How fast do you want to go?

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Functional Artist

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There are (3) main variables to figuring out how fast a (given) motor will propel your kart :thumbsup:

1.) Motor RPM's

2.) Gear Ratio

3.) Tire Circumference


By inputting your

...motor RPM's

...gear ratio

...& your tire circumference

in to this equation, you can figure out what your, potential, MPH would/could be :wai:


MS/GR=ASxTC=IM/FT=FMxHR=FHxMM= MPH


Motor Speed/Gear Ratio=Axle Speed x Tire Circumference = Inches per Minute traveled/Foot(12) = Feet per Minute traveled x Hour(60) = Feet per Hour traveled x MPH Multiplier(.000189) = Miles Per Hour


* Using e-Lemon-aid, as an example

...@ 24V (2,500 rated RPM's)

...an 8:1 gear ratio

...& tires with ~32" circumference



2,500/8 = 312.50

312.50x32" = 10,000.00"

10,000.00"/12 = 833.33

833.33x60 = 49,999.80

49,999.80x.000189 = 9.45 MPH :cheers2:


Motor speed is (2,500 rpm's) divided by the gear ratio (8) = axle speed (312.50)

Axle speed (312.50) times the wheel circumference (32") = inches per minute traveled (10,000.00")

Inches per minute traveled (10,000.00") divided by inches in a foot (12") = Feet per minute traveled (833.33)

Feet per minute traveled (833.33) times minutes in an hour (60) = feet per hour traveled (49,999.80)

Feet per hour traveled times miles per hour multiplier (.000189) = 9.45 MPH :2guns:

.
 

anickode

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So if I put a predator 212 with a centrifugal clutch and no governor on my kart with 18" tires and a 3:1 gear ratio, I can go 90mph? Sweet. :smiley_omg::lolgoku::roflol:
 

Functional Artist

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So if I put a predator 212 with a centrifugal clutch and no governor on my kart with 18" tires and a 3:1 gear ratio, I can go 90mph? Sweet. :smiley_omg::lolgoku::roflol:

Ya, maybe :thumbsup:

...if ya

...skip the clutch

...& go direct drive

...put the kart on jack stands

...get in (& hold on)

...have some one pull start 'er

...& knock it off the jack stands

...@ full throttle

Yup! 90 MPH :2guns:
 

itsid

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Ya, maybe :thumbsup:

...if ya

...skip the clutch

...& go direct drive

...put the kart on jack stands

...get in (& hold on)

...have some one pull start 'er

...& knock it off the jack stands

...@ full throttle

Yup! 90 MPH :2guns:

NOPE!
not even then!

One side-question if you allow since it makes your posts tough to read for me..
why the excessive use of blank lines?

Anywhoo, 90mph you cannot reach (not even 60mph) with a stock predator;
and it's not the rotational speed limiting you, it's wind resistance and road friction stopping you.
in a vacuum... maybe [if you manage to still provide the engine with enough air of course] but no...
the predator does not have the power to go 60mph (you'll need 12hp or more to do so)
much less 90 (which requires about 28kW of power or 38hp)
and thats for just a 150kg kart/driver package

'sid
 

Functional Artist

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NOPE!
not even then!

One side-question if you allow since it makes your posts tough to read for me..
why the excessive use of blank lines?

Anywhoo, 90mph you cannot reach (not even 60mph) with a stock predator;
and it's not the rotational speed limiting you, it's wind resistance and road friction stopping you.
in a vacuum... maybe [if you manage to still provide the engine with enough air of course] but no...
the predator does not have the power to go 60mph (you'll need 12hp or more to do so)
much less 90 (which requires about 28kW of power or 38hp)
and thats for just a 150kg kart/driver package

'sid


Your totally right! :thumbsup:
I was bein' sarcastic :cornut:
I am NOT a small engine expert but, I believe that a Predator + 3:1 gear ratio + 18" tires = Burned Clutch :ack2:
That's why I suggested to "skip the clutch"
But, direct drive & an abrupt start like "knockin' it off the jack stands" @ "full throttle" would cause it to pop a h3ll of a wheelie or more likely, break something :ack2:
But, if physics DIDN'T get in the way
A predator @ 3,500 RPM's & a 3:1 gear ratio & 18" (~80" circumference) tires would do the magical 88 MPH
3,500/3 = 1,166.67
1,166.67 x 80" = 93,333.60
93,333.60/12 = 7,777.80
7,777.80 x 60 = 466,668.00
466,668.00 x .000189 = 88.20 :2guns:
*I am not a fan of the "wall of text", it makes it tough for me to read & I use the spaces or sometimes double spaces & triple spaces to separate important stuff or to help separate one step or idea, from another. I think it helps clarify things :cheers2:



What do you think of the "simple" equation?

I know it doesn't "take into account"

...the total weight (kart & driver)

...the rolling resistance (2 wheel or 4 wheels, wide tires or narrow, aggressive tread or smooth)

...the terrain (pavement or grass)

...or even the incline


Your equations cover that stuff in detail in the "Electric go kart motors.. the essence thread :cool:

http://www.diygokarts.com/vb/showthread.php?t=25218


But, this one should "simply" help put 'em in the "Ball Park" :wai:


See, isn't that better/clearer :lolgoku:
 

tinamcjittles

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How low would you have to get wind resistance to go 60 on a stock predator (6.5hp)? Those Maybachs have tapered trunks so that the turbulent vacuum doesn't happen at the rear to slow it down, most people just increase horsepower (because honestly its flippn' fun) but if you could make a 160HP Honda Accord go 180MPH wouldn't it be awesome??

Edit: Here just found this... my car has >100HP lost to drag alone! Time to get fiberglassing...
 

anickode

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How low would you have to get wind resistance to go 60 on a stock predator (6.5hp)? Those Maybachs have tapered trunks so that the turbulent vacuum doesn't happen at the rear to slow it down, most people just increase horsepower (because honestly its flippn' fun) but if you could make a 160HP Honda Accord go 180MPH wouldn't it be awesome?

Edit: Here just found this... my car has >100HP lost to drag alone! Time to get fiberglassing...

That's why racing karts have some basic aero and the drivers practically lay down.

That, and they aren't running stock predators.

I don't think it can reasonably be done. Air resistance isn't the only factor. Mechanical inefficiencies and rolling resistance also play a huge role. My little 6hp Briggs kart can hit 40 on flat pavement with the tires at 30psi. At 15 psi, it comes in about 6mph slower.
 

bob58o

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I’m waiting for Denny to give us the top speed of the MB200-2.
I’m fairly confident those are geared to do about 60mph at 3600 RPM with a 196cc engine and TC.

59mph if you assume 10T TC sprocket and 6” Driven Pulley.
Either it never shifts into high gear, or RPMs stay low, but I bet 50mph is possible with that set up.
 
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