The endless search for more speed

Larry Oslund over on the Cruzbike Forum has very kindly organised a virtual Time Trial challenge where all participants choose a 12 mile route either in the real world or Zwift, and then go full gas once a week for 21 weeks. Points are awarded for various categories such as W/KG, improvement since last week etc. It has been a great thing to do during lockdown, as all events I was entered for this year have been cancelled. Kudos to Larry for organising this, and to all his hard work collating all the numbers from 70(!) riders each week. A lot of effort!

I’ve been riding the CHR up and down the A7 with a turn around point at Heriot. It’s interesting to see how obsessive you can become about bike optimisation when you’re trying to get a slightly faster time each week! I started out with a fairly normal setup, but have been tweaking this week after week and finding more and more ways of getting a slightly more aero setup.

I started with a CdA of around 0.19.

The raised return idler is now gone (it deconstructed during my recent double century), and I’m running an over/under idler setup which is not quite as extreme chain / wheel interference as a full drop chain, but is not far off it.

I removed the 2 bottles from the cage mount behind my head and put the Angletech Aeropod bag back on. Despite the weight increase it does appear to give a modest aero boost.

Drop chain and aeropod
Drop chain and aeropod

I replaced my 11-32 rear cassette with an 11-25, to get closer spacing between gears for small adjustments. I had previously thought this a bit pointless and that you should just learn to spin at a wider range of cadences, but practical experience has forced me to eat my words – it’s definitely much easier to maintain a steady threshold power level.

11-25 Ultegra Cassette
11-25 Ultegra Cassette

I added a set of bar ends to the bars, pointing towards me, and put the TT shifters on the end of these, gunner bar style. This made a huge difference aero wise, as my arms are right out of the wind now. I wasn’t keen on putting the brakes on there too, so I left them on the bars. Previously, I had discovered that holding the brake levers close to the stem was more aero as again it got your elbows out the wind, but it blocked your view a bit and wasn’t very comfortable. This is much better. Also, the shifters are right next to your fingers so you can change gear very easily. Before, I would have to move my hand down to the end of the bar to change, which resulted in a slightly higher drag each time I did that.

I then raised the front of the seat slightly (about 5 mm), which made more difference than I would have imagined, both in terms of aero gains and restriction of forward view. As a consequence of that, I had to move the brakes on the bars. My first attempt was to use TT reverse brake levers and have them facing towards me, palm activated. This was a great setup and was definitely more aero as the brakes were behind the bars instead of above them, but there just wasn’t enough pull in the front brake mechanical disc caliper – braking was dodgy at best. The online blurb did say that they didn’t work well with mechanical disc calipers, but I took a chance thinking that they would probably be OK. They weren’t 😦 The back brake was fine with the Ultegra caliper rim brake, but the last thing you want on a recumbent is all your braking power on the rear.

I decided this wasn’t going to work, and so I then reverted back to the Sram flatbar levers, but attached to the gunner bars this time, running parallel to the tiller stem. This was the setup I had tried to avoid as I felt perhaps it might be a bit twitchy when braking on tricky descents, but so far it has felt OK. The ‘proper’ bars are now completely devoid of any components, but it’s nice to have them there for security when winching up a steep climb at low speed. The bar ends are angled a bit, which splays the two gunner bars out rather than pointing straight at me. This is great and gives a more natural position for the arms.

The final bar setup
The final bar setup

I could theoretically make a new ‘bar’ with a short, straight piece of tube and have a full gunner setup with no extra bits of bar sticking out at all, which would then allow me to shorten the tiller as there would be less interference between my legs and the bars. A shorter tiller means better control and also even more of the arms in line with the body, but this seems like a step too far and is quite extreme. I think I’ll ride with it as-is for a while and see how it feels.

The end consequence of all this futzing is that my CdA, when riding in full race kit with face shield on the helmet, is now around 0.16 – 0.165. That’s a massive improvement! I’m pushing up towards 27 mph for the TT effort for an average power of aroud 275W, which again is quite an impressive speed for me given the amount of incline on the route. I think the biggest impediment I have to reducing my CdA further is my muckle big size 48 feet pedalling in the very wide and completely flat soled Lintaman Minimal shoes. These are great shoes for midsole cleat placement but are basically two big sails pushing into the wind.

The last interesting observation – this week I used my Endura MTB gloves instead of my usual short fingered Boardman gloves. I get bad Raynaud’s and some mornings I just can’t keep my fingers warm enough in the short fingered gloves. TT conditions were perfect, not a bit of wind, but despite this, I was half a minute down at the turn, and was losing more on the return leg. Analysis when I got back showed that just wearing those bigger, bulkier gloves pushed my CdA up to about 0.175. I couldn’t believe that at first, but the numbers don’t lie. Just goes to show – don’t assume anything, and test everything. I’ll stick my hands in front of the garage fan heater for 5 minutes before I leave next time, and just hope I generate enough heat to keep them warm 🙂

4 thoughts on “The endless search for more speed

  1. Interesting mods , drop the aero bag and bite the bullet and get the M5 carbon tail box an awesome bit of kit Cheers Alan

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  2. I second that – the carbon tail box (21 l) will propably give you more of a speed boost than the aero pod and will propably be even lighter too. It’s not cheap, but for me worth its money. Quite practical and awesome look.

    Interesting handle bar setup, I will propably change mine for something similar.

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  3. I can’t justify the cost of the carbon tail box yet. The aeropod is good for now – if I ever turn the CHR into an audax bike I will probably spring for the tail box though. The aeropod bag has a lot less volume inside for storage. I like the fact there’s no rattles though, and I can pick it up and take it off easily.

    I really recommend the bar setup – for me at least, it feels like a much more natural arm position. it is a little bit twitchier though.

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  4. Just switched to drop chain setup too, to see what kind of a difference it makes (I had a setup with raised return idler before, like you).

    Turning the cranks backwards feels easier now (I did shorten the chain, so it doesn’t come from less chain tension).

    More noticably, the power transmission from the pedals to the wheel feels more direct now, which propably comes from the fact that I was able to move the power idler closer to the frame, by about 1 cm (swapping power and return idler, so power idler is now on the inside). This improves the chain line which is now almost parallel to the frame, from power idler to the big chain ring.
    Because of the shorter levers, this should reduce frame side flex and also vertical flex of the idler mounting bolt (though the bolt flex is probably negligible compared to frame flex).

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