[Mountain Bike] I have a question about tires on a mountain bike

July 10, 2015 10:42 AM

Can I pump my tires over the recommended psi? and should I?...

I bought a bike about 13 years ago (Trek Alpha) I believe. I literally rode it a few times and put it away. It is in like new shape. I noticed that when I ride, the back wheel (looking down on it) seems flat. I understand that that might be a good thing as it provides better traction but I will be mostly riding on paved trails or very flat dirt so I want a rounder tire to make pedaling easier. The tires don't seem to be losing air after left overnight etc.

Here's the thing, the tires say 35psi - 60 psi. I have them pumped to 55psi and they still do this. I am 6'0 220lbs.
Should I pump them higher?
Can I go over 60psi? (I've read that these are just suggestions that tire makers use)
Is this "flatness" going to happen no matter what?
Am I missing anything?

Any ideas would be great.

posted by Busmick to Sports, Hobbies, & Recreation (20 answers total)

On old tires? I wouldn't. The tires are probably not in great shape anyway. But the worst you can do is get a flat, and you're probably not going fast enough for even a blowout to be that dangerous. Did you change the tubes getting it out of storage?

You're probably due for new tires anyway, so you can get some meant for pavement/higher pressure.
posted by supercres at 10:52 AM on July 10, 2015 [1 favorite]

You can probably go a tiny bit higher, yes.

The 'flatness' is inevitable, and will mostly affect the rear tyre. You can only reduce it, not eliminate it. The only thing that really matters is that the rims aren't grounding - you'd feel/hear it if that happened.
posted by pipeski at 10:59 AM on July 10, 2015

The late, great Sheldon Brown has some suggestions here. The link goes directly to the pressure chart, but you should read the whole article.

The short answer is that correct pressure depends on 1) the width of the tire, 2) how much weight it's carrying, and 3) what kind of riding you're planning on doing. Lower pressure means a cushier ride but increases the risk of pinch flats.

You could probably go a bit over 60 -- it depends on the tire, both width and condition -- but consider whether you really need to. The consensus on bike forums seems to be that tire makers are conservative in stating an upper pressure range, but also that low pressure, as long as it isn't stupid low (i.e., low enough that you're pinch flatting) isn't necessarily a bad thing.

For reference, I weigh about as much as you, and I run about 70 psi in the 26x1.5 slick on the rear wheel of my commuter. That is probably higher than I need to go, but it is lower than I used to run. I can tell you that, for me, lower pressure feels pretty good, as long as I don't obsess too much over what the tires look like, and as long as it isn't so low that I'm flatting out.
posted by Opposite George at 11:00 AM on July 10, 2015

Yeah, this is just something that happens. The center of gravity of the bike with you on it isn't exactly in the center, it's slightly aft, so the rear wheel is taking more of the weight. Consider also that the flex you're witnessing is probably exaggerated by the angle you're looking from (basically straight down, looking against a hopefully true wheel, any bulge is going to look much bigger than it is).

If you want an easier ride, you could go to your local bike shop and see if they can recommend higher pressure tires for your wheels; they may or may not be available. You could also change to a smaller tread (I think you should even be able to get slicks at standard MTB sizes).
posted by backseatpilot at 12:02 PM on July 10, 2015

I have a friend who blames overinflation for a mountain biking crash she had; apparently things can get too bouncy and hard to control. I think that's only in more mountainey trails; the stuff you describe should sounds like it would be fine.
posted by aubilenon at 12:05 PM on July 10, 2015

If these are knobby tires the issue is that at high pressures you get a lot less road contact because the tire can't deform enough and you're just touching at the end of the tire knobs.

Assuming these are tires in the 1.5" to 2" range, they will always visually look flattened a bit when you ride. Only narrow road bike tires at 120 psi are going to look otherwise.

As a big dude, you're generally going to want to go on the high end of tire pressure.

If you're riding on paved roads and flat dirt/small gravel you may want a less knobby tire if you don't already have one. Two advantages: smoother ride and generally they have higher pressure ratings. I generally get commuter tires that are rated to 80 psi or so (and I weight ~210 lbs). Even at 80 psi they're fine for dirt roads in terms of grip. Like a Schwalbe Marathon or a similar tire.
posted by GuyZero at 12:11 PM on July 10, 2015

If you've got a mountain bike and you're riding on paved roads or packed dirt, get new, slick tires that tolerate higher pressure.

I think most tires can handle considerable overinflation, but if these tires are 13 years old, they're probably breaking down anyhow.
posted by adamrice at 12:31 PM on July 10, 2015

I would say get new tires. My bike is 7 yrs old and i replaced tires 4 times.
Check the size of your tire, most probably 26" tires with 2" range. Your tire should have them marked on it.

I have the bontrager connection trail which have knobbies if you decide to go off trail a little bit but good for road ($20 a tire) and inflated to roughly 55-60 psi . If you are doing more road and no trails, then see tires that are easy rolling and no knobbies.

Also while you are at it, get a tire lever ($2) to change your own tires
posted by radsqd at 12:41 PM on July 10, 2015

Like most of the others here, I don't think the higher pressure is going to give you what you want. I'd consider smoother, slightly thinner tires. I really like Panaracer Paselas in 26 x 1.5 at 60 psi. Plenty cushy while being really nice and efficient.
posted by advicepig at 1:29 PM on July 10, 2015

The Panracer Paselas in 26x1.25 go up to 100 PSI which is basically a road bike tire. It would ride somewhat differently than what you have now, but it would have a lot less rolling resistance.
posted by GuyZero at 1:33 PM on July 10, 2015

High pressure doesn't make you faster. It just makes you feel faster, because you feel more road vibration. As an article from Bicycle Quarterly explains, you want a tire that drops about 15% of its total thickness when you are sitting on the bike. That's a good compromise for paved road riding between rolling resistance, which decreases as you increase pressure, and suspension losses, which increase as you increase pressure.
posted by brianogilvie at 1:34 PM on July 10, 2015 [1 favorite]

Response by poster: Thanks for all of the answers so far, they have been very helpful. I guess the main thing was that the "flattening' concerned me but it seems this is normal. I was worried I would get a flat but it seems that is what these tires are designed for. And they aren't so flat that the rims touch, its actually a comfortable ride. Ultimately as some have mentioned, I will look into getting new tires (from my local shop).

As far as the resistance/pedaling issue maybe I should embrace that, after all the point of riding is for me to get some exercise!
posted by Busmick at 1:41 PM on July 10, 2015

No, really, don't get knobbies if you don't need them. You just wear them out faster, and you get a less comfortable ride. You want more resistance? Ride faster.
posted by adamrice at 3:08 PM on July 10, 2015 [2 favorites]

Yes, you can certainly overinflate a bike tire. I've had blowouts before from overinflated tires; the bead of the tire comes off the rim and the tube distends out from the gap in a sort of aneurism, and you hear a *shh, shh, shh* sound for a few revolutions as it rubs against the stays followed by a *POW!* when it gives way. You can overinflate tires a bit (I usually run mine about 5 psi high) but there's a definite limit.

Higher pressure gives you a faster, smoother ride at the expense of traction and shock absorption. If you're riding on pavement then this is usually a good tradeoff. Slicker tires have similar benefits and drawbacks compared to knobbies. This is why road bikes have slick, high-pressure tires. If you're riding your bike on the road then all else being equal it will ride better on slicker, higher-pressure rubber. (This will also generally mean narrower tires, since narrower tires tend to have higher pressure ratings.) You'll put forth the same effort but you'll go faster and roll more smoothly.

The Panaracer Paselas people are recommending are a great all-around tire that isn't terribly expensive, I've used them before and loved them. Spring for the Tourguard version and you can pretty much wave goodbye to punctures, as well. Absolutely worth it.
posted by Anticipation Of A New Lover's Arrival, The at 8:32 PM on July 10, 2015

I run 100 - 110psi in my 90psi tire; that being said; I'm riding a pair of Schwalbe tires; and I beat the crap out of them on and off the pavement. Fighting a rolling resistance is a quick spoil to a bike ride; be it a commute, exercise, or recreational.
posted by buzzman at 8:32 PM on July 10, 2015

When I was commuting in London on my mountain bike (a big heavy Kona Hoss), I had to replace the tyres every 3 or 4 months, because I ran them at low pressure. I used Specialized Pro 2.3 knobblies. The problem was that the inner binding (whatever it's called) of the tyre used to split and pinch the tube, causing big gashes. From the outside the tyre looked fine, but taking it off I could see diagonal slashes all the way around the inner wall. The splits in the inner tyre were the only times that I got a flat, because I used slime in the tubes to protect against sharps.

Long story short, depending on the type of tyre you have, if you run at low pressure it could damage the tube. So, if replacement costs are an issue for you, I'd recommend going as high on pressure as is comfortable for you to ride with.

(I didn't actually realise that there was a recommended maximum pressure for bike tyres, but I suppose it makes sense that there is.)
posted by veedubya at 1:34 PM on July 11, 2015

Just another vote for Paselas! They are really nice tires that strike a good balance between performance and durability.
posted by werkzeuger at 2:29 PM on July 11, 2015

don't get knobbies if you don't need them. You just wear them out faster, and you get a less comfortable ride.

In addition, knobbies are less safe on pavement than slicks because the contact patch is smaller and more squirmy. Knobbies are great on dirt, but crap on pavement. Bikes don't hydroplane. They don't need tread on their tires. Slicks are by far the best, safest tire on pavement.

The Paselas are great tires. I've been using them as my main urban tire for years. Highly recommended.
posted by bonehead at 6:44 AM on July 12, 2015

I don't want to hijack the thread, but the idea that narrow, high-pressure tires are inherently faster than wider, low-pressure tires, mentioned a couple times above, has been shown to be a myth by research conducted by Jan Heine and a few others and published in Bicycle Quarterly.

What Jan et al. found was that the most important factor was how supple a tire's casing was. Until recently, high quality tires with supple casings were available only in narrow widths (or in tubular tires, which tend to be narrow too, since the UCI limits the maximum tire width that can be used in UCI-sanctioned races, and few non-racers use tubulars these days). Not too long ago, Grand Bois, a Japanese company, started making high-quality tires with supple casings in wider sizes (more precisely, they worked with Panasonic to design the tires; Panasonic manufactures them). So it's now possible to have more comfort from pneumatic suspension without sacrificing speed by using wide tires with moderate pressure.

On the other hand, Jan and his co-researchers found that tire pressure has almost no effect on speed. High pressures just make people feel like they're going faster.

Some people have quibbled with Jan's findings because they aren't double-blind tests and they go against conventional wisdom. But he points out that the studies showing higher pressures produce less rolling resistance were done in factories using perfectly smooth stainless steel drums as the riding surface, not real-world surfaces.

BQ articles aren't online (except for a few samplers), but Jan has written more briefly about some of the results on his blog. If, like me, you enjoy geeking out over bicycle technical details, it's worth nosing around there a bit.

Note that Jan was himself a devotee of narrow-high pressure tires until he tried to figure out why he could ride faster on an old Alex Singer cyclotouring bike from France, with wide tires, than on his road bike with narrow tires.
posted by brianogilvie at 2:50 PM on July 12, 2015

If you don't want to buy new tires, and if you have some decent wire cutters, you just clip the knobs on the contact area and leave the side knobs. Or you can lock up your back brakes on a dry downhill road to wear the knobs down very quickly then swap the tyres round and do the same with the front tyre - I've done this - it works well.

I generally use my old mud tyres in the summer. Knobs are worn down but the side knobs still hook up well on the dirt when you need it for cornering.
posted by guy72277 at 12:30 AM on July 13, 2015