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comfortable inflation vs. manufacturers recommended range

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comfortable inflation vs. manufacturers recommended range

Old 05-23-22, 06:53 PM
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Originally Posted by tomato coupe
I thought everyone knew, inflation is on the rise.
When I saw the thread title I was like totally expecting a thread about bike prices. Iím totally bummed out.
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Old 05-23-22, 09:28 PM
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Iím surprised I havenít seen a reference to the Silca tire pressure calculator:

https://silca.cc/pages/sppc-form

Thatís the one that seems to consistently jive with where I end up running tires. The SRAM calculator tends to give higher numbers than I like.

Otto
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Old 05-23-22, 10:08 PM
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Originally Posted by LarrySellerz
The "max" pressure rating on a bicycle tires about half of what it takes to actually fail.
Next thing we know, Larry would justify the above by telling us that if it were up to Continental's German engineers, tires would indicate what the "real" max pressure is, but because of damn American lawyers, tires can only indicate approximately half the "real" max pressure.
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Old 05-23-22, 11:04 PM
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Originally Posted by SoSmellyAir
Next thing we know, Larry would justify the above by telling us that if it were up to Continental's German engineers, tires would indicate what the "real" max pressure is, but because of damn American lawyers, tires can only indicate approximately half the "real" max pressure.
id expect the germans to undergo a more scruninous process. The idea that a wheel fails due to overpressure is rather absurd frankly
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Old 05-23-22, 11:15 PM
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Originally Posted by LarrySellerz
id expect the germans to undergo a more scruninous process.
Germans are the most scruninous people on the planet. In fact, they're universally known for their scruninality.
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Old 05-23-22, 11:23 PM
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I think we all know that the inflation range can be worse for comfort. But has anyone found that the cornering performance is better in the higher pressure range? My 26mm turbo pro measures 29mm and the inflation range is 100-125psi. Absolutely absurd.

I've been testing different tire setups and I really like how the tire feels at 65-75psi. I guess I'll test at 100psi and report back if that's any good.
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Old 05-23-22, 11:28 PM
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Originally Posted by LarrySellerz
There are some benefits, for instance I have a commuter bike that mainly sees nice tarmac but has a 37 knobby up front. When I pump it up to 100 psi the knobs aren't in contact with the road when going in a straight line. sucks in corners but its great for rough terrain and potholes
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Old 05-24-22, 12:20 AM
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Originally Posted by LarrySellerz
The idea that a wheel fails due to overpressure is rather absurd frankly
I have read about instances of carbon fiber road wheels failing due to overinflation.

Originally Posted by LarrySellerz
There are some benefits, for instance I have a commuter bike that mainly sees nice tarmac but has a 37 knobby up front. When I pump it up to 100 psi ...
I guess you could never know when all hell would break loose and your nice commute turns into a scene straight out of Mad Max, and you need to pop a wheelie and smack someone in the face with your 37 knobby inflated to 100 PSI.
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Old 05-24-22, 02:58 AM
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Originally Posted by LarrySellerz
The "max" pressure rating on a bicycle tires about half of what it takes to actually fail.
That's a dangerous blanket statement.

It's true that some tire models are nominally tested against blowoffs to a very wide pressure margin, but that's not the same as guaranteeing that a tire will work to that margin. Rims and tires have manufacturing variances, different tires seat differently on different rim designs, different people set up their rims differently. Furthermore, many consumer pump gauges are extremely inaccurate. And, tire pressure changes dynamically as the temperature within the tire's air cavity changes, a danger which is exacerbated when rim brakes are used.
A big part of why wide testing margins exist is to compensate for these factors.

Furthermore, it's not actually the case that all tires are tested to 2x margins, especially within some recent target use cases (i.e. hookless tubeless rims). For instance, apparently ISO4210-2 permits tested blowoff margins as low as 110% of the listed maximum, and in that article, Mavic states that the margin they use is 140%.
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Old 05-24-22, 04:06 AM
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Originally Posted by aliasfox
Oh - apologies for writing that in a confusing manner. I DO NOT recommend going beyond the recommended limits for the tire or the rim. What I meant to say is that I've put my numbers into tire pressure calculators, and they always seem ridiculously low to me. For example, with my (measured) 32mm front and 28mm rear, Silca suggests, for my 215lbs total system weight, that I should be riding 66psi in front, and 84psi in the rear. I can say for certain that I'm not a fan of how my front feels below 75psi, and I generally pump it up closer to 80psi. As for my rear, I can deal with 84psi, but I'm more comfortable at 90psi. That's what I meant by going higher than recommended.

Now, it may also be because the gauge on my Serfas pump isn't accurate, or maybe I'm just so used to riding on 23-25mm tires at 100-110psi for so long. But within reason (read: within the limits of what your tire/rim says), I say every rider should just go and experiment and see what makes the most sense to them - and different people will optimize to different criteria - personal comfort, perceived performance, time over a certain Strava segment, etc. After all, the calculators really are just recommendations.
I agree. The calculators don't know exactly what tyres you are using or the exact road surfaces you are riding. As you say, they are merely a suggested starting point based on their data.

I find the SRAM calculator most useful (as it takes rim width into account) and I always cross reference with what the tyre manufacturer recommends. For example my Conti GP5000S TR (30 mm) have a max pressure rating of 73 psi and the SRAM calculator recommends 61/65 psi front & rear on my 22 mm wide hooked rims and I find those values work fine for me. The Silca calculator recommends running a bit more pressure (69/71 psi), but doesn't have an input for rim width. I do find that some other calculators recommend a very low front pressure relative to the rear, which I don't like.

It's a good point you raised about accuracy of your pressure gauge. I have a good quality digital gauge which I check against my track pump gauge. They both agree within 1 psi, so I'm reasonably confident they are accurate. But I know some pumg gauges can be a long way out.
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Old 05-24-22, 04:11 AM
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Originally Posted by ofajen
Iím surprised I havenít seen a reference to the Silca tire pressure calculator:

https://silca.cc/pages/sppc-form

Thatís the one that seems to consistently jive with where I end up running tires. The SRAM calculator tends to give higher numbers than I like.

Otto
That's odd, I find the exact opposite i.e. Silca calculator recommends a higher pressure for my inputs.
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Old 05-24-22, 04:24 AM
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Originally Posted by SoSmellyAir
Next thing we know, Larry would justify the above by telling us that if it were up to Continental's German engineers, tires would indicate what the "real" max pressure is, but because of damn American lawyers, tires can only indicate approximately half the "real" max pressure.
Funny. Decades ago Interbike had an expo in Philadelphia. I got free passes and went with a riding buddy. We talked to a Continental rep. He told us the max rating on the tire is half what it takes to blow it off. He blamed company lawyers for the lower figures on tires. True story.
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Old 05-24-22, 05:53 AM
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Originally Posted by PeteHski
That's odd, I find the exact opposite i.e. Silca calculator recommends a higher pressure for my inputs.
I ride crushed stone, not roads. Maybe that makes a difference? Just ran it for the bike with 700x32. Silca gave 56/59 and SRAM was 60/64, which would be pointlessly high.

Otto
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Old 05-24-22, 06:05 AM
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Originally Posted by indyfabz
Funny. Decades ago Interbike had an expo in Philadelphia. I got free passes and went with a riding buddy. We talked to a Continental rep. He told us the max rating on the tire is half what it takes to blow it off. He blamed company lawyers for the lower figures on tires. True story.
You mean, you met LarrySellerz all those years ago before he joined Bike Forums?
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Old 05-24-22, 06:33 AM
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Originally Posted by SoSmellyAir
You mean, you met LarrySellerz all those years ago before he joined Bike Forums?
Just telling it like it is. Or at least was.
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Old 05-24-22, 08:00 AM
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Originally Posted by LarrySellerz
The "max" pressure rating on a bicycle tires about half of what it takes to actually fail. You wouldn't ever be close to that, play around as much as you want. Cubewheels was claiming that the rim could blow out at high pressures, but idk if he is to be trusted and thats not a failure of the tire anyways. Its like how ladders are normally rated to 250 lbs but routinely take loads of 400+. also tubes don't have a max pressure lol..

The current consensus seems to be that wider tires with less pressure are preferable, but that has changed over the years, back in the day people were trying to get narrower than 23s. Who knows what people will be doing in 20 years
uhm, no. Running pressures substantially over the recommended level is a recipe to crack carbon clincher rims, and blow tubeless tires off rims.

particularly if youíre using hookless rims, Iíd be very careful about exceeding the tire or rims recommended pressure.

Obviously manufacturers put a margin of error in their calculations for safety. However, when you consider the intersection of tire and rim made by different manufacturers, and potentially each on.the opposite side of the tolerance range ( I.e a tire at the large side of the tolerance, and a rim at the small side of the tolerance range) the actual safe working pressure may be no higher than the max specíd on the rim or tire.
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Old 05-24-22, 08:03 AM
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Originally Posted by ofajen
I ride crushed stone, not roads. Maybe that makes a difference? Just ran it for the bike with 700x32. Silca gave 56/59 and SRAM was 60/64, which would be pointlessly high.

Otto
The Silca calculator though offers 3 or 4 types of gravel surface to choose from. AFAIK, the sram one only has a single 'gravel' to choose from. Also have to be aware that the sram calculator presumably makes an attempt at guessing your tire volume based on the rim width, while the Silca calculator asks you to provide the actual measured inflated width. Of course different brands/tires will inflate to different sizes for the same nominal tire size that's printed on the side of the tire.
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Old 05-24-22, 09:27 AM
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Originally Posted by Sy Reene
The Silca calculator though offers 3 or 4 types of gravel surface to choose from. AFAIK, the sram one only has a single 'gravel' to choose from. Also have to be aware that the sram calculator presumably makes an attempt at guessing your tire volume based on the rim width, while the Silca calculator asks you to provide the actual measured inflated width. Of course different brands/tires will inflate to different sizes for the same nominal tire size that's printed on the side of the tire.
Yeah, the other reason I like the Silca calculator is the specific types of surfaces since I ride some stuff that would be Category 1 gravel and some Category 2, and so on. But mostly it seems to give me a starting point that ends up just about right.

I ran it again. SRAM says 60.6/64.5. Silca says 56.5/59. I just did a ride Sunday and the front tire felt a little soft, but only when on pavement and riding out of the saddle. Turns out I was running about 50/53 that day. Below that starts to feel a bit squishy.

Otto

Last edited by ofajen; 05-24-22 at 09:39 AM.
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Old 05-24-22, 10:00 AM
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Originally Posted by ofajen
I ran it again. SRAM says 60.6/64.5.
Anyone with any cycling experience would know that 60.7 / 64.4 would be much, much better.
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Old 05-24-22, 11:51 AM
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Originally Posted by ofajen
I ride crushed stone, not roads. Maybe that makes a difference? Just ran it for the bike with 700x32. Silca gave 56/59 and SRAM was 60/64, which would be pointlessly high.

Otto
Yeah, could be. I was using the "worn pavement" setting on Silca and "road" setting on SRAM. Silca gave 69/71 vs 61/65 for SRAM. Sort of proves the point that they are only approximate guidelines based on various different assumptions. The roads I ride are actually very mixed and so no single pressure setting would be perfect for all. But as they are generally on the rougher end of the spectrum I tend to favour lower pressures.
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Old 05-25-22, 05:56 AM
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the range might also be limited to the size of tube being used (if using a tube) . A road tire stuffed with a tube bigger than recommended might be capable of pushing the tire out from the rim before reaching an engineered psi threshold.
Safe bet to stay within the average min/max range if the optimum PSI is unknown & the riding weight isn't on the heavier side.
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Old 05-25-22, 08:03 AM
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fwiw - after reading the tire sidewall, I use trial & error. I also consider what/where I'll be riding. meaning, strictly pavement? or an I gonna get adventurous & ride the road bike on some hard packed dirt, etc. also, my front tire is lower than the rear. maybe 5-10psi
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Old 05-25-22, 09:49 AM
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The big problem with most of these onlie calculators is the assumption of nearly 50/50 F/R balance. Anyone who has measured with scales knows this is bogus even for shorter riders who tend to have a somewhat more neutral position over the wheels. If 50F/50R were true, tire wear would be about equal and I don't know about anyone else but I get close to twice the miles out of a front tire. And, I brake mostly with the front so braking isn't the factor. Being tall exasperates F/R bias but something to consider.

I think the correct pressure is the highest that you can ride comfortably. With 25mm tires and 220 lbs, that ranges from 75 to 89 psi depending what bike I am on and what roads I am doing that day.
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Old 05-25-22, 10:52 AM
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Originally Posted by Troul
the range might also be limited to the size of tube being used (if using a tube) . A road tire stuffed with a tube bigger than recommended might be capable of pushing the tire out from the rim before reaching an engineered psi threshold.
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.
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Old 05-25-22, 12:04 PM
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Originally Posted by GhostRider62
The big problem with most of these onlie calculators is the assumption of nearly 50/50 F/R balance.
I havenít 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. Iíd 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
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