A gearing question

[Shmigy02]

Hello all,

I have a question about the correct gearing for you. I've just finished my first go kart build and the kart runs great, but I was hoping for a little more speed and acceleration.

I currently have a predator 212 that is ungoverned with a stage 1 kit installed. It also has a torque converter and the current gearing is 10t sprocket to a 60t sprocket. It also has 18 inch rear tires. With me in it, the kart weighs roughly 400 pounds, maybe more.

I do plan on using this kart for fun trips around the neighborhood and trail riding around my house. I also don't live in the flattest part of town, but the hills aren't big by any means. I find acceleration more fun than top speed, but don't want to have a ridiculously low top speed that is in the low 20s or so.

My question for you all is, what sprockets should I look into buying? I just bought a 48t sprocket for the axle but I'm thinking about canceling that order as I think it will not only destroy my acceleration but also my torque converter belt.

Any and all feedback is greatly appreciated.

 

[Mrmonk7663]

6” or 7” driven on the torque converter? Right now with a 6” driven you have a theoretical top speed of about 50mph assuming 5100rpms. With a 7” around 40. You definitely don’t want a 48 tooth sprocket. If anything, you want a 9 tooth sprocket on the torque converter which will give you better acceleration, less belt wear, and a theoretical speed of 44mph with a 6”, 35 with a 7”

The 48t will give you a 4.8 gear ratio which will destroy belts in conjunction with 18” tires.

 

[Shmigy02]

The diameter of the driven portion of the torque converter is 7 inches. Is that what you were asking for?

---------- Post added at 03:11 AM ---------- Previous post was at 02:55 AM ----------

Also, the jackshaft bore accepts 3/4 inch, but all 9t sprockets that i can find for sale is 5/8. I also do have a 8t sprocket already but it is 5/8 as well. I was thinking I could weld it onto a spare 12t sprocket that I'm not using and make use of it that way because the 12t sprocket is 3/4.

 

[Mrmonk7663]

So your torque converter jackshaft is the same diameter as your crank? 5/8 is the normal size for a 30 series torque converter jackshaft.

I believe 10t is the smallest size you can get in a 3/4 bore that fits 40/41 chain. I could be wrong but I didn’t see anything less than 10.

The other option is keeping your 10 and installing a 72 tooth axle sprocket. This would give you a lot more torque and acceleration and keep the belt happy.

 

[landuse]

Unfortunately I do not think you are going to be going any faster than what you are without destroying belts. Your tyres are too large to gear higher (like if you bought the 48T) I would agree with the others that you should get a 72T axle sprocket. You will lose top speed, but gain torque.

If you don't have the flattest ground, this would be the best way to go in my opinion

 

[Shmigy02]

This sounds the best idea in my opinion as well. The only problem is that almost all 72t sprockets that I can find are 35 chain, meanwhile i have a 420 chain that fits the 10t sprocket. Is there much of a difference between the teeth to warrant getting a 35 chain 10t sprocket and a new 35 chain or is it ok to run the 420 chain on a 35 chain sprocket?

---------- Post added at 04:24 AM ---------- Previous post was at 04:20 AM ----------

Yes the jackshaft is 5/8. It's not a normal looking torque converter setup either. Normally they come with the plate that positions the driven portion correctly but for the torque converter I have there is no plate to mount it to so instead it is mounted to the frame.

 

[Mrmonk7663]

We need pictures. If the jackshaft is 5/8 then there is no issue. But the 9t sprocket. The sprocket goes on the jackshaft. Not the crank Pulley. Clutches have the sprocket on the crankshaft. Something is getting lost in translation.

Azusa makes a 72 tooth sprocket for 420 chain.

 

[itsid]

Hm.. with a 7" driven the 6:1 chain isn't bad at all..

my conservative calc doesn't moan at all...
in fact it claims to have backup for additional 165 lbs of weight with that gearing.

KartInfo by kartcalc.net:

[FONT="Verdana"]
[B][U]KART[/U][/B]
[INDENT][I]RW diameter[/I]: [B] 45.72 cm | 18 in[/B]
[I]Total weight[/I]: [B] 181.44 kg | 400 lbs[/B]
[/INDENT]
[B][U]ENGINE[/U][/B]
[INDENT][I]Original HP[/I]: [B] 6.5[/B]
[I]Asummed HP[/I]: [B] ~7.25[/B]
[I]Torque[/I]: [B] 12.86 Nm | 9.48 ft lbf[/B]
[I]RPM[/I]: [B] 5500[/B]
[/INDENT]
[B][U]TRANSMISSION[/U][/B]
[INDENT][I]Final ratio[/I]: [B] 6:1[/B]
[I]TC type[/I]: [B]  series 30 7" driven[/B]
[I]Lowest ratio[/I]: [B] 18.78:1[/B]
[I]Highest ratio[/I]: [B] 6.72:1[/B]
[/INDENT]
[B][U]PERFORMANCE[/U][/B]
[INDENT][I]Max Wheel Torque[/I]: [B] 241.51 Nm | 178.13 ft lbf[/B]
[I]Min Wheel Torque[/I]: [B] 86.42 Nm | 63.74 ft lbf[/B]
[I]Acceleration[/I]: [B] 3.26 m/s² | 10.7 ft/s²[/B]
[I]Top Speed[/I]: [B] 70.53 km/h | 43.83 mph[/B]
[/INDENT]
[/FONT]

More torque will never cause a warning,
so bigger axle- or smaller tc sprockets will always work
(lower top speed quicker acceleration more grunt on hills etc..)

if you want to go faster than the ~44mph however
and use a smaller axle sprocket
the limit is about 52 Teeth (only 25 more lbs and the calculator moans about that gearing)

KartInfo by kartcalc.net:

[FONT="Verdana"]
[B][U]KART[/U][/B]
[INDENT][I]RW diameter[/I]: [B] 45.72 cm | 18 in[/B]
[I]Total weight[/I]: [B] 181.44 kg | 400 lbs[/B]
[/INDENT]
[B][U]ENGINE[/U][/B]
[INDENT][I]Original HP[/I]: [B] 6.5[/B]
[I]Asummed HP[/I]: [B] ~7.25[/B]
[I]Torque[/I]: [B] 12.86 Nm | 9.48 ft lbf[/B]
[I]RPM[/I]: [B] 5500[/B]
[/INDENT]
[B][U]TRANSMISSION[/U][/B]
[INDENT][I]Final ratio[/I]: [B] 5.2:1[/B]
[I]TC type[/I]: [B]  series 30 7" driven[/B]
[I]Lowest ratio[/I]: [B] 16.28:1[/B]
[I]Highest ratio[/I]: [B] 5.82:1[/B]
[/INDENT]
[B][U]PERFORMANCE[/U][/B]
[INDENT][I]Max Wheel Torque[/I]: [B] 209.36 Nm | 154.42 ft lbf[/B]
[I]Min Wheel Torque[/I]: [B] 74.85 Nm | 55.21 ft lbf[/B]
[I]Acceleration[/I]: [B] 2.82 m/s² | 9.25 ft/s²[/B]
[I]Top Speed[/I]: [B] 81.44 km/h | 50.61 mph[/B]
[/INDENT]
[/FONT]

Since I think a 35mph top speed not only makes a nice cruising speed but also offers
some noteworthy grunt on the roads..
I'd agree with the suggested numbers above..
well I'd say 75 teeth to be precise

KartInfo by kartcalc.net:

[FONT="Verdana"]
[B][U]KART[/U][/B]
[INDENT][I]RW diameter[/I]: [B] 45.72 cm | 18 in[/B]
[I]Total weight[/I]: [B] 181.44 kg | 400 lbs[/B]
[/INDENT]
[B][U]ENGINE[/U][/B]
[INDENT][I]Original HP[/I]: [B] 6.5[/B]
[I]Asummed HP[/I]: [B] ~7.25[/B]
[I]Torque[/I]: [B] 12.86 Nm | 9.48 ft lbf[/B]
[I]RPM[/I]: [B] 5500[/B]
[/INDENT]
[B][U]TRANSMISSION[/U][/B]
[INDENT][I]Final ratio[/I]: [B] 7.5:1[/B]
[I]TC type[/I]: [B]  series 30 7" driven[/B]
[I]Lowest ratio[/I]: [B] 23.48:1[/B]
[I]Highest ratio[/I]: [B] 8.4:1[/B]
[/INDENT]
[B][U]PERFORMANCE[/U][/B]
[INDENT][I]Max Wheel Torque[/I]: [B] 301.95 Nm | 222.71 ft lbf[/B]
[I]Min Wheel Torque[/I]: [B] 108.02 Nm | 79.67 ft lbf[/B]
[I]Acceleration[/I]: [B] 4.07 m/s² | 13.35 ft/s²[/B]
[I]Top Speed[/I]: [B] 56.43 km/h | 35.06 mph[/B]
[/INDENT]
[/FONT]

108Nm on the rear wheel for a 400 lbs kart ... is awesome
(oh and before you ask.. 485lbs more [yes a total of 885 lbs] can be carried with such gearing setup... not too shabby, is it? )

'sid