Carbon Wheel Safety and Performance

CARBON WHEEL SAFETY & PERFORMANCE

Clickbait vs Reality

I am old enough to remember when everyone ran tubular tyres for racing, they were usually 23mm wide and always above 120psi. Tubular tyres were invented in 1888 and were last used by the professional peloton in 2024. That’s a hell of a long run. I also remember, in some editions of the TDF, tyres rolling off rims resulting in crashes when the glue melted.  Although this was not overly common it had consequences.  I could have shouted this article into a camera and posted it on YouTube but I believe that’s part of the problem, not the solution.

Regardless of the popularity of the tubular wheels for racing, and considering I was still racing on tubular tyres into the late 90’s myself, clincher tyres were much more popular with club and leisure riders as they were much easier to install and maintain. The fast rise of tubeless tyres for performance, and in many cases convenience, has sparked a real marmite love/hate debate especially among road cyclists.

Rim & Tyre Types Explained  

Captive vs Non Captive Spokes 

This issue is not new however thanks to Jayco and Cadex, it  has raised its head again during the 2026 classics season. 

There is little to no discernible difference in a wheel’s durability during use between captive and non captive spokes. The issues occur after an accident or failure in one part of the system. If you carry on riding a captive spoke wheel then the above implosion is very unlikely however when a non-captive spoke wheel suffers from an accident or failure it can quickly deteriorate to the above state. We do not build or recommend non captive spoke wheels as its an unnecessary risk in our opinion. The below shows you how to identify captive or noncaptive spokes. 

Exploding Sidewalls 

In recent years we have seen a spate of brands suffering from exploding sidewalls on Carbon rims. This is a bit of a hot topic and I have watched countless YouTube videos to help curate this article. My problem is despite nearly all of being entertaining, none of them really explained all the facts. 

Blaming Rim Tape  

Rims don’t hold pressure, if they did  could we seat our tubeless tyres without any tape? When we tested this, using a single layer of rim tape, we pumped a tubeless tyre up until the tape failed over the spoke holes (this allows the air to rush into the rim). This test allowed us to eliminate the tapes that could not hold pressure. These tests reached 110+psi on many occasions and when the tape gave out the rim never blew out into the sidewall. The rims we have manufactured go through rigorous testing to ensure quality and safety. Also worth noting here, this is with rims that do not have any drainage holes in the sidewall which some of the shouty YouTube videos suggest would be the answer to all these concerns. 

We have been able to recreate this effect, and I will say that we have seen this failure on a small number of rims we produced. Each time we saw this failure it was down to the carbon fibre layup not being completed correctly. Again, I cannot stress how rare this has been in a factory producing around 80,000-100,000 rims per year. 

Pressure Release Valves 

We have noticed a few manufacturers using these recently and we are blown away by this. To design a valve to assist in covering up for what we would deem to be poor quality manufacturing is insanity. Especially when you could consider simple drain holes in the sidewall of the rims. If this is a case of making the rims so light that they have to compromise on this vital safety margin then they really should stop. I also doubt this as we have made much lighter wheelsets and still have zero issues like these. 

Conclusion as to why Carbon rims explode? We are certain that whatever the cause of the explosion or catastrophic delamination, it came down to poor quality manufacturing and lax standards that are to blame.  

Spoke Tension Decay 

The ugly truth that brands do not want to publish is that in this age of tubeless ready rims, we have seen a rise in the tyre affected tension decay. In simple terms, the tension of the spokes drops significantly when tyres are mounted and inflated. We have been recording data on this for the last 6-7 years and we have seen and recorded a huge range of results:  between an 8-28% tension drop. For reference we are using a tubeless 28mm tyre at 70psi as the control for these tests. Our own rims have hit a maximum of 18% which we considered too high and the results above that figure all came from known so called premium brand wheels. We have been checking final tensions and the dish (if a wheel is centred) of wheels with the tyres mounted and inflated to realistic ride pressures for a long time.  We actively encouraged customers to buy the wheels with tyres installed so we can ensure the best possible results for them. 

The worst example of this for us came when we were asked to build the rims of a major brands onto a set of hubs supplied to us. These rims had a 28% spoke tension decay. To add to the conundrum, they had internal spoke nipples meaning that to make any adjustments we had to remove the tyre and rim tape. This took 3 times longer than usual as we had to first build the wheels and measure the decay. Once we had the decay results, we removed the tyres and tensioned the wheels. We also offset the dish of the wheels as after decay they moved around 1.5mm to the higher tension side. Unfortunately, we only got close to where they needed to be the first time and had to remove the tyres and rim tapes again to make further adjustments. Thankfully after these further adjustments the wheels landed in the middle with the required tension. This was from one of the most expensive brands in the market and we were very disappointed to learn what they are getting away with in terms of marketing over substance. 

Tyre Pressures Explained

I don’t want to sound like a stuck record; I probably can’t avoid it here. I grew up riding 700x23mm tyres at 120psi or more. Before every race we pumped our tyres up to 120psi and again probably once a week we also pumped our training tyres up to 120psi. A good friend who was heavier used to buy tyres he could pump up to 140psi as he suffered a lot of pinch or impact punctures from hitting potholes when racing in a bunch where these were difficult to avoid. This was my normal from 1995-2010 at least. In 2015, 25mm tyres were getting used a bit more and I know one tyre manufacturer labelled wider tyres as 23mm because people were not buying the wider versions which they knew tested better. Since then, things have raced ahead and in 2024 the last bastion of tubeless road tyres, Cofidis, stopped using these in the pro peloton .  From 2025 it was all tubeless, although some have been using latex tubes in tubeless tyres as [they?] also test as a very fast option. Tubeless tyres are fast and 30mm is apparently the fastest. Then comes the safety debate and the lots of punctures debate. These debates rarely consider all the elements in play at the same time. Like the pro peloton and races getting faster and faster, therefore potholes etc are hit at higher speeds. Crashes are more common as teams are fighting harder than ever to be at the front with higher stakes. 

I use an online guide to work out my optimal tyre pressure and my chosen guide is the SRAM AXS tyre pressure guide. I round up these numbers and in my 30mm tubeless tyres on the road I run 65psi rear and 60psi front. I also pump my tyres up every time I ride unlike my once a week in the past. If I ride two days in a row I pump my tyres up just before my ride. Optimal tyre pressure means more comfortable safer rides.

Hooked or Hookless

Having produced our first hookless road rim in 2017 I have been dismayed by the bicycle industry’s  inability to solve the issues facing users regarding hookless road rims. Initially we tested our hookless road rims with the Schwalbe Pro One TLE tyres and had great results in both the blow off test and ride tests. We were achieving over 120psi and often as much as 140psi in the blow off tests - the ride quality of 28mm tyres at 65psi were both fast and comfortable. At the time Hutchinson were known to have some good tubeless road tyres but we liked Schwalbe’s offering. We also tested Panaracer gravel tyres as these were very popular at this time. We launched the rim as a road and gravel option with some early success and then Continental launched a tubeless road tyre. As I had always been a fan of Continental tyres I ordered some and fitted them to my own wheels. I pumped them up to the 65psi and got ready for my ride. While my bike was leaning up outside, my tyre popped off the rim. It held pressure as the part that had popped over the lip of the rim was against the sidewall creating a seal. I was worried and let the tyre down, reseated it and pumped it up to 60psi before talking it for a ride. When I got back and took a better look at the tyre it said in almost invisible writing not for hookless rims. I rode these Continental tyres on my hookless rims for another 3-4 months before it popped off the rim again and I went back to my trusty Schwalbe Pro Ones. I was given some Challenge tubeless tyres to test with varying failures. I also tried some Pirelli tyres that stated max pressures of around 75psi on hookless rims. I found these did the same thing as the Continental ones and popped off even when pumped to the rated 75ish psi. Eventually Continental brought out a hookless compatible tyre but again it was limited to 73psi and had no scale for that limit for the different width options. These tyres again came off the rim when pumped up to the recommended pressure and we received calls from a customer who had installed them saying the rim was no good as these new Continental tyres had blown off. In testing on our hookless rims with the Schwalbe Pro One tyres we were not seeing them blow off until 120-140psi which is a great safety margin when most of us are running less than 75psi. 

In conclusion, we have moved most hookless options to the gravel/all road section and introduced a mini hook rim for road use. This, in our opinion, is down to the tyres not being able to work with these rims. It’s far too much to expect consumers to keep up with these changes and as an industry we should act responsibly.  To think, these wheels could be purchased second hand, resulting in an unsuspecting consumer  having a potential disaster.   

Note if you have hookless rims always check the tyres you are purchasing are suited to hookless rims.

Tubeless Tyres: Facts vs Myths

Why use tubeless instead of tubes? 

Often people are put off tubeless by a friend or club mate who has made a real hash if it. 

I have had my own measure of success and failure early on in my tubeless journey but that’s before I learnt the key points to success.

• You need a good tubeless tape - one that adheres well to your rim and is easy to remove if needed in future.

• The right tape will only require one lap around the wheel with a small overlap by the valve.

• Your tape should be wide enough to lap up the inner sidewall of your rim so you get a better seal and this also helps prevent sealant getting under your tape and into your rim. I usually go for 3-5mm wider than the inner rim width as this allows for the internal shape of the rim.

• Some tapes need a lot of stretch when fitting and others don’t.

• First rub the tape down into the centre of your rim then rub it into the edges on both sides.

• Making the right hole for your valve is important - if you split the tape you will get sealant under it and into the rim cavity. We heat up a metal bradawl and melt the perfect hole for valves as this is the most consistent way to ensure best fit for our valves. If you are using a spike go carefully as a split can cause sealing issues.

Tubeless valve:

• Select a good valve that’s the correct length for your rim depth. 25-30mm after the nut is optimal.

• Throw away the stupid o-ring that comes with all valves and if possible replace it with a nylon washer that matches the rim profile. The o-ring actually prevents the valve tightening properly and interferes with the nut. This o-ring forms no part of the sealing process required.  

• The only seal you need is the one on the inside of the rim between the valve head and the hole that’s taped.

• There are many new valve types appearing on the market - we like the V-max valves a lot as they don’t clog up with sealant. These new valves make everything work better. 

Tyres

• Make sure your tyre is s tubeless compatible tyre. Not all high-end tyres are tubeless this could fail on you if you get it wrong.

• Yes you can use tubes in tubeless tyres we do it all the time.

My Tyre is so hard to install

• If your rim is not deep enough in the middle the part we call the tyre well then this will make it hard to get on the rim but not hard to seat the tyre once installed

• Some tyres have a very thick tyre bead this takes up a lot of room in narrower rim wells and therefore makes that brand harder to install. 

• You need to push the tyre bead off the edges or the tyre shelf so that it’s a slack as possible when installing the tyre on the rim and we repeat the process when we get to that last bit that’s super tight.

• Start opposite the valve as this also allows maximum space when installing your tyre.

• If its too hard try some tools, we recommend a tyre installation tool like the speedier lever and often we use this to hold the bead from slipping back off while we use a challenge tool to lever on that last bit of tyre.

• You must use a bead lubricant to seat a tyre. In the past I have used this but only on setups that were particularly difficult the newer rims and tyre combinations have been easier, and I rarely see the need for this.

• I can’t get the tyre off the rim. First, you must push all the sidewall on both sides off the shelf this can occasionally be very difficult. Once the bead is in the middle your tyre should come off easily with a speedier lever or two. 

Tyre Sealant

• My go to sealants are from Joes No flats - I use Elite Racer for road tyres and Super Sealant for MTB. Joes manufacture sealants and other bike related cleaners and lubes and for my money they know their stuff. While their marketing is not all glitter, the products are first-rate. Note, Vittoria and Schwalbe both offer a good range of tubeless accessories and sealants.

• Not all sealants work. In my experience I avoid any non-latex based sealants as they have let me down. I have also seen some disasters from many known brands. For reference Stans make Doc Blue for Schwalbe and Joes made Continental’s sealants in the past.

• Sealant can have a shelf life so don’t buy too much.

• You can take the core out and inject it or like us carefully chuck it in the tyre during installation (this is only recommended for pro installers as it can be messy). 

• Sealant works most of the time - if the hole is too big or you get a huge slice that would prevent a tube working. It’s game over the same as with tubes.

• If you get a puncture that seals, don’t rush to top up your pressure as you can blow the plug out before its had time to properly form a good seal, then you will be locked in a cycle of sealant spraying out/stopping on repeat. I tend to ride as far as I can and slowly reintroduce pressure. 

So, we recommend following this and you will be as happy as we are with your tubeless set up:

1. Make sure your tape is the correct with and is installed correctly

2. Get the right valve for your rim

3. Choose a good compatible tyre

4. Throw in some sealant

5. Enjoy your riding

How wide is too wide? The importance of rim internal width and tyre interface

Rim width has been changing a lot in the last few years so we have done a handy guide for road and gravel. The MTB one will be a little harder as there are some wide rim specific tyre models and its not as simple as it looks. Be aware that the specified width of your tyre is based on an internal width of x the manufacturer uses to measure. A wider internal than the manufacturer of tyre  used can mean your tyre is stretched out to a wider profile. This profile may be to the detriment of the tyre design in terms of handling and possible stability. 

This is the last updated ETRO standards chart for reference. 

We caught up with Schwalbe and here is what they said: 

Q: What internal rim width do Schwalbe base tyre widths on, and have there been changes as tyres get wider for this measurement?

A: We design our tires according to the stated measuring rim of the ETRTO. For example a 28mm tire requires a 19mm internal rim width while a 30mm tire requires a 21mm internal rim width as a reference

Q: Do Schwalbe design the tyres with an optimal internal rim width in mind? Especially the gravel and mountain bikes tyres - are they designed to work with a wide variety of internal rim widths. 

A: The main concern is of course the rim dimensions that are fully compatible by the ETRTO. Knob position is the main concern for the design of the tires. The current development towards super wide rims (that are sometimes outside the ETRTO regulation) definitely is challenging for the tire design but so far we have found a good way to manage that.

Q: What are the risks of running a tyre on too wide an internal width?

A: The most prominent effect will be, that the tire is not fully supported and might crease/bend under load.

Q: What are the trade-offs between performance and safety when it comes to tyre and rim width compatibility?

A: Wider rims in combination with narrow tires put more stress on the bead core. Only high-end material will be able to withstand the load over the lifecycle of tire and rim.

We also spoke to Vittoria: 

Q: What internal rim width do Vittoria use to determine the labelled widths of that tyre, and are there changes as tyres get wider for this measurement? 

A: Vittoria is an active voting member of ETRTO. All Vittoria tyres are designed and tested in accordance with ETRTO recommended standards

Ref. https://int.vittoria.com/blogs/magazine/vittoria-is-member-of-etrto

With reference to the tyre section width, it’s dimensioned on the ETRTO “measuring rim”, and measured at the maximum stated pressure after 24h, as prescribed by the ISO standard.

In case the tyre is mounted on a wider rim than the prescribed measuring rim, the tyre width changes (it increases approximately by half mm for each mm of additional rim width).

Q: What are the risks of running a tyre on too wide an internal width?

A: For safety reasons, we strongly recommend using rim widths within the recommended ETRTO compatibility range, published on our website.

The main risks of running a tyre on a too wide rim are related to lower burst overpressure margin, increased pinch-cut and rim flange exposure to impacts.  

There are cases of ultra-wide rims out of this range, but with declared tyre-rim compatibility: these special cases are analysed and tracked within ETRTO and included as “experimental standards”. In all these cases, we collaborate with the main wheel manufacturers, carrying on extensive joint compatibility tests, before declaring the specific compatibility of said wheel models and tyre models.

Q: What are the trade-offs between performance and safety when it comes to tyre and rim width compatibility?

A: Performance-wise, the wider the rim (within ETRTO standards/experimental standards) the better the rolling performance is, with more margin to decrease the inflation pressure (because of the increased air volume) hence improve the grip and the riding comfort without penalizing the handling.

But while the rim width increases, the contact patch increases in its width too, exposing more the tread side or even the tyre sidewall to possible cutting objects from the road.

For this reason, Vittoria has developed specific road products in size 29mm optimized on rim width 25mm, providing the advantages of wide rim, while keeping a cross sectional area adequate for the aerodynamics, with a wide tread to offer enhanced puncture protection and cornering stability at high lean angles.

Based on our research with rims and input from Schwalbe and Vittoria, we have produced the chart below on our recommendations for matching tyre and rim combinations.

Our Conclusion?

Too wide a rim to tyre relationship and there is a significant risk to durability and even safety. There is possible detriment, especially where treaded tyres in gravel and mountain bike are concerned. 

The Manufacturing Process

Carbon fibre rims are not that complicated but after recent recalls and horror stories its obvious how important the layup design is. Having worked with many rim factories and building many big branded rims I can tell you the price tag doesn’t indicate the quality of manufacture.  Once the rim shape is modelled the carbon layup engineers will look at a map for the sheets of carbon which are then cut out to the exact requirements. The carbon sheets go into moulds very carefully following the map. Once these are all stuck in place the rim is vacuum formed and a bladder is inflated inside. These moulds then go into a big oven to be cooked. The resin is pre-impregnated in the sheets and as its heated these bond. After cooling the mould is removed and the rims are cleaned as the resin flash has to be removed. After that the bladder is usually removed through the valve hole and  the rims are then drilled. After drilling the rims are sanded and filed again are before quality control and inflation tests.  Good factories do 100% inflation testing on their rims before they go off for finishing/painting depending on the final aesthetics required.  

Carbon layup design how this impacting safety and performance 

I would say this is where the skills lay in terms of quality and safety. Poor design and poor layups often lead to mass recall and they also lead to failures like exploding sidewalls. Creases in rims are less common these days and are usually a lay up error leading to resin migration. Too thin a spoke bed to save weight is a poor choice in my opinion as I have seen better techniques to achieve the desired weight without so much compromise in quality or the need to use nipple washers inside the rim. 

Wind Tunnel fast vs Real World Fast

Fastest in tests. Whose tests? I once spoke to a leading aerodynamicist who told me we could conduct tests and present the data to beat most of our competition. This made me think a lot harder about wheels and what is important.

• Wind tunnels are static cyclists are not 

• Real world drag tests are new and I don’t know enough to trust them fully

• Less spokes is more aero however with disc brakes it’s a performance compromise

• Nobody designs rims/wheels and tyres specifically for a frameset yet 

• Rider aerodynamics make up way more of the drag than any bike or wheel could

• Inertia is very important. As most of us regular riders never carry an average speed of a pro cyclist, we need to take into account all the other factors when choosing a wheelset. Rim depths affect us in crosswinds where we expend excess energy for example. Every acceleration and deceleration costs energy. Professional riders race on closed roads while regular riders stop start a lot more. 

• Deeper rims are subject to greater deflection on rough roads so can also cost us kilojoules of energy loss. 

In a perfect world what would be the best option?

The wheel build would stay the same, but the rim depth would be chosen for the exact course conditions and expected speed. It would also take into account the riders goal for the ride or race. For example if a rider needed to attack and gain time over a tough climb and then TT to the finish solo. I would like to design an algorithm to aid these choices so if any there are any tech heads out there who want to join us in that then let me know.

In a perfect world we would probably have 2-3 different wheel options per bike.