I bought this MTB for commuting. Yup, I found out later that I should get a road bike instead. Too late. Not planning to use on rough terrain. Can I inflate the tires more than the manufacturer recommends? If I can, how much?
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Probably you can go up to about 75 psi with reasonable safety. I wouldn't push them all the way to 100 (and you probably don't want to anyway, as the ride would be harsh for commuting).– Daniel R HicksCommented Jan 28, 2019 at 3:58
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350PSI in MTB tires is a lot! Unless you are on a heavy side or carry substantial load, that's in range for 32mm+ road tires. What are you trying to achieve with higher pressure? I'd argue the comfort is more important. Maybe consider getting tires that roll better.– Klaster_1 Нет войнеCommented Jan 28, 2019 at 4:13
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7Yes, your tires have some margin to allow for overinflation, but that will not make them roll more efficiently--past a certain point, all you're doing is making the ride harsher. Getting slick tires, however, will vastly improve efficiency and comfort when riding on pavement.– Adam RiceCommented Jan 28, 2019 at 4:37
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1I too use a mtb for commuting and I wont recommend to inflate tires that much: in my experience, you will not get any significant decrease in rolling resistance, but get a lot of vibrations which could actually slow you down.– k102Commented Jan 28, 2019 at 8:57
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1@AdamRice: “vastly improve efficiency” might be an exaggeration. It’s surprising how good some MTB tires are compared to some slick “touring” tires, at least according to bicyclerollingresistance.com– MichaelCommented Jan 28, 2019 at 11:16
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1 Answer
How wide are the tires compared to the rim? Wide tires at high pressure put stress on the rim’s sidewalls which can result in sudden, catastrophic failure. If the tires are relatively narrow it’s probably okay to over-inflate, but I doubt you’ll see much benefit. There are diminishing returns for rolling resistance.
See for example this test of 56mm wide Vittoria AKA tires https://www.bicyclerollingresistance.com/mtb-reviews/vittoria-aka-2015 which have a very high rolling resistance to begin with:
Rolling Resistance Test Results (Speed: 29 kmh / 18 mph / 8 m/s, Load: 42.5 kg / 417 N)
Inner Tube Conti MTB 29 (225 gr butyl)
Rolling Resistance 55 psi / 3,8 Bar 35.6Watts
CRR: 0.01067
Rolling Resistance 45 psi / 3,1 Bar 36.3 Watts
CRR: 0.01088
Rolling Resistance 35 psi / 2,4 Bar 38.0 Watts
CRR: 0.01139
Rolling Resistance 25 psi / 1,7 Bar 40.7 Watts
CRR: 0.01220
As you can see, the effects of pressure on rolling resistance are surprisingly small (though I guess for a tire of this width 1.7 bar is already a relatively high pressure). Going from 45 psi to 55 psi for this tire saved only 0.7W per wheel when measured at a relatively high speed of 29km/h. At the same time you’d start to feel every tiny bump in the road and you’d have decreased grip on pebbles or debris.
I dimly recall an experiment where high pressures even started to increase rolling resistance on rough surfaces above a certain point.
As others have said in the comments, getting some good, slick (i.e. treadless) tires will improve rolling resistance much more.
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Presumably over-inflated tyres increase rolling resistance because they can no longer deform over small bumps and must lift the whole bike over them. Commented Jan 28, 2019 at 15:41
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Thanks for the detailed answer. I will stay on 50 PSI then Commented Jan 28, 2019 at 18:12