Reason kart slower than calculator estimate?

[pdude86]

Been lurking and using this great site for a couple months, and just registered.

Finally got all mechanical stuff resolved and just trying to figure out why my go kart has a slower top speed than its estimated to max out on with the calculator.

Engine: 5hp Briggs
Tires: 13"
Sprocket: 60 tooth
Drive: 12 tooth - from the output shaft it goes to clutch, then a belt to an extension which runs to the 12 tooth gear I'm referring to that has the chain on it, as well as the sprocket (in case this matters).

Confirmed tiny tach rpm of 3680rpms max and gps verified 14.8mph. Calculator says 28mph at 3600rpm. Why the large discrepancy?

I weigh about 160lbs, but figure that's irrelevant since it is reaching the correct governed max rpm.

Thanks.

 

[ML-TOYS]

On your shaft that has the belt. Are both pulleys the same size ?

Post pics of drivetrain

 

[pdude86]

No they are not, and now that I look at it, I can see why my ratio may not be what I was putting into the calculator now. Here is the picture:

 

[sideways]

Well there's your problem. You've got roughly a 2:1 reduction with those pulleys, hence you're only going half the expected speed.

Replace the larger pulley with one the same size as the one on the clutch and your issue will be fixed.

 

[rocketkart]

i think i have the same gokart as you same set up and all my kart will do about 28mph the problem i had was the belt was sliping i had to losin up the engine and push it forward and frome that i went from about 16 mph to 28mph

 

[OzFab]

That could be a problem but, in this case, it's not the problem. The main issue here is the compound gearing as explained by sideways

 

[itsid]

I'm with sideways here.. you changed the overall gear ratio with your pulleys...
BUT I don't think you will be able to replace it with a 1:1 pulley setup, with a
gear ratio of 1:5 and 13" tires you will not get the 5HP kart going very fast (or very good)
I would even think you will only burn through clutches alot.

'sid

 

[landuse]

I'm with sideways here.. you changed the overall gear ratio with your pulleys...
BUT I don't think you will be able to replace it with a 1:1 pulley setup, with a
gear ratio of 1:5 and 13" tires you will not get the 5HP kart going very fast (or very good)
I would even think you will only burn through clutches alot.

'sid

I agree. The calculator also only gives you the THEORETICAL speed you might reach. There are many factors that would affect it. 5:1 might give you a great speed on the calculator, but you might be geared too high to even reach that

 

[BigThieme]

The other thing is it probaly doesn't calculate the wheight in the equation. Really 160 plus your frame you are losing some speed trying to hall all the wait. And you didn't fracture in the torque converter.

 

[BigThieme]

Really if you want lots of torque and speed use a lawn mower shifter box. That's what I'm doing. You can use vertical or horizontal engine and have a 8 inch pulley to a 3 or 3 1/2. And if the transmission has a sprocket, use a 12 to 60

 

[landuse]

And you didn't fracture in the torque converter.

That is not a TC. All it is is a pulley centrifugal clutch going to another pulley.

 

[BigThieme]

Well ok but he didn't fracture it in

 

[landuse]

Well ok but he didn't fracture it in

No, he didn't factor it in. You are correct