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I've been procrastinating for several years about converting from Presta to Schrader on my Trek 4200 with Bontrager AT650 (erto 559x19) wheels. What finally convinced me was getting three flats on a recent ride. I had only one spare tube and getting a repair shop here in Thailand to deal with the Presta valves was a challenge; even though I had an adapter.

What still concerns me is assertions that doing so will weaken the rim.

I also have a Trek 7.2 FX which uses Bontrager AT750 wheels which have much narrower rims but use Schrader valves.

Does Bontrager do something special with the 750s that enables them to use the larger valve stem hole without weakening the rim?

Or, will I be OK drilling the 650s out to 8.5mm?

Buadhai
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    Possible duplicate of Schrader tubes in Presta configured Rims? – mattnz Nov 15 '19 at 04:20
  • I was going to post there, but the guidelines seemed to indicate that I should ask a new question. So I did. Sorry, my first time posting here. – Buadhai Nov 15 '19 at 04:41
  • Its the same question as the suggested dupe, but differs in your exact rim construction. All the answers there apply just as well, so on that basis it is a dupe. Your other option is simply to lay in a supply of presta tubes - a 10 pack would be reasonable, and order more when you get down to your last 3. Or learn to patch tubes yourself - its not hard. – Criggie Nov 15 '19 at 09:55
  • @buadhai do also take a moment to browse the [tour] if you haven't seen it already. The site is a Q&A format, so quite different to a common chatty web forum. – Criggie Nov 15 '19 at 09:57
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    To extend @Criggie's comment, patching tubes is very easy; there are many videos on YouTube that will explain the process. Unless you were very unlucky, three flats on one ride suggests an underlying problem. Either your tyres are very worn, which makes it easier for sharp items to penetrate, or you didn't remove the penetrating item after the first puncture. – David Richerby Nov 15 '19 at 10:01
  • I get more flats than anyone I know. Dozens per year. My success rate at patching inner tubes is around 33%. I always stockpile spare tubes. On the trip referred to above I got one flat from a tiny wire in the front tire (120 tpi Kevlar), a flat in the rear tire from a tiny thorn and anther flat in the front tire from a source I never identified in spite of removing the tire and doing a visual and tactile inspection. I don't believe in bad luck, but I do believe that some people just end up at the wrong end of the bell curve when it comes to frequency of bicycle flats. I'll check out tour. – Buadhai Nov 16 '19 at 04:23
  • I bought this 4300 at a local Trek dealer in early 2015. They set it up, pumped the tires and set me out on a test ride. After that I rode it home; about 7k. On the way home I had two flats. Brand new bike. Brand new tires. Brand new tubes. Two flats. I had a spare tube which handled the rear flat. The front flat happened only a kilometer from my house, so I just did pump-ride-repeat until I made it home. It's been all down hill from there. – Buadhai Nov 16 '19 at 06:57
  • Maybe get more puncture resistant tires? It makes a huge difference. Or go tubeless. – Michael Nov 16 '19 at 11:25
  • It's always been difficult to get good tires in the part of Thailand that I live in. The boom in online sales has made that a bit easier. The last tires I bought (120 tip Kevlar) were supposed to be puncture resistant, but weren't very good. Last week I got some Schwable Marathon Plus tires. We'll see how it goes. – Buadhai Nov 16 '19 at 21:49
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    Still, no one has an answer to my original question" "...will I be OK drilling the 650s out to 8.5mm?" – Buadhai Nov 16 '19 at 21:50
  • @Buadhai Ultimately noone can tell you if something is safe. Its up to you to decide on whether there's enough metal left after drilling. However this will not do anything for your punctures. I'd suggest ordering a bunch of spare tubes, and some better patches and learn how to do it yourself rather than risk weakening the rims. Also, check out https://bicycles.stackexchange.com/questions/13007/ as a starter. – Criggie Nov 18 '19 at 09:46

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Regarding original question: I have personally drilled out approximately 6 wheelsetsto convert them from prestato schrader valves. I have not yet had any of these rims break even though I use them to drive down flights of stairs and such. Mind you I am a lighter rider (approx 80kg), these (aluminum) rims were used on hardtail mountainbikes. Make sure to debur(remove sharp edges from ) the drilled hole properly.

To try and decrease the amount of flats you get you could do a few things:

-make sure the rim tape is in good condition (no tears/holes, make sure it's properly aligned in the rim)

-remove rim tape and check if any spokes protrude more than approx 1-2mm past the top of the spoke nipples, if they do consider shortening these spokes with a file, dremel or the like or adjusting the spokes such that they are no longer protruding (if possible whilst keeping the wheel true/round)

-check rim bed/edges (where the tire contacts the rim) for damage (sharp/pointy spots which could potentially damage the tire), if you find any sand/file them down so they're smooth

-check your tire for pieces of metal/glass/other objects embedded in/under the surface (by rotating the tire whilst removed from the wheel and pinching it every 2cm approx to reveal any splinters, do this on both the inside and outside of the tire

-check if valve hole has any sharp edges

-whilst installing inner tube make sure it is not pinched in between rim and outer tube (inflate inner tube just a bit, check if it is not pinched anywhere and if all is good inflate the rest of the way)

For fixing flats I personally find it useful to clamp the inner tube with patch in between a bench vice (potentially with some pieces of wood in between the vice and the tube/patch for wider inner tubes), you could also use screw clamps for this purpose.

If you're a heavier rider you might want to refrain from drilling the hole larger but as mentioned I have had no issues with it so far and have been using the 'converted' wheels for considerable time now.

Maarten -Monica for president
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  • Thank you very much. I am 77kg. I've almost always been able to identify the source of my flats. And, it's always a puncture. I've not experienced pinched tubes or damage from the rim or spokes. – Buadhai Nov 19 '19 at 09:38
  • @Buadhai some of the punctures may be caused by pieces of glass or metal that are still in the tire after patching the hole. So it might be worth checking if this is the case . Sometimes you can't easily see them since they are below the surface but when you ride the bike they get pushed through the inner tube causing a puncture – Maarten -Monica for president Nov 19 '19 at 09:40
  • That's certainly possible, but whenever I repair a flat I always remove the tire from the rim and do a visual and tactile inspection to find whatever made the puncture. It's very rare that I can't find the culprit. – Buadhai Nov 19 '19 at 21:26