BMX wheel anomaly?...little help here...
05-24-13, 12:45 AM
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BMX wheel anomaly?...little help here...
Having experience albeit none with BMX, I recently pieced together a "junior" sized BMX race bike for my son. I was careful to order wheels designated 20 x 1 & 1/8 (ISO 451). The tire size matched - 20 x 1 & 1/8 (no decimals, ISO 451) but the tires seemed sloppy - just slightly big on the rim. Sure enough, the rear tire blew the bead off at pressure. Twice. The front holds pressure but concerns me to the point that he's not riding it.
Wrinkle #2: using my Park truing stand and a metal ruler, I can clearly see that the radius of the rear wheel is about 2.5 MM LESS than the radius of the front and, this is AFTER I allow a millimeter for vertical true variance. A 5MM diameter difference seems remarkable to me. ("SINZ" wheels - about $300 retail; tires are "Tioga Power Block."
Reactions? Do I need a different tire? Return the wheels? What's up with BMX stuff?
Wrinkle #2: using my Park truing stand and a metal ruler, I can clearly see that the radius of the rear wheel is about 2.5 MM LESS than the radius of the front and, this is AFTER I allow a millimeter for vertical true variance. A 5MM diameter difference seems remarkable to me. ("SINZ" wheels - about $300 retail; tires are "Tioga Power Block."
Reactions? Do I need a different tire? Return the wheels? What's up with BMX stuff?
05-24-13, 01:07 AM
#2
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What kind of tyre-bead? Steel-bead tyres don't stretch and can tolerate quite a bit of looseness in fit.
One thing that helps is to pump up the tyre just 1/2 a pump after installing so it has shape.
Then manually pull and tug on the tyre's low-spots so that it's evenly centered on the rim-edge (compare circumferential moulded lines with rim-edge).
Once the tyre's perfectly even all the way around, pump it up.
One thing that helps is to pump up the tyre just 1/2 a pump after installing so it has shape.
Then manually pull and tug on the tyre's low-spots so that it's evenly centered on the rim-edge (compare circumferential moulded lines with rim-edge).
Once the tyre's perfectly even all the way around, pump it up.
05-24-13, 01:32 AM
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OK. Still concerned...
Understand your suggestion. I AM using steel bead tires so it might well be that perfect centering will fix it. (I tried that and blew up another one.) Still, it really seems like the tires are either too big or the rims too small. Should I try a folding tire as that will have tighter bead? Can't tolerate even the chance of that thing blowing in use...
What kind of tyre-bead? Steel-bead tyres don't stretch and can tolerate quite a bit of looseness in fit.
One thing that helps is to pump up the tyre just 1/2 a pump after installing so it has shape.
Then manually pull and tug on the tyre's low-spots so that it's evenly centered on the rim-edge (compare circumferential moulded lines with rim-edge).
Once the tyre's perfectly even all the way around, pump it up.
One thing that helps is to pump up the tyre just 1/2 a pump after installing so it has shape.
Then manually pull and tug on the tyre's low-spots so that it's evenly centered on the rim-edge (compare circumferential moulded lines with rim-edge).
Once the tyre's perfectly even all the way around, pump it up.
05-24-13, 01:37 AM
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Understand your suggestion. I AM using steel bead tires so it might well be that perfect centering will fix it. (I tried that and blew up another one.) Still, it really seems like the tires are either too big or the rims too small. Should I try a folding tire as that will have tighter bead? Can't tolerate even the chance of that thing blowing in use...
05-24-13, 09:35 AM
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+1, My first reaction was that someone mixed the rim sizes, but it seems that there's no common size a bit smaller than 451, so if there's a difference of over 1mm in the rim's diameters one is defective. If the tires fit OK on the larger wheel, the smaller is clearly defective and must be replaced.
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Just because I'm tired of arguing, doesn't mean you're right.
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05-24-13, 09:49 AM
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+1, My first reaction was that someone mixed the rim sizes, but it seems that there's no common size a bit smaller than 451, so if there's a difference of over 1mm in the rim's diameters one is defective. If the tires fit OK on the larger wheel, the smaller is clearly defective and must be replaced.
05-24-13, 09:52 AM
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Absolutely, but I don't think anybody could make a 45mm mistake, nor would the tires come at all close to fitting.
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An ounce of diagnosis is worth a pound of cure.
Just because I'm tired of arguing, doesn't mean you're right.
“One accurate measurement is worth a thousand expert opinions” - Adm Grace Murray Hopper - USN
WARNING, I'm from New York. Thin skinned people should maintain safe distance.
05-24-13, 10:23 AM
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Looked at the diameter some more
+1, My first reaction was that someone mixed the rim sizes, but it seems that there's no common size a bit smaller than 451, so if there's a difference of over 1mm in the rim's diameters one is defective. If the tires fit OK on the larger wheel, the smaller is clearly defective and must be replaced.
