Suggestions on rear gears By rcq92130 (Read 812 times)

[rcq92130]

Am just about to do an engine makeover on my little retro scooter and will no doubt need to re-gear.  Suggestions needed.

Old engine:  150cc GY6 with a 60mm BBK, free flow top & bottom, 30mm carb, decent variator.  10" wheels, scooter is about 225 pounds and I'm 175.  Takeoff was very good; top end pooped out at 60 to 65 (have a barn-door windshield).

New engine:  190cc Taida "B" block, 63mm piston, +3mm stroker.

Probably should have re-geared before, but will definitely need to now.  Again - this is a short block with 10" wheels.

Suggestions as to good gear ratio to try?

[Alleyoop]

First off welcome RC, good to have you on the forum. I have been reading your HOTROD BUILD that Dan is doing for you with nothing but TOP NOTCH PARTS. Well with that build you will have a lot of low end torque like I have mine is 182cc 62mm with a 2.2 stroker and it pulls my 16/37 gears just fine and my trike is 350lbs and I am 180lbs. I have 18/36 gear setup that I have not put in yet the trike runs so good I haven't bothered slapping them in.

Here is what the difference on the gears from OEM 13/40 to 18/36: I don't have a comparison of the ones in my tranny the 16/37 but here is a picture of them in my tranny:

[rcq92130]

Hi Mr. Oop!

So going from OEM to 18/36 would be changing from 3.08-1 to a 2-1 ratio ..... is that right?  And your 16/37 is 2.31 ... right?

I was not unhappy with off-the-line performance before with the small engine - I suppose because of the steep gear ratio.  But I'm not looking for more there ..... hope to have better high speed hill climbing and top end.

Would you recommend 16 or 18?

EDIT

Now I'm REALLY confused.  I get there is probably a "best guess best rear ratio" for the bike, engine and me.  But in scanning the available gear sets it seems there is a lot of overlap in what ratio you can achieve (eg:  14/37, 16/42 and 18/48 all result in about the same ratio).  Is there an advantage with going with a smaller (or larger) counter shaft gear???

[Alleyoop]

I cannot say one way or the other but the counter shaft gear is the one that is turned by the BELL so If SMALLER it would have to spin faster to turn the Final Drive gear more times which then turns your wheel.
So I see it as SMALLER Requires more RPMS and BIGGER less RPMS maybe that is why I can do 50mph at 5100-5200 rpms and 60mph at 6100-6200 rpms. While before stock it would do 50mph at around 8200 rpms.
So I like it cause it is easy on the motor and the motor is not screaming. I hardly every get the rpms over 7000 rpms once in a while I will crank her up to around 7300 rpms but that is to fast I think for the trike and scary to boot(HAHA).
Alleyoop

[jaxrhapsody]

Sept 21, 2015 19:35:00 GMT -6 Alleyoop said:

I cannot say one way or the other but the counter shaft gear is the one that is turned by the BELL so If SMALLER it would have to spin faster to turn the Final Drive gear more times which then turns your wheel.
So I see it as SMALLER Requires more RPMS and BIGGER less RPMS maybe that is why I can do 50mph at 5100-5200 rpms and 60mph at 6100-6200 rpms. While before stock it would do 50mph at around 8200 rpms.
So I like it cause it is easy on the motor and the motor is not screaming. I hardly every get the rpms over 7000 rpms once in a while I will crank her up to around 7300 rpms but that is to fast I think for the trike and scary to boot(HAHA).
Alleyoop

So the belt pulley is connected to the smaller gear, which spins the larger gear, and I guess turns the reduction gear? Can you change the reduction gear size?

[jaxrhapsody]

Sept 21, 2015 16:29:58 GMT -6 rcq92130 said:

Hi Mr. Oop!

So going from OEM to 18/36 would be changing from 3.08-1 to a 2-1 ratio ..... is that right?  And your 16/37 is 2.31 ... right?

I was not unhappy with off-the-line performance before with the small engine - I suppose because of the steep gear ratio.  But I'm not looking for more there ..... hope to have better high speed hill climbing and top end.

Would you recommend 16 or 18?

EDIT

Now I'm REALLY confused.  I get there is probably a "best guess best rear ratio" for the bike, engine and me.  But in scanning the available gear sets it seems there is a lot of overlap in what ratio you can achieve (eg:  14/37, 16/42 and 18/48 all result in about the same ratio).  Is there an advantage with going with a smaller (or larger) counter shaft gear???

From what I can see is the smaller gear is like the pinion gear, and the larger gear is like the ring gear if we were looking at a shaft driven car type axle, but if you kinda apply a little bicycle dynamics, the smaller gear is like the crank that you pedal. Don't worry about what is available, persay. It's not that cut and dry, you can get a few, and mix and match gears to your liking, say a 16/48.

[Alleyoop]

Yes you can mix and match to your liking. But keep this in mind you also have to have the power to pull the taller gears. If your power is low forget about taller gears it will be a dog.

Regarding the reduction Gear they do have different size ones BUT then that would also require the Clutch Shaft to be replaced to match the different size Reduction Gear.
Alleyoop