RoadTarmacTec

Tarmac: SRM Powermeter Crank

In the first iteration of the Tarmac was the Quarq DFour91 GXP the powermeter of choice. Solid and very accurate. But a few months later I had the choice get THE POWERMETER – the SRM Origin Carbon. The price was good, the money worth it… and there is a difference!

The Origin comes in different flavors. This piece of German engineered perfection is the Carbon Tri-Lobe crank with a 24mm axle and the Shimano-Spider. The Dura Ace R9100 chain rings matches perfectly.

These tools are needed:

  • Bike Stand
  • 3mm Allen
  • 10mm Allen
  • Torx 30
  • Torque Wrench
  • Rubber Mallet
  • Grease
  • Carbon Paste
  • Loctite 222 (purple)

Official Service Manual:

Service/Spare Part:

  • SRM Origin Carbon, Tri-Lobe, 24mm Spindle, Shimano Spider
    • SRM PM7 (custom order)
  • Shimano Dura Ace FC-R9100, 53-Tooth
    • Y-1VP98030
  • Shimano Dura Ace FC-R9100, 39-Tooth
    • Y-1VP39000
  • Shimano Chainring Bolts (M8 x 10,1)
    • Y-1H598160

Related Post:

Post as guidance? No warranty in ANY case of damage!

Information
SRM is THE Powermeter manufacturer. Accurate, durable and premium supported.

The SRM Origin Carbon is the first crank which is carried out in partnership with the French bicycle manufacturer LOOK. The benefit of this carbon crank is the Tri-Lobe design. It is possible to change the crank length between three steps: 170, 172.5 and 175.

Before this cooperation SRM modified OEM cranks like the Shimano Dura Ace. They integrated a Powermeter spider which was more than complex and expensive. Now with the Origin it is quite flexible – you can change everything (by SRM).

The chainrings are quite new, so this is a disassembly, cleaning and reassembly. I will also re-use the chainring bolts, so Loctite is needed because of the cleaning process as well.

Now for the weight check. The chainrings and bolts are at 146.2 grams, the SRM Origin comes with 558.3 grams.

First part of the assembly party is the installation of the chainrings. To prevent creaking noises I always apply some grease on the contact surfaces.

After that the chain rings can be aligned. The smaller ring has a mark which must point to the right rank arm.

Now for the bolts. When they come out of the pouche they are coated with some “green bolt glue”. Because of cleaning and re-use I apply some Loctite 222 (purple). This is as good as from the factory.

Then for the right torque in a criss-cross pattern. Every TX30 bolt need 12NM (SRM specification).

After that the Powermeter crank is ready for installation. Put a small amount of grease on the Bottom Bracket and the axle.

Then put it through… maybe a gentle hit with the rubber mallet is needed.

Now the non-drive side. Just a small amount of grease on the spindle, so that the crank reduce will slip easier in its position (plus noise reduction).

The slit of the reducer must face the crank arm on the drive side. This is very important. The left crank arm opening must be inline with the slit.

After that it is time to prepare the non-drive crank arm. Just a wisp of carbon paste on the teeth. This helps to prevent creaking noises.

Note
This is not part of the official SRM installation guide. It is based of my own experience with creaking noises during dusty conditions.

Then straight in its position.

Now it is time to secure the crank. The SRM Origin Carbon is not secured like a Shimano or Quarq cranksets. Those “standard” cranks are torqued down up to 45NM. This one is on low torque because it is clamped.

First is the clamping screw with a few drops of Loctite 222 (purple). After that 4-5NM of torque with the 3mm Allen.

Second and last step is the axle bolt. Loctite 222 (purple) on the bolt plus 5NM. But this time with the 10MM Allen, counter-clockwise.

Just gorgeous… the Tri-Lobe comes with the pedal installation… so stick around!