Topic: Repeated questions

[gaustin]

I've read all the other posts so I know I should most likely have a front fender and brace so I'm looking for one, but two questions-
what year's fender will fit a 750, 74 k4 with a 19'' front wheel?  Secondly what exactly is "Tank slap"  I can guess but I'm not exactly sure.

I'm loving my CB now that its running.. but at higher speeds (60-75mph) I feel uncomfortable, I'm not sure if its the lack of a brace or if these bikes just don't handle that great at higher speeds?  Last time I rode it was three years ago with a Yamaha R6.   I know its not a fair comparison... since the cb looks so much cooler but still.   

   

[gregwaits]

I can address the tank slap question.

Tank slap is when you lose control of the bike, usually at higher speed. The bike begins to whip back and forth, left to right. In my opinion, it starts with front wheel wobble.

The outcome is almost always inevitable; the rider will get dumped. I have seen a video of a road racer who miraculously pulled out of a tank slapper. Someone posted a video of a classic tank slapper earlier.

[andy750]

The lack of front fender/ fork brace has been reported by some on this Forum to adversely affect handling (while others mention they have no problem), but this may explain your lack of feeling safe at higher speeds. Many of us here ride above 80mph on our CB750s/550 etc and feel quite safe so I dont think its  the bikes (although granted they have less braking than a modern bike  ). Id put a fender or brace on and then re-test your high speed handling.

As for fenders that will fit - post-73 (pre-73 fenders are different with respect to front brake fittings) to 76 (K model) will fit for sure - the rest I dont know.

cheers
Andy

[Bodi]

tank slap is when the steering wildly oscillates with the handlebars "slapping the tank" at each side as they swing back and forth. Most 70's bike will manage this if you let go of the bars at high speed, the frame and forks flex and things get exciting then hurty. Usually just holding on to the bars damps the oscillation and you don't have a problem. I've only seen it once when a rider got thrown off his Mach III by a monster pothole at about 60mph in front of me (OK, I was trying to race him) and the bike went really wild without him before hitting the ditch. Amazingly the bike was OK (for a '69 Mach III anyway), I guess the tankslapping really slowed it down and the rider just needed new helmet and pants (no...) and some ointment and bandages on his butt. Sitting down may have been painful for a few days.

[heffay]

tank slap occurs most often when there's not much weight on the front end... like pulling away from a light or setting it back down after a wheelie.

you can see why... at high speeds, bikes like to go into a tank slap (not much weight on the front at that point)

also, tires can really affect handling... on my 7r i had a metzler front w/out the center groove and they handled rock solid... i switched over to the dunlops w/ a center groove and it wont go into a full slapper but there are times when i get a little nervous if i let my hands off the bars.

my opinion: it all comes down to tires

[Bob Wessner]

..if i let my hands off the bars.

And you were taking your hands of the bars because..?

[heffay]

so i can stand on the seat of course 

[Gordon]

And you were taking your hands of the bars because..?

If you can think of another way to send a text message while riding my bike, please let me know.

[TwoTired]

And you were taking your hands of the bars because..?

Okay, I'll play...

Those grips get really hot in the sun?

I can't keep my back straight and reach those grips at the same time?

My feet do all the steering while I lean onto the backrest?

The gravel from that truck ahead really hurts when it smacks your knuckles?

Doesn't every one bite their nails while riding?

Oh, another bike.. must wave!

Oh, a nice pair... must wave!!

Oh, a female walking at the side of the road...must grab!


Cheers,

[WJL75]

Love the replies on this thread. LMAO

[steam-powered man]

if you like the look of a fenderless front, just install a fender brace.  that way, you can still be but not wobbly.  i ran that way for awhile but couldn't get it inspected w/out a front fender.  i am uncool again.

if you are very lucky, you can survive a tank slapper.  loosen your grip, don't touch front/rear brakes, wait it out.  worked for me, and i didn't buy that bike.
bobp       

[bistromath]

A tank slapper is caused by too MUCH weight on the front end, not too little. Braking will inevitably make it worse. If you find yourself in a slapper, about all you can do is hold on and try to accelerate out of it to take some weight off the front end and bring it under control.

It's caused because motorcycles are inherently neutrally stable in steering, or nearly so (to allow quick handling). Increasing caster distance (moving the steering axis forward of the front hub) will prevent tank slappers but make the rider work much harder to bring the bike into a turn.

[gaustin]

Thanks for all the replies..  I take it I can just buy a front fender for a 73-76 k bike and cut out the brace.. so that's what I'll try.

and I try not to take my hand off the bars for any reason... well except to flip the birds or pick the nose, but normally one hand off suffices.   

[rhinoracer]

It's not the weight or tire alone what causes the tank slap.

If you take that tire and wheel, insert the axle thru the hub center then grab the axle with both hands.

Ask somebody to spin the tire while you hold it by the axle ends. If you misalign the axle even slightly away from the rotating axis of the wheel, you'll feel the wheel trying to wrap itself around your arms. I think it's called gyroscopic effect and it's got something to do with the inertia polar momentum or whatever the correct name is in english.

Now imagine that force that's trying to rip your arms acting on two separate and independently moving (i.e. braceless) fork legs which for all practical purposes are floating, suspended by a spring and held down by the bike's weight and you get the idea of what causes a tank slapper. Road imperfections, wheel balancing and any other force that tries to throw the axle off the spinning axis will only make it worse.

[333]

What I don't understand is why anyone would go without a fender.  Sure, it's a clean look, but if you actually ride the bike, the rest of the bike won't stay clean for long.  The dirt and grit get sandblasted into the fins on the engine.  And any puddle you hit gets thrown up into the air where you and your helmet are.

[TwoTired]

What I don't understand is why anyone would go without a fender.

I think it's the urge to be different, and be hip with or set new trends.

IMHO

[ronlarimer]

The "Death" Wobble, as mentioned before can be caused by lots of stuff.  It is worse if there is too little trail in the front suspension.  Fighting it makes it worse and it "caused" by too tight of grips on the bars.

[GammaFlat]

Here's a "not too good" result of a tank slap: