[Chris Hatch]

On your snipers, you can have zero toe and equal weight left to right and still have a pull.  What you are wanting to do is “square” your kart.

You will need a long carpenters level, or string, or another long but very straight object.    Place the level so that both edges of the right rear rim are touching it.  Measure the distance from the level to the front of the right front time and the rear of the right front rim.  When those measurements are the same, the right front is now “square” with the rear of the kart.  From there, set your alignment to the left front with zero toe.  Now your kart is completely square.  From here you can set toe on each front wheel.

[Chris Hatch]

One other thing that contributes to this problem more with 4-cycles than 2 cycles is that a 4-cycle has a great deal of torque at lower RPM’s.  As a result, when returning to the accelerator, that torque causes weight transfer to return to the left rear and a loss of grip at the RR.

You might be surprised to see the effects of putting a hard axle.

[Chris Hatch]

I have never had a successful 4-cycle sprint kart work with 53-53% rear weight.  Those are oval track/offset numbers.   The Margay will like 57-59%.  Maybe 56-57 percent with the hard tires.

[Chris Hatch]

In my experience working with drivers complaining of a snap loose condition, it is almost always a result of an under-steer condition first.   The driver believes the kart is turning in, but there is not enough weight being moved to truly initiate a smooth turn.  What happens is that the kart begins its initial turn in, but is sliding the front a small amount.  When the kart gets to apex, the kart has lost enough speed to allow the front tires to stop slipping and gain the traction they needed to not only initiate the turn in but the full rotation needed for the turn.

Now the hard part:  What is not working?

I look to weight placement and seat mounting.    As a tall and heavy driver, 57-59% rear weight has worked best for me on the Margay.  I would have the seat tilted back at about a 45-50 degree angle.

I also used long front hubs on the Margay to stiffen the spindle arms.

 

 

[Chris Hatch]

A.  Use whatever hubs are needed to get to 55″.  In many situations, longer hubs will actually help free up the kart.  This goes against some of the traditional thinking.

B.  When using a 6″ wide tire, use an 8″ (212mm) wheel to keep the kart free.

[Chris Hatch]

Thanks, that’s an interesting observation.

[Chris Hatch]

TJ,

I am curious about your comment about moving the rears in 4mm when the track gripped up.  While this is a very slight adjustment, I am curious as to what the purpose was.  Conventional wisdom of course is to run full width (lower center of gravity, more resistance to weight transfer) when things grip up.

Not questioning the effectiveness, just what to understand your theory.

[Chris Hatch]

Adding grip to the rear does not mean taking it away from the front unless you are moving the seat back (or forward).

Most kart adjustments are not about adding or taking away grip but rather where/what you are doing with the weight that is unloaded from the inside rear.    For example, adding more negative camber as the track grips up means moving less weight to the outside rear and towards the outside front.  The weight may not always get to the outside front because once the driver unwinds the wheel, the weight is being shifted back to the inside rear.  Therefore, I have taken away weight (grip) from the outside rear, moved a little to the outside front, and kept much of it suspended in the frame = free.

 

[Chris Hatch]

I believe we often simplify our understanding of “adding grip”.   The where and how it adds grip is often more important.

FOr example, adding castor really doesn’t add front grip.  It increases the weight jacked on the inside front tire as well as increases the speed at which that weight transitions.  This will help the initial turn in (which people often think of as grip but isn’t).  However, be aware that it also increases the weight that arrives at the right rear.   Turns in good but may bind and even hop.  Get it right it turns in well and then returns the weight it the right time to get good forward bit off the corner.

 

COnversly, stiffing the front bar doesn’t actually add front grip.  It stiffens the front and resists weight transfer.  In doing so, you help prevent some weight from moving to the outside front tire that can cause overload it causing it to slip.  This helps the front primarily at apex and exit but will do nothing for turn in.   I like to think if the front bar as a broom handle, which one adds more grip to the broom head?

[Chris Hatch]

First off, most engine builders would likely tell you that the cylinder to piston clearance is much larger in a stock engine than what we use when we can build from scratch.  Why do I want a looser fit?  It would seem what you’re really looking for is less ring tension.  However, by this grit method, you would achieve less resistance by loosing ring seal.  Not good.  Compression is king on these engines.

Speaking of compression, what kind of damage will you be doing to the valve seats as the grit is smashed into the seat by the valves resulting in serious pitting.  You may be able to cut/grind the seats enough to get rid of the pitting, although you might be surprised.  Again, the minimal gain you might get will be offset by the loss of valve seal = Not good.

[Chris Hatch]

DO they prep your track with asphalt sealer (old school guys call it bear grease).  If so, used tires typically work better.

In general, low HP tires will like new front tires but can get more time out of the rears.

[Chris Hatch]

Softer axles will free the kart up until they flex to the point of chassis bind.  At this point, common adjustments no longer work to free the kart up (camber, caster, widening).  At this point a harder axle will return the kart flex back into its functional zone in terms of degree of flex and also rate of flex.  I have had this work on every chassis in which someone has had the guts to try it on a locked down track/kart.  The Tony Kart drivers are more successful with it, IMO, because they typically follow the leader and their leaders have figured it out.   I give props to Gary Lawson who first turned me on to this concept in 2004 with a Margay.  On a gripped track it was worth .5 seconds a lap.

A harder axle will give you more side-bite when there is not enough traction to force the chassis to flex much RE: green tracks or even wet. In this case you are using the sidewall of the tire to make grip rather than lateral weight transfer to the outside rear of the tire.

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