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Had a little scare this morning on the way to work. As I’m approaching my freeway exit I get over with plenty of time and fall in line with other traffic slowing for the exit. We had collectively slowed to around 50mph when my bike went into a violent wobble that must have lasted 2 or 3 seconds. My feet were thrown of off the pegs and the rear started alternately beating the insides of my legs while the bars whipped back and forth. I thought for sure I was going down, but I kept my cool and reacted without panicking. My legs are killing me, but I kept the bike up.
Speeds were about 50mph and slowing gently, no hard braking, no known road obstacles. It felt like the rear brake was locked up for the whole wobble. Riding the last mile to work felt odd every time I applied the rear brake….once I parked the bike I found that the rear brake lever is bent up and out which drastically changed its position relative to my foot. That’s why things felt different.
Could that lever have been bent (out and up) by my leg smashing into the side of the bike? It wasn't like that when I left the house. Think I can just step on it to bend it back, or would I be putting weird stress on other components that I can’t see?
I'm still trying to replay the whole thing in my head in the hope that I can determine the cause of the wobble. The bike has never done that, and aside from cars ahead and behind me conditions were pretty favorable.
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From experience: you most certainly could have bent that lever with your leg if the wobble was violent enough, but I think it wouldn't be a question for you to ask us, because you'd have some kind of very obvious bruising/injury on your leg as a result. I haven't had a Tank Slapper (and frankly, i thought they could only happen at high speeds, so this is pretty terrifying to read), but I've had an incident where a car *very nearly* murdered me by splitting (yea, a car lane splitting) past me on the freeway, hitting my leg, causing my foot to catch the pavement, and slingshotting it back into my bike. My brake lever was bent at the time, too, though it was on a CBR500.
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Wow. Have you made any mods to your front end? Or raised the rear? I thought the rake on the cb1100 was long enough to make a tank slapper very unlikely.
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(04-23-2018, 03:32 AM)misterprofessionality_imp Wrote: From experience: you most certainly could have bent that lever with your leg if the wobble was violent enough, but I think it wouldn't be a question for you to ask us, because you'd have some kind of very obvious bruising/injury on your leg as a result. I haven't had a Tank Slapper (and frankly, i thought they could only happen at high speeds, so this is pretty terrifying to read), but I've had an incident where a car *very nearly* murdered me by splitting (yea, a car lane splitting) past me on the freeway, hitting my leg, causing my foot to catch the pavement, and slingshotting it back into my bike. My brake lever was bent at the time, too, though it was on a CBR500.
Yup. Those are surfacing now. Left is worst than the right.
(04-23-2018, 03:33 AM)chync_imp Wrote: Wow. Have you made any mods to your front end? Or raised the rear? I thought the rake on the cb1100 was long enough to make a tank slapper very unlikely.
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No mods, but my front tire is nearly bald. New tires go on tomorrow.
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(04-23-2018, 03:37 AM)egleaves_imp Wrote: (04-23-2018, 03:32 AM)misterprofessionality_imp Wrote: From experience: you most certainly could have bent that lever with your leg if the wobble was violent enough, but I think it wouldn't be a question for you to ask us, because you'd have some kind of very obvious bruising/injury on your leg as a result. I haven't had a Tank Slapper (and frankly, i thought they could only happen at high speeds, so this is pretty terrifying to read), but I've had an incident where a car *very nearly* murdered me by splitting (yea, a car lane splitting) past me on the freeway, hitting my leg, causing my foot to catch the pavement, and slingshotting it back into my bike. My brake lever was bent at the time, too, though it was on a CBR500.
Yup. Those are surfacing now. Left is worst than the right.
(04-23-2018, 03:33 AM)chync_imp Wrote: Wow. Have you made any mods to your front end? Or raised the rear? I thought the rake on the cb1100 was long enough to make a tank slapper very unlikely.
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No mods, but my front tire is nearly bald. New tires go on tomorrow.
there it is. no traction on that front. it was just skating along on the road while your rear tire was pulling away. Just like a wonky shopping cart. still, at 50mph? the low speed is probably the reason you were able to recover.
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In addition to your bald tire, I've noticed one other thing about the CB that's different from any other bike I've ridden, and I noticed it while riding in your neck of the woods, up I-80 to Auburn. While traveling in a straight line, pushing on either grip produces the expected result. The bike just moves solidly in that direction. However, if you waggle each grip back and forth, yep, this results in something that feels very much like a tankslapper. I tried the same test on my XSR900, and it didn't get nearly so out of shape. The rubbery-feeling oscillations of the CB are crazy, they're so wild. They're so dramatic that if I kept waggling the bars, the bike would easily oscillate right out of control. It doesn't take much.
Like I said, I've never felt anything like it on any other bike. It's easy enough to avoid, and I guess it's just a characteristic of the chassis.
Moral of the story, don't waggle the bars even a little, and don't run bald/underinflated tires.
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That doesn't sound good at all. Harleys had the same issue. Incorrect inflation and balding tires can definitely cause it. I buy tires before I "need" them. Glad you made it through that.
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Is it part of the skinny tire syndrome?
I had a terrible time on a sandy road with my CB1100 with fairly new tires.
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Motorcycle physics can be strange and confusing. Wish I knew more about them.
Here are a couple of links that explain in English (vice math) some reasons for the slapper.
https://motorbikewriter.com/avoid-tank-slapper/
https://en.m.wikipedia.org/wiki/Speed_wobble
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Only time I have ever experienced tank slappers is coming down out of a wheelie on sport bikes.
I've never had it happen on any of my other street bikes, or dirt bikes for that matter. Definitely not on my CB1100, and yea I've done wheelies on it and will be even more inclined now with the larger rear sprocket.
Now I am curious- going to go look up the front rake to my old FZR (25) vs the CB (27)
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