Wilsons Sandbox

In a message dated 2004-06-01 8:54:13 PM Pacific Daylight Time, mikfash@... writes:

> > A-18 2700 miles. all speeds, all terrain, and never a twitch. then > all of a sudden at interstate steady crusin about 65-70 a major > slapper. > anybody, any ideas. what can make this happen ? > >

Steering head bearings loosened up(?) Pat G'ville, Nv [Non-text portions of this message have been removed]

mikfash@... wrote:

>A-18 2700 miles. all speeds, all terrain, and never a twitch. then >all of a sudden at interstate steady crusin about 65-70 a major >slapper. >anybody, any ideas. what can make this happen ? > >

Loose steering bearings. Low tire pressure. Funny cupping on the front tire. Loose subframe bolts (don't laugh, this makes the bike wiggle more than you think) Weird pavement surface, like grooves or ruts in the blacktop left by trucks. Maybe you need a fork brace (not all KLRs do). Any of the above. -- Devon Brooklyn, NY A15-Z '01 KLR650 '81 SR500 cafe racer "The truth's not too popular these days....." Arnold Schwarzenneger, in The Running Man

On Wed, 2 Jun 2004, Michael Facchiano wrote:

> A-18 2700 miles. all speeds, all terrain, and never a twitch. then > all of a sudden at interstate steady crusin about 65-70 a major > slapper. > anybody, any ideas. what can make this happen ?

How was the bike loaded? What about preload in the back? Tire pressure? Loose fork bolts? I've never heard of KLR's doing tank slappers before (that's something that typically happens only to bikes with fork-mounted windshields), so there's definitely something wrong that needs fixing. _E

Eric L. Green wrote:

>On Wed, 2 Jun 2004, Michael Facchiano wrote: > > >>A-18 2700 miles. all speeds, all terrain, and never a twitch. then >>all of a sudden at interstate steady crusin about 65-70 a major >>slapper. >>anybody, any ideas. what can make this happen ? >> >> > >How was the bike loaded? What about preload in the back? Tire pressure? >Loose fork bolts? I've never heard of KLR's doing tank slappers before >(that's something that typically happens only to bikes with fork-mounted >windshields), so there's definitely something wrong that needs fixing. > >_E > >

Not necessarily. First of all, the tank slapper is more typically the affliction of the race / sport bike. Hence the steering damper. Without the damper, it can be all too easy to get a slapper if the front wheel is deflected while you accelerate (== light front end) in a turn with rippled pavement. If the deflections conspire with the resonant frequency of the front end (as it oscillates about the steering axis), that's perfect conditions for a slapper. But it does not have to be a series of deflections. One time I screwed up in the carousel at the old Sears Pt and ran off the pavement on the inside of the turn, trying to keep a really tight line that was a deviation from the usual racing line. The inside pavement edge was not a perfect arc - a chunk was missing, and I nailed it while cranking along at race pace. This one hit sent the bars into a wild slapper (bent the stops). I couldn't hang on to the bars, so all I could do was hang on with the legs and ride it out as long as the riding was good and make peace with the possibility of seeing Elvis in short order. As it happened, I shot across the track (didn't take anyone out, thankfully) and near the outside edge of the exit of the carousel the bike stabilized itself and I was back in the race. Back to the slapping KLR. We have two oscillating castoring-wheel systems here. One is the front wheel (and all the crap attached to it that turns about the steering axis), and the other is the the rest of the bike with its rear wheel. They have their own resonant frequencies, which vary with parameters such as the moment of inertia about the axis of oscillation. When you put a lot of weight high on the back seat of the bike, you effectively end up reducing the (road) speed at which that castoring-wheel system can go unstable. With respect to the front end, things such as a fork-mounted windshield not only subject the front end to deflection from wind gusts, but add undesired inertia to the sytem - a double whammy. Furthermore, adding a lot of weight on the back reduces the loading on the front, which makes the front more succeptible to deflection and/or (I am not sure about the physics here) creates a less favorable combination of restoring torque and inertia. If you consider these things in concert, it is definitely conceivable that a KLR loaded in a particular way can get pushed into the unstable territory, particularly if the front is deflected by bumps / rain grooves / etc. I think it is premature to conclude that the bike is somehow broken, although indeed loose or broken fasteners or frame / suspension bits can cause the problem as Eric points out. That's my 2 pesos. Dr. Krok - does this pseudo-physical discussion hold water? Cheers, -S

I had a similar episode awhile back i found that a low tank of fuel and air in the front forks can cuase this situation ...... the little air vavles on top of the forks are not there to add air but to bleed excess air that builds in the forks due to temperature differences.. --- Michael Facchiano wrote:

> A-18 2700 miles. all speeds, all terrain, and never > a twitch. then > all of a sudden at interstate steady crusin about > 65-70 a major > slapper. > anybody, any ideas. what can make this happen ? > > > > List sponsored by Dual Sport News at > www.dualsportnews.com. List FAQ courtesy of Chris > Krok at: www.bigcee.com/klr650faq.html > Unsubscribe by sending a blank message to: > DSN_klr650-unsubscribe@yahoogroups.com . > > > Yahoo! Groups Links > > > DSN_klr650-unsubscribe@yahoogroups.com > > >

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An oft-neglected issue that will cause or contribute to high-speed instability is a misaligned rear tire. The last time my KLR wouldn't track right on the highway I spent hours chasing down fantom problems before I realized that the alignment was at fault. -Lujo bigfatgreenbike wrote:

> > mikfash@... wrote: > > >>A-18 2700 miles. all speeds, all terrain, and never a twitch. then >>all of a sudden at interstate steady crusin about 65-70 a major >>slapper. >>anybody, any ideas. what can make this happen ? >> >> > > Loose steering bearings. > > Low tire pressure. > > Funny cupping on the front tire. > > Loose subframe bolts (don't laugh, this makes the bike wiggle more than > you think) > > Weird pavement surface, like grooves or ruts in the blacktop left by > trucks. > > Maybe you need a fork brace (not all KLRs do). > > Any of the above. >

[Non-text portions of this message have been removed]

On long runs I oft times rest by placing my feet on the passenger pegs. I was cruising about 75 one day when I decided to stand up for a second to stretch my legs, bad idea. The added weight in the rear/versus/loss of weight on the front and and I was wabbling in a microsecond. Never ever ever ever try this boys and girls, I about bought the farm. --- Lujo Bauer wrote:

> An oft-neglected issue that will cause or contribute > to high-speed > instability is a misaligned rear tire. The last > time my KLR wouldn't > track right on the highway I spent hours chasing > down fantom problems > before I realized that the alignment was at fault. > > -Lujo > > > bigfatgreenbike wrote: > > > > mikfash@... wrote: > > > > > >>A-18 2700 miles. all speeds, all terrain, and > never a twitch. then > >>all of a sudden at interstate steady crusin about > 65-70 a major > >>slapper. > >>anybody, any ideas. what can make this happen ? > >> > >> > > > > Loose steering bearings. > > > > Low tire pressure. > > > > Funny cupping on the front tire. > > > > Loose subframe bolts (don't laugh, this makes the > bike wiggle more than > > you think) > > > > Weird pavement surface, like grooves or ruts in > the blacktop left by > > trucks. > > > > Maybe you need a fork brace (not all KLRs do). > > > > Any of the above. > > > > > [Non-text portions of this message have been > removed] > > > > List sponsored by Dual Sport News at > www.dualsportnews.com. List FAQ courtesy of Chris > Krok at: www.bigcee.com/klr650faq.html > Unsubscribe by sending a blank message to: > DSN_klr650-unsubscribe@yahoogroups.com . > > > Yahoo! Groups Links > > > DSN_klr650-unsubscribe@yahoogroups.com > > >

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from the enlightened KLR of Harry Seifert bseifert71@... Elden went through my front end at the last Julian Tech Day. After a new set of Pirelli MT 90 S/T's (my Siracs lasted 6K miles) and the .04 shims he added on each side of the front wheel, this A13 runs on rails. I put a set of 4mm Bridgestone tubes in the new tires; could the extra rotating mass be creating a stringer gyro effect at speed? I'll have to ask Elden about that one ; > >anybody, any ideas. what can make this happen ? > Funny cupping on the front tire. > > Maybe you need a fork brace (not all KLRs do). > -- > Devon > Brooklyn, NY > > A15-Z '01 KLR650 > '81 SR500 cafe racer > > "The truth's not too popular these days....." > > Arnold Schwarzenneger, in The Running Man > > > > List sponsored by Dual Sport News at www.dualsportnews.com. List FAQ