Do you stiffen the axle for more grip?

[Paul Kish]

I think for everything depending on circumstances any adjustment can give opposite on track results.  This is an in general what would you expect question.

Will you in general expect more grip when going to a stiffer axle?

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[TJ Koyen]

You aren’t tuning “grip” when you change axles, you’re tuning “rate of lift”. You can’t literally change the durometer of the tires with an axle change, which is where your “grip” is generated.

Stiffer axle on the OTK kart generally frees up the rear. It’s usually the opposite on other karts.

As with anything regarding tuning on a kart, it’s all very conditional. You’ll find in some situations that a stiffer axle will free the kart up and in other situations it will do the opposite.

A super sticky track will sometimes over-work your axle if it’s too soft. In this case a stiff axle might actually free the kart up by providing a stronger spring under load.

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[Paul Kish]

Thank you for the info.

 

 

paul

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[Cory-Milne]

I agree with TJ harder axles generally take “grip” away this is my experience with crg and crg variant chassis. also shorter axles with take exit grip away. longer softer= more grip,  shorter stiffer=less grip  atleast in my experience  best way to test this is go to the track and see for yourself

[Rob Kozakowski]

As TJ says, it absolutely depends on the chassis.

In my Italkart, “in general” the softer axle frees up the rear of the kart, harder axle gives more grip.  That’s the opposite of OTK karts.

More often than not, most of us are best off sticking with the “baseline” axle, which is normally a medium stiffness axle on most karts, and looking to your driving or other smaller adjustments, unless you’re running in a big event on a very “rubbered in” / grippy track, or a very “green” / slick track.

[Paul Kish]

Thank you all again for the input.

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[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.

[Paul Kish]

 

First off thank you all again for the input.

I just happened to look at email and saw there was an additional reply.  I’m also a little into sprint cars too.  Frankly all cars work alike because performance is always about your ability to use your tires as needed on the track.

Over the years I have found the only real difference is the ability of what your racing to apply weight to and from tires, the capabilities of the tires, do you have a solid or locked axle >AND are your racing a “real race car” which turns both left and right or are you racing a “LTO” which turns only left.  If there is a major difference, it’s between “real race cars” and “LTO’s”, the difference is how the rear tires are used to be efficient in turns.

Enough on that.  Here’s a correlation I just now thought of from your kind input which I think now may relate to the question.

 

With a sprint car weight application to the RR or outside rear is via the chassis through a torsion bar(spring), then via a lever(RR torsion arm) to the RR bird cage(bearing assembly, mounted directly to the right end of the solid axle).

 

We recently reversed the tubes on the back of our car.   Tubes are just that tubes that go across the back of the car, which hold the torsion bars inside.

They are installed one ahead of the other.  Let’s just say one is 2″s in front of the other because they are 2″s in diameter.  A normal sprint car today will have the tube closest to the axle(the one positioned ahead of the other) holding the torsion bar, with a torsion arm mounted to the end extinding forward to the axle, connecting to the bird cage(the lever) on the right side.

And the rearward tube and it’s torsion bar and longer torsion arm, connected to the left bird cage, again which is mounted to the axle, but on the left end of the axle.

 

Ok, if we look at the engineering of it for each side to work equally with different length levers, you will also have to use torsion bars which have different spring rates.   Generally speaking, it should not matter which side the longer lever is on, because if the spring rate is adjusted to the lever length, both side per the math and would operate the same.

 

But here’s why “I” feel even though the math will be the same,  on track performance will differ.

Just the fact that you have one lever longer then the other,  defines each side as different even though the spring rate math will work out the same.  “I” in this case can relate the longer lever to not only working differently, just because it’s longer and different, but because the longer lever will have a bit more flex.

In this case there also a 2″ difference in where forces are applied which “I” also think will make a difference, but for the sake of this discussion the longer lever also will provide more flex, if even a small amount.

It’s flex which takes time to occur and IMHO, will alter how weight is presented from the chassis to the tire.

IMHO, even though an engineer will tell you the transmission of dynamic weight through the parts instantaneous,  my experience has proven to me it will alter how weight is applied by the tire.

It’s tough to define which came first, the flex or chassis movement, or the instant dynamic weight transfer.  Engineers will tell you the weight transfer is instantaneous.  If that’s the case then in actual operation of any chassis, forces cause dynamic weight to transfer and then the relocated weight is what causes your chassis or kart frame to operate.

I can look at it either way.  In reality it’s a constant process, but at any moment in time it would have to be looked at from one perspective or another.  It’s simple, either weight causes the chassis to work and the working of the chassis applies the weight, or weight instantly transfers and then the weight from it’s new location causes the chassis to function.  Six of one and a half a dozen of the other. … :)

Long story short, if on track needs are such, that I want to bang weight into the track to making a tire operate as needed to provide required grip, I’ll go with shorter stiffer levers and if I need to ease or finesse a tire into the track, I’ll go with longer, softer levers.

 

After reading again today others inputs, I’m going to say a softer axle is akin to my thoughts on longer softer levers verses shorter stiffer levers.

Now there has also been input on here about how one chassis needs one thing and another needs just the opposite.  The ONLY difference that ever occurs is in the final application of the tire to the track.  It’s all a matter of how close or away you are, from the limit of grip of individual tires.

One stiffer chassis may direct forces with a softer axle in such a manner that the outside rear tire lets loose.  Another softer chassis with a stiffer axle may do exactly the same.   It’s all about the spring rate, and the length and flexibility of the levers  involved, applying weight to your tires.  It’s not just about knowing the capabilities of your tires and your chassis ability to apply weight, it’s knowing if your racing situation requires you to bang the tire into the track to be fast or if your going to need to ease the tire into the track to be fast.

 

You can calculate things 100% accurately given what you have to calculate.  But in the end, racing is about application, not calculation.

 

thanks  for reading and I never know if I’m close to right or not because this is all just IMHO and ain’t necessairly right anyway. … :)

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[Paul Kish]

I need to add in one additional item to the mix.

Grip does not follow weight transfer.  You first have to have grip before you can get any mechanical or dynamic weight transfer.

 

The sequence is(maybe) get a grip on it, on track forces will move dynamic weight to the grip and then the relocated weight will pull the parts of the chassis towards the grip.

 

When grip goes away, so does weight.

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