200lb'er in 30mm kart? Some questions

Alex Granelli · Joined: 04 Aug 2006 Posts: 15

I am about 200lbs even and have a 2008 Intrepid Cruiser 30mm kart. It has a Tag leopard motor. The local track (Reno/ NNKC) is somewhat dusty. Should I be running this kart with or without the torsion bars (the kart has 3)? What type of air pressures in the tires? It seemed to be better at a slightly high pressure. 10psi was hard to keep the back from coming around.

Oscar Biondi · Posted: Sat Aug 25, 2012 5:42 pm Post subject:

Alex, here is some general chassis tuning info and when to use torsion bars:

http://www.lascommotorsport.co.nz/karting_technical/chassis_tuning.htm

You may need to narrow the front track.

Josh Buttafoco · Posted: Sat Aug 25, 2012 5:59 pm Post subject:

Pm sent... what tires are you running?

TJ Koyen · Joined: 03 Oct 2004 Posts: 1425

The main issue that comes with a bigger driver on a 30mm kart is that the inside rear picks up too violently with all the weight transfer, giving you almost immediate oversteer. It's hard to plant the outside tire effectively. Working to alleviate that through narrower front track widths, reducing caster etc. will help.
_________________
T.J. Koyen
OKTANE VISUAL - Custom Helmet Paint & Graphic Design
www.oktanevisual.com
www.facebook.com/oktanevisual
--------------------------
DB Motorsports
Exprit/Leopard

Alex Granelli · Joined: 04 Aug 2006 Posts: 15

Yea I believe that's what was happening. The rear would swing around without notice. The front tires are showing slightly excessive inside wear. I think it needs less camber or more castor

Mike Goebel · Posted: Sun Aug 26, 2012 5:02 am Post subject:

We have a magnum class here in SoCal (440lb) and a few of the drivers have tried the 30mm Tony and love them.

Mike G.
_________________
Closet KZ Lover!!!
mfg Technology Centre
So Cal’s #1 Non Profit Engine Builder

Oscar Biondi · Posted: Sun Aug 26, 2012 9:42 am Post subject:

Since your kart doesn't have camber/caster pills, try narrowing the front track first. Try to get the kart to pick up the inside rear a bit slower (i.e., smoother) to make it more controllable. I think negative camber helps slow down inside rear wheel lift too, so reducing neg camber may not help the handling in this case.

Alex Granelli · Joined: 04 Aug 2006 Posts: 15

Hey Oscar, do I just pull a spacer from each side on the front to narrow the track?

Trying the kart with all of the torsion bars, it felt like the tires just couldn't keep up with the grip demand. Does this seem correct? On a larger circuit with less tight turns, I could see the torsion bars making the kart a little smoother.

Oscar Biondi · Posted: Sun Aug 26, 2012 3:45 pm Post subject:

Yes, move one 5mm spacer to the outer side of the wheel on each side. Try no torsion bars and see how that feels. You may even want to loosen the rear third bearing.
Are you using the MG yellows or the Bridgestones? Those Bridgestones may be too old and have very little grip left. Tuning with old slippery tires is just going to be frustrating.

Alex Granelli · Joined: 04 Aug 2006 Posts: 15

Im on the last leg of the Bridgestones, I'll throw on the MG's tomorrow after I burn off the last of the bridgestones.

Mick Gabriel · Joined: 06 Jun 2008 Posts: 66

Typically with a heavy driver you would tend to use a stiffer front bar, if your tires are showing excessive inside wear your not able to use the front end correctly, inside wear also leads me to believe that the kart has a push/snap issue. Seat posistion is critical at your weight try to mount the seat as far below the frame rails as legal. Run rear width at 55 no rear bar no side bar increase castor until the front tire wear pattern is corrected.