Hub How-To - Powertap

This installment of our How-To series on hubs is for Saris’ CycleOps Powertap. We’ll cover the current generation (G3) and the previous generation (G2).

The important thing to note is that this articles does not deal with any of the ‘guts’ of the Powertap hub – the torque tube, strain gauges, and hubshell bearings. Why not? That type of service can only be performed by CycleOps (some services can be handled by If you are having trouble with power readings or anything electronics-related, your best bet is to contact CycleOps customer service directly.

We will cover a few things:

1. Freehub removal, service, and replacement
2. Battery cover removal and battery replacement
3. Firmware updates (G3 only)

We’ll start with the one-generation-old SL+ hub. The procedures here are the same for all similar hubs of the same G2 generation (i.e. SLC+ with ceramic bearings).

To begin, you’ll need your handy Hub Cap Wrench:

Saris says this wrench is used on all SL, 2.4, 2.4+, Comp, Elite+, PRO+, SL+, SLC+ and 2012 PRO Hubs. Press it down firmly on the hub and unthread the cap (standard right hand threads).

After the cap is off, it will look like this:

To replace the batteries, you want to remove the entire battery pack first. Do so by pulling gently on the black tabs on either end.

Once the battery pack is out, pop the batteries out. I’ve found the best method is to push from the bottom with one finger, and from the back with another (having at least some semblance of a fingernail will help). Be extra careful doing this – you do not want to damage the chip or wire.

This generation of hub requires model #303/357 batteries. Saris quotes 300 hours of use for a pair of batteries.

To reinstall everything, simply reverse the above procedure (push the battery pack back in place and thread the plastic cap back on).

Next, we’ll cover battery replacement and firmware updates on the newer G3 hubs. As you can see, the plastic cover is a different shape than on the older G2/SL+ hubs:

This updated cap shape requires a new tool:

Similar to the SL+ and older hubs, place the tool on to the hub and unthread the cap.

Next, use the sharp edge of the tool to gently pry up on the electronics unit.

The whole unit comes off to reveal the battery and USB plug-in:

This is a good time to check for hub firmware updates. To do so, remove the battery first (you may need to use a pair of needle nose pliers if the battery is tight).

You’ll need the CycleOps USB plug-in – it is compatible with all of the G3 hubs, as well as the Joule GPS. To update the hub, simply plug it in to your computer, launch the Power Agent software, click ‘Tools’, ‘Firmware’, and finally ‘Check for firmware update’.

After the firmware update is complete, unplug the USB cable, and pop a new battery in.

The newer hubs use a single CR2032 battery, rather than the dual 357’s in the old hubs. While the 2032 is very common, it unfortunately has a shorter life – 200 hours for the G3 hubs. Just to do some simple math for you, if you ride 6 hours per week, that gets you about 33 weeks of operation. Even if you ride more than that, you probably won’t have to change the battery more than every six months or so. I lump it in with other service – cassette cleaning, for example.

For reinstallation, place the red o-ring back in to the hub:

If you want to be super safe with your electronics-carrying rear hub, it is a good idea to use grease on the o-ring, and on any joints or seams. For applications such as this, I use silicone-based grease (also called dielectric grease), because it won’t harm electronics. You probably have some of this if you’ve ever worked on automotive brakes. If not, you can buy a tube of it from your local auto parts store that will last a lifetime.

I put grease around the threads of the cap, the outside of the cap, and around the hub’s end cap:

To put the hub back together, simply reverse the process. Be sure to carefully line up the electronics pack before you go pressing it in to the hub.

NOTE: If you have the Powertap Pro MTB Disc brake hub, you may notice that the supplied tool does not fit:

What gives? Due to the wider 135mm mountain bike rear hub spacing, the axle caps stick out further on either side (compared to the 130mm road hub). The bore in the plastic tool is not large enough to accommodate this. I spoke with CycleOps customer service, and they are aware of the issue. In lieu of using the tool, you can simply wrap a rag or piece of rubber inner tube around the plastic cap and use your hands. It isn’t quite as elegant as using the tool, but it worked just fine for me.

Freehub Service

Lucky for you, freehub service is the same for both generations of hub. The freehub itself is even the same – they are interchangeable between the older G2 and newer G3 hubs.

Well… the service is almost the same. On the older G2 hubs (SL+ and similar), you remove the freehub simply by pulling it off with your hand:

CycleOps received feedback that some customers didn’t like the ease with which the freehub comes off (which I don’t quite understand), so they reduced the clearance between the end cap and axle on the G3. You may be able to pull the freehub off with your hand, but I was unable to. I used my trusty axle vice:

If I didn’t have an axle vice, I’d likely use channel locks and wrap the end of the axle in an old inner tube to protect it.

Once the freehub is off, remove the axle spacer:

Now is a good time to spin the axle itself. If the hub bearings feel rough, you must send the hub back to CycleOps for new bearings. With most other hubs, you can replace the bearings at home, provided you have your own bearing press.

The reason you cannot replace Powertap bearings is that the hub needs to be recalibrated after new bearings are pressed in. It’s a slight bummer, but you probably won’t have to do it more than once every season or two, depending on the amount you ride in poor weather conditions. In all honesty, I know fewer than three individuals who actually own a bearing press – so most people have to send every brand of wheel back to the respective manufacturer for service.

Assuming your bearings are in good shape, wipe the old grease out from the ratchet ring area:

I’m taking this opportunity to install a Shimano 11-speed-compatible freehub on my hub. CycleOps now offers this as a spare part for all G2 and G3 hubs. It does not require any re-dishing of the wheel.

The new freehub includes a spacer to make it retro-compatible with 8, 9, and 10-speed cassettes.

To lubricate the freehub pawls, I’m using my favorite freehub grease, Morningstar Freehub Soup:

It is thick enough to last a long time, but thin enough to not gum up the pawls. I put one ‘large drop’ on each pawl and spread it around. I also put a light layer on the hub’s ratchet ring.

If you are simply performing service and NOT replacing the freehub, wipe the old grease off of your existing freehub and lubricate the pawls as mentioned above.

To reassemble the hub, all you need to do is slide the axle spacer back on, reinstall the freehub, and press the drive side end cap back on (noting that the G3 end cap will require more effort than the G2).