Gearing

[Czamora84]

Ok first timer on the site. I just hopped a predator 212cc.
Milled head to the max I think .65 or something. Flat top piston. Arc rod. Biggest cam they make. 32 mm intake valve. Tilley carb on methanol. Billet flywheel. Were riding on a dirt oval we made at our house about a 1/8 mile maybe smaller its a nice size track So the question I'm trying to ask here is what should I gear it to. I know it probly depends on the track conditions and tire setup and what not I'm just looking for the general. Like what size clutch sprocket I should run and what size drive sprocket. I have 11" tires by 6by 5 inch rim. Any help would be greatly appreciated.



"drive it like its stollen"

 

[OzFab]

The general "rule of thumb" is somewhere around 6:1. Any higher & you will lose torque, any lower & you'll lose top speed.

 

[Doc Sprocket]

Under the current circumstances, that ratio is probably not appropriate. Gotta wait for somebody like Anderkart with race experience to chime in. Be warned though- he might tell you it totally depends on your engine and the track.

 

[anderkart]

Gotta wait for somebody like Anderkart with race experience to chime in. Be warned though- he might tell you it totally depends on your engine and the track.

Yes, toystory is 100% correct; It does...

With an engine like this racing on a track, I'd definetly want a tach, and then gear the kart to max out at like 6500rpm (or whatever max-rpm you feel is safe & fastest) at the end of the straightaways.

Practicing on the track with someone using a stopwatch to record your lap times is a good way to help determine the best gear ratio too. Most kart racers (that win...) have several extra sets of different gears so they can perfectly gear their kart for that particular track and conditions. Those 'split' axle sprockets can be replaced in just a few minutes...

If I had to guess at your gear ratio: I'd prolly start out with a 12-tooth clutch/55-tooth axle sprocket (thats for use w/#35-pitch chain) Where your estimated top speed would be somewhere around 46mph at 6500rpm, with 11" rear tires.

You can calculate aprox. top speeds using other max-rpm's/gearing-combonations here at this link:
http://www.diygokarts.com/speed-calculator.html

PS:
Its really dificult (and dangerous) to be looking down at your tach when entering a corner at full speed. For this reason; you'll find that many racekart tachs will have a special feature where you can re-call the max-rpm reached on your previous ride...

But w/o an accurate tach, you'll pretty-much just be guessing at your gear ratio: So you'll either be giving away potential acceleration-ability (by gearing to low) or possibly blowing up your engines from over-revving.

If you want to get some really good info about what RPM you should be revving your engine, I'd suggest you research, and/or post that question at this kart racing forum: http://karting.4cycle.com/forumdisplay.php?f=120

 

[Czamora84]

Hey thanks allot everyone I really appreciate it. And Anderkart what you said is absolutely right and makes sense. I don't have a tach because they are too expensive even thought I already dumped a boat load of money in my engine it would make sense to buy a tach that way I don't blow it up.

I'm currently geared at 12 tooth front and 70 rear. On my track I noticed at the end of the straight away my engine is screaming and going Into the turn by the time I'm out the engine has calmed down a bit and then into the straight away it peeked out right into the next turn. What I think is also saving me is I have a max torque clutch and it engages faster so It doesn't let my engine stay at high rpms maybe I'm wrong idk.

We just raced this past Sunday. First time trying the motor with the tilly and big valves on methanol. What a blast it was

 

[mysteryboy28]

"drive it like its stollen"

A Stollen is a fruit cake containing dried fruit and covered with sugar, powdered sugar or icing sugar. The cake is usually made with chopped candied fruit and/or dried fruit, nuts and spices. Stollen is a traditional German cake, usually eaten during the Christmas season, when called Weihnachtsstollen or Christstollen.

-Wikipedia

i think you meant STOLEN - unless you like to drive fruit cake. lol.

 

[Doc Sprocket]

Driving a herd of fruitcakes, huh? Where to? LOL