Low tire pressure vs manafacturers guidelines

[baldbones]

Apologies if this has been covered before
I've been running my vittoria paves 25 at 75/80psi on a pacenti's sl23 rim
My wrench pointed out to me minimum is 115psi....
It feels fine but....

[Llewellyn]

You'll find a ton of threads here about running lower pressures - the general consensus is that down to around 65psi is OK unless you're a Clydesdale. Try experimenting with different pressures front and back to see what feels best. Lower pressures are definitely more comfortable. For the record I run 25mm Conti GP4000S's at 65F/75R - nice and comfy!!

[Cicli]

It feels fine but....

Then it is. No pinch flats, no problem.

[oldpotatoe]

Apologies if this has been covered before
I've been running my vittoria paves 25 at 75/80psi on a pacenti's sl23 rim
My wrench pointed out to me minimum is 115psi....
It feels fine but....

yer wrench is wrong...as long as it 'feels' good, isn't squishy, doesn't come off the rim(more a gig of too much PSI rather than less), and if you look at a pot hole you don't get a pinch flat or dent the rim.

[ergott]

I have often wondered why they put minimums like that.

[Peter P.]

I have often wondered why they put minimums like that.

Because you need to start SOMEWHERE.

Years ago I at the recommended pressure and reduced by 5psi. every ride until I felt them riding soft or I got a pinch flat. Then I went back up 5psi. from there. It's roughly such that I have to top off my tires once a week.

I weigh 130lbs. and if I pump up my tires to 100psi. I can go a month without touching them.

Now I ride at 80psi. and they feel firm to start and are good for a week. I could probably get away with 70-75 but I don't want to inflate my tires every ride.

Ignore the mechanic and begin to experiment.

[ergott]

Because you need to start SOMEWHERE.


Right, but minimum, that high?

I've seen tires with a recommended range which is a better idea.

[Lewis Moon]

Right, but minimum, that high?

I've seen tires with a recommended range which is a better idea.

It may be akin to water chemistry hold times; that's just where they stopped taking data.

[baldbones]

Thanks very much for the replies
Food for thought

[rburnham13]

I am 150 lbs and run 25c tires. I run 82f/85r PSI and they feel great. Super smooth and great for the New England beat up roads. No pinch flats, and very comfortable. I run Conti GP 4000 usually, but have been testing out some Vittoria Rubino Pro (the new ones with Graphine) and they are a more supple ride than the Conti, at the same PSI. Just my opinion.

[benb]

I really wonder about this too.. I just mounted up some Challenge Gravel Grinders last night (sexy tire!) and am going to be going through the tire pressure thing.

No issues with where I'd want to run them being out of range, I think they say 45-80psi.. with "recommended competition pressure 45psi" right on the sidewall. Total weight of the bike + me is > 200lbs so I'm going to start more like 60psi rear/50psi front probably.

I have been running pretty low pressures on my current bike and I'm actually wondering if I'm bottoming out and hitting the rim on some potholes.. is it possible to do this without damaging the rim or getting a flat? Just seems like I get some really nasty shocks sometime.. It's mostly in the front and I was running my front tire in the 45-50psi range. The tire I had on prior to the Gravel Grinders measured out to about 37mm on my rims.

Just riding the gravel grinders in the dark in my driveway and the sidewalk in front of my house I can tell they are way way more supple than the tires I took off so we'll see what happens.

[sandyrs]

I really wonder about this too.. I just mounted up some Challenge Gravel Grinders last night (sexy tire!) and am going to be going through the tire pressure thing.

No issues with where I'd want to run them being out of range, I think they say 45-80psi.. with "recommended competition pressure 45psi" right on the sidewall. Total weight of the bike + me is > 200lbs so I'm going to start more like 60psi rear/50psi front probably.

I have been running pretty low pressures on my current bike and I'm actually wondering if I'm bottoming out and hitting the rim on some potholes.. is it possible to do this without damaging the rim or getting a flat? Just seems like I get some really nasty shocks sometime.. It's mostly in the front and I was running my front tire in the 45-50psi range. The tire I had on prior to the Gravel Grinders measured out to about 37mm on my rims.

Just riding the gravel grinders in the dark in my driveway and the sidewalk in front of my house I can tell they are way way more supple than the tires I took off so we'll see what happens.

50-60 is pretty high for tires that size. I wouldn't expect to bottom out at all, and I weigh within a few pounds of you.

[benb]

50-60 is pretty high for tires that size. I wouldn't expect to bottom out at all, and I weigh within a few pounds of you.

Really wondering if I am though or if there was something odd with the tires I took off.

I was often starting the ride, feeling like I was feeling a lot of vibes & bounciness and I'd let a little air out. It would seem better but then later in the ride I'll hit a bump and it hurts like hell. (Like worried about getting injured hurt level.) I've been blaming the frame & fork but I'm really wondering if I'm hitting the rim.

The tires I took off were marked 35c... and I'm mostly concerned about the front tire being the one that was bottoming out. That wasn't 50-60psi, it was more like 40-45psi. If they were measuring out more like 37c on my rims, does that mean anything in terms of their height being reduced?

When I do a sanity check anything approaching 40psi does seem way too low for a 35-37c tire. I tend to run my front 26x2.3" tubeless tire on my MTB around 35-40psi depending on conditions. That tire measures bigger than 2.3" wide. I know 700c/29" changes some stuff but that 2.3" tire is more like a 60c width.

[benb]

For the hell of it today I rode with higher pressures after this discussion...

Went out with 60 front/70 rear in the Challenge Gravel Grinders I installed yesterday. Rear felt a little squishy so I put some air in it... front probably could have been lowered a bit so I'll maybe try something like 57/73 next time.

I did 15 miles, about 2 of which was "gravel" covered with leaves.. it starts out pretty hardpacked and fast and eventually has a sandy section and finally ends with what I would legitimately call singletrack. It's really an "easy" MTB trail more than a gravel road.

So those higher pressures were super fast on the road. (These tires are clearly way faster on road than what I took off.) Maybe a little bumpier on the small stuff but there were no "bang" moments that hurt on potholes and hard edged road cracks, etc.. so I really do think I was bottoming out my old 35c front tire running it in the 40s.

Buzzy in the gravel but still fast and no real traction issues.. the gravel section is very slightly uphill and I averaged 15mph. Not much turning though. I did break both tires loose braking to go around a barrier to keep cars off the road but it was super easy to control.

LOVE these tires. I don't feel like I'm giving up a whole lot on this bike vs the Conti Grand Prix 4 Seasons in 28c I ran for "go fast riding" most of the summer and they are much better in the dirt than my 35c tires I just took off. They do make a really weird sound on pavement though.. almost like your chain is dirty, but you stop pedaling & you can clearly hear it's the tires. Hopefully it's just that some of the "flashing" in the middle of the tire needs to wear off.

[DrSpoke]

Tire Pressure - Have you ever asked anyone what tire pressure to use? Has anyone ever asked you what tire pressures to use? For me, the answer to both questions is yes. A good articles on the subject is by Jan Heine (editor of Bicycle Quarterly and owner of Compass Bicycles), here: https://janheine.wordpress.com/2010/10/18/science-and-bicycles-1-tires-and-pressure/ The article includes a chart originally produced by Frank Berto using the concept of 15% tire drop. The problem with the chart is that it doesn't include all tire sizes and, since it's a chart, not so accurate. With a little internet research, I found a spreadsheet with a formula. I didn't like the design of the spreadsheet so created my own, attached. The inputs are the various weight categories, tires size and weight distribution percentages. From that, it calculates weight distribution in lbs and recommended tire pressures. Note that fairly small changes in weight have a larger than expected impact on tire pressure. The 45/55 weight distribution is an approximation but should be pretty close for road bikes and probably mountain bikes too. But you can actually calculate this using a bathroom scale and refine the percentages. I intend to do this for myself soon. If any questions, contact me. I tried it on Friday on my mountain bike and ended up dropping about 7 psi in front and 5 psi in back and it had a very noticeable, positive impact on the ride and handling. On Saturday, I used it on my road bike and dropped about 5 psi in front but added about 10 psi in back - again a noticeable, though subtle, improvement.

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This is from an email blast I sent out to some riding friends on Monday and seems relevant to this discussion.

Since the spreadsheet is an Excel format, I can only attach a .pdf version of it.
The first three sections are inputs for weight, tire size and weight distribution/%.
The weight distribution/% shown is, for me, an estimate as I have not measured it yet.
The last two sections are output.
The formula for weight distribution/lbs is a simple calculation of total weight * weight distribution/%.
The formula for tires pressure is as follows: =ROUND((153.6*C20)/(C12^1.5785)-7.1685,0) where C20 = weight/lbs (on that tire) and C12 = tire size (in mm).
Or: (153.6*weight)/(tire size^1.5785)-7.1685 Weight is in lbs and is per tire. Tire size is in mm.

As stated above, one of the things I have noticed is that a relatively small change in weight, and likely weight distribution, can have a significant impact on recommended tire pressure. The other thing I noticed is a much larger delta in tire pressures between the front and rear than I had expected. I would use these calculated pressures as a starting point and adjust from there depending on intended use, road/trail conditions, rim width, tire construction, tubed/tubeless, etc.


Hope this helps someone.

[coneill0422]

Interesting topic, I am about 150 lbs and have been running 75/ 80 psi for both tubulars and clinchers for the past couple of years.