m.c. 

My specialized crosstrail had its first flat, in the rear, after about 3-4 uses. I had the LBS, where I bought it, change the innertube. The one they put in was clearly a different brand/type than whatever came on the bike because the stem was a different color and extended farther out. The rear end has felt like the tire is squishy/moves around, especially in turns. I've also noticed I've needed more air than I used to, even going above what the tire has as max. I asked the LBS about this and they told me there should be no difference. I just figured it was all in my head or the bike was just feeling different as it got used, looser maybe.

Tonight the new tube went flat, I noticed that the tube in it is for a 700x28-35 tire. My tires are 700x38.


Could the fact that the tube is for a smaller tire cause the issues I noticed?


Thanks

10 Wheels

Tubes expand when pumped up.

No Problem.

Find the hole in the tube and relate it to the same spot on the tire.

wschruba

No, a tube with that small of a difference would only suffer from slightly easier puncture flats. It's more likely the cause of the original flat was a puncture, and a small piece of whatever it was was still stuck in the tire, causing the pressure to slowly drop. Squirmy tires are only caused by low pressure.

m.c. 

The new puncture/hole is on the inside, against the rim. I don't know where the original one was.

Thanks

10 Wheels

Flats are part of bike riding...I get one on an average of every 385 miles.

Had 156 on the road, not counting garage flats.

Best to learn how to determine the cause of each one and learn how to patch the hole.

Never had one from the rim tape.

alcjphil

Flat tires always have a common cause. There is a puncture in the inner tube. Finding out where the puncture occurred is part of the detective work that helps find out why it happened. By inflating the punctured inner tube out of the tire you can find where it was pierced. By relating the place where that happened to the wheel and tire you can find the cause. If a second flat occurs soon after a first, it is often because the second one was for the same reason

m.c. 

Since the hole is against the rim, not the tire be from pinching against the rim?

The tape covering the holes for the spokes is intact and there doesn't appear to be any spokes loose or coming through to the tape.

alcjphil

Where in the first post was there any suggestion that the hole in the inner tube was against the rim?
Sorry, i read a the later post and it may be that the later flat was caused by insufficient inflation
Pinch flats are common if your tires don't have enough air

m.c. 

It was in my second post.

james_v

See OP's post #4

alcjphil

I hadn't seen that one, sorry. Sounds like a pinch flat

m.c. 

Thanks. The flats don't really bother me. I know they will always happen. I was really curious as to why my bike felt so different after the new innertube. I think I may just order the specialized tube, I'm guessing the one from them may be the one the bike originally came with.

alcjphil

you have to understand what an inner tube is. It is nothing more than a(more or less) airtight bladder that holds the air inside your tire. If your bike handling feels different, it is because the air pressure in your tires has changed. Changing inner tubes will not change this you have to monitor the air pressure in your tires

m.c. 

I always kept my air at 90 PSI, this is 10 psi less than the max on the tire and what was recommended by the shop. Once the tube was changed I had to go up to 110 for it to feel normal, like it did before the change. Thats why I thought it could be that the new tube was for a slightly smaller tire may have played a factor in this.

Bill Kapaun

Whose pressure gauge? Different gauges can vary wildly.

m.c. 

My bourdon type gauge I've used for years. Even if it isn't exactly accurate it is consistent. Only variable has been the tube.

I am going to try and find the same model tube that came with the bike or put the tube from the front tire into the rear and see what results it provides.

m.c. 

Looks like the original is a Chaoyang 700x38-45 and the replacement is a kenda 700x28-35

zoom996

Make sure the tire bead is seated evenly along the rim. If you see a shift in the amount of tire side wall sticking into the rim then that could cause a "shift" or lumpy ride. Use a dry lube like GT85 to spray along the bead before you air it up to make sure the tire seats correctly. The tube sizes you mention are fine. I would add baby powder to the inside of the tire before adding the tube to allow the tube to seat inside the tire correctly as it airs up as well.

dabac

Well, its your time and effort. But it really shouldn't change anything. Tubes have - for the circumstances - no important amount of structural strength. Try inflating one outside the tire and you'll see.
Expect to face serious questioning if you post here about brand and minor change of tube size having an important influence on ride characteristics. Tire pressure, or tube getting caught between bead and rim, or tire not seating properly are far more likely reasons for your experiences. Even a yet undetected tire sidewall/carcass failure would be more likely.
You wouldn't expect the holding capacity of your dustbin to vary with the brand of bin liner you used, would you?

Trakhak

If you get a job in a bike store, by the time you've fixed a couple of thousand flats, you'll have forgotten any theories concerning mysterious differences between inner tube brands or between nominally different but similar tube sizes. Bike inner tubes are as fungible as it gets.

habilis

In addition to this, smear the entire outside of the tube with baby powder, then inflate it slightly before installing it in the tire. I also carry a powdered spare tube for fixing road flats. I haven't had a pinch flat since I started using the powder.

rm -rf

Tire pressure
On a 38c tire, even 90 psi is more than you should need. 110 psi is way too high.

With 38c, I'd probably start with 65 psi front, and 80 psi rear, and then try even lower pressures. I weigh 170 pounds.

~~~~~
Causes of flats
You need to examine the tube when you get a flat to determine the cause.
--What does the hole look like? A tiny hole, a small slit, a long split?
--Where is it located, top or bottom?
--Check the tire at the hole location: Mount the tire with the tire label at the valve hole. Then, after a flat, you can see how far around the rim the hole is, and can measure off the tire label to see if anything is stuck in the tire where the hole occurred. I've seen very tiny pieces of wire stuck in the tire.
~~~~~
Stretchy tubes
An inner tube easily expands to fit. Try pumping up a tube off the bike. Just a few pumps blow it up like a balloon.

The tire and rim won't stretch, so the tube just expands to fit inside, and there won't be any difference between tubes that would affect your ride.

~~~~~
Squishy in turns
Maybe you are just getting more used to the bike's handling, and are noticing more effects? You really don't want to pump the tires rock hard, they need to absorb bumps instead of bouncing over the bumps.

Are you riding on paved roads when you feel the squish? Do the tires have knobs? Maybe you are going faster and are leaning over more in the turn. Knobs would feel squishy.

~~~~~
Pump
I suppose your pump could be way off on it's gauge. But that's very unusual.
When pumped up, you want to be able to press hard on the tire with your thumb and feel it push in a little. It shouldn't be rock hard.

EDIT-- You use a separate pressure gauge? Doesn't your floor pump have a gauge?

m.c. 

I replaced it today with a tube in the proper range for my tires. All squishy-ness is gone. Feels normal again. Went to a different shop, guy said having tire even slightly larger than the tube range will cause what I was feeling. Especially since I am heavy, 250lbs. confirmed I need to have it around 90 psi.

All is well again.

02Giant 

I run 18-23 tubes in my 25's no problemo.

Wanderer

the "guy" is an idiot - find another shop to do business with!