How do I make my foldable tires round to fit on my (700C) rims?

I'm old (66) and have a 50-yr old French racing bike (Mercier 300). New tires are all foldable, I don't like them. Last time I mounted them (so to speak), the tires had a hard time becoming round and actually fitting the rim. Sealed fine, so maybe I'm just crabby.

My foldable tires were mail order, but when I go to bike shops ALL of the tires are foldable. Sew-ups were foldable, and properly so. Tires with wire beads are not, even if the "wire" is kevlar or some such.

I'll stop being crabby now. How do I get my tires into round so as to mount them easily? As in the "old days".

  • 1
    Awkward problem - 700c might mean modern 622mm or 630mm or maybe even 635mm bead seat diameter. Does the old tyre have any of these numbers on the sidewall ?
    – Criggie
    Jan 6, 2023 at 21:14
  • 2
    @Criggie 700C should only ever be 622mm. 635mm is 700B and 700A was 642mm. If 700C is anything other than 622mm it's an error - but tyre sizing systems could have been designed to induce errors, made worse if at some point it was 700<blank> and some helpful person added the familiar "C". 630mm maps to 27" only, nothing in the 700 series
    – Chris H
    Jan 6, 2023 at 21:24
  • 1
    @Criggie I didn't even think of that - the original wheels are probably 630mm/27" for a bike that old. Trying to get a modern 622 with folding kevlar bead on those rims would probably involve a profusion of 4- and 12-letter words. Jan 6, 2023 at 21:26
  • @AndrewHenle this bikeforums thread suggests that the 200 with tubulars was 700C, but the 100 was 27". Nothing on the 300 there, and of course the original wheels might have been replaced anyway
    – Chris H
    Jan 6, 2023 at 21:31
  • So your new tyres you are complaining about are clinchers, not sew-ups? Jan 7, 2023 at 5:34

2 Answers 2


I've always done as Andrew suggests in his answer and simply persevered with mounting folding tyres despite the strange shapes they sometimes make. But if it's hard for you to keep the bead under tension as you work your way around the rim, I'm told it's possible to get the tyre into a friendlier shape.

A friend of mine suggested, when I complained about it, that I take a tube and put fractional pressure in it; just enough it's not completely floppy. Then push the tube into the tyre (unmounted) which also forms the tyre into shape around the tube. If the tube is a bit floppy put a touch more pressure in it so it holds the shape of the tyre in a proper circle.

Leave the tyre somewhere warm (but not hot) overnight; hang it above a heating vent, perhaps, or in the boiler room. The warmth and pressure should give the tyre something a bit closer to its intended shape.

(Do note this is second-hand information; I've not tried it myself.)

  • 2
    or in the boiler room Be careful with tires around machinery. Electrical machinery emits ozone, and certain types of rubber are susceptible to ozone cracking: "Tiny traces of ozone in the air will attack double bonds in rubber chains, with natural rubber, polybutadiene, styrene-butadiene rubber and nitrile rubber being most sensitive to degradation. ..." Jan 6, 2023 at 21:20
  • 1
    @AndrewHenle Excellent point. The effect is surprisingly strong too—it doesn’t take much ozone for cracks to start appearing.
    – MaplePanda
    Jan 7, 2023 at 7:14
  • I did this just yesterday with a 20" foldabe (Swalbe Kojak) tyre, in an unheated garage (at about 15 C.) The tube got in hardly any pressure, then got a bit more pressure to get the tire to shape properly. I let out a bit of the tube pressure, mounted the tyre onto the wheel, let out some more pressure, mounted the tube and put the tyre on fully, to pump up the tube properly. (I have one side mounted wheels, so slightly different from most bikes and I use Schrader valves, on this cycle.) I had no need to leave the tyre overnight.
    – Willeke
    Jan 7, 2023 at 11:55

I'll unfold the tire by hand, getting it as round as I can.

I then usually have to turn at least parts of the tire "right-side-out" because there are likely sections of the unfolded tire that are "reversed" with the body of the tire on the wrong side of the bead, outside-surface-in.

Once I get the tire as close to "round" and "right-side-out" as it seems like it's going to get, I start mounting the tire.

Note that it's never going to be as round as a non-folding tire. But it doesn't need to be that round to be mounted.

I'll start by holding one bead in the rim, then work around the rim, getting that one bead seated - note that the tire being "round" doesn't really matter now, other than being a bit easier to handle if it doesn't keep flopping in the way of working around the rim.

Once that one bead is seated inside the rim, I'll insert the tube, starting at the stem. I'll push the tire aside so the stem can be inserted (make sure you push the tire to the side that allows the tube to wind up on the inside of the tire - I may have done that wrong some time in the past...) and once the valve stem is fully inserted I'll work around the rim, inserting the tube into the tire as I go.

Once the tube is seated in the tire, I'll push the valve stem some to push the tube away from the rim to make sure that I can seat the second bead around the tube at the valve stem without pinching the tube between the bead and the rim.

After getting the second bead started, I'll work around the rim, seating the second bead. If the tire isn't too tight, I'll usually be able to roll the last section of the second bead over the rim with my hands. If that doesn't work, I'll use a Park Tool TL10 (a great tool - I have no idea why Park Tool discontinued it.) and seat the tire.

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