“stable” is a good way to put how the kart feels in fat mode 
I’ve become a simple man on axle changes. Bent the N axle, had a new A sitting around. Too lazy to take it back out. A = new baseline. My butt and hand sensors are not fine enough to notice a difference between the N and A.
They are close anyway. Speaking in-depth with drivers last weekend, the difference is small and requires a very sensitive butt/hands to tell the difference in handling. But the driver I spoke to noted the A did feel freer.
I’ve been wondering, I’ve always read that stiff=more grip & soft=less grip, but then I’ve seen statements here that seem to contradict those thumb rules. What am I missing?
Chassis stiffness and track conditions make it very. You don’t know until you try them. It’s a pain in the ass but start on medium, throw in a soft and a hard. OTK general rule is harder frees up the kart. But that being said I went to a Q the other day to gain grip and I lost it. Went H and and got what I was looking for.
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You gotta stop thinking in terms of grip.
Think about the lift instead. And how the axle and chassis flex together. Grip doesn’t change, inside rear lift does.
I think it’s been covered in earlier posts in this thread.
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My switch from N to HD visibly reduced the inside rear lift height according to my dad lol. Where before my inside rear was lifting high and setting down hard and subsequently hopping on exit, now my inside rear lifts just slightly on initial turn-in and my hopping issue didn’t go away completely but it’s much less aggressive. I think I just need to make adjustments to my driving style and approach to the corner to find the sweet spot.
That’s a very large jump in stiffness. I would go try starting the day on the HD go to the N and see if you can make the kart work. Pay attention to how hard you are loading up the kart and when you are applying the throttle. It was a hard habit for me to correct, but I’m a very early and aggressive accelerator. I was always asking to much out of the chassis and tires causing the kart to hop badly.
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Wow 4 posts before I could finish mine.
Like Clayton and TJ said. OTK: typically it’s hard > less grip and soft > more grip on the outside rear tire. While cornering, the axle has most impact on the outside rear side bite/traction/grip and a secondary affect on the inside rear lift profile by controlling chassis torsional flex (maybe). A kart can have too much outside tire grip which increases the tire slip angle resulting in a excessive forward motion drag. In addition, in grippy conditions too soft an axle could add forward motion drag and slow the kart down on fast corners and even on the straight.
Tire slip angle is the angle of the of the wheel it is mounted to. As the tire rotates the sidewall of the tire near the contact patch flexes from zero slip angle to the slip angle and then back to zero This flexing is what generates the heat in the tire.
One might ask, if slip angle generates drag then why have it at all? Because the tire slip angle generates the side/lateral force in the tires for cornering. Slip angle also is the major source of heat in the tires.
It does seems to me that the newer OTK are less sensitive to axle changes.
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I’ve been told the new OTKs like to be driven more progressively into the turn. OTK have been 90% of my karts for past 12 years and I’m not the expert but I have to agree with that observation.
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I agree. I tried to order the H but out of stock seemingly everywhere. Anyway, I feel like it helped somewhat but I definitely need to work on my technique. I got caught up in the common “chassis tuning will fix my problems” attitude and now I’m realizing I’m the problem.
For sure I want to try to make the N work! Im pretty confident I was asking too much from the kart before.
Well put. And to TJ point imagine if you never lifted the inside rear tire. The kart would never turn and you would drive straight on thru the corner. You have so much rear “grip” and the fronts having less rubber/weight being applied to them cannot over power the larger width rear tires.
By increasing/decreasing the lift via an axle stiffness change you are changing the springy-ness of the kart. Limiting or allowing the inside tire to pick up and set down at different rates.
Again you kind of need to play around with the axles to see and feel what they do. Generally, unless you’re really hoping, it’s super cold/hot just stick in the medium and tune from there.
Also there is so many ways to miss a bolt or a set screw on a race weekend it’s not worth changing the axle unless you’re out of other tuning options IMO.
Trying to summarize this. Tell me where I’m wrong &/or could break it down further for better detailed description.
Track width:
Front: narrow → slower lift → oversteer; wider → faster lift → understeer
Rear: narrow → faster lift → oversteer; wider → slower lift → understeer
Caster: less → slower lift; more → faster lift
Camber: less → understeer; more → oversteer
F/R torsion bars, rear axle: soft → slower lift → ; hard → faster lift
Edited.
This one depends on a lot of stuff.
More caster is a faster harder lift.
Less caster is less and slower lift.
Narrower front track is less initial jacking.
None of this is really a grip thing. It’s lift and set adjustments.
Grip is tires - air pressure, temp, etc.
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Again, grip is tough to quantify since the tire is the provider of grip, and the tire is constant for the most part. Thinking about it in terms of grip rather than how an adjustment changes the chassis flex is how things get confusing.
There’s a great Korsasport video that goes over every adjustment and explains this all better than my fingers could…
“Grip” is a misnomer. Always look at an adjustment from the perspective of how it affects chassis flex and lift. This will change how you view chassis setup.
Burpo is right, the only thing that affects “grip” is tire changes.
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I actually had caster correct in my notes, but transposed it incorrectly. Is the edited version more correct?
Adding in what the kart does on exit would also be useful. I like to think of IR movement (lift and set-down) in terms of timing in the turn. So track width map might look like:
Front track increase: Advances when the IR lifts and advances when the IR sets down in a turn.
Front track decrease: Delays when the IR lifts and delays when the IR sets down in a turn
The subtle affect of how track changes affects the exit is sometimes missed. A kart could have a too much turn-in without feeling like oversteer but kart bogs on exit because the IR is set down too early.
Doesn’t axle hardness, axle width and wheel type affect grip/side bite?
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Sorry to revive an old thread, but I’m trying to understand how the axle intersects with other factors like use of the third bearing and cut axles. It doesn’t help that the progression from N->H->HD is not linear. But is this a correct way to approximate in order of “hard”:
N axle, No-3rd Bearing, 1030mm
N axle, Yes3rd Bearing, 1030mm
N axle, No-3rd Bearing, 1000mm
N axle, Yes3rd Bearing, 1000mm
H axle, No-3rd Bearing, 1030mm
…
Basically, is there a logical progression, or is it all multivariate and too complex? 
I think the logic there is fairly sound.
I personally never have a good result adding the third bearing. If I think I need the extra stiffness I’ll swap axles. I immediately pull it out of every new build.
It just makes for a weird interaction with the kart that just seems to bind it up more than stiffen the rear if that makes sense.
Also I personally believe the axle length has more to do with the amount of material engaged inside the hub versus the effects of having a longer axle. But I’ve got no way of backing that up. Just a hunch and seat of the pants feel.
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Shifters typically use the 3rd bearing and as Clayton said, the single speed usually use only 2 bearings.