Lowering my 1975 Z900

One more try:

What is the size (such as 120/90-18) of the rear tire currently on the bike? Ed

650ed wrote: One more try:

What is the size (such as 120/90-18) of the rear tire currently on the bike? Ed

Sorry Ed, :blush: :ohmy: thought I had answered that, bike is at a friends shop, but whatever stock tire size is that's what I had put on it, either 120 or 130- 90 - 18 sounds right as I recall. When I bought the new tires I used an on line conversion from Dennis Kirk which I where I had bought the tires, either that or they actually had a reference for the bike with current recommended stock sizing. I remember from stock which I think was originally 400.18 and bought modern equivelent.
Wish bike was here I would look , unfortunately its at my friends shop and he's gone .
Does "Stock Size" help..?? Thanks for your patience!

Nope, not gonna toss current rear shocks, they are new, only been on the bike since 2011, maybe 5000 miles total on them. Think I got them from the KZ supplier out in California.used to be highway 66 Kawasaki ? or something like that?.?? Or... maybe Z1E, cant recall now.
Ya know , I used to work in the Auto parts business ED, and we always had reference books that showed diameter, compressed length, each end mounting type etc. etc. so if we had a customer come in with a shock off an old vehicle that we had no "Official Listing" for, we would simply measure the shock identify each ends mounting type ( Eye opening size, Stud etc. ) compressed length etc. etc. compare it to our book and "voila", we had a close match that almost always would work. Granted , we could not guarantee no interference but we always told folks to check that. wonder if there's such a thing as a reference book for Motorcycle shock supplier?? Thanks for all your help ed!
TennesseeZ ED

Most older, inch-designated tires had sidewall heights approximately equal to their section width, so an original 4.00 inch wide tire would also have a sidewall height of approximately 4.00”.

The aspect ratio on metric tires can be used to calculate their approximate height by multiplying it times their width. The height of a 120 width tire (which I believe is the best metric replacement for a 4.00 inch designated tire) varies depending on the aspect ratio. So a 120 x 90 x 18 tire = approx. 108mm (4.25”) sidewall height and a 120 x 80 x 18 tire = approx. 96mm (3.78”) sidewall height.

Given that, if you switched the 120 x 90 x 18 rear tire for a 120 x 80 x 18 tire the rear of the bike would be approximately ½” lower without moving the tire any closer to the fender. I know ½” is not a lot, but if it was done in addition to the other changes you are contemplating it might help. Maybe consider it for your next tire change.

Regarding the shocks, you may want to contact Dave Quinn at davequinnmotorcycles.com . He sets up and sells Hagon shocks and is extremely knowledgeable about shock lengths, spring weights, etc. I bought shocks from him about 6 years ago and he was very easy to talk to and seemed happy to share information. So even if you don’t plan on buying Hagon shocks it might be worthwhile to call him to pick his brain. BTW, I love my Hagon shocks; they replaced my S&W shocks and they work every bit as well and they are stainless steel. Regards, Ed

650ed wrote: Most older, inch-designated tires had sidewall heights approximately equal to their section width, so an original 4.00 inch wide tire would also have a sidewall height of approximately 4.00”.

The aspect ratio on metric tires can be used to calculate their approximate height by multiplying it times their width. The height of a 120 width tire (which I believe is the best metric replacement for a 4.00 inch designated tire) varies depending on the aspect ratio. So a 120 x 90 x 18 tire = approx. 108mm (4.25”) sidewall height and a 120 x 80 x 18 tire = approx. 96mm (3.78”) sidewall height.

Given that, if you switched the 120 x 90 x 18 rear tire for a 120 x 80 x 18 tire the rear of the bike would be approximately ½” lower without moving the tire any closer to the fender. I know ½” is not a lot, but if it was done in addition to the other changes you are contemplating it might help. Maybe consider it for your next tire change.

Regarding the shocks, you may want to contact Dave Quinn at davequinnmotorcycles.com . He sets up and sells Hagon shocks and is extremely knowledgeable about shock lengths, spring weights, etc. I bought shocks from him about 6 years ago and he was very easy to talk to and seemed happy to share information. So even if you don’t plan on buying Hagon shocks it might be worthwhile to call him to pick his brain. BTW, I love my Hagon shocks; they replaced my S&W shocks and they work every bit as well and they are stainless steel. Regards, Ed

Thanks Ed
Interesting idea about going to an 120x80x18 rear tire :woohoo: ,that combined with a slightly shorter rear shock would be a good inexpensive compromise!! OR , Someone had also suggessted checking JC Whitney for a rear shock lowering kit, I did that ( Original cost just $15.00!!) and it is on their website, however its discontinued. Maybe I should just fire up the welder and make one? That way no shock to buy period, just relocate slightly the stock shocks rearward. Your Thoughts on that approach?? Wonder if anyone has attempted to do/ make that??
Thanks Again
TennesseeZ aka ED

They come up on ebay . That would be the way to go.

Hey ED...I suspect that making any permanent changes to your shock mount position on your Z-1B using a welder is ill-advised.

Hello All,
Roguedog here, first posting. Great Forum by the looks.
These range of shocks might help in lowering. Good Luck.
www.gazisuspension.com/products.html