It’s just less axle inside of the hub, with all else being equal. I’ve gone down to 1000mm axles with standard hubs and had no issues running max width.
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Yeah that’s the theory but you’re correct on your follow up - reducing the amount of axle inside the hub by cutting it down has the effect of allowing more flex at the hub rather than in the axle. Effectively making it act like a super soft axle.
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Others feel free to chime in, but in my experience a cut axle invariably encourages rapid jacking or lift.
Could it be we are mistaking hopping for the “re-jacking?” As I’ve always understood it, hopping is basically the axle and rear is the kart loading and then releasing in quick succession.
If we consider the axle and hub assembly from the bearing carrier outward in total isolation, ignoring the rest of the axle attached to it, it stands to reason that you’d have less axle in the hub, and therefore a “softer” system which is easier to bend under load. When it distorts and bends under load, that creates slip and less “bite” into the track.
But in reality the outer axle and hub is connected to the rest of the axle and chassis. So what I’ve been taught by others happens is that the shorter axle essentially reacts to a load at a more rapid rate than a longer axle. The way I try to think about it is imagining a really long I beam vs a short one. One would distort and flex a lot vs a shorter one being much more rigid and less prone to flexion - the lever arm is shorter.
Anyway, a lot of words to say that I think there are competing factors contributing to how a cut axle behaves in a kart. Your mileage may vary, but generally* a cut axle will jack and release more quickly than a wider axle.
I agree with the sentiment that less axle in the hub makes it act like a soft axle, but the other factor of shortening the lever arm of the axle is something that I think often outweighs that affect.
I think I’ll stick to aircraft engineering it’s easier to understand 
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For what it’s worth, on the KT4 and KT5, we always wound up on a short (as short as 980mm) axle. We tested T6, M20, M25.
The big “Aha” moment came when we changed spindles to the “D” model. I believe the karts always arrived with “C”.
What’s the difference between the two?
The main difference is the angle of inclination (relative to 90 degree) versus the king pin angle.
Most people call this “drop angle” in the US.
According to the ‘23 catalogue for CRG, the C spindle is 10.5 degrees, and the D model has 11 degrees.
The deeper the drop angle, the ‘faster’ the rate of lift/ jacking as you turn the wheel. Several chassis brands offer varied spindles, but not all. OTK does now as well.
Ryon feel free to chime in, if I’m incorrect.
Otk has had the 1B spindles for a while now
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Sorry to derail the thread…
…but I’m curious to know more about this. I’ve cross referenced previous threads and understand KPI/drop angle, but am interested in how this is applied practically.
If you start with 0 camber and a 10.5* spindle, are you resetting camber back to zero after changing to an 11* spindle?
Is there a reason this adjustment would be preferred vs changing the steering rate on the steering column?
What about this adjustment vs. caster? Specific reasons to change one vs. the other?
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I don’t think you’re derailing the thread, as every setup change is related to other ones.
While changing steering rate is a great adjustment for a multitude of reasons, it’s not going to really change jacking leverage in the same way a spindle adjustment will. It will change the rate at which the spindle turns and the kart can feel more responsive or more heavy in steering, but the lever mechanism of the spindle remains unchanged.
Adjusting your alignment is one good point about changing spindles and drop angles. Normally the spindle yolk (frame) is angled to compliment the stock spindle drop angle so that at neutral settings the spindle is nice and level when the steering is straight. Changing this means you’ll have to adjust your king pin inclination out of “normal” spec to have the Sniper readings look correct.
But where the difference is made is primarily at any point other than going straight. As soon as you turn the wheel the additional drop angle will “dig” harder sooner.
Making a spindle change is similar to adding castor to the chassis.
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I appreciate the detail! There’s got to be someone on here that can put together a graphical representation of steering input vs. caster and camber angles, and overlay spindle “A” vs. spindle “B, C, etc.” calling @dodo @DIG78x and any other wizards out there…
As Eric mentioned, it’s a different Kingpin angle. This is accomplished by changing the angle the stub axle itself is welded to the kingpin boss at the time of manufacture. A few have mentioned OTK’s 1b spindles, this is a change along the same lines.
These are typically a “it works or it doesn’t” type of change, you’ll know within a couple laps if they’re the answer you’re looking for or not. That said, they are not necessarily just a “bolt it on and go” type thing, as in the case of the CRG, it will also require re-alignment as the camber must be adjusted, and if I recall correctly the ackerman as well. (OTK just camber via a zero pill on top) If those things aren’t done, you won’t have isolated the variable intended and will have a bad representation.
Anyhow, you’re changing the stub axles sweep angle/path of travel. it can be useful when you have a situation where the kart won’t hike a tire, or inversely when you can’t get heat/graining out of the front tires. Caster will be a change relative to the axle path, however KPI will change how “aggressive” the ramp is as the “starting” caster angle remains the same as the other spindle.
That probably could have been explained more clearly, I’ll work on a better explanation and revisit.
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I was actually talking with a buddy of Thanksgiving about something like that but boiled way down to ‘where the rubber meets the road’. We came up with the idea of making a sweep of wedge as a function of steering angle (he’s a left-turn only guy). It would be interesting to see how your cross-weight percentage changes at different steering angles based off of things like caster, camber, front bar, axle hardness, etc. Could be very eye-opening. Or a huge waste of time, haha
I bet you could say “here’s my current setup and it gives me this cross-weight curve”. With a stiffer axle, I’d expect a steeper curve much like more caster might do, so you could possibly come up with a way to see if you really want a stiffer axle before committing. The big caveat is that this will not tell you anything about mid-corner handling where lateral Gs have into play, but it could help with just removing some of the voodoo of kart tuning.
All I wanted was a nice little graph and here you are going off the deep end with cross-weight curves …only kidding of course, more data is never a bad thing!
I mean, do what you want with regards to data, but really we are just changing how the kart flexes with every adjustment. Data is fun but it’s very easy to get bogged down and not see the forest for the trees.
Spending a practice day swapping through all your different axles (or your adjustment of choice) will give you all the answers you need and also will calibrate your butt to actually feel how the kart reacts and works differently with each adjustment.
You won’t truly become a contender if you can’t feel the difference in those adjustments anyway, and are relying heavily on data to tell you what the kart is doing and what you need to change.
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I think I’ve referred to this as rake angle?
This. As alluring as data is, I’ve seen countless really bright engineers at the back of the grid who would be better served just closing the laptop and spending a few days just driving and trying stuff. Everyone who I’ve known who’s spent countless hours making models and trying to take full account of every last variable, would be appalled at how uh, “not scientific” much of the process really is at the highest levels.
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I think of this as two related, but almost opposite, ways of accomplishing the task (integrating knowledge to alter performance).
One approach is to come at it from the intellectual/logical/data direction where you use that type of ‘knowledge’ as a framework to support/influence execution of, and/or changes to, your actual driving process/feel.
The opposite approach is to take the knowledge contained within your experience/feel, and then try to use intellect/logic/data to ‘understand’ why what you are doing (driving and/or tuning) is or is not working.
The problem with the first approach is that trying to take intellectual/logical concepts and turn them into changes on track is a bit like trying to create an analog signal from a digital signal; the nuance, color and character are missing, so it can be harder to bring to reality. However, if you already have good driving skills and sufficient experience, it can certainly be done.
With the second approach, you already start with the analog signal (the full, contextual, holistic experience of driving), so then it’s much easier to run that through your brain’s analog to digital (logic) converter where you can pick the experience apart looking for the how, what, where, why information about why your driving and/or setup is or is not working the way you want.
Anyway, no matter how you approach it, the more deeply you integrate your experience and understanding, the more complete a driver you will be.
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It’s not an either/or but a both/and. I can collect cross-weight data with a beer in my hand at 9pm. I can collect handling data with my butt in the seat, but spending all day swapping axles is a luxury most of us don’t have in the real world.
I’m not proposing that anyone sits at home doing science experiments instead of driving, but I’ve heard plenty of advice from people who clearly don’t understand basic physics at the track. As a friend once told me, getting the sign of a number is only a problem if you do it wrong an odd number of times. Lots of decently quick guys got there with -1x-1=1 and didn’t realize it.
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This is actually TJ’s secret algebra equation for tire pressure change from qualifying to heat 1.
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