I think I posted this about a year ago but I can't find it. Anyway, about 95% of the time when I check my tire pressure, both of the tire valves are at the same location on the respective rims. If the front is at 5 o'clock, so is the rear. I checked today and found them about 40° different which is unusual.

Anyone else ever notice the tire valves end up at about the same spot front and rear?

Totally random here. Maybe because the front is in the air too much.

I can look at this two ways. Both have 17" rims and if I timed both stems, most likely yes, meaning, in 360 degrees they'd line up again.

But if I install a tire with the outer diameter larger than the other, then no, not going to happen. See, If I took a tape measure, wrapped it around the diameter of the tires, the tape will show the larger tire. Now, if I took the rim alone, rolled the rim the length of the tape measure, I am going to walk off the tape before the other rim runs off that rear wheel length.

We see how yes, the odds of it coming around and you seeing both line up at the time?... Just that... ODDS.

But if I install a tire with the outer diameter larger than the other, then no, not going to happen.

It seems to make no dif with me. I'm using a 190/55 and the old tire was a 190/50. The valves are almost always in the same spot. I haven't used a protractor to measure or anything but they are always very close.

Always seems to be Murphy's law with me. I always seem to need to roll the bike to get to the stem. Then roll it again to check the second one.

1 = OD diameter ~ 190mm
2 = across the tire ~ 55mm
3 = ID is 17" rim ~ 17" fr/rr

I would think any turning would change the stem location. Like start them on the top and roll your bike in a complete circle. Are they still the same. I am too tired to try, 90 + here in Minnesota and enjoying time at the cabin.

Hub...
#1...that's the width of the tire, not the diameter

#2...that's the aspect ratio in percentage of the width
a 50 tire is 50 percent of the width while a 55 is...yup, 55 percent of the width
Both refer to the height, so a 55 tire is taller than the 50

Anyhow, the rear will make less revolutions than the front while rolling the bike..so Rook, coincidence!

:)

Have to admit I have no idea. LOL Rook. Am curious now though. Just got home from a 4 hr trip back from San Fransisco. Will look later though. Yall have me curious.

Maybe the tire pressure elves come out after I leave the garage .

"Hank Has It!" Thanks. I should know this but...

... I was more trying to show How the elf OD and elf ID do not equal 17" front and rear: where it's not looking at both 17's coming around thinking you are rolling on a 17 to 17 stem ratio. The difference is the OD you are looking at. Eventually the stems are going to turn out of sync with each other. And at the same token, the stems will sync back in.

The same effect is to mark the link on the rear chain directly across from the tooth number on the sprocket. Take your pick looking, but that one turn of the wheel, the chain mark coming around will not line up with the number. It syncs out of phase. At the same token, you run the wheel so many turns [I remember in the 60's was how many] and see how many times it took to sync that link to sprocket number again.

So if you play the ratios, what are the odds you come back from a ride, check the stems and wait for them to sync to the bottom so they are easier to fill.

So if you play the ratios, what are the odds you come back from a ride, check the stems and wait for them to sync to the bottom so they are easier to fill.

HA-check the tire pressure every 253.723694 miles. there will be no problem reaching the tire valves without moving the bike!

Unless you only ride in a straight line, which gets old in a hurry, the front wheel and the rear do not follow the same path when turning. You can see it clearly when you turn the bike at low speeds with the front traveling a much longer path than the rear. But even at high-speeds the front leads and the rear follows.

So even if the two tires were exactly the same diameter (which they are not) they don't travel the same distance. So while I'm hesitant to say the relative positions of the valve stems is random, if they end up the same it's just a coincidence.

No Rook. But you do know tires for front and rear are supposed to be different sizes right?

Just checked tire pressure today. Both valves were the same. Went on a 70 mile ride. Mostly expressway and ramps. some pretty hard conering. Raced a Corvette (yes won easy). Took a little ride through town in rush hour. That's about as much variety as can be. When I got back I decided to check tire pressure after the tires were warmed up to compare to cold check. Tire valves were exactly the same position.

Next ride, I'm going to get them off kilter on purpose and see if they go back on kilter by the time I get back.

Unless you only ride in a straight line, which gets old in a hurry, the front wheel and the rear do not follow the same path when turning.

Yup i know. I can't explain this.

But you do know tires for front and rear are supposed to be different sizes right?

55% of 190mm is 104mm. 104 mm = 4.09 inches 4" + 17" rim = 21 inches tire O.D.

70% of 120mm is 84mm. 84mm = 3.3 inches. 3.3" + 17" rim = 20.3 O.D.

Is that correct? If so, close but not nearly close enough. Even if they were the same OD, I would never guess this would happen bacause of turning and maybe a little spinning and loosing road contact.

Second ride today. Valves were out of synch just a bit after making a few tight turns back and forth to roll out of the garage. They were both near 6 oclock but opposite...like mirror image. Went a on a hellacious ride and came back... They got closer. Almost perfect again. This is obviously no coincidence. Maybe it's the aluminum valve stems that are heavier than rubber. Happens on both bikes all the time. I don't think it has to do with the wheel balancing weights. Those are not right near the valve stems.

Rook, have you talked to a therapist about this? Just kiddin ya.

Your close on the math but it is 2 times the tire height plus rim diameter so 2x4=8+17=25" then times that by the formula pie 3.1416 to get the tire circumference 25x3.1416=78.54". The math on the front tire is 2x3.3=6.6+17=23.6x3.1416=74.14". The difference in circumference is 4.4" so if you divide 78.54" rear tire by 4.4" you will find that the valve stems line up every 17.85 revolutions of the rear tire. I don't know the math to figure out the number of revolutions before the line up at the lowest point on the wheel and like others have said turning, wheelies and the raw power wheel slip will also effect this so ya it is pretty random.

So now that we are all OCDing on this, enjoy the ride

Dave

If this happens again tomorrow after I get the bike on the stand and turn the stems so they are opposite......IDK....? Maybe the therapist will have me committed! Hope they have a nice race funny farm somewhere with a race track .

Rook, have you talked to a therapist about this?

Or maybe an exorcist....lol!

Seriously though, I synchronize my valve stems before every ride, improves cornering and top speed, adds 3 HP also.

pi(r)squared?

No... pie are round!

Yum.

LOL @ Kruz, I heard 2.5HP but that might just be with the Canadian exchange rate right now :/

Actually, I'm not really sure why we're still talking about this, HanksZX already answered the question, the diameters of the wheels are different, even if they were exactly the same the tires would wear differently and change slightly.

Unfortunately it rained today. Looks like there is a good chance we'll get a break this weekend. Then I do the off kilter test. If I come back and the valves are the same, next step is video to prove to you guys I'm not BSing.

Hell...I b'lieve ya Rook!Mine have done that.Strange thing though...it's usually my spokes lined up.Even if I loft or whatever...they seem to 7 times outta 10 wind up in the same position.

Actually, I'm not really sure why we're still talking about this

Give me any pie round or square any flavor as long as it is warm and has a scoop of ice cream.

* Last updated by: david5525 on 6/11/2015 @ 8:49 PM *