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2 Weeks off Bike - Rear Tire Pressure Way Down

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2 Weeks off Bike - Rear Tire Pressure Way Down

Old 07-28-19, 09:21 PM
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puma1552
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2 Weeks off Bike - Rear Tire Pressure Way Down

Recently swapped wheels/tires and am running 25mm GP 5000 clinchers, with Conti Race 28 butyl tubes in the smaller 18-25mm size. Not the Conti Race Light tubes, just the regular Race 28s.

I run my front at 80 psi, rear at 90 psi.

I noticed from the onset that the rear bleeds pressure quicker, can be 10 psi or close to it overnight the first night, and then drops off more slowly after that. Front drops maybe 5 psi the first night, and less after that.

I've been off the bike for 2 weeks, and thought just now to check the pressures. The front was at 60 psi (seems perfectly fine for that length of time), but the rear was down to just under 35 psi, which seems way low to me.

I understand tubes at higher pressures will drop quicker as air permeates out through the pore tubes, but is this normal? Or can I expect that I have the world's tiniest leak in the rear tube?
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Old 07-28-19, 09:37 PM
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If the valve cores are removable, I'd pull them out, and clean them.
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Old 07-29-19, 09:10 PM
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Not sure if they are, but the tubes are new so should be nice and clean.
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Old 07-29-19, 10:49 PM
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On occasion, valve cores aren't tightened enough in brand-new tubes. You might try tightening it a bit.

Even though the rear tire started at a higher pressure, it shouldn't lose air so fast as to beat the front tire to 35 psi. Might be good to check your rear tire for any tiny shards embedded in the tread that could be causing a very slow leak.
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Old 07-29-19, 11:25 PM
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Originally Posted by puma1552 View Post
Not sure if they are, but the tubes are new so should be nice and clean.
Yes, they should be perfectly clean, but that's not always the case.

Remove, clean, and install the valves again.

Eliminate possible problems, or just replace the tubes(after checking the tires for things that caused a puncture).
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Old 07-30-19, 03:21 AM
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You have Conti tubes and you don't know if you have removable valve cores?
Of course you have removable valve cores. You have not prepped correctly. Check valve cores.... ..... .....
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Old 07-30-19, 08:40 AM
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Can I tighten the core without removing the wheel/tire/tube? Guessing the answer is no?
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Old 07-30-19, 08:47 AM
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Answer is YES
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Old 07-30-19, 08:55 AM
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Originally Posted by puma1552 View Post
Can I tighten the core without removing the wheel/tire/tube? Guessing the answer is no?
Yes.
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Old 07-30-19, 09:18 AM
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Originally Posted by puma1552 View Post
Can I tighten the core without removing the wheel/tire/tube? Guessing the answer is no?
You see the opposing little flat spots on the smaller set of threads? Them's for removing/installing the removable core.

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Old 07-30-19, 09:21 AM
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I use two pairs of needle-nose pliers and gently turn them together. The amount of movement you can get with a light touch is all it takes.
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Old 07-30-19, 10:35 AM
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My last batch of Conti tubes all had loose cores.
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Old 07-31-19, 10:30 AM
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I got on a bike, yesterday, that I hadn't been on since April. The tires were in tip top pressure. I was puzzled for a moment, and then remembered that bike shares a wheel set with the bike which was active last week.
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Old 07-31-19, 08:29 PM
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Thanks guys, and thanks @WhyFi for that diagram...I checked both front and rear, and oddly enough I was able to tighten both of them about half a turn, so I did that and pumped the tires back up. Will see how that goes, guess I know now to always check that on new tubes.
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Old 08-01-19, 04:38 AM
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Originally Posted by puma1552 View Post
Thanks guys, and thanks @WhyFi for that diagram...I checked both front and rear, and oddly enough I was able to tighten both of them about half a turn, so I did that and pumped the tires back up. Will see how that goes, guess I know now to always check that on new tubes.
Yeah.. it's especially fun to find they're not tightened enough when roadside, after fixing a flat, and you have a screw-on pump head -- then when removing takes the core out at the same time.
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Old 08-01-19, 06:34 AM
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Originally Posted by Sy Reene View Post
Yeah.. it's especially fun to find they're not tightened enough when roadside, after fixing a flat, and you have a screw-on pump head -- then when removing takes the core out at the same time.
That's such a kick in the nuts when it happens.
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Old 08-06-19, 08:38 PM
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Sees to have done the trick. After tightening the cores, pumped the rear back to 90 on Sunday morning and now, Tuesday night, it was sitting at 80, so that seems just right. Much better than before, glad I don't have to deal with swapping a tube.
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Old 08-06-19, 08:46 PM
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Originally Posted by puma1552 View Post
Sees to have done the trick. After tightening the cores, pumped the rear back to 90 on Sunday morning and now, Tuesday night, it was sitting at 80, so that seems just right. Much better than before, glad I don't have to deal with swapping a tube.
Good deal, but now that you have mentioned not changing the tube... a flat tire is around the corner.
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Old 08-10-19, 07:18 PM
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Originally Posted by trailangel View Post
Good deal, but now that you have mentioned not changing the tube... a flat tire is around the corner.
So far I've made it all three seasons since I started cycling without a single one...my luck is surely about to run out, and it surely will be the rear, and it surely will happen when I'm at the turn around point, furthest from my car, and in an area with no shade.
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Old 08-11-19, 04:22 PM
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Originally Posted by puma1552 View Post
So far I've made it all three seasons since I started cycling without a single one...my luck is surely about to run out, and it surely will be the rear, and it surely will happen when I'm at the turn around point, furthest from my car, and in an area with no shade.
Guaranteed to happen now. You've angered the flat gnomes by bragging about not getting a flat.

If I were you, I'd start carrying two spare tubes and a patch kit.

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Old 08-11-19, 07:14 PM
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Originally Posted by puma1552 View Post
So far I've made it all three seasons since I started cycling without a single one...my luck is surely about to run out, and it surely will be the rear, and it surely will happen when I'm at the turn around point, furthest from my car, and in an area with no shade.
You've never had a flat while riding? Practice changing a tube at home, should only take a few minutes.

If you have doubts about a tube you can submerge it in water and look for bubbles.
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Old 08-12-19, 01:27 PM
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Originally Posted by Sy Reene View Post
Yeah.. it's especially fun to find they're not tightened enough when roadside, after fixing a flat, and you have a screw-on pump head -- then when removing takes the core out at the same time.
I've done that TWICE with the CO2 screw on inflator
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