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Old 09-20-12, 10:16 AM   #1
Andy_K 
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Pinch flats!

I've always been skeptical about the pinch flat. Everyone talks about how you have to be careful with your tire pressure if you run clinchers, but I usually weigh around 200 pounds and I've run my clinchers as low as 30 psi and only flatted once and I wasn't entirely sure that was a pinch flat. Well, last night I definitely pinch flatted, and I was running around 35 psi.

The thing is, I didn't know I had pinch flatted until this morning. I finished the race without even suspecting a problem, but this morning my front tire had no air.

I have a pretty good idea where it happened. There was a section of the course with a short steep descent across very hard bumpy ground. I checked the results today, and I see that there were 11 DNF's out of 90 racers in my category and 11 more DNF's out of 52 racers in the other category that raced at the same time.

We've got six more races at this same venue. We could really use some rain.
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Old 09-20-12, 01:04 PM   #2
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I was wrong!

Another racer who got a gash in his tubular asked about it on the local mailing list wondering if it was construction debris, so I went and took a look at my tire. Sure enough, I had a half-inch thorn in buried in the tire.

So, I'm back to my previous belief of low pressure with good tubes being fine.
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Old 09-21-12, 09:57 AM   #3
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Lots of factors at play here

1) What kind of tires you running? How wide? What about your rims?

2) What was the terrain like? Any spots that could induce a pinch flat? Like a pothole, hard edge etc?
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Old 09-21-12, 10:57 AM   #4
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Pinch flats are not an urban legend. I am quite certain on this matter.

The punctures tend to come in pairs (snake bit), which is when you know for certain it was a pinch. Also, they'll typically come right after a hard hit, and there's no mistaking it. (Slow pinch leaks do happen, but are less common.)
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Old 09-21-12, 11:22 AM   #5
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the pair of holes will be rim width of course, but perhaps only one place
was the root or rock or pothole edge hard enough to cut a hole..
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Old 09-21-12, 12:30 PM   #6
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Consider yourself lucky then because pinch flats are absolutely real. They usually happen because you don't see the object that you hit. Most objects that you see you can either avoid or weight the bike over appropriately but a sudden thud will compress the tire to the rim causing the pinch flat.
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Old 09-21-12, 02:19 PM   #7
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Quote:
Originally Posted by simonaway427 View Post
Lots of factors at play here

1) What kind of tires you running? How wide? What about your rims?

2) What was the terrain like? Any spots that could induce a pinch flat? Like a pothole, hard edge etc?
I've used Michelin Mud2's (nominally 700x30, but really much wider than that) and Schwalbe Racing Ralphs (700x35) on everything from Alex AT-450's (~17.5mm) to Velocity A23's (~23mm). I just got the A23's this year. Most of my luck has been with the AT-450's, which from everything I've read should be pinch flat machines. I use fairly robust tubes (non-light Continental 700x28/47) and cover them in baby powder before installation. I try to ride out of the saddle and let the bike bounce under me on any kind of rough terrain when I'm going fast (i.e. downhill). I'm relatively slow on anything that is even slightly uphill, so I guess that helps too.

I've heard my front rim hit pavement on transitions before, so I guess it was 100% luck that I got away with that. One time I hit a submerged pothole hard enough that it rotated my handlebars in the stem. The tube had no business surviving that, but it did.

I've done 48 races over the past 4+ years, so I'd say it's statistically very unlikely that I've just gotten lucky. I must be doing something right. The only time in those 48 races that I got a flat during the race I was using the Racing Ralphs and I forgot to even give them a squeeze before the race, to say nothing of checking the pressure. The rear tire was around 25 psi when the front went flat (three laps into the race). I think this incident happened making a fast turn on pavement. My theory is that the tube got pinched as I leaned through the turn. It took about half a lap to go flat and there was only one hole in the tube.

I'm really not suggesting that pinch flats are an urban legend, but I am suggesting that my fellow Clydes don't need to go tubular to drop below 45 psi.

I'm still hoping for rain, the 0.05" we got overnight last night (tripling our total since July 1) not withstanding.
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Old 09-21-12, 04:22 PM   #8
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How fast do you go and what category are you in? This could also have something to do it. Aggressive/Fast riders might pinch more than slower guys like myself
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Old 09-21-12, 05:41 PM   #9
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How fast do you go and what category are you in? This could also have something to do it. Aggressive/Fast riders might pinch more than slower guys like myself
Yeah, that's definitely a factor. This year I'm racing in the 'old, slow and fat' sub-group of the Clydesdale category (which ranges from 'huge, fast and lean' to 'old, slow and fat'). I don't corner aggressively, but I do let gravity work its magic when I get the opportunity.
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Old 09-22-12, 07:38 PM   #10
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I just got my tubeless conversion holding air. Plan to test it tomorrow at low 30s and then high 20s to see what happens. One thing I know, they'll be no pinch flats.
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Old 09-24-12, 03:25 AM   #11
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I'm 6'1 190lbs and ran both tubbies and clinchers. I went back to clinchers this year because the tubulars were not worh the hassle for my level of racing (lower cat 4). I typically run clinchers around 42psi front and 45 rear with good success. The courses here are very rooty and I'll pinch flat if I go lower. By the way, I just picked up a pair of Velocity A23s myself and love them - and the wider rim should help with pinch flats. I run them with Mich Mudd 2.

So I agree that a Clyde can go below 45psi without a tubular. And in fact, tubulars for a Clyde are not good at lower pressure because they are very likely to roll on fast hard turns. Happened to me twice. I would much rather deal with an ocassional pinch flat than a rolled tire. Clinchers are a much more predictable and reliable option for a Clyde.
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Old 09-24-12, 06:37 AM   #12
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One thing I know, they'll be no pinch flats.
You can pinch-flat a tire.
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Old 09-24-12, 06:31 PM   #13
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You can pinch-flat a tire.
I guess it's possible, but unlikely especially with sealant. Have you actualy heard of this hapening?
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Old 09-24-12, 08:06 PM   #14
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I guess it's possible, but unlikely especially with sealant. Have you actualy heard of this hapening?
It's happened to me. It just takes a hit that smashes the sidewall between a rock and a hard place. Sealant won't seal that hole. I grant that it's less common than pinch-flatting a tube.

I've pinch-flatted tubes, tubulars, and tubeless. And I like to think that I ride pretty smooth. But s#!t happens when you're trying to go fast. (That's why tubeless set-ups wait until a race to fail.)
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Old 09-26-12, 06:37 PM   #15
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It's happened to me. It just takes a hit that smashes the sidewall between a rock and a hard place. Sealant won't seal that hole. I grant that it's less common than pinch-flatting a tube.

I've pinch-flatted tubes, tubulars, and tubeless. And I like to think that I ride pretty smooth. But s#!t happens when you're trying to go fast. (That's why tubeless set-ups wait until a race to fail.)
Being a mountain bike guy, I'm still trying to wrap my brain around these teeny weeny tires. It's amazing how volume affects the ride. Still, at 155lbs I'll consider pinch flatting a tire an accomplishment.
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Old 09-28-12, 02:52 PM   #16
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I'm 6'1 190lbs and ran both tubbies and clinchers. I went back to clinchers this year because the tubulars were not worh the hassle for my level of racing (lower cat 4). I typically run clinchers around 42psi front and 45 rear with good success. The courses here are very rooty and I'll pinch flat if I go lower. By the way, I just picked up a pair of Velocity A23s myself and love them - and the wider rim should help with pinch flats. I run them with Mich Mudd 2.

So I agree that a Clyde can go below 45psi without a tubular. And in fact, tubulars for a Clyde are not good at lower pressure because they are very likely to roll on fast hard turns. Happened to me twice. I would much rather deal with an ocassional pinch flat than a rolled tire. Clinchers are a much more predictable and reliable option for a Clyde.
What was the hassle with tubulars? I mean sure they take more time to mount but I am going on 3 years now without flatting or having to remove the tires on one of my wheel sets and I am just about to retire another one that has been on for 5 years. I only race on these so the treads last so long but once you get them on there real good they stay.
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