I am by no means an expert or as experienced as some. I will say I changed axles and what surprised me was how much the kart felt differently at very low speed. I noticed the difference at under 10 mph and even 10 kph.
I theorize that axle stiffness can affect mechanical jacking and jacking from cornering force differently. Even to the point of where the 2 would intersect if plotted on a graph. That is just how I picture it in my hypothetically little world. If you could add in where other bits intersect on the graph and that would be neat to see. For example it would be neat to see how adding seat struts with a softer axle vs less struts with a harder axle, and the kart having the same deflection at a given load would compare. Iâd guess that even though the kart would twist the same amount something would make it feel different. Resonance/dampening vs spring rate type of thing.
As far as flex one could test that by anchoring a length of one end of an axle and weight the other, then measure the deflection.
Wheel hubs are widely accepted as making a difference.
I went to a race to help a friend with his kidâs kart. He had an issue the day before with a hub stripping. They through a unmatched hub on in a pinch. In the morning he had handling issues. Watching video I noticed it was only in left hand turns. A third guy starts looking over the rear and notices the 2 different hubs. Put a pair of new hubs on an that solved that issue.
Iâve always wanted to chuck up various axles in a lathe and spin it, relatively slowly 800 to 2000 RPM. Might need a wheel and tire on the free end and chuck it up where the bearing would be.
This is interesting. I have soft, medium, & hard CRG axles & although I havenât measured them, the wall thicknesses are visibly distinct, particularly in the case of the T5 (hard) axle.
This has always confused me too! The modulus of elasticity (stiffness), I thought, was the same for all steels. How do they make one axle soft, or medium or hard? With a fixed diameter, it could be done with thinner wall thickness.
Having done only race weekends this year I mainly changed axles because either it did something and iâd go better or it didnât do something and iâd stay the same. As you know @DavinRS, we didnât have many test sessions. At Rok the Rio I ran 7 different axles stiffness and the kart felt the same the whole time but the track was getting grippier so was it doing what it was supposed to or did the grip of the track have no real effect on âreleaseâ with the axle having no real effect either.
Iâve been wanting to test different stiffness seats all year but no one would just give me a tillet or jecko soft seat (what is wrong with people )
Iâd like to hear comments on why laydown enduro karts have no visible nor feelable (I know thatâs not a word) lift but seem to handle just fine. I assume that the inside rear gets light but again it canât be seen or felt.
Thoughts??
Put an enduro kart on a sprint track and I think youâd find that it wouldnât feel like it handled as well anymore. Road racing doesnât require nearly the amount of rotation you see on a typical sprint track. Road racing also typically runs a harder tire, so the karts arenât penalized as much for dragging the inside rear wheel.
A kart that isnât lifting enough or at all actually feels great. Itâs a classic issue we run into all the time⌠Driver says, âthe kart feels great, itâs just slow.â Thatâs because the kart is just flat stuck to the track. You have all the grip in the world; thereâs no sliding, nothing that feels particularly wrong with the handling. But the kart is slow because both rear tires are binding up off the corner.
Narrow track width promotes the load transfer.
Larger radius bends reduce the need for excessive caster\jack and lift.
Narrower tires on the rear (from what Iâve seen in most cases) which seem to âreleaseâ better.
Iâve driven a short circuit kart on a long circuit. They are too pointy. I suggest the corners are a large enough radius and that driving it you tend to lower your speed and power through them and that drifting the kart is faster then lifting a wheel.
I have to completely agree that a long wheelbase, narrow track enduro would be horrible on a sprint track. Your comment about the harder tire (necessary due to length of races) is a factor as well.
There are a few road racing tracks that have at least one corner that requires big time rotation for example Grattan Raceway but they seem to work just fine.
James, think about this, I agree that the narrow track promotes transfer BUT the lower center of mass likely negates much of that.
Most classes do indeed run a narrow tire, sometimes silly looking narrow but my twin engine ride uses the same sizes that you would run on a shifter.
Al, after 50 years of experience with enduro karts I have never ever witnessed nor felt the inside rear lift even a little bit. So I donât think that itâs just some kind of idea.
I think there is jacking going on in an enduro but no visible lift. Not enough caster and it will push, that was my experience many years ago building enduro karts.
Technically speaking, youâre just looking for less adhesion on the inside wheel, because it needs to slip, because of our solid axle.
You can achieve that two ways, decrease the adhesion by decreasing the force on the inside wheel (lift), which can vary from a foot off the ground to enough for the tire to slip but not lift, or you can slide the rear.
Additionally if there is any caster, then the inside wheel is being lifted by some degree (its physics!) when you turn the wheel.
Very useful, as is reading through the rest of this thread - itâs amazing what the internet provides with a few seconds of googling
Iâm enjoying browsing these forums and finding some âoldâ threads⌠apologies for bumping them up.
Just a bit of story-time here rather than anything super insightful⌠hopefully someone enjoys the read. ;).
Because most of my kart racing was done on a low budget, I rarely did much axle-swapping so theyâve largely remained a mystery to me. There are however a few stand-out days I remember.
One of the most vivid memories I have was in a Rotax Senior race event. We were struggling massively with the kart bogging down/getting stuck on slow corner exits after a few laps. Weâd be ok for the first handful of laps (so qualifying was ok) but then it was like a switch turned on at around lap 4 and Iâd lose 4-5 tenths. It wasnât a gradual change from lap to lap⌠more like the kart saying âhaha itâs lap 8 BAM no more slow corner exit speed for you sucker!â
We had originally first gone softer on the axle, and that didnât seem to make any difference, so we decided to try harder⌠and the kart got stuck ~ 4 laps later into the session.
Went even harder for the pre-final, and it took another ~4 laps before it got properly stuck.
For the 25 lap final we even found a rear bar to throw on the back of the kart, and that got us to lap ~20 before it got stuck.
Edit: Itâs entirely possible that some of the axles were actually a different wall thickness on that day - not just different âstiffness.â
For whatever reason back then the general consensus seemed to be that you need to go âsofterâ at the back of the kart to free up the kart⌠which is why we first went for a softer axle initially. Now that I understand the significance of chassis stiffness, particularly the relative stiffness front to back and how it relates to load transfer⌠it makes sense.
That day was definitely enough to convince me that different axles isnât just marketing - although Iâd definitely love to head out and test more, and I always keep reading more (such as this thread).
Another experience I had with âstiffnessâ was not with the axles, but with the frame.
I was testing two BRM frames. This was a blind test - the BRM guys didnât tell us what to expect, just to test the two.
One was painted black, the other one red.
I donât remember much about the red one other than it was maybe too planted for a low-grip test day⌠but the black one I still have a vivid recollection of driving it through a medium-speed corner and thinking âwhat the hell thatâs differentâ. It felt like it was wobbling/wallowing through the corner. I think my general âexpertâ feedback on it was that it felt âweird.â
The only difference between the two frames besides the color, was in the steel used. The black one was âcheap steel.â I donât remember the exact difference in pricing, but it was in the region of 6eur/kg for the cheap stuff, and 18eur/kg for the better feeling frame. IIRC they said that the supplier for the pricier stuff was the same that OTK used.
One final related story-timeâŚ
Remember those âillegalâ Intrepid frames that werenât very magnetic, and forced a re-write of the CIK regulations? We sent a section of a bent frame we had lying around to BRM/V.Orlandi to be analysed. Analysis came back as âstandard stainless steel.â
The mystery of the rear axle. One of my favorite subjects. I know they do make a big difference, tested back to back etc.
Here an interesting chart on how damping changes by type of steel and stress (axle bending load and deflection). Note how some materials the damping varies by 2x and others vary by almost 30, as a function of stress.
I loved this concept of ârate of liftâ. The concept and the video are really interesting.
I was trying to understand the whole explanation, but his Australian accent is a little bit difficult to me to understand since I am from Brazil and my English isnât up to scratch.
I watched the video thousand of times to try to overwrite what he says but some parts became really hard.
Below you can find what I´ve got from the video and what I couldn´t.
If any English native speaker could help me to feel the blanks I would be very grateful.
"Rate of lift is a term invented by _______ and myself to help the driver in ______ group to discuss the behavior of the go kart. I founded it really helpful term to use and I encourage you to use too if you find it works for you. Basically, rate of lift means the fast you lift the wheel, the fast you drop the wheel. So, here we come discussing rate of lift is helpful in karting. Basically because there are conditions where a fast rate of lift is an advantage and there are conditions where slow rate of lift is an advantage. Judging the conditions you are in and choosing the rate of lift suit those conditions is where the strength of this analysis comes from. When the track is slippery you need to get the inside rear wheel off the ground as quickly as possible in order to allow the nose of the kart to turn in to the apex. Not only that. But in the exit of the corner having additional rubber on the track in both front and rear wheel can actually be an advantage because the track is slippery. In this conditions, a fast rate to lift is to go. Lift the wheel quickly, then put the back down on the track and go.
*When the track is grippy the front tires can generate a lateral G forces required to start turning the kart before the rear wheel start to lift. So, this mechanical jacking effect becomes less and less important. Not only that, but as you come round to exit of the corner you need to keep inside rear wheel unloaded for as long as you physically can. In this conditions, a slow rate of lift is what you are after. Bring the wheel up slowly, not necessarily very high, let a _____ there for as long as possible, and when it does come back then to make the track do so very slowly and gently. * Rate of lift is obviously not something you can measure with the steel ruler. It is a relative term we use to compare the kart with those of other competitors around you. So, had you know your rate of lift is like, if kart comes on really quickly and goes off really quickly youâve got a fast rate of lift. If kart takes forever to come on youâve got a slow rate of lift. You can also look the type of the corners and whether you go strong or weak compared to the competition. If you are really strong in the tight corners and hops on the sweepers, youâve got a fast rate of lift. If there are hops in the tight stuff but the kart are _______ in sweepers, youâve get a very slow rate of lift. Hopefully Iâve convinced you the tuning your rate of lift is a powerful way of get the setup of your kart right. So, how we change the rate of lift? Well, by changing just about anything. Almost all the changes you make to a kart will affect the rate of lift. You often hear me refer to the rate of lift when we are discussing a particular setup change in the rest of this tech videos. Iâll give you a couple of examples to think about now though. Anything that increases your mechanical jacking effects so changes like more caster, more ________ , more Ackerman, or bolt on front hubs. They will all increase your rate of lift. The more mechanical jacking you put into the kart the faster your rate of lift will become. Changes at the rear of the kart that causes the outside rear tire byte harder also increase the rate of lift. Examples here might be running a narrower hear track or raising the seat height. Both of these changes will increase the rate of lift in the kart.
*I often say, karters get frustrated when they canât get their kart setup right. It particularly happens when you are in conditions they arenât familiar with or the track where they aren´t familiar with. When you are outside of your comfort zone, using rate of lift analysis tool can be a really helpful way of getting the kart setup right. * Watch your kart out on the track, compare where on the track or when in the session it is fast or slow compared to the other guys around you. Say what that says about your rate of lift. Is it your rate of lift too fast or too slow? Having made that decision, have a look at the kart setup and say what changes can be made to adjust that rate of lift to better suit the track.
I think you´ll find this to being extremely effective way of thinking about kart setup."
Some of you guys such as @Marin_Vujcich and @Thomas_Williams said that Youngâs modulus is quite the same in diferent kind of steels.
This video confirms and explains very well why? Mainly after minute 5.
But my question for you is: Youngâs modulus is measured by stretching the steel, right?
As in a rear axle the steel is submitted to flexion and torsion, so what is the relation between youngâs modulus and flexion/torsion? I mean, youngâs modulus has any link to flexibility?
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