Gear question

[speedy_moe]

OK I have a question for all the gear heads out there. I am wanting to know what number of teeth on the engine sprocket and the axle sprocket? My kart is going to be about 100 pounds and the engine is going the be the HF 6.5. Any help on this would be great. Also any help on understanding the gearing would also be great.

Monte

 

[zenki86]

hey monte

here use this:
http://www.diygokarts.com/speed-calculator.html

depends on how fast you want to go? I'm not sure how much torque and RPMs that HF 6.5hp has but the faster you go, the slower your acceleration will be and vice versa.

example: my minimoto aircooled 39cc engine 5hp has 13,500rpms geared up on a 6 tooth pinion/60 tooth sprocket and a 10.5 wheel diameter, it goes top speed of 42mph on a long straight away (1.2 blocks/4.5 house distance @ 10 ratio). the take off is decent but nothing compared to feeling of some G's on a 5 tooth pinion at 35mph with the loss of some topend but gets to 35mph quicker (1 block distance @ 12 ratio). power to weight ratio also plays a roll in acceleration. my minimoto at 45lbs, me at 200lbs with full racing suit/helmet vs a kid thats light as a feather he'll get much better results on take off but get about the same top speed (give or take about .5 mph to 1mph).

I usually get several pinions and sprockets to play with to figure out what I'm happy with. its all in the process of "trial and error" but try to start off at a gear ratio of 3.21 (assuming this HF 6.5hp engine has about 3600rpm to 4500rpm?) still depends on how huge your wheels are?

 

[oscaryu1]

Try getting a 1:5 ratio. Like 12:50 (12 teeth on clutch, 60 on sprocket), or a 1:6 ratio.

People who want to go faster get lower ratios... I've heard of a 1:1 ratio...

 

[zenki86]

Try getting a 1:5 ratio. Like 12:50 (12 teeth on clutch, 60 on sprocket), or a 1:6 ratio.

People who want to go faster get lower ratios... I've heard of a 1:1 ratio...

1:1 ratio is basically direct drive! imagine launching a 5 speed manual car on 4th or 5th gear? you won't go anywhere without some serious push, just enough to get the thing barely moving, then slowly taking off to gain speed. getting great top end on go karts puts tons of strain on your engine and clutch/centrifugal clutch. plus you'd need a good stretch of area to run this bad boy! :arf:

ever seen the Bonneville salt flats runs in Utah, they hit some amazing top speeds but can't even do a stand still burn out on asphalt lol. check out this example launch with some serious gear ratio on first gear: http://youtube.com/watch?v=BTFNY4Vfm74 (notice how long 1st gear is held before shifting and the RPM drop when they let go.)

my opinion, I'd rather break "tire traction" then my engine, tranny or burnt clutch... (skeerrrrt...!)

 

[zenki86]

......Also any help on understanding the gearing would also be great......

here this might also help you, if you are a visual person.
"time for school boys and girls"

Gear and Wheels Part 1
http://youtube.com/watch?v=D_i3PJIYtuY

Gears and Wheels Part 2
http://youtube.com/watch?v=nYXCMs4a4BY

don't fall asleep like I did

 

[2or3wheels]

those videos have good info but arent that entertaining

 

[ironman]

ok im using 35 pitch chain on a h.f. 6.5 motor with a 12/60 setup on the mini cart it runs with me on it 195lbs. 27 mph. not super fast but will take any of my carts on take off it flies thats on a 11inch total wheel height. which is a 6 inch rim.with governor on.

 

[Jerryburger]

Are intending it for flat and mild hills? Are you looking to tear up & down the neighborhood? My kart (the lowrider) is geared to hit 38 mph @ 3600 rpm- great for flat stuff, ok acceleration, but not too great for starting out on hills, sand, etc. I'd recommend shooting for 30mph @ 3600 rpm as a goal. If you decide to yank the governor, that'd put you at 38mph @ 4500 rpm, which is considered pretty safe for those motors. The lowrider weighs about 90 lbs and I'm fat. 'nuf said!