Hi Ian!
I've been following Loopwheels' development since the beginning, and find them very interesting.
The basic design goes back to within 30 years or so after the development of the Safety Bicycle; I have seen designs where springs served as spokes and provided suspension within the wheel. Loopwheels' use of modern, composite materials is the most promising development yet of this historic design. The Shockwheel is conceptually similar. Their primary website is down, but it can be seen here:
https://www.youtube.com/watch?v=O11hFiu43RQI have been fortunate to try a couple of prototypes of this same basic in-wheel suspension idea. These ranged from long-travel designs that felt pretty sloppy to hubs equipped with elastomers that had little noticeable effect and provided only about 3-4mm of travel and would still work with rim brakes if the rim sidewalls were tall enough to tolerate the movement. Pantour is one short-travel example that has come to market:
http://www.manualslib.com/manual/364248/Dahon-Pantour-Suspension-Hub.html The later iterations adopted by Dahon had some adjustment for vertical and fore-aft (horizontal) travel.
There are some potential problems related to scalability -- not in manufacture (and the reason for the Kickstarter funding), but in wheel size. There are a surprising number of problems related to in-wheel suspension, and they become more challenging as wheel size -- and therefore travel -- increases. The real issue is movement control. Things can become sloppy at the rim/tire as the wheel grows in size.
Conventional, tangentially-spoked bicycle wheels are fairly rigid both radially and axially, and -- except for a radially-spoked wheel -- are efficient transmitters of torque. Hub-suspended wheels are not so good at either task. The same ability to collapse around their axis makes these wheels subject to some noticeable windup in both acceleration and braking. For this reason, I think in-wheel suspension generally works better up front than in the rear. Also, costs are reduced as the front hub only needs to spin, where a rear hub must also accommodate a drive mechanism.
Depending on materials and configuration, the wheels tend to be a bit soft laterally as well, and this can be felt to a degree in cornering -- it just doesn't feel as sharp or precise, but this can be attributed partly to the suspension effect, which is constant and cannot be locked out, though it has a rising rate as materials compress.
Hub-centric brakes must be used, as the rim moves and so would not work with rim brakes if travel is to great. Drum brakes or discs work well, but again induce reverse torque under braking. This isn't such a big problem with small 16-20in wheels, but can become more problematic as the wheel grows to 26-28in (700C) in diameter. Lateral rigidity and control become more problematic also.
Hub-centric suspension wheels look to be a real panacea because it appears they can replace regular wheels on existing frames -- at first glance. The reality is, the bicycle really must be designed with clearances for them if the suspension is anything more than minimal.
• Because the wheel moves independently from the hub, fitting mudguards can be a real challenge. The only real solution is 'guards elevated beyond the point of maximum travel.
• Lateral and vertical clearances at the stay bridges and fork crown must be generous to clear the maximum travel of the suspended wheel.
On the long-travel in-wheel suspension prototypes I tried, handling could become a bit dodgy at full compression. Unlike a suspension fork with linear action that affects only trail and weight distribution, in-wheel suspension also affects wheelbase -- at least momentarily. Hitting a bump while braking had the greatest effect, as both trail and wheelbase were suddenly altered. At worst, it felt like the bike was swallowing its own wheel and it wouldn't take much to endo from there. I also discovered one glaring problem on a large-wheel design: The compression of the suspension could bring the tire rearward and upward into contact with my toe, not a good situation and one that would require a frame redesign to avoid. Another Bad Situation was hitting a bump laterally off-axis. With the materials used in the examples I tired, this skewed the rim momentarily sharply to one side, enough for the tire to rub the inside of the fork blades; a wider fork or greater lateral control were needed. I think the overlapping lateral anchors of the Loopwheel would go far toward aiding lateral stability and overcoming some of these problems.
Given these drawbacks, the design seems best suited for smaller-wheeled bicycles, and in that application seems to work best. They also have a greater need for suspension. Small wheels are less likely to bridge gaps in the road surface, and the smaller radius is more affected by road surface irregularities. Smaller wheels tend to ride more harshly for this reason, even if tire section width and profile are held constant.
I think Loopwheels are an interesting development of in-wheel suspension, and I wish the designers well. They've already dealt with a number of challenges. It will be interesting to see if they can expand and develop their product line beyond 20in wheels.
Best,
Dan.
