My New Olympic Edition Sprint Bike

The Southern hemisphere’s summer track cycling season is fast approaching, and I've been busy designing and testing some new tech while setting up the new season's whip.

Frameset

I recently acquired a rare Rio Olympic edition Avanti Sprint frameset, one of only a handful in the public domain. frameset was only released in an XL of 60cm, specifically for the New Zealand team Sprint trio Ethan Mitchell, Sam Webster and the now retired Eddie Dawkins for the Rio Olympics. The team also used them at the recent Tokyo Olympic games. With Ellesse Andrews receiving a silver medal in the Womens Keirin.

Despite really enjoying riding the Velobike M2 frameset last season, I thought for this season it would be good to ride something new to learn from a top level frameset, take those insights and implement them into my new frame development. Frame design and bike fit has changed quite a bit since this frameset was released back in 2016. In particular, the length of modern track framesets are increasing - right out to the UCI limit. 

For more information on modern track bike fitting and equipment, read my previous ‘Insider Update’ here.

Cockpit

For the Tokyo games, we developed the Elite Longboi Stem for the squad. Each rider had a custom version specifically modelled to optimise their bike fit. These custom Longbois were not only designed to suit the rider, but specific to the Rio Avanti Sprint frameset. The tailstock of the stems were designed to integrate perfectly into the headtube cutout. This feature ensures the air flowing past this zone has a smooth transition and does not get caught up in any pockets creating drag.

Of all the various custom Elite Longboi Stems I designed for the team, none of the geometries worked for me, so I opted for one of my standard 6 deg 150mm Longboi stems flipped downward. Now some of you guys are probably wondering why I have opted for a tall(ish) spacer underneath the stem, rather than slamming the stem and running it pointing up? The steerer tube on this frame is a little bit longer than what I would usually run. Personally I prefer the cleaner aesthetic of a stem raised with spacers underneath rather than a stem slammed with spacers on top. I'm also a bit hesitant to chop it due to how rare the part is. Once you chop it, ya can't just glue on more carbon to raise it back up. But if that is the case with you, we make the Steerer tube extenders to solve this problem. Maybe in the future I will design another custom stem for the frame set to suit my riding position - at that point I will consider trimming it down a little. I think I'll decide what I want to do later in the season once I get used to the bike.

When it comes to a cockpit, it's the extra details that count. It's the area of the bike you're looking at and interacting with when riding. It's an important area to make you feel in control, confident and secure on the bike. On Top of the stem I have the first prototype Velobike Top Cap and with an extra long 40mm titanium bolt. The extra thread length adds a bit more strength and resistance to stop the headset loosening during high intensity sprint efforts. This can be a common occurrence with longer reach stems and bars as you are putting more torque through the system.

The bars are a prototype 300mm wide Longboi Sprint bar. They feature an updated airfoil profile from the previous prototypes and a stiffer tube shape in the transition of the drop. These bars were developed using fluid dynamic and load analysis software to refine the fuselage forms for the best combination between strength and aero. This updated design will be going into production later this year - with an official release expected for the Commonwealth games in 2022.

I personally prefer running no tape or grips on my bars. I feel more connected with the bike. It gives me a greater sense of control and awareness of the vibrations resonating through the bike. Running with no bar tape or gloves does come with its issues. Before a race I tend to get sweaty hands with the nerves. Even whipping the sweat away on the skinsuit sometimes it isn't enough. This is why I carry a bottle of liquid track chalk with me in my gear bag. Just before an effort, I'll squirt some on, and rub my hands together. The Alcohol evaporates and leaves behind a nice even tacky layer of dried chalk. Sweaty hands are no longer a problem.

In the ends of the bars are a prototype bar-end we have been developing. These are designed to fit in bars with or without bar tape. They offer a seamless aerofoil transition off the rear of the grips. When it comes to optimising aerodynamics, eliminating sharp edges or abrupt transitions is the simplest way to make gains. Something as simple as a bar plug could save a few fractions of a watt. It might not sound all that large a saving, but it all adds up.

Drive chain

For the drive chain I'm running a 165mm Dura-Ace 7710 crankset. Personally I find shorter cranks faster with my relatively short legs. I also believe short cranks can have some aerodynamic and biomechanical benefits as a result of bike fit and frame design. Perhaps I will go into more of this in another blog post in the future.

Fixed to the crank is a prototype 100 tooth chainring. Yes you heard correctly - 100 tooth! What makes this possible is that the drive chain has an 8mm pitch, where a standard ½” pitch chain is 12.7mm. This means more teeth for the same diameter. Currently set up on the bike is a 100 x 25 tooth gear combination. This is equivalent to a 64x16 ratio and in physical size. 

What is handy about the 8mm pitch system is that with each tooth change, the gear ratio changes at a finer frequency - see the tables below. 

8mm Pitch

½” Pitch

Starting in the middle of the tables are the 100x25 tooth chainring and sprocket in 8mm pitch, and its equivalent 64x16 tooth combination in ½” pitch. Side to side and up and down in each table table is one tooth change between chainring and sprocket respectively. 

When changing gears on a track bike there are three changes that can be done while maintaining a fairly stable chain length:

•  A Marginal Change - Changing a chainring by one tooth alters the gear ratio by a small fraction. Experienced riders may notice the difference in the relationship between RPM and speed, but it is very subtle. 

• A Medium Change -  Changing a sprocket makes a much larger difference in the gear ratio. Changing a sprocket is equivalent to moving up or down chainrings by about 4 chainring teeth in one go. This large jump in gear ratios is noticeable when you get back on your bike.
  
  
• The Awkward Change - This is an in-between change between the marginal and medium change. I dubbed this the awkward change because you need to change both the chainring and sprocket. This can take a bit of time - especially when you're in a hurry between races. 

Smaller pitch chains are a fairly recent adoption of technology within track cycling. We saw Team GB using ⅜” (9.53mm) chains at Tokyo2020 and our innovation partners New Motion Labs released the new 8mm pitch Enduo Evolve drive system at Eurobike 2021. 

The theory behind the shorter pitch chains is to decrease the angle each link needs to pivot as it moves around the drive chain system.This means that the 360 degree loop of the chain around the chainring and sprocket system is divided into more segments. The same theory applies to why chainrings and sprockets are increasing in size. The more teeth you have, the more links are used to wrap around the system - effectively reducing the bend angle of each link.

Efficiency testing by New Motion Labs, has proved that increasing the tooth count improves efficiency - whether this is done by larger gear diameters, or finer pitched chains - it all contributes. I will talk more about drive chain innovations and our New Motion Labs partnership in a future ‘Insider Update’.

For my new framesets component selection, I worked backwards by identifying what the largest standard chainring I could fit on the frameset, then converting that into the equivalent 8mm pitch size. The Rio Avanti Sprint matched with a Dura-Ace bottom bracket and crankset can fit a 65T chainring before becoming really close and potentially rubbing under a high powered effort where the ring may flex a little. Using this knowledge, I established a list of chainrings and sprockets that would provide me with a good range of gear ratios I'm likely to use this season. I also took into account selecting a chainring and sprocket size that would optimise my chain length and wheel position in the dropouts. These are the gear ratios listed in the table above. The range provides me with ratios between 102.8 and 113.6 - a good selection for an outdoor asphalt 333m track.

The chainrings feature the same general design as our aerospace grade aluminium Elite Track Chainrings. They have the same scaled down tooth profile with a low friction compound infused anodised coating. The recesses in the back eliminate excess mass, while maintaining a stiff and aero dinner plate form.

The Sprockets are machined from 630 grade Stainless Steel - one of the hardest stainless steels available. Material hardness is one of the defining characteristics of an efficient sprocket. Hard materials are more resistant to deforming as the chain presses into the tooth surface. Just like the contact patch of a tire on the track, contacting materials also have a contact patch. Soft materials have a larger contact area through deformation thus more friction.

I noticed when I set up the 8mm pitch drive chain that the chainline is even more important than with your regular ½” pitch setup. A standard chain line tolerance is 42mm +/- 2mm. My chain line is in spec at 42.5mm at the chainring and 42mm at the sprocket, but I noticed that when rotating the cranks, the chain would want to ride up over the inside of the chainring. This 0.5mm difference in alignment made a huge difference with the finer pitch chain. It is evident that when you scale down the pitch you also need to scale down the chain line tolerances.

Using one of our 0.5mm sprocket spacers, I was able to space out the sprocket to an accurate 0.0mm offset. Since doing that I haven't noticed any jumping. It's also so much quieter. Chain line is one of those overlooked adjustments on your track bike that can make huge differences with minimal effort. If you haven't already done so, check out my ‘Insider Update’ on how to measure and adjust your chainline for marginal gains.

Axles

When it comes to axle nuts, nothing beats Runwells newly released Elite Hub Nut. Available in 3 colours (gold, silver and black), there is a colour combination suited for every bike.

Runwell hub nuts feature a very early thread zone inside the nut. This allows the nuts to be of a lower profile while still maintaining plenty of thread to engage with the axle. The Rio Avanti Sprint frameset features some chunky stainless steel dropouts that take up a bit of axle space. With the low profile Velobike Chain Tensioners, there is still some a wee bit of axle left sticking out the end of the Runwell Hub Nuts. 

Concluding thoughts

That pretty much wraps up my new build! As always, it is a work in progress. I'm always swapping parts out and experimenting with new ideas. No doubt this setup will look different by the end of the season to how it looks now (cranks cough cough). There are also a few bits and pieces missing. That i'm yet to set up. The Pedals on the bike are Shimano 105 pedals that are quite a few years old now - I think it's time for an upgrade. I have some new Dura-Ace R9100 ones on their way - which I will set up with some Velobike Track Straps. I'll keep you updated.