My KG 361 is comfortable and handles well but wobbles around 48 mph and up. It's carbon with aluminum lugs and "stock" HSC 4 fork. Recently hit 56.5 on ride and scared the heck out of me because of the wobble. As my strength is increasing I notice the flex. I weigh 175 and have a few miles under my belt so I'm comfortable with virtually all descents. Is the wobble a result of this fork? Would another help? Is it the model? Does wheel flex contribute to high speed wobble? Also, I'm 41 so I want a reasonably compliant ride but I can't race next year with this! HELP! Thanks.

My KG 361 is comfortable and handles well but wobbles around 48 mph and up. It's carbon with aluminum lugs and "stock" HSC 4 fork. Recently hit 56.5 on ride and scared the heck out of me because of the wobble. As my strength is increasing I notice the flex. I weigh 175 and have a few miles under my belt so I'm comfortable with virtually all descents. Is the wobble a result of this fork? Would another help? Is it the model? Does wheel flex contribute to high speed wobble? Also, I'm 41 so I want a reasonably compliant ride but I can't race next year with this! HELP! Thanks.

http://www.bikefanclub.com/forum/showflat.php/Cat/0/Number/3914/page/0/view/collapsed/sb/5/o/all/fpart/1

IMO, the HSC4 fork is plenty stiff. Sometimes a larger frame can flex enough to start a high speed wobble. A loose headset or unbalanced wheels may also contribute.

Are you getting a resonant wobble, that gets worse quickly (often called the death wobble) or is the handling just twitchy, perhaps due to a rough road surface? Dips and waves in the pavement don't bother cars much, but there are road surfaces toally unsuited for riding a bike a 50 mph. In the mountains, you have to watch the roads carefully. If you hit a rough patch (or a pothole) at that kind of speed, it may be all over.

You must have some steep hills to hit 56 mph. I've hit 50 with a big tail wind, but never any more and I descend the Colorado mountains all the time. Then again, I only weigh 135.

Feet at 3 and 9, butt a bit off the saddle and knee against top tube... should clear it up.

IMO, the HSC4 fork is plenty stiff. Sometimes a larger frame can flex enough to start a high speed wobble. A loose headset or unbalanced wheels may also contribute.

Are you getting a resonant wobble, that gets worse quickly (often called the death wobble) or is the handling just twitchy, perhaps due to a rough road surface? Dips and waves in the pavement don't bother cars much, but there are road surfaces toally unsuited for riding a bike a 50 mph. In the mountains, you have to watch the roads carefully. If you hit a rough patch (or a pothole) at that kind of speed, it may be all over.

You must have some steep hills to hit 56 mph. I've hit 50 with a big tail wind, but never any more and I descend the Colorado mountains all the time. Then again, I only weigh 135.

Thanks for feedback on fork. It's a resonant wobble. Headset and wheels are good, tight and true. The road is smooth and I know the section, I usually descend there at 41-44 but had a strong tailwind and a bus passed me. Grade hits about 10 or 11%.

http://www.bikefanclub.com/forum/showflat.php/Cat/0/Number/3914/page/0/view/collapsed/sb/5/o/all/fpart/1

Thanks. Was informative. I'll try shifting my weight back and lightening up on the bars...know I'm guilty of leaning forward and a death grip when the wobble begins.

I discover, the other day, that my commuter bike started wobbling after I added a rear rack and a child seat. I notice it loads the rear wheel quite a lot.

I wonder if the shimmy has a lot to do with weight distribution... Looks like it in this case. Then in your case: you mention leaning over the front wheel and gripping hard? This would be the opposite?

weird.

I discover, the other day, that my commuter bike started wobbling after I added a rear rack and a child seat. I notice it loads the rear wheel quite a lot.

I wonder if the shimmy has a lot to do with weight distribution... Looks like it in this case. Then in your case: you mention leaning over the front wheel and gripping hard? This would be the opposite?

weird.

Wobbles caused by loaded rear racks is not uncommon. But the reason isn't fore-aft weight distribution, but a lateral oscillation of the rack. Racks are typically made from narrow tubes and are not laterally triangled, so they have low lateral stiffness. When loaded, the rack can oscillate side to side, and this moving mass can cause the rest of the bike to wiggle back and forth in opposition. The steering geometry can then translate this lateral oscillation into steering motions, creating a feedback loop and amplifying the wobble.

The very best rear racks are made from lots of heavy-duty tubing, which is not just for strength (although this is an added plus), but so that they are stiff enough to prevent a load from oscillating and causing the bike to wobble.

As a quick experiment, if you notice the bike starting to wobble with a load on the rack, reach and around and grab the rack to steady it, and see if the wobble doesn't dissipate.

My KG 361 is comfortable and handles well but wobbles around 48 mph and up. It's carbon with aluminum lugs and "stock" HSC 4 fork. Recently hit 56.5 on ride and scared the heck out of me because of the wobble. As my strength is increasing I notice the flex. I weigh 175 and have a few miles under my belt so I'm comfortable with virtually all descents. Is the wobble a result of this fork? Would another help? Is it the model? Does wheel flex contribute to high speed wobble? Also, I'm 41 so I want a reasonably compliant ride but I can't race next year with this! HELP! Thanks.

lots of posts in general discussion area on the this subject.