Bike Tyre Technology – Myths Busted

Tyre-ing Up While Avoiding Tiring Out !!!

A lot of explanations become overly technical and longwinded only serving to prove the mathematical truth that “The Longer the Spoke the Greater the Tire” … lol!
Recently I was down at my local bike shop sorting out some new rims and tyres and had a chance conversation with a top mechanic who had just returned from working for the BMC Team on Roubaix and other Belgian classics.
This has prompted me to post this generalised straight to the point guide to tyres and tubes based on my own research and tips from the BMC guy who knows.
The main point of this article is to clarify understanding and get quickly to the key issue of Rolling Resistance, providing some ideas on how to improve it whilst busting some myths.
Here are the basics for road cyclists.

 

Basic Definitions
Bead – The edge of the tyre that holds the tyre on to the rim – can be a rigid wire insert or a soft foldable rib
Fabric – Cloth fabric makes up the body of the tyre. The cloth is woven between the two tyre beads. The most popular material used is Nylon Cord.
Clincher tyres – A tyre where the bead “clinches” the rim.
‘Grippy’ or ‘Grippier’ – A great word to use to sound like a pro when talking about tyre traction but also used to describe the general edginess of a road or circuit or tightness of corners when you’re describing your last heroic ride like you’re Paul Sherwin.
Kevlar – A synthetic material used for durability and flexibility in tyre beads and flat protection panels.
Pinch Flats – Punctures caused when the tube is pinched between the edges of the rim and a hard object such as a kerb or pothole– also known affectionately as ‘Snakebite’ because there are often two identical punctures side by side.
PSI – Pounds per square inch, a measurement of tyre pressure.
Rolling resistance – A measurement of how easily a tyre will roll across a road surface – can be expressed as a ratio or co-efficient – but the important thing is that tyres which naturally roll well DO make a big difference to your speed and effort.
Rubber – the tyre shape is dictated by the shape of the cloth fabric, which is then coated with rubber or nylon / silicon latex to protect it from damage.
TPI – Threads per square inch, a measurement of tyre fabric thread counts – the more the better.
Tread – Patterns of rubber on the tyre which make contact with the road surface.
Tubular tyres – Also known as sew-ups, these tyres are used primarily for racing. Tubes are sewn inside the tyre, which is then glued on to the rim.
Vulcanisation – This is the key step in turning natural rubber from an unstable and unusable sticky mess into what we know lovingly as ‘Rubber’. The ‘vulcanising’ process invented by Mr Goodyear cooks the raw material with sulphur (or in today’s bike technology, with carbon or silicon), causing the rubber molecules to link together whilst managing its hardness or softness.

 

Two Main Types of Tyres
This is a ‘Clincher”
Most of us use these and Gators should be familiar.. Also known as “wire-ons.” They consist of an outer tyre (the “casing”) with a U-shaped cross section, and a separate inner tube. The beads of the tyre hook inside the edges of the rim, and air pressure inside the inner tube holds everything in place. Different tyres might have more ‘O’ shaped, ‘U’ shaped or ‘V’ shaped cross sections which affect handling and traction. TIP : – The pros will tell you that ‘foldable’ clincher tyres will give you less roll resistance than hard wire beaded clincher tyres.

Clincher Tyre

This is a “Tubular”
The more serious cyclists or racers often prefer to use tubular tyres. (Don’t call them ‘Tubeless’ – it’s incorrect and you’ll sound like a dufus!) These tyres are mounted on special tubular specific rims and are GLUED on to the rims. The inner tube is sewn inside the casing of the tyre and the entire combination is made into a single sealed unit.

Tubeless Tyre

Tyre and Tube Sizes Explained
In NZ we generally use the French sizing system
Tyre Diameter: Adult road bikes tyres are measured in metric and are typically 700 (622mm) in size.
You can only fit 700 (622mm) tyres to most road racing bikes. However you can fit a variety of tyre widths of tyre to most rims.
Tube Size Your Tube size will reflect the tyre size and the most common is 700 or 700C
They used to use a suffix letter ‘A’ to ‘D’ to categorise width – A being skinny, D being fat but this is largely unimportant now.
Often you’ll see other numbers on the packet such as 19 / 23c / 25 – just means it will fit various widths but will probably still fit a 28 mm wide tyre ok too.
28 X 1 ½ or ¾ or 5/8 – these are Imperial measurments for USA or Canada.

Valve Sizes – Presta valves are used on road bikes. The other type you hear about are Schrader – forget this word !!! Presta valves are easier to pump, because they have no valve spring to overcome. They are also slimmer so a smaller hole needs to be drilled in the rim avoiding loss of strength especially in skinny rims. The other valve type is used mainly on mountain bikes.

Which Stem Length? Presta come in long and short stem – anything from 36mm, 48mm, 51mm and even 60mm. The depth of your rim dictates which is best and you only require enough stem exposed to secure a pump head.
Having said that, your Joe Blow floor pump usually needs a bit more stem than your manual bike pump.
Bear in mind also that if you’re out riding and need to lend a tube to a companion who has fancy deeper rims like 404 Zipps, carrying long stems is always going to be more useful.

 

Bead Seat Diameter – B.S.D. (Not a cycling transmitted disease …lol)

RIM MEASUREMENTS

 

ISO, the International Organization for Standardization has developed a universal tire sizing system that eliminates confusion. (This system was formerly known as the “E.T.R.T.O.” system, developed by the European Tyre and Rim Technical Organisation.)

The ISO system uses two numbers; the first is the width of the tire or rim in millimeters (The actual tire width will vary a bit depending on the width of the rim. The rim width is the inner width measured between the flanges as shown in the diagram.) So a 23-622 is 23mm wide and 622mm diameter. The width is not critical – it’s the second ISO number which is the critical one. It’s the diameter of the bead seat of the rim, in mm (“B.S.D.”) – this measurement must be right in order for the bead of the tyre to seat properly in the rim.
ISO 23-622 equals the French 700–23.

 

Tyre Pressures
Kiwi riders are commonly obsessive when it comes to having rock hard tyres – it’s called ‘Dynamiting Your Tyres”
Myth No 1 : Harder Pressure vs Softer Pressures – Rock hard tyres are the better because they have less roll resistance and you’ll conserve energy – WRONG.
All you do is end up bouncing all over the chip seal, putting stress on your bike frame and yourself while using up more energy and also reducing your traction and handling capabilities.
For the front tyre it’s fine to use 80 to 90 PSI and for the rear 100 – 110PSI. This will give you comfort without loss of efficiency.

 

Tyre Tread Patterns
I haven’t found that any tread pattern makes any real difference to traction in the wet or dry – and the pro mechanic agreed.
If it’s really wet or slippery you may wish to drop the tyre pressures by 10 – 15 PSI and it will give you better grip without measurably increasing the rolling resistance.

 

Tyre Width
Tyre width plays a significant role in how a bike will behave on different surfaces.
Skinny Tyres are defined here as 20 – 23mm wide vs ‘Wide’ tyres which are defined as 25 – 28mm
The most popular width on road bikes in NZ is 23mm wide. This is a fairly narrow profile but seems to be a good compromise and is popular for fast riding on a smooth road surface.
The wider a tyre the more comfortable the ride is likely to be, due to the increased air volume – but too fat and you start to lose ‘road feel’ as well as experiencing other negatives such as brake or frame rubbing.
On the other hand if you go too narrow you risk tyre damage or even rim damage  from road hazards.
If your rims take 23mm width then you can probably safely fit any width from 23mm to 25mm and even possibly 28mm without too much trouble.
You may notice some added effort required to pull your tyre off and put it back on during roadside puncture repairs with some wider profile tyres on some rims so check this out with your bike shop.
Myth No 2 – Skinny vs Wide :  Skinny tyres go faster because they are more aerodynamic and lighter – WRONG
The guys at Bike Race Info explain it brilliantly (http://bikeraceinfo.com/tech/tires.html)
“The people making the Torelli tires had noticed that the pro teams that they sponsored asked for 23s because they felt they were faster. When they investigated and did the testing, they found that the riders were correct. Here’s why ………
Let’s assume a 200 pound rider and bike unit. Let’s also assume that the weight is distributed half over each wheel. That means that each wheel is supporting 100 pounds. Now, with a pressure of 100 pounds per square inch, the contact patch is one square inch. This is true no matter how fat the tire.
What changes when the tire gets fatter is the shape of the contact patch. With a 20, the contact patch is a long oval. With the fatter tire, the contact patch gets shorter and wider.
When a rider is using a skinnier tire, the long contact patch means he is flexing a wider arc of the tire casing, flexing more of the tire, causing more wasted energy from the internal friction of the tire and tube. The rider with the fatter tire is flexing fewer cords at a time.

 

Tyre Shape
The shape of the tyre or its ‘Profile’ has a significant effect on traction (as does the hardness of the rubber compound – see section below).
Myth No 3 – Oval vs Round Profile : Round profile tyres are not aerodynamic and will slow you down. WRONG
Again riders might like the thought of an oval tyre being more aerodynamic but for most bunch rides you’ll get far better performance from a more round profile.
As demonstrated in the Torelli story above you’ll get a more comfortable ride and reduced rolling resistance on a more rounded tyre. Again it’s mostly because the contact profile with the road is more round shaped than elliptical which means the stresses are dispersed more side to side and less forward and back meaning less stress and less energy wasted flexing the tyre over the tube inside.

 

Tyre Compounds
Myth No 4 – Hard Vs Soft : Soft compound tyres are spongey and slow. WRONG
Softer compounds will generally provide better traction and less rolling resistance but won’t last as long.
Why are some tyres blue Mummy? “Well dear, when the man makes the better quality tyres he will sometimes ‘vulcanise’ the rubber he uses for coating of the fabric with silicon (which is often a pretty colour) instead of carbon (which is black) This of course strengthens and protects the cloth fibres, Kevlar fabric or Nylon cord fabric which forms the ‘skin’ underneath the thick rubber tread layer.”
Silicon flexes better and distributes the stresses along the cloth fibres more readily again reducing the energy wasted in the tyre ‘fighting’ excessive stresses along the fabric threads. Hence they generally have less roll resistance.
There are some clever compromises found in ‘mixed compound tyres’ and these are worth trying to determine your preference.
So what about those ubiquitous Gator Skins or Kevlar reinforced tyres? The point is that even though they don’t roll as well as some tyres, they are certainly not the worst, they wear really well and best of all in Winter you will definitely save yourself a heap of roadside puncture repair time if you fit them to your bike. The shorter the time we spend out in the rain in Winter the better – so we all love them for general purpose training.

 

Tubular Tyres ( Sew Ups) – Positives and Negatives
Myth No 5 :They ‘re dangerous and peel off during hard cornering and heavy braking. MOSTLY INCORRECT.
The main problem is where inexperienced but well-meaning mates try to fit them or you try to do it yourself.It’s critical that you match the tyre size, rim compatibility and adhesive …best still …get the pros at your bike shop to fit them.
Negatives -
1) They can be difficult to repair and punctures are not so easily fixed on the roadside – hence the need for a support vehicle with a new wheel.
2) They can indeed peel off on long downhill sections if the rims get too hot and the glue melts – this is why even pro riders have been known to swap to clinchers on big downhill’s in the Grand Tours. This will all be resolved when disk brakes become common on road bikes and permitted in racing.
(Riders who are less confident and use their brakes excessively can also experience tyre explosions using clinchers- I’ve witnessed this on K2.)
3) If they aren’t permanently glued in they can ‘squirm’ against the rims and then become slower than high performance clinchers which are also made ultra-light.
Positives
4) They weigh less
5) They handle better
6) You look like a ‘Pro’.