Cush Core setup seems to lose pressure faster than I'm used to

[Myfingersaresore]

I've searched around the Cush Core website and here on EMTB, but I'm not finding anything about this.

My other bikes with a non-Cush Core setup hold pressure for a week within a couple of pounds, but my Cush Core setup seems to lose 5 lbs or more in a week. I'm running 25 PSI front and rear.

Is anyone else seeing this?

 

[Richridesmtb]

I messed around for ages trying to figure out why one of my tyres kept going down. Turned out to be the valve core leaking. Only found it during a wash. Check them.

 

[Myfingersaresore]

Well. I’d go through my logical deduction of what could cause it and are there any signs supporting it.

1. Did I fuck up my rim tape?

2. Is sealant leaking from the sidewall?

3. Is sealant leaking from the stem?

once you can answer those you’ll be able to attack the problem or problems. If you can’t do it by eye a bathtub always helps. (Don’t let your wife see).

All reasonable; I was hoping to avoid any work on my part, lol. Thanks!

 

[Growmac]

It makes sense that it would lose pressure faster, all else being equal. You've reduced the volume of air in the tyre by 30-50%. That means that the same absolute volume of air lost is a larger % of the total volume, therefore a larger pressure drop. I top up my tyres weekly, I just view it as the price to pay for zero hassles on the ride itself.

 

[Clubby]

Did you add a larger amount of sealant when you set it up? Rimpact advise an extra 50% to account for the larger surface area inside the tyre with the insert in.
No difference on my two bikes running inserts compared the ones without. I did have the same as you and when I took the set up apart again, I found a small bit of rim tape had torn during the instal. Retaped the wheel and it’s been fine.
Like the others have said, I’d tighten the valve stem ring and check the valve core is tight first though. Eliminate the easy stuff first.

 

[RustyMTB]

It makes sense that it would lose pressure faster, all else being equal. You've reduced the volume of air in the tyre by 30-50%. That means that the same absolute volume of air lost is a larger % of the total volume, therefore a larger pressure drop. I top up my tyres weekly, I just view it as the price to pay for zero hassles on the ride itself.

Absent a leak, this is the answer. Smaller loss of air but larger proportion.

 

[Myfingersaresore]

It makes sense that it would lose pressure faster, all else being equal. You've reduced the volume of air in the tyre by 30-50%. That means that the same absolute volume of air lost is a larger % of the total volume, therefore a larger pressure drop. I top up my tyres weekly, I just view it as the price to pay for zero hassles on the ride itself.

I'm a sucker for science - I did have thoughts along this line, but I didn't have the numbers at hand - thanks!

 

[Myfingersaresore]

Did you add a larger amount of sealant when you set it up? Rimpact advise an extra 50% to account for the larger surface area inside the tyre with the insert in.
No difference on my two bikes running inserts compared the ones without. I did have the same as you and when I took the set up apart again, I found a small bit of rim tape had torn during the instal. Retaped the wheel and it’s been fine.
Like the others have said, I’d tighten the valve stem ring and check the valve core is tight first though. Eliminate the easy stuff first.

My LBS did the installation, so IDK about the amount of sealant. I could add another dose myself to be sure.

I'll definitely check the other easy stuff - thanks!

 

[Myfingersaresore]

I found a bin large enough to swallow a 29" tire up to the top of the valve stem; filled it with water and checked for leaks.

None found.

I put in an extra dose of sealant.

So whatever happens now is likely down to reduced air volume as was suggested.

Thanks for everyone's input!

 

[Pauliemon]

For future reference, use a spray bottle with soapy water. Spray and look for bubbles.