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I have a e-mountain bike and I use to commute to uni every day. I have heard that higher tire pressures give you a bit more speed. My tires say I can pump to 55 psi (380 kPa) but I don't know if my tube can handle the same pressure. Don't want to buy a new tube. I currently have them at 40 psi (280 kPa). Will 47 to 50 psi (320–380 kPa) burst my tubes?

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    I happen to have just bought a tube so I have the packaging and the tube on hand to examine. Mine happens to be a Continental tube for 26x1.75-2.5. There is no mention of maximum pressure on the packaging or the tube itself. The pressure limit is set by the tire, so if the sidewall of the tire says max 55 psi, then go with that. – Gaston Mar 11 at 12:03
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    I would avoid over-inflation. It's unlikely to help and will make your ride less comfortable. You will also be more likely to get a flat if you hit a pothole or curb. Using smoother or even thinner tires is a better option. There are styles that have a smooth center line and knobby sides if you want to have a fair off-road capability. – JimmyJames Mar 11 at 13:39
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    Shouldn't snakebite flats be caused by too-low pressure, not too-high? – Vladimir F Mar 11 at 13:50
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    @PeterA.Schneider "Unless the road is damaged" Maybe roads are better where you are. In the UK, that's a bit like saying "Unless the sun rises in the east." – David Richerby Mar 11 at 16:45
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    In short - your tube hold the air from leaking while the tyre holds the pressure. – Criggie Mar 12 at 2:06
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It can't burst the tube, because the tube is completely surrounded by the tyre and rim.

Bear in mind, though, that higher pressures don't automatically mean a faster ride. There are two competing factors: a soft tyre is constantly losing energy due to being squashed flat against the road, but a hard tyre loses energy because any bumps you go over have to lift the whole bike, instead of just deforming the tyre. I don't ride mountain bikes so I don't know where that trade-off starts to bite.

On an e-bike, I'm not sure this will make much difference, though: it just means that the assist motor will have to work less hard at any given speed.

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    You could make it clearer that the tube does not take any significant part of the pressure; the tyre does it alone. One can see how little pressure a tube can hold by pumping one up, without the tyre. It's a better balloon. – Peter - Reinstate Monica Mar 11 at 13:53
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    @Adonalsium OK but any such difference is going to be negligible: a 1% increase in tyre outer diameter will give a 1% increase in speed. – David Richerby Mar 11 at 15:43
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    @PhilFrost Nothing is 100% efficient, so the energy you lost on the uphill side won't be fully restored to you on the downhill. – David Richerby Mar 11 at 16:22
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    Better than rolling resistance, which converts energy to heat which isn't recovered at all. Lower pressure makes a larger contact patch, reducing sheer forces on the soil which means more "grip". But it certainly doesn't make the bike roll more efficiently. – Phil Frost Mar 11 at 16:41
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    @Phil Frost it depends very much on properties of the tyre, such as sidewall stiffness. So called suspension losses may contribute considerably to overall rolling resistance. Thus doesn't even take increased fatigue into account. The rider is the main inelastic member. The jolts that dissipate energy in their body also have to be compensated by muscular action. Eccentric contraction doesn't generate biochemically useful energy. – gschenk Mar 11 at 17:52
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The tensile forces are borne by the tire, not the tube. So go ahead and pump it up to the maximum pressure on the tire if you're riding mostly on roads. I think you'll find the bike rolls significantly easier.

David Richerby argues a tire too hard will lead to a less efficient ride. JimmyJames gives two examples of testing lower pressures in road tires. Apparently there is a significant "lower is faster" camp of roadies. Their argument isn't applicable to your situation, in fact the data suggest 55 psi is what you want. A higher pressure would probably be better, if the tire could handle it.

Here's a graph from the first example:

enter image description here

This is the time taken to roll down a test hill: less is better. For the two clinchers tested (your tires are almost certainly clinchers), in neither case did they find a pressure that was "too high". For the tubulars, they did find a higher pressure that was slower, but look at the pressures involved: the lowest pressure tested was 85 psi! Not to mention of course your tires aren't tubulars, you aren't on a road bike, and you probably aren't riding as fast and you probably don't have high-end tires. Also note the potentially misleading axis which starts at 24: this makes the differences between tests look much more significant than it really is. Also note the author of this article is selling something.

The data from the second example:

enter image description here

This shows the power required to sustain 40 kph. Lower is better. Note in every case, higher pressure was better. In some cases the margin was very small. And again note the pressures tested: the "low" pressure is too high for your tires: 84 psi.

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    Apparently there is a significant "lower is faster" camp of roadies. Their argument isn't applicable to your situation I'm glad someone did notice that a 2"+ (50+ mm) MTB tire designed to handle at least some off-road use at 55 psi isn't really comparable to a 1"/25mm or less road tire at 120 psi. – Andrew Henle Mar 11 at 22:35
  • The magazine in the second example has a followup velonews.com/2018/06/from-the-mag/… And that one shows a very different story. For a 35mm tyre they found 30PSI to be the fastest on a gravel road. – Vladimir F Mar 12 at 15:58
  • @VladimirF When the OP is riding gravel roads on a road frame and a high quality 35 mm tire, I'll change my recommendation. But since he's on roads with a mountain bike and what's likely a low quality, much wider tire, I maintain the tires will explode well before they are "too hard". – Phil Frost Mar 12 at 16:07
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I know from my own experience (several decades of riding bicycles of various sorts) that harder tyres roll quicker and resist puncturing more (particularly on the road), but softer tyres grip better (particularly offroad). Only your own experience will find you the best compromise between the two for your riding style. The one thing I found could force a tyre off the rim (and therefore explode the tube - with a very load BANG!) was a flat spot on the rim, but I did pump the tyre up to 115 PSI. The tube was in no way to blame. A round rim would prevent this from happening at recomended pressures.

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