Grand Prix Chassis Seminar Part 1: Basic Set Up & Adjustment

[Music] hi i'm john copeland and we're back here at fox valley for another of our 2021 grand prix video seminars today we're going to take a closer look at the cart chassis and all the adjustments that are available to you and what they do but before we get into the cart chassis there's some terminology we need to get straight understeer is where the front end slides and doesn't want to turn in this is also referred to as push oversteer is when the front end of the cart grips and the rear end wants to slide out or come around this is also referred to as loops there will be points around each lap when the car may push and other times when it may be loose the key is to understand these natural transitions and how to use them to your advantage before you ever put the card on the track you need to make sure that the starting setup on the chassis is correct even though it hasn't been driven since the last grand prix it may have gone out of adjustment during the race or it may have been tweaked by car to cart contact here are some things to check to make sure you're at a good starting point first of all check to make sure all four tires are inflated to the same pressure it doesn't really matter what that pressure is as long as they're all the same for the purposes of setting things up this is the kingpin this is the bolt that the spindle swivels around start by measuring from the top of the kingpin to the axle on each side these dimensions need to be equal or the cart will be crabbed shorter on one side than the other if the dimensions aren't equal bring it in and we'll put it on the frame table and get it straight make sure you have the same number of spacers above and below the spindle this will affect steering response sometimes people use an unequal number of spacers from side to side to compensate for a frame that's twisted don't put a band-aid on a twisted frame fix it measure the height of the top of the kingpins on each side this is a good indicator of whether the frame is twisted or not this can have a big impact on how the cart behaves in left and right hand turns if the frame is twisted it's off to the frame table to be straightened use a tape measure to measure the circumference of all four tires the front should be approximately the same side to side and so should the rears in some types of racing they use stagger in which the outside tires have a larger circumference of the inside tires that helps the race car turn in one direction better than the other at the grand prix track you have to be able to turn both ways so stagger is of no advantage there are also spacers on the front wheels that let you move the hubs in and out to adjust the handling start out with the front wheels centered on the spindles with the same number of spacers or equally divided between the sides on the inside and the outside we'll talk about how this affects handling a little later you can also move the rear hubs in or out on the axle that has a huge effect on how the car handles in general you'll want to run the rear at almost the maximum width grand prix allows but to start with set the hubs so the overall width from the outside of the rear tire to the outside of the rear tire is two inches less than the 55 inch maximum allowed this will give you more grip early in practice when the track is cold and dirty and doesn't have any rubber built up on it then you can always make it wider as you need to and as the track changes set the distance from the wheel bearing to the rear hub equally on both sides camber is the angle the front tire sits relative to vertical most carts are designed to run best with between a half a degree and two degrees of negative camber that means that the tops of the tires lean in slightly towards the middle of the cart since the chassis flexes under load and that flex affects the camber always check camber with the cart on a solid surface and with the driver's weight in the cart caster is the angle that the kingpin leans back from vertical when viewed from the side most carts run between 12 and 8 degrees of caster the last baseline setting is toe in or toe out and these are just what the name suggests it's how the front tires are set relative to straight ahead when the steering wheel is centered each manufacturer has their own recommendations for toe in or toe out settings but they'll always be less than an eighth of an inch either way if you don't know what the recommended toe setting is for your cart give us a call and we can help you out just loosen the lock nuts on the end of the tie rod and rotate the tie rod until you get the toe in that you want too much of either toe in or toe out creates tremendous drag and really slows the cart down like all the other front end settings always set toe with the driver's weight in the cart once you get the cart set to these baseline settings you can head to the track and start adjusting things to make the pro the handling better it's important to know that many of these settings are interrelated so if you change one it may change another towing in particular is likely to change if you adjust caster or camber so let's look at each of these changes and what they're likely to do on the track a good starting point here is a half a degree negative camber but if your chassis manufacturer suggests a different starting point start there if the cart turns into the corner well but it wants to understeer push coming out try adding a little more negative camber conversely if it under steers as you enter the corner then transitions to oversteer as you exit if the driver has to counter steer to catch the car at the end of the turn taking camber out of the front end standing the tire up straighter will help some carts use an offset pill under the kingpin as you can see the kingpin is offset in the pill as you rotate the pill it moves the head of the kingpin like moving around a clock face the more the head of the kingpin is towards nine o'clock viewed from the driver's position the more negative camber the more towards three o'clock the more positive camber the other predominant front-end setup is the sniper system that adjusts camber and caster independently start by loosening the nut on the top of the kingpin slightly then by loosening the set screw on the in board side of the sniper and tightening the set screw on the outside you can move the kingpin the top of the kingpin in adding more negative camber and vice versa don't forget to tighten the nut at the top of the kingpin when you're done caster affects the way the cart transfers weight from the front end to the outside rear tire it also takes weight off the inside rear tire which helps the car rotate remember we said that if your car uses the offset pills to adjust the front end rotating those pills changes camber and caster the closer you move the top of the kingpin to six o'clock the more caster you have the more you move it towards 12 o'clock the less caster you have with the sniper system you'll need to loosen the nut on top of the kingpin and then lift the top plate out of the little teeth and reset it either farther forward for less caster or farther back for more if the cart wants to flat slide in the turns increasing caster will increase rear grip if the cart hops through the turn less caster reduces the weight transfer and the rear grip please note that increasing the caster increases the scrub on the front tires and will reduce corner exit speed the spindle height washers are used to raise or lower the spindles to change the front ride height raising the spindles up putting more spacers underneath and fewer on top lowers the front of the car and increases front grip but it may induce on power over steer conversely lowering the spindles putting more spaces or spacers on top raises the front end and transfers more weight to the rear increasing rear grip finally let's talk about adjusting toe in and toe out there are a number of ways that you can use to find a good reference point for measuring toe there are very nice laser alignment systems like we use here in the shop or you can just spin the front tires and scribe a line on them with a pen or you can use these steel wheel alignment discs the key is that you have to have a solid repeatable reference point to measure always remember you need to keep the driver or some equivalent weight in the driver's seat to set toe correctly just measure between the lines on the tires or between the discs front and back and the difference between the two is the toe end just loosen the lock nuts on the end of the tie rod and rotate the tie rod to change length as they lengthen toe in increases try to adjust both tie rods more or less equally when the toe is where you want it re-tighten the lock nuts and measure one last time if the cart feels too darty or too jerky in front increase the toe in a tiny bit if on the other hand it oversteers as you exit the corner try reducing the toe in or increasing toe out in general once the toe is set to a recommended setting it will only need to be adjusted if you've changed caster or camber or you've been involved in an accident on track [Music] well that about covers it for the basic chassis setup but there's a lot more things for us to get into next time we'll talk about torsion bars and weight distribution axle stiffness and the critical role that rear rim width plays in how your card handles we'll also look at some of the critical parts of the drivetrain and how to get those right remember we want you to go fast and have fun so we're here to help don't forget to send us your comments and questions and share these videos with your grand prix friends if you have any suggestions on how we can make these videos better or more helpful please let us know don't forget to like us on facebook and we'll see you next time

Channel: Fox Valley Kart

Views: 44,165

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Id: qdVAolFIDlI

Length: 12min 27sec (747 seconds)

Published: Fri Feb 19 2021