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Old 05-20-06, 02:46 PM   #1
Blimble
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Does Extreme Obesity Cause Flat Tires? If So, What Helps?

Here's the problem: I'm morbidly obese (245lbs, 5'11"). As a result, I get flat tires every ten miles or so.

I've had three different mechanics look at the bike and tell me that there's nothing wrong with it. The tubes are new, the rims and rim tape look good, the tires are kept inflated to the maximum pressure for the tires (120psi), and the tires are almost new Continental Ultra Gatorskins (700x25c) which are supposed to be relatively resistant to pounctures. On top of my considerable body weight the bike typically carries about 20 pounds of gear.

I'm riding the bike around the city, and although this means sometimes the bike has to go over cobblestones and cracks that cause the rear wheel to jump and drop, on the whole I'm not doing anything unusual.

The wheels use Shimano Sora hubs, and Alex DA22 32h rims. The tubes are Novara Presta tubes, 700 x 20-25.

I'm at my wit's end with this: none of the techs seem so think that my body weight is an issue, yet the equipment apparently isn't an issue either, and yet the problem keeps happening.

At this point I'm thinking the only option I have to is to get gastric bypass surgery, and put aside the bicycle until I've lost 100 pounds by that means. However, this is an extreme solution and if there is any mechanical way to stop this from happening, even with my body weight as it is right now, I'd like to give it a try.

So, is there anything I can do here?

For what it's worth, the flat tires always seem to be preceded by the rear wheel dropping, e.g. over poor concrete that causes it to bounce. I never ride over curbs (instead walking the bike over them) so we're talking about unavoidable cracks in the middle of a lane of traffic that I can't avoid.

Should I keep the tires inflated to something LESS than 120psi?
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Old 05-20-06, 02:52 PM   #2
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I think you're snake-biting. You need higher pressure very fat tires. Before going over bumps, unweight the pedals etc. Or learn to bunnyhop.
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Old 05-20-06, 02:55 PM   #3
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When I weighed that much, I exclusively used 700x28c tyres pumped up to 120-130psi. Also add:

- Mr.Tuffy tyre-liners
- tyre-savers (scrapes off glass & thorns in 1/2 wheel-revolution)
- kevlar-belted tyres (seems to work better than kevlar-casings alone)
- thorn-resistant tubes
- slime
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Old 05-20-06, 04:48 PM   #4
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OK, let's get it straight - your "obesity" is NOT the cause of your flat tires! I (burnin' hunk-o-love that I am), weigh in at 275 and I DON'T get flats!

So what IS the cause of your flats? I can merely speculate... Possible causes include:

Tires too narrow (you should be riding 28c tires at a minimum width - I use 37c!)
Really bad glass & debris (solve this by using "thorn-proof" tubes)
Low air pressure (keep those tires AT the "max" recommended pressure on the sidewall - and check your pressure before EVERY ride!)
Cheap rubber rim strips inside the rims - Buy the cloth "Velox" strips - they keep internal spoke heads from puncturing the tubes.
Failure to clean the tire casing of protrusions before putting in the new tube - If a wire, glass shard, or other item is still through the tire, you'll just get a fresh flat - check the rolling surface AND the sidewalls!
Wire bead of the tire itself has worked free of the tire casing - I actually had this happen once and it drove me nuts until my LBS sussed out the problem...

In any case, once you get the tires set up right, they'll be GREAT. Don't give up & good luck!
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Old 05-20-06, 05:19 PM   #5
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OK, let's get it straight - your "obesity" is NOT the cause of your flat tires!
New physics?
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Old 05-20-06, 05:25 PM   #6
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I'd recommend filling your tires up to 105-110 or so, instead of the max pressure. But losing those pounds would definitely not be a bad idea, either.
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Old 05-20-06, 05:33 PM   #7
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if the flats are "pinched" or "snakebite" flats due to the rim crushing the tube against some uneven spot in the road, the damage should be recognizeable: two creases in the tube at the 10 o'clock/2 o'clock position. The damage can happen right through the outer tire without harming it. You may also hear the click or feel the rim bottoming out just before you get the flat. I second the other posters' suggestion...fatter tires to give you some extra rim clearance.
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Old 05-20-06, 06:00 PM   #8
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OK, let's get it straight - your "obesity" is NOT the cause of your flat tires!
Quote:
Originally Posted by operator
New physics?
Experience!
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Old 05-20-06, 06:25 PM   #9
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Quote:
Originally Posted by DannoXYZ
When I weighed that much, I exclusively used 700x28c tyres pumped up to 120-130psi. Also add:

- Mr.Tuffy tyre-liners
- tyre-savers (scrapes off glass & thorns in 1/2 wheel-revolution)
- kevlar-belted tyres (seems to work better than kevlar-casings alone)
- thorn-resistant tubes
- slime
you don't even need to add any of that stuff, just change your gatorskin 25's for 28's, pump them up as recommended above, and rest easy. at 245, I never flatted on that setup. ever.
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Old 05-20-06, 06:28 PM   #10
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Every 5 mi or so I inspect my tires and remove all imbeded glass with the a pocket knife.
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Old 05-20-06, 06:36 PM   #11
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I weight about 215, and I never have a problem with pinch flats on 700x25 Gatorskins -- even when carrying a full load of groceries.

If you're actually getting pinch flats (and not punctures from some other source), you might just need to learn to ride lighter. Stand up and "post" over bumps to let your knees absorb some of the shock, and for larger bumps do a little hop to unweight the wheel (the bike doesn't have to leave the ground).

Switching to 28s might also help and there's no real reason not to.
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Old 05-20-06, 06:47 PM   #12
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Pinched flat illustration.
Attached Images
File Type: jpg pinch.JPG (23.2 KB, 76 views)
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Old 05-20-06, 08:11 PM   #13
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I totally agree that it is not the weight. I now weight 315 (used to be 365) I have only had one flat is 7 months of riding on 700x23
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Old 05-20-06, 08:18 PM   #14
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Gastric bypass for 245? Are you joking?

Anyways, I weigh roughly the same and run 700x23c Vredsteins and I average about 1 flat per 500 miles (usually broken glass). 120-140psi depending on what I feel like that day.
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Old 05-20-06, 08:47 PM   #15
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On the surface of it, it sounds like pinch flats, a.k.a. "snakebite," as illustrated by cooker's pics there.

However, at 245 pounds with 700x25's at 120PSI, it still shouldn't be that frequent of an occurrence. I wonder if you have perhaps a tiny piece of wire embedded in your tire casing, which causes a slow leak. After a while, your tire pressure would then be reduced enough to bring on pinch flats where you ordinarily wouldn't get one. So I would go through the tires extremely carefully, feeling the inside of the casing with your fingertips for the slightest sign of embedded wire or glass. And inspect it very closely from the tread side too.

Or if your tire's valve is leaking, that would be another way that your pressure could gradually drift down and leave you vulnerable to pinch flats, too. Check for a valve leak by topping the tire off, closing the valve's centerpin lockdown nut (assuming Presta valves here), and then submerging the valve in the bathtub to see if air bubbles are coming out of the valve.

That said, it will help to use thorn-resistant tubes if you're fighting pinch flats. They're so thick that it's extremely difficult to pinch-flat them. I also would endorse a little bigger tires for your weight if you've got bad roads, especially considering you have the additional 20 pounds of cargo too. If your bike's got clearance for typical 700x32's, here's one that might be worth a look: Panaracer 700 x 32 Kevlar-belted folding road tire


If you get more flats, ask the mechanic to give you the old tube so you can do a post-mortem submersion test and check for both snakebites and also slow leaks that could lead to snakebites.
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Old 05-20-06, 09:45 PM   #16
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Hi,
I weigh more than you and get about one flat a year. Any time
I get more than one I get heavier tires. I use Rivendell Ruffy Tuffy tires.
They are 27c and the front gets 85 psi and the rear gets 95 psi this time of year.
As I get used to biking over the course of the summer, I add more pressure, but never go much over 100. The front never goes over 90. No need, none at all.


So.. down to brass tacks. Something is wrong, let's do a process of elimination
1) Bike shop.... yup, they ought to be able to fix the problem. First thing I'd do is to take it elsehwere and see if they can fix the problem.
2) larger tire (if it will fit). The bigger the tire, the longer between flats, as a rule of thumb. Some guys go thousands of miles between flats. If you have a pinch flat problem, even one size larger will eliminate it. I don't think you have a pinch flat problem. I have used your tire, my Ruffy Tuffy's have a much nicer ride.
3) Wheel, sometimes a burr or something will show up. Your description makes me wonder about this possibility.
4) You can try thorn proof tubes, I have never used them.
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Old 05-20-06, 11:42 PM   #17
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First off, good on you Blimble. You're out there doin' it. I started biking to loose weight and get in better shape.

If the other suggestions don't work, you might try this product: http://www.nomorflats.com/

They guarantee no flats ever. For life. There is a slight weight penalty. I don't care, because I'm in it for excercise. Innerstin product. Walmart.com carries it, but not my local store. Too bad, I'd like to see it. ~$20/tire. If you try it, please let us know how it works.
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Old 05-21-06, 06:19 AM   #18
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Technique!

I'm no that far from you weight wise. Was 230 lbs. but with no gear. (down to 205 now). The problem may be your technique.

Aside from all the other things the other posters mentioned which may help, use this techinique before spending a dime.

Once your front tire rolls into hole/divot/crack, etc., immediately attempt to stand on your pedals and shift your weight forward, (lean forward) . Do NOT sit through the hole as it approaches your rear wheel.

Once you learn it, it becomes second nature; an unconscious reflex to a bump in the road.

(I know most advice for us big guys is to run tires as fat as motorcycle tires, but I've been riding 20c at 230 pounds with no flat issues, I do use 23c's now though) (Michelin Carbon in particular)

Good luck..
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Old 05-21-06, 08:08 AM   #19
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I wouldn't call 245 at 5'11" morbidly obese, maybe if you compare yourself to the little shrimps that get all dressed up in their team jerseys/
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Old 05-21-06, 09:20 AM   #20
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I am also 205, down from 217, about the same height. I wouldn't even call it obese, just overweight.
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Old 05-21-06, 02:37 PM   #21
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I'm 6'3", and the same weight, and if that's a problem for bikes, then I can't cycle! I have a bunch of bikes, but my morning rider road bike runs 700 x 22, and I don't get flats. I'd like to be lighter but hell, bikes can take that weight. Something else is wrong.
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Old 05-21-06, 07:02 PM   #22
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245 lbs at 5'11" puts you at a body mass index (BMI) just over 34. In order to be considered Morbidly Obese, your BMI must be 40 or more. That said, I was Morbidly Obese with a BMI of 50. I had Gastric Bypass surgery and now am down to 260 lbs. GB surgery is not to be undertaken lightly, it is a life altering experience. Any competent physician would probably recommend other means for you to lose the weight. I ride on 700cx23 tires and in 400 miles I have had one flat and that was today. Follow the suggestions here, learn to ride light, stand with knees slightly bent when going over bumps, avoid potholes, glass, rocks, and broken pavement. This will prevent alot of flats. And by all means keep riding!
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Old 05-21-06, 08:10 PM   #23
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Quote:
Originally Posted by radeane
Technique!

I'm no that far from you weight wise. Was 230 lbs. but with no gear. (down to 205 now). The problem may be your technique.
That's the other half of it aside from getting bulletproof equipment, eh? Think about this, if you left the bike hanging on the wall, you'd never get a flat!
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Old 05-21-06, 08:40 PM   #24
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Check the rim tape. I had a similar problem and found that the rim tape had shifted allowing the tube to get pinched by the spoke hole.
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Old 05-21-06, 08:54 PM   #25
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Quote:
Originally Posted by the beef
I'd recommend filling your tires up to 105-110 or so, instead of the max pressure. But losing those pounds would definitely not be a bad idea, either.
Why?

This is the first time I've heard that lower inflation will help prevent pinch flats. Our tandem grosses out at about 350 lbs when fully loaded. I use 28 or 30c tires and if I don't max out the inflation (120-130 PSI), I can usually count on a pinch flat the first time I hit a serious bump. Keep the pressure at max and it will help.
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