BORG wheels hubs - 2:1 testing
For some time I have had a plan.
Why 2:1 lacing? Well it's been around for a while .Ford used it in the early 20th century in car wheels. It is a lacing pattern where the spoke tensions are more equal than in a conventional wheel. This reduces the stress in-balance around the spoke holes so rims are less likely to crack. Also the reduces the difference in loads on the rim actually increases radial stiffness. In addition there are 16 spokes on the DS at low bracing angle which contribute more to radial stiffness than the non drive side spokes. Torsional stiffness can so be higher given there are 16 spokes drive side which can be laced 3x and therefore tangential to the hub flange. So if done right spoke life can be extended.
It started in 2015 and for my 40th birthday I ordered a set of Royce UK Titanium carbon hubs. These have Titanium flanges, carbon fibre shell, Titanium axles, Titanium freehub body..... Rather special. I did however specify a geometry for 2:1 lacing. So that's a 24h rear hub (20h front) with 16 spokes DS and 8 spokes non drive side. 9 months later they arrived and they were built into a set of wheel I still ride today using Pacenti rims. The Sl23 V1 rim was crack prone. This set has not cracked the reason is simple, the 2:1 lacing means more even spoke tension and that reduces the stress differences caused by the loads placed by the spokes on the rim and that in turn reduces the fatigue rate.
The wheels feel great and the hub offers a 74% tension balance. These wheels are on my winter bike. The basics design was therefore proved.
Now to the geometry and a bit of physics.
2:1 lacing is not something that can be done with any hub. It needs specific geometry. The reason is the 8 NDS spokes. More than 50% of the lateral stiffness imparted by the spoke comes from the non drive side spokes due to the higher non drive side bracing angle.
This means a a 2:1 hub with conventional geometry will build into a wheel with lower lateral stiffness than if the wheel is laced conventionally. That not good for how the wheel feels or for spoke life. Brake rub is more likely.
To avoid this the non drive flange has to be pushed out much further than you normally see. 45mm from centre is the tipping point compared to a conventional 11 speed hub like the Shimano hubs where by there is no loss in lateral stiffness. My Royce UK hubs have NDS flange 46mm from centre and the DS flange 17mm from centre. This reduces the tension balance so for the Royce hubs with a symmetric Pacenti SL23 rim its it 74%. Asymmetric rims increase the tension balance. Kinlin rims have an offset of 3mm. So BORG 2:1 hubs have
DS flange 18.4mm from centre PCD 54mm - derailleur clearance seems to be good.
NDS flange 49mm from centre PCD 44mm
OLD 131mm (the one mm increase has been used on the DS flange to push it out).
Tension balance is over 95% with a offset Kinlin rim or 75% with a symmetric rim.
The bearing are the best NTN. NTN bearing are class 4 and that good. That means long bearing life. The seals are the contacting LLU. While non contacting bearings are often used in bicycle hubs so the wheel spins more freely in the stand in reality it less than 1W for both hubs at 30 kph is saved and that nowt to me. Bearing life is reduced as worn bearings have higher drag. If the LLU (contacting) and LLB non contacting seals are compared for drag at 30 kph the saving is 5%. Drag from seals varies with speed and load in a non linear way. The faster the bearing spin the smaller the difference. Hense non contating seals wont be offered. How a hub spins in your hand or in the frame with no load on it is no guide to how is roll on the road. What seems obvious really isn't.
The rear hub has 2x 61902 bearings and the freehub 2x 6802 bearing running on a 15mm axle. The freehub has 4 pawls and a 36T ratchet ring. This means fast engagement but the large diameter ring means a low rate of wear on the ring and pawls.
Freehubs for Shimano 9/10/11 speed Campagnolo 9/111/12 speed and XDR 11/12 speed will be available.
The front hub has a 69mm flange separation distance and 38mm PCD. 6901 NTN with LLU contacting seals are used.
A full range of spares will be kept along with the bearings which are bars to find in the U.K. use of more readily available bearings will lead to shorter bearing life. A limited number of hubs with non contacting seals maybe made available but bearing will be shorter and I wonder what the point would be. You won't finish your ride any faster.
The rims that I will use are Kinlin XR26T and XR26RT asymmetric for the rear. My instincts were correct this rim is perfect for this hub. There will be a Carbon rim too. A 55mm deep 25mm wide rim drilled for this hub only.
Any centre drilled rim is suitable for 2:1 lacing but deep rims need to be drilled for the rim to minimise spoke bends at the nipples on the non drive side.
The price of the hubs is expected to be £200/pair. Weight is 266g for the rear and 122g for the front. The hubs will be available to the trade. Availability from later 2019 assuming there are no issues which need addressing.
The test wheels (BORG26) are tubeless compatible and shod with IRC Formula Pro RBCC tubeless tyres. Bare weight is 1600g and use Sapim Force spokes for the rear wheel and Sapim Laser for the front. These might be replaced with Sapim CX-Force and Sapim Cx-Rays or that option offered when retail begins.
Tension balance is 1280N/1180N = 92 to 93%