Help! My 600 feels heavier than America's debt!

[ducatilover]

Hey guys, my ZZR600 is turning like an absolute pig, far worse than standard and it's dropped 20+kg off original weight.
I'm thinking my USD conversion has thrown the geometry out somewhat.
Could somebody please tell me:
Length between front axle and the lower clamp
If the axle is offset forward/rearwards?
If anyone has a ZZXR400/600 can they do those measurements?
If anyone is clever with set-ups, what would make the front end feel horribly heavy and slow to turn on the road?

The bike:
ZZR600d chassis
ZXR400H1 forks, 10W fluid (Fuchs), 6th position in on the damping, 1 whole turn on pre-load
Standard ZZR600d rear shock, good condition, damps fairly well, about half way on the pre-load adjustment.
Pilot powers, 120/70 and 160/60 at 32 and 36 psi respectively.
Sits around 175kg dry, standard is quoted at 195kg.



Anyone able to shed light on how I've destroyed my handling gets an internet beer! Cheers.

I will drop the forks in the yokes a bit and see what happens, but it feels seriously heavy at open road speeds and the forks are even with the top clamp.

[GrayWolf]

Hmmmm OK... dont know if you 'just' replaced the forks, or the complete triple tree as well, soooo

IF triple clamps/stem replaced..... Are head bearings correct size? Over tightened? are the shoulder measurements identical between the stems for clearance, positioning? IF you replaced the stem, there could be some very subtle differences for diameters and heights...
If you measured the headstock against the OEM one... is the distance from stem to fork holes the same? the clamps may not only spread the forks wider, but MAY physically position them fore or aft by a few mm of the original clamps position?? that few mm if forwards WILL slow down the flickability a little.

If they are upside down forks, did the donor bike have the same rake angles? I have noticed a lot of upside down sprotbike forks have a very steep angle... if your forks are at a more 'relaxed' angle... is it causing 'stiction' on the sliders?
Are you 100% sure the 'new' forks are straight?
Are the new forks 'slightly longer'?? Slightly shorter?
is the front wheel 'identical' between the two bikes? it may look identical, but again a mm here or there, especialy if the forks were wider/narrower spacing could leave the forks being 'pinched or spread' to accommodate the wheel.
Leading/centre/trailing axle?? again will affect trail/angle...........

[ducatilover]

New triples, old forks were right way up (not when I finished with them...)
The top triple sits s tiny bit lower (3 or 4mm) than original
Correct size bearings, steering is mint at low speeds and no notching or anything when stationary.

Wheel has had the spacer and speedo drive machined down, fits spot on.
Distance from stem to fork leg is 2mm less on each side from memory (I think there was a total of 4mm machined off spacer/speedo drive)

Fork length is something I am unsure of, because the old forks looked like this:


That's why I've asked for someone to check for me if anyone else has one floating around, same with the axle, this one's centered and I'm fairly sure the original was too.

New forks are not bent.
Wheel is a ZZR600 wheel, and as said, spacers made to fit it.

Low speed riding is okay, tipping in at 80k+ it feels as fat and heavy as fuck. Heavier than it previously did.

As for fork stiction, they work well at low speeds and the damping rate is okay, sure don't feel slow to react over bumps

[ducatilover]

The forks that are on it are off set a fair bit further forward, I think that answers my question, I'm struggling to find the original rake/trail specs.

[HenryDorsetCase]

It might be the offset of the forks ("forward" relative to the centreline of the headstock.): it it is longer then even if everything else is the same it would slow the steering down.

There is a recent Performance Bikes article that discusses this (with pictueres) because they are racing a Triumph 955i and the replaced the whole front end with one from a CBR900RR. It quickly got quite technical but the factoid (opinionoid?) above is something I remember from that article. I dont know if I still have the magazine: will check.

or you could buy Tony Foale's book:

http://www.tonyfoale.com/book.htm

or look at his website: He knows things about stuff.

[Fast Eddie]

no doubt new triples and forks will have changed something

lets see how you fix it..

dropping forks will make its steer quicker eh? got a steering damper on it?

[tigertim20]

New triples, old forks were right way up (not when I finished with them...)
The top triple sits s tiny bit lower (3 or 4mm) than original
Correct size bearings, steering is mint at low speeds and no notching or anything when stationary.

Wheel has had the spacer and speedo drive machined down, fits spot on.
Distance from stem to fork leg is 2mm less on each side from memory (I think there was a total of 4mm machined off spacer/speedo drive)

Fork length is something I am unsure of, because the old forks looked like this:


That's why I've asked for someone to check for me if anyone else has one floating around, same with the axle, this one's centered and I'm fairly sure the original was too.

New forks are not bent.
Wheel is a ZZR600 wheel, and as said, spacers made to fit it.

Low speed riding is okay, tipping in at 80k+ it feels as fat and heavy as fuck. Heavier than it previously did.

As for fork stiction, they work well at low speeds and the damping rate is okay, sure don't feel slow to react over bumps

firstly, are you sure its not just from being used to riding geoff the last wee while? not riding your bike for ages can mess with your perception of weight and power.

did you check your tyre pressures as well?

other than that, Id say that you are on the right track with getting the axle to triple length confirmed - but its going to take you all of ten minutes to drop the front 10mm, and take it out and see if its better or worse, youve changed a hell of a lot, so getting measurements from a stock bike probably wont help much.

also consider what weight you have removed from where, and how much this affects the weight distribution, rather than just overall weight, and how much weight is currently being help up by the 400 forks, compared to how much weight was on them on their original bike.

[Fast Eddie]

they are racing a Triumph 955i and the replaced the whole front end with one from a CBR900RR.

did they? what year? wtf for haha.. are they any good? I'd be keen on readin that

[carburator]

check your new triple trees against your old ones for the difference in offsets to the bearing head.
low speed it would be fine, high speed you have less leverage ratio against the effects of centralfugla force
of the said turning moment of the front wheel ( feels like its in cement )

http://community.jpcycles.com/articl...-geometry.aspx

[GrayWolf]

The forks that are on it are off set a fair bit further forward, I think that answers my question, I'm struggling to find the original rake/trail specs.

2 possibilities I can see.....

1) the forks are set further forwards.. physicaly 'lengthening' the bike between axles.... longer bike, more stable but slower steering.

2) they are longer.. this has lifted the bike physicaly at the front if you have put then in 'flush'.... try dropping the clamps 4-5mm and see if anything changes for a kick off.

[HenryDorsetCase]

did they? what year? wtf for haha.. are they any good? I'd be keen on readin that

they started with a stock 955i a year or so ago and put it on a hell of a diet, upped the performance significantly, and raced it in one class last year. This year they are racing it in a thing called Golden Era Superbikes which is unrestricted (vs I think thunderbikes which was power to weight ratio restricted),... let me see what I can come up with.

[ducatilover]

It might be the offset of the forks ("forward" relative to the centreline of the headstock.): it it is longer then even if everything else is the same it would slow the steering down.

There is a recent Performance Bikes article that discusses this (with pictueres) because they are racing a Triumph 955i and the replaced the whole front end with one from a CBR900RR. It quickly got quite technical but the factoid (opinionoid?) above is something I remember from that article. I dont know if I still have the magazine: will check.

or you could buy Tony Foale's book:

http://www.tonyfoale.com/book.htm

or look at his website: He knows things about stuff.

Will have to have a light read methinks thanks

no doubt new triples and forks will have changed something

lets see how you fix it..

dropping forks will make its steer quicker eh? got a steering damper on it?

No steering damper, except for when my wrist hits the frame in a tank slapper...

firstly, are you sure its not just from being used to riding geoff the last wee while? not riding your bike for ages can mess with your perception of weight and power.

did you check your tyre pressures as well?

That popped in to my head, but it's not that, it is properly heavy in the steering at speed.
Tyre pressures were double checked, 32 front, 36 rear.

other than that, Id say that you are on the right track with getting the axle to triple length confirmed - but its going to take you all of ten minutes to drop the front 10mm, and take it out and see if its better or worse, youve changed a hell of a lot, so getting measurements from a stock bike probably wont help much.

also consider what weight you have removed from where, and how much this affects the weight distribution, rather than just overall weight, and how much weight is currently being help up by the 400 forks, compared to how much weight was on them on their original bike.

Will drop the front and see what it's like
The 600 is 175kg dry at the moment, ZXR400 claimed at 163kg from memory.
The dry distribution was pretty even too.

check your new triple trees against your old ones for the difference in offsets to the bearing head.
low speed it would be fine, high speed you have less leverage ratio against the effects of centralfugla force
of the said turning moment of the front wheel ( feels like its in cement )

http://community.jpcycles.com/articl...-geometry.aspx

Old triples were kind of snapped and the scrap man ate them. Looking at pics though, it seems the original ZZR triples offset the forks closer to being inline with the stem
Actually, I might have kept a snapped triple for teh lulz, will have a look soon

That makes sense to me

2 possibilities I can see.....

1) the forks are set further forwards.. physicaly 'lengthening' the bike between axles.... longer bike, more stable but slower steering.

2) they are longer.. this has lifted the bike physicaly at the front if you have put then in 'flush'.... try dropping the clamps 4-5mm and see if anything changes for a kick off.

Will be giving it a go, but I reckon it's how far forward they are.

[Ocean1]

The forks that are on it are off set a fair bit further forward, I think that answers my question, I'm struggling to find the original rake/trail specs.

Too much trail.

If you project a line down the centre of the steering head to where it intersects the road then trail is the distance from that to the centre of your theoretical tyre contact point.

Changes to the angle between the fork clamp centre and the steering head angle will change the trail, so will changes to axle offset in the forks. So will changes to the distance between the fork clamp centreline and the headset centreline.

Too much trail makes it difficult to turn the steering, not enough makes it twitchy.

Edit: if it's a huge change your fukct. You'll get some improvement pulling the forks up the clamps, try 5mm, check clearances and go ride. Try some more...

[nzspokes]

Was this the same frame that you crashed on? Head stock in frame bent?

[ducatilover]

Was this the same frame that you crashed on? Head stock in frame bent?

Nope, different frame, a straight one
The old 400 frame was twisted and cracked in a few places

Too much trail.

If you project a line down the centre of the steering head to where it intersects the road then trail is the distance from that to the centre of your theoretical tyre contact point.

Changes to the angle between the fork clamp centre and the steering head angle will change the trail, so will changes to axle offset in the forks. So will changes to the distance between the fork clamp centreline and the headset centreline.

Too much trail makes it difficult to turn the steering, not enough makes it twitchy.

Edit: if it's a huge change your fukct. You'll get some improvement pulling the forks up the clamps, try 5mm, check clearances and go ride. Try some more...

Just found the broken original triple, the new forks are about 7mm further forward.
Have pulled the forks up 10mm, will give it a go if it's dry tomorrow.
ZXR400 trail is 24 degrees/85mm rake/trail
ZZR600 is 24.5 degrees/97mm rake/trail.
I'm running a 120/70 vs the ZXR400 running a 120/60