Possible wheel out of balance?

[proximity]

I am having a bit of a problem with my bike at high speeds, the bike is a zephyr but the previous owner has fitted a set of GPZ 600R forks (and wheel etc).
Problem is when i reach about 90 i get pretty much a tank slapper, its fine up to then, and then it just starts to wobble.

It seems the individual road makes it better or worse, today it really freaked me out on a dual carriageway, i got to about 85 ish and i basically had to hit the brakes because i almost had a full on tank slapper going.

I was thinking it could be the front wheel out of balance as this happened to a mates car, any ideas?
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2004 Aprilia Tuono

[MarJay]

No its more likely that the GPZ600R forks are just shit.

Why anyone would fit a pair of forks and front wheel from a bike which has a 16in front wheel and the most archaic fork design since Noah worked out how he could get rid of his chopsticks, is beyond me.

Personally I'd look very carefully at the forks, and how they are fitted to the bike. Some bikes just are bad at high speed.

I think that your problem almost certainly stems from this ill-advised modification.

Things to check:

head bearings correctly tightened (and that they fit the steering stem) and in good condition

fork oil level and the condition of the fork internals

condition of the rear suspension (has a surprising amount of effect on the front end).

Tyre pressures, condition and sizes (must be correct).

if all the above is OK, I'd check the swingarm bushes too, but its more likely the GPZ600R forks are just a pile of poo.

or, it may very well be that a zephyr 550 was never made to do over 90mph safely.

I think wheel balance is not likely to be very high on the 'likely causes of tankslappers' list.
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British beauty: Triumph Street Triple R; Loony stroker: KR1S; Track fun: GSXR750 L1; Commuter Missile: GSX-S1000F; Cheap project: CBR900RR FireBlade
Remember kids, bikes aren't like lego. You can't easily take a part from one bike and then fit it to another.

[MarJay]

Isnt the Zephyr 550 a newer bike than the 600R anyway?

Seems somewhat strange...

{edit} checking about on the 'net leads me to believe the front wheel may be the cause. The Zephyr 550s in the pics that i've found appear to have 17in front wheels... so why someone would ditch that in favour of some 16 pile of crud is beyond me. The bike may have been crashed, which would explain a lot. Plus the earliest Zephyr 550 I can find is 1991, which is also odd cause the GPZ600R hails from around 1987 to around 1990. Curiouser and curiouser... {edit}
____________________
British beauty: Triumph Street Triple R; Loony stroker: KR1S; Track fun: GSXR750 L1; Commuter Missile: GSX-S1000F; Cheap project: CBR900RR FireBlade
Remember kids, bikes aren't like lego. You can't easily take a part from one bike and then fit it to another.

[proximity]

I think it was probably crashed, and the GPZ front was just cheap.
I agree its shit but the GPZ was actually fast.

Anyway, the forks seem to all be fitted fine, i stripped them down not long ago and inside is fine, new oil and seals done.
I checked the head bearing torque and its ok, and i checked the play in them.

The tyres are correct for the wheels.
Rear shocks seem fine, they look in good condition and they do what they do (how am i supposed to check this). I can bounce on the rear nicely with someone fat on it, and its nice and smooth over bumps.

Maybe i should just ditch the front end, but i dont really have the cash at the moment.
A guy in a shop said the front wheel may be buckled a bit or the tyre might have been changed with the old weights left on or somet.
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2004 Aprilia Tuono

[veeeffarr]

Would these work mate?

Zephyr 750 Forks - £10.00 - 2 days, Milton Keynes Or Zephry 550/400 Forks - £58.75 - Southport (Near me)

[proximity]

They would but then i would have to find a wheel, discs, calipers, yokes etc etc.
I would prefer a full front end.
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2004 Aprilia Tuono

[veeeffarr]

[MarJay]

I think the problem is that the front wheel is 16in. This means you have a higher profile tyre which will completely change the handling characteristics of the bike.

The forks may very well be adequate for the bike, but I'd seriously consider a front wheel change.

There is a nice RGV250 front end on ebay at the moment but I think the forks would be too short. Even so, the brakes and wheel would work...

edit
Bandit would be perfect!
https://cgi.ebay.co.uk/1200-BANDIT-FRONT-END-COMPLETE-WITH-POLISHED-RIM_W0QQitemZ8042417284QQcategoryZ10534QQrdZ1QQcmdZViewItem
____________________
British beauty: Triumph Street Triple R; Loony stroker: KR1S; Track fun: GSXR750 L1; Commuter Missile: GSX-S1000F; Cheap project: CBR900RR FireBlade
Remember kids, bikes aren't like lego. You can't easily take a part from one bike and then fit it to another.