With infinite funds, the imaginary (or very wealthy) cyclist would be able to tailor their bike and equipment to the ride and conditions on a daily basis – a bit like an infinite dress-up flip book, no two occasions would yield an identical ensemble. The reality of course is that few of us are able to invest in the level of kit required to get it right every time. Perfection must be compromised on a daily basis.
This certainly applies to wheels: there is no such thing as one wheel to rule them all, but most of us cannot afford to construct a wheel wardrobe with a lightweight set for mountain rides, deep sections for dual carriageway time trials as well as something with an infallible hub for the winter. So if we’re to have just one set – how deep should the rim be?
Aero over weight
The consensus is that aerodynamics overrides weight in all but the most mountainous cases.
Dov Tate, founder of British wheel brand Parcours told us: “If you run the numbers you literally have to climb Alpe d’Huez or equivalent before weight become more important.”
The good news is that the capabilities of modern wheels mean that the weight penalty is often minor, anyway.
Looking within the Parcours range, as an example, the 77mm front/86mm rear Chrono set weighs in at 1625g vs the 40mm Grimpeur at 1320g: 305g. For reference, the full 500ml bidon sitting on my desk right now weighs 576g, and I wouldn’t attempt my two hour lunch time ride without it.
All of this said, it’s important to know that the biggest jump in performance comes in the move from a box section rim to a 30mm-40mm wheel with an aero profile; adding more depth is marginal gains territory.
Tate has run the numbers. Comparing a Parcours Grimpeur 40mm wheelset with a popular box section (standard, alloy non optimised rim), he discovered a 22.9W saving. Moving to the Chrono 77mm front/86mm rear pair, the saving was 29.7W – that’s a 6.7W difference.
“A modern [well designed] 40mm wheelset will have an optimised rim profile, so even though you’re losing out on the depth, you’d still see a benefit in a time trial or solo effort, when compared with an older style or box section rim,” he says.
Additional research carried out by cycling coach James Spragg of Spragg Cycle Coaching found a difference of 3W when comparing a rider on a Specialized Venge with Roval CLX 64mm wheels versus Roval CLX 32mm wheels, when at 40km/h riding at yaw angles between zero and five degrees. The test was carried out in initial profiling of an athlete targeting the Etape du Tour.
Aero Lead and Senior R+D Engineer at Specialized Mio Suzuki agrees that a lot of the initial savings come from the jump between a traditional box section rim, and the wider 30mm-40mm group.
“I think one of the important aspects of choosing a deeper rim wheels is to know how well and precisely the rim shape is designed. It looks like a simple structure, but, the side wall curvature shape contributes a lot of both drag and side force. So deeper is not necessarily the better.”
However, he still believes that there’s merit in going deeper for those chasing speed. Commenting on the data collected by Spragg, Suzuki told us: “At that particular riding speed of 40km/h, and at those yaw angles (zero and five degrees), the numbers we have from our wind tunnel also demonstrate similar range of wattage gains.”
Yaw angle is the degree to which drag deviates from forward motion. Pro riders sitting in a peloton and moving very fast will experience a low yaw angle, a solo rider battling crosswinds at 25kph will be experiencing high yaw angles.
“We have computed yaw angle profiles of an entire Grand Tour stages from a 2017 event. The computation was done for various power-to-weight ratio riders and the calculation considers the corresponding variation in speed and road gradient encountered so that we can truly understand where and when aerodynamics matters for all kinds of riders. Yaw angles above five degrees matter, and based on our internal numbers, the power difference keeps increasing to over 10W at higher yaw angles at 40km/h.”
A saving is 10W could be huge for a rider who has optimised every other element – including kit and position on the bike – but if not, there could be cheaper ways to reap rewards. The human body on the bike accounts for the lionshare of drag on the bike/rider unit.
“There’s far more to be gained in optimising position – for example spending your money on wind tunnel time – than spending money on wheels or whatever. You are 85 per cent of drag – so look at the big things first. When people think of wind tunnel sessions, they think it’s super scientific and only for those looking to find marginal gains – but its not – we’re getting the 85 per cent of the picture right first!” Spragg comments.
Windtunnel testing at the Boardman Performance Centre starts at £195, for an Aero Experience including 30 minutes in the tunnel, and extends to £695 for a complete Aero Fit.
Weight and control
The other part of the equation is control – there’s little point opting for an 80mm rim if you’re going to struggle to keep it in a straight line.
“As soon as you come out of your aero tuck on bars or drops, you’re giving up more aerodynamically than you gain from the depth of the rim. So its no good racing a super deep front wheel if you can’t hold an aero position with it, if that’s the case, you should go with a shallower profile,” Tate says.
“When considering this, I would look at your rider style, build and experience. A lighter rider is going to be more impacted by crosswinds when using a deep wheelset, and also handling a deep wheel does come down to some level of experience.”
Mid-sections for most
When it comes to making that all important, single wheelset purchase, the overarching theme has to be compromise – but given advancements in technology, that compromise is perhaps not as great as previously believed.
“I would say choose wheels that are most tailored to what you do most of the time, with your riding style, level of experience and weight factored in,” Tate adds.
“For most people the ideal would be a mid-section rim of 40-60mm; that’a a jack of all trades. But if you live in the mountains, look for something shallower – a modern 40mm wheelset will have an optimised rim shape, so even though you’re losing out on the depth, it’ll be faster than older styles, and it’ll still give you an advantage even in a flat time trial.
“If you plan to focus on time trials, don’t be afraid to look for an 80mm rim – they’re not heavy and modern design means they’re greatly improved in terms of handling.”
A consensus is always reassuring – and we got that when we asked Suzuki the same question.
“Having evaluated many leading brands’ wheels and having designing some in my bike-industry career, my recommendation for performance or race-focused consumers would be 40mm-50mm wheels. But, if a consumer is weight conscious, and doesn’t like the feel of handling the deeper rim wheels, then 32mm is a good choice.”