Grass Shifter/Karting?

I seem to be having a hard time finding much info about using shifter karts as backyard or grass kart racing. Seems like i remember a website years ago by the name of grasspass.org, Im guessing thats now be reallocated to the recreational marijuana businesses. Anyways, Ive mostly just been wondering if theres much modification involved to using the shifter karts to yard duty? I assume tires, but wasnt sure if there was any suspension changes?

Id appreciate any websites or anything related to this as apparently I suck at Googling.

My twins are 3 months old so Im rapidly running out of time to get them prepared for Formula 1.

thanks

Nick

Like, real 125cc two stroke 30+ hp shifter karts? On grass? Not that it wouldn't be possible, but why? I dislocated a rib driving a slightly slower kart on pavement, I can't believe that driving one across a bumpy yard would be anything other that terrifying pain. 

In reply to mazdeuce - Seth :

basically because i have a large backyard and cutting a dirt/grass track into it would be insanely cheaper than pouring a concrete track. But thats why Im asking if the karts Ive seen on grass/dirt are actually shifter karts, or if theyve been modified to run on dirt.

I think this might be what you are looking for: http://www.grasspass.com/

The dirt/yard carts are cvt belts & not performance oriented.  They're great for kids- easy to drive, big balloon tires. A more popular choice for our kids were little atvs, then bigger atv's. As far as I know kid oriented shifter dirt carts don't exist because they are just way to fast & you'd have little Ricky & Ronnie launching through the fence & into the woods.

pirate said:

I think this might be what you are looking for: http://www.grasspass.com/

Yea, those are all 8-ish hp Briggs or Briggs clone engines. That sort of stuff is perfect for the backyard. You "can" run a proper kart chassis, but like suggested, baloon tires have a lot more give and make for a better experience overall. 

In reply to mdshaw :

I personally recommend bikes. Start with balance bikes, and from there the Stacyc electric bikes are the new hotness. You can throw them in the trunk of a car and take them anywhere. Learn to ride one of those when you're 4 and everything will be easy. 

They do some dirt road racing in karts in Australia (bc of course they would). Just a race track with left and right turn cut into dirt. I've thought about the land requirements to build one for myself. Just take a bobcat and build a racetrack for the cost of equipment. I can't see running shifters on it, though. Most of the high level kart races are in single speed karts these days.

I can't imagine driving my old Honda RS125cc powered Birel shifter kart on grass! It made 40+hp would go 120mph and was simply the most intense thing I've ever driven. Things happen so fast it's indescribable unless you've done it. That said, if I was younger, I would try it but don't know that it would be much fun. I think between spinning the tires, shifting every second, constant counter steering and the rough ride that the rigid chassis would transmit thru your body, other types of suspension karts would be a better choice. 
 

Now, transplanting that motor in a kart with suspension would be tons of fun. 

You would definitely want the flexiest chassis made.