Bontrager Aura 5 wheels

The new Bontrager Aura 5s are very good aero wheels that, although not cheap, offer impressive value for money.

First, well done to Bontrager for getting the weights right. The Aura 5's published weights are 770g (f) and 970g (r) – and that's exactly what they measured on the road.cc scales, plus 68g and 70g for the quick release skewers.

The rims are what Bontrager call an Aluminium Carbon Construction (ACC). That means they're 6061 alloy with unidirectional carbon profiles running inside. So the braking surfaces are alloy and the spokes extend straight through the carbon and into the alloy spoke bed.

Those carbon walls are flexible; you can easily pinch the two sides towards one another with your finger and thumb. I guess that might make them more prone to some kind of damage but nothing untoward has happened during testing and it keeps the weight down.

The sides of the carbon curve in slowly. The profile is nothing like the almost constant width of Zipp's Firecrest design, for example, but it isn't a traditional V-shape either – it's more rounded than that. Bontrager have done loads of work on wheel aerodynamics over the past couple of years, developing their Aeolus range which they reckon offers the best aero performance out there for any given depth.

The Aura borrows from the same aero technology and Bontrager say that it provides the highest performance you can get for the price (of course they do). According to Bontrager's own test results, the Auras aren't as aerodynamically efficient as their Aeolus 5 clinchers (£1,900 per pair) – both are 50mm deep – but they're not a million miles off.

At 0° yaw (a head-on apparent wind) the Aura has 140g of drag – 5g more than the Aeolus 5. At 10° it's 80g – again, 5g more – while at 12.5° the difference is more than 10g. According to Bontrager, 5g of drag equates to a time saving of 1.5-2.5 seconds per hour.

The rims are 23mm wide, following the trend towards wider wheels in the aero market. Bontrager have designed them this wide to reduce the drag with 23c tyres fitted, recognising that this is what most people want to use. The idea is that the wider profile will control the airflow that's separated by the tyre before it can create a large wake. The smaller the wake, the lower the drag.

The alloy hubs contain sealed bearings with the freehub using a three-pawl drive mechanism. It's Shimano/SRAM 9/10-speed compatible although you can get a Campagnolo-compatible freehub body if you need one. The front wheel is laced with 18 DT Aerolite bladed spokes while the rear uses 24.

The alloy braking surfaces mean you can use the Auras in all conditions without sacrificing control. Get caught in heavy rain and water can get inside the carbon section through the spoke holes but it soon comes out again via holes in the sidewall; that's not a problem.

These are certainly quick wheels – quicker on the flat than wheels of a similar price with standard-depth rims. You roll faster with aero rims, no question about it. Okay, there's a slight weight penalty and that affects acceleration slightly, but the carbon sections on the Aura 5s really aren't heavy and the overall wheel weight is reasonable. On all but the steepest climbs, you're at an advantage using these.

Handling is fine. I've been using these wheels over the course of a couple of months and I've only been on one ride where the Aura 5s were difficult to control in a crosswind. Even then, they were manageable; I just needed to be switched on to the possibility of a sudden gust affecting the steering. On all my other rides, I didn't give them a second thought.

One thing I would say about these wheels is that they're not the stiffest option out there. There's a noticeable amount of flex when you get out of the saddle and sprint. I prefer more rigid wheels but these do add some comfort that you might appreciate, especially if you have a harsh-feeling frameset.

As for durability, a quick inspection reveals that no water or gunk has got into the sealed bearings or the freehub during testing and the rims are still true. The closest I've been to damaging them is when I went to hang up a bike by the front wheel. You can't do that because of the flexibility of the carbon.

Verdict

Fast, mid-section wheels that offer good control in a wide variety of conditions.