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NoCoGreg

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Reply with quote  #1 
For anyone who might have missed Leonard Zinn's optimal gravel tire pressure:

https://www.velonews.com/2018/06/from-the-mag/optimal-tire-pressure-gravel_468329

This test is only for one tire and one size rider but I for one was very surprised by the results.
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Koyote

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Reply with quote  #2 
I'm a bit heavier than the test subjects, and I am also riding some very rough events which would cause rim strikes at 30psi...So I tend to run about 34f/40r. 

But if I were 150 lbs and riding smooth gravel exclusively, I could see running 30psi.
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bobknh

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Reply with quote  #3 
Thanks for the link. I somehow missed this. A lot of very interesting observations and conjecture- all be it with a limited sample of one make and model of tire. Jan Heine at Compass Tires/ Bicycle Quarterly must have a big "I told you so" smile on his face if he read this report. J H has been touting the benefits of wider, more supple, lower pressure tires for a long time. Heine also noted the fact that harder tires "feel" faster, even though objective tests demonstrate that they aren't. This has to do with proprioception of higher speed due to the sensation of high frequency vibrations. One other advantage of wider lower pressure for gravel - or any rougher road surface- is less muscle fatigue and greater comfort on longer rides. Although the test didn't discuss body suspension, I've been using a Kinekt Body Float suspension seat post on my gravel bike this season and have experienced a significant improvement in comfort and less pain and fatigue on longer gravel ride - especially my lower back. Of course, this is a subjective observation; but I've even noticed this improvement when riding mostly on paved roads.
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clarksonxc

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Reply with quote  #4 
Quote:
Originally Posted by Koyote
I'm a bit heavier than the test subjects, and I am also riding some very rough events which would cause rim strikes at 30psi...So I tend to run about 34f/40r. 

But if I were 150 lbs and riding smooth gravel exclusively, I could see running 30psi.


Totally agree, and this is also the reason I keep the front tire pressure much closer to the rear tire pressure on gravel as compared to the road

"Obviously, some tire setups will be vulnerable to pinch flats on square-edge impacts at 30psi"
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NoCoGreg

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Reply with quote  #5 
Quote:
Originally Posted by clarksonxc


Totally agree, and this is also the reason I keep the front tire pressure much closer to the rear tire pressure on gravel as compared to the road

"Obviously, some tire setups will be vulnerable to pinch flats on square-edge impacts at 30psi"

At 190 (ish) pounds and riding the 40 mm X'Plor at 36/40 has worked well.  I can definitely feel the additional squish but I haven't had any issues with pinch flats.  

Hopefully Leonard continues his testing with different larger and small riders, wider tires and some additional brands.  Yikes, one could make a career in testing just tires! :-) 
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Zurichman

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Reply with quote  #6 
I am @ 200

started out @ 40/35 rear/front

now riding 45/40 rear/front and like that better. I think everybody has to find their sweet spot and what works for one doesn't work for another. If I rode heavy gravel all the time I probably would go back to the 40/35.

Zman

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moe53

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Reply with quote  #7 
Mountain bikers have known about low psi for a long time, particularly those riding tubeless, rigid, or hardtail. Low psi just floats over bumps, it's what I call the sweet spot. It's in a range of about 2 psi.
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pushstart

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Reply with quote  #8 
At 175-180lbs, I run the 38mm Schwalbe G-One at around 28/32 (F/R) for a mostly-gravel course/ride.  Thinking that this might be a little slower, I started with it at a higher 32/38 psi for a recent gravel race in WV -- and while those pressures might have been a bit faster (can't really tell) on smooth or paved sections, it was beating me up a lot more and made for sketchy descents and cornering.  Halfway through the race I let out air and the difference in comfort & confidence was very noticeable and it didn't feel any slower.  So my lesson learned was just not to mess with what I know works 😉

Of course, it depends a *lot* on the tire.  On a ride that was more significantly paved, I would probably run 38mm Compass tires which I'd need to run at higher pressures (more supple sidewall) -- probably 40/45 psi -- for similar comfort & confidence (and they'd be a lot faster than the G-One tires, especially on anything smooth/hard).
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BluesDawg

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Reply with quote  #9 
Pretty close to what I've found. I'm more interested in finding what rides more comfortably than faster, but I don't want sluggish. I'm about 165 lbs and I run 42mm WTB Resolutes tubeless. I'm still refining this, but 25f/35r is what I've settled at for now. Lower in the rear was smoother in a straight line, but felt a little squirmy in turns. About 10 psi lower in front seems to work best for me on all surfaces. Running the front at the same pressure as an adequate pressure in the rear feels unnecessarily harsh.
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DrSpoke

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Reply with quote  #10 
A very nice article.  It does seem to confirm what many, especially Jan Heine, have been saying.  Another good source of information re tire width/pressure is a series of blogs by Josh Portner at Silca and formerly at Zipp:  https://silca.cc/blogs/journal/118397252-tire-size-pressure-aero-comfort-rolling-resistance-and-more-part-1-how-we-got-to-now

Personally, I use the 15% tire drop method developed by Frank Berto and publicized at Jan Heine/Compass Bicycles:  https://janheine.wordpress.com/2016/03/09/tire-pressure-take-home/  The recommended pressures are based almost exclusively on tire size and weight.  I ride a variety of bicycles including mountain, gravel & road.  Accordingly, also a range of wheel sizes, rim widths and tire sizes.  Wheels are 26, 27.5 29/700c in a variety of widths.  Tire sizes include 23, 25, 28, 30, 35, 38, 40, 2.1, 2.25, 2.35, 2.6 & 2.8.  I was able to find online a formula for the psi calculation based on the Berto method.  So I set up a spreadsheet that allows me to calculate a tire pressure for each bike/tire size combination.  I use the calculated psi as a starting point and adjust up or down depending on tubed/tubeless, rim width, road/trail conditions, personal preferences, etc.  It's also proven to be very handy as I can print it out, leave a copy in the car and don't have to memorize anything. 

When I first started using it the results were quite amazing.  I dropped the tire pressures I'd been running on my mtn bike substantially front & rear with great results.  It's also amazing the difference in psi from front to rear.  I used to run about 5 psi more in the rear.  Now it's more like 15 or 20 for my road bikes and about 10 on my mtn bikes.  It's also eye opening how much the psi changes w/just a few pounds of less or more weight or an extra mm or 2 of width.

All of this makes me laugh when I see the recommendations to the often asked question of what tire pressures should I run.  Most answers fall into two categories - go by feel or this is what I use so this is what you should use.  Both are pretty worthless, IMO - especially the 2nd as there are so many variable for correct pressures.
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TiGeo

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Reply with quote  #11 
Love the lower pressures just like on a mtb.  I run low to mid 20s tubeless on gravel/rough stuff and only hit 30+ if I am riding primarily road at 170 pounds with 40s.  I see many folks running WAY to much air for their weight b/c of the old-school super high pressure = lower rolling resistance mentality.
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NoCoGreg

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Reply with quote  #12 
Quote:
Originally Posted by DrSpoke

... I was able to find online a formula for the psi calculation based on the Berto method.  So I set up a spreadsheet that allows me to calculate a tire pressure for each bike/tire size combination.  I use the calculated psi as a starting point and adjust up or down depending on tubed/tubeless, rim width, road/trail conditions, personal preferences, etc. 

Doctor,
Thanks for sharing the other links.  Lots of good info...  And speaking of which, is there any chance you'd be willing to share the formula you use?  

Regards,
Greg



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ChillyWilly

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Reply with quote  #13 
Quote:
At 190 (ish) pounds and riding the 40 mm X'Plor at 36/40 has worked well.  I can definitely feel the additional squish but I haven't had any issues with pinch flats.


Just for reference for any truly Clyde guys out there...
I'm 270 pounds/ 122kg. 
I run the 40mm X'Plor at 55 front, 65 rear. That's probably actually too high for me, but I like it. No pinch flats, that's for sure. I could safely drop them 5 psi I think, possibly more. But I hate flats and don't feel any need to run tubeless. 


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7rider

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Reply with quote  #14 
I'm 140 pounds and I'm riding the Terrene Elwood 650x47. If I'm mostly on the road, I'll have the tire pressure at 30 psi. If there's gravel/dirt trails involved, I'll drop the pressure to 25 psi. All day comfort on this tire and pressure is very nice.
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Koyote

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Reply with quote  #15 
To support Dr. Spoke's concluding paragraph, above: If I ran the tire pressures that some of you are running, I would get rim strikes and probably occasionally wreck a rim. I'm over 170 lbs and sometimes ride (race) on some very rough, rocky descents. Hence the importance of figuring out what works for you, and not choosing a psi based on what works for someone else.
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pushstart

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Reply with quote  #16 
This is good advice. It cwetainly depends a lot on what you are riding, especially when we talk about "gravel" which can mean almost anything. I definitely found the lower limit for my front tires bottoming out in a stream crossing in a race a few years ago. That was expensive, but at least I didn't flat. -- I added a few psi and also switched to carbon rims for gravel races.

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keepamonte

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Reply with quote  #17 
Quote:
Originally Posted by TiGeo
Love the lower pressures just like on a mtb.  I run low to mid 20s tubeless on gravel/rough stuff and only hit 30+ if I am riding primarily road at 170 pounds with 40s.  I see many folks running WAY to much air for their weight b/c of the old-school super high pressure = lower rolling resistance mentality.


Very similar here.  I run 26/27 psi in my terreno dry for gravel and around 28/30 if theres some paved road.  I weigh 160lbs and have never hit rim.  I blew a spoke on my rear 35miles into Rebeccas Private Idaho and was given a SRAM nuetral zipp with 32mm tubed somethings.  I asked what they were at and was told probably 32/34.  I counted at least 3 rim strikes and was worried I was replacing a zipp carbon rim on my own $.  It came out unscathed! 
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