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Tire pressure

Old 12-02-23, 04:45 PM
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Tire pressure

In tubed road tires what are the problems if the pressure is either higher or lower than what is stamped on the tire?
Wouldnt higher pressure reduce rolling resistance and lower give a more cushioned ride?
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Old 12-02-23, 05:04 PM
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You can experiment to find your ideal pressure. Too high and it will ride rough and ping off of everything. Too soft and you risk pinch flats and rim damage. Also, if it's too soft it feels squirmy to me. I prefer road bike tires around 100 psi on 25mm tires. I'm 200 pounds.

On my mountain bike I use 15 psi in the front tire and 17-20 in the rear. Those tires are 2.8 inches wide.
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Old 12-02-23, 05:05 PM
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For road and quality tires, I use an online tire pressure calculator.
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Old 12-02-23, 05:32 PM
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Originally Posted by big john
You can experiment to find your ideal pressure. Too high and it will ride rough and ping off of everything. Too soft and you risk pinch flats and rim damage. Also, if it's too soft it feels squirmy to me. I prefer road bike tires around 100 psi on 25mm tires. I'm 200 pounds.

On my mountain bike I use 15 psi in the front tire and 17-20 in the rear. Those tires are 2.8 inches wide.
Im 225#. I have been inflating my tires to 90#-95#. I was curious what a little more and a little less would do. How much makes a difference that can be felt? In my Jeep Wrangler 10psi makes a huge difference.
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Old 12-02-23, 05:43 PM
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Originally Posted by pepperbelly
Im 225#. I have been inflating my tires to 90#-95#. I was curious what a little more and a little less would do. How much makes a difference that can be felt? In my Jeep Wrangler 10psi makes a huge difference.
What size road tires are you using? I think 10 psi would make a noticeable difference either way. When I weighed 225 I was using 23s and I used 110 in the rear and 100 in front. You could try one of the on-line pressure calculator or just drop it a little and see if you like it. At that weight I would be most concerned about going too low.
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Old 12-02-23, 06:10 PM
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Originally Posted by big john
What size road tires are you using? I think 10 psi would make a noticeable difference either way. When I weighed 225 I was using 23s and I used 110 in the rear and 100 in front. You could try one of the on-line pressure calculator or just drop it a little and see if you like it. At that weight I would be most concerned about going too low.
They are 28 Vittoria Saffiros. Hooked rim. The range printed on the tires is 72-100psi.
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Old 12-02-23, 06:12 PM
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Normally the pressure on the tires is the maximum. Use an online pressure calculator to start. You can drop it some but at a point you risk pinch flats. Going up will be ok for smoother roads.

Your weight and tire width are important to start. A wider tire you can run lower pressure.
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Old 12-02-23, 06:19 PM
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Originally Posted by pepperbelly
Wouldnt higher pressure reduce rolling resistance and lower give a more cushioned ride?
Higher pressure will reduce rolling resistance on a smooth surface. On real roads, a lower pressure usually reduces rolling resistance, as it absorbs bumps (as well a giving a smoother ride).
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Old 12-02-23, 06:21 PM
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Originally Posted by pepperbelly
I’m 225#. I have been inflating my 28mm tires to 90#-95#.
The sram calculator recommends that exact pressure for 28mm tubed road tires ... if you weigh 290.
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Old 12-02-23, 07:17 PM
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Originally Posted by pepperbelly
They are 28 Vittoria Saffiros. Hooked rim. The range printed on the tires is 72-100psi.
Why don't you try lowering the pressure a bit and see if you like the ride? Probably no reason to go over the max.
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Old 12-02-23, 07:21 PM
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Originally Posted by big john
Why don't you try lowering the pressure a bit and see if you like the ride? Probably no reason to go over the max.
Im not going over 100psi. I have been inflating to 90psi.
I was curious what going to 80psi would do.
With a range like that what would the difference be between the upper and lower pressures. Are there any advantages in certain conditions?
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Old 12-02-23, 07:22 PM
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Originally Posted by SurferRosa
The sram calculator recommends that exact pressure for 28mm tubed road tires ... if you weigh 290.
What does it show for 225#?
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Old 12-02-23, 07:36 PM
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Originally Posted by pepperbelly
Im not going over 100psi. I have been inflating to 90psi.
I was curious what going to 80psi would do.
With a range like that what would the difference be between the upper and lower pressures. Are there any advantages in certain conditions?
I would stay on the high side at your weight. Like I said, I don't like a squishy or vague feeling. You could lower pressure for wet roads or to increase comfort on the bumpy stuff.
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Old 12-02-23, 07:40 PM
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Originally Posted by big john
I would stay on the high side at your weight. Like I said, I don't like a squishy or vague feeling. You could lower pressure for wet roads or to increase comfort on the bumpy stuff.
I think I used the calculator correctly. It shows 85psi front and 90psi rear. I will use that tomorrow.
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Old 12-02-23, 07:50 PM
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Originally Posted by pepperbelly
What does it show for 225#?
Guessed a rim width if 18mm. 80 front and 85 rear. Id drop 5 psi unless you ride through pot holes.

Edit: start with what you list above. The go down.
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Old 12-02-23, 08:05 PM
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Tire pressure is all about trial and error. Different tires and tires sizes react differently at different pressures. This is very easy to experiment with, as your tires will gradually deflate after you fill them up to the labeled pressure. In time you can find that sweet spot where you get a good combination of comfort and rolling resistance. When it feels right, check the tire pressure, and stick with that pressure.
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Old 12-02-23, 08:59 PM
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Originally Posted by biker128pedal
Guessed a rim width if 18mm. 80 front and 85 rear. Id drop 5 psi unless you ride through pot holes.

Edit: start with what you list above. The go down.
I had to go look at my rims. They are DT Swiss 622x14.
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Old 12-02-23, 10:47 PM
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Originally Posted by 50PlusCycling
In time you can find that sweet spot where you get a good combination of comfort and rolling resistance. When it feels right, check the tire pressure, and stick with that pressure.
This user hit it right on the nose.

When newbies ask about wanting the bestest psi for them to cycle better, it simply means they haven't cycled enough.

They need to put on more miles, and then they will figure it out.

(Bro tip: optimizing the human body is much better than optimizing anything on a cycle.)
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Old 12-02-23, 11:13 PM
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Originally Posted by soyabean
This user hit it right on the nose.

When newbies ask about wanting the bestest psi for them to cycle better, it simply means they haven't cycled enough.

They need to put on more miles, and then they will figure it out.

(Bro tip: optimizing the human body is much better than optimizing anything on a cycle.)
I am just curious about the real differences. Is lower pressure more comfortable but slower due to more rolling resistance. About what is the sweet spot- generally closer to max or min pressure? Is it different for everyone and every bike and every tire?
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Old 12-02-23, 11:36 PM
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Originally Posted by pepperbelly
Is it different for everyone and every bike and every tire?
Doesn't the existence of the online calculator tell you that?
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Old 12-02-23, 11:59 PM
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Originally Posted by SurferRosa
Doesn't the existence of the online calculator tell you that?
I dontcwant to think. I just want easy answers. 😎

That is exactly what that it means isnt it?
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Old 12-03-23, 12:19 AM
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Originally Posted by pepperbelly
I dontcwant to think. I just want easy answers. 😎

That is exactly what that it means isnt it?
A trivial answer doesn't exist.

Increasing pressure tends to reduce rolling resistance because it causes you to lose less energy to deformation off the tire.
But.
Increasing pressure can increase rolling resistance if the tire becomes too stiff to serve as suspension for small surface irregularities.
Or, put another way: if increasing pressure causes the bicycle to become less comfortable, it's probably also making you slower. The energy that's being used to vibrate your hands and feet and butt is being stolen your forward motion.

For a given rider on a given surface, there tends to be an "optimal" pressure, where the tire is functioning as suspension and isn't overly squishy. Going above this pressure tends to produce larger performance penalties than going too low, so it's usually good to err on the low side.

It's possible to measure performance by using a power meter (and using methods like RChung's Virtual Elevation technique to characterize rolling resistance). But if you're not going to bother with that, a good starting place might be an online tire pressure calculator.
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Old 12-03-23, 01:01 AM
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Increasing tire pressure never decreases rolling resistance, ever. But higher pressures, besides making for a harsh ride, shrink the contact patch, decreasing traction, and increasing the chances of skidding or losing control. FWIW, I worked for some time the motorcycle division of the Pirelli tire company, and understand a little bit about the subject.

Tire pressure influences shock absorption and the size of the contact patch. Lower pressures increase yield and the size of the contact patch. A larger parch gives more traction, to a point, but also has the effect of decreasing tire circumference and deflection angle. The compression and decompression of rubber absorb energy, some of which is converted to heat, too-low pressures increase energy absorption and heat generation.

What you need to do is simply fill the tire to the sidewall pressure and ride the bike.
Over the course of a week ot two, the pressure will decrease, you will, or you should be able to feel the difference. Fill the tires again to the sidewall pressure, and ride another week or two. You’ll eventually find the particular pressure which suits you.

if you are a heavier rider, you may want to go a few psi above the sidewall pressure, but the overall process is the same. On my conventional bikes I run a little south of the sidewall pressure, on my suspension bikes, like my Moulton or Birdy, I higher than the sidewall pressure.
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Old 12-03-23, 02:16 AM
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I ride on 25mm tires with a psi max of 120. I generally ride between 105 and 110. I weigh around 190lbs which is down from a year ago at 205.
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Old 12-03-23, 05:17 AM
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Originally Posted by 50PlusCycling

What you need to do is simply fill the tire to the sidewall pressure and ride the bike.
A great way to guarantee a harsh, slow ride on anything other than perfectly smooth tarmac.
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