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Old 04-02-09, 09:05 AM   #1
TallRider
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how to mount tires so there are no hops?

Sometimes when I mount a tire on the rim, and then spin the wheel, there are noticeable hops in the tire as the wheel spins around. That is, at some points the tire is further from the rim than others.
I've had this happen with road tires and mountain tires, although of course it's more noticeable with mountain tires since the tires are much thicker. In all cases the rim is round, this is not a function of the rim having a vertical hop.

I don't know how much this is a problem - perhaps the bumps aren't going to be felt while riding because weight on the tire will compress it to the same spot no matter if it's further from the rim or not. But I suspect otherwise.

What causes a tire to have a vertical hop when mounted on a rim? Are some tires more likely to get this, because they have tighter (or looser) beads? I don't know.

I usually try to find the low spot, and, starting from the opposite side of the wheel, pull more tire toward the low spot. But this is very hit-and-miss.

Are there any better, more confidently surefire ways to avoid hops in tires?
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Old 04-02-09, 09:15 AM   #2
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"Hop" can sometimes occur if the tire beads are not seated evenly around the rim. When installing a tire, I air it up to just a few psi, and look around the rim to make sure that the bead is seated evenly. You can usually use a line or seam on the tire as a reference. On sew-ups, you make sure that the seam tape protrudes the same distance on either side, and is consistent around the circumferences of the rim.

Some bicycle tires will still retain a little hop, even if properly installed. Some tires are made better than others, and a more expensive, high thread count type tire will probably be much more round than a less expensive tire.
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Old 04-02-09, 09:23 AM   #3
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i have a conti gatorskin that has a hop, but it is due to poor manufacturing. it is because of the mold of the tire, not poor mounting.

unless it is pronounced, you should just try to forget about it. you probably won't feel it, but i might trick you into thinking your wheel isn't true unless you take a closer look at your rim.
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Old 04-02-09, 09:38 AM   #4
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First of all, is it a real hop or is it just some marking or coloured strip on the tire that appears to hop.

If it is a real hop, first place to look at is whether you are seating the bead properly where the valve is. That's usually the place it occurs, but it could be anywhere else, I suppose. Tubes have a thicker bulge around the valve which, if you don't seat the bead properly under it, is guaranteed to give you a bump.

Many super high quality tires are in fact not perfectly round. This is because they are handmade and have never in the history of cycling been perfect. This applies in particular to tubulars, but also to some racing clinchers. Of course, very cheap clinchers could have imperfections too.

All that being said, it's best not to be anal retentive about it unless it's a noticeable hop as you ride.
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Old 04-02-09, 09:46 AM   #5
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Make double-dang sure that you don't have a bit of tube trapped under the bead.
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Old 04-02-09, 10:27 AM   #6
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Quote:
Originally Posted by Kotts View Post
Make double-dang sure that you don't have a bit of tube trapped under the bead.
Yup, and check your valve stem too.

The inner tube is a skosh thicker where the vavle stem is attached. If that thick portion gets trapped under the tire bead it'll give you a high spot. The cure is to push the valve stem in toward the rim before you inflate the tire.
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Old 04-02-09, 12:26 PM   #7
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On MTB tyres, they typically don't have as tight of a fit of the bead to rim as road tyres. So without much pressure in the tyre, you can actually pull and "true" the tyre on the rim before fully pumping it up. A lot of the hops is visual tricks too, the moulded lines on the sidewall may not be perfectly concentric with the bead. But if you look at the OD of the tread, it may be spinning perfectly with the rim.
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Old 04-02-09, 12:35 PM   #8
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I should clarify the problem more.
First, I only have experience with clincher tires.
The hop is not connected to tube being trapped under the bead, and hop can occur anywhere, sometimes by valve stem, mostly not.
It is real hop, judged from the outer edge of the tire (the part that contacts the ground). (Longfemur, you're right that sometimes painted lines on the tire aren't perfectly consistent around the tire, so the line can appear to hop even if the tire doesn't.)
Most of the time, this happens with tires with a tight bead, where the bead is too far in (closer to the bed of the rim and axle of the wheel) at one spot, and in the correct spot the rest of the way.
Some of the time it's probably just due to the tire not being very round.
It's most noticeable with fat mtb tires (2+ inches) that will show a proportional hop a lot more. Perhaps their size means more "slop" in how/where they can seat.
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Old 04-02-09, 04:58 PM   #9
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In all my riding years, I've actually had that same problem only with a few mountain bike tires (I've mostly ridden road bikes). Sometimes they just won't seat themselves properly onto the rim. Probably has to do with just an unfortunate combination of tight tire and oversized rim. Not sure what you can do other than to inflate it to a higher pressure to try and force the bead to go where it's supposed to.
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Old 04-02-09, 05:40 PM   #10
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First, before inflation, push the valve up to ensure the tube is not caught between tire and rim; look around both sides of the wheel circumference to check no part of the tube is protruding; next bounce the wheel lightly on the ground while completing one revolution; inflate to about 20 psi and spin it to see if the tire is evenly seated; if not, work the tire to get it even; inflate to normal pressure or a little higher so that the tire will pop into place on the rim, and then back off to normal pressure.
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Old 04-02-09, 05:49 PM   #11
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Get a plastic bag with half a cup of baby powder in it. Before installing a tube throw it in your bag and shake it around.

Now that you got your messy tube put a little bit of air in it, maybe a stroke or two from the pump and install it as you normally would. Pump up to say 20-40lb and spin the wheel. Are there any low places? If so try to work them out with your thumbs. Now pump it up all the way.
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Old 04-02-09, 06:19 PM   #12
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Whenever I mount a tire I make sure that the first part of the bead that gets seated is the part around the valve stem. The tube is thicker there and won't get pushed in all the way unless I start seating the bead there.

I also put enough air into the tube that it takes a round shape, rather than being flat. It seems to help.
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Old 04-02-09, 07:57 PM   #13
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I actually used baby powder to get the tires on my fixed-gear bike mounted without hops. And I could feel those hops while riding with tires at high pressure.
I may try that trick in my current case (a 2.3-inch mountain bike tire). There's a very fluctuation in outside diameter of the tire. But since I put the tire on with the purpose of running a fat tire at lower pressure to provide some suspension on my unsprung singlespeed mtb, maybe I won't notice the hop while riding.
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Old 04-03-09, 11:16 AM   #14
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All tires have a line around near the bead. Check to make sure this line is equi distance around from the rim edge. If not, push the edge down with a tire lever. For rims that are using a too side a tire, you may need to put a little tire spray or bike polish to help it slip down.
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