable, tough, bright, 60 hours with 2 AAA batteries.

Rear fender lights are vulnerable to damage, sooner or later you will smack it against a door post or bike rack.
Rear rack bracket is a much better location, out of the way but visible. I lash stuff to my rack with a lamp no problem at all. You have to take care with the cable routing, some racks have hollow tube access for running cable. I run from the seat cluster, to the rear fender, protected by tape, then along the top of the fender, then up to the lamp. Use glue and ductape.

Note the metal Guard for mudguard taillights , bottom of the page Busch & Müller: Accessories

I would go for a rack mounted light. Anything on the body is really really silly. People don't need to see where your head or other part of your body is they need to see where the bike is. Plus having something lower is good so cars can more easily see it. The rack is more stable and less likely to flex and bend and bounce and whatnot, plus many can mount lights whereas fender you will usually have to drill out.

For those saying go battery, that is fine, have a battery/usb back up for extra light or if you are using usb charging.

Basically I tell my customers and friends to start with a good set of lights on the bike (such as Light and Motion), maybe have some battery backups and for the third or fourth sets of lights go for something on the helmet or body. Helmet lights are great for you being able to see things and certainly can add a bit of safety to what you already have but as your sole light on road they just aren't going to cut it.
I always shudder inside when I see people with bag mounted or helmet mounted lights people can barely see. It makes cars hate us more and doesn't keep us safe.

Interesting perspective. I have an L&M Vis 180 (very bright, 180 degree visibility) taillight on my helmet on pulse mode, and most of the time it will be the exact same place as my bike, just a little higher, which is good because cars will be able to see it better. Particularly cars that are behind other cars. If for some reason I became separated from my bike, as in a crash, I'd much rather have a car driver know where my head is than where the bike is. I agree that weak, poorly aimed taillights on a backpack are next to useless, but no one is suggesting that. I actually use a rack mounted taillight and a helmet mounted taillight, but if using only one, my preference is the one on the helmet.

I think that helmet mounts are a little high and if you move your head to look at a driveway or a cross street or a good looking person walking by or are looking down at the bars or something, that won't be quite as useful. The L&M is at least very bright and has more visibility than most other things on the market but I still would rather have thing firmly on the bike. Though I dig what you are saying about crashing but hopefully that doesn't happen and I may end up getting a VIS just for extra light and for potential MTB'ing

I bought it but left it off. It's almost twice as big as the Secula so it looks really weird.
But since the light is mounted on a plastic fender that can twist and the light itself feels really compact and sturdy I don't think it will really be that succeptible to damage.