I just got into cycling and I got a puncture yesterday. Regarding the puncture, I found 3 small shards of glass going through the tire and into the inner tube, now that I've removed them do I still need to replace the tires or just the innertube? Also, out of curiosity how small/large tires can I fit on my rim?

If it's relevant I have a Cannondale Synapse, and these are the photos of the rim/tire.

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  • As for the tyre size: the current ones are 28-622. That is 28mm wide, and an inner diameter of 622mm. Going by the ETRTO (Those figures i just mentioned) usually lets you get the best match. You need the same inner diameter, and more or less the same width, lest you need to replace the tube.
    – Burki
    Nov 3, 2021 at 14:56
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    Somewhat tangential, and not really an answer, but if you’re new to cycling and have not done so yet, I would highly recommend getting at least one, if not two, spare innertubes to carry with you (ideally on the bike itself, you can get holsters designed specifically for this purpose that attach to the frame or back of the saddle) when cycling, as well as a decent frame pump and a compact tire pressure gauge. Flats are one of the most common issues to deal with when cycling, but they’re also very easy to quickly fix in the middle of a ride provided you have the right things to do so. Nov 3, 2021 at 19:15
  • I just had a look at the full size photo and it shows that the rubber is cracking. I think it means that it's time to replace the tires next time they are punctured.
    – ojs
    Nov 4, 2021 at 14:55

2 Answers 2


You don't need to replace the tire or the innertube. You can patch the innertube, and patching is a useful skill to master, although I usually wait until I have a few tubes to patch, and repair them in bulk. Don't bother with "glueless" patches, and don't be stingy with the vulcanizing agent. Do be sure to clean the area you're going to patch (there's mold-release compound on the tube that prevents a good bond).

Small penetrations as you see here don't damage the tire enough to warrant replacement. If you want to get fancy, you can clean up the tread cuts and squirt a tiny amount of cyanoacrylate glue (crazy glue) into them to repair the tread. If the tire gets a long slash (or other larger damage), such that the innertube could squeeze through, then insert a boot as an emergency measure and replace the tire as soon as you can.

I agree that these Vittoria Zaffiros are not good tires (Zaffiro Pros are actually pretty good). They're also not long-wearing. You might want to budget for replacements. But you don't need to replace them now on account of this damage.

The diameter of your tire is 700C (in conventional nomenclature) or 622 mm (in the ETRTO system). There's no wiggle room on diameter. You can fit a range of widths, and the width of tire you can fit will depend on the rim width (here's WTB's rim/tire compatibility chart), and also on the frame and parts that might interfere with the tire. It's possible, for example, that the rim could handle a 32-mm tire but the frame will interfere with anything bigger than 30 mm. You seem to have an earlier version of the Synapse; you should dig up Cannondale's spec sheet for your model year.

  • I didn't even know that you could patch inner tubes. I just ordered kit to do that, thank you! Nov 3, 2021 at 18:10
  • @MarcusSaye Patching tubes can be frustrating. There's a lot of technique to it. Consider joining Bicycles Chat if you get stuck, or read the answers at bicycles.stackexchange.com/questions/13007/… for a run-through (not the question)
    – Criggie
    Nov 3, 2021 at 18:55
  • On the point about glueless patches, while they are useless for long-term stuff, but the better quality ones can still be handy for a quick fix just to get far enough to be somewhere where you can safely sit down long enough to either swap in a spare tube or do a proper patch job. Nov 3, 2021 at 19:12

Unless there are any large cuts from the glass (it doesn't sound like there are) then once you have removed the glass, then you don't need to replace the tyre.

That said, my personal preference would be to change those tyres anyway. Tyres make a huge difference to the way a bike performs and i'd always recommend buying the best you can afford.

As for what size tyres will fit. You should be able to find a size on your rim somewhere. Once you know the rim width, then this question has a handy chart for recommended sizes. Before changing to a bigger tyre, be sure to check you have enough clearance in the fork and at the chainstays. How do I know what size tyres can I fit on my rims?

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    If the OP is in the Northern Hemisphere, I'd say leave those on over winter, and upgrade when the weather is better and the roads are cleaner. I put tougher, slightly grippy tyres on for the winter than summer even on the quick bike (which still gets used in all weathers)
    – Chris H
    Nov 3, 2021 at 11:54
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    The Zaffiro isn't tough or grippy, or really good anything except putting on a new bike to save on components.
    – ojs
    Nov 3, 2021 at 12:11
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    Actually the Zaffiro is not that bad. Upgrading to a good tyre like the Continental GP5000 might be noticeable but not world changing. Maybe 5W of power savings at 30km/h. That’s like a 3% improvement assuming 160W total power. Probably more difference when it comes to grip and puncture resistance.
    – Michael
    Nov 3, 2021 at 13:48
  • @ojs it might be better at handling wet leaves, mud etc. on tarmac than something fully slick. I was thinking more to save the wear on expensive new tyres when riding in conditions that won't benefit from them - Saturday's ride for me meant holding back on all descents because so much muck had washed onto the roads, and I picked up a puncture from some glass riding through a flood (on a Gator Hardshell). Time for the Marathon Mondials for me.
    – Chris H
    Nov 3, 2021 at 15:37
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    @ChrisH: The tiny amount of tread won’t help in any situation. You’d need real knobs for noticeable difference on soft surfaces.
    – Michael
    Nov 4, 2021 at 5:59

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