Z1 dual disc conversion with KZ900 wheel

Hi guys, I know this subject has been beat to death but I have a specific question that I have not found the answer to. I have a 1975 Z1 that has a bunch of KZ parts on it. I just found a good set of Z1 forks. The forks on it were KZ1000 so I know the calipers won't fit unfortunately. I am using wire spoke wheels. Anyways reading about the subject it seems people suggested keeping the single disc on Z1 since the rotors weigh so much you will be adding a ton of weight. My question is can't you just run a KZ900 wire wheel with the thinner brake discs so save all the extra weight? The rotors look to be both 296mm with the 7mm thick z1 vs the 4.5mm thick KZ. Anyone know?

Yes, that would work. I have a set of Z1R 4.5mm discs on a KZ900. Weight don't matter too much unless you are in to some type of racing. Don't forget about using the 5/8" bore master cylinder for dual disc.

Thanks for the reply z1kzonly, the threads I saw were saying the extra z1 rotor alone weighs something like 8 pounds and to use stiffer fork springs, heavier fork oil etc. etc. for all the added weight. Several people said it changes the way the bike handles and that they preferred the single disc setup. I already have a completely rebuild kz900 wheel with new rotors, kz1000 dual brake setup etc. I just need to figure out the z1 calipers since the mounts for the fork legs are different. I just wanted to make sure there wasn't some reason not to do it before I spend more money on parts I don't have.

WTH does the fork springs have to do with the rotor weight. Someone needs to educate themselves on sprung/unsprung weight. Either way, it's a 45 y/o bike, only thing you'll notice is it will stop better. Run drilled rotors if it's that big of a deal.

The dual brake setup was an option back in the day. No mods to the front end were necessary. I have the option on one of my Z1B's and I really like the much softer response of the dual brake with the larger master cylinder. Some people turned their forks around but I left mine in the standard position.

KZ802 wrote: Thanks for the reply z1kzonly, the threads I saw were saying the extra z1 rotor alone weighs something like 8 pounds and to use stiffer fork springs, heavier fork oil etc. etc. for all the added weight. .....

Does not compute! Think about it - no matter how much weight an extra rotor might add how much of that weight is supported by the suspension? Answer - none. If you read threads that recommended heavier springs, fork oil, etc. those threads were either referring to something other than adding a rotor or they were written by someone who does not understand motorcycle suspension. Ed

Doesn't a heavier wheel have more inertia after hitting a bump, thus requiring more damping to control it? Also, doesn't a heavier wheel have more resistance to changing direction than a lighter wheel?

suspensionspot.com/blogs/news/improve-yo...cing-unsprung-weight

From a motorcycle-specific perspective.

www.motorcyclenews.com/news/2001/june/th...-lightweight-wheels/

TexasKZ wrote: Doesn't a heavier wheel have more inertia after hitting a bump, thus requiring more damping to control it? Also, doesn't a heavier wheel have more resistance to changing direction than a lighter wheel?

Wouldn't heavier damping simply make the rest of the bike rise more when a bump was hit? The wheel would still rise over the bump regardless of the wheel's weight. I agree that a heavier wheel would have more resistance to changing direction, but I don't see how changing the amount or viscosity of the fork oil would make any difference. Ed

I put a dual brake setup on my KZ-1000 when I went thru it. I never understood why these bikes didn't come with a dual disc setup because the bike needed it as well as some other things. I found a guy that had one of the dual disc brake kits from Kawasaki and it had everything but the master cylinder which I had to source elsewhere. After researching this subject it became obvious that on the factory dual disc bikes of the time they used a thinner rotor than the single disc bikes. However the dealer installed kits in the US had a thicker rotor that matched the rotor on the bike the kit was being installed on. Otherwise both rotors would have had to be replaced which would have added to the cost substantially. It's my understanding that bikes sold in Europe had dual disc brakes from the factory and they were the thinner discs.

In any event the partial kit I received/bought had the splitter, disc, brake hose, hose bracket, brake line, caliper and caliper holder and all necessary bolts. No instructions were in the box. The person I bought it from said he had the kit for a long time and needed the master cylinder in the kit for another bike so he used it, but was never able to find another factory one to replace it. There was no part number tag on the box, but there was a spot that looked like it had a pasted on tag of some sort but was long gone. I have never found the factory part number for this alleged conversion kit, but have been told it did exist and several were installed by dealers.

The installation was pretty straightforward and bleeding the system was quite easy. In operation the dual brake system works great. My only concern is that the new rotor looks "new" while the old original rotor looks "old". At some point I will send the rotors out to be machined so they look the same. The bike handles bumps and such quite well and the front wheel seems well planted when going over them. How much additional weight is offered by a 5mm rotor as compared to a 7mm rotor is of no real concern to me as it isn't a race bike. I have had the bike well over legal speeds and it stops beautifully with no pull or irregularities. Lever effort is just what I would expect on this bike and it WILL lock up the wheel if you get too rambunctious. I have had no problem trail braking with this setup and it is what the bike should have had right from the factory. I suppose there is some slight initial extra resistance when getting the bike moving from a dead stop but it is expected with more weight on the ground. That resistance is of little consequence and once moving is history. The extra resistance when stopping to the extra weight of the dual disc setup is counteracted by the additional caliper. Is there more resistance to changing direction with the dual disc setup? Perhaps but if there is any I certainly don't notice it.
Rick H.

Great looking bike! Ed

hi rick ,yes very nice and a good update with 2 disc ,what brake pads do you use up front to be able to lock it up if a bit quick to to react ,its a lot of weight to pull up ,,i guess any new pad is way better than 40 year old material ,thanks ,david