Front-end wobble??

[Ragingrob]

Ok this is weird and has just started occurring this past week.

Pretty much the bike rides absolutely fine and straight apart from between 60-65kph, where there is a really odd front-end wobble. It's pretty unnoticable until you take one hand of the bars and then you can see the front wheel wobbling like a mini as tank slapper, but then once you're past 65 it's completely straight again...

So what the fuck?

Any ideas? Maybe a wheel weight dropped off? But wouldn't that affect the handling even more at higher speeds?

:(

Confused!

[Coldrider]

Mine does that just before the time i have to buy new tyres.
Either the front is worn or the rear has flat spotted.

[Ragingrob]

Mine does that just before the time i have to buy new tyres.
Either the front is worn or the rear has flat spotted.

Argh that could be it the rear has probably flattened out a bit... I better go for a decent burn to even it out!!!

Why does that wobble only happen at the one speed though?

[vifferman]

I don't know why that speed triggers it, but that's the way it is. VFRs do it at that speed too, especially downhill (like on the downhill run on the Harbour Bridge). It's not always a simple explanation, as so many things come into it, including steering geometry, tyre tread pattern and carcase construction, suspension settings. It's often from "cupping" (unusual and uneven wear) of the tread blocks on the front tyre, but can also be caused by the rear end: a bit of a wobble at the back can be exacerbated by the suspension, somehow the small wiggle turns into a large one at the front.
Check the following:
Your front tyre - that it's not worn unevenly, and is correctly inflated. It might help if you get the balance checked, but this isn't usually the problem.
Steering head bearings - that they're not worn, loose or notchy (you'll need to lift the front end off the ground to do this).
Rear tyre condtion and inflation pressure.
That all your tyre weights are still in place.

[Meanie]

Tyres................

[Blackbird]

Possibly head bearings but you haven't got an old Avon Storm up front perchance have you?

The other thing which I've read that affects some bikes at certain speeds is the presence of a Givi top box.

[Meanie]

Possibly head bearings but you haven't got an old Avon Storm up front perchance have you?

The other thing which I've read that affects some bikes at certain speeds is the presence of a Givi top box.

Ive had two storms do that to me, but even my pilot road 2ct when it got to the end of its life started to vibrate the front of the bike. New tyres problem gone

[vifferman]

Possibly head bearings but you haven't got an old Avon Storm up front perchance have you?
How dare you slight the beloved Storm, Mr Blackbird! :nono:
Actually, the Bridgestones were the worst for that - I've had no problem at all with the Storms - they don't seem to wear unevenly like that. However, I do have tapered roller bearings on the bike, which it didn't have when the Bridgestones were on the bike.


The other thing which I've read that affects some bikes at certain speeds is the presence of a Givi top box.
Or other weight on the back, like luggage.

[Blackbird]

How dare you slight the beloved Storm, Mr Blackbird! :nono:


Hahaha:msn-wink: I was referring to the first production batch which occasionally overlaid the reinforcing belting in the carcass. This caused a lateral oscillation at a certain speed. However, I haven't heard of this problem since they discovered the root cause.

[Ragingrob]

I don't know why that speed triggers it, but that's the way it is. VFRs do it at that speed too, especially downhill (like on the downhill run on the Harbour Bridge). It's not always a simple explanation, as so many things come into it, including steering geometry, tyre tread pattern and carcase construction, suspension settings. It's often from "cupping" (unusual and uneven wear) of the tread blocks on the front tyre, but can also be caused by the rear end: a bit of a wobble at the back can be exacerbated by the suspension, somehow the small wiggle turns into a large one at the front.
Check the following:
Your front tyre - that it's not worn unevenly, and is correctly inflated. It might help if you get the balance checked, but this isn't usually the problem.
Steering head bearings - that they're not worn, loose or notchy (you'll need to lift the front end off the ground to do this).
Rear tyre condtion and inflation pressure.
That all your tyre weights are still in place.

Definitely going to check tyre pressures again when I head to Puke this arvo. The front tyre seems absolutely fine but there is a definitely flat spot on the rear, damn winter commuting!!!


Possibly head bearings but you haven't got an old Avon Storm up front perchance have you?

The other thing which I've read that affects some bikes at certain speeds is the presence of a Givi top box.

Nope got dunlops.

Ah that's another option, I have recently chucked a top box on the back... When I head out this arvo I'll double check it without it and see if it still wobbles.

If it is the case that the top box causes a wobble at 60kph, is that a worry at all? Or just that the certain vibrations at that speed cause it and it's just a fact I'll have to deal with but no danger at all?

:2thumbsup Cheers guys

[ajturbo]

i would check your pressure first.... pump them up a couple of psi...nice, easy and cheap

[F5 Dave]

C'mon dude, you haven't even mentioned what kind of bike you are talking about or what tyres you are running. Finally 'Dunlops'. What? Dunlop Knobblies? Slicks? Are they in std sizes?

But yes as said above it was very common in the 80s to have a hands off wobble. Some bikes were very prone to it but it was exacerbated with mismatched tyres, weight over the back (loaded topbox or packrack) & mostly when the rear tyre got worn. (+ front tyre, steering bearings, alignment, suspension issues etc). Any of these can still be a cause on modern bikes.

[Ragingrob]

C'mon dude, you haven't even mentioned what kind of bike you are talking about or what tyres you are running. Finally 'Dunlops'. What? Dunlop Knobblies? Slicks? Are they in std sizes?

But yes as said above it was very common in the 80s to have a hands off wobble. Some bikes were very prone to it but it was exacerbated with mismatched tyres, weight over the back (loaded topbox or packrack) & mostly when the rear tyre got worn. (+ front tyre, steering bearings, alignment, suspension issues etc). Any of these can still be a cause on modern bikes.

1990 vfr400r nc30 as in my profile pic, dunlop gpra10 on front gpr100 on rear standard sizes.

Just about to head out without the top box to see if it's the cause, if there's still a wobble I'll double check tyre pressures, then see what's the haps.

[F5 Dave]

well I wasn't about to stalk you to find out the info:Pokey:

If you don't report back in 2 hrs we'll assume the worst. Good luck.

[vifferman]

Hmmmm... Dunlops. :(
The very worst front end wobble I ever had was on my '85 VF500, with a Dunlop on the 16" front wheel. You had to have two hands on the bars at all times. I took both hands off once, going down the Port Hills with the wife on the back. I was very lucky it didn't turn into a tankslapper (and that the fright it gave her wasn't turned into a slapping). :dodge:

Come to think of it, I did get a slapping! That was the same ride when I thought I'd give the bike a bit of brief burst of speed going around the Lyttleton Harbour road. The pounding on the back of my leather jacket was a fairly clear message that 160 was a bit fast. :o

I think from memory that (1996?) was the last time she pillioned with me, up until about 6 years ago...

[Ragingrob]

well I wasn't about to stalk you to find out the info:Pokey:

If you don't report back in 2 hrs we'll assume the worst. Good luck.

Well I survived...

No wobble whatsoever without the top box so there ya go!

So it much be the weight/wind force at so far back on the back that causes a slight rear wobble that is exaggerated at the front. Since the wobble is only between 60-65kph do I need to worry at all or is that sweet? Sure if it got worse with speed I'd get rid of it, but it rides fine <60 and >65.

:2thumbsup

[sinfull]

Prolly be the wake of the wind coming round you and getting turbulance on the top box, exagerated by the fact your rear tyre is almost kaput ! Check ya pressures anyway !

[vifferman]

So it much be the weight/wind force at so far back on the back that causes a slight rear wobble that is exaggerated at the front.
Yes.
It's a factor of a couple of things:
Firstly, the topbox is making the load on the front wheel slightly less (so it's less "planted").
Secondly (but perhaps most importantly), the aerodynamics of the topbox are a bit 'dodgy' at some speeds.
Fifthly, there's the leverage effect: anything right at the rear of the bike and high up exerts more force than something closer to the centre of mass of the bike.

[Ragingrob]

Prolly be the wake of the wind coming round you and getting turbulance on the top box, exagerated by the fact your rear tyre is almost kaput ! Check ya pressures anyway !

I hate it how commuting does your tyres just through destroying the middle :bash:

Only one more week of commuting though so I reckon it'll last out most of summer cause I'll be using the edges :headbang:

[Ragingrob]

Yes.
It's a factor of a couple of things:
Firstly, the topbox is making the load on the front wheel slightly less (so it's less "planted").
Secondly (but perhaps most importantly), the aerodynamics of the topbox are a bit 'dodgy' at some speeds.
Fifthly, there's the leverage effect: anything right at the rear of the bike and high up exerts more force than something closer to the centre of mass of the bike.

Sweet then, all good now I know what's causing it! :banana:

[F5 Dave]

Hmmmm... Dunlops. :(
...
So all tyres manufactured by Dunlop are the same? I think you'll find that they have been going for quite some years* & they may have changed their construction in that time. let alone with different models.



*[quick google]: "In 1888, John Dunlop invented the air-filled or pneumatic tires, "

[F5 Dave]

Many Police bikes have been made unstable by fitting a whole lot of crap to them causing much litigation. I remember my poor CBX550 was a bit prone but one cold kiwi I loaded up with a big pack hung out the back & set off to go pick up a girl.

I didn't make it further than the top of the drive until I turned back to check tyres & see if the forks were loose. It wobbled like crazy. But all checked out. So I turned the pack so it was over the pillion seat & the bike handled fine. Got to her house & with pack turned around again but her on the pillion it returned to it's wayward ways, but only half as bad & only at low speeds. Course I didn't tell her this.

That was the year the storm hit & the desert road was closed. We'd left on the thursday to spend night in Turangi & went through the road just as it was closing & snow was falling at about 20kph following a car's wheel tracks.
It was interesting.

[sinfull]

I reckon it'll last out most of summer cause I'll be using the edges :headbang: Bwahahaha looks forward to the pics of you weaving up and down the Highway !!!