How is stiffness measured?
That’s above my paygrade!
If you can change an axle in less than ten minutes- you should be changing tires for an F-1 team!..
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I’ve ran both a Birel RY-30 and various OTK chassis (the 4 stroke version and 2 cycle versions with 206 and WF)… we modify the 2 cycle chassis by cutting engine side seat strut (here’s where everyone cringes) and replace it with a straight universal seat strut to allow clearance- not having to offset the engine so much… we follow Briggs advice on not offsetting engine so much (sometimes to another zip code or time zone) because it’s not good for the engine or balance of the kart…
my son likes the (2021) 401R but it took some time to set up out of box and OTK are known for their softer chassis… we’re going to try out a Kart Republic and I’m leaning to a 2 cycle chassis just because they tend to be proven more in racing and come with the third bearing option… it suppose to be a stiffer chassis with some CRG DNA in it… try to stay away from generalized advice and set up kart to the driver and particular track you are running at seems to be our way (logical?) on setting up… we’ll see if he can still keep winning just to try out another make/model… not that it’s better or worse…
Each manufacturer and brand have different softnesses and they don’t correlate well.
Yep, it’s very subjective on what’s soft or stiff. Often without taking sidewall stiffness or seat type into consideration.
I’d be curious to see the deflection amount, observed load transfer numbers and spring\rebound lateral load transfer on front and rear, longitudinal front to rear and diagonal transfer (Jack\Drop).
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Fast axle changes are 10% work at the track and 90% preparation at the shop.
Are all three bearings perfectly aligned both up-down and fore-aft? Has the axle been polished until it shines? Have you deburred your brake and sprocket hubs? Have you filed the keyways 0.005" oversize? Is the axle straight at the end that you’re trying to remove?
If all of those are true, then removing an axle takes three minutes with an electric impact wrench or five minutes with hand tools. If not, then there is the slow process of banging it through the bearings a few thousandths of an inch at a time.
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With a brand new Tony Kart 401 R chassis- after sanding it smooth and deburring all set screw marks and loosening or removing every bolt on axle hubs and bearing cassettes- it still took me about 1/2 hour to bang it out even with a axle removal tool?!?!… I must be still doing something wrong???…
True- just wish I knew what it all means!… sorry…
Make sure your bearing cassettes are aligned. That’s a major one that most people overlook.
Also, loosening the brake rotor and sprocket on the carriers helps a lot too.
And apply WD or lube to the axle as well.
I do all that and almost any kart axle should come out relatively easily. Even my crusty axle I had in my kart for a year with a bunch of corrosion on it came out in 10 min last weekend.
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Bearing cassettes as well as the bearings in the cassettes. I’ve had to show a lot of people how to properly align bearings and they’re always amazed how much easier the axle slides in, not to mention better rolling.
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I have seen and struggled with set screws that have actually deformed the axle from being over-tightened, so even deburring the set screws your still going to have issues. If it is any of the clamp-style hubs causing issues, try spreading them with a flat head screwdriver and a hammer driven in parallel to the axle. I’ll use a screwdriver for the brake hub and sprocket hub so they slide easily and leave them in place till I have the axle out.
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My rule of thumb on set screws that I’ve had very good luck with is zero loctite ever. Run them down snug to axle, then 3/8 of a turn. I always use an extra long Allen socket (set at HF 
) and 1/4" ratchet which makes set screws so easy.
If the axle isn’t round, its tough to get out. When axle get bent and straightened the axle might get out of round. I’d also check the diameter of the axle. I’ve had axles that were larger in diameter than others and it was very difficult to get out.
A quick way to remove burrs, is to remove 2 set screws but leave one in but turned out enough to clear the axle. Insert an allen key in the set screw and turn the axle until allen key is stopped by some part of the kart. Turn the axle a few times and the burrs are gone.
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I have a good idea on how to do this, but curious on what your method is, if youre willing to share!
I’m guessing you’re talking about aligning the bearings?
To do so you need to have your third bearing (if you have one) either removed or loose and floating. Loosen up the pinch bolts that hold the bearings tight in the carriers. Slide the axle in from a side of your choosing until close to the other bearing. Move your axle up and down checking the play in the bearing (there’s always some even in new bearings), you want the play to be equal in reference to the bearing the axle isn’t slid into, if it is not then make adjustments to your bearing as needed. Repeat this step but by checking the play forward and backward. Once you have an equal amount of play up, down, fore, and aft then tighten your pinch bolt on the bearing you just adjusted. Remove the axle and repeat the process from the other side of the kart. The third axle bearing is the hardest to really get perfect, usually I just leave it’s pinch bolt loose and mounting bolts loose when installing the axle, and then tighten the mounting bolts first and pinch bolt last. If it’s obviously not true to the axle and carrier mount you can tap it around until it meets up nice and parallel to the carrier mount.
Hopefully this makes sense. 
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