80' Z50R with CT70 (tb88) engine -> which sprockets ?

Guys,

I need a hand here. Any ideas?

BR,
Adam

Is the rear a stock 37? I'd start out with a 16-17 in the front and adjust from there.

I'm just doing the same to my Z50R, although I'm only running 75cc.
Mine runs out of legs at about 30mph (hard to tell an accurate speed).
I'm running a 12 tooth front and am just changing the 37 tooth rear for a 31.
Gotta shorten the chain which is a PITA, should've played around with the front sprocket instead as Thomas suggests.

I'll let you know how I get on.

Just remembered this was posted a while ago on a UK forum.

Honda50.com Gear Ratio - Speed Calculator

Having run the calculator, my new 31 tooth rear isn't gonna make much difference to the top end.
Looks like a 16 tooth front is needed too.
I'll hold off chopping the chain!

Guys,

Is gearbox the same in CT70 and Z50? Can I use Honda50.com Gear Ratio - Speed Calculator as proper example?

Stock is 37T on rear but at this step I do not have one.
I will start with 16T on front. What you suggest to buy for rear?

Thnx,
Adam

16 over a 13 will make a HUGE difference.

-HFM

It does list CT70 gearboxes on the calculator, both 3 speed semi & 4 speed.
I'd take the readings with a pinch of salt, but it is a good indicator to show if your'e heading in the right direction.

Thanks for advice!
I will try with 16T and 37T.

How about a spark plug? Should I use CR7HS or a different one?
Maybe NGK CR7HIX is a better idea?

Red Dwarf said:

It does list CT70 gearboxes on the calculator, both 3 speed semi & 4 speed.
I'd take the readings with a pinch of salt, but it is a good indicator to show if your'e heading in the right direction.

Click to expand...

Correct. I developed the calculator. It generates mechanical speeds if you have enough horsepower to pull the given speeds, but is dead on accurate in regards to engine rpms at each given speed.

However, if the rider is 300lbs, and is running a stock 50cc engine, you won't be able to pull 75mph even if you are geared for 75mph.

Here's my rule of thumb.

88cc with race head, good exhaust, 20mm carb and all the goodies will net you 50-55mph if properly geared on 10" wheels.
108cc's with all the fixins will net you 60-65mph if properly geared
117cc's with all the fixins will net you 65 mph if properly geared

The gear ratio calculator keeps people honest on what sprockets they should run, not what speeds they will actually reach as there are too many unknown variables.

On that combo I would think 16/30 would get you pretty close. Should be a good mix of acceleration and top speed.

Carlo

I'll be trying 16-31 as son as the new sprocket arrives, no mail here at the weekends!

Z, well done for making the calculator. Funny that a guy from over the pond posts it back to you!

Flip the plate over??

It is symmetrical - it won't help...

Dunno what you got there mate. I bought a 420 one for a Stomp pitbike & it fitted fine.

Just had a blast with the 16-31 set up and it's great! Much more range in each gear and a top speed around 45 ish.

Our speed limit is only 35mph on open roads and 25 in town so I'll have to be careful!

Had to brake so hard for a junction I was reminded I need to do a fork bush job as the front wheel was rubbing the skidplate!

karasman said:

Ok, there is a hope
I had fixing plate for Z50J, part #23802-045-670 – now I will try with #23802-040-000. It should arrive tommorow
View attachment 94969

Click to expand...

That should sort it mate. After all, it only has to line up with the holes on the sprocket.
Takes me a month to get stuff from CMSNL though!

I run a 16 on the front and a 37 on the back on my z50 hardtail. The motor is the original z50 that I've converted to a high compression 75cc with cam and 19mm carb, but stock exhaust. With this combination I max out at 46mph on 8 inch wheels. I weigh 180lbs.