Introduction

One of the problems of hand cycles is that they tend to make use of standard wheelchair to provide the 'chair' part of the package. This does have some advantages for the user in that there is a good variety of chair designs available. Thus getting one that fits and is comfortable should not be impossible. However, when it comes to the question of ride, the answer is always the same – no suspension so all the bumps are transmitted to the frame.

There have been some attempts to solve this issue and the Speedy, reviewed elsewhere in this site, is one example of a chair with suspension. There is also a relatively new design of chair in the USA that is based upon the seat having suspension rather than the whole chair. Apart from that, there seems to be little on the market. That is why the Loopwheels idea appeared to be so interesting with their website claiming they provide “A shock-absorbing wheel with integral suspension, for enhanced performance and greater comfort. For bikes, wheelchairs and more”.

The Loopwheels System

Like all the best ideas, the Loopwheels system is conceptually simple. Rather than building suspension into the wheelchair frame, it provides for sprung flexibility within the wheel itself. When a bump is encountered the springs flex allowing the rim to move closer to the hub. The springs, after absorbing the energy from the bump, bounce back returning the wheel to its normal circular form. There are three looped springs in each wheel, hence the name Loopwheels. They are available for bicycles and for wheelchairs and offer the prospect of retrofit suspension for these machines.

Loopwheels on a Hand cycle

The set up under test in this articles was a special order set with 24” rims and Sturmey Archer brake hubs. These were requested to ensure that the hand-cycle continued to have brakes on all wheels. The hand-cycle previously was fitted with home made bicycle style calliper brakes. These were effective enough, but made the machine very difficult to dismantle. The Speedy, reviewed elsewhere on this site, was fitted with drum brakes and they facilitated three wheel brakes plus easy wheel removal, so drum brakes seemed a good idea.

In discussion with the vendors the issue of wheelchair user safety was raised. The vendors pointed out that the wheels needed to be quite 'stiff' for a wheelchair application. This was because, if the user were to reach out to one side, a 'soft' spring could compress too much and the chair might overbalance to one side. As a counter argument it was explained that for hand-cycle use that issue would not arise since this machine was never used as a domestic wheelchair. It was also pointed out that the whole purpose of trying Loopwheels was to retrofit suspension and get a softer ride whilst out cranking.

Fitting the Sturmey archer drum brakes to the wheelchair required the backing plate containing the brake shoes and actuator to be securely fixed to the bushes into which the quick release axles fits. The bush needed to be turned down to 16mm for about 1cm and then threaded M16. This allowed the backing plate to be fitted against the shoulder and secured in place with an M16 half nut. The backing plate also includes a 'torque arm' which needs to be securely anchored. This device prevents the backing plate rotating when the brakes are applied. Not a modification for every user, but relatively simple if one has access to a lathe.

The wheels looked to be sturdily constructed and consultation with the supplier enabled them to arrive colour coded to exactly match with the existing colour of the chair.

Loopwheels in action

Once fitted to the chair, there was no obvious difference in the functioning of the hand-cycle. The drum brakes operated quite well and the chair was just as easy to stop as before. The ride did not seem to have changed much from that of the previous conventional wheels. Indeed with the new Schwalbe Marathon tyres pumped up to 70psi, the ride was possibly harder than when the conventional wheels with the fatter unbranded tyres pumped hard. One of the wheels also developed an annoying squeak as it rotated, presumably relating to the loading and unloading of one or more of the spring units. Some quick squirts of oil have made no difference and closer examination has not yet been made.

Since 'ride' is a very difficult concept to assess it was decided to do a 'compression test' to see the extent to which the Loopwheels flexed under load. The test method used was a static weight test in which weights were added to the static chair and the extent to which the Loopwheels had compressed was measured. For the test the tyres were left in place but pumped to 70psi. It was felt that at such pressure, the tyres would provide little of the compression movement. It would have been possible to measure the change in the rim height from the ground as the test progressed to assess the impact of tyre deflection, but this was not thought to be worth the effort. Also, whilst the frame is likely to have flexed under the test weights, this was expected to be so slight as not to be worth measuring.

The normal foam cushion was removed from the chair and replaced by a sheet of chipboard, slightly lighter in weight than the cushion. This was to make a stable base on which to load the weights. The quick release axle on one side was replaced by an M12 hexagonal head bolt which was set so that the bolt head protruded beyond the brake hub. A length of 12mm steel plate shorter in length than the wheel diameter was placed next to the wheel below the protruding bolt head. It was then possible to use a digital calliper to measure the distance from the underside of the bolt head to the top of the steel plate. The distance from the bolt head to the steel plate was measured at no load and then after the addition of each set of weights. The change in the reading represented the amount of compression caused by the added load. Each 'set' of weights comprised four bricks weighing 9.9kg together. Ten sets of weights were added in the experiment.

The results of this experiment are shown below:

Load Kg (X)

Cumulative Compression (mm) (Y)

9.9

0.9

19.8

1.9

29.7

2.8

39.6

3.4

49.5

4.1

59.4

4.8

69.3

5.9

79.2

6.7

89.1

7.6

99.0

8.6

Whilst this cannot be called a highly accurate test, it serves to show the magnitude of deflection in relation to load for this set of wheels. Repeating the experiment with a test dial indicator could perhaps increase the accuracy of the measurements, but would not change the conclusion that the amount of deflection of this set of wheels is small.

For comparison purposes, it is perhaps appropriate to consider the total deflection offered by other suspension devices:

Brompton folding bicycle rubber bush – Approximately 4mm. This provides negligible damping and pretty hard ride.

USE Shockpost (soft) bicycle seat pillar – Approximately 8mm. This provides a small degree of damping but needs pairing with a sprung seat to provide real comfort.

Speedy sprung suspension wheelchair – Approximately 10mm (at the suspension unit. Wheel movement at the end of the wishbone is more). This actually provides a 'sprung' ride which is fairly comfortable when matched with a good seat cushion.

In the Loopwheels test the user's weight, 49.5kg, falls in the middle of the tested range suggesting that, once seated, the potential further movement for shock suppression would be in the region of 2-4mm.

Moving next to the weight penalty of adding suspension to a wheel chair it seems best to compare the Speedy wheelchair with the chair for which the Loopwheels were purchased. The basic Speedy chair without wheels weighs 15.5kg compared to 16.2kg for the other chair. Of the latter, 2.7 kg is made up of the strengthening bars and hand-cycle connection. The strengthening bars are required because this is a folding chair. Clearly, a custom built suspension chair is better than a converted chair from the weight point of view. It also manages to include the weight of the suspension mechanism and still be lighter than the tested chair.

The Speedy's conventionally spoked wheels with hub brakes weighed in at 2.3kg each compared to the Loop wheels at 3.3kg each. Once again the Speedy has the weight advantage.

Overall the Speedy chair has a total weight of 20.1kg against the modified chair with Loopwheels at 22.8kg.

Conclusions

The Loopwheels although operating in the advertised manner, do not provide “A shock-absorbing wheel with integral suspension, ... and greater comfort” with this particular wheel build. It certainly cannot be described as successful retrofit suspension solution, nor were the Company too bothered about the product not meeting our expectations. Perhaps softer springs allowing (say) twice the compression of this build would begin to feel like a softer ride.

Alternative ride improvements for a pre-existing wheelchair include running the tyres at a lower pressure (say) 50psi for a rider of this weight or going for a wider mountain bike tyre again run at a lower pressure. This would have the penalty of slightly higher rolling resistance but would avoid the 4kg extra weight penalty of a pair of Loopwheels.

Thus the Loopwheels concept is a good idea, but one that did not solve the problem for us.

 

© 2016 Peter Cuthbert & Cycling Otherwise