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My '17 Bobber had no issues until I put new tires on it at just over 16,000 miles. Opted for Avon Cobra Chromes because I was happy with the ride, handling and wear of the original Cobras. Our dealer had the best price and availability, and I had both front and rear mounted and balanced by them. DIY'd the removal and installation and checked tire pressures before heading out for a test ride.

The new tires were questionable at first, familiar side roads felt less smooth. When I got out on the highway, though, I felt a surging harmonic vibration up through the seat that sent me back home. I checked and readjusted the chain, rechecked tire pressure, and set out again. No improvement. The harmonic came on at about 45 mph and disappeared when I pulled in the clutch, so I removed the rear wheel when I returned home and checked the balance. It was balanced perfectly.

The dealer replaced the rear tire for me. I noticed there were less weights on the rim than with the first Chrome, so I was encouraged that the tire was the problem.

Sadly, I still have a surging harmonic vibration. It seemed better than with the first Chrome, appearing at about 3000 rpm and only in 4th gear.

I read a post somewhere about someone with a Bobber that had an eerily similar issue, but it didn't have a resolution. Anyone here experience anything like this? I'll address it with the dealer, and have thought of replacing the chain and sprockets. But why only 4th gear? And why only after installing new tires?
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