Patching "Snake-bite" Punctures.

Philistine
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Patching "Snake-bite" Punctures.

Postby Philistine » Fri Feb 02, 2018 6:08 pm

I have got a terrible record with punctures, mainly pinch flats, and an equally appalling record of fixing them. I am trying to address the frequency of the punctures by paying closer attention to tyre pressures, and, if that doesn't work, going from 23 mm to 25 mm tyres.

Regarding the poor quality of my repairs, it has taken a while, but I think I have finally worked out what I have been doing wrong. I have been identifying only the larger of the two snake-bite holes (they are not always the same size) and repairing that hole. When I come to test my repair, I have observed a leak at the edge of the patch (the second snake-bite hole) and assumed - wrongly - that I made a poor job of positioning the patch. Because I dislike putting patches on top of patches, I have then removed the patch and started again - often with exactly the same result!

My patches are 15 mm circles - ideal for single holes but slightly small to cover two snake-bite holes. I have some larger patches, but they would have to wrap around the tube, which is only 19 mm wide. Is it a reasonable practice to cut a patch to size with scissors? What do other cyclists do?

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trailgumby
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Re: Patching "Snake-bite" Punctures.

Postby trailgumby » Fri Feb 02, 2018 6:42 pm

For snake bites I use a bigger patch, usually a rounded rectangle, to cover both. While not ideal to cover so much of the tube cross-section's outer circumference with a non-stretch patch, the reality is you don't notice the difference. There is no sensation of having a flat spot at all.

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Re: Patching "Snake-bite" Punctures.

Postby trailgumby » Fri Feb 02, 2018 6:45 pm

Regarding tyre pressures, I maintain mine at least weekly on my 700x25c Conti rubber. I run 80psi front and 85psi rear for 85kg on some pretty ugly chipseal roads and haven't pinch-flatted for 5 or 6 years.

However, if I do tomorrow I will come looking for you. :P

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Thoglette
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Re: Patching "Snake-bite" Punctures.

Postby Thoglette » Fri Feb 02, 2018 7:10 pm

Patch over patches - not a problem. As trailgumby almost says, the tube doesn't set the shape, the tyre does.

I'm running 32mm tyres so I need to be really low (c. 35psi) or very heavily loaded (groceries AND booze) to pinch flat. I still get them occasionally on really good potholes or grates.
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bychosis
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Re: Patching "Snake-bite" Punctures.

Postby bychosis » Fri Feb 02, 2018 8:38 pm

Yup. Bigger patch over both holes. It is harder to wrap a big patch around a small (road) tube, but it can be done.

When finding the holes I usually locate it with a partially inflated tube, then hold my finger over the hole for a moment to see if it is the only one and/or stretch the tube in the location of the leak to make the hole bigger and therefore easier to see.
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uart
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Re: Patching "Snake-bite" Punctures.

Postby uart » Fri Feb 02, 2018 9:26 pm

Philistine wrote:I have got a terrible record with punctures, mainly pinch flats, and an equally appalling record of fixing them. I am trying to address the frequency of the punctures by paying closer attention to tyre pressures, and, if that doesn't work, going from 23 mm to 25 mm tyres.


Pinch punctures are really the most readily avoidable in my opinion. No matter how well you keep a lookout you are never going to avoid every patch of broken glass or sharp wire etc, but usually you can keep away from really rough stuff and holes and steps etc if you're a little careful. If you get a lot of these "snakes bites" then I'd definitely consider going up a size (or two) on the tyres.

I've never really been successful with patches over patches either, so I try to avoid that. I've also never had a lot of luck with removing patches. I guess I must do a better than average job of roughing them up and gluing them, because once the patch has been on for a long time and fully cured, I usually end up destroying the tube before the patch will peel off. As such, for me a failed patch job almost always means binning the tube.

Like most people I get the occasional puncture from glass or thorns etc, but I've only had just the one pinch puncture in the past five years or so. And that was the day I went off road (trying to find a shortcut between two suburbs that are only connected by the one main road that I was trying to avoid). What started out as just gravel dirt and sandy trails ended up getting progressively worse until I was going through creek crossings and over large rocks and boulders in what was strictly mountain bike only territory, and me on my old steel roadie with 25c tyres. :shock: I was actually just starting to get a bit chuffed as to how far I'd made it with my "mad skillz" on such an inappropriate bike when the inevitable happened and the rear tyre went down. Not much fun walking out of about 5km of bushland through creeks and thick mud in cleated road shoes. :oops: - But when I'm not doing totally stupid stuff like that, pinch punctures are not normally an issue for me. :D

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Re: Patching "Snake-bite" Punctures.

Postby CKinnard » Fri Feb 02, 2018 10:00 pm

if you are getting snake bites regularly, sounds like your routes are dodgy, and maybe you need a heavier duty tire. The wider the better in that case. I've never had a flat yet with the 35mm on my CX running 50-60psi, and they get a pounding on rough stuff.

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Re: Patching "Snake-bite" Punctures.

Postby AUbicycles » Fri Feb 02, 2018 10:44 pm

I would only expect snake bits on 23 / 25mm tyres if I did something really wrong, like knowing overlook a curb and hitting it at speed.

If you are attracting regular snake bits then you need to increase your tyre pressure - the limits mentioned by Trailgumby would be absolute low limits on a road bike. For city and urban I can run lower but have to take more care to avoid pinch flatting.

Philistine
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Re: Patching "Snake-bite" Punctures.

Postby Philistine » Sun Feb 04, 2018 4:40 pm

I live close to the M5 and on most days I either start or finish a ride with a few km along the motorway shoulder. The rubbish on the M5 has always been bad but this past few weeks it has been worse than ever. Couple that with the fact that I go a bit faster than elsewhere (gentle gradients and the wind tunnel effect of passing traffic) and there is a high risk of a pinch flat.

Having said that, I have just bought a new pump. I have started topping up my pressures almost daily and I have come to realize the "pinch test" is next to useless for determining tyre pressures. Yesterday I took my MTB for a spin (first time for weeks) and the pinch test indicated the front tyre was OK and the rear was a bit soft. When I came to pump up the rear I found it was only 2 bar, which I took up to 6. Then, by comparison, the front seemed soft. It turned out to be 3 bar, which I also took up to 6. Presumably, if both tyres had been 3 bar (44 psi) when I pinched them, I would have thrown my leg over the crossbar and pedaled off.

Thank you all for your responses. This forum never ceases to amaze me. If you post something a bit controversial, it immediately precipitates what polite society refers to as a "frank and open exchange of views", but, if you ask for help, you get it.

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Derny Driver
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Re: Patching "Snake-bite" Punctures.

Postby Derny Driver » Sun Feb 04, 2018 5:27 pm

Philistine wrote:.... This forum never ceases to amaze me. If you post something a bit controversial, it immediately precipitates what polite society refers to as a "frank and open exchange of views", but, if you ask for help, you get it.

haha so true
PS Buy spare tubes in bulk and throw away the silly patches. Stupidest thing ever invented.
PPS Keep pressure to 100psi minimum to minimise the pinch flats.

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bychosis
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Re: Patching "Snake-bite" Punctures.

Postby bychosis » Sun Feb 04, 2018 6:32 pm

Philistine wrote:Yesterday I took my MTB for a spin (first time for weeks) and the pinch test indicated the front tyre was OK and the rear was a bit soft. When I came to pump up the rear I found it was only 2 bar, which I took up to 6. Then, by comparison, the front seemed soft. It turned out to be 3 bar, which I also took up to 6. Presumably, if both tyres had been 3 bar (44 psi) when I pinched them, I would have thrown my leg over the crossbar and pedaled off

You put over 80psi in MTB tyres? What sized tyre? Don’t think I’ve ever run over 50psi in my tyres (26x2.1) and normally would run them about 45 on road and 35 (tubed) off road.
bychosis (bahy-koh-sis): A mental disorder of delusions indicating impaired contact with a reality of no bicycles.

Philistine
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Re: Patching "Snake-bite" Punctures.

Postby Philistine » Sun Feb 04, 2018 7:26 pm

bychosis wrote:You put over 80psi in MTB tyres? What sized tyre? Don’t think I’ve ever run over 50psi in my tyres (26x2.1) and normally would run them about 45 on road and 35 (tubed) off road.


Sorry I didn't mean to mislead anyone. I called it my MTB because that is what it is, but I have long since punted the fat, knobbly tyres in favour of a pair of Maxxis Detonator 26 x 1 1/4 road tyres. It is a comfortable but slow ride and I take it out when I don't feel like pushing too hard.

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Re: Patching "Snake-bite" Punctures.

Postby AUbicycles » Mon Feb 05, 2018 2:25 am

Think it is time for some pinch test practice - an intensive two week full time course should get you back on track.

I ride different bikes with vastly different pressures and also completely different tyre types. The pinch test on the rolling surface and side walls still helps provide a rough idea. On my road bike the correct pressure is critical so I can go for a few rides without checking but at least once a week I check and toip up properly. On the MTB I might adjust the pressure to suit conditions and terrain so the pinch test is fairly important. On the commuter I rarely check - just a pinch test every so often - usually when riding I can tell that it needs more as it rolls / floats differently on uneven surfaces and is a good indicator for me.

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bychosis
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Re: Patching "Snake-bite" Punctures.

Postby bychosis » Mon Feb 05, 2018 6:53 am

Plus one. With practice you should be able to tell whether your tyres are near the desired pressure.

Pinch test. Pump them to what you want and do the pinch test again. Feel the difference. You’ll gradually learn how much give there is in the tyre under a pinch wether it’s close, or low.

Unless it’s been a while since I’ve ridden the pinch test will tell me wether to add air or not. If it’s been a while The bike will usually need air so I pump first.
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Thoglette
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Re: Patching "Snake-bite" Punctures.

Postby Thoglette » Mon Feb 05, 2018 12:51 pm

Derny Driver wrote:PS Buy spare tubes in bulk and throw away the silly patches. Stupidest thing ever invented.


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