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03-01-10, 12:45 PM
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reckoner13
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Do your tires look flat with all your weight on the bike?
I'm 6ft 250lb and I've noticed that when I get on a bike my weight seems to make the tires look like they are flat. When I'm off the bike the tires are fully inflated but riding the bike makes the back tire seem like it's practically riding on the wheel with a flat piece of rubber underneath. Is this normal for us big guys, or am I doing something wrong (do I need special tires)?
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03-01-10, 12:51 PM
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Doohickie
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What pressure are you runnning? Inflate the tires (especially the rear) to the max pressure stamped on the sidewall. When you look down, though, the tire will appear to bulge out at the contact point; the view from directly above makes it look worse than it is. From the side it probably looks normal.
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03-01-10, 12:51 PM
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Wanderer
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You need to put more air in them. What size are they, what is their pressure rating, what pressure do you have in them**********
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03-01-10, 12:54 PM
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reckoner13
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I don't know, I'm a complete newb, I'm buying my first bike today so these are the bikes I've tried at REI (Novara Portal and Marin Pioneer Trail, which would you prefer? I listed the specs at https://www.bikeforums.net/showthread...ovara-or-Marin) I'm assuming they have the correct tire pressure, they feel pretty inflated.
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03-01-10, 01:17 PM
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CliftonGK1
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Originally Posted by reckoner13
I'm assuming they have the correct tire pressure, they feel pretty inflated.
Never assume, always check with a gauge. I rode 28mm higher pressure tires (115psi) when I was your weight, and I'm still 230 but just swapped out to a wider (32mm) lower pressure (95psi) tire recently. Neither one looks flat when I'm on the bike. Running a low pressure, you risk what's called a "snakebite" or pinch-flat.
The walls of the rim pinch the tube between the bead seat (the hook part of the rim the tire latches on) and the inner casing of the tire as it flattens out. The resulting punctures, one at either side of the rim, looks like a snake sank its fangs into your tube.
Remember, a tube is constantly bleeding a very small amount of pressure. Just sitting on the stand last week, my tires went from 95psi to 75psi. The only things I check before each ride, every time, are the condition of my brake pads and my tire pressure.
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03-01-10, 01:35 PM
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reckoner13
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I will make sure to check the tire pressure, it's kind of embarrassing being a big guy and riding a back that looks flat lol.
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03-01-10, 01:43 PM
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Doohickie
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When you get the bike, get a decent floor pump too. It will have a gauge built in.
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Originally Posted by bragi "However, it's never a good idea to overgeneralize."
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03-01-10, 02:05 PM
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IAmCosmo
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I don't know what kind of valves those tubes on that bike have, but if they have Presta (the kind you unscrew) they can leak down a couple pounds a day, so you can lose 10 psi per week (sometimes more). ALWAYS pump them up to the correct pressure before riding. Even at ½ or ¾ of the recommended pressure, you probably won't be able to squeeze them so that's not a good indicator.
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03-01-10, 02:18 PM
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Mr. Beanz
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I run 26X2.1on my MTB. Pressure rec on tire says 33-55 psi. I'm heavy so I run 50 psi. Never had a flat and eventhough not much more at 55 psi, I just figure I will have a wee bit more traction on some of the slippey sandy steep sections while climbing.
Yes, they do look flat when I sit on the bike compared to my road bikes' narrow tires at 120 psi.
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03-01-10, 02:59 PM
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rumrunn6
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use a gauge and crank those babies up to their MAX
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03-01-10, 03:37 PM
#11
Doohickie
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Originally Posted by IAmCosmo
I don't know what kind of valves those tubes on that bike have, but if they have Presta (the kind you unscrew) they can leak down a couple pounds a day, so you can lose 10 psi per week (sometimes more). ALWAYS pump them up to the correct pressure before riding. Even at ½ or ¾ of the recommended pressure, you probably won't be able to squeeze them so that's not a good indicator.
Perhaps but I haven't see that... yet.
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Originally Posted by bragi "However, it's never a good idea to overgeneralize."
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03-01-10, 03:46 PM
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Mr. Beanz
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Originally Posted by Doohickie
Perhaps but I haven't see that... yet.
Seriously?
...Part of the reason I inflate my tires beofre every ride. This also tells you if you have an upcoming problem. If Saturday's infation was to 120 and Sunday morning your tires are at 80, there's a problem, maybe a slow leak that's going to get you on the road.
You should also get a gauge to check the tires. I use one to compare/ calibrate floor pump gauges since they are known to be inaccurate. Aftra few times, you get to know the pump gauge, but it's good to have an accurate hand gauge anyways.
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03-01-10, 04:45 PM
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Greg_R
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at 55 psi, I just figure I will have a wee bit more traction
Lower pressure = more traction due to a larger contact patch. However, rolling resistance is increased and it doesn't help tire wear. Take a look at offroad vehicles... they often lower their tire pressure before trying to go over obstacles.
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03-01-10, 04:51 PM
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Mr. Beanz
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Originally Posted by Greg_R
Lower pressure = more traction due to a larger contact patch. However, rolling resistance is increased and it doesn't help tire wear. Take a look at offroad vehicles... they often lower their tire pressure before trying to go over obstacles.
You interpreted it incorrecly and only quoted part of the statement.
It reads "I run 50 psi", and eventhough 55 is not much more psi than the 50, I figure I am getting a little more traction with 50 than I am at 55.
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03-01-10, 04:56 PM
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mickey85
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Originally Posted by Mr. Beanz
Seriously?...Part of the reason I inflate my tires beofre every ride. This also tells you if you have an upcoming problem. If Saturday's infation was to 120 and Sunday morning your tires are at 80, there's a problem, maybe a slow leak that's going to get you on the road.
You should also get a gauge to check the tires. I use one to compare/ calibrate floor pump gauges since they are known to be inaccurate. Aftra few times, you get to know the pump gauge, but it's good to have an accurate hand gauge anyways.
Crazy...
I'll fill my tubes when they're looking low, and I"ll check out the pressure once a week, but at those intervals, and checking with a pencil-style gauge, I never lose more than 3-5 lbs a week, no matter which valve I use. Do you have the Prestas completely screwed closed? Are you sure the cores are in there very tight? Are you using the plastic valve caps? All three of those things will keep me pressure-loss free for months at a time. I honestly don't remember the last time I filled the 26X1-3/8 tires on my Raleigh, but I just checked them and they're still at about 60 lbs (I inflate them to 65). It's probably been 2 months, and those are Schraders.
The Prestas on my commuter are rarely checked, and those check out at about a 5 lb drop a month.
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03-01-10, 05:09 PM
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Mr. Beanz
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Hmm, there are several threads in several forums about butyl rubber tubes losing pressure onvernight.
I don't sure a pencil style gauge, they are also known to be inacccurate. I use a Zefal bike specific gauge.
Are you talking 700 X 23 tires when you say you lose 3 -5 lbs a week? Besides, I check mine for safety reasons like I said, if it's real low, something is wrong.
Took about 30 seconds to find a thread, you better go talk to these guys!
https://www.bikeforums.net/showthread...=tube+air+loss
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03-01-10, 06:33 PM
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d4c4c8
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Remember that every time you check your tires with a gauge you are letting out some amount of air. When you clip your pump onto the tire, if you have presta you'll lose more air.
When i rode mountain bikes regularly, i set my air pressure based on the trail i was riding. Some trails when muddy or super technical, i'd ride below the minimum air pressure.
I notice riding my road bike 700x23 i look down and think, mmmm i look like i'm low, ask Jen and she laughs and says you're tires are FINE.
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03-01-10, 07:22 PM
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tardman91
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My tires look fine on my road bike when I sit on it. I'm 6'3, 270lbs. I keep them at 120 psi. The minimum on the sidewall is 110 and the max is 145.
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