Are carbon wheels right for you?
Wheels are often considered to be the best upgrade we can make to our bikes if we want to improve our rigs. Despite the high price tag when compared to aluminium, most serious cyclists considering a new wheelset will look to carbon wheels. But in what situation are they the right choice?
It’s important to be well informed on the drawbacks to carbon wheels in addition to the more well known advantages. I have been umm-ing and ahh-ing about this for a couple of years, and have just pulled the trigger on some sweet new hoops! In this post I will tell you my thoughts and conclusions from many hours of research.
There is absolutely no doubt that carbon wheels look incredible. The profile of deep section rims is now synonymous with speed, and adding them to your bike just make it look faster. The pro peloton is full of sexy, deep section aero rims and that’s the aesthetic we’re all after! I can’t remember the last aluminium box section wheel I saw on a pro bike, despite the fact that these wheels are still great in many ways.
The deep section of carbon rims is loved by manufacturers as they can plaster the brand name all over it, and create some cool effects at speed in the process. Some brands do this to great effect. Some need to look for new graphic designers! Each to their own. I prefer the subtle black-on-black branding the likes of Enve have moved to.
Weight vs Aero
It’s no so much that carbon wheels are always lighter than aluminium, but it is a lighter material. This means that more aerodynamic shapes are achievable for the same weight of material. So you’ll get some aero gains on the flat, but the resulting extra weight will not hold you back significantly when the road heads uphill.
Aluminium wheels can still be made to be incredibly light, but this comes at the expense of aerodynamic efficiency. This means you will be laughing in the hills, but will lose out (a bit) on flat terrain.
Shallower rims usually perform better in swirling or cross wind situations. It can in fact be argued that for most real-world riding the wind is hitting the bike at an angle, not straight on. Lots of manufacturers test their wheels inside a wind tunnel which can’t replicate these conditions very effectively. This is why I take aero statistics from wheel and bike manufacturers with a pinch of salt.
Are carbon wheels weaker?
Well, not exactly. Carbon fibre can be made to be incredibly strong actually. But it all comes down to design of the component and how the material is laid up. A poorly made component will contain voids and the fibres may not be bonded correctly. Quality issues such as this can have a big impact on structural integrity. It’s not something I want to be riding! This is why I would always look to the reputable brands when it comes to carbon fibre components – stay away from Ali Express! A wheel from a good brand should be no problem in terms of strength, regardless of the rider’s weight or terrain. You really do get what you pay for here.
There is however the problem of carbon’s behaviour under impact. Big hits directly to the surface can cause damage which is not always apparent when looking at the surface itself. If you crash a set of carbon wheels it may be prudent to at least have them inspected by an expert, or even replace them just to be sure.
The most crucial factor in choosing a wheelset is in considering the brakes you run. If there is one drawback to carbon wheels it would be the braking.
Now, for disc brake equipped bike carbon wheels are a great option. The rims have nothing to do with braking so the biggest problem with carbon doesn’t apply. If you have the budget for carbon and you run disc brakes, fill your boots I say!
For bikes with rim brakes, it is not so easy. Carbon fibre is inferior as a braking surface as it’s a poor conductor of heat. It is good enough in the dry, but if the heavens open and the braking track becomes wet, stopping power drops off a cliff. Braking track coatings and carbon-specific brake pads help a great deal, but it doesn’t get you near to the performance of an aluminium rim.
What makes carbon wheels inferior for braking?
In order to work, your brakes take kinetic energy and convert this to heat. This heat has to go somewhere. It is dissipated around the brake track, rim (and even into the tyres) and to the air from there. If the heat cannot escape to the air at the rate it is being produced, then the heat keeps building to a point where braking performance drops. This is known as brake fade and can be experienced on long descents where the brakes are applied continuously.
Carbon rims typically suffer from brake fade much quicker than aluminium wheels. But that’s not the only problem you might encounter.
On carbon rims, the heat does not transfer from the brake track as well as aluminium. The resin bonding the carbon fibres together beings to degrade, weakening the structure. This would not be so potentially catastrophic if you run tubular tyres, as the pros do. It’s more likely that you run clinchers, with the pressure inside the tyre forcing the tyre bead against the rim. This force combined with the weakening rim can cause the rim to fail. The tyre then blows out of the rim sending you headfirst into the asphalt!
Wheel manufacturer Alto carried out some testing with a number of carbon wheels under constant braking. There’s a good video of the results that is definitely worth a watch!
If I lived in the flat plains of Kansas or Lincolnshire I would be quite comfortable running carbon wheels. But some of my local rides are very hilly, meaning fast and technical descents are not uncommon. I also need to consider that I am quite nervous going downhill, and I really rely on good braking to get me out of jail where I’ve cocked up my line or misjudged a corner.
The stellar looks of carbon wheels increase the psychological effect of feeling like the wheels are making you faster, when in reality they may only offer a marginal improvement. I’m not poo-pooing this though – a psychological effect is still an effect. Moreover, it can be a very powerful one. If you feel faster, you will probably ride harder. And that will definitely make you faster! If you are going down the carbon clincher route, look for a manufacturer who is releasing test data on wheel safety.
Carbon fibre technology has come a long way since the early days but with rim brakes we are still asking it to perform a job that it’s not naturally good at. It all depends on your situation and your skill as a rider. If you are concerned about your ability, then either convert to disc brakes or run aluminium wheels.
For me, the additional cool points that come with carbon wheels are just not worth the extra worry. So it’s aluminium rims for my new wheelset, handbuilt in the UK by DCR Wheels. There’ll be a post on these coming soon so keep an eye out!