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Cyclocross and Gravelbiking (Recreational) This has to be the most physically intense sport ever invented. It's high speed bicycle racing on a short off road course or riding the off pavement rides on gravel like : "Unbound Gravel". We also have a dedicated Racing forum for the Cyclocross Hard Core Racers.

How low is too low?

Old 03-26-23, 10:40 PM
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Symox
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How low is too low?

I have a gravel bike with 30mm external/26mm internal tubeless ready 650B rims. With 2.6 tires Im finding with my weight (160lbs) and bike weight (about 30 fully loaded) that 18psi rear and 12psi front gives the most comfort without bottoming out, no burping on turns or getting squirmy on my rides. This is while running the tires tubeless.


I think I have to get to 9 ish psi before handling gets impaired with this setup.

with that in mind and 47psi max for these Panaracer tubeless ready tires, what are your thoughts on 18/12 R/F psi? Is it likely Im in the sweet spot or too far from it?


Im new to tubeless and just want to double check with more experienced riders

thanks
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Old 03-27-23, 04:31 AM
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That seems fine. I run 13 rear and 9 front on my MTB with 27.5 x 2.8 tires. As long as you're not getting rim strikes and the tires don't roll over in turns, its all good.
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Old 03-27-23, 07:42 AM
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I'm so confused (okay, sorta)... 2.5" gravel tires? 13psi? That seems like a (soft, slow) mtn bike setup. I run my 40mm gravel tires at 40psi (I'm 178 lbs) and still have have (occasional) issues with rim strikes and pressure burps on fast rocky downhills.

Am I that behind the times/tech (it's a distinct possibility)?
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Old 03-27-23, 08:06 AM
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Originally Posted by Zaskar View Post
I'm so confused (okay, sorta)... 2.5" gravel tires? 13psi? That seems like a (soft, slow) mtn bike setup. I run my 40mm gravel tires at 40psi (I'm 178 lbs) and still have have (occasional) issues with rim strikes and pressure burps on fast rocky downhills.

Am I that behind the times/tech (it's a distinct possibility)?
it is a Poseidon Redwood which can handle really wide tires. They call it a gravel bike.

it is similar to the Surly Grappler so possibly it is a trend of gravel bikes taking wider tires but I dont know. What I do know is it is a lot of fun to ride
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Old 03-27-23, 08:07 AM
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Originally Posted by dsaul View Post
That seems fine. I run 13 rear and 9 front on my MTB with 27.5 x 2.8 tires. As long as you're not getting rim strikes and the tires don't roll over in turns, its all good.
Thanks for the feedback and info, that helps put it in context for me.
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Old 03-27-23, 08:26 AM
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Originally Posted by Zaskar View Post
I'm so confused (okay, sorta)... 2.5" gravel tires? 13psi? That seems like a (soft, slow) mtn bike setup. I run my 40mm gravel tires at 40psi (I'm 178 lbs) and still have have (occasional) issues with rim strikes and pressure burps on fast rocky downhills.

Am I that behind the times/tech (it's a distinct possibility)?
Yeah, it raised my eyebrows too. Doesn't sound like my idea of gravel, but I am not that tuned in. I need to run 30 front 36 rear on my mountain bike with 2.2" tires even without and fast downhills here in Tallahassee or I get rim strikes (lots of tree roots where I ride).
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Old 03-27-23, 11:33 AM
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2.6 tires on a gravel bike ... hmmm ... really ?

18 and 12 psi sounds too low for even a very wide tire like a 2.6
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Old 03-27-23, 12:25 PM
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My (rather old fashioned) take and advice - put a good frame pump on your bike. Now you can alter pressure at will while on the roads you ride. Each time, pinch the tire to get a feel for it. Develop that pinch sense in correlation to the ride feel and strike likelihood. (I've never run tires so soft. A pinch might not be the best approach. Perhaps a full squeeze with you hand? Push the tire down into the rim? Whatever.

With your "pinch" well educated, you will no longer need a gauge or pump/cannister with gauge and with just that one pump will be able to ride anywhere with confidence. (My garage pumps have gauges. I squeeze after pumping to keep my hand's education current. Yes, road pressures, 85 to 110 psi; my hand would flunk your test like a doctor would the LSAT exam for lawyers.)

I do not know what the best frame pump is for big tires, low pressure. I use the excellent (for road bikes) Zephal HPX pumps. I'd research to find a large diameter pump with the same high regard as the HPX.

My gravel experience is limited and I have stopped doing it as it is clear that often rough gravel is harder on my NFL-syndrome brain (bike crash TBI) than I have any business subjecting it to. But while I dallied in it I rode about 35 miles of Oregon coast range logging roads on 1-1/2" gravel and several thousand feet of up and down plus another 60 miles of pavement on a crazy 90 mile day.. 38c front and 35c rear. The HPX. I had the proper pressure all day, adjusting several times on the gravel and riding the pavement at close to 70 psi. No flats. But my pump got borrowed maybe a dozen times to bail out others. (A dozen of us. I think two went flat free.)
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Old 03-29-23, 08:22 PM
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The tire pressure guide in the Silca website yields excellent results for just about any road condition and equipment combination. I find I am often within a pound or so of what the guide says when I feel really dialed in. Be sure you have a good accurate pressure gauge as pump gauges (even Silca's) are often very inacurate.

SILCA Professional Tire Pressure Calculator
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Old 04-01-23, 07:53 AM
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Originally Posted by dwmckee View Post
The tire pressure guide in the Silca website yields excellent results for just about any road condition and equipment combination. I find I am often within a pound or so of what the guide says when I feel really dialed in. Be sure you have a good accurate pressure gauge as pump gauges (even Silca's) are often very inacurate.

SILCA Professional Tire Pressure Calculator
do you find the calculator under or over estimated the pressure when you are dialed in?
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Old 04-01-23, 02:06 PM
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Originally Posted by Symox View Post
do you find the calculator under or over estimated the pressure when you are dialed in?
Just ran the calc for both my gravel bikes (one is 650B tubeless, the other 700c tubed). Came in almost exactly where I set my PSI (at the beginning of rides. I tend to start on the higher end and then let some air out as I go - just habit).
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Old 04-06-23, 09:59 PM
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Originally Posted by pbass View Post
Just ran the calc for both my gravel bikes (one is 650B tubeless, the other 700c tubed). Came in almost exactly where I set my PSI (at the beginning of rides. I tend to start on the higher end and then let some air out as I go - just habit).
the calculator predicted 12.5/13.5 psi F//R


I settled on 12/14 and am very impressed at what it is capable of on trails. Thanks!
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Old 04-09-23, 03:58 PM
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Originally Posted by Symox View Post
the calculator predicted 12.5/13.5 psi F//R


I settled on 12/14 and am very impressed at what it is capable of on trails. Thanks!
That does sound quite low, and cushy. The lowest I tend to go is 17-19 on my 650Bx47's, tubeless. I weigh about 138lbs., bike is about 30lb I'd guess. Could get away with lower. It is very rocky here though, and I do ride my gravel bike "like a mountain bike"
Interesting how the Rene Herse calc comes in much higher than the Silca one for my spec (though there's not many variables in theirs):
https://www.renehersecycles.com/tire...re-calculator/
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Old 04-09-23, 08:41 PM
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Originally Posted by Symox View Post
do you find the calculator under or over estimated the pressure when you are dialed in?
Just about dead on, maybe a PSI either way...
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Old 04-16-23, 09:00 PM
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Tried 13/12 recommended psis

Worked fine. Rear feels a bit squishy but worked great on gravel.
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