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Have Your Tires been Lying to you?

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Have Your Tires been Lying to you?

Old 01-10-20, 01:01 PM
  #26  
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Originally Posted by 79pmooney
One thing I take real issue with is anyone telling me I should be using less than 5 psi lower in front than in back. That was what we all were taught back when we came from eggs (remember the dinosaurs). But there is a really good reason for so much pressure up front. There might just come a day when you have to slam on the brakes and do maneuvers to save your butt. At that moment, all your weight is on that front tire. Not 40-45% of your total. Not the 55-60% that the rear tire sees. No, that front tire is looking at 67% more weight than either tire sees normally. And at that moment, control is paramount. A blowout or rim failure disaster.
While hard braking does put far more load on the front tire than normal, focusing on the front-rear difference doesn't make much sense as a means to combat this. Suppose you use 95r/91f on a smooth road ride, but on a ride with some rough chipsealed sections you drop to 78r/75f. These numbers aren't out of the ordinary for recommendations from guys like Poertner. But if you actually needed that 91f for braking safety on the former ride, there's no reason that you wouldn't still need it on the latter ride! Yet nobody actually does this.
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Old 01-10-20, 01:16 PM
  #27  
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Originally Posted by cyccommute
I have problems with some of the points in this video. The first is the statement that tire pressure is set to 1/2 the blowoff value of a "standard rim". I've heard this stated in lots of places but I have yet to find a credible citation of where that comes from. Yes, it's higher than the maximum pressure but twice as much? I find that very hard to believe for all tires in all widths and all possible rim widths. I've had tires that blew off at the nominal highest pressure setting.
The rated pressure is half of what it took to blow off of the test fixture "rim", not half of what it takes for the tire to blow off of rims in general.
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Old 01-10-20, 01:22 PM
  #28  
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Originally Posted by Wildwood
My earlier reply didn't post. So this time with brevity.

Then - 'He is talking about what is faster' - means someone is dreaming about going faster over XX miles on a rough road or off-road or gravel road (how about CX, too? - that's a natural follow). And I would offer that there are so many variables to FASTER as to be a subjective and highly variable answer, requiring far more analysis than tires.
Gosh, if only we had someone with a couple of decades in the business, who'd helped develop the first carbon wheels for Zipp, worked with riders like Sagan, Contador, Armstrong, and their teams, and worked closely with other engineers in the aerospace and auto racing industries. Maybe someone like that would be a believable source, especially if he spent years doing research and talking about/explaining his results in print, on line, and in podcasts/videos, etc. Maybe someone like that would be a credible and informative authority...
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Old 01-10-20, 02:37 PM
  #29  
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Originally Posted by HTupolev
The rated pressure is half of what it took to blow off of the test fixture "rim", not half of what it takes for the tire to blow off of rims in general.
Do you have an actual citation for that? A "standard" that can be quoted? I've heard the same thing from lots of people but have never been able to find any kind of reliable source. Additionally, how does that "test fixture rim" compare to a general rim?
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Old 01-10-20, 02:41 PM
  #30  
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Originally Posted by cyccommute
Do you have an actual citation for that?
No, but I'm fairly certain it's what Poertner is claiming. He's well aware that different tire setups have different blow-off points.
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Old 01-10-20, 02:48 PM
  #31  
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Originally Posted by burnthesheep
I'm almost to the point of not correcting misinformation about low pressure and big tires being faster simply for the fact I'll be up 20w over the schmuck who shows up to the race.

Oh, cute, 28's at 40psi. Have fun!

Now, comfort, do whatever floats your boat. Sure.

Oh, and the evils of latex. Tell me how evil it is. Or how it isn't any faster. Right.

If you had an advantage over the 40 psi guy, then you would be down 20w, right? 20 watts less to go as fast/faster.
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Old 01-10-20, 02:56 PM
  #32  
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Originally Posted by HTupolev
No, but I'm fairly certain it's what Poertner is claiming. He's well aware that different tire setups have different blow-off points.
The problem is that without knowing the differences in blowoff pressure between a test rim and a "regular" rim, you can't jump to the conclusion that it's okay to exceed the recommended maximum pressure. He states that it is a legal requirement by a standards and testing agency. If there is such a test and even a "legal" requirement, why is it impossible to find the standard? I work with standards a lot and can easily find them through Google. I have never been able to find any kind of standard for maximum bicycle tire pressure or a method for testing it.
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Old 01-10-20, 03:05 PM
  #33  
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Originally Posted by cyccommute
That really has an impact on your overall speed, doesn't it? The number of bent rims I see at my co-op because people are running low pressure on tubleless is staggering. This is one of the more egregious examples I've run across.
<-------->
That's a Hadley thru-axle hub on a downhill wheel. It's a $400 to $500 wheel that is just beat up. We got it because the idiot who did the beating didn't realize the value. Unfortunately, it's mostly scrap. I salvaged the hub but it's not something our clientele really ever uses.

If the idiot had run the tires at 35 to 45 psi, he'd still have the wheel.
Haha, I don't think that person had anywhere near enough air in his tire to prevent this, and I'm betting Josh Poertner wouldn't have recommended it either, especially for what looks like a Mountain Bike wheel. I think his recommendations are mostly for people that want to go as fast as possible on their particular bikes over the road, not rock climbing.
I posted this video for those, including myself, that are trying to learn a bit about tire pressure.
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Old 01-10-20, 03:31 PM
  #34  
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Originally Posted by cyccommute
The problem is that without knowing the differences in blowoff pressure between a test rim and a "regular" rim, you can't jump to the conclusion that it's okay to exceed the recommended maximum pressure. He states that it is a legal requirement by a standards and testing agency. If there is such a test and even a "legal" requirement, why is it impossible to find the standard? I work with standards a lot and can easily find them through Google. I have never been able to find any kind of standard for maximum bicycle tire pressure or a method for testing it.
My guess (and that's all it is), is that there might be a regulation that is worded more along the lines of that the tire's marked max pressure can be no more than 1/2 of the tested blowout pressure on the steel test rim. That is to say, perhaps the regulation does not say "must read as 1/2 the tested blowout pressure..." The tire makers themselves can opt to put more reasonable restraints if they wish to.
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Old 01-10-20, 07:03 PM
  #35  
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Originally Posted by .mockingbird.
Both you and that Stuart guy are just guessing. The rider could have had proper inflation but suffered a big sidewall gash during a rocky descent, a decent sized tread puncture that slowly dropped pressure until the next rock garden, etc. Anyone who has ridden chunky stuff at speed knows that stuff can get bad pretty quickly.

Calling the rider an "idiot," as the Stuart guy has done, speaks volumes about Stuart, as opposed to the rider.
Actually, I'm basing what I said on the fact that cyccommute stated lack of air pressure was the cause of the bent rim. If not, then it doesn't belong in this conversation.
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Old 01-10-20, 11:48 PM
  #36  
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Originally Posted by .mockingbird.
Both you and that Stuart guy are just guessing. The rider could have had proper inflation but suffered a big sidewall gash during a rocky descent, a decent sized tread puncture that slowly dropped pressure until the next rock garden, etc. Anyone who has ridden chunky stuff at speed knows that stuff can get bad pretty quickly.

Calling the rider an "idiot," as the Stuart guy has done, speaks volumes about Stuart, as opposed to the rider.
Look more closely at the picture. There are 4 dents in the rim. None of the dents line up with each other so they are separate impacts. The rest of the rim had dents all the way around the rim. I have some (35 years) of mountain biking experience and know that impacts hard enough to dent a rim are pretty singular. You might dent both rim walls but you are unlikely to dent a rim wall a few inches apart in a single hit, much less several inches. The rider didn’t gash a sidewall and then hit a rock. He rode it on low pressure and hit many rocks.

I’m calling the guy an idiot because he ruined a $500 wheel for a few minutes of fun. I’m also calling him...and I’m pretty sure it is a “him”...an idiot because he donated an exceptional wheel because he didn’t understand what he had. A wheel with a $350 nearly new hub isn’t one that you just throw out. It’s worth rebuilding...several times if needed. You can ruin and discard cheap wheels. Ruining expensive wheels get costly.

Of course a little bit of pressure in the tires would have solved the whole problem.
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Old 01-11-20, 09:46 AM
  #37  
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Originally Posted by .mockingbird.
That's one possibility. It's also possible that, as I noted above, he had a catastrophic failure at speed in a rock garden - that's results in multiple impacts as you try to slow down on the rim. It's also possible that he had a slower puncture and ran it out through the chunk. That's based on my 35 years of riding lots of chunk at speed.

The bottom line is you don't know exactly what happened any more than I do, yet you label the guy an idiot.

You also judge the guy an idiot because he donated a hub that you couldn't imagine donating. Everyone's financial situation is different...
Sorry but your scenario could account for a couple of dents or even just couple of large dents and smaller dents as the wheel slows down. Maintaining speed without air in the tires is very, very difficult. It can’t account for large dents all the way around the wheel. Like I said above, this is on the most egregious example I’ve seen. I’ve seen lots and lots more dented rims with dents about this size and all of the largest ones are on tubeless that are being run at low pressure. Tubed tires can’t be run at the low pressures that low because of the snakebite problem. People believe that snakebites are bad without realizing that they are an indicator of possible rim damage.

That’s also my problem with the video and the pressure calculator that Silca has. It says that I should run 28 psi pressure on my loaded bikepacking bike on the roughest roads. My rims wouldn’t last 20 miles at those pressures. It also suggest that I use something like 70 psi in wide tires on a loaded touring bike. I had to do that once because the Continental touring tires blew off at the nominal pressure. It wasn’t “comfortable”. It was squishy and slow with corners being highly exciting because I was never sure if the tire was going to fold over or not.

And I can imagine donating a wheel of this quality...I have done so in the past...but I wouldn’t donate one in this shape. I also wouldn’t donate one this new. It’s a current model and the hub was absolutely pristine. It’s new enough and was clean enough that it could have been used only once.
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Old 01-11-20, 10:15 AM
  #38  
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Originally Posted by cyccommute
Sorry but your scenario could account for a couple of dents or even just couple of large dents and smaller dents as the wheel slows down. Maintaining speed without air in the tires is very, very difficult. It can’t account for large dents all the way around the wheel. Like I said above, this is on the most egregious example I’ve seen. I’ve seen lots and lots more dented rims with dents about this size and all of the largest ones are on tubeless that are being run at low pressure. Tubed tires can’t be run at the low pressures that low because of the snakebite problem. People believe that snakebites are bad without realizing that they are an indicator of possible rim damage.

That’s also my problem with the video and the pressure calculator that Silca has. It says that I should run 28 psi pressure on my loaded bikepacking bike on the roughest roads. My rims wouldn’t last 20 miles at those pressures. It also suggest that I use something like 70 psi in wide tires on a loaded touring bike. I had to do that once because the Continental touring tires blew off at the nominal pressure. It wasn’t “comfortable”. It was squishy and slow with corners being highly exciting because I was never sure if the tire was going to fold over or not.

And I can imagine donating a wheel of this quality...I have done so in the past...but I wouldn’t donate one in this shape. I also wouldn’t donate one this new. It’s a current model and the hub was absolutely pristine. It’s new enough and was clean enough that it could have been used only once.


Are you talking about the wheel you posted with hundreds of paint nicks like a starry night?

That was some ride!
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Old 01-11-20, 03:39 PM
  #39  
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Most of the time I don't use tire pressure gauge and I go by feel...When I ride on pavement I pump my tires just hard enough so they roll good without causing pinch flats...When I go riding off road I lower the pressure just enough to provide extra comfort and improve traction and handling but not too low to damage the rims. Tire pressure is not rocket science, it's common sense....I don't use tubeless, the biggest disadvantage of tubeless is that people think they can go as low as they want because they don't have to worry about pinch flats but they end up destroying their rims instead.
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Old 01-13-20, 09:37 AM
  #40  
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I have no clue what the max pressure is for any of my tires, I've never looked, because I would never run that much pressure. I run around 80psi in my 28's on the road, and 30-40psi in my 40mm tubeless gravel tires. I'm 185lbs and rarely pinch flat (even less so since going to 28s, had a few on my 23s at higher pressure), and have had zero issues offroad. I use a digital gauge and check my road pressure every other ride (if I'm riding daily, if it's been more than a day then I check it), and my tubeless pressure every ride.
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Old 01-13-20, 10:27 AM
  #41  
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I run 100 lbs in my front and 110 lbs in my rear of my Waterford RS33 on 23's and have had excellent performance and wear with no issues. YMMV.
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Old 01-13-20, 12:17 PM
  #42  
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I only ride for exercise now, but I still get discouraged if I'm not turning my accustomed gear. I pump up the tires, and feel young again.
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Old 01-13-20, 05:16 PM
  #43  
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Originally Posted by Rides4Beer
I have no clue what the max pressure is for any of my tires, I've never looked, because I would never run that much pressure. I run around 80psi in my 28's on the road....
And this is part of the curiosity of the whole issue. Take Enve as an example, 80psi is the absolute max they recommend for a 28 tire on any of these rims -- SES 2.2, 3.4, 4.5, 5.6, 7.8. But 80psi is only recommended for those 240lbs or over.
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Old 01-13-20, 06:33 PM
  #44  
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Originally Posted by cyccommute
I have problems with some of the points in this video. The first is the statement that tire pressure is set to 1/2 the blowoff value of a "standard rim". I've heard this stated in lots of places but I have yet to find a credible citation of where that comes from. Yes, it's higher than the maximum pressure but twice as much? I find that very hard to believe for all tires in all widths and all possible rim widths. I've had tires that blew off at the nominal highest pressure setting.

Going over to the Silca calculator, I have definite problems with their pressure. While some of the pressures would be valid for racing conditions, they become invalid for people who have to actually pay for their parts rather than have a sponsor. The suggested pressure for a mountain bike for me is 23 and 24psi front/rear, respectively. If I add a bikepacking load of 40 lbs, the pressure suggestion is 26 and 28 psi, front/rear. First, I've ridden tires that have that little pressure in them for off-road without a load and it wallows. It doesn't turn well. But, more importantly, that kind of pressure is going to result in the tires bottoming out on hard edges which risks not just a pinch flat but a damaged rim. I've seen some very nice rims ruined because someone was using the "optimum" ride pressure and completely ignoring the other function that tires serve...to protect the rims.
I recently read that modern MTB carbon rims are made extra strong and thick to help them survive the large impacts that running low pressure tubless tyres can impart on the rim.
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Old 01-13-20, 06:34 PM
  #45  
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Originally Posted by cyccommute
I have problems with some of the points in this video. The first is the statement that tire pressure is set to 1/2 the blowoff value of a "standard rim". I've heard this stated in lots of places but I have yet to find a credible citation of where that comes from. Yes, it's higher than the maximum pressure but twice as much? I find that very hard to believe for all tires in all widths and all possible rim widths. I've had tires that blew off at the nominal highest pressure setting.

Going over to the Silca calculator, I have definite problems with their pressure. While some of the pressures would be valid for racing conditions, they become invalid for people who have to actually pay for their parts rather than have a sponsor. The suggested pressure for a mountain bike for me is 23 and 24psi front/rear, respectively. If I add a bikepacking load of 40 lbs, the pressure suggestion is 26 and 28 psi, front/rear. First, I've ridden tires that have that little pressure in them for off-road without a load and it wallows. It doesn't turn well. But, more importantly, that kind of pressure is going to result in the tires bottoming out on hard edges which risks not just a pinch flat but a damaged rim. I've seen some very nice rims ruined because someone was using the "optimum" ride pressure and completely ignoring the other function that tires serve...to protect the rims.
I recently read that modern MTB carbon rims are made extra strong and thick to help them survive the large impacts that running low pressure tubless tyres can impart on the rim.
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Old 01-13-20, 07:41 PM
  #46  
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The last thing I will do on a ride is to stop, measure psi, pump or deflate, measure psi depending on what the surface conditions changed into.

my fingers are the most precise psi gauge, squeeze and judge and pedal 😀
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Old 01-14-20, 06:08 AM
  #47  
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Originally Posted by .mockingbird.
Key information that was left out of your post:

"Note: Tire pressures are intended as a starting recommendation based on the listed wheel being set up with tubeless tire. The pressure value is calculated considering a tubeless set up, intended road surface, rider's weight, average bike weight, inner rim width, and tire volume."
Which is the key part that we didn't know? 80psi is where the maximum value the chart goes to and then stops increasing. I believe we're talking about road surfaces. This series of wheels is intended for asphalt per Enve. These are 21mm internal width rims which might slightly possibly mean 28s would inflate a bit wider than nominally rated, vs. Rides4Beer's? And, the riders's weight we've been talking about -- in the context that Rides4Beer is mentioning that he's well under the tire's maximum inflation, so interesting IMO to point out that he's at one rim maker's maximum recommended and he's nowhere close to 240lbs.
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Old 01-14-20, 07:53 AM
  #48  
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I used to run them at 50-60 on the road it seemed good, I would go 40-45 for actual gravel rides
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Old 01-14-20, 07:23 PM
  #49  
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Originally Posted by .mockingbird.
Here, I'll bold it so it's easier for you to follow along:


"Note: Tire pressures are intended as a starting recommendation based on the listed wheel being set up with tubeless tire. The pressure value is calculated considering a tubeless set up, intended road surface, rider's weight, average bike weight, inner rim width, and tire volume."
Yeah.. got it. And either you're being intentionally obtuse, or you don't see anything curious about someone using 80psi which is way lower than on the tire sidewall, aligning with a rim maker saying that's the way extreme on the high side?
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Old 01-14-20, 08:05 PM
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Originally Posted by .mockingbird.

It's especially important that you pay attention when reading/quoting manufacturer's recommendations so that you don't confuse a recommended psi starting point with max pressure...
I interpret the fact that when the rim manufacturer has a point in their inflation chart, where they stop increasing the recommended PSI for increasing rider weights, it's the same as the max pressure they permit. Though they don't actually come out and say this. Not sure what other interpretation you can make, as tire drop for given pressure and rider weight is a fairly mathematical progression, and if safety rating for the rim isn't a factor, then there should be no reason to not continue increasing recommended PSI as weight goes up.
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