plgcp

I have 2 questions:

I got a new cross bike recently and just got road tires for it. I just changed one of the tires, which was my first time ever changing a tire. Once I had the old tire off I noticed that the tube is "longer" than the rim - ie if I put the stem through the hole in the rim and hold the wheel vertically the tube hangs lower than the rim at the bottom. Is this normal or should the tube fit snugly on the rim? The tube is the correct size (700x28-32) with the tires being 28mm. As a result, when I installed the new tire, at one point I had to stuff the "extra" tube in and this seems to have caused a bulge in the tire once inflated. The bulge is quite noticeable when I spin the wheel.

Secondly, I just received a Lezyne Sport Floor Drive pump. When I connect the flip chuck to the presta valve of an already-inflated tire, the gauge on the pump remains at zero. If I pump a few times it rises to about 20psi even though the tube is likely at about ~80 psi. Basically the gauge only seems to measure the air I'm adding as opposed to indicating the pressure in the tube. I assume that this is not normal... is there likely something wrong with the gauge/pump?

Thank you.

dabac

Tubes have basically no structural strength in themselves. They don't need it, as in use there's always a tire and a rim there to to contain them. The consequence though is that outside the confines of the tire, even a little bit of air pressure will cause them to stretch and expand.
Tubes that are a tight fit to the rim can make it quite difficult to install the tire.

Bill Kapaun

Are you unscrewing the tiny nut on the end of the valve and "burping" the pin slightly??
Make sure you are sliding the chuck onto the valve stem far enough.
Some pumps have 2 holes. one for Presta and the larger one for Schraeder valves.

IF you add a slight amount of air to a tube, it should "snug up" a bit around the rim.
You'd probably be better off to look for a tube marked 25-28mm next time.

10 Wheels

Did you Open the Presta Valve before connecting the pump?

woodcraft

Reinstall the tire, with the tube inflated just slightly. 'Shrinking' rather than stretching the tube as you place it in the tire/rim, to avoid a fold at the end.

The tire may not have been seated properly on the rim, possibly because of some tube being pinched between the bead & the rim. Once the tire is installed, inflate to a few pounds and work around the rim, pushing the tire over from both sides to check for and release any pinched tube. Then add more air & spin the wheel, checking that the tire is seated evenly to the rim.

Before pumping, make sure that the presta screw is open and if necessary 'burp' the valve- it can get stuck in the closed position.

FBinNY 

1- tubes are longer than rims partly because they sag (and stretch a bit under their own weight. Also, they are sized by fit within the tire which is a larger diameter than the rim. It's nor,mal and OK. In fact, those who install plenty of tubes will tell you a longer tube is far more preferable to a short one which keeps pulling down into the area where it's most likely to get linched on installation.

2- Presta valves are simple check valves. When the air in the hose is greater than that in the tire it opens the valve and flows through. When it's lower outside, the internal pressure pushes the valve closed. So you won't get a pressure reading until you pump enough to open the valve and allow flow.

BTW- in case you haven't crossed this bridge yet, PVs often stick when they've been closed a while. So it may be necessary to "burp" the valve by letting a bit of air out before fitting the head. Otherwise you'll be struggling against a valve that simply won't open with the air pressure alone.

plgcp

Thanks for the replies.


Before installing the new tire I read the relevant comprehensive Sheldon Brown article so I think I took most of the recommended steps. I put about 2 pumps worth of air into the tube before starting just for it to take a round shape.
I'll pull one bead of the tire off and try to determine whether the tube is seated properly. It is good to know that it's normal for the tube to seem too long.


To answer some of the questions about my steps with the pump, I am sure that the presta valve was unscrewed all the way and I did tap the end to "burp" it. Also, the chuck on the Lezyne pump is threaded and I threaded it onto the stem valve as far as it would go. I tried both the front and rear tires and in neither case did the gauge move when I connected it and it only rose to the extent that I pumped. FBinNY mentioned having to pump enough for the valve to open. Does this mean that I should not expect the pump gauge to display the amount of pressure in the tube upon connection?

FBinNY 

Yes, when you start, there is more pressure in the tube than the pump hose or head. So the valve will be closed, the same way it was before you attached the pump. It won't open and equalize pressure until the pump side has more pressure than the tube side.

This is a one way relationship. Air in the hose can flow into the tube, but air in the tube cannot flow back into the hose.

Bill Kapaun

Presta valves are NOT threaded. Some have "ridges".
You simply PUSH the pump head on firmly and lock the lever if equipped.

FBinNY 

Huh?!

If Presta valves aren't threaded, how do valve adapters attach?

Of course the valve is threaded. Though most PV pump heads are push on, most hoses thread on.

Bill Kapaun

You're right-
I was thinking about regarding the pump head and totally forgot the nut.

howeeee

yea they are threaded, you can put a schraeder adapter on them, adapters are threaded

FBinNY 

There are two threads.



The larger fine thread that runs the entire length, though many modern valves are smooth here.
And the smaller diameter thread ar the business end, which accepts a valve cap, PV adapter, or threaded pump hose. To my knowledge, all valves still have this thread.

plgcp

Update, mainly for any other noobs who find this thread.
The issue I was having with the tube seemingly not stuffing into this tire properly as well as the uneven rotation when I spun the wheel with the tire newly installed resolved themselves. I had followed Sheldon Brown's suggestion and inflated the tube to only about 30 psi to inspect for bulges after getting the new tire on. At this point both tires seems to have bulges as they didn't rotate true. I couldn't seem to correct this so I went ahead and inflated the tubes to 95 psi. When I reached about 80 psi during inflation there was a sort of pinging sound. Turns out this was everything sorting itself out. Now both tires rotate true.