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Roll on: Part 2 of EVERYTHING about Tyres

This is the second part of the two part FAQ feature on bike tyres from Dr David
If you haven’t read the first one, I recommend you see it here before reading this second installing episode…
By the way, some people have responded to ask: so which tyres do I buy? As before, we’re not telling you the right brand, but if you want to know a selection of what we use, contact us and we will drop you a list
road-tire-rolling-resistance

Click to see a larger version of this graph

Rolling resistance Some tyres roll faster than others and sometimes you can feel the difference. As stated in the previous blog, the faster you go the more wind resistance is the overriding factor slowing you down. As the drag due to wind resistance increases with the square of the velocity, the frictional losses of bearings, chain and tyres pale into insignificance. But why waste 40 watts on inefficient tyres? Tyre construction and pressure play an important part. Fine flexible tyres that deform easily are more efficient than thicker walled tyres. Extra puncture protection layers may also increase rolling resistance.

The Coefficient of rolling resistance (Crr) has been studied and quoted by numerous web sites and manufacturers. The study methods are never the same but there are some group tests. Looking at this chart you could lose 20 watts per wheel by using a GP3000 rather than an Open Corsa Evo CX!

Compound
Softer rubber compounds generally grip better than hard. But who wants a tyre that is super grippy and only lasts 500miles? One solution is to have a harder compound in the centre of the tyre and soft compound on the sides of the contact area to give grip in the bends e.g.Vredestein Fortezza TriComp. There are dual and tri compound tyres available especially as winter tyres. Continental promote their “Black Chilee” compound which seems to come out well in tests but there are others.

Weight
Lightweight tyres will accelerate better but generally are less robust and wear out faster. Not all lightweight construction will have a lower Crr though.
Winter tyres. The rain and wind spread all sorts of rubbish onto the roads so puncture resistance is essential. Various manufacturers have their own solutions including Kevlar, Duraskin, V Guard etc. When the rain comes we want grip so a good compromise is dual or triple compounds.

Butyl vs. latex inner tubes
As the tyre rolls it deforms which affects its rolling resistance. The inner tube has to be deformed as well and there is friction between the tube and the tyre. More flexible and lighter latex tubes are more efficient and produce a lower Crr by 10% but this is dependent on weight. Latex tubes are more porous so go down faster. They are also more prone to failure due to contamination with oil etc and they have been known to explode!  Read about the myths of punctures.
Some say they are more comfortable.

Wrapping up
It is all a matter of compromises. A few points stand out though:
opencorsaevo

  • 25mm is the way to go unless you are time trialling
  • Use the spreadsheet to work out ideal pressures
  • Do not over-inflate tyres
  • If your ride is uncomfortable and you are vibrating then they are overinflated
  • Some tyres roll faster than others
  • If you keep getting punctures it is time to try another tyre
  • Use tyres that you are comfortable with and have confidence in.

References/ further reading:
http://rouesartisanales.over-blog.com/article-1503651.html
http://www.terrymorse.com/bike/imgs/rolres.gif
http://janheine.wordpress.com/2012/06/13/bicycle-quarterly-performance-of-tires/
http://www.slowtwitch.com/Products/Things_that_Roll/Tires/Fast_Tires_2013_3787.html
http://roadcyclinguk.com/gear/buyers-guide-winter-tyres.html
http://hubpages.com/hub/The-Best-Road-Cycling-Tyres-For-This-Winter
http://www.bikeradar.com/gear/article/bicycle-tires-puncturing-the-myths-29245/

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