Thursday, November 23, 2017

Wheelbuilder Aero Disc Cover

For those looking to get the final little bit of speed out of their Time Trial bike, a carbon disc rear wheel is often one of the ultimate upgrades.  Indeed, some experts claim that a disc wheel could be worth as much as 33 seconds over a 40 kilometre time trial.

But… and it’s a big but; disc wheels are horrendously expensive! About £1,400 seems to be the going rate for a good example. Which puts them well out of the price range for most of us, including me! (Ed Note: OK, I now have a disc! But read on, it's still relevant)

So I was interested to hear about a rear disc cover – sometimes know as an aero jacket – which fits over a standard wheel to effectively give it similar aerodynamics to a full disc. The one I opted to try is essentially the Wheelbuilder Aero Disc Cover, cut to fit my Planet X 101mm rear carbon tubular (supplied in the UK by Bike Science).

Fitting

Aero Disc CoverFitting is… well to be honest, I totally cheated and had my sponsor The Big Adventure Store fit the jacket, but I can talk quickly to the methodology.  Essentially what you get is two sheets of lightweight plastic which sit either side of the wheel (fitting requires removal of the cassette) and then some male/female screws secure the two halves to the wheel.

There is a cutout on one sheet that gives access to the air valve on the tyre/inner tube.  This aperture can be covered by supplied self-adhesive ‘patches’. You’d be advised to get a right-angled pump valve to ease pumping up the tyre with jacket in place.

In Use

Close upIn operation, the wheel cover does rattle a little bit at low speed over poor road surfaces, but as you pick up speed this seems to dissipate and the wheel is quiet in operation.

As for any wind tunnel testing or anything like that; don’t be silly! I’m just a regular joe with no access to such technology.  So the performance review that follows is entirely based on perception.  Even riding the same route on different days doesn’t really provide a decent comparison as wind direction and strength can have a dramatic effect on results.

I’ve raced twice using the Aero Disc Cover on my bike – at Dambuster (40km undulating bike course) and Newbury Duathlon (25km hilly course).  At Dambuster I averaged 34.9km/h (max 48km/h on straights) and at Newbury I average 33.4km/h (about 46km/h max on straights).  Without having raced the same courses with the 101mm wheel without the cover, it’s difficult to be definitive about the difference it made, but with hindsight I might have been tempted to ditch the cover for Newbury.  Whereas Dambuster featured several long and level straights that allowed you to get up and maintain a good speed, Newbury was devoid of these and was much more stop/start in nature.  As neither course had especially strong side winds, I’m discounting wind as a factor.

As such, I am inclined to think that, at Dambuster, the aerodynamic advantage of the disc outweighed the additional weight.  However, with Newbury’s lack of long straights and addition of long slow hills, if I was to race it again tomorrow, I’d probably switch back to my ‘standard’ 101mm rear wheel.

Conclusion

I’m acutely aware this hasn’t been a particularly scientific review – and so I encourage other triathletes or cyclists with experience of disc covers to share their thoughts.  However, as it would be unfair not to reach a conclusion I’d say that the Aero Disc Cover is a good addition to your bike if a) you’re already strong enough to reach and maintain a high speed and just want that extra 0.5km/h and b) you pick the right bike courses.  Fast flat courses are ideal, with minimal climbs or stop/start style road junctions.

Once up to speed, my experience is that the Aero Disc Cover holds that speed well and keeps the airflow over the rear wheel clean.  However, the thin plastic sheets do add some significant weight (about 400g) to the bike, which is probably not the best idea if your bike course includes a number of climbs.

Pros

- Does seem to enable a higher top speed on straight roads with no significant cross-winds
- Far cheaper than a full carbon disc wheel

Cons

- Adds a considerable weight to the bike, won’t help on climbs
- Doesn’t have the full effect of a true carbon disc (including the sound!)

 

Now, back to multi-sport racing… ;)