Durometer, or sometimes just 'duro', refers to the hardness of your wheels. Measured in numbers and letters, duro measurements are a little bit like bra sizes – they're somewhat cryptic at first, they vary between manufacturers, and everyone has to find their perfect fit.
Just like different bras are made for different occasions, the durometer of a wheel determines its purpose. Whilst softer wheels are better for outdoor skating, providing cushioning against rough surfaces and more grip, harder wheels have a slickness that increases potential speed – but also reduces stability.
Science! Pressing science, actually.
In simple terms, to determine the durometer of a material, you push down on it. The durometer is decided by how far the material indents based on the pressure applied. Harder materials will resist pressure more, or for longer, than softer materials.
If you want to get more into the science, you can read about it here.
What does the 'A' stand for?
Durometer is used to measure the hardness of a number of materials – everything from chewing gum to steel rods. There are 12 different scales for measuring durometer, each reflecting the properties or usage of the materials being tested – you can read about it in depth here. For soft plastics, such as the urethane that most skate wheels are made from, the durometer is measured on the 'A' scale – so the duro number is followed by the letter 'A.'
What wheels should I get?
The age-old question! As with many things in roller derby, your wheels depend on your preference, ability, and a whole host of other personal factors, such as:
What surface are you skating on?
If you're playing roller derby, the chances are you will be skating indoors, on a polished concrete sports floor or similar. Indoor floors tend to be a little slippy, but don't typically feature the small obstacles outdoor skating poses – such as twigs and pebbles.
Here's a breakdown of which duro ranges suit which surfaces.
78A-80A – Outdoor wheels.
These are pretty much as soft as it gets. Perfect for skating outdoors on asphalt or rough outdoor concrete, though they will feel sluggish on an indoor surface.
84A-85A – Hybrid wheels.
Straddling the border between outdoor and indoor wheels, hybrid wheels are great for wobblier skaters, or if you're just looking for one set of wheels for all surfaces. These wheels give a lot of grip, but are slower as a result.
86A-89A – Soft indoor wheels.
A common range for derby skaters, this range gives good grip on gym floors, polished concrete and slippy wood surfaces. Whilst they will slow down sooner than a harder wheel, the added friction allows for greater acceleration – perfect to start you off on a small burst of speed.
90A-93A – Medium indoor wheels.
If you're feeling more confident on your feet and your floor isn't super-slick, a medium durometer may be right for you. Wheels in this range give great speed with less friction, though this can feel unstable for beginner skaters.
94A-96A – Hard indoor wheels.
If you're skating on a sticky floor, such as sticker concrete or a typical indoor skatepark surface, this may be just the range for you. The low grip allows for faster skating on grippier floors, though slick floors may be difficult to skate on.
97A-103A – Super hard indoor wheels.
Only appropriate for special sufaces, such as specially-designed roller rinks or sticky coated floors, super hard wheels give the least friction of all skate wheels, allowing you to glide nimbly along – as long as the surface is right.
How heavy are you?
Heavier skaters will receive more grip from their wheels, whilst lighter skaters will find their wheels slippier. In conjunction with Atom Wheels, the WFTDA has come up with a handy chart to show how weight and surface can affect wheel choice – you can find it here.
How stable are you?
This will change over time, as you become more confident on your skates, but as a fresh skater, softer wheels are usually easier to skate on. The added friction gives you more grip, which can be handy when you're already struggling to find traction with your wheels. Conversely, more agile skaters may find softer wheels to be slowing, reducing their reaction time and leading to a sluggish feeling.
Of course, duro is just one factor in choosing your wheels – there's also things like width, profile (height), hub material and weight to consider – but that's for another blog post!
Like everything else in derby, wheel choice is personal, so be sure to track-test a variety of wheels before you settle on what suits you best. If you're unsure about what's right for you, remember you can always try before you buy. Ask your teammates to swap wheels, get opinions on mixed-durometer set ups, or maybe even try Double Threat Skates' Test-A-Wheel Programme – all great ways to find the perfect fit.