Posted by: Ian | May 8, 2011

PowerTap and Van Nicholas seatpost maintenance

“Two steps forward and one step back” has been the slogan for this weekend. I wrote recently that the power readings from my CycleOps PowerTap had been getting erratic and then finally crapped out. Brian from my LBS surmised that this was because the unit needed new batteries. As soon as he said it it rang true; before then it had not occurred to me that the PowerTap even had batteries. Prior to looking for them I reassembled the freehub. A problem I’ve had a few times now is that when I try to remove the cassette from the freehub the shell comes off with it. This is because the sprockets bite into the freehub while I ride and stick into the splines. A rider with more souplesse might not have this problem but I tend to power up hills in too high a gear, driving the cassette into the freehub.

Following Brian’s advice, after removing the sprockets I filed down the freehub shell, getting rid of any burrs. As you can see in this photo, this leaves indentations of a millimetre or two where the sprockets in the middle of the range have eaten away at the splines.

The reason I called Brian in the first place was to figure out how to get the shell back onto the hub. There are three sets of two pawls – small sprung wedges that hold the shell on a sawtoothed ring set into the wheel – that you have to negotiate. Only having two hands, I couldn’t immediately see how. Brian explained that rotating them against the ratchet you can slip in each pair of pawls in turn. Once he explained this it was easy.

Removing the plastic cap on the other side of the wheel was, for me (with a non-yet-fully-functional left hand) impossible to do without tools. I opened up my vice wide enough to stick in the entire width of the plastic cap. Using the vice, this was easy too.

The batteries are housed in a removable plastic unit under the cap and it’s obvious how to remove it (tug it out) and how to unclip the batteries. The type of battery – a pair of EXP76’s – is unusual enough that it isn’t normally stocked in local stores; I got mine from Amazon. After replacing the battery unit, before screwing back on the cap it’s a good idea to grease it since you’re turning plastic onto metal and it would otherwise be easy to damage the thread.

The cassette I put back on the PowerTap was an Ultegra 12-25 that came (we think – there has been much swapping) from Emily’s original Scott. I removed the Conti 4 Seasons tyre that I was using previously for riding the PowerTap on my Astraeus outdoors through the winter and put on a Conti training tyre, specifically formulated for use on a turbo trainer. (The turbo trainer trashes normal road tyres.)

This morning, having done all of the above over the past couple of Saturdays, I was ready to see if the PowerTap now worked. I swapped the wheel onto the Astraeus and mounted the Astraeus in my CycleOps turbo trainer.  This was my first “step forward”.

Looking at the seat angle, I decided that I wanted slightly more down tilt on it. Also, I saw that one of the two bolts that holds the seat clamp tight was coming out so I needed to do something anyway, giving me the incentive to overcome my reluctance to mess with the infernal clamp. There now followed a very frustrating period in which I tried everything I could think of with an assortment of tools to get the saddle positioned within the clamp in the way that I wanted. In the end, I couldn’t even get the bolts back in properly without using so much force that I was concerned I might damage the thread. While the seatpost looks great on the bike, the mechanism for adjusting it is pathological. I can’t imagine the guys at Van Nic sitting back and saying something in Dutch along the lines of, “Job well done! Our customers will now be able to fine-tune their riding position with consummate ease.” I can only think they had to rush off early that day for the holidays and never got round to fixing the design.

Since I was getting stressed I decided to stick the seat post/saddle in my courier bag and ride it down to Bicycle Chain. I had a great ride on the Felt through Staple Fitzpaine into Taunton, getting there from Crickleaze at an average speed that was flattered by my 2 minute miles down the hill. At the shop Brian tapped out the clamp so that the bolts ran in comfortably and, after a cup of tea, I rode back home by way of Corfe Hill. Today Corfe Hill seemed easy and when I got to the steep final hill from Bishopswood I remained in my big ring and that felt easy too. Paula explained that this was because Corfe Hill and Bishopswood hill are not Dunkery Beacon, which I cycled up yesterday; that’s true but some days are just easier than other days and today was one of those.

Back at home, I re-greased the seatpost and slipped it into the Astraeus. This time I made the adjustments I wanted quickly and without any trouble. Finally I could turn the pedals over – and the power meter worked! I’ll see how the PowerTap and the new saddle position hold up on the road next weekend.



  1. […] it was a breeze but I first had to switch my carbon seatpost for the Van Nicholas Ti one. As I’ve written before, the Van Nic post looks great and works well but it’s a pig to change saddles on it. Despite […]

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