Tankslap caused by windshield?

[bbueche]

I had a concours many years ago and normal top speed with extra tall fairing was 130, but on downhill roads I would have problems.

I chalked it up to 2 things downhill part of you speed vector is falling down less weight on the tires and the angle of your body and the wind blast changes. up hill you tuck your head better downhill yyou raise your head a bit for balance so that all your body weight is not on handle bar. it seemed like the down draft over my body caused the rear wheel to have more pressure levered the bike and the front wheel was lighter.ie changed the fore and aft weight distributuion of the bike and made the front wheel more susceptible to wobble.

Also the wind coming down from higher angle more pressure on the top part of the shield

just some random thoughts

BB

 

[Texan]

Sounds like I should replace the front - it has 6K on it, but still looks good.

I had fully loaded rear bags and the wind was a bit high that day. Additionally, there's really no need for me to go that fast in the first place. (I just need to keep repeating that last line over and over.)

 

[beacher]

Could someone please enlighten me. . . What the heck IS "tankslap"? I've been riding for about 50 years, and I've never heard of it. Then, again, I'm pretty solitary, and don't spend a lot of time with other riders. . .

 

[luvtoride]

Could someone please enlighten me. . . What the heck IS "tankslap"? I've been riding for about 50 years, and I've never heard of it. Then, again, I'm pretty solitary, and don't spend a lot of time with other riders. . .

Tank slapper... also known as speed wobble. In this case it'd be a tankslapper... referring to the action of the handlebars hitting/slapping the gas tank.

Here's Wikipedia's definition:

Wobble, shimmy, tank-slapper,[1] speed wobble, and even death wobble are all words and phrases used to describe a quick (4 - 10 Hz) oscillation of primarily just the steerable wheel(s) of a vehicle. The rest of the vehicle remains mostly unaffected. Vehicles that can experience this oscillation include bikes, both motorcycles and bicycles, skateboards, and in theory any vehicle with a single steering pivot point and a sufficient amount of freedom of the steered wheel; this does not include most automobiles, however, coil-sprung vehicles with a track bar setup such as the Jeep WJ, XJ, ZJ, TJ, and JK with both stock and after-market suspension lifts may have this problem also. This instability occurs mostly at high speed and is similar to that experienced by shopping cart wheels and aircraft landing gear

 

[Ed_Grant]

The classic tankslapper at the TT.

 

[beacher]

Well, THAT certainly explained why it's called "tankslapper". . . My heart hurt for the guy. . .

 

[happyPuppy]

+1 on the bags , they really change the characteristics and Yamaha warns about them over 85. I had one once in CA in the 1980's and it scared the sh*t out of me. A loose grip and slowly easing off the throttle stopped it.

 

[Ed_Grant]

I had a tankslapper accident on a V-Strom back in 2003. Here is my description of that incident.....

The accident was caused by a combination of factors but mainly very strong headwinds (30-40 mph) and excess speed with the Suzuki hard bags mounted.

The wind was blowing really hard but it was warm so I went for a ride. My big mistake was not taking the saddlebags and top box off of the bike. Anyway I was following this pickup truck that was towing a cattle trailer and when I finally got the chance to pass him I went around him in the manner the V-Strom is capable of (quickly) and I gave myself lots of room before pulling back into my lane. The problem was that with the strong headwind the front end of the bike was not planted firmly and when I countersteered to go right it started the tankslapper. Within about 3 seconds it was stop to stop and I closed my eyes, brought my hands into my chest and bailed.

Luckily I suffered only bruising and a small road rash on my lower left calf but the bike managed an excellent gymnastic floor exercise (or so I'm told).

I was going about 75 mph when the wobble started but might have slowed a little before I hit the ground.

Luckily I didn't hit anything solid and just slid and tumbled on the grassy shoulder about 150 feet.

I never had a problem with the V-Strom in 17.000 miles before that. Very stable at high speeds and in the twisties but those Givi/Suzuki hard bags stick way out in the wind and can cause handling problems at high speeds or in very windy conditons. The bags were empty.