Brucey wrote:ukdodger wrote:..... I run on 55-65lbs which is within Schwalbe's limits because I like a soft ride (though if you get any sidewall cracking Schwalbe will claim their limit is only a 'guide' and 55-65lbs is too soft to prevent it)....
this is another case of weaselry IMHO. Tyres that are underinflated typically suffer the consequences of the sidewall flexing excessively, which normally results in the casing failing in some way (including the wire bead failing in some types of tyre). But the sidewall is made of rubber, and should flex repeatedly without issue. Were it not so, you would see cracking on (say) rear tyres and not fronts; but you normally see cracking on both.
Schwalbe tyres have gone through a very bad patch where they suffer sidewall cracking even when they are not used at all. You can park the bike with clean tyres in a cool dark shed and come back and find the tyres perished. This is nothing to do with underinflation whatsoever; it is just substandard manufacturing of some kind.Question: What is the measure of tyre suppleness? I once had a pair of tyres made but Hutchinson that were wonderfully comfortable to ride but werent 'soft'. They dont make them anymore but knowing what to look for would help. Thanks.
Obviously if you can obtain meaningful CRR data that will help, but do bear in mind that real roads are nothing like the rollers they usually use to measure such things. For ad-hoc techniques;
1) if you can see a pair on the rim, correctly inflated, flick them with the end of your finger. Listen to the noise; if it is a resonant noise then the tyre may roll a whole lot easier than a tyre where flicking it produces a dull thud instead.
2) If you are able to take a bare wheel with the tyre fitted, and simply drop it (on smooth concrete) so that it bounces up again, then look at how high the wheel bounces. You will need other wheels/tyres to compare, and you will have to practice nice straight drops. Good tyres will cause a bare wheel to bounce up to 60-70% or so, and it will likely sound resonant; bad tyres won't bounce so high and the noise will be duller.
3) Handle the carcass of the tyre. To a good approximation there are three things that create rolling resistance; a) the tread squishing vertically when loaded (so soft rubber and a heavy tread pattern count against you here), b) the bending properties of the tread (the circumference of the contact patch is flexed at any one time) and c) the stiffness of the sidewalls. Typically if you have a light racing tyre you can get all three to be good but any amount of puncture protection tends to add to b) at least. [It isn't clear to me which of a) b) c) is most important; it may vary with the tyre.]
If you look at easy rolling tyres they usually have a vertically firm tread that usually isn't very thick; this is built on a carcass that is made very supple by having very little rubber in it and lots of fine cords (high tpi). The reason high tpi works well is that you can make the sidewall (say) half as thick. If you do this (which might require four times as many threads in the same material, each half as thick, to get the same strength) then the bending strains in the sidewall (and therefore the hysteresis) is very greatly reduced; half as thick potentially means 1/8th the strain in the sidewall. [BTW That isn't a reduction of 1/8th, that is a reduction of 7/8...! It really can be a powerful effect!]
So I hope this helps, anyway. You clearly don't get owt for nowt here; if you insist on tough rubbery sidewalls, a heavy tread, and good puncture protection, you had better get used to the idea of relatively sluggish tyres.
BTW the marathon 'greenguard' tyres are quite clever because the puncture resistant layer is made in highly elastic rubber that cannot squirm excessively; this means that the CRR is nothing like as bad as it would be if you had a tread that was as thick as all the layers put together. It isn't a quick tyre like this, but it is nothing like as slow as it might be otherwise.
cheers
Thanks Brucey. That's all good to know.
