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school me on finding correct pressures with tubeless
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Not looking for a debate on whether or not tubeless is a good idea. Anyone with experience, please chime in with your thoughts on finding the proper tire pressures.

I'm riding with 28 Pirelli P zeros. Wheels are Bontrager Aeolus RSL 37 (21mm internal width, hooked rims) on a 2022 Emonda. Using Stan's sealant.

The chart that came with the Pirelli's said for my weight (~178lb) they recommended 90 psi. That seems high to me.

One of the benefits of tubeless is enjoying a more plush ride at lower pressures. 90psi isn't what I'd call low pressure.

I've also heard anecdotally that if you ride with high tire pressure, if the tire gets a hole, the high pressure will result in the sealant squirting out too fast to create a seal. Not sure if that's true or not.

I've found a few websites that seem to all use the same basic calculator for tubeless tire, such as on SRAM's site for Zipp:

https://axs.sram.com/guides/tire/pressure

That calculator recommends pressures for me in the mid to upper 60's.


What's the best way to find proper pressures? Concerned about safety and having the sealant do its job if tires get punctured. Not so obsessed with getting the absolute lowest rolling resistance.

Thanks in advance.
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Re: school me on finding correct pressures with tubeless [Vapor Trail] [ In reply to ]
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Re: school me on finding correct pressures with tubeless [jimatbeyond] [ In reply to ]
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ditto!
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Re: school me on finding correct pressures with tubeless [jimatbeyond] [ In reply to ]
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Thanks for the quick class. I've seen this calculator as well.

I guess my point of confusion is the documentation on the box of Pirelli's where the pressure table was much more traditional in the numbers it listed (again, recommended 90 psi for my instance). The values obtained from these online calculators are much more appealing.

Anyone able dispel or confirm the higher pressure = sealant failure point?
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Re: school me on finding correct pressures with tubeless [Vapor Trail] [ In reply to ]
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"Anyone able dispel or confirm the higher pressure = sealant failure point?"


Confirmed, higher pressure just blows the sealant out.
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Re: school me on finding correct pressures with tubeless [jimatbeyond] [ In reply to ]
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Thanks Jim.

Going to try some lower pressures!
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Re: school me on finding correct pressures with tubeless [jimatbeyond] [ In reply to ]
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jimatbeyond wrote:
"Anyone able dispel or confirm the higher pressure = sealant failure point?"


Confirmed, higher pressure just blows the sealant out.

Agreed. On my mountain bike I run about 20psi. Sealant works just fine.
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Re: school me on finding correct pressures with tubeless [Vapor Trail] [ In reply to ]
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Vapor Trail wrote:
Thanks for the quick class. I've seen this calculator as well.

I guess my point of confusion is the documentation on the box of Pirelli's where the pressure table was much more traditional in the numbers it listed (again, recommended 90 psi for my instance). The values obtained from these online calculators are much more appealing.

Anyone able dispel or confirm the higher pressure = sealant failure point?

i can't imagine riding a 28mm tire at 90psi, at least on the wheels i'm riding. there's a ton of volume in these newer wheels, and 60ish psi is pretty typical for 28mm tires on these wheels. or even 50ish. if you snap the tire with your finger, or press down on the tire, you'll see it's pretty hard at 60psi.

Dan Empfield
aka Slowman
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Re: school me on finding correct pressures with tubeless [Vapor Trail] [ In reply to ]
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Vapor Trail wrote:
Not looking for a debate on whether or not tubeless is a good idea. Anyone with experience, please chime in with your thoughts on finding the proper tire pressures.

I'm riding with 28 Pirelli P zeros. Wheels are Bontrager Aeolus RSL 37 (21mm internal width, hooked rims) on a 2022 Emonda. Using Stan's sealant.

The chart that came with the Pirelli's said for my weight (~178lb) they recommended 90 psi. That seems high to me.

One of the benefits of tubeless is enjoying a more plush ride at lower pressures. 90psi isn't what I'd call low pressure.


.

Are you sure that's their recommended pressure for a tubeless setup and not tubed? Sometimes tubeless ready tires have recommendations for both (since the tires can be set up either way), and companies aren't always great at being clear at what's what. Because I agree with everyone here, 90 psi seems too high for a tubeless setup on those tires (as you've seen when looking at the other calculators, they are all recommending well below 90).
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Re: school me on finding correct pressures with tubeless [ntl_tri] [ In reply to ]
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ntl_tri wrote:
Vapor Trail wrote:
Not looking for a debate on whether or not tubeless is a good idea. Anyone with experience, please chime in with your thoughts on finding the proper tire pressures.

I'm riding with 28 Pirelli P zeros. Wheels are Bontrager Aeolus RSL 37 (21mm internal width, hooked rims) on a 2022 Emonda. Using Stan's sealant.

The chart that came with the Pirelli's said for my weight (~178lb) they recommended 90 psi. That seems high to me.

One of the benefits of tubeless is enjoying a more plush ride at lower pressures. 90psi isn't what I'd call low pressure.


.


Are you sure that's their recommended pressure for a tubeless setup and not tubed? Sometimes tubeless ready tires have recommendations for both (since the tires can be set up either way), and companies aren't always great at being clear at what's what. Because I agree with everyone here, 90 psi seems too high for a tubeless setup on those tires (as you've seen when looking at the other calculators, they are all recommending well below 90).

Even for tubes that seems high to me. I've been running 25mm tires with tubes that measure out to 28mm on my rims, and as a Clydesdale I've found my ideal pressure to be between 75-80psi (depending on road surface)...

"I'm thinking of a number between 1 and 10, and I don't know why!"
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Re: school me on finding correct pressures with tubeless [Warbird] [ In reply to ]
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I think I've seen 90 psi as the MAX for a tubeless tire, but I don't know why anyone would try to go that high with it.
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Re: school me on finding correct pressures with tubeless [Vapor Trail] [ In reply to ]
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I'm running P-Zero 28's on Roval C38 wheels (also 21mm internal) around 70 psi. I'm around 172lbs and haven't had any issues. FWIW the Roval specs say 73psi for my weight.
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Re: school me on finding correct pressures with tubeless [Slowman] [ In reply to ]
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Thanks for all the comments. Really relieved! Now can't wait to get out there and enjoy some cushy rides.
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Re: school me on finding correct pressures with tubeless [Slowman] [ In reply to ]
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Slowman wrote:
Vapor Trail wrote:
Thanks for the quick class. I've seen this calculator as well.

I guess my point of confusion is the documentation on the box of Pirelli's where the pressure table was much more traditional in the numbers it listed (again, recommended 90 psi for my instance). The values obtained from these online calculators are much more appealing.

Anyone able dispel or confirm the higher pressure = sealant failure point?


i can't imagine riding a 28mm tire at 90psi, at least on the wheels i'm riding. there's a ton of volume in these newer wheels, and 60ish psi is pretty typical for 28mm tires on these wheels. or even 50ish. if you snap the tire with your finger, or press down on the tire, you'll see it's pretty hard at 60psi.

I wonder if Josh will join in this discussion. It seems the pressures on the calculator are about 10-20 psi higher than you would expect. I am on 25mm at 200lbs (rider and bike) and 90 psi is the recommendation.
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Re: school me on finding correct pressures with tubeless [Greatzaa] [ In reply to ]
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Greatzaa wrote:
Slowman wrote:
Vapor Trail wrote:
Thanks for the quick class. I've seen this calculator as well.

I guess my point of confusion is the documentation on the box of Pirelli's where the pressure table was much more traditional in the numbers it listed (again, recommended 90 psi for my instance). The values obtained from these online calculators are much more appealing.

Anyone able dispel or confirm the higher pressure = sealant failure point?


i can't imagine riding a 28mm tire at 90psi, at least on the wheels i'm riding. there's a ton of volume in these newer wheels, and 60ish psi is pretty typical for 28mm tires on these wheels. or even 50ish. if you snap the tire with your finger, or press down on the tire, you'll see it's pretty hard at 60psi.


I wonder if Josh will join in this discussion. It seems the pressures on the calculator are about 10-20 psi higher than you would expect. I am on 25mm at 200lbs (rider and bike) and 90 psi is the recommendation.

that's because you're on 25mm and you're 180+ lb of pure cornfed beef. if you move to 28mm tires the pressure goes down quite a bit. if you move to wider inside bead widths on your wheels i think there's a legitimate case for the pressure going down further. if you look at the article on the front page on the new zipp wheels, and the charts therein - there's a very animated thread on this forum about this - you'll see ideal pressures are quite low.

but on those charts the 25mm tire is pumped up higher. there's between 15lb and 20lb of difference between the assumed pressure on a 25mm versus a 28mm tire.

Dan Empfield
aka Slowman
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Re: school me on finding correct pressures with tubeless [Slowman] [ In reply to ]
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Slowman wrote:
Greatzaa wrote:
Slowman wrote:
Vapor Trail wrote:
Thanks for the quick class. I've seen this calculator as well.

I guess my point of confusion is the documentation on the box of Pirelli's where the pressure table was much more traditional in the numbers it listed (again, recommended 90 psi for my instance). The values obtained from these online calculators are much more appealing.

Anyone able dispel or confirm the higher pressure = sealant failure point?


i can't imagine riding a 28mm tire at 90psi, at least on the wheels i'm riding. there's a ton of volume in these newer wheels, and 60ish psi is pretty typical for 28mm tires on these wheels. or even 50ish. if you snap the tire with your finger, or press down on the tire, you'll see it's pretty hard at 60psi.


I wonder if Josh will join in this discussion. It seems the pressures on the calculator are about 10-20 psi higher than you would expect. I am on 25mm at 200lbs (rider and bike) and 90 psi is the recommendation.


that's because you're on 25mm and you're 180+ lb of pure cornfed beef. if you move to 28mm tires the pressure goes down quite a bit. if you move to wider inside bead widths on your wheels i think there's a legitimate case for the pressure going down further. if you look at the article on the front page on the new zipp wheels, and the charts therein - there's a very animated thread on this forum about this - you'll see ideal pressures are quite low.

but on those charts the 25mm tire is pumped up higher. there's between 15lb and 20lb of difference between the assumed pressure on a 25mm versus a 28mm tire.


My road bikes can't handle anything wider than 25mm....My TT bike is a Cervelo PX with the DT Swiss 1100 dicut wheels, 20mm inner rim width. Can I run 28mm tire on a wheel with internal width of 20mm?
Last edited by: Greatzaa: Aug 22, 22 14:28
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Re: school me on finding correct pressures with tubeless [Greatzaa] [ In reply to ]
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Greatzaa wrote:
Slowman wrote:
Greatzaa wrote:
Slowman wrote:
Vapor Trail wrote:
Thanks for the quick class. I've seen this calculator as well.

I guess my point of confusion is the documentation on the box of Pirelli's where the pressure table was much more traditional in the numbers it listed (again, recommended 90 psi for my instance). The values obtained from these online calculators are much more appealing.

Anyone able dispel or confirm the higher pressure = sealant failure point?


i can't imagine riding a 28mm tire at 90psi, at least on the wheels i'm riding. there's a ton of volume in these newer wheels, and 60ish psi is pretty typical for 28mm tires on these wheels. or even 50ish. if you snap the tire with your finger, or press down on the tire, you'll see it's pretty hard at 60psi.


I wonder if Josh will join in this discussion. It seems the pressures on the calculator are about 10-20 psi higher than you would expect. I am on 25mm at 200lbs (rider and bike) and 90 psi is the recommendation.


that's because you're on 25mm and you're 180+ lb of pure cornfed beef. if you move to 28mm tires the pressure goes down quite a bit. if you move to wider inside bead widths on your wheels i think there's a legitimate case for the pressure going down further. if you look at the article on the front page on the new zipp wheels, and the charts therein - there's a very animated thread on this forum about this - you'll see ideal pressures are quite low.

but on those charts the 25mm tire is pumped up higher. there's between 15lb and 20lb of difference between the assumed pressure on a 25mm versus a 28mm tire.


My road bikes can't handle anything wider than 25mm....My TT bike is a Cervelo PX with the DT Swiss 1100 dicut wheels, 20mm inner rim width. Can I run 28mm on a wheel with internal width of 20mm?

i sold my prior edition Cannondale supersix EVO because of that. (the more recent model has a lot more clearance.) my imperative became tire size. i made a tire size decision and that informed my wheel and bike purchases. over the past few years i've revamped my fleet accordingly. i don't know if the 28mm tire will work on the skinner rim - if that will skinny the tire up enough.

Dan Empfield
aka Slowman
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Re: school me on finding correct pressures with tubeless [Vapor Trail] [ In reply to ]
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Whatever pressure you settle on, you can probably go another 5 psi lower.
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