Mickmeister

I'm new to biking and I'm now teaching myself how to change the inner tube in case I get a flat. I just noticed that the spare tube that my LBS sold me is the right diameter (27.5), but the wrong width. My bike's tires say they're 2.1", whereas the new tube says it's 1.75". Do I need to exchange it for a 2.1?

dabac

It will be fine.
Tubes have very little strength in themselves and simply stretch until stopped by the tire.
An undersized tube will have to stretch more, making it thinner. And in theory more prone to punctures. I’ve never mer a rider claiming to actually notice this in use.

Berg417448

It will probably be just fine. In the past I have actually used 26" tubes in a 29er MTB tire because it was all that I had at the time and it worked fine.

Iride01 

Usually tubes will specify a range or widths they are intended for. So that will assure you if the tube is appropriate.

Even if you have a tube that is outside that, then just try to determine if it will be wrinkled or kinked inside the tire. If it is, then that will just be more wear on the tube and a future flat. Also, if it's wrinkled or kinked bad enough the tire won't be supported evenly throughout by the pressure in the tube and you might perceive it as being bumpy on smooth roads.

In a situation where you have to ride and have nothing else available, anything goes. It's only 4 to 6 dollars.

Mickmeister

Ahh...I went back and read the label again and there IS a range...1.50-1.75. So...it sounds like it would do in a pinch, but if I go through the hassle of changing it on the road, I don't want to have to do it again when I get home using a more appropriate size. So I guess it's off to the shop to exchange it!

Thanks to all for the advice.

Camilo

I always use a tube that is one size smaller than the tire. They're easier to install without bunching up, are smaller to store in the saddle bag and (last and least) are a little lighter. I have never noticed any difference in puncture resistance - I think that 99.9% comes from the tire itself.

In the "is the tube too small for the tire" dep't: My wife now has a 650B (AKA 27.5) gravel bike. I use 26" inner tubes because it's hard to find small-ish 27.5 innner tubes. She's riding 35mm (1.3") and it's hard to find 27.5" inner tubes that small, let alone a little smaller. The 26" tubes are very easy to install and seem to work perfectly.

Warbird21

After two recent flats, getting the right tube has been puzzling to me. I learned a range works.
On the left, my OEM and on the right, the replacement I bought. I'm told both work and I guess the new, smaller tube takes up less space.

Iride01 

Academy Sports and other big box discount stores sell these. Here is one that I think is in your size. I use the Bell 700C tubes for my bikes and I've had good results from them. Not a light tube but not the heaviest. Inexpensive and last a long time if you don't ride on thorns.



Bell Standard Bicycle Inner Tube $4.99

Note that it is a Schrader valve.