Johnny Alien

So I just got a new set of wheels for a new build. The rims are Velocity A23's and I have a set of Schwalbe Kojaks on them. When I have the tire properly mounted in the front fork and spin it I can see that there is an uneven part. (This is going to be a nightmare to describe I think). Looking at it dead on from the front there is a part in the spin cycle where it appears the whole wheel bumps down and then back up again. Using a visual cue (such as zip ties on the fork or the brakes) you can see that it looks like the wheel is running true the whole time. Is it possible that the tire is deformed at some part which is what is making it go down and back up? It seems like that would be the logical case but maybe the wheel is the issue and I can't see that using an indicator? If it's the tires does that mean they are bad or that they will fix themselves up as they are ridden.

This is probably a stupid stupid question.

ursle

Not knowing if you have a bike stand, if you stand the bike up, upside down and spin the front wheel, take a pencil or something with a small tip and put it on the brake for support, now place it very near the rim and watch(with the wheel spinning), if there's a flat spot in the rim it will be evident, if the tire isn't seated properly, it will also be evident, soapy water on the tire bead will usually help seat a tire properly, the max pressure on the sidewall is 1/2 the bursting pressure of the tire, but if the tire's not seated properly, the tube could sneak out and explode, tmi

A new wheel with a flat spot should be an easy fix, an old wheel with a flat spot might be in trouble, yes there's a tool to re-bend the rim to shape, if the rim is of quality and doesn't just contort, it fit's around the outside of the rim and has a threaded set of "fingers" that grab the inside of the rim and pull it back into round, did a look on google and didn't find one, might be the one I used back in the 70's was an antique, also had tools to install the hard rubber tires on wheel chairs(wire in the middle of the tire), definitely antiques.

Johnny Alien

I will try the pencil trick. I had the brake off and used zip ties and the wheel seemed to be running true. I am almost sure it's the tire. It is a used tire not new so maybe there is an issue there. So maybe I should remove it and try some soapy water on the bead.

dsaul

Check around the tire where it meets the rim. I suspect that the bead of the tire is not fully seated on the rim in the low spot. Usually some persuasion with your thumbs can pull the bead up into position, but you may need to deflate the tire and put some soapy water around the tire bead before inflating.

FBinNY 

20:1 it's a simple issue of a poorly seated tire on the rim. You can check this easily by looking ar the molded "reference" line on the tire just outside the rim. Turn the wheel slowly and watch the line, it should be the same distance from the rim all the way around. If it dips anywhere that's the problem. Don't forget to check both sides.

If the reference line checks out, mount the wheel and spin it while watching the rim as it passes the brake shoes. It shouldn't wobble or dip more than 1mm. BTW, wheels don't have to be perfect, but long, gradual changes won't be noticeable, while short local dips or hops will be felt as thumps once per revolution.

sreten

Hi,

The odds of it being a seating issue are a lot lower than 20:1

As one cause of this can be a innertube trapped under the bead,
which can then split, thoroughly check out the tyre seating and
the position of the innertube in the tyre.
Usually its only trapped on one side, that side not seating properly.

rgds, sreten.
on one side, that side

cny-bikeman

Well, I would thing it's actually higher than 20:1, as the only other things that cause tire deflection are a ripped bead or damaged cord/casing, and both would cause the tire to go up, not down. The same would occur if inner tube or rim strip were under the bead.

If the reference line (what I call the bead line) does dip into or toward the rim make sure first that it does not go away from the rim at any point. If it does then you will indeed need to check for inner tube or rim strip sitting under the bead. If only the low point is a problem then do the following:

1. Temporarily mark the entire area where the bead line is not the same distance from the rim as it is on the rest of the tire. (Crayon, pencil, tape, etc).
2. Deflate the tire/tube.
3. Spray some mild household cleaner (Fantastic, 409, etc.) along the entire marked area - one or both sides depending on what the tire is doing. You can also apply soapy water, some say alcohol works.
4. Reinflate the tire carefully, watching to make sure the bead line stay consistent on both sides on the rest of the tire. You will almost surely need to overinflate (or if you have one of the wide range Kojaks, at least on the very high end of the range). Be prepared for the large POP sound that may occur when it suddenly moves out to the correct seating.
5. Adjust inflation to the correct amount. The lubricant will do no harm, but if you used soapy water rinse the area.

sreten

Hi, Depends on what you mean, FB surely initially meant 20:1 on, rgds, sreten.

(Odds are assumed to be against, unless qualified with on.

Odds are expressed as say 2/1 which = a 1:1 ratio, out of 2 times it will happen
once, so 20/1 odds are in twenty times it happens once. The actual ratio is 1:19.
Odds of a number on a dice are 6/1, ratio 1:5. Not throwing a number on dice
is 6/1 on, in six times it will not happen once, it will happen 5 times, 5:1.)

cny-bikeman

A bit off topic but of course he meant "odds on," or for it being a seating issue - "20:1 it (is)..."

Johnny Alien

Thanks guys! The math hurts my head but at least I know I can likely fix the issue.

FBinNY 

20:1 odds man that first event is 20 times more likely than the second. Out of 21 attempts 20 will happen as predicted, 1 one won't. This is different than a 1 in twenty chance which implies 20 tries total, and would be 1:19 odds.

Odds are expressed as the ratio of two outcomes, out of a number of tries equal to the sum of the expresed outcomes. ie, 2:1 means 3 tries, with the first outcome twice as likely as the other.

By that logic greater odds in favor would imply than instead of 20:1, it would be 40:1 for example.

jon c. 

In horseplaying parlance, 20:1 is a longshot. 1:20 is sure thing.

FBinNY 

Yes, it's that way in horse parlance, because it's the bookmaker who's expressing the odds. He's betting against your horse, saying he'll put up $20 to your $1 bet on that nag. He's willing to do that because he doesn't expect the horse to win.

However, In my first expression of the 20:1 the tone of the post makes it clear that I'm expressing a high likelihood that it's a tire seating problem. If it were a horse bet, you'd have to put up $1 to my $20, and would collect $21.00 if I were wrong.

sreten

Hi,

Expressing odds as ratios might be mathematically correct, but they are generally not expressed
that way in terms of betting and common parlance, e.g. 1:1, 1 to 1 = 2/1, 2 for 1 = 50%.

Or throwing a number on a dice, which is 6/1, not 1:5 in common parlance.

Confusingly in the UK a 2/1 or evens wager, is referred to as 2 to 1, not 2 for 1.
As are all betting odds, to instead of for, X/1 is referred to as X to 1, not X for 1.

It makes a lot of sense rather than ratios, for every 1 you
bet you win X. For X/1 on, you win 1 for every X stake.

Perhaps something is lost in translation, the chances are 20:1 is perfectly
clear in UK English, but the odds are 20:1 is somewhat ambiguous in
common UK English, (unless you happen to be a mathematician),
though I always knew what you initially meant, nearly all the time its ....

Generally in the UK if the chance of something happening is low the
odds are high, e.g. the chance of winning on a lottery ticket is low
because the odds of it happening are high (stacked against you).

rgds, sreten.

Retro Grouch 

Sometimes that's easy to fix. Is the low spot next to the valve stem?

If that's the case, deflate the tire to about 10 psi, push the valve stem in toward the hub with your finger, and reinflate the tire to operating pressure. That'll work if the thicker part of the inner tube by the valve stem is what's keeping the tire bead from seating against the rim.

cny-bikeman

Wow, tangent time still. Again, FB made it quite clear when is said that "20:1 it's (it is) a simple issue..." not just "odds are 20:1." Betting parlance is indeed odds against but that doesn't make it necessarily "common parlance." When I took statistics classes the odds of something occurring were always the first part of the expression, the odds of it not occurring the latter. Even in gambling the positive is often first. Look at the published odds on a lottery ticket, such as 1 in 175 million.