Countran

I just set up my Maxxis ramblers tubeless and put them around 40psi. My rides are a mix of asphalt and pockmocked but otherwise fairly smooth dirt roads, with occasional gravel (southern Michigan). The 40 felt good on the road but just wondering what people run their tires? I weigh 195 lbs

dgodave

Whats a good reliable gauge for lower pressure with presta valves.

I need to buy one. Then I'll post here.

Spoonrobot 

IMO this is the best standalone pressure gauge.

I run various pressures since I ride tires with significantly different sidewall stiffness. For mixed terrain I go 15-20% sag and for pure gravel or singletrack I like 20-25%. This ends up being about 35-45psi for 40mm tires, 25-30psi for 47mm tires, 20-22psi for 55mm tires, and 25-27psi for 54mm tires.

When I get a new tire I like to determine sag using the method here in this post from MTBR. I think it's a ton more helpful to talk sag as opposed to pressure but that's definitely a minority opinion.

TimothyH

Step number 2 in the MTBR post says...
He has a method for setting the amount of sag once it is determined but it seems like determining the correct level is the big question. How do you do this, find the correct level of sag?

Not trying to challenge. The engineer in me is sincerely interested.


-Tim-

dgodave

Thank you, spoon.

My floor pump gauge is off by appx 20#. So for the last few years its by feel every time.

Spoonrobot 

I wondered if the poster meant "calculate level of sag" since it appears split the different and picked 18.75%. Anyway, I do trial and error, with historical norm as the starting point. But to be fair I don't really care too much about slicks and road sag. I'm way more interested in knobbies and dirt.

I don't think this is anything different than what most people do, just standardized on a value that is more easily repeatable between people and tires. I start at Frank Berto's/Michelin recommended 15% and see how it feels. Add or remove pressure as needed based on suppleness of tire. Mostly like a little more sag than 15% since a lot of my riding even on the road is over cracked pavement or has significant sections of bumpy trail/widewalk pathway as well as gravel sections. When I do a ride on what I feel are going to be much smoother roads/no gravel I'll take the pressure up and do more like 10% sag as I don't need the comfort and feel a little faster - for the tires I'm using now I think 10% is right under the breakpoint so I'm right at the lowest rolling resistance.

For most knobbie tires I start at 20% and do the same. What I look for to tell me to increase or decrease sag is sidewall collapse during cornering - I test on pavement to get an idea and then try again on singletrack before adjusting sag. A lot of times aggressive knobbies dig in more on asphalt and feel squirmy but are actually perfect for dirt. When I ride singletrack I want to make sure I'm getting just enough compliance during bumps while the bike is leaned over. Straight up and down is not as important - getting knocked around while leaning the bike has a much greater effect so I like to fiddle until I can go over rocks and roots with maximum compliance from the tires while making sure the sidewall still holds up. I like to really mess with tire pressure on dirt, when the total pressure in a tire is 25 psi, 1-2 psi marginal can make a big difference, that's 4-8% which I think is relevant to ride quality and feel.

DrIsotope

I just fiddle with starting pressure until the tire feels "right." Currently running staggered Gravelking SKs, front 43mm @ 42psi and rear 38mm at 55psi, rider + bike weight ~230lbs. True mixed surface riding, a 30-miler might have 8-10 miles of pavement in there, because this is SoCal, and they've paved... most everything. I'm not driving the 3-4 miles to get to the fire roads, utility access paths, or singletracks. So the tires have to be ready for whatever. Dropping 5 or more PSI would likely make the rougher offroad sections nicer, but really put the drag on the pavement during the last leg home.

TimothyH

This makes sense based on my understanding of tuning auto suspensions.

Pressure should be low enough that the tire rolls over irregularities rather than bounces off them, but not so low that it rides on the sidewall.

Thanks.


-Tim-

jimincalif

Even most of our "rivers" are paved.

"They paved paradise
And put up a parking lot"

chas58

Well, the only real way is measuring the height of the sidewall (wheel to ground) at max pressure unladen, then laden at the pressure you are riding.

Personally I want to see the contact patch >50% of the tire width. Thus on a 40mm tire, I want the contact patch to be 20mm. I can eyeball this taking a wet tire through a damp section of pavement.

The best method I am aware of is the CX method. Ride the course slowly dropping pressure until you hit the rim, then add a couple PSI back in.

chas58

I would have written yesteday, but I was out riding my ramblers on the gravel roads of MI for most of the morning. It was about 3 hours into the ride before the water in my water bottle thawed out. Well, at least the single track was rock hard until the sun hit it...

I ran about 30 front 35 rear. A little lower than normal as the freeze/thaw cycles have made the roads pretty rough.

Typically on dirt I'll ride them 35F-40R PSI. up to 45-55 PSI for road only.

jp911

I'm about 5 lbs heavier than you and I'm running my 700x40 ramblers (tubeless) at 40 front and 45 rear on hard pack and pavement, and I drop 5lbs (35F, 40R) for loose trails.

Countran

Thanks for the inputs everyone. I'll have to try those sag methods when I take it out to the trails (if it ever dries here)!

Hondo Gravel

700x40 WTB Nanoraptors 60 psi. Ride on hard packed gravel and semi rough pavement. I like higher air pressure than most because of less rolling resistance but parts on gravel get somewhat jarring. Rougher gravel I would lower the air pressure.

aggiegrads

Higher pressured don't reduce rolling resistance except on smooth machined drums that are used to test tires. On normal roads, high pressures better transmit the bumps to the rider, who perceives the increased frequency as speed.

You instead want a tire that will "push" itself off of the backside of a bump instead of bouncing over it. Think of it like riding a pump track. You need the tire to deform so you get the benefit of the "downhill" side of the bump.

Spoonrobot 

Remember the main guy behind this whole movement is most interested in riding 200km+ on the road and has noted his favorite rides are around 40 hours in length. What works best for him is not necessarily going to be the same for someone interested in shorter rides on different surfaces.

Higher pressure does reduce rolling resistance on the road/gravel/singletrack, the science is pretty settled on this but the message has gotten muddled due to marketing of the idea. If it were not true we'd all be running around with just enough PSI in our tires to keep from bottoming out the rims. So we all need pressure, but how high is too high? Issue #1 is there is a breakpoint that most riders exceed. Above a given pressure rolling resistance increases as seen in the graph below from this thread before falling again as very high pressures are reached. Jobst Brandt famously recommended extremely high pressures, this is why. At such high pressure tire life is reduced, susceptibility to punctures increases and overall comfort is extremely low.

Gravel is much more difficult to determine since consistency in results is much harder and I do not believe anyone has produced good data at this point. In my own testing I am pretty convinced the same holds true as above but with one small caveat: There is a rolling resistance breakpoint due to pressure (noted above), but there is also a personal comfort breakpoint. Pressure above which the rider cannot accommodate with their body and will be slower on gravel or singletrack for a given pressure. This is most obvious watching riders hit washboarding at speed, certain riders have the body position and strength to handle it at a higher speed than others.



Unfortunately your second statement doesn't really make any sense and is a talking point that was abandoned. Similar to the 2000 watt "tank study" that used to be referenced that is no longer mentioned since the interpretation of the results was incorrect. Rolling resistance goes to zero when a tire is not in contact with the ground, anyone who has aggressively ridden singletrack knows that sending every bump is much faster than rolling over them - infinitely more fatiguing but much faster. There is no free energy push that the tire somehow receives at lower pressure, it's not analogous to a pump track since that's not how pump tracks work either.

Everyone interested should read the Silca Journal entries on this subject.

Hiro11

700 x 50 Clement MSOs: 35 psi
700 x 44 Compass Snoqualmies: 40 psi

I run them both tubed.

aggiegrads

I know that the second statement is not exact, but I am trying to explain hysteresis in a way that can be better understood. This concept is still compatible with the observation that "sending it" is faster than keeping full tire contact with the ground.

I know what works for me, and running 40mm tires at 60psi is not it. Even that actually works out to be faster, to me it isn't worth the sacrifice in comfort.

Abe_Froman

Wow...can they really be off by that much

Hmmm

As a newbie to gravel, could I get away with running low pressure's like 35 and 40psi with Maxxis Ramber 40mm's tubed? I went to a friendly cyclocross practice and they lowered my tire pressure by quite a bit. I couldn't believe the comfort. I would like to run lower pressures on long mixed rides in the future. Should I just be looking out for pinch flats and other than that I'm safe?

I will make the jump to tubeless one day, but as of now I will be running tubes.

shoota 

Yeah you're running the risk of pinch flats at that PSI. But as long as you're aware of it do whatever you want.

68venable

700x43mm Gravel Kings with tubes @ 40psi front and rear.

DomaneS5

I run 40psi on 40c WTB Nanos (with tubes). Works well for me.

Caliper

I use the Berto Tire pressure app. It claims to target a 15% drop based off some basic bike geometries (ie: upright vs road distributes rider weight differently), bike weight, tire size and rider weight. I haven't independently measured the drop, but the pressure recommendations haven't resulted in any pinch flats despite being much lower than what I used to run.

For me (180# rider, including gear, and 20# bike) I put 35/50psi in my 40mm Ramblers, also tubed, (the app said 33/48 so I rounded off) and had no pinch flats even though I hit some nasty potholes that ejected a water bottle on one descent. If you are a total newbie to cycling and aren't good at unweighting the bike in bumpy spots you may want to add more.
In CX, I believe they get away with lower than one might on a road because the grass/mud is a bit more forgiving and less likely to cause a pinch than hardpack/pavement.

Hmmm

Perfect. Thanks! I'm 180 as well with about a 20lb bike. This advice is great. The comfort was great and I'd like to run the lower pressure it for mixed rides. I'll go with a little inbetween what I had and where it was lowered to and feel it out from there.

Appreciate all the help.