Definitely no personal experience with the P5 but I've had a P2 for 10 years with the aero seatpost--I used a 'regular' rechargeable light and attached it to the 'frame' of my xlab behind the saddle water bottle holder--it worked well enough. Not sure if you are using some type of behind the saddle hydration or a saddle bag (at least in training) but most lights can attach to something like that.

I have this one: https://www.ebay.com/...1:g:Iu4AAOSwW9NcsA-x

Due to the silicone "rubber band" it fits aero seatposts. It's only 15 lumens. so it works fine a dusk/night, but isn't bright enough for daylight.

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ECMGN Therapy Silicon Valley:
Depression, Neurocognitive problems, Dementias (Testing and Evaluation), Trauma and PTSD, Traumatic Brain Injury (TBI)

The Lezyn Strip Drive should work. It is shaped to work with aero posts and has a long rubber band to attach the light to the post.

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Brian Jacobson
Fit2Ride Velo Studio
http://www.fit2ridevelo.com

Check out the Knog lights! They attach with elastic bands, and I had no trouble putting one on my Shiv's aeropost (I attached 2 sized bands together).

I use a Cateye Rapid X It mounts on the seatstay with a rubber band. On my road and TT bike.

I've used several from the various taillight manufacturers. I just recently ran across a new one from Niterider the Sentry Aero 260 and have found it works great with aero seatposts. The light comes with a longer rubber strap that allows mounting on an aero post. It outputs up to 260 lumens and the sideways lighting really makes it stand out. https://www.niterider.com/...088-sentry-aero-260/

Good one.

https://www.cyclingweekly.com/...ee-aero-x-rear-light

I have a Bontrager R-Fare on the seat post at two Serfas Thunderbolts on the seat stays. I also have a Bontrager Ion in front. This combo gives me high flash in the daytime and the battery life is great and USB rechargeable. I use them every (non-race) ride . . . it is just like putting on my seat belt.

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David
* Ironman for Life! (Blog) * IM Everyday Hero Video * Daggett Shuler Law *
Disclaimer: I have personal and professional relationships with many athletes, vendors, and organizations in the triathlon world.

I use the Comet-X Pro.
What I have done is used a small loop of bungee/shock cord to create a loop wide enough to fit around an aero seat post. (I had some lying around from my dive gear, but easy enough to source)
I am currently using it on my P5, but I did it on my Felt IA4 without any issue.

(Sorry for bad pic, can get some better ones when I get home from work if you want)

Garmin varia radar and keep an eye on the traffic behind you. Been using this for years. The latest iteration will last for a 5+hr ride with the radar active. Nice mount for TT seat posts

+1

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IG -frebay | Strava

Do you need a rear bottle cage holder, the kind that attaches to the seat? If so, I use an XLab Super Wing and then attach lights to the back of that. This cage has several holes on the back surface so that you can screw in any kind of mount you need.

I run a Garmin Varia radar light, so I installed one of these onto the cage to hold the light: https://www.amazon.com/...le?ie=UTF8&psc=1

I sometimes run a Trek Bontrager Flare R light (great light BTW), and used this to hold the light onto the cage: https://www.trekbicyclesuperstore.com/...mgQ50hRoCLqgQAvD_BwE

My XLab cage can hold both of the above lights at the same time, if I wanted.

Lookup Bup Labs and see if any of his mounts suit your needs. I've got one that attaches to a Fizik saddle that I really like but now there are some new more universal models and a few more saddle model specific options too. Good operation to do business with too, in my experience.

I use one by Apace Vision, about $17 on Amazon, 100 lumens, lasts about 45 hour before recharge, uses bands for attachment. Works great on my Shiv.