auto-x vs road race and sprint track setups?

[Ryan D Thompson]

I was wondering if any of you guys road race and auto-x your karts. If so do you have to make any special chassis or motor adjustments when changing between the two. I'd like to do some long track road racing and also auto-x. Also tire choices and any other info would be helpful.
Thanks
Ryan

[Pete Mottaz]

[Bob Monday]

I race with Great Lakes SKUSA as well as autocross. We always do 2 long tracks (Gingerman and Grattan this year) with remainder sprint tracks. There are a TON of differences between chassis and motor setup for long tracks vs. autocross/sprint. In brief:

Road Race
Need: no quick kart responses at high speed, torque to pull long gears.

Take out all ackerman by using the center holes in the steering shaft, both tie rods on one bolt. If you have inner and outer holes on the spindles, use the outer ones to slow steering. All this may require longer tie rods.

Take out all the caster you can. Keep all 4 wheels on the ground since no sharp corners. Permits drifting around large radius corners, not a lot of side bite.

No toe. No camber.

19 driver and whatever axle gear (22, 23) is required. A 19 is as large as you can put on the CR125 and with certain chains, will still bite into the case a bit. No significant damage, though, like holes that leak oil. In some cases, you can get adequate gearing with an 18 driver.

Probably a narrow front-end. 54.75" rear. (Above 55" is illegal.)

Lower the kart as much as you dare. Titanium on the bottom of the seat is a good idea.

Put caps on the valve stems. At about 90 mph, the cores will sling into the stems (straight-aways) and without caps, when you go into the corner you'll have no air. Tires come off and/or you'll not be turning much.

Motor:
"Large" pilot jet. It's the only lubrication the motor will get at the end of long straights, when it's red-hot and you drop throttle for several seconds. At a minimum, a "60". Expect to bog at the start and slip the clutch accordingly. Between gearing and rich at idle, there's no wheelspin! As for main jet, maybe increase one size over what you'd run at an autocross. You still need to make good power, and going way large is not going to do that.

Do "whatever" to get torque. Header spacers, changes in pipe or silencer. You will be lugging the motor a lot more than on a sprint track due to motor gearing and long straights.

Make sure your fuel pump is working well and your pulse line is as short as possible. Fuel starvation is not uncommon and will seize the motor at the worst possible time.

Stand the radiator up as much as possible to decrease wind resistance. Use a large faring if permitted. Use your hand/arm to block air to the radiator if there's a really long straight. It is possible to overcool the motor at 100mph+, and with the piston hot and cylinder cold, it seizes and can be ugly. Watch motor temps around the track (you have time for a change!).


Autocross:
Need quick response, lots of side-bite.
Never on the throttle for extended periods.
Pretty much the opposite of all the above, realizing that it is still possible to seize the motor with too lean on pilot. Much more forgiving, though.

Bob Monday