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Clydesdales/Athenas (200+ lb / 91+ kg) Looking to lose that spare tire? Ideal weight 200+? Frustrated being a large cyclist in a sport geared for the ultra-light? Learn about the bikes and parts that can take the abuse of a heavier cyclist, how to keep your body going while losing the weight, and get support from others who've been successful.

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Old 04-16-11, 11:23 AM   #1
magohn
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OT: Use a Shox pump on a schrader valve?

I recently bought a Trek Fx 7.3 with 700c tires/tubes. The tubes are "schrader" valved (car type). I have an old topeak MTB shock absorber pump that is both tiny and has a pressure gauge built into it. Can I use this pump on the Trek's tubes?

Also, would there be any disadvantage to switching out the tubes to "presta" type?

Thanks much.
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Old 04-16-11, 11:53 AM   #2
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whether or not you cna use that pump depends on if it can deliver high enough pressure vs high volume. As for changing out tubes, many people run presta valves in shrader rims, some people choose to put a piece of tape around the valve hole as a precaution but I've heard of others not bothering to do so.
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Old 04-16-11, 12:46 PM   #3
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Originally Posted by magohn View Post
Can I use this pump on the Trek's tubes?
If the pump will connect to the Schrader tubes, you can use it. The problem with a shock pump is that it is designed for very low volume and very high pressures, so it will take forever to inflate a completely empty tube. My Topeak Road Morph takes approximately 100 strokes to go from 0psi to 100psi when inflating a 700x25 tube. Based on the volume of the pumps, I would expect that a shock pump would take 5-10X more strokes to fill the same tube.

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Also, would there be any disadvantage to switching out the tubes to "presta" type?
Presta inflation stems are smaller than Schrader stems. Ideally, you need to install a shim or grommit in the rim before installing a Presta tube. In theory, if you don't install the shim the Presta stem might move around enough to get damaged. I've no idea if this really happens or not... but then again I've always used the shims.
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Old 04-16-11, 04:23 PM   #4
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The only reason I could ever think of for switching from Presta to Schrader valves would be the ability to compleatly deflate the tube so I could pack it up and fix it at home. I carry spare tubes when I ride and do the patching at home. I just switched to valve caps with a core tool built in and I solved that problem.
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Old 04-16-11, 04:36 PM   #5
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I switched over to presta-valved tubes on the Fisher, only because I come from a road bike background, and that was the kind of pumps I had. Since then, though, my latest floor pump has a universal chuck, so I guess it doesn't matter anymore, except for my frame pumps.

Either way, I've seen no real advantage to either, other than availability of tubes sized for your tires. Schraders allow you to fill up at gas stations, but that's a practice that's fraught with pitfalls - those pumps are made to move a lot of air and you can blow out a bike tire in no time. Prestas, on the other hand, don't deflate from high-speed centrifugal force, as John Howard learned the hard way when he tried to set the bike speed record many years ago. Not that we have *that* particular problem.
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Old 04-16-11, 05:13 PM   #6
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Originally Posted by sstorkel View Post

Presta inflation stems are smaller than Schrader stems. Ideally, you need to install a shim or grommit in the rim before installing a Presta tube. In theory, if you don't install the shim the Presta stem might move around enough to get damaged. I've no idea if this really happens or not... but then again I've always used the shims.
Presta valve stems are metal so evenif they move around a bit they shouldn't get damaged which is why I think many people report not putting anything in the valve hole and not having problems. OF the people that do put something in the valve hole, it's probably a case of rather being safe than sorry. I would think once the tire is inflated, it's pushing against the tire, it's not going to move around a whole lot or get caught up in the valve hole but I suppose it's possible.
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Old 04-16-11, 05:36 PM   #7
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Thanks guys - I never thought of the smaller capacity of the shox pump being an issue with regards to amount of pumping to pump. I think thats a deal killer.

The reason I am curious is that my road bike has presta and my new hybrid has schrader - I guess I will have to buy schrader speciific mini-pump for my panniers bags until I get around to switching out the tubes for presta's.

Thanks again, magohn
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Old 04-16-11, 06:30 PM   #8
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Originally Posted by motobecane69 View Post
Presta valve stems are metal so evenif they move around a bit they shouldn't get damaged which is why I think many people report not putting anything in the valve hole and not having problems. OF the people that do put something in the valve hole, it's probably a case of rather being safe than sorry. I would think once the tire is inflated, it's pushing against the tire, it's not going to move around a whole lot or get caught up in the valve hole but I suppose it's possible.
Yes, it is possible. In fact, I've had something similar happen to me. When I built the wheels for my touring bike, I decided to try using Velocity's VeloPlugs rather than rim tape. The notable problem with this system is that there is no protection around the hole where the valve stem goes through the rim. Sure enough, every tube that I installed developed a leak near the base of the valve stem within short order.

A good cloth rim tape will help prevent problems like these... but it's still not a bad idea to install a shim or grommet. Let me tell you from experience: successfully patching a hole near the base of the valve stem is not easy.
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Old 04-16-11, 06:37 PM   #9
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Hahahaha!...........I had this one cheap dude taht would ride with us cause I carrried a frame pump. Very annoying, even came to th epoit where he started asking to borow tubes.:ek:

I finally told him, if he couldn't be self sufficient that I'd rather he didn't ride with us cause I can't afford to SAG for him week after week. So he got the cheapest pump he could find which was a shock pump. One day a lady walking in the park with her little kid on an itty bity bike (waterstop) asked if we had a pump. Trying to be Mr. Romantical Superhero he immediatley shouted out "YES!

He looked at me and I gave him that "you said yes" look.

We sat there for about 20 mintues while he hacked away like a jackrabbit trying to pump up the itty bitty tire. After the incident he said, "I need anew pump".
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Old 04-16-11, 07:31 PM   #10
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Originally Posted by magohn View Post
Thanks guys - I never thought of the smaller capacity of the shox pump being an issue with regards to amount of pumping to pump. I think thats a deal killer.

The reason I am curious is that my road bike has presta and my new hybrid has schrader - I guess I will have to buy schrader speciific mini-pump for my panniers bags until I get around to switching out the tubes for presta's.

Thanks again, magohn
Many mini pumps go both ways.
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Old 04-16-11, 08:02 PM   #11
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We sat there for about 20 mintues while he hacked away like a jackrabbit trying to pump up the itty bitty tire. After the incident he said, "I need anew pump".
ha! - I see a trip to the LBS in my near future. Pumping air isnt my fav past-time as it is

Thanks all.
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