Mountain Biking - Tube size?

I have Alex DH 20 rims and my tires are specialized 26x 2.00 What size tube do i need? Do i go by tire or rim size?

Go by the tire size. Tubes will have a range of tires it can fit (i.e., 26x1.75-2.25). Just find the tube that accommodates your tire size.

One of the mechanics at my LBS (he's also a pro cyclocross racer), gave me the following advice (not just for mtbs but for road-bikes also):

For a given size of tyre, to go for the smallest tube possible in order to minimize weight, remember an ounce off the rim is worth at least two off the bike.

- Wil

One of the mechanics at my LBS (he's also a pro cyclocross racer), gave me the following advice (not just for mtbs but for road-bikes also):

For a given size of tyre, to go for the smallest tube possible in order to minimize weight, remember an ounce off the rim is worth at least two off the bike.

- Wil

Well if you're running 2.7 tires and you put a 1.5 tube in it, the tire will come off the rim while riding and it will be a real pain to deal with (not to mention the tube would probably get pinch flats and go flat from hitting the sides of the rim while it bounces around).

Well if you're running 2.7 tires and you put a 1.5 tube in it, the tire will come off the rim while riding and it will be a real pain to deal with (not to mention the tube would probably get pinch flats and go flat from hitting the sides of the rim while it bounces around).

Well, what you say is interesting. It would seem from your response that perhaps you are not speaking from experience… Would you care to explain exactly what you think might happen when you inflate a 1.5 (or any tube, for that matter) outside a tyre…

- Wil

Tube outside a tire: It expands and explodes (talking from experience, one less DH tube too..).

I've accidently bought too small a tube and it rode like crap before I noticed it, although your point about it saving weight is true, this isn't the greatest thing to do if you're hitting jumps and drops.

Fair enough…

…but how big did it get before it exploded?

- Wil

Fair enough…

…but how big did it get before it exploded?

- Wil

Well it was a 3.0 DH tube so it got pretty damn big. :D

Half the tube manufacturers in Asia only make two sizes of 26" tubes. The other half do actually make three. Many Tire/tube distributors list their tubes as 26x1.5 - 26x1.75, 26x1.80 - 26x1.95, 26x2.0-26x2.125, 26x2.2-26x2.5 showing four sizes but they actually label the exact same tube in more than one box to get the shops to stock more sizes. When I worked in the industry 14 yrs ago we boxed two tubes in three different boxes to cover the tire size range back then. Since then of wider sizes have been added. Remember most of the factories made tubes for 26x1.75 and 26x2.125 for wide tired street bikes long before the mountain bike was in existance and they continue to make those sizes and market tubes from those same molds. Let's face it a 26x1.5" tube will expand to fit in a 26x2.1 tire just fine. That's what I've got in mine. The rubber may strectch a bit more but it works fine.

This indeed is an eye-opener! Thanks a lot gm for the inside information...

Let's face it a 26x1.5" tube will expand to fit in a 26x2.1 tire just fine. That's what I've got in mine. The rubber may strectch a bit more but it works fine.

Like you said, with your setup the rubber will stretch and the tube walls will be thinner. This will result in an increased likelihood of punctures, especially pinch flats.

Can honestly say in all my years of riding, including the prehistoric days before front suspension I've never had a pinch flat on mountain bike. During the pre-suspension era we ran our tires at between 32 and 35 PSI for better bite and a softer ride.

I ran 1.5 tubes in both my 2.4 motoraptors and my 2.35 minions all season and only got one flat that I can remember. Those big DH tubes are overkill IMHO.