This article is joint work with Dr. John Newhook of Dalhousie University.
In earlier articles, we documented the mass of commercial brush heads and in addition documented that today’s commercial brush heads distribute pressure across the brush pad in very different ways. In parts 1 and 2 of this article on “Try before you buy”, we argued that brush handle characteristics do matter and, in the second part, presented measurements of various commercial handles with respect to handle diameter.
In this, the third part of “Try before you buy”, we present measurements of another important characteristic of brush handles: flex, or more properly their bending moment, or flexural rigidity. As curling equipment manufacturers continue to offer lighter-weight products, athletes may discover that there are significant differences amongst the various commercial offerings of handles in roughly two dimensions: weight and flex, in much the same way that today’s hockey sticks come in a variety of “flex” degrees as do tennis or squash racquets, or golf clubs. The rigidity of the handle matters a great deal to the “feel” of the brush when under maximum force by that athlete, and hence the reason that we looking at flexural rigidity in this article.
Examples of brush handle cross-sections
Hardline Hybrid Helium – 20mm mandrel
Balance Plus EQualizer – 23mm mandrel
Balance Plus LiteSpeed – 26mm mandrel
End Game Red – 26mm mandrel
Ultima CF – 20mm mandrel
Hardline Ultra-Lite Carbon Fibre – 20mm mandrel
Experimental setup
To measure deflection, we use a “Yes 4 All” multi-function squat rack with a 550 lb capacity. Brush handles are supported between the two pillars of the squat rack 107 cm apart, so that the rack can accommodate brush handles of approximately 48 inches in length. All of the brush handles described in this article are 48 inches long but for three: Balance Plus Lite Speed handles are 47 inches in length, and in addition we tested a 54-inch Asham Velocity handle to test if it had similar flex to its sister 48-inch model. Aside: we note that Asham also manufacturers 40-inch brush handles for children but these handles were omitted from our study.
Each brush handle was tested without an attached brush head. As our collection of brushes included both prismatic and tapered handles, for consistency we applied the identical testing procedure to each handle regardless of each handle’s cross-section. A confounding factor with testing handles is that Balance Plus handles are tapered towards the top end of the handle, whereas tapered handles from Performance, Asham, and Hardline are tapered closer to the brush head. The table below indicates the nominal handle diameter along with each handle’s “grip diameter”, the outside diameter of the handle at a position 12 inches from the end of the handle nearest the brush head. We use 12 inches as a consistent measure of the bottom hand position on the brush.
To test deflection, a 40 lb (18.18 kg) weight consisting of a 25 lb and a 15 lb weightlifting plate was hung from the middle of the handle. An 88N3101 Dial Indicator, available from Princess Auto Supply, was used to record the deflection of the handle when under load. Multiple tests were performed on a selection of handles to ensure accuracy of the deflection measurement.
Results
The above table presents the results of our analysis, giving the flexural rigidity value (EI) for each of the 17 handles tested (higher EI values indicate greater stiffness). A detailed table of handle dimensions and each handle’s measured deflection is shown below.
A handle’s flex is due to a combination of factors: the material used, the specifics of the construction of the handle’s layers, and the thickness of the handle walls. Carbon fibre is desirable because it is a stiff, very lightweight material and so, all things being equal, one would expect that all carbon fibre handles would have less flex than handles made of other materials, such as fibreglass, or composite constructions. However, there are a multitude of carbon fibre suppliers and carbon fibre is available in different grades, thicknesses, and strength, and how the brush handle is bonded together can make a significant difference in the handle’s rigidity.
Our results show that there is significant variability in the flexural rigidity of brush handles, even carbon fibre ones. In addition to the material, it would appear that other factors, including handle construction and wall thickness – both of which influence the weight of the handle – play a significant role. The inexpensive Hybrid Helium brush has the least flex of the brushes tested; the fully carbon-fibre Hardline tapered handle comes a very close second. In contrast, the composite Asham Velocity handles ranked amongst the least rigid in our tests, but the Asham V2 carbon fibre handle also lacks stiffness. We believe that the reason is that the Asham V2 handle has very thin walls (see image at right) where the handle narrows to 20 mm to accommodate the brush head mandrel, and the thinness of the walls yields additional flex that is disproportionate to the overall stiffness of the handle as a whole. On the other hand, the Asham Composite Easy-Lite, a prismatic composite handle, ranked sixth overall in flexural rigidity. Along with Asham’s brush handles, the very lightweight Balance Plus LiteSpeed handle, along with the company’s older EQualizer models, are less rigid than average.
Summary
World Curling currently permits athletes to mix-and-match brush handles and brush heads as long as the “fit” of the brush head mandrel to the handle is supported by a manufacturer. For this reason, some players prefer a type of brush head, but will use a handle from a different supplier in order to get a brush that is best for them. “Best” properties include flex, weight, but especially grip.
In my experience in running clinics, I have found that many players do not prefer a tapered handle due to the reduced grip diameter, despite the existence of a rubberized coating on the handle to mitigate the issue. My own personal preference is the Goldline Impact handle with Grip Zone Technology, which is both lightweight, stiff, and provides superb grip. The Impact’s diameter and the rubberized coating are important to me because I suffer from Dupuytren’s contracture; I cannot use a tapered handle without slippage.
In summary, we encourage athletes to keep the characteristics of the brush handle in mind when choosing a brush, including weight, diameter, grip, and flex, since each characteristic does impact the “feel” of the brush. Since all manufacturers offer brush components for sale in addition to complete brushes, one can mix and match heads and handles to achieve the best combination.
| Manufacturer | Model | Weight (grams) | Stiffness Rank | Grip diameter (in) | Prismatic? | Nominal diameter (in) | Deflection (mm) | Difference from mean (mm) | Mandrel size |
|---|---|---|---|---|---|---|---|---|---|
| Hardline | Hybrid Helium | 260 | 1 | 1.125 | Y | 1.125 | 6.91 | -2.005 | 20 mm |
| Hardline | Ultra-lite | 178 | 2 | 1.030 | N | 1.125 | 7.39 | -1.523 | 20 mm |
| Goldline | Impact w/ Grip Zone | 166 | 3 | 1.131 | Y | 1.126 | 7.42 | -1.497 | 26 mm |
| Ultima | Carbon Fibre Lite | 302 | 4 | 1.128 | Y | 1.128 | 7.44 | -1.472 | 20 mm |
| Olson | Pyro | 179 | 5 | 1.145 | Y | 1.145 | 7.75 | -1.167 | 26 mm |
| Asham | Composite Easy-Lite | 280 | 6 | 1.13 | Y | 1.13 | 7.95 | -0.964 | 20 mm |
| Goldline | Carbon Fibre | 170 | 7 | 1.137 | Y | 1.137 | 7.98 | -0.938 | 26 mm |
| Performance | Spyder Grip | 165 | 8 | 1.034 | N | 1.115 | 8.15 | -0.761 | 20 mm |
| Goldline | FibreLite | 212 | 9 | 1.126 | Y | 1.126 | 8.33 | -0.583 | 26 mm |
| Asham | Ultra Lite (Taper) | 167 | 10 | 1.025 | N | 1.125 | 8.53 | -0.380 | 20 mm |
| End Game | Red | 165 | 11 | 1.113 | Y | 1.113 | 8.76 | -0.151 | 26 mm |
| Balance Plus | EQualizer - White | 186 | 12 | 1.112 | N | 1.126 | 8.92 | 0.01 | 23 mm |
| Balance Plus | EQualizer - Blue | 186 | 13 | 1.125 | N | 1.133 | 9.14 | 0.230 | 23 mm |
| Balance Plus | Lite Speed | 141 | 14 | 1.090 | N | 1.150 | 9.96 | 1.043 | 26 mm |
| Asham | V2 | 166 | 15 | 1.129 | N | 1.136 | 10.80 | 1.881 | 20 mm |
| Asham | Velocity | 306 | 16 | 1.136 | Y | 1.136 | 13 | 4.091 | 20 mm |
| Asham | Velocity (54 inches) | 321 | 17 | 1.136 | Y | 1.136 | 13.1 | 4.192 | 20 mm |
| Mean | 208.8 | 1.108 | 1.13 | 8.91 | |||||
| Median | 179 | 1.126 | 1.128 | 8.33 | |||||
| Standard Deviation | 59.5 | 0.039 | 0.009 | 1.84 |
Caveats
Ideally, we would have performed this testing in an Engineering lab with precise equipment, including a concrete base, precise scales, and laser measurement tools. We would also have multiple instances of each brush so that we could not only test several samples, but cut each handle into pieces to observe their thicknesses at various points. Nevertheless, we have reasonable confidence in our approach, and confidence in our measurement accuracy given the available apparatus.
