Front-end wobble??

**Ragingrob** · 15th October 2009, 22:30

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** · 15th October 2009, 22:33

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** · 16th October 2009, 08:26

Originally Posted by 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.

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** · 16th October 2009, 08:55

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** · 16th October 2009, 09:00

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

**Blackbird** · 16th October 2009, 09:03

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** · 16th October 2009, 09:07

Originally Posted by 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.

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** · 16th October 2009, 10:23

Originally Posted by Blackbird

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!

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.

Originally Posted by Blackbird

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** · 16th October 2009, 10:41

Originally Posted by vifferman

How dare you slight the beloved Storm, Mr Blackbird!

Hahaha

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** · 16th October 2009, 11:08

Originally Posted by 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.

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!!!

Originally Posted by 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.

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?

Cheers guys

**ajturbo** · 16th October 2009, 11:11

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

**F5 Dave** · 16th October 2009, 12:09

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** · 16th October 2009, 12:33

Originally Posted by 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.

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** · 16th October 2009, 13:41

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

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

**vifferman** · 16th October 2009, 14:01

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).

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.

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