You could stay with the single sided and save some more money then buy a dual sided PM. Im on Garmin Vector 3 pedals and they seem quite nice (3 rides so far). They were 800 plus tax from my LBS.

You could also consider the Watteam Powerbeat. Install is a bit more involved, but honestly not too bad. It's hard to be 2-sided power for $400, plus it's compatible with your 105 crankset.

What is the weight difference between the 105 and the Gossamer Power2Max?

Or, for around the same price as the P2Max, you could go with a single sided Favero Assioma and then upgrade to dual sided later.

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get the powertap chainrings for $300 and mount them on your 5800 cranks

That seems like it would work </pink>

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shit! you're right. ignore my suggestion completely! (though I still think the C1 at $350 is by far the best deal on power meters... IF you have a compatible crank. which the 5800 definitely is not)

Just keep it. If you don't like the way the Praxis chainrings shift move to SRAM instead (Force or Red). Shimano tends to be the best shifting chainrings out there but Praxis shifts good enough imo.

I had a Gossamer crank with an SRM....those crank arms seem like they are built out of solid material. I also didn't like their looks but solved that with some vinyl tape that looked like carbon fiber to make the arms look plain. But besides a bit of weight you won't really feel the difference riding them vs the 105 crankset. Only reason I don't have my SRM anymore is because I went shorter crank arms and couldn't easily find a replacement to swap out on my spider.

Another thing I assume is you got the Gossamer that is a Megaexo spindle...while the spec sheets say it is 24mm it is slightly larger OD than a Shimano Hollowtech (I measured it with a caliper and forget the exact numbers but it was something like 0.010" at its larger at the points near both edges closest to the crank arms). It will fit in a Shimano BB but with only a very strong "nudging" and is very tough to get back out. I solved that by hand sanding the Gossamer spindle so it fit into the Shimano BB better (plus these are easier and cheaper to find than Megaexo BB's).

Or if you want to keep using Shimano chainrings spend a little extra and get the Rotor 3D24 version with the 4 bolt Shimano spider version. That will fit perfectly in your current bike BB and you can reuse your 105 5800 chainrings.

suahoi wrote:

get the powertap chainrings for $300 and mount them on your 5800 cranks

I second this suggestion. I've run 52/36 C1s with my 165mm 105 cranks for 3 or 4 years now and a Wahoo ELEMNT Bolt (recent addition) and it all just works.

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I have the dual Assioma and they are excellent, easy to switch between bikes and very sound performance. Wouldn’t go anywhere else, especially at the price.

Commenting on the shifting issue...
Is your chain line on the P2M exactly the same as your 105 crank? Did you take the time to get it spaced exactly the same?

If you didn't then i wouldn't expect it to shift as well without some adjustments.

Isn't the 4!!!! upgradable to dual sided? maybe start with the 1 sided and upgrade the 2nd side in 6 months.

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Only with Dura-Ace 9000 cranksets

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Yeah your right.
However I bet that it will trickle down to 105 in 6 months to a year (well maybe not bet, but assume).

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Possibly, but it may not be the same version, making you upgrade both sides, or something. Who knows? I'd rather go with something that has the upgrade path available now rather than at some date to be determined, if it comes at all.

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Thanks everyone for your words of wisdom!

I would have loved to do C1 chainrings, but I would have needed a new crank for that aswell. the 105 crank I have is the 4 bolt design.


After much though and deliberation, reading through all the comments... I think I decided to just stick with the power2max. I'm sure with the weight I was just overthinking it too much. IIRC its about 300-400 more grams, but its not like my bike is a crazy lightweight bike. I also figured if I sent it back, id be about 60 dollars in shipping and restocking fees. No Bueno!

I mounted the crank this morning and Loxx, you were definitely correct! it took a but of muscle to get them into the ultegra bb. I had to use a rubber mallet to get it to go in, This is ok, correct?

jaretj- I'm still some-what noob, so correct me when and if I am wrong. I have a bb86 press fit bottom bracket, with the 105, there was no room for spacers, and when I installed the power2max with the gossamer, there was also no room for spacers. It came with a wavy washer, but since there was no play or gaps, I didn't install it.(hope that's ok?) . Using some google, I found that the 105 is 43.5, and power2max is 45 chainline.


Once installed, I got the chain and everything on big ring and big ring and I may not actually need a new chain. Attached a picture, should be ok?

Thanks again everyone for your info!

Post 7 & 8 already commented above that this isn't possible. Pretty sure a 5 bolt C1 chainring set won't fit on a 4 bolt Shimano 5800 bolt pattern....but unless you know something I don't they don't line up.

P2M make great power meters. I love mine. I personally would take duel-side over a couple hundred grams an day. I used a Stages previously, and the P2M is a huge step up.

The one issue is their app is pretty horrible. But I understand they are updating that very shortly.

Kent

Please check again for room for the wavy washer. It sets the preload on the bearings. It's very possible you bearing spacing is exactly correct but I'd check it over again after a trainer ride.

Since the chainline may have shifted 1.5mm outboard, you may have to tighten your Front Derailleur cable slightly and/or adjust the end stops. It really depends on how it was adjusted with the 105.