Planet Minis

EddieNewYork

Hey guys, what would be a good sprocket combo for a tb108 w/ahp 4 speed for the street? Something that can hit 70mph without losing too much bottom end. Not sure it that's possible with this motor, but what are your thoughts. Please share.... thanks.

Note: It's going into my monkey (110/80/10 on 3.5 rims) and I weigh about 110lbs.

And, anyone know what these motors rev too (max)?

cdoublejj

think they have higher rpms than the big blocks. Oh i hope i didn't piss you off

fatcaaat

I am going to run this same motor with a VM26 carb on a set of 120/90-10 tires on a ct70...and I weigh 185. I plan on gearing it 17/35 or 15/31....

This should rev out nicely to about 11k but after that, you may have clutch failure. I'd plan on cruising in the 7k range.

RySem

How bout with a Tak Special Clutch?

shift26

I'd be curious to know the same thing... oh, but does anyone make sprockets or know where i can get one? I'll be running a XR/CRF rear wheel with 10" street tires. Also, I think my countershaft sprocket is a 428 width and I think Honda's use 420. Should I go 420 or 428? I have a 34T rear on my XR with an 88 kit... I was thinking of doing a 30T 50stunt rear sprocket, then replacing the countershaft sprocket on the 110 for a Honda one... new 420 chain. any thoughts?

Z

Eddie,

A 108cc won't go 70mph. You'll need to revisit your expectations unless the course you plan on running 70mph is down a very large hill.

People claim a out of the box TB 108 will go 70, but I have yet to see one that actually does on 10" tires.

My Kitaco non SE 108 with all the correct supporting parts hits 65-67mph depending on the day with a 16T 31 and a 130/70 on the rear.

I'd personally run a 16T front and 31T rear or somewhere close to this give or take a size or two in the rear. At 10,500 rpms, that will give you 70mph if you have enough HP to get there.

Honda50.com Gear Ratio - Speed Calculator

cdoublejj

Whats Primary Reduction Gear Ratio?

Z

Valid question. The Big gear (Primary) behind the clutch divided by the small gear attached to the clutch.

67 Primary Gear / 18 clutch gear = 3.722

cdoublejj

Some one said that calculator is rocket science i must say i disagree i couldn't use it with out a couple hours of study.

EddieNewYork

Thanks fatcaaat. When do you plan on getting your motor running? And, how much do you figure your CT70 will weigh when it's all said and done?

EddieNewYork

I see... that's okay. Thanks for the sprocket recommendations. Btw, I tried using the calc but I couldn't get past the Secondary Reduction Gear Ratio. How do we get this number?

RySem

This stuff is automatically filled in when you select your clutch and gearbox type from the first few drop-downs. All you need to do is select the things in the first 6 drop-downs and click calculate.

Z

This stuff is prepopulated.

The secondary reduction ratio is your rear sprocket divided by your front sprocket.

Use the drop down menus. The only thing you have to calculate if you are running a Honda engine is a tire size if I don't have your size on the list. You can use the tire "manual Calculation" button if the tire size isn't listed.

Ignore the "Tire revision" box.

This isn't rocket science folks.

EddieNewYork

Sorry Dan, I'm must be stupid or something. I put in...

Primary Reduction Gear Ratio: 3.722
Secondary 37/15 = 2.46
1 - 3.182
2 - 1.706
3 - 1.238
4 - 0.917
Major Diameter: 430
Circumference: 1289 but it changes it to 1351?

And I get 598mph at 10k in 4th gear, lol!

EddieNewYork

I'm using the TB clutch with AHP 4 speed, 15/37 gearing, and 110/80/10 tires.

RySem

1351 is what the circumference is with a major diameter of 430.
Circumference = pi x diameter = 430 x 3.14159 = 1351

EddieNewYork

I see, thank you.

cdoublejj

they don't have generic china 4 spd gearbox selection butany i'll just have to expiriment might try 17/30

Z

That's because we don't support anything chinese related and have zero interest in it. You'll have to manually enter those numbers if you are fortunate enough to own a chinese powerplant. Not our cuppa.

EddieNewYork

I re-entered the numbers and it worked this time.

Here's what I got with 16/31.

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