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Discussion Starter · #1 ·
Hi Gentlemen,



Yet another, "What's causing this?" question for you. This one has a narrative...



I've had this bike for a little less than a month, now. After a few rides I noticed that the bike had a wobble in the handlebars between 35 & 50 MPH. It was mostly on decel or coasting. The bike had an oversized front tire that needed to be replaced. I had that done last weekend. In the process, the shop that I took the wheels to, installed my new tire with the old tube still inside. When they came back with the same metal valve stem I asked them to remount the tire without the tube. I'm assuming this necessitated a re-balance. But I don't really know how much the tube affects the tire balance. Maybe they can get away without rebalancing it? I took the new wheels home & mounted them up. They rode great. The wobble was still there, but barely noticeable now. That is, until I swapped out the handlebars this weekend. I installed a set of BikeMaster GP Touring bars that are a couple inches narrower than the stock bars. Now with less leverage on the bars I can really feel the wobble. One-handed decel between 45 & 40 as the speedo reads is enough to make me a little nervous. I've checked the rear swingarm & the fork bearings for play as I've seen described on this forum. I couldn't feel any play at all. I also didn't feel any notchy-ness when turning the forks back & forth. I checked the runout of the front wheel. It came in at 1.3mm which is within the 2.0mm spec. I found the front brake caliper is dragging a little. I'll be working on that one pretty soon, but I don't know that it's enough to cause the wobble that I'm getting.



I've read on this forum that the steer tube bearings can be bad even if there's no play. I also know (from my experience as a Honda auto mechanic} that car tires improperly balance will usually vibrate worst at 65-68mph due to the frequency of the suspension. Would anybody be able to shed some light on why this wobble would occur in such a specific speed range?



(Also, I'm guessing actual speed is 38-43mph, since the speedo is a little generous with a 3.25X19 tire.)
 

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The steering head bearings probably are the culprit... Like you have hypothesized...the tires and suspension have a resonate frequency and yours apparently is in that range.

Have your front wheel double checked for balance. Sometimes an unbalanced wheel will start being a problem at the 45mph range. This is why some of the smaller scooters don't need to worry about balancing, because the lower speeds don't accentuate the problem until you start getting up to about 45-50.



David
 

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Discussion Starter · #3 ·
Sorry David, I just saw your reply. Never got an email notification for some reason.



I tried a static balance, but I think I made it slightly worse. My method was to loosen the axle nut & axle holder, remove the caliper, prop the front wheel up & check the vertical w/ a level. I disconnected the speedo cable, but didn't pull the speedo sender off the axle. Am I silly for thinking I should be able to static-balance it this way? Is there still too much resistance in the wheel bearings to get a good reading? The bearings appear to be in very good shape.



-Nathan
 
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