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How do I avoid pinch flats? - Update

Posted: Tue Mar 15, 2011 7:44 pm
by hitchhiker
Hello, I'm looking for a bit of help

I'm new to commuting and have been getting a lot of pinch flats (5 in 3 weeks). I ride 26km each way and the roads can be bumpy, generally the punctures occur just after I've hit a large bump. The punctures are always in the rear.

I'm riding a Repco Superlite with a rack and rack bag. I don't carry much weight (change of clothes) and I weigh 75 kg.

I'm using 700x23 Continental GP4000 tyres which I suspect is my problem. I have some 700x25 Specialised All condition pro tyres although I'm not sure if they would make much difference.

Other then avoid the bumps, would the best remedy be a larger tyre?

If so what size? and can I just fit one to the rear and leave the 23 on the front?

Thanks

How do I avoid pinch flats?

Posted: Tue Mar 15, 2011 7:50 pm
by sogood
Get a pump with gauge and pump your tyres to appropriate pressure to weight. For 75kg, 110psi would be around the mark. Further, stand and unweight yourself when going over bumpy sections.

Re: How do I avoid pinch flats?

Posted: Tue Mar 15, 2011 8:03 pm
by hitchhiker
Thanks for the reply,

That's been my strategy so far, check the tyre pressure each morning and stand up over the bumps. Unfortunately I invariably still manage to hit some bumps while seated.

I'm hoping there's a more robust solution for the bumps I fail to avoid

Re: How do I avoid pinch flats?

Posted: Tue Mar 15, 2011 10:12 pm
by lethoso
more pressure, and/or fatter tyres.

Although the obvious solution of not hitting the big bumps would do wonders for your comfort as well as puncture rate :)

Re: How do I avoid pinch flats?

Posted: Tue Mar 15, 2011 10:17 pm
by wookie661
im not too sure about 110psi, usually on the side wall it will say what the max pressure is.

saying that ive only dealt with 25 tyres or wider and the max pressure ive ever seen is 85.

but yes avoid the bumps, stand up, or get a bike with suspension.

maybe wider tyres.

Re: How do I avoid pinch flats?

Posted: Tue Mar 15, 2011 10:20 pm
by sogood
wookie661 wrote:im not too sure about 110psi, usually on the side wall it will say what the max pressure is.

The accepted reference on this issue is late Sheldon Brown.
http://www.sheldonbrown.com/tires.html
http://www.sheldonbrown.com/flats.html

Re: How do I avoid pinch flats?

Posted: Tue Mar 15, 2011 10:24 pm
by trailgumby
More pressure will help. I think GP4000's will be fine with 110psi, although ride will be harsh.

Not riding on footpaths at speed will help (my usual culprits - still carrying too much speed coming off the roadway to get away from grumpy traffic)

Re: How do I avoid pinch flats?

Posted: Tue Mar 15, 2011 10:49 pm
by Cruiserman
Try going tubeless. No tube = no pinch flats and slightly lower pressures 90psi.

Re: How do I avoid pinch flats?

Posted: Tue Mar 15, 2011 11:20 pm
by mikesbytes
Its not normal to get that many pinch flats

I'm 75kg and I run 120 rear, 110 front. About 10 psi more than Seldonbrown. Check the link that sogood has posted and set your tyres accordingly.

And don't get hung up on the rating on the sidewall, that has been determined by lawyers, the safe legal limit where my a isn't going to be sued if the tyre comes off the rim

Re: How do I avoid pinch flats?

Posted: Wed Mar 16, 2011 6:59 pm
by hitchhiker
Thanks for the replies,

I cut my losses today and rode the mountain bike with slicks. No punctures and although it felt slower, the travel times were about the same.

I still prefer to ride the Superlite so I'll follow the tyre pressure advice to see if that solves the problem

Re: How do I avoid pinch flats?

Posted: Wed Mar 16, 2011 7:27 pm
by Mugglechops
I run 28mm tyres at 120kgs and don't get pinch flats. No idea what pressure I just pump them up till they are hard.

How do I avoid pinch flats?

Posted: Wed Mar 16, 2011 7:57 pm
by Comedian
Mugglechops wrote:I run 28mm tyres at 120kgs and don't get pinch flats. No idea what pressure I just pump them up till they are hard.

Gawd! The 28mm vittoria randonneurs I run on my hybrid run at 65 front and 75 rear :o

Re: How do I avoid pinch flats?

Posted: Wed Mar 16, 2011 9:25 pm
by Mugglechops
Comedian wrote:
Mugglechops wrote:I run 28mm tyres at 120kgs and don't get pinch flats. No idea what pressure I just pump them up till they are hard.

Gawd! The 28mm vittoria randonneurs I run on my hybrid run at 65 front and 75 rear :o



I probably should have written that as"I run 28mm tyres and weigh 120kgs...."

Re: How do I avoid pinch flats?

Posted: Thu Mar 17, 2011 12:54 pm
by waynohh
81kg, Hutchinson tubeless (AT) 80psi.

Re: How do I avoid pinch flats?

Posted: Fri Mar 18, 2011 8:26 am
by Jason22
130kg's run at 110psi front and back, no issues. Only ride on good road however, luckily my commute there is bike lanes as long as the eye can see :D

Re: How do I avoid pinch flats?

Posted: Sat Mar 19, 2011 6:43 pm
by hitchhiker
A further update:

After my last flat a couple of days ago, I replaced the tube and rode home. Today was the first chance I've had to look at the bike. I was pumping up the rear tyre, at about 110 psi there was a loud bang.

Upon inspection I found the tyre was ripped and a decent hole in the tube underneath. The rip wasn't there when I replaced the tube after the flat a couple of days ago. This is a new tyre that's done less than 300km.

Image

Tyres shouldn't do this should they?

Re: How do I avoid pinch flats? - Update

Posted: Sat Mar 19, 2011 6:53 pm
by sogood
I wouldn't be surprised if you've already damaged the carcass of the tyre at some stage. Tyres don't bust like without damage. The damage would be consistent with impacts that caused the pinch flats.

Re: How do I avoid pinch flats? - Update

Posted: Sat Mar 19, 2011 7:21 pm
by ZepinAtor
There are heaps of different types of tyres that are less likely to pinch flat. Specialized make a tyre called "Roubaix" with an Armadillo 3mm thick top section. They're sized as a 23/ 25, strange I know, but it refers to the 23c bag & a 25c top section. Continental make a range of commuter tyres which are as heavy as, but designed to resist punctures & impacts.

Re: How do I avoid pinch flats? - Update

Posted: Thu Mar 24, 2011 12:31 pm
by Hamster
I run Continental Travel tyres front and back at a pressure of 80 - 85 psi on the MTB which I use for commuting. Total weight would be a little under 90 kg. My commute doesn't involve much rough stuff, just the normal urban environment.

Since changing the rimtape there has been no flats (touch wood) and none at all due to penetrations or pinching.

Re: How do I avoid pinch flats? - Update

Posted: Mon Jun 06, 2011 9:18 am
by Xplora
Time to go with the full puncture resistant tyres, because that's a LOT of flats.

Re: How do I avoid pinch flats? - Update

Posted: Mon Jun 06, 2011 1:01 pm
by trailgumby
Pinchflats are cuased by crushing the tube against the rim, not by anything penetrating the casing, so "puncture resistant tyres" won't help.

The only thing that will help will be avoiding the hitting of square-edged bumps, and / or more tyre pressure. @82kgs riding weight + panniers, I run about 95psi which seems a good balance between comfort and pinchflat avoidance.

That ruptured sidewall has been caused by striking something sharp that's cut the casing.

Re: How do I avoid pinch flats? - Update

Posted: Mon Jun 06, 2011 1:42 pm
by goneriding
Unfortunately, it does happen. I've had brand new puncture resistant tyres that have been destroyed very quickly by that kind of cut. Not a lot you can do about it. Definitely time for a new tyre.

One piece of advice is to do a deglass and check of the tyres once a week. You'll be unpleasantly surprised as to just how much glass and bits of metal the tyres pickup in a week.

Another is to cut 2 -3 pieces of tyre from an old tyre to use as liner, between the tube and the tyre wall, for tyres that get this kind of cut. It will keep you going until you can get a new tyre.

Do a search here for tyre recommendations for commuting as it has been discussed at some length!

Re: How do I avoid pinch flats? - Update

Posted: Tue Jun 07, 2011 12:23 pm
by find_bruce
goneriding wrote:cut 2 -3 pieces of tyre from an old tyre to use as liner


The limp home trick someone taught me years ago is that any polymer bank note between the tube & tyre will stop the tube squeezing out through the hole in the tyre & its enough for you to get home on.

Re: How do I avoid pinch flats? - Update

Posted: Tue Jun 07, 2011 12:48 pm
by goneriding
find_bruce wrote:The limp home trick someone taught me years ago is that any polymer bank note between the tube & tyre will stop the tube squeezing out through the hole in the tyre & its enough for you to get home on.


That's great, unless you need to stop for coffee. Then what do you do!

Whilst a bank note will stop the tube coming out it won't stop anything sharp getting through whereas an old piece of tyre is far more likely to stop the sharp nasties.

Re: How do I avoid pinch flats? - Update

Posted: Tue Jun 07, 2011 12:52 pm
by Kenzo
goneriding wrote:That's great, unless you need to stop for coffee. Then what do you do!

Get change...

goneriding wrote:Whilst a bank note will stop the tube coming out it won't stop anything sharp getting through whereas an old piece of tyre is far more likely to stop the sharp nasties.

It was a 'limp home trick'.... not a be-all end-all. :roll: