Constant flat tires?

[clearlybored]

Hello everyone,
I'm 6'3", 270lbs and just got a specialized sirrus sport 2011. On my first ride I got a flat tire in the front. Before this bike I had a felt road bike and I got a flat tire everytime single time I rode it. Both in the front and rear. Before the felt I had a MTB and never had a flat tire. Does anyone else have flat tire problems? Is it because of my size? Thanks in advance.

 

[Paul Schmidt]

It would depend on the type of flat....

Flats that look like a snake bit your tire (two small punctures close together) are caused by too low tire pressure, you need to read the sidewall of the tire, find the maximum pressure rating, pump the tires to that, if you still get flats of this type, then you need a wider tire rated the same, or a tire the same size rated higher.

Single puncture flats, there may be something inside the tire, take a wad of bathroom tissue, and run it along the inside of the tire, examine all snags for something poking through. The other possible cause, do you live where there are plants with sharp seed pods, puncture vine for example, the solution there is a thick tube (there is an advantage to cheap tubes, they are thicker) and an armoured tire.

If your getting a flat every ride/img/vbsmilies/smilies/eek.gif, then you must be getting good at fixing them/img/vbsmilies/smilies/rolleyes.gif, I usually get one a year, I've had 2 this year, one caused by a wondering rim strip, and the other is just a flat, but looking at the tire, it needs replacing, funny thing is the front wore out first, but there are 4800km (about 2900 miles) on those tires so they really don't owe me anything.

 

[swampy1970]

Clearlybored,

I'd invest in a good "track pump" - which is a floor standing pump with a gauge on it that'll make it easy to get upto 110 to 120psi. Get a good metal pump like those made by Silca. Given the importance of correct tire pressure I'm surprised that bike shops don't try to sell you one of these when you buy a good bike - or even throw one in to sweeten the deal.

As for tires... When I got back into cycling again I was almost 230lbs and found that the Continental Attack/Force combo was not only a good racing tire (lightweight, gripped like dog poo on a shoe etc etc) but it never had a puncture. They're designed to be a specific front/back tire with the rear being a tad wider and a bit stronger.

 

[clearlybored]

My LBS did sell me one of those.. Its a serfas fp-55. It was 20 bucks or so. The guy at the shop told me I should be at 100 psi but when I was changing my flat it got pretty hard at 60psi. I'm sure I could force it to 100 but what are the chances that it'll pop?

 

[swampy1970]

Originally Posted by clearlybored .

My LBS did sell me one of those.. Its a serfas fp-55. It was 20 bucks or so. The guy at the shop told me I should be at 100 psi but when I was changing my flat it got pretty hard at 60psi. I'm sure I could force it to 100 but what are the chances that it'll pop?

None.

When you put the tire and tube back on, inflate it enough to get to round, give the wheel a spin to make sure that the tire is on properly and then pump it all the way to 100.

There'll be a max pressure on the side of the tire and it's designed to well exceed that amount.

There's also the question of your rims too. Most manufacturers will have a recommended max pressure. Mavic for the Ksyrium wheels have a min and max given values.

Part of your problem would be that at only 60psi on narrow tires you'll be greatly increasing the chances of 'snakebite' punctures. You'll also greatly increase the surface area of the tire on the road and may even be close to running the tire on the edges of the tread/sidewall - something it was never designed to do. Plus the edges of the tread have less rubber on them and may not have the usual puncture strip underneath - most tires, taking my preferred Conti GP4000S, have a puncture resistant strip between the tire tread and tire casing. Some super light tires such as the Conti Supersonic save weight by removing this but this increases the risk of punctures.

 

[doctorold]

I've ridden some 6000 miles since I started riding and I've never (knock on wood) had a flat.....ever. I know it's just a matter of time. My advice, avoid rocks and glass.

 

[Paul Schmidt]

Tire maximum pressures are designed this way:

Engineer uses computer to design a tire, say the maximum design pressure is 150PSI, then comes the tough part, legal states that the maximum pressure should be low, because that avoids the chance of a lawsuit. Marketing wants it high, because it makes the tire seem more durable, so they negotiate. The number those negotiations come up with is what gets moulded into the sidewall of the production tire.

What we don't know when looking at a production copy of the tire, is what the engineer started with for a working number, only that it's something higher then what is moulded on there, but is it 10PSI or 50PSI, nobody really knows, what you also don't know is how accurate your pump gauge is, it could be a little high, it could be a little low, on a $20 pump, it's probably within 5PSI, so always pump the tires to the maximum pressure. If the maximum pressure isn't enough, you need a different tire.

 

[davereo]

This chart is a good reference point. It takes into consideration the weight of the rider along with the size of the tire. http://www.michelinbicycletire.com/michelinbicycle/index.cfm?event=airpressure.view

 

[Desertrider 119]

Clearlyboared, When I got back on the bike last June my weight was at 250#'s. Because of that I installed Specialized All Condition 700x25 Armadillo tires. I inflate them to 125 #'s, the tire max, and have had only 1 puncture in almost a year. I ride on very rough roads here in Northern Arizona. For our size 100 psi in the tires seems low to me. I also check my pressure each time I ride, about every other day.

 

[Paul Schmidt]

Considering the number of people over 180lbs who want to ride a bicycle, the chart should be much longer, really though there are a number of conditions, tire sidewall stiffness being one of them, wheel load weight, pressure. Another way of determining this, is the 15% drop rule. If you measure how far the rim is above the road when the bicycle is unloaded, then when you load it, the rim should drop ~15% so if the rim is 30mm off the ground when unloaded, then it should drop between 4 and 5 mm. The theory is that this gives the best balance between comfort and rolling resistance, if it's much more then 15% then snakebites become more and more likely, and pedalling effort is much higher. Less then 15% and road buzz and bumpiness become more of a factor and the amount of rolling resistance gained is very small.

 

[clearlybored]

Wow, a lot of good info. Thanks everyone

 

[davereo]

Originally Posted by Paul Schmidt .

Considering the number of people over 180lbs who want to ride a bicycle, the chart should be much longer, really though there are a number of conditions, tire sidewall stiffness being one of them, wheel load weight, pressure. Another way of determining this, is the 15% drop rule. If you measure how far the rim is above the road when the bicycle is unloaded, then when you load it, the rim should drop ~15% so if the rim is 30mm off the ground when unloaded, then it should drop between 4 and 5 mm. The theory is that this gives the best balance between comfort and rolling resistance, if it's much more then 15% then snakebites become more and more likely, and pedalling effort is much higher. Less then 15% and road buzz and bumpiness become more of a factor and the amount of rolling resistance gained is very small.

The disclaimer on the chart recommends to use the max air pressure taken from the side wall for all riders over 180 lbs.

 

[Paul Schmidt]

Originally Posted by davereo .




The disclaimer on the chart recommends to use the max air pressure taken from the side wall for all riders over 180 lbs.

Yes, but what if the maximum pressure is not enough for a rider that size, take a 300lb rider, and a 23mm tire that is rated 100PSI, that will not be sufficient, in fact 140PSI may not be sufficient, unfortunately the same tire in 25mm is only rated 95PSI, and the 28mm is only 90PSI. Try finding a 35mm tire that will take 100PSI, that doesn't cost $100 a piece....

 

[davereo]

Originally Posted by Paul Schmidt .




Yes, but what if the maximum pressure is not enough for a rider that size, take a 300lb rider, and a 23mm tire that is rated 100PSI, that will not be sufficient, in fact 140PSI may not be sufficient, unfortunately the same tire in 25mm is only rated 95PSI, and the 28mm is only 90PSI. Try finding a 35mm tire that will take 100PSI, that doesn't cost $100 a piece....

Why would a 300lb rider select a 23MM in the first place? /img/vbsmilies/smilies/rolleyes.gif

 

[Paul Schmidt]

Originally Posted by davereo .





Why would a 300lb rider select a 23MM in the first place? /img/vbsmilies/smilies/rolleyes.gif

There are a couple of reasons, if you want a road bike, many have 23mm as a maximum tire width, which I always thought kind of silly, I can't really see a 23mm tire for anything but, low end racing, but nobody really makes a tire for larger riders, a 35mm 100PSI tire would be about perfect, put it on a frame that will take a 35mm tire and your all set. Unfortunately there are not a lot of 100PSI tires that wide.

It all comes down to the bicycle industry being possessed with the idea that 99% of all people interested in a bicycle for road use, are 140lb racers, not realizing that the general public is averaging about 250lbs these days. You get the same thing with clothing, the rack has 22 in extra small, XS, 45 in small, 12 medium, 3 large (always designs to make the person look larger), and if your really really lucky, one extra large, in a colour you wouldn't be caught dead wearing.

 

[DaPunisher]

Originally Posted by Paul Schmidt .
, if you want a road bike, many have 23mm as a maximum tire width,

Do you have any examples of roadbikes that spec a 23 max tire? The last 3 I have purchased were equipped with 25's.

 

[DaPunisher]

What happened to Paul S? I'm still waiting for an answer. Hopefully I can avoid such bikes in future purchases.

 

[ccallana]

The rear tire that came stock on my Z85 (Very low end Vittoria) wore out almost immediately. Well, in less than 1000 miles. After getting 2 flats in 2 rides, I replaced the rear tire with a Conti GP4000 All Season - sort of expensive, but I've put almost another 1000 on it, and not a single flat, barely looks worn.

The front seems to be doing ok.

I run the rear at 100, front at 90-95 usually. They are both 25c.. I'm ~230lbs.

 

[frbock]

Back to the pumping question (sideline on the thread). I use a little Cambell Hausfield 12V pump. It takes roughly 20-30 sec to pump a tire from 60 psi to about 80. Faster and easier than I can do it by hand, and far safer than any industrial unit.

I pack an air-rush on the bike... just in case, but, i haven't had to use it yet.