KZ1000 manual correct for trail figures?

Im looking in both my 77-88 and 79-80 KZ1000 factory manuals and they have the trail listed at 90mm. That seems like a extremely low trail value.

To put that in perspective, a 2008 GZXR1000 has a trail value of 98mm.

Could it be that the manual is using a mechanical(real) trail value instead of a ground trail value? Even if this was the case, a real trail value is approximately 90% of a ground trail value, which would make the KZ ground trail value be about 100mm. A 2005 ZRX has a ground trail value of 106mm.

I have opened a huge can of worms with all the geometry changes i have done on my KZ1000 project. The ZRX triple trees I am using have very little offset. This combined with the 18" front wheel have given me a rather large trail figure. I am going to raise the rear to get the trail back to a more manageable figure, but i was going to use the stock figures as a measuring stick.

To get my trail values close to the ones listed in the manual I would have to have a rake of 23 degrees to get a trail value of 99mm. To get my rake to this it take a 16 3/4" rear shock. ridiculously long.

Any suspension gurus out there?

Well, since no one bit, I thought I'd put this info up in case anyone is looking for it in the future. After farting around with numbers for a while, i have determined the factory specs for a KZ1000 are indeed for mechanical trail at 90mm. Ground trail, which is what most people look at for trail, is 97mm stock. if you drop to a 18" wheel with a 100/90 tire, trail is reduced to 91mm. Pretty extreme trail figures even by todays standards. I think that the relatively long wheel base of the kz1000 at 59.3" necessitates this minimal trail.

Since the longer shocks, and reduced offset triple trees have shortened my wheelbase by 2 inches, i decided to play it safe on the trail figures, and have ended up with a trail of 109mm. Thats 3mm over the '04 ZRX1200 which has a wheelbase that is 57.7"; the zrx wheelbase is 0.6" longer than where I'm at.

I decided a while back i wanted to make some custom adjustable offset triple trees for this thing, but I want to ride this thing first to get a good reference point before doing any additional geometry changes.

Maybe if you could get some leading axle forks as on early kz550, 750 Ltd and 1000 Ltd you might be able to get most of your trail back?

I've done this both ways, but I'd maybe put the calculator away and instead try it very carefully, I think if it is badly out it will feel odd even at low speed. Your proposed 23 degree castor seems quite extreme for such an old bike: GPz1100 B is 29 degrees, z1000R is 27.5... even a Fireblade is around 24 degrees...

I went from 19 to 18 inch front on my short wheelbase GPz550 D1 and got quite a nice improvement.

In changing the yokes, did you want to change the geometry? Were you wanting to sharpen the steering up or increase high sped stability? Seems old kz were quite conservative in their frame geometry, and going longer on the rear shocks or going down to 18 inch front wheels seems a quite common modification.

Sorry I should have clarified. I ended up with 24.5 degrees for the rake. 23 seemed too steep to me as well, stock is 26. the headstock has been thoroughly braced to compensate for the increased forces put on it as well. I didn't want to change the geometry, but the fork swap ended up doing that. Now that the wheelbase has been shortened quite a bit and the trail has been altered I want to get a baseline before anymore changes are made. I thought it would be stupid to spend the time and money making some triples only to be unsatisfied with the geometry, which also part of the reason I want to make the offset adjustable.

You are correct the 18" wheel change is quite common and does quicken the steering, thats why I initially wanted it. I was just surprised by the extremely low trail figures on these bikes. 97mm is comparable to modern bikes; 91mm is lower than almost all modern sportbikes. i think you can get away with this because the wheelbase is so long.