Bicycle Tyres.... We're no longer in the 90's

Times have changed

Back when I started cycling, in the early '90s, I used to train and race on 21mm Continental Grand Prix clincher tyres. I still remember how flash I was rocking up to school cycling training with these amazing tyres. They were pumped up to 110psi and super narrow (which at the time I thought meant they were more aero). I even remember ordering some 19mm tyres for a race, and a few weeks later, deciding they were far too narrow when the leading edge of my rim started connecting with the pavement whilst going over small potholes and broken paving. Back in those days punctures seemed to be an all too common occurance, possibly a weekly thing, and my mates and I seemed to crash our bikes (wet and dry conditions) a lot for some reason, and I still remember the how sore the palms of my hands were after a ride.

Fast forward 30 years and it's all making sense to me. After making 2-3mm increments over the years following the trend of tyre widths (23mm, 25mm, 28mm) I've recently fitted some 32mm Continental Grand Prix 4-Season tyres to my Cannondale Super6 Evo for the winter months of training and I can't believe how good they are. I still spend time on 23mm tubulars, 25mm clincher and 28mm tubeless tyres depending on the wheels I'm using and if I'm training or racing in certain conditions. But the important thing to understand now is that tyre choices comes down to many different things, and not just the ones you think look the best.

The onset of these wider tyres hasn't just happened independently, we have also see the advent of disc brakes and wider clearance frames to allow for the extra width of the rim and the tyre, so it's taken a few generations of bike to get to where we are now. And we're also now using Tubeless Tyres which completes the whole package.

I'm going to give you a bit of a run down on my thoughts on wider tyres, the why, the why not and the what next.

Why go wide?

As cyclists we want 3 things.... 1) We want to be faster 2) We want to be more comfortable  3) We want to be safer. How you order the importance of these is up to you, but for me this is my prefered order. I want to ride fast, I know how to position myself for comfortable riding and I know how to handle my bike safely in all conditions.

The thing you will find with riding an appropriately wider tyre is all three of these preferences are catered for. 

Aerodynamics

If you think a narrower tyre is more aerodynamic then it's time to step out of the 90's and look into how airflow passes over a tyre, and how modern wheels facilitate the use of wider tyres to optimise the aero gains. There are a much smarter people than me who can explain it more elloquently than I can, but the basic principle states that if there is enough of a trailing edge behind the tyre (rim depth) then the width of the tyre hitting the air becomes more aerodynamic, it's all about smoothing the flow of the air as it passes over the rim. 

Now if you had a wide tyre mounted to a flat and shallow rim then that's not very aerodynamic, there will be a lot of disturbed air behind the rim and that's going to slow you down, and it may even be less stable in strong crosswinds. There are a lot of things to consider with the trailing edge profile of the rim, but that should be saved for a future article.

If you had a wide tyre that was mounted to an older style rim (which typically had narrower widths than todays wheels) the tyre will balloon out and give you a very unstable ride. You don't want the side wall being much wider than the width of the external wall of the rim. Not only is this ballooning tyre dangerous to ride on, it will also be less aerodymic due to the turbulent air building up against the rim behind the tyre, and you will probably have a higher risk of pinch flats as you will undoubtably be running them at lower pressure (as per recommendations). You can now see why rim and wheel designs had to change to allow of the onset of wider tyres.

You may wonder if there is a limit to how wide is too wide to be aerodynamic. I think 28mm is about as wide as we need to go if racing on a fairly typical road surface with modern day wheels. Any wider probably starts to compromise aerodynamics as the rims will require some fairly dramatic designs to make it all work. If you are fitting 32mm tyres to your bike you aren't doing it for aerodymic purposes...you're going for comfort and safety.

Some Triathlon bikes may only fit certain width tyres if they have Rim Brakes, for example the rim brake versions of the Cervelo P5 and Giant Trinity and Scott Plasma seem to only work with 25mm or less tyres, and in some cases heavier/stronger riders may even experience tyre rub on the chainstay from wheel and frame flex. On my Specialized SWorks Shiv, for races, I am using a 26mm Tubular on my Disc Wheel as it has a wider rim width and matches nicely with that tyre. My front Trispoke is a 23mm Tubular as it has a narrow rim width and a tyre any wider will be less aerodynamic, despite it being a pretty harsh ride at times, it still goes very fast. On my Zipp 202 training wheels I'm able to use a 28mm tyre, which match perfectly to the rim so they feel great when I'm bombing down hill and are so much more comfortable than riding on a 23mm or even 25mm tyre. In road races I use an NSCarbon50 wheel set which I will use either 25mm or 28mm tyres.

Comfort

I have spent many many years riding the horrible coarse chip roads we are blessed with here in New Zealand. I have had countless rides over these years where I've experienced hand numbness or a constant buzzing feeling, I've had the neck and shoulder pain, I've lost bottles from hitting bumps and sheared off seatpost bolts from constant vibrations through the frame. Wider tyres certainly won't resolve all of this for us, but they will make life a lot more comfortable and your 6hr ride a lot more enjoyable.

Again, I will caveat this with much smarter people will be able to explain this better, but this is how I understand it....

With a wider tyre you have room for more air, and therefore have have a much higher amount of cushioning between your bike and the road. That being said, if you're using 28mm tyres it doesn't mean you have to pump your tyre up to the same pressure as you would your 23mm tyre. That will make the tyre feel much harder and totally defeat the purpose of having a wider tyre in the first place. It all comes down to the term 'Hoop Stiffness'. 

Hoop stiffness refers to the resistance of bicycle wheel rim, to deformation when it is under load. This is related to the tyre pressure, in that the higher the pressure, the greater the hoop stiffness of the tyre. When tyre is inflated to a higher pressure, the air inside the tire exerts a greater force on the inner walls of the tyre, causing it to become stiffer and more resistant to deformation. This increased stiffness results in a tyre that is more efficient at transferring power from the rider to the road, as well as being more responsive and agile. However, inflating a tyre beyond its recommended pressure can lead to a harsh ride, reduced traction, and increased risk of punctures. So that means, 100psi in a 23mm tyre may be 85psi in a 25mm tyre, 70psi in a 28mm tyre and 55psi in a 32mm tyre....in the end there is probably close to the same amount of air in the tyres, it's just that in the larger volume ones the air is able to spread out further.

Think of a Stand Up Paddle Board. You know how big they are, and when fully inflated they feel rock hard and are very very firm, there's no bending at all, most SUP boards are pumped to a maximum of 15psi, but there is A LOT of air that gets pumped inside. There is no way you can get anywhere near the 70psi of your 28mm tyre. If you pumped your 28mm to 15psi you wouldn't be able to take one pedal stroke without damaging your rim, there's no way you will ride that. So take that logic and think of your flash new disc brake equipped Triathlon bike with nice new wide NS Carbon 50mm wheels running a fresh new set of 28mm Continental GP5000TL. If you have just come off an older style Triathlon bike that had 23mm tyres you had to pump to 100psi, there's no way you should put that much air in your 28mm tyres, and in fact most wheel brands won't warranty damge to a rim if it's been pumped over a maximum pressure (NSCarbon allow a maximum of 70psi for a 75kg rider if riding on 28mm Tubeless tyres). If one of the main reasons you chose to use a wider tyre was comfort, why would you want to take this away?

An over-inflated tyre is actually more prone to punctures as the tread and sidewall isn't allowed to conform around an object that you ride over. A sharp enough object may pierce your tyre, or cut your sidewall. However the opposite may occur if you under-inflate the tyre, you are too spongy and risk a pinch flat. If you are unsure as to the ideal Tyre Pressure for you, visit the Silca Tyre Pressure Calculator website and enter the details to determine the best pressure for you.

When I went from 25mm to 28mm tyres the difference was incredible. I rode the same 130km course 2 days in a row, the 2nd one on the 28mm tyres, and I was so much more comfortable. It has become a now brainer for me when logging big long training miles.

Safety

Having ridden narrower tyres for years I have experienced many sketchy moments when descending a wet off camber corner...it's not a nice thing to go through. Fortunately I haven't come off second best too many times. Now that I am on wider (and correctly inflated) tyres my confidence has improved a great deal and I have a lot more faith in the connection I have with the road.

When you ride your tyres are the only thing that contacts the road. The point it does this is called the 'Contact Patch'. A wider tyre creates a larger contact patch, and this improves your traction. By now you should figure that an over-inflated tyre reduces the contact patch, thus reducing your traction on the road, another good reason to ensure your tyre pressure is optimal. The contact patch may be different between the front and rear tyre due to the distribution of load when riding, which is why you may have a different tyre pressure between the front and the rear tyres.

The contact patch discussion is relevant when talking about using a wide tyre on an older style rim with a narrow internal with. That ballooning becomes a real issue, as you may well have a good contact patch, but due to the shape of the tyre on the rim and if you're going around a corner at speed you effectively roll off the side of tyre, which may have very bad consequences.

Having a larger contact patch doesn't necessarily mean you will be slower. The tread compound of very high quality race tyres, when used with a latex tube, or set up as tubeless, can indeed roll extremely fast. 

A high performance 28mm tyre correctly inflated when ridden over a bump in the road will perform much better than an over-inflated 25mm tyre. This is because the tyre's sidewall will conform to the bump and the lower pressure allows it to deform from the pressure of the bump and the weight of the rider. The result of this is a mostly smooth, and safer experience. If you do this on a tyre that is a higher pressure you will get a lot more vertical osscilation and your tyre may even leave the road. This will slow you down and increase the risk of crashing.

Next steps

If you're wanting to go down the path of riding on wider tyres it's not just as simple as heading to the bike shop and grabbing a fresh set of 28s. As mentioned above there are a few things to consider, and your Local Bike Shop is probably the best place to discuss this as they will have a better idea of what will work for your bike. But I will throw a few things at you to keep in mind.

Disc or Rim Brakes

Most modern Disc Brake bikes will be able to take a 28mm tyre, and for riding on our roads this is absolutley perfect. Some later frames have even more clearance and you can go up to 32mm, but this is more than you will need to ride if you're doing all your riding on the road. I've ridden my 32mm tyres on a gravel Rail Trail and they worked great for that, so it will allow for a bit more terrain freedom if you're after that.

A Rim Brake bike will probably only take a 28mm tyre, and even this may be a stretch due to the amount of room you have in the brake calliper. As mentioned earlier, some models barely allow for 25mm.

Rim width

A popular wheelset from the early 2000's was the Mavic Kysrium (which I still ride on one of my training bikes), this had a rim width of 22mm and would really only work well with a 23mm or 25mm tyre as the widest. Anymore and you feel that ballooning effect when cornering at speed.

Another popular wheelset from a few years later is the Zipp 202 Firecrest (which I ride on my Specialized Shiv Tri Bike). These have a rim width of 25.4mm. I've usually had 25mm tyres on these and they work well, however recently I fitted some 28mm tyres successfully, without rubbing on the chainstays or brake callipers. The 28mm feel significantly better than the 25mm for no apparent loss of speed.

A modern Carbon Disc Brake wheelset such as the NSCarbon50 (which I use for racing on my Cannondale Super6 Evo) have a rim width of 25mm. On these wheels I'm running a 28mm tyre and they feel fantastic. If I was riding on a mixture of gravel and road surfaces I would easily be able to fit 32mm tyres for the advantages they offer.

Tubeless, Clincher or Tubular?

You may notice I have purposely steered away from this part of the discussion. There is so much that we can go into with regard to the for and against for the various options, and I would like to address this in a future article.

So as you can see, we have progressed a long way from the bone shaking, teeth rattling days of the 110psi 21mm tyre...thankfully. Now we are entering into an era where it's getting much more confusing, but the cycling is getting faster, more comfortable and safer for it. There are many differing opinions out there, and really the only opinion that matters is yours as we all have different riding styles, ride different bikes and in different places. So spend some time finding out what works for you, and be prepared to change your mind if suddenly you try something new that works really really well. I did that after finding out I could fit 28mm tyres to my Shiv, and they do feel better and seem to ride faster.