It’s amazing how two different people’s concepts can be so different. So different in fact, I have to believe that one is correct and one is incorrect!
For instance, you say raising the inside left tire quicker, I say you’re raising the tire higher, the fact that you’re raising it in the same amount of time (not quicker, just higher) has nothing to do with it. The tire does not come down “quicker”, it comes down as you straighten out the steering. The fact that it comes down from a higher distance, what I think you’re calling “quicker”, has nothing to do with it. You want that tire to have minimal traction as long as your turning. How fast it travels that distance has nothing to do with anything. I might even argue that, because of weight transfer in the turn, the time it takes to travel that distance is longer, not shorter. It’s my contention, that the longer you can keep that wheel off the ground, or with minimal contact pressure, the faster the kart will be coming out of the corner.
Lots of questions but I’ll try and answer in order.
In 95% of situations where grip levels are normal, a kart needs the inside rear to be unloaded to accelerate without the inside tire scrubbing. If the inside rear wheel is loaded while trying to accelerate out of a corner, it will scrub and slow you down. Yes, you are getting more traction because you have two contact patches on the ground, but you are getting more scrub in the inside wheel as well. Traction or “forward-bite” is generally not an important thing in a kart, as we never really have enough power to spin the tires and power slide on exit. Unless it’s raining or in very low-grip situations. So it’s far more beneficial to get the kart unloaded and rotating without scrub.
Now, on very low-grip surfaces, this is less of a problem, because the increased amount of scrub from having both rear tires on the ground doesn’t hurt you as badly, and provides more traction without sapping as much power from the engine. @chris1388 can attest to this, as we worked on this last year with his very low-grip track and tires. He was constantly fighting oversteer, even with the ride height raised in the rear and with a narrower rear track. We could not get the kart to dig on the outside tire. So we went to low rear ride height to try and get both rear tires to set down earlier and provide more traction at exit. Because the track is very low grip and he’s running on hard tires, the increased scrub was barely noticeable but the kart was no longer oversteering. But keep in mind, this is a very unusual situation. Extreme conditions require out-of-the-box thinking sometimes. This is why it’s important for a driver to really feel what the kart is doing from the moment they turn the steering wheel, so you can tell if you need more or less inside rear wheel lift.
Your last question regarding scaling… If you raise the ride height on one end of the kart, the front-to-rear weight % does not change. That’s what I was referring to. The center-of-gravity changes, which is what is transferring more weight while cornering. But static weight distribution does not change in any measurable amount. So yes, the first option you mentioned. Some people have a theory that changing the height on one end will change the % of front-to-rear distribution, and add more load to one end of the go-kart during acceleration, but that’s not something I’ve seen in my experience.
I actually thought we were on the same page, so maybe I’m not coming across clearly in my reply.
Let’s look at it this way. If you put max caster in a kart, it will lift the inside rear wheel more effectively (quicker or harder) on turn-in. The weight-jacking process is more sensitive because the kingpin angle is greater. If that weight-jacking happens too quickly (or too high), you risk overloading the outside rear tire. That’s why a kart hops or flat-slides. A kart that has little caster or front-end geometry to jack the weight will load up more slowly and be able to carry the wheel around the corner further.
The chassis is a spring. If you load a spring up with more force, it will spring back harder. If you load it up with less force, it will spring back softer.
@alvinnunley, I believe @tjkoyen meant that, when we use rear axle with greater elasticity (spring effect), it will bring the inside rear tire quickly to the ground, no matter the height it was lifted.
If you lift the inside rear wheel higher in the same time period, it is lifting faster. When you lift the inside rear too fast, you risk overloading the outside tire.
I think what Al is saying is that rate-of-lift does not affect how the kart comes off the corner, and the only thing that matters is that the inside wheel is unloaded for a longer period of time, or that a higher inside rear wheel lift is more desirable in the sense that it keeps the inside rear off the ground longer.
Which is where we disagree I think. If that were the case, we would all be running max caster, narrow rear track width, and super stiff front bars all the time.
I got it and I agree we can make some setup changes to increase the rate of lift, such as stiffen the frame with removable bars, utilization of axles with different flexibility indexes, different front-end setups, etc. But I also agree with @alvinnunley when he says that the time to lift the inside rear wheel is more linked to the angle change speed in the steering wheel decided by the driver.
I mean, some setups make it easier or harder to lift, but who decides the speed of lift will be the driver by revolving the steering wheel faster or slower.
So, I believe there are two important variables in this conversation. One is the maximum height of the inside rear wheel and the second is the time needed to reach that height decided by the driver handling.
But you are right @tjkoyen when you say that, a greater rate of lift will make it lift quicker with the same amount of angle change in the steering wheel.
Since almost all kart handling topics eventually involve the rear axle “stiffness”, we need to have some basic understanding of how it flexes without that understanding, we probably can’t characterize how a kart works. (Knowing probably doesn’t really matter but it’s interesting)
So the question I have is: Does a “soft” axle deflect more than a “hard” axle under the same static load?
This is all very complicated and confusing. Don’t want to hijack, but topic relates to a specific question on my off-road kart. I currently have 14x5.71-6 on front and 16x8-7 on rear. I was given some 18x9.5-8’s and want to put on the rear to “beef it up” and add traction with a new larger engine. Is the extra 2" rake going to kill handling or make dangerous? I’m not racing, but my 9 yr old might as well be. Thanks.
What a great thread. I have a question that maybe you guys can help with. First, everything I’ve been taught and learned through experience is 100 percent aligned with what TJ has posted throughout this thread so far … Except for one thing.
I have always been under the impression that a soft axle will take away rear grip… essentially that It reduces roll resistance, reduces dynamic jacking effect (dynamic = jacking from roll moment created at CG from centripetal force generated by turning at speed, which is variable, vs strictly jacking from front end geometry which I call static jacking effect, which is not variable with speed or radius of corner, sans the direct relationship to how much the wheel is turned), causes the kart to lay more flat relatively and is somewhat similar in effect to lowering ride height. I saw tuners at Skusa who were applying TJ’s logic (to OTK karts) so clearly I’m the odd man out, but wondering if you all could help me understand how this works?
We don’t run OTK if that matters… we run all 30mm energys and also a 30/32 energy in X30. Maybe I misunderstood but if I had a hop and had to address with an axle only, I would soften. If I was binding and needed more lift I would harden up the axle (and or tighten 3rd bearing and or longer rear hubs). Do I have this backwards? If so, help me visualize how it really works.
I think one thing to keep in mind is that different karts have different materials or different designs that may influence how they flex, which will change how you tune with axles.
Growing up on a variety of other European karts, it was always “go softer on the axle to free the kart up”, but for the OTK kart it’s the opposite. My theory has always been that the OTK kart flexes differently because the tubing is different material, so the way it interacts with the axle is different.
This is something me and some friends have been discussing. Around here most OTK karts eventually break and need to be welded. They seem to be shorter life race bred machines compared to some of the other manufacturers.
Thanks TJ. I am glad to hear that OTK is opposite of many other Italian brands, that at least makes me feel like I wasn’t losing my mind… however, it gives me little faith that it’s accurately understood across the industry. I believe that two kart brands would react differently for sure, but i am not smart enough to envision how they would react opposite of each other. This is when my friends at the track would say “quit overthinking it and throw in a soft axle”. And if that doesn’t work try a hard axle”. Ha. And they would be right!. But I think most people on here strive to truly connect all the dots… I’ll try the axles but I will never quit overthinking it!!!
The more I think about this the more I don’t see the axle stiffness doing anything but effecting rate of rear weight transfer / lift and that of course directly relates to the front stiffness. Given no other change, it seems a softer axle would provide less rear roll resistance thus loading the outside rear slower than with a harder axle because the outside front would be taking lateral load quicker in response to being ‘less’ less resistant to the roll moment. I could see this adding rear grip on early entry due to two tires contacting longer but adding more potential binding to exit because setting down on two tires sooner. Essentially like adding more front bar. If you are already max front bar, then a softer axle would give you more adjustment I think. THIS IS NOT ADVICE BUT MY THOUGHTS TO SOLICIT COMMENTS… does anyone think that makes any sense? By this logic OTK would be right that a harder axle would ‘free’ up the kart. It seems it would lift earlier and set down later. And if you had oversteer issues, they would be more obvious on entry and exit as the kart would be unloaded earlier and later. If CG was too high or rear too narrow and you developed too much lift to the point of a hop (or close) then I think a soft axle could potentially help, but only because the extra deflection (debatable) would create a bit of negative camber that could fend off the hop. Of course the right adjustment would actually be to lower CG and or widen rear track. My head hurts! Ha. Please blow holes in this theory!!!
I think you are on the right track here. It definitely depends on the flex in the chassis. However, the flex I think is also in the waist not just the front end. From what I have gathered, OTK chassis’ have more flex in them than others. Comparably, the axle deflects more or less depending on the stiffness of the chassis. For OTK, hard axle stiffens the chassis and slows down inside wheel lift from flex. On a stiff chassis, a softer axle may soften the chassis and slow down the mechanical wheel lift. Both variations can achieve the same effect, but for different reasons.
I grew up around cars and auto racing. Many of them had torsion springs on the front suspension arms. I like to think of a kart chassis as a torsion spring. Some springs are soft and some are stiff. Depending on their spring rate, you can adjust other things around it to achieve the desired result.
The front bar can stiffen the front end (between the wheels), but little effect on the waist. So if you have maxed out the front bar on an OTK, then the next step would be a “harder” axle. On a stiffer chassis, if you have taken out the front bar, the next step may be a “softer” axle. Its a means to an end. Control rate of lift. Given the spring rate of the chassis, it may be necessary to approach it from a different angle.
Thanks Greg. You bring up a good point about the waist I didn’t consider. Given it’s not adjustable I sort of left it out, but it certainly is a 3rd element to consider. My aging well pickled melon thinks It would reduce roll resistance for the front but without mandating deflection about the stub axles (front bar, spindles, front of frame, etc) to do it, allowing one to still have a stiffer front geometry for responsiveness and accuracy while not dominating the rate of load transfer over the rear… due to the softness built into the waist And the overall ‘low’ roll resistance. Do I have that right? And me thinks this is especially soft AND springy on an OTK compared to most others. This is probably why you never see an OTK without a front bar! And that springiness, which seems to go away over time, may be getting the rear to lay down faster to allow a setup for a long lift but ‘springing’ it down when it starts to unload to manage oversteer on exit that so many karts get when they get too soft on the front and Also have an understeer condition and then the unloading causes the front grip to go way up but with still only 1 rear wheel on the ground. This is quite genius of OTK actually. - assuming this mess of thoughts I just had is even remotely correct!
Again, I appreciate the reply! Unfortunately I am not able to visualize going to harder axle in OTK when out of adjustability for front bar stiffness. I must be missing a key piece of understanding (which is not so uncommon for me ). If you were max front bar and you wanted even more front bar, I assume to increase front roll resistance compared to the rear to slow the rate of lift, why would one go to a harder axle in OTK? I’m guessing there is some effect here besides roll resistance that I am not considering… thanks SO much for your help and dialog. I’m learning and confirming a ton.
Edit: you said spring rate, not softness! I get it now. The variation in spring rate among different Mfg’s is a key attribute beyond just how ‘soft’ or ‘stiff’ the chassis is… ah ha moment for me. Getting it to deflect is one thing. The rate of change of force to further deflect is another! Now the torsion bar example also makes sense. Thx!!
I am just saying an axle change is a Big Change. It seems to be something you do when you run out of other, less dramatic adjustments. In my limited experience with axle change, I believe you may have to undo all the little changes prior to the axle change to pick up where those adjustments left off. Or maybe you throw another axle in because you know your settings cannot not compensate for the amount of change needed. There are others on here that are far more experienced and knowledgeable than I am when it comes to axle changes and brand variations.
The front bar is just another way to adjust the spring rate of the chassis. If you look at how a chassis twists under loads from front corner to opposite rear corner, it is basically a big spring. Front bars and axles can change their rate of flex. How they change it depends on the chassis design and materials. As I keep hearing, OTK are very flexible out of the box, but like a spring sprung over its limits their performance falls off very quickly compared to other brands that have less flex in them. It was probably not the best choice for me being a tall heavy guy, but hindsight is 20/20 right.
Ive notice alot of tony cadet karts running lower rode height in front. We run our middle front middle rear. Which works great for us in grand junction but we really struggled at action getting the kart to rotate. We had rear width past the end of axle. Quite a bit of negative camber(helped a little) and a super hard A axle
). If you were max front bar and you wanted even more front bar, I assume to increase front roll resistance compared to the rear to slow the rate of lift, why would one go to a harder axle in OTK? I’m guessing there is some effect here besides roll resistance that I am not considering… thanks SO much for your help and dialog. I’m learning and confirming a ton.