Christa Kojima in her Top Kart Cadet kart

Christa's first Racer

By Mike Kojima

What does a 9 year old girl want, a pony? An all-you-can-carry gift certificate from Hello Kitty?  No, apparently she likes carbon fiber.  OOOH! Carbon fiber!  My daughter Christa squealed when she saw the Noonan Racing foot box that I got so she could reach the pedals on her Top Kart, racing go kart.

Christa Kojima's Top Kart
Christa's Top Kart Chassis is a 2006 so its technology is nearly the same as the late model Top Karts.  The chassis was completely redesigned and rehomologated by the FIA in 2006.  Every chassis used in WKA and IKA competition must carry an FIA certification for rules compliance and safety.  Most local sanctioning bodies require a current certification so be sure that what you buy used is still eligible for racing!
Top Kart Cadet model
A Cadet class kart is no kids toy, it is capable of pulling over 2 g's in a corner and speeds of over 60 mph.  It is quite a sophisticated racing machine, that bristles with engineering alloys and billet parts.  It has more in common with a formula car than a sedan. Let us take you on a tour of what makes it tick.
Christa Kojima's Top Kart
The kart's backbone is a seemingly simple tube frame made of tig welded 28mm chrome moly tubing, however there is much more than meets the eye.  Since the kart has a live axle with no differential, it is critical that the inside rear wheel lifts to different degrees in cornering.  Too little lift and the kart understeers and the bind wastes power on corner exit.  Too much lift and the kart oversteers and can't put power down out of turns.  The frame must flex in a controlled way to tune the lift.  Since the kart has no suspension, the chassis flex also helps the tires find traction.  The tube diameter, bends , layout and wall thickness are all carefully engineered to give controlled flex.  The search for optimization of the chassis is continuous and many manufactures come out with new chassis variants every year to chase the state of art.
Christa Kojima's racing Top Kart
This ugly plastic bumper messes up the lines of the kart but it is required for racing in 2010 in some local races.  It is FIA tested and certified.  Its job is to prevent wheel to wheel contact which can cause flipping and to absorb impact.

Christa had been tearing it up on track days at California Speedway in her Emmick kids Kart inherited from Ground Control's Jay Morris's kid's when they outgrew it.  Christa wanted to start racing and we found that she was too old to race Kids Class and she would need a new Cadet class kart to be able to run.

Top Kart Side Pod
The side pods and nerf bar do several things.  These parts must be tested and certified by the FIA for impact absorption and to help reduce the chances of tires touching which can cause a bad accident.  They also help aerodynamics and the nerf bars are part of the system to tune chassis flex.  On the Top Kart Cadet chassis, they are designed to be fully floating and not affect the chassis stiffness, probably because cadet drivers are lighter and the chassis needs more flex.  You can see the articulated joint to keep the bar free floating.
Top Kart nose section
The front bumper is also certified for impact absorption and anti wheel touching.  It also helps aerodynamics.  It's support bar is an adjustable torsion bar who's mounts are adjustable.  When the bar is tight, it stiffens the front end helping traction on a slippery track.  On tracks that have good grip, it can be loosened to help reduce weight transfer.  The wide washers on the mounts help with tuning from full loose to full stiff by adding variable friction.

A real racing kart is not a lawnmower engine powered kids toy but a serious and sophisticated racing machine with a lot of technology and a development history that goes way back to the late 50's when the kart was first invented.  Although in most classes the engine is a spec engine with closely controlled and inspected internals, the chassis is highly adjustable and the art of kart chassis tuning very critical for being competitive.

Tillet Seat
Most of the mods we did were to fit Christa's small frame in the Cadet kart that was probably designed to fit tweens to teenagers.  We changed the stock seat to this smaller Tillet seat.  On a kart, the seat is actually a tunable item that is part of the chassis.  This Tillet is medium stiffness and we installed it with slippery plastic washers and slightly loose bolts so it would have minimal affect on the chassis stiffness.  Some people set the seat in the chassis stiffly and add extra stays to stiffen the chassis more.  We opted for a padded seat to take up room in the seat and to get Christa higher in the kart so she could see.  For light drivers a higher CG  helps the kart find traction.  Kart chassis set-up is about opposite as a cars so throw away what you know when setting up a kart.
Noonan Racing pedal box
Carbon fiber and CNC machined billet aluminum makes a little girl raised in a racing household drool.  Although a little expensive, the Noonan racing pedal box is a lifesaver when fitting a small driver in a large chassis.  The pedal box is just like one found in real race cars.  It gives more flexibility to place the pedals closer and gets the driver's legs above the tie rods.  There is no way Christa could even come close to fitting in the kart without it.  The price is still cheaper than our time if we were to fabricate something ourselves and it is so pretty.

A bit of research led us to the Top Kart brand.  Made in Italy, Top Karts seemed to be a Kart with a winning trend in Cadet class.  There were also several Top Kart dealers in our area with a large inventory of parts and good service which is important for racing.  A Cadet kart is a medium size kart with a track width of less than 50" that bridges the gap between adult karts and kids karts.  Chassis choice is critical in kart racing with a good fairly current chassis needed to be competitive as kart development is always progressing.

Christa Kojima Kids Kart
Although Christa fits in her Emmick Kids Kart perfectly, she has to move up to the much larger Cadet Class due to her age.


Christa Kojima's Top Kart

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Monday, February 15, 2010 7:57 PM
I remember reading in the Forum section that you're going to need to add around 80lbs of weight to the seat because she's so light relative to the competition... If that's the case would you be better off mounting the seat more rigidly so that the weight doesn't shift around or are you still better off with some slip in the seat?
Monday, February 15, 2010 8:11 PM
That,s so cool!
Mike Kojima
Mike Kojimalink
Monday, February 15, 2010 10:20 PM
I don't know yet, have to test.
Tuesday, February 16, 2010 2:47 AM
Go Karts are a ton of fun. I work at the local public kart track and even though those karts are fairly slow (they top out around 40 or so), they are a blast to drive. They're also incredibly easy to work on, so she could easily do all the work herself (it takes about an hour to disassemble one of our karts and about two hours to rebuild it. Motor rebuilds are about 2 hours).
Tuesday, February 16, 2010 6:04 AM
Karting is too much fun! Ive been trying to find a decent used kart for awhile, but selection is pretty thin were Im from. Dirt track karts are plentiful though, as well as tracks, so ive been thinking about getting into that...

How much did you pay for this one before the rebuild?
Mari Umekubo
Mari Umekubolink
Tuesday, February 16, 2010 6:54 AM
Nice change of pace....Great article Mike!
Mike Kojima
Mike Kojimalink
Tuesday, February 16, 2010 7:29 AM
I paid $1500 which was a bargain considering that the engine alone normally goes for more than that.
Tuesday, February 16, 2010 2:33 PM
Such a nostalgia.....coming from Europe....I experienced the same thing.
At 7 I got my first kart, but 16 I had 7 karts laying around....best way to learn how to drive in my opinion.
Tuesday, February 16, 2010 7:13 PM
The safety wire doesn't surprise me. It's good practice to safety wire everything on track day motorcycles too. I guess it makes sense... a part flys off a kart of bike, it's flying straight into the person behind it. No car body to protect the driver/rider!
Tuesday, February 16, 2010 10:53 PM
Mike, I wish my parents were as cool as you! I had to make due with soccer and basketball. Have a blast!
Wednesday, February 17, 2010 2:08 AM
Nice write-up Mike. You mentioned how different the set-up theories are when compared to street cars. When tuning cars, it's all about working around the relatively fixed center of gravity, and on the karts, you're finely tuning the c/g to make the chassis handle.
Mike Kojima
Mike Kojimalink
Wednesday, February 17, 2010 7:30 AM
This is the Kart I wished I had when I was a kid. My dad bought me one when I was the same age as Christa. I wanted a Margay with twin Mac 101's but I got a no name kart with a Briggs and stratton lawnmower engine. Still that was a pretty extravagant thing for my Dad to get me back then as it cost $120 bucks or something. Our family had a black and white tv, an AM table radio, only one car and my mom didn't work (thats how American families used to be!).

That poor kart, it survived me grinding the head on the sidewalk to get the compression up ( could not afford the $10 high compression head!) and me gutting out the muffler with a big drill bit (boy did my dad get mad) and I drove the crap out of it until it had no compression and would not start anymore. Then my dad traded it for a new gate for our yard!

My dad helped me build a dirt oval with an infield road course in our 1/2 acre backyard and I used to drift all over the place. It was so fun. One kid brought his real Mac powered real racing kart over and I smoked him probably because I could out drive him.

My friend down the street's family owned a nursery and we would drive there because that place had real long straights where you could get probably 30 mph! I would push my kart 1/2 mile to their place sometimes. Then one day he crashed and wrecked a greenhouse. That was the end of that.

Christa doesn't know how lucky she is. I would have died to do what she gets to do!
Wednesday, February 17, 2010 11:13 AM
Bumpers may be ugly but I can def see it on a lightweight cart, wheel to wheel has some bad potential outcomes. I saw up close and personal my father's F Atlantic car launched airborne off wheel-to-wheel contact and flip full 360 (guy stuffed his front wheel into Dads, trying to close the door on a clean pass). Car landed wheels down but not before doing a full corkscrew-like turn in the air, slammed into the barriers on the outside of the corner (old Turn 9 at Portland OR). I was working behind the pit wall, and the entire thing happened in front of and toward me, I will never forget that.

That is so cool how the compensation works for the live axle, taking into consideration chassis, etc. Sure is different from the days I remember of B&S motors on simple chassis running NASCAR-like Ovals...awesome stuff Mike, def write more as you can find time, please.
Mike Kojima
Mike Kojimalink
Wednesday, February 17, 2010 11:19 AM
How much did the shunt cost your family? Atlantic parts are expensive! I made some mistakes on the adjustably part as I forgot a lot of other adjustments. Caster, camber, track width, ride height and corner weight are all highly adjustable on this kart. I re-edited.

The lack of diff makes everything pretty critical. A 1/4" change in track makes a big difference. Right now I am in the process of training Christa how to give feedback on the handling so I can tune the chassis.
Wednesday, February 17, 2010 3:50 PM
Wow, that is a deal Mike. I think my track paid like $5000 a piece for its Sodi Karts. And they aren't anywhere near that high tech.
Wednesday, February 17, 2010 8:35 PM
I was browsing the Tillett site and ran across their "seat forward" brackets. Maybe you could fab up something like them to help out with the size of the new kart?

Thursday, February 18, 2010 12:10 PM
So mike, what will be Christa's first car?
Mike Kojima
Mike Kojimalink
Thursday, February 18, 2010 1:08 PM
Her seat is pretty forward to where it is pretty close to the steering wheel support.

I dunno what her first car will be. She seems to like Top Fuelers. She told me Pro Stock is to slow and boring.
Thursday, February 18, 2010 1:46 PM
This is so cool. I'd love to grow up in a "racing household." =) Best of luck and I look forward to reading all the updates!!
Thursday, February 18, 2010 5:26 PM
Does anyone have one of those midevil people stretcher machines somewhere ? She might be able to fit the kart next week ?

Maybe some of those really tall platform go-go shoes ?

As serious as I get karting is heading to Dromo1.
Chris "Shaggy" Allenlink
Friday, February 19, 2010 5:24 PM
Ohhhhhhh No Mike... No you didn't..... How much is one of them to build??? I can put Mercedez in one.. We can get youth league going of all the kids
Sunday, February 21, 2010 7:42 AM
Very cool. Thanks for the write-up!
Christa, I am looking forward to hearing more about your carting as we move into spring and summer. Way to go!
Miles (San Antonio)
Miles (San Antonio)link
Friday, March 05, 2010 6:54 AM
Very glad to see she is following the family traditions. She is going to shatter a lot of young boy pride.

Great to see you are encouraging her. When my youngsters come around to it, I will be doing a similiar route for them if they so choose.
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