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Old 07-22-02, 10:51 AM   #1
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Tube questions / Presta question

I have a few questions about tubes. I have 700/30-32c tires on my Marin Sausalito. The tires are "Alterrainasaurus" and are an external tread thin hybrid style. When I bought the bike, the shop threw in a couple free tubes. The size of the tubes is 700/35. I went to a bike shop to buy other tubes. They offered to sell me some 700/28s which woudl fit my application. I declined because I feel like these people may be offering what is more convenient for them, but not ideal for my bike. I would like to eliminate flats, bent rims, etc as much as possible.

I'm curious what is the best size tube to use and what are the dis/advantages of using other sizes?

Also I figure 700 is the diameter in mm (rim/ID of tube?). 30 I'm guessing is the width in mm, correct? What is the second width # (followed by a c) ? Is the first one tread width and the second one sectional width? Which one woudl I use to choose a tube?

What is the best brand of tube to use, I would like to assure myself as few problems as possible and I don't mind spending a couple extra bucks for a good quality tube. Are some brands better than others?

Presta question - it looks like to fill the presta valve I need to unscrew the little thing at the top of it (the top of the valve, I'm not talking about the valve cap). How many turns is recommended?


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Old 07-22-02, 11:23 AM   #2
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Hi robzr, welcome to the forums!

Those Allterrainasaurus tires are a nice design, Marin deserves a pat on the back for spec'ing those

I used to be a weight weenie and tried to save weight by using... *twitches involuntarily* ... 700 x 19 tubes in 26" x 1.7" Smoke Lite mountain-bike tires. The moral of the story is that tubes can stretch a bit to fit bigger tires, if they have to. However, this stretches them thinner, making them more prone to seam failure, puncture and impact flats ("pinch flats"). If possible, look for tubes designed for 700 x 32-35 tires, they will not have to do so much stretching. If you needed to use a 700 x 28 on a temporary basis, it would get the job done.

The Presta valve's center pin is held shut by the little knurled guy. You can back it off until it reaches the end of the pin... usually it won't come off because the end of the pin is crimped to prevent this. After it's backed off, you can use a Presta-type pump to pump it up directly, or use a Presta-to-Schrader adapter to convert it to an automotive-style valve. When using an adapter, screw it on until the O-ring begins to make contact with the larger-diameter part of the stem, then give it another 1/2 turn. If you screw it on too far, the valve's center pin may stick out far enough to prevent good sealing with an air chuck on a hose. I'd recommend taking the adapter off and closing the knurled cap down snug when you're done, to seal the valve.

As for brands of tubes, even cheap ones from Taiwan and China will get the job done. Continental and Michelin would be a couple of "premium" brands that come to mind, if you want something that's "brand-name."

The 700C x 35 designation... 35 is the nominal width of the tire in millimeters. 700C is a wheel-size standard. As I understand it, there was a 700, 700B and 700C. Originally, the outside of the tire was the size being measured, and different sizes of 700 tires therefore had to have different rim sizes to achieve the same outside "rolling" diameter. Now we are using a 700C rim, based on 622mm bead-seat diameter, and the outside diameter of the tire is what varies when different tire sizes are fitted to the rim. Hope that sort of makes sense.

Last edited by mechBgon; 07-22-02 at 11:26 AM.
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Old 07-22-02, 11:25 AM   #3
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For the Presta valve, just unscrew it until it stops.

As for tube size - Most tubes have a size range, not just one specific size - for my road bike they say 18-25mm, or on my mountainbike they say 1.8-2.0. If your within that range you should be ok, however I ran 1.8-2.0 tubes in my 2.2 tires for the longest time witn no problems, but I tried to put a 35mm tube in a 25mm tire and it was'nt pretty. I would say you could go a little smaller with the tubes, but not bigger.
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Old 07-22-02, 11:59 AM   #4
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Pick a tube with a range covering your size, but opt for smaller rather than larger.
I just got a Continental 28 to 47 inner and it is way to big for my 32mm tyres. I replaced it with 25 to 32 which fits the 32 about right.
I usually just undo the presta nut a few turns. If you press the needle and air comes out, it is undone sufficient for pumping up.
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Old 07-22-02, 07:07 PM   #5
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When inflating a tyre, I find it helpful to press on the tip of the Presta valve to let out a short burst of air before I attach the pump. If I do not, the valve may stick and resist me for the first several strokes.
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