Adding Oversized Pulley Wheels to OM-1

[Caleb]

Hi all!

Sharing my success with replacing the OM-1's stock pulley wheels with oversized ones.  

I am running an 11-36 7 speed cassette and 48-30 double on my Bike Friday All-Packa. Chain wrap capacity needed for this setup is 43t. The OM-1 is rated for 39t. I didn't take this issue into account until after everything was purchased and installed. 

With the stock 11t pulley wheels, the smallest 3-4 cogs were inaccessible while in the 30t chainring, and the chain was generally slack in all but the larger two cogs. 

My original plan was to buy an Altus rear derailleur from my LBS and harvest the 13 and 15 tooth pulley wheels from it. However, I was able to pick up two generic Shimano 13t pulley wheels and one 15t Altus takeoff from the LBS without having to waste a new derailleur. 

Glad I didn’t buy the Altus - the 15 tooth wheel would absolutely not have fit in the lower position of the OM-1's cage. Also, FYI the Altus pulleys are thicker than the stock OM-1 pulleys, but the generic Shimanos from the LBS were identical in width. 

Anyways, the 13t does fit in the lower position, though just barely. I had to file the cage down about .7mm in order to get sufficient clearance for the chain to pass through. Fits fine in the upper position. 

I also had to swap to a longer B screw with a hex head and insert it backwards to obtain sufficient clearance between the pulley wheel and the largest cog. This may not be an issue if you’re running something smaller than a 36t cassette or if you’re willing to use a road link - not really an option on 20” wheels though. 

Anyways, the oversized pulleys got me at least another 2 teeth of chain wrap - I now have 13 of 14 gears available, with only small/small being inaccessible. Pretty happy with these results! Though it’s a bummer of course that oversized pulley wheels didn’t make it into the production design… one can dream about the OM-2 though 🙏🏻 

Happy to answer any questions! I hope this helps someone. 

Caleb in Nashville

[Caleb]

Before and after pics

[Caleb]

Voiding the warranty pics

On Friday, June 19, 2026 at 11:51:46 PM UTC-5 Caleb wrote:

Before and after pics

[Johnny Alien]

I personally prefer the look of the larger pulleys and honestly its the main thing that is keeping me from getting one. I would guess that microshift wanted a design they thought they could also sell themselves and thats a bit of a Riv specific look

[Richard Rose]

Question; I run a 38/24 crank on my Gus & a 11-36 Jim cassette. I think that combo results in a 39 chain wrap? That maxes out a OM-1, correct? Is that wise?

Sent from my iPhone

On Jun 20, 2026, at 12:50 AM, Caleb <others...@gmail.com> wrote:



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[Bud Suttree]

Richard, I think you should be fine - you’ve got a difference of four less chainring teeth than I do. The worst thing that can happen is that your chain is too slack in the 11-24 gear which isn’t a big problem IMO as that’s not a very efficient gear. Definitely give it a try! 

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[Joe Bernard]

Agreed, that chainring/cassette combination is practically the stock Rivendell setup. It should work fine.