TPU versus butyl rubber tube in a folding bike?


in Upgrade Your Strida: Get rid of those AV/Schrader valves! i had a picture that showed a TPU tube so the question arose, whether You feel a difference in rolling resistance or not. Well, yes, You do if You are in a controlled environment and sensible enough to feel it. Stop - End -
But that would not be a discusion of TPU (Thermoplastic PolyUrethane ) vs. butyl rubber.
I know, the rolling resistance of TPU tubes is less than that of butyl rubber tubes. Was that the reason why i bought a TPU tube?
A bit maybe, but it wouldn’t have been enough of a reason for buying it. There must have been other reasons as well.
1st) The AV/Schrader valves work so bad, that i sought to get rid of them as quickly as possible. So i had a reason to get me new tubes with good valves in the first place.
2nd) TPU tubes are significantly more lightweight than butyl rubber tubes. AS everyone counts the grams of weight of their folding bikes while carrying them around as a peace of luggage, even in the small wheels of a Strida, two TPU tubes are ~46 to 66 g of weight where 2 butyl rubber tubes are 204,0 g so TPU spares You some 138 to 158 gramms of weight. The difference is metal valves (2x33=66g) versus plastic valves (2x23=46g) in the TPU tubes.
3rd) TPU tubes are told and tested to hold the pressure constant much better than butyl rubber tubes and even more better than latex rubber tubes. And pressure in the tires of our small folding bikes is more essential as it would be in a 28" bike.
4th) TPU tubes are said and tested to be much more puncture resistant as compared to butyl rubber tubes.
5th) Last and maybe least. Yes! TPU tubes do have a lower rolling resistance as compared to butyl rubber tubes.

Of course, You can get Yourself Sclaverand valves in a butyl rubber tube.
So there are 4 reasons left to compare the two technologies and in 2, 3, 4 and 5 the TPU tubes are superior to rubber tubes. Could be enough of a reason to purchase these.

However, the question unanswered remains a sole question: Do TPU tubes really have a lower rolling resistance? Do You feel it?

Here we go:

Riding in a gusty wind You won’t feel any subtle difference in bicycle performance.
You do feel the different rolling resistance if You change from one asphalt quality to another on a roadbike for sure. But that’s an immediate direct comparison. The “new asphalt” will allow You to slightly accelerate or force You down to a slightly reduced speed.
It’s much more difficult to actually feel the difference between two bikes or setups if You have some time between the two impressions.
But You might be able to feel it.
I feel a difference if i wear a warm pair of underpants as they cause significantly more friction between my thigs and my pairs of trousers.
I feel a difference if i wear a slim pair of jeans as compared to a relaxed pair of jeans.
Another effect but yet another difference You might well feel: Heavy winter boots versus lightweight summer shoes. At a high pedaling frequency, heavy boots are much more annoying as compared to lightweight shoes.
The difference between TPU tubes and butyl rubber tubes is about like that. It’s about as much as riding without or with a pair of warm untderpants.
To make it possible and actually feel that difference, as much influence factors as possible are to be eliminated.
A) Tires: heavy tires versus lightweight (high performance tires).
You wish to eliminate as much friction as possible but the internal friction of the tubes to make it as likely as possible that You can actually feel a difference. I performed test runs with the extremely narrow Strida (Innova) 32-355 at 5 bar and the extremely high performing and lightweight Schwalbe Marathon Racer 40-355 at the lowest recommended pressure of 4 bar.
The lower the pressure the higher the rolling resistance and we want the rolling resistance to be felt better than the wind resistance…
B) Pedals: My pedals were mounted with more than a stiff bearing setting. They had lots of resistance to them so of course, i opened the pedals (thin knife and take care to not make them become too ugly) and carefully adjusted the bearings using a 14 mm and a 12 mm socket wrench. All this takes is some experience and some patience, as it is a trial and error approach. But it can be done routinely. After 3 or 4 trials i will have found my perfect setting.
C) Belt drive: When i got my SX, it felt like having an awful lot of resistance to it. It didn’t feel high performing at all. Most of that was due to the low air pressure in the tires, but pedals and belt contributed to the overall impression. I loosened te bottom bracket and adjusted the belt tension to an optimum low resistance without any margin of safety.
D) I even changed a more narrow pair of warm underpants for a more convenient pair of underpants and of course, i changed my boots for lightweight jogging shoes.
E) We had a lovely nice high air pressure day, where i live. On days like this, You have as good as no wind. That’s essential for being able to perform such a test. Wind is stronger than all of the more subtle differences i adressed earlier.

But so i went and so i changed tires and tubes and so i went again. Always the same track always on the same dry road (anther influence factor: wet roads have a higher resistance than dry roads)

You need to pick a nice day, keep it as controlled as possible and eliminate as much of all other influence factors to really feel a difference. However i can confirm, that in close to ideal conditions You can feel a difference in rolling resistance. It’s like no pants versus additional pants. It’s like dry road as compared to wet road. It’s like fine asphalt as compared to rough asphalt. It’s not much but it’s there.

As everyone talks about the small wheels of our folding bikes and small wheels let us feel the diffeence between high performing tires and tubes more intensly than larger wheels, folding bike users should be as interested in low resistance tires and tubes as race bike riders actually are.
It does make sense to discuss this subtle difference in performance here more than elswhere.
There have been tests comparing different tubes, like on
Reading those tests, i notice, that the results are exagerated rather than underestimated as they test on a 77 cm cylinder. So rather than expect larger differences on a folding bike, better assume that a race bike will see smaller differences in real life and we can expect TPU tubes in both wheels to save us some 5 to 6 watts of power alltogether. That’s some 8 to 10 % of an ordinary bicycle rider’s power and it should raise our average speed by somewhere around 1 km/h. That’ s more than nothing. But it is not gamechanging, is it?

Would i get me new TPU tubes just because of the rolling resistance? No.
It’s not enough of a difference to throw away good butyl rubber tubes.
But It’s defenitely good enough of a difference to get TPU tubes next time.

regards: Klaus

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As of today I use TPU tubes in a 44-355 tyre ( Schwalbe Marathon) without any problem of any kind.
As i have only used transparent Eclipse TPU tubes ( not continued but a last few seem to be available in the market, still ) and I compare these to videos of other TPU tyres I can‘t help to notice, what Schwalbe write about the TPU they use for their „aerothan“ tubes: TPU and TPU is not always the same.
The eclipse TPU tubes come with a 6 mm wide sample of the actual tube used as a „rubber band“.
It‘s fairly elastic. The chord length of this „rubber band“ is 106 mm and it is easily stretched to 280 mm.

Pic 1: some TPU is fairly elastic.

Stretching it like shown reduces the width of the „rubber band“ to 4 mm, but this still means an increase in surface area of 176%.

There is a saying, that once You have mounted TPU tubes to a wide tyre, You can‘t use them on a narrower tyre anymore. It is not true for the transparent eclipse TPU tubes.
Even after being used in a 44-355, that is beyond the specification, there‘s no problem utilising it in a 32-355.

regards: Klaus

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