Today marks the first step of the final stage of this new wheelset’s development. What is this step? Well, the first test prototype was delivered to us, and we sent it to our local 80kg+ UCI pro rider with a challenge to destroy them.
Background. Their development started almost 12 months ago when we asked GLM (Giant Light Metals) to make us 25mm carbon/alloy clincher rims since this would automatically grant us a UCI standard wheelset given our spoke lacing preferences (steel only, 20/24 minimum).
The brief seemed simple since the technology for making carbon reinforced alloy rims is not new and GLM after all has some major clients and technology at their disposal. Alas, the original samples that we received were anything but usable. The rims weighed 530g and 540g each! GLM and I both found this actually comical so they went back to the drawing board. The follow-up promise was 470g while meeting all the strength and stiffness requirements. This was getting closer to what we were expecting, and to GLM’s credit they did not rest there, they kept pushing themselves and their technology to make something extraordinary, something that would make us happy.
The final version samples were delivered two weeks ago, weighing 405g and 410g each. This weight is excellent and was achieved by careful re-engineering of the G609 alloy base, as well as by welding the rims, same as what we specified with the Tenax rims.
Gram SL intended end use is pro racing. Yes it is a clincher, but you will find many clinchers in pro races around the world and the 25mm profile is remarkably versatile and robust.
With the pro racing in mind we wanted to deliver a wheelset that can withstand the power outputs of top racers and satisfy the acceleration and handling requirements, without excuses. They also need to be serviceable in the field without requiring special tools, or unreasonable amounts of time.
The front wheel is laced with 20 spokes in the “elbows out” configuration to maximize the bracing angle, while the rear wheel uses 27 spokes (!) in a 2:1 pattern with 18 crossed spokes on the drive side and 9 radial spokes on non-drive side. To my knowledge this makes the Velocite Gram SL the only modern wheelset with a 27 spoke rear wheel. 18 crossed spokes on the drive side should mean absolutely amazing power transfer and “pick up”.
By using the 2:1 lacing we also achieved very good spoke tension ratios between drive-side and non-drive side. Non-drive side spokes are at 80% tension of the drive side, which is a lot better than the usual 50% tension with some 1:1 laced wheels. 2:1 lacing should extend the fatigue life on non-drive side spokes due to less variation in tension.
Spokes are Pillar PSR X-TRA 1422 aero blade spokes that distinguish themselves by being some of the least ductile spokes on the market, and by having very high ultimate tensile strength for their weight. Low ductility means that the wheels will remain true under extreme stress, and that they should be very stable over rough terrain.
To assist the spokes with their job of keeping the wheel true, we are using Alpina ABS locking alloy nipples. These alloy nipples use a special, patented nylon insert made by DuPont that locks the spoke in place, without seizing it. This means that building the wheel is straight forward and rebuilding it is not any different to rebuilding any other spoke and nipple wheelset.
Locking the spokes in place and using low ductility spokes means that the wheels should remain true until nipples, spokes, or hubs reach their fatigue failure point, a long time in the future. In theory.
This is why we are conducting this first live test with a pro rider, and why if they survive for at least a couple of weeks, we will order more samples and open the live testing to more volunteers. We need to make sure that our theory stands up in practice. Velocite Gram SL are intended to change the game, so the expectations of their performance are very high indeed.
The last thing is also one of the most important things. The weight. Gram SL prototypes built as above with our (Chosen) Velocite OS15 hubs with oversize axles and bearings is just 1382g actual. There is no rider weight limit, but our assumption is 110 kg max before premature failure is expected.
I will keep you updated on the live testing progress, which will hopefully start by proving our theories and design direction right…