I was going to put a post up recently because when cornering I can hear a sort of howling sound, it seems like a recent occurrence but I wasn't sure if I was imagining it. It sounds more like simply tyre on road noise. Anyway I have been aware of it for a while and I can hear it even during low speed weaving. Ok put that on the shelf for the moment.

Last year I installed a chunky aluminium fork brace and after I installed it I'd check it out by riding down the road at say 60km/h take my hands of the bars and give one side of the handlebar a hefty whack. Which felt pretty stable, not dramas, all good.

First thing I did when I notice the howling sound was to put the bike up on the centre stand lift the front wheel and feel for play. No play at all, bearings feel good. No notchiness when turning bars from side to side. I will note though that while there is no play it doesn't feel like there's any friction, but again there's no play.

I've also been wondering if this mysterious howl is coming from the front brakes.

OK now cut today, I'm going down the road, not fast about 40km/h and I take both hands of the handlebars to do up the zipper on my jacket and instantly the bike goes into such a severe tank slapper that I thought for a moment it was going to high side me, it was so extreme and sudden. Whoa...

Now I try it a few more times to see what's going on here and if I take my hands off the bars it's all good, but it just takes a pretty ordinary whack to set up a monster tank slapper. Checked the free play on the front wheel again and it all seems good.

Had the gf on the back and tried it then and no problem I gave the handlebars a massive whack but it was rock solid no tank slapping at all.

So that's it, any ideas?

thx.

are your forks leaking oil?

are the wheel weights still on the front tire?

is the front tire oddly wearing?


sounds like the front forks might be sticking a little bit.. or low on oil, with your passenger on back the bike is sitting lower over all. and the forks have less "travel" because of that, so what maybe if they are leaking, oil is left, is actually doing something. 

@J Walker,

Fork seals done 20 months and 25000kms ago, all look good no oil at all leaking onto forks. New BT45's 6 Months and 7,000kms ago, look even all the way around. Weight after last tyre change is still attached.

Have you changed the rear shock to one of the popular ones that jacks up the rear and changes your steering angle?

@Suzuki Stevo, Are you suggesting that as a cause or a cure? But anyway no, standard shock.

Quote from: user11235813 on September 04, 2017, 02:31:19 AM
@Suzuki Stevo, Are you suggesting that as a cause or a cure? But anyway no, standard shock.

It would be a cause, steep steering angles can give you head shake and that leads to tank slappers, but probably not in your case if your stock.

Okay, another reason for a tank slapper is the front wheel is traveling slower then the rear wheel.

Check if your front brakes are dragging on the rotor, or if the rotor is warped, or too much play, causing it to bump into the brake pads slowing it down enough.

"Had the gf on the back and tried it then and no problem I gave the handlebars a massive whack but it was rock solid no tank slapping at all."

-Well that reveals all eh?
With the Gluten-Free -I mean Girlfriend on the back the wobble completely disappears.

Change your diet... or, better still... Back off the rear preload. Is the rear shock and spring standard? Sounds like she's running nose-down to me. (The bike not the GF!)
Can't see those other things being the problem, surely it's the front/rear 'balance/attitude/angle' if extra weight on the back fixes the wobble.
I'd certainly take off the fork brace before tracking the problem down. Fix the problem, THEN add the fork brace to see if it might be causing the problem. E.g. it's possible that the fork brace is slightly 'pre-loading' causing sticktion on the fork travel, they can do this if you add a fork brace to stanchions that are slightly misaligned (bent).

@J_Walker, well that's a good theory about the front brake drag and it does coincide with the 'howling sound', while I can hear a bit of dragging, If I give the front wheel a hard spin by hand with the front off the ground (obvs) the wheel will make three complete revolutions, I don't have anything to compare to but that does seem OK, what do you think?

@Joolstacho Well I don't know what it reveals but it might means something to someone. The rear shock is standard and it's at it's standard setting. The fork brace is not some tricky unit, it's just a slab of thick aluminium that replaces the iron fork brace, I can't see how that can possible cause a problem, the worst it could do is nothing at all.

The reason I put the fork brace on (apart from it looking good) is to get some extra rigidity when hitting an uneven surface while cornering. As I said earlier after installing it I tested it by seeing if I could induce a tank slapper by doing exactly what I'm doing now, that is giving on handlebar a thwack. When I did that it did not induce a wobble and I was happy.

So I repeat that this problem has only occurred during the past few months because it was very stable earlier. When I discovered this yesterday, I didn't even do anything other than remove my hands from the handlebar and it caught me by surprise.

I took the bike up to the local bike shop to get their opinion on the bearing because I felt that the side to side turning was very easy but they said it was fine because there was no play, and there was no play in the bearing that they could detect.

If this problem was there from the beginning I'd just accept it but it wasn't and I have not done anything to the bike that would effect it. It's really quite strange it doesn't take much of a whack on the handlebars to induce it maybe just 10 nm of force.

Would increasing the preload on the rear shock help this situation? Is it possible that the spring has become a little 'fatigued' and that increasing the preload may compensate?

Quote from: user11235813 on September 05, 2017, 02:26:19 AM
Is it possible that the spring has become a little 'fatigued' and that increasing the preload may compensate?

No, and no.

Contrary to legend steel springs do not fatigue. They can of course bend or break, but it would be nearly impossible to affect a commercial motorcycle coil spring this way through operation on a vehicle.

Even if the spring were damaged, increasing preload wouldn't compensate. Preload doesn't affect spring rate.

@mr72

Should this behaviour which has only recently occurred, be a cause for concern if otherwise everything else if fine? Should I just not worry about?

I don't have any useful input about the front end wobble or shimmy you had. I was just commenting about the rear spring question. BTW I also don't think the rear suspension is involved at all in your problem. If I had the same issue I'd suspect tire pressure, wheel or fork alignment, dragging brake or stuck caliper, sticking fork. But for all I know could be road surface and nothing with the bike. Or normal. I don't ride with no hands so I wouldn't know.

Is it just me, or is riding hands free and then whacking your handlebar a particularly unsafe way to test for stability?

Are motorcycles really designed to be that stable?

My GS has low clip ons, and my other bike is a Triumph Daytona.  Moving the bars about 1" would be enough to get them to start into a turn.  I wouldn't say either bike is particularly twitchy, but I can't imagine they'd be too happy with a test whack on the bars.

Quote from: Endopotential on September 05, 2017, 11:16:48 AM
Is it just me, or is riding hands free and then whacking your handlebar a particularly unsafe way to test for stability?

I was wondering that as well tbh... I never ride with both hands off the bars, and that'd be one of the last things I'd wanna do is whack the bars while doing so. I've been following along this thread though cuz I'm always up for reading about bikes and learning things !!!

Old school normal practice to check front end stability/tires/headraces etc - Hands free, slap bars smartly - massive wobble = problem, nada twitches = OK
Just sayin...

Haha see? That's why I read this stuff all the time... I never know what new thing I'm gonna learn!

Quote from: ShowBizWolf on September 05, 2017, 11:48:20 AM
I never ride with both hands off the bars

How are you supposed to flip the bird?

Here's a couple of images of a local corner, I don't like taking it overly wide due to this being a tourist area and I could find myself close to a Winebago during the corner. This manhole cover is right on my cornering line and it's hard to see on the photo but is in a larger depression. I tried coming around that corner really tight one day but wouldn't you know it there was a crested pigeon sitting in the gutter and I killed it :¬(

I should point out that a tank slapper is more than a wheel wobble, a wobble dies down but a tank slapper increases amplitude quickly and will have you off the bike, if you don't react fast enough. You have to somehow counter with some input by loosening your grip and letting it hit the palm of your hand to deaden it.

took the weights off and it's not any worse.

What you're experiencing is a fairly common decel wobble. The simple solution is to keep both hands on the bars.

As to root cause, the most common is a worn front tire. How many miles on the one you have?
The second most common is a worn rear shock. The lack of damping allows oscillations that "feed forward" into the front and cause the wobble. Stock shocks are short of damping to start with and once they get beyond 20 or 30k miles they're about done. A good aftermarket shock is the best solution.

Really neat information Rich... I love when ya check in on us here on the forum!

That's interesting too, I just hit 20k on my bike and now I'm even happier I got rid of the stock shock. Can't wait to buy those springs finally!

Tyre is good, but the shock has got 26k miles so seeing as I've eliminated everything else, that looks like I might need the R6 shock upgrade sooner than I thought.

Quote from: RichDesmond on September 05, 2017, 07:14:35 PM
What you're experiencing is a fairly common decel wobble. The simple solution is to keep both hands on the bars.

As to root cause, the most common is a worn front tire. How many miles on the one you have?
The second most common is a worn rear shock. The lack of damping allows oscillations that "feed forward" into the front and cause the wobble. Stock shocks are short of damping to start with and once they get beyond 20 or 30k miles they're about done. A good aftermarket shock is the best solution.