Axles-Soft or Hard for more grip

[Stephan Gaudreau]

I am curious to see if there's truth to one particular expert saying that a softer axle provides more grip than a harder one. He explained that the hard axle tends to slide across more when the track is really gripped up. The softer axle flexes more and squats the rear down more for more grip.
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[Scott Formanek]

what brand kart are you talking about?

[Barry Hastings]

The question is more what kind of grip do you have/need?

A softer axle will give more overall grip, up until the track grips up enough to overflex the soft.

At the same time the soft axle will "free up" the kart by letting the kart not overload the outside rear with the available grip.

Now depending some point the grip will rise to the point you will need to go stiffer axle to keep the kart free. That point is when the grip is enough to hold the kart on the outside rear.

Until the grip is that high. The stiffer axle will tend to push the tire pS
past the available grip.

Not the easiest thing to pick.

[TJ Koyen]

Don't tune for "grip", tune for "lift".

A stiffer axle with lift quicker and give a more direct mechanical jacking effect. However, it also sets down quicker on exit. So if you have tight corners, you need quick changes of direction and the stiff axle will facilitate that.

Softer axles absorb some of that weight jacking and will not lift as quickly, but will maintain their lift longer throughout the corner. If you have understeer on exit, a soft axle can alleviate that by keeping the inside rear wheel up longer. However, you still have to make sure you have enough initial front geometry to get the kart to turn-in.

A sensitive and experienced driver will be able to tell you if the kart is not lifting on turn-in (go stiffer) or if it's lifting so quickly that it sets the inside back down right away (go softer). A less observant driver would tell you in both situations that the kart just won't turn and won't feel the super quick initial lift you get when your axle is too stiff.

Axles don't add or remove grip, they change the rate at which the inside rear wheel lifts.

If you identify where your perceived "grip" issue is, you can then move forward with an axle change. Always break the corner down into turn-in, apex, and exit.

Both a soft and a hard axle could either "take away grip" or "add grip" depending on how the rest of the kart is setup.

If you have understeer on turn-in, you may want to go stiffer on the axle to help facilitate the inside rear lift. You may not be getting the direct and snappy weight jacking a stiffer axle will provide.

However, it could also be the case that you're already TOO stiff, and the inside is picking up too quickly and setting back down right away as you overload the outside rear with all that lift and break traction, making it feel like the kart is flat. Then you would want to go softer in order to slow that lift down and get the kart to stay within it's traction limits to keep the lift up and not break free.

It's about finding a balance of the right amount of lift rather than adding or taking away "grip". It's true that the "spring rate" of the axle's stiffness may also come into play as well, with a stiffer axle pressing harder into the track's surface, and a softer axle absorbing some of the flex and not putting as much force into the track. But I think the rate of lift aspect comes first when tuning with axles.

Just my theories based on a ton of testing and experience.
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T.J. Koyen
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[Barry Hastings]

agree, i have had the same observations, just much harder to type that much on the iPhone. BUT you did say it much better.

Those are along the same lines I was speaking of, and my point is/was its not a A then B game every time. The softer to hold the lift longer would be because the stiffer would put the load on the Outside Rear too fast for the available traction to keep the lift.

AND changing axles for an experienced driver for a gain is much easier than for the less experienced driver. I have gone the opposite way from "what they say" and really did well.

[Vernon Head]

Everyone seems to have their own opinion about this, and you should probably try a few different axles yourself and see what you think.

[Stephan Gaudreau]

Thanks for all the info. Great stuff. To answer Scott. I have a 2012 CRG Blackstar with an M20 in it.
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