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Tire Pressure

Old 11-28-23, 11:12 AM
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Originally Posted by bblair
Exactly my thoughts. How do I know how accurate my gauge is? Probably close enough.

If I were going for the world hour record on a track I would worry. Riding to the next town with a bunch of 70-year-old for cake and coffee, not so much. As long as I don't get a flat.

That said, I run Conti 5000 tires at about 90psi. Or so my pump says.
What if that first 70-year-old takes the cake & leaves you with burn coffee?
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Old 11-28-23, 04:05 PM
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Originally Posted by Troul
digital Air Pressure Regulators with a zero-out feature tends to be a less expensive route to test tire inflation tools for accuracy.
Starting at zero, like analog gauges also do, is no guarantee of accuracy. A digital gauge can be just as inaccurate as an analog gauge. I use these for calibration and various irrigation system monitoring. They are accurate enough for me. I have some 160 and some 100 psi models.

https://www.amazon.com/Winters-Stain...69&sr=8-6&th=1

Last edited by DaveSSS; 11-30-23 at 01:11 PM.
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Old 11-28-23, 08:07 PM
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I’ve got a cheap Topeak digital gauge that I’ve had for years. I use it to set my car tyre pressures and it always gives the same reading as the TPMS sensors on the wheels. The analogue gauges on my two track pumps also read the same within the 1-2 psi I can read off them. So I don’t worry about it. But I would always check a new gauge against a proven one.
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Old 11-28-23, 08:58 PM
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Originally Posted by DaveSSS
Starting at zero, like analog gauges also do, is no guarantee of accuracy. A digital gauge can be just at inaccurate as an analog gauge. I use these for calibration and various irrigation system monitoring. They are accurate enough for me. I have some 160 and some 100 psi models.

https://www.amazon.com/Winters-Stain...69&sr=8-6&th=1
bar/atmospheric reset has worked for my use. ymmv.
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Old 11-28-23, 09:42 PM
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Not to interrupt the great gauge accuracy debate, I run my tubeless Conti GP5ks at 70 front 72 rear, and I weight 165. That pressure helps absorb irregularities and provides me with a quick tire. If I am going out for a relaxed Zone1-2, then I will run them 10 lbs less for the pure comfort.
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Old 11-28-23, 10:25 PM
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I just recently purchased a JACO "FlowPro™ Digital Tire Inflator" along with their presta chuck. The gauge is certified to be +- 1% with a half PSI increment on the display. The combination was around $70, and so far I am pleased with them. Since I have two different compressors with the appropriate quick coupler on them it is a great way to go.

I do have a Hirame presta chuck and I prefer the JACO chuck. Reality is that both are pretty good.

BTW, it reads a couple of PSI above the TPMS on my car, and I believe the gauge, not the TPMS. But if the TPMS is reading low by 1 PSI and the gauge is reading high by .5 PSI with the .5PSI resolution of both systems they are within a believable range.
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Old 11-28-23, 10:48 PM
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Roads here in Idaho are all chipseal. I’ve gone to 32mm tubeless tires, I run 70-72 psi rear and 64-66 front. I weigh about 206#. On my older tubed bike, I have 25mm and run about 100 rear and 90 front. But I don’t ride it as much on chipseal, prefer the smoother ride on the bigger tires. YMMV.
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Old 11-29-23, 03:14 AM
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Originally Posted by DangerousDanR
I just recently purchased a JACO "FlowPro™ Digital Tire Inflator" along with their presta chuck. The gauge is certified to be +- 1% with a half PSI increment on the display. The combination was around $70, and so far I am pleased with them. Since I have two different compressors with the appropriate quick coupler on them it is a great way to go.

I do have a Hirame presta chuck and I prefer the JACO chuck. Reality is that both are pretty good.

BTW, it reads a couple of PSI above the TPMS on my car, and I believe the gauge, not the TPMS. But if the TPMS is reading low by 1 PSI and the gauge is reading high by .5 PSI with the .5PSI resolution of both systems they are within a believable range.
So all 4 TPMS sensors read lower than your gauge?
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Old 11-29-23, 05:53 AM
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Originally Posted by rclouviere
I’m confused about what air pressure to use for the most speed on tubeless tires. I’ve read a lot of info saying you should decrease the pressure a lot. However, the Silca guide says much higher (for me on smooth roads, 96 rear and 93.5 front).

Anyone have testing results/opinions?
Seems high for a tubeless setup, unless you are a heavy rider using narrow TL tires.

At 185lbs total weight on a measured 28mm tubeless tire, I am at 78.5PSI rear and 76.5PSI front with the Silca calculator, which is a little higher than the pressure I like. I tried increasing the total weight to 270lbs and I get 85PSI rear / 83PSI front. Not that much of an increase for an extra 100lbs of mass.

FYI, these have been my preferences through my different setups:

1) Tubed 25mm tire = 100PSI rear / 95PSI front
2) Tubeless 25mm tire = 80PSI rear / 75PSI front
3) Tubeless and hookless 28mm tire = 70PSI rear / 65PSI front
4) Tubeless 28mm tire = 75PSI rear / 70PSI front

Last edited by eduskator; 11-29-23 at 06:02 AM.
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Old 11-29-23, 06:12 AM
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Originally Posted by eduskator
Seems high for a tubeless setup, unless you are a very very heavy rider.

At 185lbs total weight on a measured 28mm tubeless tire, I am at 78.5PSI rear and 76.5PSI front with the Silca calculator, which is close to the pressure I like. I tried increasing the total weight to 270lbs and I get 85PSI rear / 83PSI front. Not that much of an increase for an extra 100lbs of mass.

FYI, these have been my preferences through my different setups:

1) Tubed 25mm tire = 100PSI rear / 95PSI front
2) Tubeless 25mm tire = 80PSI rear / 75PSI front
3) Tubeless and hookless 28mm tire = 70PSI rear / 65PSI front
4) Tubeless 28mm tire = 75PSI rear / 70PSI front
Is there any physics that would support why a 25mm tire should be inflated differently based on whether or not you have a tube in it?
Isn't deflection and rolling resistance (and why Silca doesn't differentiate between rim or tire type) effectively based on inflated volume of the tire?

A 205lb system weight on 26mm tires returns 95r/92.5f, so OP could be there. For your 185lb system weight and if tires actually measure 25mm, it returns 94/92 -- which doesn't seem at all close to your #2 setup above.
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Old 11-29-23, 06:46 AM
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Originally Posted by Sy Reene
Is there any physics that would support why a 25mm tire should be inflated differently based on whether or not you have a tube in it?
Isn't deflection and rolling resistance (and why Silca doesn't differentiate between rim or tire type) effectively based on inflated volume of the tire?

A 205lb system weight on 26mm tires returns 95r/92.5f, so OP could be there. For your 185lb system weight and if tires actually measure 25mm, it returns 94/92 -- which doesn't seem at all close to your #2 setup above.
Tubeless tires can be run at lower pressures mainly because they have stiffer sidewalls. They are less likely to pinch due to this as they deform less. Not sure about the physics though, but I prefer to run my tires at the ''sweet spot'' between high comfortability and low rolling resistance.

I don't really care about what a calculator says; I rely on how I feel riding the bike at a certain pressure. It can be a good starting point though.
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Old 11-29-23, 08:18 AM
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Originally Posted by Sy Reene
Is there any physics that would support why a 25mm tire should be inflated differently based on whether or not you have a tube in it?
The SRAM pressure calculator adds around 2 psi for 25 mm tubed vs tubeless. I presume it's due to the slightly reduced air volume with a tube. For my 30 mm setup, the difference is only 1 psi for tubes v tubeless.
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Old 11-29-23, 11:06 AM
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Originally Posted by Troul
What if that first 70-year-old takes the cake & leaves you with burn coffee?
You are obviously not in our demographic.

'Cause then you'd know that the sprint is for the restroom, not the bakery counter.
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Old 11-29-23, 02:11 PM
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I ride Gatorskin 700x25 at 100 PSI. I weigh about 160 pounds.
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Old 11-29-23, 02:22 PM
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Originally Posted by PeteHski
So all 4 TPMS sensors read lower than your gauge?
Yes. But my car is British... The indicated speed is also 2 MPH slow as well.
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Old 11-29-23, 02:52 PM
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Interesting read. I've always rode close to max tire pressure, around 100 psi.
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Old 11-29-23, 03:24 PM
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Originally Posted by eduskator
Tubeless tires can be run at lower pressures mainly because they have stiffer sidewalls.


I kind of doubt that. The GP5000 TR ("tubeless ready") has 3 layers of sidewall casing at 220 threads per inch (versus 3 layers of 330 TPI for normal GP5000), but I don't think that adds much at all to the sidewall stiffness.


Originally Posted by eduskator
They are less likely to pinch due to this as they deform less.
A tubeless tire is very unlikely to pinch flat, but that's because there is no inner tube to puncture.
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Old 11-29-23, 05:05 PM
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https://www.amazon.com/JACO-Bike-Pre.../dp/B07P7ZTZNK

https://www.mcmaster.com/product/1093K4

this would let you check your pump for less than 20 bucks. A less crappy prv would be more accurate and still cheap
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Old 11-29-23, 06:58 PM
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Originally Posted by DangerousDanR
Yes. But my car is British... The indicated speed is also 2 MPH slow as well.
What has being British got to do with it?
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Old 11-29-23, 07:49 PM
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Originally Posted by PeteHski
What has being British got to do with it?
Do I really have to explain? OK. Let me try...

In the Beatles movie "Help" there is a scene where the "baddie" points a pistol at Mr. Starkey. He in turn sticks his finger in the barrel and says, "It's British you know...won't work." Like the old joke about warm beer and Lucas refrigerators.

I have owned three British motor vehicles: a Norton Commando (with a Boyer-Bransden ignition that would stop working when the temperature was above 90F), a Series II land Rover, and my current Jaguar XE. All three of them have been absolute hoots to drive in their preferred environment. Not a one of them was what you might call reliable. I have also tried to buy two Lotus automobiles, but the deals fell through.
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Old 11-30-23, 04:37 AM
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Originally Posted by DangerousDanR
Do I really have to explain? OK. Let me try...

In the Beatles movie "Help" there is a scene where the "baddie" points a pistol at Mr. Starkey. He in turn sticks his finger in the barrel and says, "It's British you know...won't work." Like the old joke about warm beer and Lucas refrigerators.

I have owned three British motor vehicles: a Norton Commando (with a Boyer-Bransden ignition that would stop working when the temperature was above 90F), a Series II land Rover, and my current Jaguar XE. All three of them have been absolute hoots to drive in their preferred environment. Not a one of them was what you might call reliable. I have also tried to buy two Lotus automobiles, but the deals fell through.
Ah I see now! JLR do have a poor reliability record, but AFAIK it doesn’t mean that all their TPMS sensors read low by exactly the same amount.

Lotus = Lots Of Trouble, Usually Serious!
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Old 11-30-23, 08:49 AM
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I believe LR is the most unreliable car brand on the planet. Great looking cars, but man, you buy new and get rid of this after 3-4 years of ownership. Resale value must be low too.
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Old 11-30-23, 09:06 AM
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Originally Posted by datlas
The Silca calcuator is a good starting point/guide, NOT gospel. Be sure you put in correct weight and actual measured tire width.

You probably can reduce the pressure by a few PSI and see how it feels.
Josh Poertner (owner of Silca) has suggested the same. He suggests that if your are going to err, better to err on the low side than the high side. Their numbers are based on real world testing, but there are still a wide range of variables (specific tire, exact road surface, rider form, etc) that could sway the numbers one way or the other.

Using the Silca number as a starting point, trial and error should help you dial in the sweet spot between hard enough to be efficient and squishy enough to be compliant.
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Old 11-30-23, 10:32 AM
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For what it’s worth. I weigh 165 pounds , riding a 2022 Scott Addict RC with Princeton Carbonworks wheels wrapped in size 28 tires..I run no more than 65 PSI front/rear. Sometimes a tad lower in the front.

I’d say the tire pressure calculators are fairly good starting points as long as you enter your info on tyre size etc correctly.
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Old 11-30-23, 10:33 AM
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Originally Posted by DangerousDanR
Do I really have to explain? OK. Let me try...

In the Beatles movie "Help" there is a scene where the "baddie" points a pistol at Mr. Starkey. He in turn sticks his finger in the barrel and says, "It's British you know...won't work." Like the old joke about warm beer and Lucas refrigerators.

.
John Lennon … probably unaware of his tire pressure … smh
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