Wobbly back wheel

[mikeloveshisrockhopper]

Afternoon all,

On my last two rides on my specialized Rockhopper, I've felt a strange wobbly feeling from my back wheel when descending quickly. I don't feel it at any other time.

With the wheel on my bike and the bike upside down, when I spun the wheel, I can see a clear wobble. When I deflate the tyre and spin it again, no wobble.

What's happening? Is the tyre defective? Is it just not sitting properly? My plan is to inflate it slowly making sure it sits nicely but would be happy to hear other advice.

Cheers

Mike

 

[Slick]

Twice I've had the same, but once the quick release was just not set right and the second time the spindle or axle had sheared. It could be your tyre if it's sitting twisted but I assumed that would need to be quite noticeable.

Hopefully the fettlers will be here soon to keep you right.

 

[mikeloveshisrockhopper]

Do you think the difference in the wobble between the inflated and not inflated spin is significant? Or is that misleading me? I'm mechanically inept, btw.

 

[sanddancer]

Fit another tyre first to eliminate that.

 

[mikeloveshisrockhopper]

Fit another tyre first to eliminate that.

Yeah seems obvious I guess. I finish work on Wednesday so will do some playing around. The bike is a dream otherwise, I hope it's not a permanent feature.

 

[Slick]

It could be a manufacturing fault if it's a new tyre.

 

[mikeloveshisrockhopper]

It could be a manufacturing fault if it's a new tyre.

It's almost 2. The problem has come out of the blue. I haven't taken the tyre off in the time I had it. Very strange.

 

[Slick]

Mmm, I assume you have checked the wheel nuts and axle.

 

[mikeloveshisrockhopper]

Mmm, I assume you have checked the wheel nuts and axle.

It seems to be seated into the frame properly. The nuts are tight. What would I check on the axle? That it's straight I guess?

 

[Slick]

Mine disintegrated once.

 

[Globalti]

I'm willing to bet the sidewall of the tyre is tearing away from the bead in one place, either because the brake pad has worn, gone off the rim and is rubbing the tyre or running the tyre a bit soft has allowed the sidewall to bulge outwards and grit has fretted it where it's been touching the rim. I lost a couple of good newish tyres in both ways when I was a mountain biking novice.

 

[Ajax Bay]

Just to confirm: you sense this wobble when descending quickly but not slowly? And from the back wheel (ie not a speed wobble).
With the wheel (axle) firmly locked ie QR tight tight, if you push sideways on the rim (with the frame/bike secure/immobile), does the rim deflect? If so it may be your bearings need tightening. I think the tyre thing's a red herring. Sidewall aberrations would be self-evident.

 

[mikeloveshisrockhopper]

Just to confirm: you sense this wobble when descending quickly but not slowly? And from the back wheel (ie not a speed wobble).
With the wheel (axle) firmly locked ie QR tight tight, if you push sideways on the rim (with the frame/bike secure/immobile), does the rim deflect? If so it may be your bearings need tightening. I think the tyre thing's a red herring. Sidewall aberrations would be self-evident.

Hi. Definitely only through the back wheel and only descending quickly. I'll try what you said regarding pushing sideways on the rim. I think I've done that and it was solid but I'll try again.

 

[Tim Hall]

Adding to that, when you say you see a wobble with the bike inverted, is it the tyre that appears to go in and out, or the rim? Gauge if the rim is wonky either by eyeing it as it passes the brake block, or as it passes the tip of your finger, resting gently on the chain stay.

 

[mikeloveshisrockhopper]

Adding to that, when you say you see a wobble with the bike inverted, is it the tyre that appears to go in and out, or the rim? Gauge if the rim is wonky either by eyeing it as it passes the brake block, or as it passes the tip of your finger, resting gently on the chain stay.

I really believe the rim is true. I've done the checks you said. It turns straight when the tyre is flat but there is a wobble with the tyre inflated. It's really hard to pinpoint at which point the tyre wobbles. I guess it should be visibly obvious. I only had a look at this briefly after Saturday's ride so I'll check more tomorrow. It was quite dramatic, the difference between the inflated tyre and flat tyre.