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Old 02-25-10, 02:24 PM   #1
Jungblood
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Should your tires look flat when riding?

So I have a Schwinn Cutter with stock tires and tubes, and when I ride it sort of looks like my tires are about half flat. Is that how they should look? They're inflated to their max PSI, and they're super stiff, so they definitely aren't going flat. Do I need "stronger" tires with a higher PSI to ride on?
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Old 02-25-10, 02:26 PM   #2
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How much do you weigh ? Your 23C tires probably need at least 110-115 PSI minimum.
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Old 02-25-10, 02:27 PM   #3
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They're actually 700x28, inflated to 80 psi.... and I weigh 220 lbs

Thanks for the response, btw

Last edited by Jungblood; 02-25-10 at 02:35 PM.
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Old 02-25-10, 02:38 PM   #4
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you weigh 340, or 220? you need to up the pressure IMO.
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Old 02-25-10, 02:39 PM   #5
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80 psi is the max?
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Old 02-25-10, 02:50 PM   #6
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220... the 344 was sarcastic but I realized it probably wouldn't translate well. The dude at the bike shop said 80 psi was the max, and it feels really stiff at 80, but then again it looks half flat when riding.
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Old 02-25-10, 02:53 PM   #7
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look at the sidewall for the rating. 80 psi seems low to me, but idk everything.
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Old 02-25-10, 03:05 PM   #8
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The sites I have looked at on a Schwinn Cutter show Kenda tires K193 (700 x 23) as the stock tire. Kenda shows a max psi of 125 on the majority of their road tires on their site. i would say get a good pump with a gauge and run them at around 120 psi. 80 is too low for a 200 plus pound rider. I weigh 240+ and ride my 700 x 23s at 120

EDIT: The Schwinn site shows a 700 x 28 Kenda K193 as the stock tire for 2009 and a 700 x 23 of the same tire for 2010. Either way, I would check the sidewall and run it at max psi
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Old 02-25-10, 03:09 PM   #9
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Check out this link
http://www.vintagebicyclepress.com/images/TireDrop.pdf

You weigh 220, and lets say your bike is 20lbs. You have a road type bike, that might mean your weight on the wheels is about 40%/60% over the front and rear. Then lets estimate the weight per wheel.

Front: 96 lbs
Rear: 144 lbs

with 700x28, it looks like you should run 75 psi and 106 psi. Try that and see if it helps.
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Old 02-25-10, 03:21 PM   #10
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I have a Cutter as well (2009 model) and weigh about 215. It has 700 x 28C tires that inflate to I think 50-80 psi (per what it says on the sidewall). It really is a hybrid tire, not a road tire. If you're used to road tires, it will feel kind of soft and look kind of flat, but that's normal. Don't sweat it.

By the way... I really like the Cutter. It feels like it was made just for me... perfect fit.
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Old 02-25-10, 03:36 PM   #11
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Thanks for all the replies everyone... the sidewall says Max 85 PSI, which is about what it's inflated to.

Yeah, I like the cutter a lot. It's my first bike since getting back into riding and with some minor adjustments to it it fits me perfectly! I guess the tire issue is nothing to worry about then.
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Old 02-25-10, 04:08 PM   #12
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Thanks for all the replies everyone... the sidewall says Max 85 PSI, which is about what it's inflated to.

Yeah, I like the cutter a lot. It's my first bike since getting back into riding and with some minor adjustments to it it fits me perfectly! I guess the tire issue is nothing to worry about then.
hmm if it keeps bothering you, you can always buy either a new wheel and new tires and tubes or just buy a new tire and new tube that will fit your bikes geometry.
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Old 02-25-10, 05:16 PM   #13
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At 220 I use ~100PSI to keep the tire from compressing to much with a 28C

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Old 02-25-10, 08:05 PM   #14
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It sounds like the tires that are on it are geared more to a comfort setting so that would be why they'll run a lower pressure and will look like they are bulging out a little more than many of us are used to.

Despite appearances if they roll nicely on level ground where you can coast for a long ways then don't sweat it. However if you pedal up to around 15 mph and coast down to a stop within a 1/4 block on level road and if you find that they seem to be sucking the life out of you then you may want to look around at some other 28's that are designed for some higher performance. There's no lack of such tires but do be prepared for a distinct lack of grooving in the tread. The easier rolling tires will tend to have minimal grooving and mostly smooth faces. They'll also have max pressure ratings up around 100 PSI. I'm running 28mm Continental Ultra Sports on one bike and if I were to do that same coast down test I have no doubt that I'd be able to go for a 1/2 block or further before I had to put a foot down. And once up to speed it feels like i hardly need any effort at all to maintain it.
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Old 02-25-10, 08:26 PM   #15
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The worst thing that can happen due to slightly low tire pressure is you'll get a snakebite flat. If, when you hit a bump, the rim can flatten the tire so much that it bottoms out against the tire which is folded against the road surface, the beads of the tire can come together in the middle and pinch a couple of holes in the tube. You'll lose air slowly, perhaps overnight.

Beyond that, it's a matter of rolling resistance. Too much PSI can be bad especially with a wider tire if you ride rougher asphalt or any type of trail, because if the tire bounces rather than conforms to the surface you'll lose energy. It's as if a small bump or pebble or piece of gravel stuck in the asphalt is a hill. If you ramp the hill, then you don't get the boost from rolling down the far side.

Too little psi causes friction losses in the sidewall and the innertube. Rubber does not flex back with the same force as when you compress it. It's the whole reason car tires need to be speed rated. The internal friction of rubber flexing can cause so much heat that the tire fails and blows out. With a bike, though, the friction mainly just slows you down.

Narrow tires and tires with no rubber over the sidewall plies are two solutions.

Last edited by garage sale GT; 02-26-10 at 02:17 PM.
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Old 02-26-10, 09:59 AM   #16
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The sidewall max is 1/2 the pressure required to blow the tire off the rim. For you and your bikes weight you need about 110psi in the back and about 80psi in the front. Here is an article in Adventure Cycling about tire pressure and weight. http://www.adventurecycling.org/reso...SIRX_Heine.pdf
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Old 02-26-10, 10:16 AM   #17
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The sidewall max is 1/2 the pressure required to blow the tire off the rim. For you and your bikes weight you need about 110psi in the back and about 80psi in the front. Here is an article in Adventure Cycling about tire pressure and weight. http://www.adventurecycling.org/reso...SIRX_Heine.pdf
This is a duplication of post #9.
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Old 02-26-10, 12:34 PM   #18
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The sidewall max is 1/2 the pressure required to blow the tire off the rim. [/URL]
Maybe for a new tire on a perfect rim. I've blown tires at far, far less than that, and I've also had belts fail at far less than that.
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Originally Posted by bragi "However, it's never a good idea to overgeneralize."
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