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PSI question on TPU Tubes

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3.3K views 59 replies 13 participants last post by  Lombard  
J
#1 ·
I recently bought TPU tubes, but I am having a hard time understanding what PSI I should get it up to. I have tried several different Bike Tire Calculators none of them have options for "TPU" tubes, and all give different answers. Please help me.

My Info:
Bike: 20lbs
Rider: 183lbs
Gear: anywhere from 2-5 lbs based on if I am decked out in winter gear or not
Tires: 28mm (700x28mm) Road tires
Rims: I'm not sure of the Rim width, but the only measurement I found on the rim is says 622x15c. The rims are 18 years old. It had 23mm tires on, but I upgraded to 28mm a few months back.
Tubes: Thinvik TPU 700ccx18-32c with 65mm presta valve

When I was using my Butyl Tubes I was running them about 74lbs int he front and 77lbs in the rear.

If you could tell me how you figured out what the PSI should be, (like the bike calculator equation or website) would be helpful moving forward.

Thanks in advance!
 
#2 ·
Being TPU or Butyl shouldn't make a difference. The tire casing is where all the rolling resistance comes from.
I'd use whatever you used for Butyl.

As far as calculators, take them with a grain of salt. Everyone has their 'theories' of the unicorn perfect tire pressure.
In reality, it's only a starting point. You have to adjust to your riding style, road conditions, and tire choice.

The whole lower pressure tire optimization was kicked off years ago by Jan Heine. For years he was a heretic among roadies who insisted 19mm tires at 150psi were lightning fast. Now we know better.

If you're interested in the backstory:


There use to be this website called dorkypantsr bike tire pressure calculator. He took Jan Heine's findings and made a calculator. The website doesn't exist anymore but it's available in the Internet Archive. It's what I've always used and find it the easiest and puts you at a good starting point.

Bicycle tire pressure calculator

road bicycle tire pressure calculators using Jan Heine 15% drop and Michelin chart methods
web.archive.org

If I put in your info, it comes up with 71 front and 88 rear. So you're in the ballpark. Your 77psi rear pressure may be a little low. You may be susceptible to pinch flats.

Image
 
R
#32 ·
tlg said:
Being TPU or Butyl shouldn't make a difference. The tire casing is where all the rolling resistance comes from.
I'd use whatever you used for Butyl.

As far as calculators, take them with a grain of salt. Everyone has their 'theories' of the unicorn perfect tire pressure.
In reality, it's only a starting point. You have to adjust to your riding style, road conditions, and tire choice.

The whole lower pressure tire optimization was kicked off years ago by Jan Heine. For years he was a heretic among roadies who insisted 19mm tires at 150psi were lightning fast. Now we know better.

If you're interested in the backstory:


There use to be this website called dorkypantsr bike tire pressure calculator. He took Jan Heine's findings and made a calculator. The website doesn't exist anymore but it's available in the Internet Archive. It's what I've always used and find it the easiest and puts you at a good starting point.

Bicycle tire pressure calculator

road bicycle tire pressure calculators using Jan Heine 15% drop and Michelin chart methods
web.archive.org

If I put in your info, it comes up with 71 front and 88 rear. So you're in the ballpark. Your 77psi rear pressure may be a little low. You may be susceptible to pinch flats.

View attachment 500013
Click to expand...
I've seen pressure spec's on the instructions for TPU tubes. They are at greater risk to overinflate and blow in my experience.
 
R
#3 ·
As said, the type or tube, or lack thereof has no bearing on inflation pressure. Tires typically state a mx pressure. Min pressure or ideal pressure is about as "interesting" or debatable a topic as chain lube or engine oil threads and can vary greatly on what you are doing, road conditions, loaded weit, etc.
 
#4 ·
Why are U so worried about tire PSI?
What is important to U? Speed? Handling? Cush?
What type of roads do you ride? Tar strips? Pavement gaps? Pavement joint disleveled?
Do you pack ride or solo? Do you ride at night or in rain?
This has more of an impact on what PSI you want to run than your tubes.
 
#5 ·
I agree with others here that tube type does not change what your ideal pressure will be. This is the pressure calculator I use:

silca.cc

SILCA Professional Tire Pressure Calculator

Dial in your bikes' tire pressure to get the most comfort, speed, and efficiency on your ride. If you are looking for the best free marginal gain, click here
silca.cc

They do have a choice as to whether you're running butyl or latex but that doesn't change the recommendations much.
 
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K
#6 ·
In addition to everyone else pointing out that tube type has zero influence on pressure, you have also implied in your post that tire pressure can be precisely calculated. It cannot. Tire pressure calculators give you a starting point from which you can drop pressure (for more traction, comfort, and better tire wear) or raise pressure (to prevent pinch flats or for firmer feel). Neither direction is "correct" but rather is determined by YOUR preferences.
 
#31 ·
The pressure should be the same but one site said it should be the same or a little lower. I could find only one site that said that, no other sites were even responding to the question, which tells me it's not a big deal, just use whatever that psi calculator that was posted earlier said to use. There's also others of those type of calculators on the SRAM and Silca webpages.

SRAM | AXS

SILCA Professional Tire Pressure Calculator
 
R
#37 ·
froze said:
The pressure should be the same but one site said it should be the same or a little lower. I could find only one site that said that, no other sites were even responding to the question, which tells me it's not a big deal, just use whatever that psi calculator that was posted earlier said to use. There's also others of those type of calculators on the SRAM and Silca webpages.

SRAM | AXS

SILCA Professional Tire Pressure Calculator
Click to expand...
I guess I've been riding with higher than optimum pressure on my 700 x 25C, according to the calculator.

I'm used to inflating 700 x 20c. They are dinosaurs I guess. I still have them on my Steel frame bike, which is now devoted to my trainer.
 
R
#36 ·
RHankey said:
I assume you meant to say they are at greater risk to blow if over inflated. Otherwise, perhaps you can explain how a TPU tube can overinflate itself.
Click to expand...
One way would be to bring the tire to maximum pressure in a cold tire. When temp's rise the tube pressure will increase past the spec. Otherwise it's a matter of overinflating the tire
tlg said:
Really? You've seen it? In the instructions.
Please... do share. What is the max psi of TPU tubes you've seen.
Click to expand...
One way to overinflate a tire is to bring it to maximum pressure in the cold and riding in warmer conditions.

I have blown TPU tubes inflating to a pressure greater than 110psi. I no longer inflate over 100.

yes...I,ve seen a spec somewhere on the Ridenow brand instructions. I recall the 24g tubes (orange) stating a maximum temp of 70psi.
 
#38 ·
riding space-time said:
I have blown TPU tubes inflating to a pressure greater than 110psi. I no longer inflate over 100.

yes...I,ve seen a spec somewhere on the Ridenow brand instructions. I recall the 24g tubes (orange) stating a maximum temp of 70psi.
Click to expand...
Maximum of 70psi 🤣

So you really don't know what you've seen. You're just recalling what you (incorrectly) think you've seen and claiming TPU tubes have instructions to prevent them from exploding. :rolleyes:

What you read was instructions to prevent HOOKLESS tires from blowing off the rim. This has nothing to do with the maximum pressure of TPU tubes.

www.elite-wheels.com

RideNow Inner Tube

For a long time, the only inner tubes available were made from butyl and latex. Now there is a new kid on the block, TPU. There are several distinct advantages to TPU inner tubes, specifically regarding their weight(or rather lack thereof), air retention, puncture protection, rolling resistance...
www.elite-wheels.com www.elite-wheels.com
Tire inflation pressure must not exceed 5 bar/72PSI When using rims with a no-ring-lip system according to ISO/TC 31.

Especially when riding on high temperature black asphalt pavement with temperature exceeding 65°C (150°F), the tire pressure may easily exceed the allowable maximum value. In addition, too high tire pressure can cause the tire to break away from the rim during cycling, which can result in the risk of injury.
 
R
#39 · (Edited)
riding space-time said:
One way would be to bring the tire to maximum pressure in a cold tire. When temp's rise the tube pressure will increase past the spec. Otherwise it's a matter of overinflating the tire

One way to overinflate a tire is to bring it to maximum pressure in the cold and riding in warmer conditions.
Click to expand...
What you describe is not unique to TPU tubes. Pressure increases roughly 1psi/10F temp increase - or that has been the rule of thumb I've personally used for decades. So, even if pumping up/checking pressure at freezing, and then going out for a ride at 100F, you're talking of a roughly 7psi increase. You might be at risk of blowing a tire if you did that after inflating to the max rating of the tire/rim type. That risk doesn't change because of the type of tube.

riding space-time said:
I have blown TPU tubes inflating to a pressure greater than 110psi. I no longer inflate over 100.

yes...I,ve seen a spec somewhere on the Ridenow brand instructions. I recall the 24g tubes (orange) stating a maximum temp of 70psi.
Click to expand...
I believe Ride Now says not to exceed 5bar/72psi if used in a hookless rim. That is a rim limitation.

Tubes can't spontaneously rupture, unless the tire, rim, rim tape, or valve stem hole give way (or become compromised). Tire/rim type determine max inflation, not the tube.
 
R
#40 ·
RHankey said:
What you describe is not unique to TPU tubes. Pressure increases roughly 1psi/10F temp increase - or that has been the rule of thumb I've personally used for decades. So, even if pumping up/checking pressure at freezing, and then going out for a ride at 100F, you're talking of a roughly 7psi increase. You might be at risk of blowing a tire if you did that after inflating to the max rating of the tire/rim type. That risk doesn't change because of the type of tube.


I believe Ride Now says not to exceed 5bar/72psi if used in a hookless rim. That is a rim limitation.

Tubes can't spontaneously rupture, unless the tire, rim, rim tape, or valve stem hole give way (or become compromised). Tire/rim type determine max inflation, not the tube.
Click to expand...
Perhaps. I do know that I blew a TPU tube at an inflation pressure of greater than 110psi. It's moot now since wider tires take less pressure. I've been inflating my 700x25c too high. I tried the nifty app that was shared on this page and it recommends less than 90.
 
#47 ·
duriel said:
Are U shure it's a fact? Do U have any documentation? Did you take it to Big O?
Hard to believe, doesn't the valve stem area have 2 layers of material? ... very strange.
Click to expand...
What's a shure?
 
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