On Saturday, I was planning a hard ‘kitchen sink’ training ride on the Tarmac. I’m doing a sportive on the ass hatchet in 2 weeks and have been doing a few training rides on the upright road bike to get back into the groove. I recently replaced the wheels on this bike, as the lightweight Fulcrum wheels it came with were ridiculously low spoke count, had nearly worn out rims and the rear hub bearings had gone. I got a decent-but-not-too-expensive set of new wheels built with a sensible 32 spokes per wheel. Last week I tried putting on a set of 28C Schwalbe Ones which seemed to just fit, however going out in poor weather I discovered that the rear tyre would just rub ever so slightly on the rear brake caliper with mud on the tyre, so on Friday evening I swapped out the 28s for the 25s off the M5. For some reason I inflated the tyres to about 100 PSI rear, 95 front. Normally I would do 85 rear, 80 front.
Next morning I set off on my ride. I didn’t feel that great, having done two threshold workouts during the week. I am slowly learning through repeated experience that I cannot handle lots of threshold work as a semi-old fogey and need to reign it in a bit 🙂 Did an hour of endurance followed by some full gas sprints. Got to the first of four threshold intervals – I do the first on the climb up Paddy Slacks from the south. Legs were like lead, fading badly by the top. I started to hear a strange rubbing noise near the top, and stopped to take a look at the summit. To my surprise, the rear tyre had popped out the rim bead and about 6 inches of tyre were hanging down the outside of the rim. Strange…. perhaps I didn’t seat it properly the previous night.
I deflated the tyre, seated it back inside the rim and used my one and only CO2 cartridge to inflate it up to pressure. Once again, it was probably a little higher pressure than I would normally use. I was getting cold by this point so jumped back on the bike and set off down Paddy Slacks. Two minutes later, I heard the same rubbing noise and stopped to take a look – darn tyre had popped off the rim again! No CO2 left either…. I deflated the tyre and removed the wheel from the frame this time. I took a good look at the rim but it was still looking brand new, not any damage anywhere that I could see. I noticed that both times though, the tyre had popped off at the valve area of the rim.
This time I had to pump it up using my emergency manual pump, which is tiny and hard to inflate to high pressure, and I couldn’t get it past 40 PSI. Getting really cold by this point, I put everything back on and set off again, this time a little more paranoid. The tyre seemed to hold this time – whoopee. My legs were a little better having spent about half an hour faffing about at the side of the road too. I managed a PR up the 7 mile climb out of Innerleithen (wind assisted – power wise I was still well off my usual pace), and was getting back into a groove on the descent down to Heriot when I hit a pothole, and of course at 40 PSI my rear wheel immediately punctured with a snake bite. Dammit.
More faffing about at the side of the road installing my spare tube, and this time I got the tyre inflated to about 35 PSI before my hands had had enough on the tiny pump. I just wanted to get home by this point so left it as-is. It felt pretty squishy but got me home.
I’m still trying to figure out why the tyre was popping off the rim. I can’t see any damage to the rim at all – it still looks brand new. The only thing I can think is that, being a pretty wide rim, 105 PSI was too much for it. Either that, or there’s something wrong with the tyre, which has about 1500 miles on it from the M5. I am still none the wiser, and will see how it goes this weekend back at my usual 85 PSI.