Strange question re tyre pressures.
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Strange question re tyre pressures.
OK, It doesn't really matter what the answer to this is, but it is kinda bugging me.
I was on Schwalbe's website, reading there article on tyre pressures. (see page 32 of this pdf)
Now, I am running 20" Schwalbe Crazy Bob's (54-406).
According to the above chart, for 54mm wide tyres I should be looking at 35psi.
But then it also says "It is recommended that higher inflation pressures are used on very small diameter tires such as recumbants and folding bikes.", but it doesn't say how much higher. I presumed knocking 10mm off the tire width might compensate for moving from 26" to 20". So that starts me at 50psi.
The next part of my calculation is based on "The recommendations are for an “average rider” weighing about 75 kg." and "For each additional kilogram that the tire must carry (bike, rider, luggage), the inflation pressure should be increased by approx. 1%." Well I weigh ~13 stone which is ~83kg. And my work bag weighs about 10kg, thats 93kg, which is 18kg over 75kg. 50psi + 18% = 59psi.
So in theory, I should be inflating the tyres to 59psi. All very well and good, but according to the side wall of said tyre - that is too low!!!
The acceptable range for inflation is apparently 65-100psi (which interestingly is also the pressures for the 47mm wide tyres - where as the 60mm tyres are 30-65psi)
Come the finish, I am inflating to ~65psi and the adjusting by visual appearance and comfort.
Its just I find their tyre markings a little strange based on the above pdf.
And before anyone mentions it, I am well aware that they said "It is impossible to make a general recommendation on inflation pressure for a specific bicycle or a particular tire."
I was on Schwalbe's website, reading there article on tyre pressures. (see page 32 of this pdf)
What is the correct pressure for my tire?
It is impossible to make a general recommendation on inflation pressure for a specific bicycle or a particular tire. The “right” inflation pressure depends mainly on the load exerted on the tire. This weight is mainly influenced by the weight of the rider and any luggage. Contrary to a car, the vehicle weight is only a minor part of the total weight. In addition there is a great diversity of individual preferences with regards to low rolling resistance or suspension comfort.
The permitted inflation pressure range is marked on the tire sidewall. The higher the inflation pressure, the lower the rolling resistance, the tire wear and the less likelihood of a puncture. The lower the inflation pressure, the higher are the comfort and grip that the tires provide. The list of inflation pressure recommendations on the right can only provide a very general guide. The recommendations are for an “average rider” weighing about 75 kg.
If the rider is heavier or carries luggage, a higher inflation pressure should be used. For each additional kilogram that the tire must carry (bike, rider, luggage), the inflation pressure should be increased by approx. 1%. It is recommended that higher inflation pressures are used on very small diameter tires such as recumbants and folding bikes.
Lighter weight riders or riders who prefer a smooth or more comfortable ride can accordingly choose a lower inflation pressure, but the actual tire pressures should never be higher or lower than the maximum and minimum inflation pressures marked on the tire sidewall.
It is impossible to make a general recommendation on inflation pressure for a specific bicycle or a particular tire. The “right” inflation pressure depends mainly on the load exerted on the tire. This weight is mainly influenced by the weight of the rider and any luggage. Contrary to a car, the vehicle weight is only a minor part of the total weight. In addition there is a great diversity of individual preferences with regards to low rolling resistance or suspension comfort.
The permitted inflation pressure range is marked on the tire sidewall. The higher the inflation pressure, the lower the rolling resistance, the tire wear and the less likelihood of a puncture. The lower the inflation pressure, the higher are the comfort and grip that the tires provide. The list of inflation pressure recommendations on the right can only provide a very general guide. The recommendations are for an “average rider” weighing about 75 kg.
If the rider is heavier or carries luggage, a higher inflation pressure should be used. For each additional kilogram that the tire must carry (bike, rider, luggage), the inflation pressure should be increased by approx. 1%. It is recommended that higher inflation pressures are used on very small diameter tires such as recumbants and folding bikes.
Lighter weight riders or riders who prefer a smooth or more comfortable ride can accordingly choose a lower inflation pressure, but the actual tire pressures should never be higher or lower than the maximum and minimum inflation pressures marked on the tire sidewall.
Code:
+-------+--------------------+ | Tire | Inflation pressure | | width | Recommendation: | +-------+--------------------+ | 20 mm | 9,0 bar 130 psi | | 23 mm | 8,0 bar 115 psi | | 25 mm | 7,0 bar 100 psi | | 28 mm | 6,0 bar 85 psi | | 30 mm | 5,5 bar 80 psi | | 32 mm | 5,0 bar 70 psi | | 35 mm | 4,5 bar 65 psi | | 37 mm | 4,5 bar 65 psi | | 40 mm | 4,0 bar 55 psi | | 42 mm | 4,0 bar 55 psi | | 44 mm | 3,5 bar 50 psi | | 47 mm | 3,5 bar 50 psi | | 50 mm | 3,0 bar 45 psi | | 54 mm | 2,5 bar 35 psi | | 57 mm | 2,2 bar 32 psi | | 60 mm | 2,0 bar 30 psi | +-------+--------------------+
According to the above chart, for 54mm wide tyres I should be looking at 35psi.
But then it also says "It is recommended that higher inflation pressures are used on very small diameter tires such as recumbants and folding bikes.", but it doesn't say how much higher. I presumed knocking 10mm off the tire width might compensate for moving from 26" to 20". So that starts me at 50psi.
The next part of my calculation is based on "The recommendations are for an “average rider” weighing about 75 kg." and "For each additional kilogram that the tire must carry (bike, rider, luggage), the inflation pressure should be increased by approx. 1%." Well I weigh ~13 stone which is ~83kg. And my work bag weighs about 10kg, thats 93kg, which is 18kg over 75kg. 50psi + 18% = 59psi.
So in theory, I should be inflating the tyres to 59psi. All very well and good, but according to the side wall of said tyre - that is too low!!!
The acceptable range for inflation is apparently 65-100psi (which interestingly is also the pressures for the 47mm wide tyres - where as the 60mm tyres are 30-65psi)
Come the finish, I am inflating to ~65psi and the adjusting by visual appearance and comfort.
Its just I find their tyre markings a little strange based on the above pdf.
And before anyone mentions it, I am well aware that they said "It is impossible to make a general recommendation on inflation pressure for a specific bicycle or a particular tire."
#2
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That looks to be based on a 700c tire, and you are using a 20" so the inflation data applicable for a 700c will not match that of what you are using.
Would base your inflation on what the sidewall of your tire says, as this will give you the info you need, you will also be able to work this out when riding, does it feel good or not.
The info is on page 31, not 32 as noted.
Would base your inflation on what the sidewall of your tire says, as this will give you the info you need, you will also be able to work this out when riding, does it feel good or not.
The info is on page 31, not 32 as noted.
#3
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I think the idea here is that with smaller-diameter wheels, the "bottom" part of the tire makes up more of the total volume, so the rest of the air volume in the tire is less able to resist the deflection at the bottom. So for the same tire width, you'd need a little more pressure to guard against pinch flats. That said, you might need to experiment to find out what pressure achieves the right balance of comfort and flat-protection for you. I was able to run my 700x30 tires in the mid-40s yesterday on a gravel ride without flatting, at a rider weight of ~155 lbs. I often use pressures at or below the recommended minimum on the front of my other bikes, too. I may have luck on my side, though.
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I've never felt a difference between different tire diameters at the same width and inflation pressure.
I go with the "around 15% depression of tire" when fully loaded method.
I go with the "around 15% depression of tire" when fully loaded method.
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#5
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With a good solid bead hook in the rim. I go with the thumb test.
when my bike feels sluggish I add air.
349-35 & 406-47. 559-47, 622 32 Or 40
On a bike tour I brought a separate gage.. pannier load quickly indicates when the
rolling resistance increases...
reading the imprint on the tire is the basic thing..
when my bike feels sluggish I add air.
349-35 & 406-47. 559-47, 622 32 Or 40
On a bike tour I brought a separate gage.. pannier load quickly indicates when the
rolling resistance increases...
reading the imprint on the tire is the basic thing..
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I might add a warning tho. In the heat of the summer, when you bike is in the garage or in the shade be carful with hight inflation. If you go to say the stated 100 pounds in the cool of the morning, think what it will be in the heat of the day on 150 degree blacktop highways.
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I might add a warning tho. In the heat of the summer, when you bike is in the garage or in the shade be carful with hight inflation. If you go to say the stated 100 pounds in the cool of the morning, think what it will be in the heat of the day on 150 degree blacktop highways.
#8
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I don't think the diameter is that important. https://docs.google.com/spreadsheet/...hl=en_US#gid=0
#9
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100psi seems like way too much for a 54mm tire, but I don't run 406 rims either... My 54mm tires on 26" MTB rims see anywhere from 20-50psi depending on what they're being used for. I've never had a pinch flat but I only weigh 130lbs. I do frequently ride down stairs and other stupid stuff.
+1 Adjust per your personal preference based on comfort and if you get any flats although I seriously doubt you'll see a pinch flat at anything greater than 50psi unless you're hitting really bad potholes.
+1 Adjust per your personal preference based on comfort and if you get any flats although I seriously doubt you'll see a pinch flat at anything greater than 50psi unless you're hitting really bad potholes.
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I'd also agree with the "around 15% depression of tire when fully loaded" method.
Those tires have a load rating of 85kg each and you're so far within that you could run them on the minimum recommended pressure marked on the sidewall if you wanted to. Respecting the minimum will avoid damaging the sidewall structure and increase the expected tire life. Any difference in tire pressure front and back should be related to the actual weight distribution.
Those tires have a load rating of 85kg each and you're so far within that you could run them on the minimum recommended pressure marked on the sidewall if you wanted to. Respecting the minimum will avoid damaging the sidewall structure and increase the expected tire life. Any difference in tire pressure front and back should be related to the actual weight distribution.
#11
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I disagree with the Schwalbe advice, in that, on poor surfaces maximum inflation can actually be counterproductive to lessened rolling resistance and speed.
Don in Austin
Don in Austin
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OK, as a dedicated "KISSer" (Keep It Simple, Stupid), I have to ask: did you look at the sidewall of the tire first, or did you just default to the website?
Tire inflation is a simple science; inflate within limits embossed on the sidewall, adjusting for personal comfort. Once you find that "sweet spot", then you CHECK psi and remember it. It may take a few test rides, but it's worth it, as every rider is different.
On my MTB, I run different tires during different times of year; right now, I'm running some real aggressive treads to handle winter conditions. These work best for me at about 44 psi (I'm 230+ lb). My other, 3-season tires roll best at 55-60 psi. Both are rated at 65 psi max.
Tire inflation is a simple science; inflate within limits embossed on the sidewall, adjusting for personal comfort. Once you find that "sweet spot", then you CHECK psi and remember it. It may take a few test rides, but it's worth it, as every rider is different.
On my MTB, I run different tires during different times of year; right now, I'm running some real aggressive treads to handle winter conditions. These work best for me at about 44 psi (I'm 230+ lb). My other, 3-season tires roll best at 55-60 psi. Both are rated at 65 psi max.
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Yes I did read the sidewall and I do inflate to personal preference, however I was reading schwalbe's site and decided to do the math.
Thanks for all the input.
Thanks for all the input.
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