Please enlight me, buying new PM, choose 4spider or 5 spider arm?

first time buyer planning to purchase a powermeter(p2m ngeco)
currently using a ultegra 6800 crankset.

i came across a question, 4 arm or 5 arm?

please educate and enlighten me.

Cheers

Hi
Different torque over the 360 degrees. Force divided over the 4 and 5 arms different.
I have Assioma Pedals and are great, easy swapping between bikes. No issue if 4 or 5 arms.

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Depends on if you want to match / use your groupset’s chainrings. If your groupset is Shimano, and you want to use Shimano chainrings, then you would select 4-bolt. If you run Campy, then select 5 bolt to use Campy Chainrings.

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One thing to note is that these 4 bolt spiders accommodate a wide variety of chainring sizes from compact (like 50t or 46t big rings) or “standard” or bigger rings (53t and up). For 5 bolt rings you’ve got to choose a 110bcd if you want to run compact rings and if you have 130bcd are limited on the smallest tooth count rings you can run.

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If you are planning on running a P2M you will need to replace a your Shimano crankset with another one anyway. So the 4 vs 5 hole will determine what chainrings you can use. The 4 hole kind will allow you to use Shimano chainrings (or Shimano compatible 3rd party rings like absolute black) and the 5 hole will have you running praxis or SRAM chainrings (or other 3rd party 5 hole rings). For 5 hole the 110 BCD can fit 50-52 big rings while the 130 can fit standard and larger.

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i wouldn’t mind to mis-match the groupset.

i am going for the rotor aldhu 24 option but the 110 / 110-S / 130 BCD hitting my decision

i lived in sloppy/hilly areas so i better choose 4bolt or 5bolt /w 110BCD to accommodate from 34T to 53T, isn’t it?

i will pick the rotor 24mm option to replace the old shimano 6800 crankset and probably buy a new set of chainrings

The 4 bolt (Shimano style) will accommodate the following chainring combinations:

  • 53x42
  • 52x39
  • 52x36
  • 50x34

For the 5 bolt, you need to choose either 130BCD or 110BCD, which gives you the following chainring options:
130BCD:

  • 53x42
  • 52x39
  • 52x36

110BCD

  • 52x39
  • 52x36
  • 50x34
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Pretty much what Alphadogcycling posted sums it up.

While it is possible to make a 130bcd 50t chainring as it would be physically possible there aren’t many offerings available in this size. Rotor Q ring coms to mind but it is an elliptical chainring which is not for everyone. Physically I believe the smallest a 130 bcd small chainring can be is 38t as I’ve seen SRAM offer that in round but Rotor does have a q ring in that size I think.

On the other spectrum for 110bcd 5 bolt you could physically run bigger chainrings like 53/39 but you won’t easily find very many offerings in those sizes I’m aware of (for round rings). If you want bigger than that say for TTs or flat terrain I’m not aware of any chainrings in a 54 or 55 tooth count in a 110bcd that are round (maybe in elliptical there are some). Same with the small chainring as finding an 39t+ isn’t as widely available either… Too big a tooth difference between small and big makes front shifting difficult to get it setup to shift smoothly or even properly at all. Plus you’ll possible run into chain rubbing in the small ring and smallest cogs few cogs on the cassette well before you are cross chained. The outside of the chain would rub on the inside of the big chainring in the smallest cogs on the cassette but with an even bigger front ring compared to the small it starts rubbing way before the smallest cog. Might or might not be a big issue for one or some.

I picked up a 53/36 Rotor QXL elliptical chainrings in 110bcd 5 bolt to run on one my cranksets. It shifted horribly (kept throwing the chain off the big ring and just wouldn’t make the shift) and the outer chain would rub on the inside of the big chainring in the small ring and 4th cog on the cassette (we’re calling the smallest cog the 1st one). Once I swapped out that 36 for a 38 (or was it a 39…I don’t recall exactly at the moment) it shifted much better and the rubbing in the small ring only happens in extreme cross chainring combos (small and 1st/2nd cogs). I’ve been running Rotor rings for quite some time and cna get them setup to shift almost as well as round rings so it’s not a matter of setup. Don’t know why they offered this combo of a 53/36 and instead paired it with a 38 or 39 instead. Even a 52/36 would probably shift much better I think. But Rotor QXL rings don’t come in smaller than a 53 big ring anyways because of the amount of oval they put int (so they say according to their spec sheet).

If I could run a 52 or 53 big with a 34 small and get it to shift properly I’d do that in a heartbeat. But alas that combo doesn’t shift very well or even not at most likely. Usually it is recommended to have no bigger than a 16 tooth max difference between small and big rings but 14 is the sweet spot for good shifting (hence 53/39 being the most common standard size). Any more than that and YMMV. Honestly I feel all crank and chainring makers could easily do away with 130bcd and stick to 110 exclusively (both 4 and 5 bolt) and offer a wide range of chainring sizes to match. But they don’t and what is available out there for each sized spider is a result of such. Shimano has moved in that direction as they used to have 5 bolt in 130 and 110bcd. But they also wanted to keep their own proprietary bolt pattern too but at least they now have rings that are universal across all their 4 bolt cranks at least.

110BCD

52x39
52x36
50x34
  • 46x36
    44x34

I went with the 4 hole Power2Max, i.e. the Shimano hole pattern. My reasoning was that although it locks me into using only Shimano chainrings, realistically, Shimano chainrings are pretty much the standard that others are measured by in terms of shifting quality. Rather than faffing about with possibly subpar shifting, I’d rather just be able to run tried and true Shimano rings. And I think it still looks pretty good, too. 7,000 km later, I’m still very happy and wouldn’t change it.