Release the Pressure : The importance of tyres in Cyclocross

   Words by Dave Butcher

   on 27/09/2017 16:51:33

Cyclocross season is upon us.

While the seasoned ‘crossers have probably refined their tyre choice and understand the importance of tyre pressures, to the uninitiated these areas may be easy to overlook as you prepare your bike and focus on getting your kit together and yourself to the line for your first races.

 

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Invest in your boots….

Arguably, the most important aspect of your cyclocross bike is your tyres. These are the only contact patch your bike has with the ground and it would seem a shame to have your beautifully fettled, expensive bike hindered by poor performing tyres and pressure selection.

So what makes a good tyre?

Ignoring tread choice – since this is course determined, there are a number of elements that come together to dictate how well your tyres perform, this is true in all tyres not just Cyclocross - but it can play a larger role in the tough and variable conditions of a ‘cross race.

Aside from your training, bike handling skills and 'hardness', the key to success in Cyclocross is largely determined by the suppleness of tyres

Supple tyres not only offer a sublime ride, they reduce rolling resistance, and enable more precise handling and a greater range of pressures. They adapt quickly as the tyre changes shape while cornering and rolling, which increases surface contact and grip while cornering, plus shock absorption as you pass over irregularities in the road or trail. Ultimately, suppleness comes from rubber compound, casing, manufacturing processes and inner tube choice.

 

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Rubber:

This is the tread on your tyre and all rubber is not the same! Many manufacturers will use petroleum based synthetic rubbers for their treads while other, more artisan tyre producers, will use natural rubber – the stuff that drips from the trees. Natural rubbers are not only more supple, they also offer far greater levels of grip

Casings:

More important in performance than the rubber used, is that of a tyre’s casing. A supple, flexible casing has multiple benefits: improved grip from its allowance of more tread adherence with the ground; improved comfort through greater shock absorption and greater speed since better adherence reduces rolling resistance.

A casing’s qualities come from the density of the weave - expressed as TPI (threads per inch) - with higher TPI improving the tyres characteristics and offering the added benefit of being stronger at the same time. This is a simple thing to look out for - and if you want to keep your tyre choice easy - an excellent starting point.

Top end pro-level tyres will likely be made with silk thread (so fine that no TPI is actually specified), with core-spun cotton (upto around 320TPI) and Polyester below this. Each step down results in a less supple but more durable tyre and this is the balance you will need to strike as you make your way in ‘cross.

 

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700cc Rider Martin Baisch putting his skills to the test

 

Vulcanised or Hand-made?

The maintenance of the natural properties of rubber and the density (TPI) of a tyre’s casing are in part determined by how a tyre is produced.

For the most part, mass produced tyres (and consequently the cheaper stuff you are likely to find in your average bike shop) are made using petroleum-based rubber-compounds and using a process of vulcanisation.

Vulcanisation is a high-heat treatment process that is used to bind materials (treads to casings) together. It is ideal for manufacturing speed but results in a drying and hardening of the rubber – eliminating its natural properties and in addition, it results in a stiffening of the tyre’s casing. If you have ever ridden a road bike with very high pressures in the tyres you will have noticed the bike ‘bouncing’ over the road with the additional stiffness in the sidewalls – ultimately, the stiffening of the casing during vulcanisation does the same thing – but you can’t let air out to correct it!

Hand-made tyres on the other hand, remove the vulcanisation process and in most cases the treads will be hand glued to the casings. This preserves the properties of natural rubber as well as the suppleness of the casings, allowing for unsurpassed adherence of the tyre, for optimal and confident bike handling and enhanced traction and safety, especially when cornering.

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Tubular, Tubeless, or ‘Clincher’?

If you watch the guys at the top levels of the sport you’ll know that they are running tubular tyres. A tubular is a handmade tyre that is sewn shut around a latex inner tube (already in a tube shape) and that is glued directly to a rim. The reason is simple, they are lighter, the casings are suppler and better able to conform to the ground. Most importantly, they can be reliably run at traction-enhancing pressures that typical clinchers can only dream of – around 20psi in some cases.

However, tubulars (tubs) also require a specific rim and to be glued to said rim – maybe a little overkill if you are just getting into cyclocross!

 

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Tubs : The choice of the pros. Be ready to spend a couple of days prepping the suckers though!

 

Tubeless tyres are on the rise and with sealant used to seal punctures they are an excellent option and becoming more so as the technology improves. However, to be assured of their ride quality it is important to make sure that your rims and tyres are a very good fit – the last thing you need is your tyre burping (spilling air and sealant) or rolling off the rim entirely. Burping during riding or a race can be WORSE than many pinch flats or punctures, as an extreme burp can result in a fast loss in pressure, the tyre coming off the rim, and perhaps, a loss of control. So, it’s really important to get your tubeless tyre system right and this may entail some internal rim build-up in order to secure the tyre and to be able to run them at low pressures. While it may seem the perfect option for those new to the sport it may cost you more in time than is worth it – particularly if it damages your experience. In addition, most tubeless tyres are constructed via vulcanisation which we know removes suppleness.

While a traditional clincher tyre is an accessible, cheap option, it will never be as supple as - or be able to be run at the low pressures of - a tub: (think 40psi for a vulcanised clincher and 20psi for a tub).

There is however, the option of a hand-made ‘Open Tubular’ clincher.

 

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Open Tubulars: The ideal balance of cost vs control, speed and suppleness.

 

An open tubular is just that: a tyre that is made in exactly the same way as a tubular tyre but rather than being sewn shut, is sewn around a bead material – usually Aramid - to reduce weight and likelihood of pinch-flats whilst allowing mounting to a traditional clincher rim.

Open tubulars occupy the middle ground in terms of pressures (around 30psi minimum) but feel and perform like a tubular. If combined with a Latex inner tube the ride becomes even closer to that of a tub, offering excellent traction and cornering, low rolling resistance, shock absorption and puncture resistance.

This moves us nicely on to tubes. If you are running a clincher or open tubular........

Latex vs Butyl Inner Tubes:

The short answer is Latex.

Latex inner tubes are lighter and more supple than butyl tubes. They adapt quickly to the tyre as it changes shape while cornering and rolling because latex stretches by 7 to 8 times its original size, butyl only about 1.5. This more flexible tube offers more speed whilst improving rolling resistance and comfort

Latex tubes have lower rolling resistance by as much as 3-4 watts per tube, and provide significantly improved ground feel through the tyre.

In addition they increase puncture protection; the latex stretches and deforms around the body which is trying to penetrate the tube instead of it trying to resist the body and shortly after being punctured through.

They will enhance the ride quality of any clincher or open tubular you put them in.

 

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Simple but effective : Latex tubes improve ride quality, reduce punctures and save watts.

 

The downside is that they lose air – quickly. While this isn’t likely to trouble you in a race, you will need to check your tyre pressures before every ride.

Like a tubeless system, all inner tubes and indeed tubular tyres can be used with a sealant. On contact with the air the liquids solidify to seal holes up to around 5mm. – saving you a trip to the pits or a DNF.

We would recommend the likes of Effetto Mariposa (Caffelatex). Tried and tested, the latex formula is the most novel – foaming during wheel rotation to fill the entire tube, helping to protect against sidewall punctures. Completely safe to use with latex tubes, it can be added through the valve of your tube or tub.

 

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Mobile pitting: Sealants help keep you rolling and can be put in inner tubes as well as tubeless or tubular tyres

 

Tyre choice, as mentioned before, will be determined by the course conditions and substrate. BUT, as a guide, modern data gathering from the upper echelons of the sport points firmly in one direction : use the lightest, most supple tyre you can find at the widest width you are able / allowed to use in your race.


Modern studies using power data and GPS tracking suggest that there are no courses or conditions in ‘cross that favour narrower tyres. For years the conventional wisdom was that narrower tyres were faster on harder pack surfaces when conditions were dry. However this simply isn’t the case. The weight advantage of a 1-2mm narrower tyre is very small and the rolling resistance penalty of higher tyre pressures on rough surfaces can be relatively high.



The importance of tyre pressure:

So you’ve chosen your tyres – how do you make the best use of them?

 

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Quality pumps make pressure reading accurate – a critical element of CX

Cyclocross combines the need for aggressive cornering, flotation, low rolling resistance and impact absorption all in a
tyre which is in many cases limited in maximum width by the rules. World class racers have long suggested that the best tyre pressure is ‘as low as possible’

A simple ‘rule’ regarding pressure is to have you (lightly) bottoming the tyre on the rim once per lap. While simple in theory it is unlikely that you will be pre-riding the course at race speed or indeed in the aggressive, over the front, position that comes with full-gas racing, and bottoming your tyre out over an obstacle at race pace could put you out - or worse still - damage your wheels!

Over recent years the approach to front vs rear tyre pressure has changed significantly, with the most successful racers at the professional levels running front pressures between 0-3% lower than the rear – historically this was between 8-10%.

If you are just starting out, you may wish to keep your pressures equal to begin with as you find your footing and don’t want too much flying around in your head to worry about – but use this as a guide. Also, be aware that if the course has steep, obstacle-strewn downhill sections, you may wish to run slightly higher front pressures.

Since tyre pressure plays such a huge part in Cyclocross it is wise to invest in a decent pump with an accurate gauge. For this there really is only one recommendation: Silca. They have been creating class leading pumps for 100 years with excellent gauge accuracy and precision. The new new Tattico Bluetooth does it all digitally too, so you can be extremely accurate to points of a psi!

This is important in a sport where pressures are low and a relatively large error of just 1psi can mean the difference between finishing or puncturing.

 

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New innovations make precise inflation simpler and consistent.


 

Ultimately there is no substitute for experience. Tyre choice and pressure will be governed by the course, your weight and riding style and by investment.

In short, buy the best tyres you can afford or justify – don’t scrimp since these will make a big difference to your ride. If you are going to run clinchers, definitely run latex tubes and if you are on the fence over vulcanised tyres vs hand-made ‘open tubulars’, spend the extra on the open tubulars – the benefits are huge while the jump in performance is less pronounced between an open tub and a tubular.

 

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Check out Challenge – they do a superb range of tyres that cover all levels and have a long established history.

 

Most importantly, get stuck in.

Simply turning up for a cross race earns you large quantities of kudos!

 


Pro Tip :

Here’s something you won’t read on the side of the box.

Since quality tyres are ‘stickier’ than cheaper ones, you may find them holding onto small stones that can subsequently work through the tyre, resulting in punctures. A pain when training or racing.

A simple trick to reduce this risk with tubulars and open tubulars, is to lightly brush vinegar – yep, vinegar – over clean tyres every 2 or 3 days. Sounds odd but it’s an old Belgian trick and really works. By drawing moisture from the tyres it makes them less likely to hold onto the small stones that cause flats.

Buy cheap vinegar mind, don’t go using up the chef’s best Balsamic….

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