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Old 10-28-07, 08:40 AM   #1
LVW
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NEWBIE Tire Question

I recently purchased an 08 Trek 7100 for tooling around at the park with the family. Does anyone know what the largest tires are that could fit this bike? The ones that came on it are very skinny and don't seem to hold air well. I would like a thicker tire that could hold more air. Any suggestions??
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Old 10-28-07, 11:18 AM   #2
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The tire is not the issue with holding air, unless you have tubeless rims/tires but that is very unlikely. Your innertube holds the air. You can have a slow leak in that. I have a tube on one of our bikes that needs to be aired up a bout every 3-4 days. Most times I only need to air every 7-14 days. Some are much more sensitive to their pressure and will air before every ride.

In any case, a new tube should fix the air holding problem. Check at your LBS for what size tires your rims can take. What size are they now that you think they are too thin? Wider tires will not roll as easily but will give a better shock effect. Although that seems a little unnecessary as I think your bike has suspension.
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Old 10-28-07, 12:08 PM   #3
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I am sorry I wasn't more clear. I was more asking about if a larger tire would hold more psi. It seems like the max psi isnt enough. For example with my mountain bike (Gary Fisher) I have 26 inch rims and the tires are big and only require about 60psi. On the Trek even with 70 psi the tire looks and feels low while riding.
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Old 10-28-07, 02:28 PM   #4
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Would increase the air pressure to at least 90-100 psi. Believe the max is 110 psi for those tires. 80-85 psi would be for wet conditions.

It's a bit different for air pressures between a 26" and 700 tire, so you can't really use one or the other for a reference/comparison. I usually run about 60-65 psi in my 26" tires but anywhere from 95-110 psi on my road bike (700 tires). Some 700 tires allow up to 125 psi and there are a few that like to run at that psi.

Just experiment with different air pressures to find the one that is most comfortable or offers the best performance for you. Some like to start at the max air pressure and work downwards to find their "sweet spot".
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Old 10-28-07, 02:54 PM   #5
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I just looked and my tires say 80 psi max. That being the case could I still load it up with 100+ psi or would they pop?
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Old 10-28-07, 03:31 PM   #6
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Go here:
tire pressure formula

Also check here:
http://www.sheldonbrown.com/tires.html#pressure

Basically, the narrower the tire, the more pressure it needs. The fat tires on your mountain bike don't need as much pressure. But, don't overinflate your bicycle tires, just like you shouldn't ever overinflate the tires on your car.

35 mm wide tires like what you have on your 7100 aren't that skinny, actually; two of my bikes have 28 and 23 mm tires.

By using the calculation in the first thread linked above, a rider at my weight (~210 lbs), with 700x35 tires like your Trek has (according to http://www.trekbikes.com/us/en/bikes...0_series/7100/ ), should be running about 65 psi rear and 60 psi front. I'd say you should recalculate with your weight, then start there and run it that way for a while. I've had success with that formula for my road bike's tires.
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Old 10-28-07, 06:25 PM   #7
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Originally Posted by LVW View Post
I just looked and my tires say 80 psi max. That being the case could I still load it up with 100+ psi or would they pop?
Good possibility. I'm not going into the whole "looks flat" BS. Don't judge by looks, but feel. ALL tires, even my 145psi tubulars, flatten under load. You can't overcome the laws of physics and chemistry. Pump the tire to the max. When the bike does NOT turn like it should, the tire pressure is too low. This isn't hard, so don't make it difficult.
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Old 10-28-07, 07:27 PM   #8
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Thanks a bunch! All very helpful.
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Old 10-28-07, 08:05 PM   #9
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FYI - In general the wider the tire, the lower the maximum pressure rating for the tire.
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Old 11-07-07, 12:52 AM   #10
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Are you using a tire gauge, or trusting your thumb or the gauge on the end of a gas station hose (those are notoriously inaccurate--they get banged around all the time)? Get a real pump and a real gauge, then check the max pressure marked on the tire sidewall. You can safely inflate a little beyond that, but there shouldn't be a reason to--35mm tires are actually pretty large, by road bike standards. I use them on my Atlantis at 75-80psi (I weigh 240), but I rarely see anyone with tires that big. Most road riders are probably on 23s or 25s.
If you have room, Panaracer makes a tire called the Pasela in 700x37 that's pretty nice. If you can't find it locally, you can order from www.rivbike.com.
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Old 11-10-07, 12:18 PM   #11
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I ride a mountain bike some with 26X1.95 tires and 80 PSI works well for road and beach riding. I am around 200 pounds.
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