KZ1000 wheel sizes and frame geometry?

So I have been doing some minor upgrades to my 78 KZ1000 LTD. One of them was getting a GS1100 swingarm so i could run a wider rear tire. I am going to re-lace my wheels, and want to get wider/bigger rims, mostly for cosmetics, but also to get a larger contact patch. Ideally I'd like a 18x2.15" in the front and a 18x3.5" in the rear. My concern is that by doing this i will be changing the geometry of the bike which could make it unstable. I'm willing to entertain different rim size combos, such as maybe a 19x2.15 in the front instead.

Someone told me that if I start changing the frame geometry I should get a steering damper to prevent a tank slapper. I experienced one on the freeway before and about messed my pants, I really really don't want to go through that again. Any thoughts on this is much appreciated.

Going bigger on the tires and such isnt too bad. Frame changes and additions/subtractions are another story...

If you're really scared about it, increase your rake (if possible) and add leading axle forks.
You shouldnt have any problems after that.

I would not be too nervous with the modifications you are making. The 18" front wheel will make it steer a bit quicker and the longer swingarm will increase straightline stability so that should make for some pretty neutral handling. You could install a steering damper as a precaution. I have the same wheel sizes with a stock arm and much more extreme geometry and my bike is rock solid on the freeway. If you want to experiment a bit you can drop the forks through the trees 0.5" to emulate an 18" wheel and see how that feels for you.

Like Sander says, it shouldn't be a problem.

I'm running 18" PVM wheels front and rear on my GPz 1100, front is a 2.5" with a 110/80/18, rear is a 4" with a 170/60/18, both Metzelers. Also a K&J (Krüger und Junginger) swingarm, Koni rear shocks and stock GPz front end.

The bike handles really well, never had even the slightest hint of a wobble and I have been over an indicated 120 mph on a couple of occasions.

As for steering dampers, personally I don't care much for them - my thought is that if you need one, you have a problem somewhere you need to address rather than mask it, but that's just me.

the 18" front wheel will probably be easier to find decent tires for than the 19".
kawasaki switched from a 19" front wheel to an 18" on the 79 z1r if i remember right and had serious handling issues,of course they also had a fairing bolted to the forks also which could of been a lot of the problem.
as long as the bike sits level,not lower in the front than the back i would think youll be fine since that wont really change the geomotry of the suspension.
its when you dump the front of bike into the weeds to quicken the steering radically that ive had first hand experiance with a tank slapper,and its no fun im here to tell ya

"...im here to tell ya"

I'm glad for that!

Bill

closed my eyes held on really tight and stayed off the brakes,no skill what so ever involved in saving that one.
i do remember thinking about how deep the misouri river was and wondering how it was going to feel clearing the bridge at 90 and landing in it though! :sick: :woohoo:

I have a GS arm and an 18 inch wheel on the front of mine. Handles a lot better now.

Could I ask if you haven't started to pull the rear apart could you measure the rear wheel offset to help me build my spoke wheelRe

wrote:

Could I ask if you haven't started to pull the rear apart could you measure the rear wheel offset to help me build my spoke wheelRe

This thread hasn't been replied to since 2011.   You still haven't explained what you are referring to as "offset".
A quick search turned up this Z1000A rear rim lacing tutorial...

z900collector.wordpress.com/restoration/...ing-z1000a1-z1000a2/

750R1, nice article. Thanks for finding that. 

wrote:

750R1, nice article. Thanks for finding that. 

Hey mate, no worries.   I'm still trying to work out what Samantha is talking about, she's rather cryptic..!!