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comfortable inflation vs. manufacturers recommended range

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comfortable inflation vs. manufacturers recommended range

Old 05-25-22, 12:29 PM
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Originally Posted by HTupolev
How would a tube "push the tire out from the rim"?

The tire is the pressure vessel with high tensile stiffness, not the inner tube. Inner tubes don't really have an engineered PSI threshold, and if they're not surrounded by a tire, they're not even capable of containing much pressure: they just get bigger and bigger like a party balloon as more air is added until the rubber tears from being stretched too far.
a tube that is ideal for a 700x32 may have more stretch when packed into a tire that is 25x700, & if the tire's engineered psi threshold is 90PSI, the tube might physically reach a size large enough to bump the tire off its seated area.
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Old 05-25-22, 01:36 PM
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Originally Posted by ofajen
I haven’t seen that. The Silca calculator actually has the user select from various standard bike geometries (TT, road, gravel and MTB) with different F/R percentages and produces separate recommendations for front and rear. I’d be cautious about lowering the front too much as there is still braking to be done and out of the saddle work, both of which put more weight on the front.

Otto
You have not seen what? Silca gives you a choice of 50/50 for Road and 52/48 for TT and 53/47 for Mtb. I have been using Berto's 15% drop rule for almost 40 years. It works pretty well for normal tires but my testing showed supple tires can run a little higher pressures than his charts indicate but he did not have the quality of tires back then. The important point of his work is the differential in pressure F/R. I cannot see10-15 psi difference is some kind of risk.....like 90 psi rear and 75 psi front.

Clearly, you have not measured and do not believe me. This is what Zinn says

I’m convinced that anybody who says the weight distribution on a road bike should be 55 percent on the rear wheel and 45 percent on the front (or 50/50, or anything in the realm below 60 percent on the rear wheel) never actually measured it.
Don’t be surprised if it comes out 70/30.
https://www.velonews.com/gear/techni...compatibility/
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Old 05-25-22, 01:38 PM
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Originally Posted by Troul
the tube might physically reach a size large enough to bump the tire off its seated area.
Tubes impose almost zero resistance to stretching when subjected to pressure. They always stretch to fill the cavity within the rim and tire no matter what nominal size they are.

Like, if you take a "25mm" inner tube outside of a tire and start pumping it up, it will happily get far larger than a 25mm tire even when its internal pressure is barely higher than that of the ambient air. The reason it doesn't get huge when it's inside of a 25mm tire is that it's being constrained by the tire.
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Old 05-25-22, 01:46 PM
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Originally Posted by GhostRider62
I cannot see10-15 psi difference is some kind of risk.....like 90 psi rear and 75 psi front.
The problem that I have with the "use a small differential to avoid front tire collapse" reasoning is that it doesn't seem like a logical solution to the proposed issue. Many proponents of the strategy will recommend dropping from 93r/89f to 75r/72f (or whatever) if a ride contains some rough sections, but hard braking or cornering on a stretch of good pavement in the latter case doesn't put less stress on the tire than in the former case.
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Old 05-25-22, 02:04 PM
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Originally Posted by HTupolev
The problem that I have with the "use a small differential to avoid front tire collapse" reasoning is that it doesn't seem like a logical solution to the proposed issue. Many proponents of the strategy will recommend dropping from 93r/89f to 75r/72f (or whatever) if a ride contains some rough sections, but hard braking or cornering on a stretch of good pavement in the latter case doesn't put less stress on the tire than in the former case.
Dunno. What you write makes zero sense. Sorry. I also think you do not understand what I am saying because I did not write 93r/89f or 75r/72f. I do not see with my riding any braking or cornering problems with tire pressures in the 75-80 psi range.

Proper tire pressure depends entirely on the road surface to optimize the suspension effects needed for the road surface. As long as you are above recommended minimums, there is no problem. And, just to sum up....I pick the highest pressure that gets me good comfort on the roads that day. Today, it was one pressure and tomorrow's nice roads will be a different pressure and always lower pressure on the front tire on my road bike
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Old 05-25-22, 02:14 PM
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Originally Posted by GhostRider62
Dunno. What you write makes zero sense. Sorry. I also think you do not understand what I am saying because I did not write 93r/89f or 75r/72f.
I wasn't disagreeing with what you wrote. I was criticizing some of the arguments that get made against significant front-rear pressure differences.
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Old 05-25-22, 03:52 PM
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Originally Posted by GhostRider62
Clearly, you have not measured and do not believe me.
I was just noting they use figures (slightly) different from 50/50.

For my way of looking at it, itís an empirical compromise and I try to run the lowest pressure that avoids issues while being as comfortable as possible. I decide that by connecting measured pressures with how the ride goes.

For my 700x32 bike, Silca recommends 56 front/59 rear. With my current tires, I typically run 55/58 using my Meiser gauge. No need for more in the rear, but much less and I donít like the feel. Same in the frontÖ no need for more but much less and I donít like it. I did a ride Sunday where it felt squishy when I was standing and came home to measure 52 psi.

Since you asked, I did quick static measurements and show that it will typically run at least 70 front/30 rear when I am leaning over the bars and standing, which happens dozens of times in a typical ride. Thatís why I notice it if the front is below 55 psi.

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Old 05-31-22, 01:00 PM
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Originally Posted by aliasfox
As long as you have a cell phone and a friend or partner (or an ambulance) whoís willing to pick you up, go as low or as high as you want!
Fixed that for you.
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Old 05-31-22, 03:52 PM
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Originally Posted by ofajen
I was just noting they use figures (slightly) different from 50/50.

For my way of looking at it, itís an empirical compromise and I try to run the lowest pressure that avoids issues while being as comfortable as possible. I decide that by connecting measured pressures with how the ride goes.

For my 700x32 bike, Silca recommends 56 front/59 rear. With my current tires, I typically run 55/58 using my Meiser gauge. No need for more in the rear, but much less and I donít like the feel. Same in the frontÖ no need for more but much less and I donít like it. I did a ride Sunday where it felt squishy when I was standing and came home to measure 52 psi.

Since you asked, I did quick static measurements and show that it will typically run at least 70 front/30 rear when I am leaning over the bars and standing, which happens dozens of times in a typical ride. Thatís why I notice it if the front is below 55 psi.

Otto
I find much the same thing. I'm more sensitive to front pressure than I am to rear in terms of "feel". If the front pressure is too low I really notice it when climbing out of the saddle.
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