KZ750 front end swap

Feel free to put your ideas on the post! I’m still looking for ideas and infos and you guys are providing a lot!

Other things to consider: stock triple has about a 1" drop, most modern triples are flat. The difference in tire size from a 100/90/19 and a 120/70/17 is about 2.5"(depending on tire model). So even though the forks are close to the same length as stock the 17" wheel swap and triple alone are loosing 2.25" of height.

A very important thing to consider is many modern bikes have very little fork offset. This has a huge effect on trail and can make the bike turn slow. IIRC stock offset is around 58mm, most modern sport bikes will be down in the low 30s. 1992 GSXR 1100 is 36mm

the increased rake from loosing the front ride height will help with lowering the trail number.

Would you recommend keeping the stock wheel instead of the 17 inch zx10r? By definition it will help with the height of the front end.

Ethan B wrote: Would you recommend keeping the stock wheel instead of the 17 inch zx10r? By definition it will help with the height of the front end.

Most newer or Modern as called, rims use tapered bearing. Without knowing the ZX10 though I do have experience with the ZX9. To use the forks you need to use the matching axle and they would more then likely be tapered bearings with races, Where as the Kz750 should be square press fit type. you have two options here. machine a new axle to combine the Kz750 hub and bearings to the forks, or machine the Kz750 hub to receive the tapered bearings. The later requires the hub to be able to be machined of course, then your more than likely to need to machine spacers for the brake rotors to space them out to match the ZX10 caliper spacing. Its not easy but anything is doable.

It is significantly more difficult to mate an old wheel to new forks. brake disc, calipers, spacers and axle will likely not fit and will require machining. There are other ways to get the ride height back such as internal fork lengthening and fork tube extensions.

[quote="Mikaw" post=835633 Most newer or Modern as called, rims use tapered bearing. .[/quote]

I'm not too sure what rims you are talking about but I've done a few rim swaps and never seen a motorcycle wheel with tapered bearings yet, steering head yes, but not wheels. { I just bought a pair of 2019 Z650 wheels, 4.5x17 and 3.5x17, when they arrive I'll confirm this}. Wheel swaps are tricky and takes a lot of homework, I've just fitted a Z1300 front wheel {18x2.15} to a 2001 Triumph Daytona 45mm showa front end, I bought new fork tubes 100mm longer so my front end retained the correct height, I had to lengthen the damper rod and make new spring spacers. I bought over the counter bearings for the wheels to mate up to the 25mm hollow Triumph axle, I had to make up 3 spacers for the axle , they had to be the right diameter so I could fit seals over the Spacers and bearings, I checked out seal availability before making the spacers. I struck it real lucky with the Z1300 wheel as the disc spacing was the same as the Triumph wheel, But I still had to either have custom discs or make brackets up to mount the calipers to suit triumph discs, I chose to make my own discs as I was lucky enough to find some 320 mm disc blanks from a disc company locally. It took a few days to make the discs on an old 4 chuck lathe but they are now mounted to the Z1300 carriers and fit well. Also I lost the speedo drive due to the swap and now will use a GPS speedo, And I haven't even mentioned the triple clamps/steering stem/front geometry yet, {that's if you want to do it properly}, lots of work and quite expensive unless you do it all yourself..... {and that's only the front} !!!!:blink:

750 R1 wrote: [quote="Mikaw" post=835633 Most newer or Modern as called, rims use tapered bearing. .

I'm not too sure what rims you are talking about but I've done a few rim swaps and never seen a motorcycle wheel with tapered bearings yet, steering head yes, but not wheels.[/quote]

Your Correct. I was confusing the spoke hub Id like to use on my future project. It has tapered bearings. I looked up the ZX9 front bearings and they are press fit. Thank you.

So I measured the forks and everything around it. So the actual forks lenght is 35 inches for the my KZ750 and the zx10r is 29.8 inches. Is this enough of a difference to say that it will affect my trail negatively? I know I'm already loosing some by the lower tire size, but still hoping I won't have to extend the forks. Is there a way for me to know what would be the lowest I could go for the forks without having to many down side effects? I still have a couple of options for the forks ( zx7r, zx6r, 636, zx9r, zx10r or gsxr1000).

Ethan B wrote:
I still have a couple of options for the forks ( zx7r, zx6r, 636, zx9r, zx10r or gsxr1000).

I have a ZX9-R fork and 17 inch wheels and i do riding my bike sometimes really fast on bumby roads. I never had any groung clearance probs.
The bike handling and cornering is perfect and it stears like a train on the track. The only issue is, i wish it had sometimes some more extra power......:whistle: :whistle: :whistle:

Ethan B wrote: So I measured the forks and everything around it. So the actual forks lenght is 35 inches for the my KZ750 and the zx10r is 29.8 inches. Is this enough of a difference to say that it will affect my trail negatively? I know I'm already loosing some by the lower tire size, but still hoping I won't have to extend the forks. Is there a way for me to know what would be the lowest I could go for the forks without having to many down side effects? I still have a couple of options for the forks ( zx7r, zx6r, 636, zx9r, zx10r or gsxr1000).

A 5.2 inch lowering of the front end only, will dramatically reduce trail. Are you sure that 35 inch measurement is correct, I have a 1982 GPZ750 R1 and the freestanding fork length is 800mm, or 31.49 inches, 35 seems a bit long ...
I did a calculation using reduced fork length on my bike and the trail reduced from 4.04 inches to 3.68, 3.68 is not enough trail, it would be very nervous and prone to tank slappers, in my opinion.. Using your numbers for fork length with my bike , which should be similar to yours the trail went down to 2.92, which would be dangerous, I think something may be wrong with your numbers. Most modern sport bikes are close to 4 inches of trail, that's a number I try and stay as close as possible to when doing these conversions.. The ZX9-R fork Sirocco has used looks longer than the the forks you've quoted. Make sure that when lowering one end of a bike, you do similar things to the rear, I read somewhere that raising the rear suspension 10mm reduces rake by 1 degree, someone please correct me if this is wrong, I tried to find the reference but couldn't, lowering the front has a similar effect, reducing rake. Remember to take into consideration changes to front wheel diameter as well as triple clamp offset, this has its own effect, reducing offset adds trail and visa versa. As I said, to do this properly can be a bit of a mission. Sirocco's bike looks pretty balanced, maybe emulate what he's done. I'm about as anal retentive as it gets when it comes to motorcycle suspension, I try to get things as close to what I consider perfect as I can get, you don't need to be as strict, but there are definitely things you need to get right...

forks are measured from top to center of axle. 35 inches is too long for stock. reducing the height alone will make the bike unstable because the trail number will go so low. but a modern triple with less fork offset can change this. Everything must be looked at as a complete package. You really need to familiarize yourself with basic motorcycle geometry concepts to do this correctly, otherwise you are just gambling. Check out Tony Foale's book "Motorcycle Handling & Chassis Design"

here is a trail calculator. i would not consider any swap without crunching the numbers first.

www.rbracing-rsr.com/rakeandtrail.html

I just realised I did that using the stock Kawasaki offset, what is the offset of the ZX10R triple clamps?