surfimp

I've just converted an old mountain bike ('92 Kona Lava Dome) to an Xtracycle. In the process I upgraded the brakes, ditching the old centerpull cantilevers and levers, and going with Avid SD7s front and rear along with Speed Dial 7 levers. Also, I removed both the front and rear wheels and trued them under the guidance of a trained bike mechanic down at the local bike co-op. They are definitely within spec in terms of true.

However I am finding that when braking, I am getting a really bad pulsing and squeaking from the front wheel, enough to deflect the fork a visibly noticeable amount and make me not want to ride the bike till I get it sorted.

I'm assuming there's a bulge or other deformation on the rim that's causing this pulsing, that for whatever reason was not evident when I trued the wheels (that doesn't make sense but that's the only explanation I can come up with). The rims themselves "seemed" OK when I was truing them, but you can see and feel that their sidewall faces are slightly concave. Are they just plain worn out? These are older Araya rims, I don't know the model number, but they were decent rims when new. 16 years ago... LOL

I tried using rubbing alcohol to clean the rim but that didn't really help anything. I can post photos if that's helpful.

Thanks much,

Steve

surfimp

Sorry for the bad English in the thread title... LOL.

Retro Grouch 

Rim brakes will eventurlly wear away the brakeing surface of your rims. That concaveness is the sign of a worn out rim. Since you have access to a mentor at your bike coop, this might be a good time to take up wheelbuilding.

cyccommute 

Although the rims could be worn, I'd start with the brakes. You may have a caliper loose or, more likely, you didn't properly toe the brake pads. The brake pad has to mounted at an angle to the wheel with the rear of the pad being up to an 1/8" further away from the rim than the front. Use a folded (about 4 folds) business card under the rear of the pad to get the proper toe-in.

Check the headset while you are at it. Squeeze the front brake and rock the bike back and forth against the headset (you may have to grab the wheel behind the fork with the brakes on to take out caliper movement). There should be no play in the headset bearings but they shouldn't bind either.

Joshua A.C. New

Yep. I'd check for proper toe-in.

surfimp

Thanks guys - I did in fact toe the brakes as mentioned above, using a torn-off piece of thin card from some of the packaging. Calipers and shoes are all tight. I've got the same exact brakes on my other bike and these are setup nearly identically. But I appreciate the advice - always good to start with the obvious.

The issue is not the squeaking per se, rather it's the fact that for a given brake pressure, there's a spot on the wheel where there is a noticeable bulge (as felt through the brake line to the lever). This is what causes the shuddering and the majority of the squeaking. The wheel itself is visually true as it spins in the fork, but you can definitely feel the "wide spot" as it comes around (through the brake lever, with a mild constant pressure held). The wide spot seems to be centered over the valve stem hole, if that makes any difference.

After posting the above, I did some research and it sounds like once your rims have gone concave, tire pressure can be sufficient to cause a bulging like what I'm experiencing. That would explain why the rim is true on the stand but obviously not true once the tire is installed and inflated.

I guess the "good news" is that I can go ahead and start shopping for that hub dynamo now

Thank you all for the good advice and recommendations,

Steve