TOPIC:

I have a question about rear rim size that I can't find an answer to so hopefully someone here can help me out.

I have a 1978 KZ1000B LTD with mag rims that I am about to replace with spokes. Currently the mags are 16" rear and 19" front. The new rear spoked rim will be 5" wide to accommodate a 170 tire.

My question is should I stick with the 16" or go to a larger 17" or 18" rim. Availability of performance tires is a main concern.

I have a fair amount of performance work done to the bike including a stretched box tube swingarm with 9.5 inches between the arms that should fit the wider tire.

Any advice and opinions are appreciated.

Thanks
Eric

What counter sprocket are you going to run?


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It is a 15 tooth front and rear is 36 tooth.

Very Nice style! I like! (sorry, needs modified back metal fender) IMO.
What's the riding plan? Track night? Cruise Nights? or daily transportation?
Go 530 chain conversion adds an extra 3/8'-1/2" clearance for wider tires.
Then you can get away with 3/8" offset for sprockets.
Stay 16" I've had this 4" x 16" Harley Hog wheel laced to a drum brake hub with a 150 tire.
Buy a 16" front car slick with tread! Or the retro 5" x 16" slick.
Seeing you have disc rear. Start looking Harley! ready laced, use 530 sprocket and the Harley disc. Easy and cheaper!
The black KZ in picture, that's a complete Harley hub rim set up. 18" x 5.5 rim
Akront makes the nice 4.25" 18 ring. 3.50 is too narrow.
Buchanan sells and makes any spoke you want or need also.
I have some old photos of my 4 x 16 hog wheel with a 150 tire on.
Looks like you certainly know what you are doing mechanical wise.
The Ol' saying: Ya wanna play? Ya gotta pay!
If serious about tire quality? Go 17". [ All the drag bike guys have 17" slicks nowadays. Plus high speed tires are more plentiful at 17"
couple of tire pics. also
Good luck!
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You only need as much tire as you need. Lol

What I mean by that is any additional mass in the tire will effect performance. A bigger tire not only has more rotational mass but it is also as far out from the axis of rotation as possible giving it more leverage. This makes the bike accelerate slower and stop slower, and because of the increased gyro, turn slower. A fatter tire also requires a steeper lean angle to turn when compared to a narrower tire. A tire that correctly matches your HP and application is best if you seek max performance. Otherwise slapping a fat tire on is purely aesthetics which is fine as well, but its important to understand the implications.

Fat tires come on many bikes that simply don't need them, but have them for the look. Same thing for header primaries. Everyone wants giant honking header tubes but it actually reduces performance in many instances. thats why you see double wall headers and header covers on many factory bikes to make the primaries look bigger than they need to be. If the OEM could figure out how to do that for tires they would.

If you go with an 18" tire I would not go bigger than a 150. If you go 170 I would go 17". Bear in mind there are not a many 170 tire options in 17" wheel., loads of 180, and 160 on 17". 170 is much more common on 16" wheels which pretty much only cruisers use for rear tire at this point. Some early CBR use 16 but options will be limited for sport tires. Another consideration is you will need an offset sprocket at the minimum. depending on the wheel you may need to trim down the sprocket carrier and/or offset the wheel for chain run. And yet another consideration is the diameter of the tire will effect the handling of the bike by raising or lowering the rear.

I am running a 140/70/18 on my kz1000 with a mild hopped up engine and have never had any issues with traction on the street

DoctoRot wrote: You only need as much tire as you need. Lol

What I mean by that is any additional mass in the tire will effect performance. A bigger tire not only has more rotational mass but it is also as far out from the axis of rotation as possible giving it more leverage. This makes the bike accelerate slower and stop slower, and because of the increased gyro, turn slower. A fatter tire also requires a steeper lean angle to turn when compared to a narrower tire. A tire that correctly matches your HP and application is best if you seek max performance. Otherwise slapping a fat tire on is purely aesthetics which is fine as well, but its important to understand the implications.
...........

So maybe the owner of the bike below made a little mistake?



Ed

Thank you for the thoughts "z1kzonly". You have a couple of cool looking Kaws in your attachments but I'm not with you on the rear fender .

I've had this bike for almost 30 years and have made cosmetic changes but was reluctant to get into the engine myself because I didn't want to find I was over my head. This year, 2020 however I started with the most thorough clean up I've ever done.
•New friction and steel clutch plates with new springs.
•New stainless cover bolts
•Powder coating everything I could remove, the tree, calipers, master cylinders, battery box, headlight mount etc.
•Braided brake lines, stainless banjos. Rebuild kits for the master cylinders and calipers.
•Wire wheeled and buffed every visible bolt and nut. If I could replace it with stainless I did.
•New wheel bearings, steering head received new bearings as well.
•Polished my aluminum fork tubes, rear sprocket and hub.
•New handlebar controls and ignition switch. Needed a fair amount of rewiring and tracking down automotive electrical connectors.
•All the 30 year old chrome came off and got cleaned and polished. Only close inspection gives away the age.
•Thought I was going to get a new Vance and Hines sidewinder but it turns out they no longer make them so this one got the old scrub down with vinegar and tinfoil. Came out so good I regret tossing out earlier ones.
•Sanded and painted the problem areas of the frame with Eastwood frame paint.
•Gasket kit to eliminate oil leaks (mostly successful)

At this point I have so much time, energy and money in my amatuar restoration I can't just repaint the engine with all the various oil leaks. The guy who previously did my engine work was busy and I didn't want to wait.

I bought a gasket kit and pulled the head and cylinders. Had the cylinder honed cleaned all the carbon from the piston domes and head. I did not polish but I wish I would have. Bought new rings for my Wiseco 1075cc pistons. Turns out Wiseco has older and newer 1075 pistons and mine are older 2835XA. The difference is in the oil ring size.

I went full OCD on this project and enjoyed every second. It took almost the whole riding season but I did finish with a couple weeks to spare. Definitely stepped out of the comfort zone but this site has a lot of helpful information and members, thanks for that.

I've always had a vision of this bike having spoked rims and it looks like I can make it happen. Thats why the question about rim sizes.

I think I'll be going with a 17/160. It looks like I can squeeze it in with minimal modifications. Maybe a slight tire offset.

I know one thing, I'm way too infatuated with this motorcycle.

I think 17” are a good choice, I’m putting together a parts cashe for a future build and found Ducati Gt1000 wheels that are 17”. Lots of tire choices. I like fat rubber on spoke rims. Here’s a quick mock up I did a few month ago.



Look at Vintage Connections for wiring needs.
vintageconnections.com

A good tool for seeing how the various sizes compare is Tire Size Calculator . I used this when I converted my cafe bike to an 18" wheel and wanted to get the front and rear as close to possible in size.