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Tire Pressure issue

Old 03-24-19, 06:22 AM
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RandyJ
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Tire Pressure issue

Hello,
I have 700x45 Bontrager H5 tires and are using a topeak d2 smartgauge to check my pressure. The tire says to inflate to 60 psi/4.1 bar to 80 psi/5.5 bar. I cant inflate the tire to that much pressure. I'm afraid it will blow. tire gets rock hard and 30 psi seems more like it. My tire pump cant even get near to those pressures. Please help, I'm using 30 psi till i figure it out.

Thank you
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Old 03-24-19, 06:32 AM
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30 is pretty low. Try a floor pump with a good gauge on it.
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Old 03-24-19, 06:40 AM
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ill try that thanks
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Old 03-24-19, 06:53 AM
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Two unknown variables. How wide is the tire when mounted on your rims? The size printed on tire is as meaningless as the pressure printed on the sidewall. How much do you weigh? Which also includes what you carry on the bike.

30psi sounds close to me. You're riding it, how does it feel? When going that low 1 or 2 psi makes a difference. Seat of your pants got you to a good starting point, if you are concerned about better than that you will want an accurate gauge.
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Old 03-24-19, 06:58 AM
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Originally Posted by RandyJ View Post
Hello,
I have 700x45 Bontrager H5 tires and are using a topeak d2 smartgauge to check my pressure. The tire says to inflate to 60 psi/4.1 bar to 80 psi/5.5 bar. I cant inflate the tire to that much pressure. I'm afraid it will blow. tire gets rock hard and 30 psi seems more like it. My tire pump cant even get near to those pressures. Please help, I'm using 30 psi till i figure it out.

Thank you
That's the maximum the tires are designed for, not what you should pump them up. My car, for example, has a recommendation of 30 psi, while the tires are rated for up to 60 psi.
There are several calculators to calculate the required pressure based on weight and riding... in the end it needs to be soft enough to be comfortable and hard enough to not strike the rim or have pinch-flats (if you have a tube)
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Old 03-24-19, 07:02 AM
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ignore the minimum pressure printed on the side of the tire. Around 40psi would be right for me but that depends on weight and what your riding on.
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Old 03-24-19, 07:15 AM
  #7  
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Just aim for a small deflection of the tyre/tire when you drop your weight onto the saddle. If you are a very light rider you may be able to use a lower pressure. Remember though that the manufacturer may state a pressure range which it believes offers the best safety and puncture protection and pinch flats. It's perfectly normal for very light riders to go a bit below the stated limits and very heavy riders to go a bit above.
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Old 03-24-19, 07:56 AM
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Originally Posted by RandyJ View Post
Hello,
I have 700x45 Bontrager H5 tires and are using a topeak d2 smartgauge to check my pressure. The tire says to inflate to 60 psi/4.1 bar to 80 psi/5.5 bar. I cant inflate the tire to that much pressure. I'm afraid it will blow. tire gets rock hard and 30 psi seems more like it. My tire pump cant even get near to those pressures. Please help, I'm using 30 psi till i figure it out.

Thank you
Couple things.. What are your wheel dimensions if you can find them on the rim?
You need a new bike tire pump if you can't get it to 80psi; though you shouldn't run these tires at 80psi.
Take a look at the guideline chart below for max ratings for TL tires; I assume you're running with tubes so you can add 10%. eg. For a 19c hooked-bead rim (TC) width, this chart would suggest a MAX of about 72psi.

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Old 03-24-19, 07:57 AM
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Originally Posted by Bonzo Banana View Post
Just aim for a small deflection of the tyre/tire when you drop your weight onto the saddle. If you are a very light rider you may be able to use a lower pressure. Remember though that the manufacturer may state a pressure range which it believes offers the best safety and puncture protection and pinch flats. It's perfectly normal for very light riders to go a bit below the stated limits and very heavy riders to go a bit above.
This. All the science about calculating and measuring pressures is complex... using sag is much better and easy to confirm without tools.
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Old 03-24-19, 08:15 AM
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There is a sticker on the rim it says... Tubeless ready, rim brake only, 6000AL, 622x17. I weight 198Lbs. This is all very good info.
Thanks
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Old 03-24-19, 08:27 AM
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I'd try 60psi and see how it goes. Is bike for pavement riding? While rim says it's tubeless ready, are you running the tires tubeless or are there tubes in there?

Last edited by Sy Reene; 03-24-19 at 08:30 AM.
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Old 03-24-19, 08:40 AM
  #12  
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I have tubes in the tires and ride mostly on pavement. I will try that and see how it goes. thanks
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Old 03-24-19, 11:30 AM
  #13  
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60 is a lot for that tire width, though. I'd get a new floor pump and shoot for somewhere in the middle, like 45psi.
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Old 03-24-19, 11:35 AM
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Originally Posted by RandyJ View Post
Hello,
I have 700x45 Bontrager H5 tires and are using a topeak d2 smartgauge to check my pressure. The tire says to inflate to 60 psi/4.1 bar to 80 psi/5.5 bar. I cant inflate the tire to that much pressure. I'm afraid it will blow. tire gets rock hard and 30 psi seems more like it. My tire pump cant even get near to those pressures. Please help, I'm using 30 psi till i figure it out.

Thank you
I'd never recommend a 700x45mm tire be inflated to either 60PSI or 80PSI, unless it was carrying the space shuttle. That is just an insane pressure range for that size of tire. Specialized recommends similar for their 700x42mm Sawtooth tires which is also nuts.

My 700x42s are usually 30-40PSI depending on the surface and load.
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Old 03-24-19, 12:25 PM
  #15  
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https://www.google.com/imgres?imgurl...DYAyUQ9QEILjAA
Take a look at this chart and there are other charts on the web. This one takes into account rider weight plus bike and assigns a larger proportion of the weight to the rear wheel. Based on that, find your weights on the chart for each wheel and pump away. The pressure you've been using are quite high.
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Old 03-24-19, 12:56 PM
  #16  
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45s are big. I inflate 35s to ~60 for a hard road ride (45psi works just fine) and as little as (say) 30 for gravel. (I always ride to my gravel bringing a pump. The garage is my last pressure check. I;ve run 37s at probably 20 psi on very rough gravel with great success. 40 psi on tires that big is a hard ride on pavement. 45s are a lot bigger than 37s. Volume goes up by the square of the diameter so a 45 is 1 1/2 times larger than a 37. So drop my numbers by 2/3s/ Then multiply by 4/3s as I weigh ~150 lbs. So 8/9s of my numbers for 37c = 90% of what I was riding.

90% X 40 psi = 36 psi; a good weight for you on the road and 90% X 20 psi = 18 psi off road.

Now; tire pressure is also a matter of the tires themselves, your preferences and riding style, etc. But this should get you in the ballpark.

Oh, 80 psi with tires that big will blow the flanges of many lighter rims with brake wear. It will sound like and be as loud as a gunshot and may blow long shards of rim off. I've heard of both chainstay carbon fiber and legs being cut. When mine blew, thankfully I was in the kitchen.

Ben
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Old 03-24-19, 02:43 PM
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All sorts of charts and calculators out there. Not saying 60psi is ideal, but it's a safe starting point (per the tire manufacturer anyway). Schwalbe lists 45-70 on their Marathons, Conti puts 45-65 on their TopContact, Spesh Nimbus lists 50-100, the OP's own tire has 60-80, Michelin Proteks list 36-72.

There's another calculator linked below.. I get a result of 59psi using a 90kg person using their guidelines and the available 44mm tire selection. Certainly the front tire can probably be less by 10lbs or so. I think maybe there's a lot of assumptions though as to what type of bike you're riding (I'm assuming a hybrid), and terrain you're riding. There's also a difference between the ideal comfort/speed recommendations (ie. 15% drop guideline), and what the tire maker thinks is necessary to hold a bead the rim if potentially doing high speed road cornering or tire flank damage from tire compressing to the rim. While I generally understand the 15% drop concept, can't and won't this drop come out of different parts of the tire (eg. bead vs bulging sidewall) as tire pressure changes, in combination with how the tire is actually constructed and where strength or compliance has been built into the tire (sidewall vs bead flexiblity or inflexibility)?

https://www.bergfreunde.eu/bike-tyre...re-calculator/

Last edited by Sy Reene; 03-24-19 at 02:49 PM.
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Old 03-25-19, 09:42 AM
  #18  
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Originally Posted by RandyJ View Post
There is a sticker on the rim it says... Tubeless ready, rim brake only, 6000AL, 622x17. I weight 198Lbs. This is all very good info.
Thanks
So, first, there's no way in hell 30 psi should be hard to pump, or that a 45mm tire should be hard at 30psi. I suspect gauge issues. Take your wheel to an LBS, have them inflate to 45psi, and check with your gauge. If the the gauge reads 45psi, and the 45psi tire is harder than what you experienced at "30psi", and , then your experience in judging hard vs soft tire inflation has been improved and you need a new pump. If your gauge reads a lot less than 45psi, then you need a new gauge.

BTW, your specs are for the rim. The tire is another beast.
Tubeless ready > The H5 is not a tubeless-ready tire, so you should have an innertube.
rim brake only> I think that this pertains to the strength of the rim. Don't use this rim in a wheel with disk brakes
6000AL> 6000 series aluminum, which is what most bike aluminum is.
622> Means you have a 622 bead seat diameter, which means a 700c rim.
x17> Means your rim width is 17mm. This is a bit small for a 45mm tire. Was this tire original issue? Are you "upgrading" the bike by using a wider tire? Probably ok, but for 45mm I'd like a 19 or 21mm rim.

Last edited by WizardOfBoz; 03-25-19 at 09:48 AM.
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Old 03-25-19, 11:08 AM
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Not that this is relevant to the discussion, but I'm curious about that "rim brake only" warning. Can't think of a single way that disc brake usage would stress a rim more than it can be stressed in rim brake usage on the rear. It would be nice to know the brand and model.
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Old 03-25-19, 11:39 AM
  #20  
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Originally Posted by ThermionicScott View Post
Not that this is relevant to the discussion, but I'm curious about that "rim brake only" warning. Can't think of a single way that disc brake usage would stress a rim more than it can be stressed in rim brake usage on the rear. It would be nice to know the brand and model.
Wondering myself. The early disc brake wheels usually had both options.
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Old 03-25-19, 02:12 PM
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After doing some reading on the forums and online I decided to put 40 lbs in the front tire and 45 in the rear tire. As of right now it seems like I found the sweet spot. I'm sure I will be adjusting the pressures accordingly.
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Old 03-26-19, 03:54 PM
  #22  
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Rock hard at 30 psi doesn't sound right to me.

My first suggestion would be to check your pump or whatever you are using for a gauge against a different one.
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Old 03-26-19, 07:54 PM
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Concerning the sticker saying rim brakes only. Disc brakes do put more stress on the spokes and their attach points at the rim and hub. So I'd imagine the mfr considers the spoke holes in the rim not beefy enough for that extra stress.
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Old 03-26-19, 08:03 PM
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The Bontrager H5 tire is a pretty thick hybrid tire with a puncture protection layer under the tread. This puncture protection layer is either very thick, very inexpensive, or possibly both, because it's not very pliable. I have a set of 35mm H5 tires on one bike, and have ridden them in 26x2 size, and they're the opposite of "supple". I can see how someone would describe them as "rock hard" if pressing straight down on the tread -- there's very little give, even when the tire isn't even mounted to a rim!

I'd probably ride these just like the OP is -- in the 35-45 psi range.
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Old 03-26-19, 08:08 PM
  #25  
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60 PSI is way too much for a 45 mm tire.
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