Raising and/or lowering the front end 2 – 3 mm and feeling the difference, … 1 mm change in angle well, … you’re a lot better driver than I ever was.
1° change in angle at 40 inches (wheelbase) equals .70 inches. How much are you raising and/or lowering the front of the kart? .1? That would be 1/7 of a degree.
Al, those are stub axle spacers, thicknesses, so the very front would a bit higher.
Not that good of a driver of but the steering effort was significantly lower. Maybe the inside rear lifted a bit more or earlier in the turn, that seems like it would reduce steering effort.
I’m not questioning your experience, or what you felt, but I have to believe that raising or lowering the front of the kart had anything to do with the easing of the steering. I could be wrong, you felt what you felt, I just find it hard to understand what forces could be at play with such a small change. By the way, how much did you raise or lower the front end?
Great topic - learning a lot and it has explained some of the tings I found when adjusting my old “CRG” shifter kart as a fairly tall and heavy driver. I’ll definitely try an shoot for that 40/60 weight split as it sounds like the troubles I had were from being too front heavy.
I have read and reread these posts and trying to wrap my head around the concepts mentioned. I understand having a higher rear ride height (high COG) helps with jacking but what happens after the inside wheel is done jacking and you are accelerating from the middle of the corner out. Does ride height change anything in this situation?
I’ve always gone with the idea that; the kart that can keep the pressure off the inside rear tire the longest (it doesn’t necessarily have to be no pressure)
it’s going to accelerate out of the corner the fastest.
It doesn’t necessarily have to be off the ground, but the pressure has to be as little as possible. Of course kart design has a lot to do with this. I think, the bigger the radius, the more important this is, most especially with a 2 cycle, because they reach peak torque and HP at a lower RPM (relative) than a 4 cycle.
2 Likes
The thing to remember regarding the weight jacking or “rate of lift” of the inside rear wheel, is always “what goes up, must come down”. A kart with a lot of jacking effect and a high rate of lift is going to lift the inside rear wheel up quickly with minimal input. This is good for turn-in, as it gives you a snappy response right away. But a kart that lifts quickly will also drop the inside rear quickly. This can hurt your exit speed and causing handling issues if the inside rear wheel sets down too soon.
In most conditions you are trying to get the inside to unload fast enough to get the kart to turn-in without understeer, but not abruptly, so it can carry the inside rear into the apex without overloading the outside tire or dropping the wheel too soon and bogging the engine down. It’s essentially the very fine balancing act that 90% of your tuning is focusing on nailing.
In extreme conditions like a rain race, you often want a lot of jacking for several reasons. There’s no grip available, so you need the kart to mechanically jack weight to turn since there are no forces coming from tire traction. By maxing out caster, narrowing the rear up, raising the seat etc., you are inducing lift very abruptly to get the kart to turn on entry. The knock-on effect of this is the kart will also set down the inside rear very quickly, providing better traction on corner exit and preventing wheel spin. That would be an example of how ride height or overall rate of lift can affect apex and exit.
I know Power Republic has a ride height video elaborating on their thoughts that ride height can affect how the kart gets traction and accelerates off the corner by changing the “squat” or weight balance, but I’m not sure I buy that theory. A lower rear ride height can add rear traction in the sense that the inside rear doesn’t unload as easily, and both tires are providing grip. Of course, if the rear isn’t unloaded at all, then the thing is going to scrub at apex. Plus, I’ve done the tests on the scales, and the weight balance doesn’t change when you alter ride height.
2 Likes
Guys, I love all your posts and opinions, but now I got confused. Let me explain why.
@alvinnunley you are saying “with less load to the inside rear tire after apex we get more traction”?
If I rephrased you correctly, it goes against my previous understanding. I thought two rear tires loaded give more traction than just one. Of course, that, when we are getting out of a corner we don’t want too load into the inside rear tire as it can generate understeering and you lose time with the fight between rear-end going straight and front-end trying to turn. But I’d like to understand better why acceleration is greater leaving the corner with inside rear tire unloaded. Unless you are talking about grippy tracks where we don’t want to drop too quickly. Is it the situation you were talking about?
It is the same question I got when I read @tjkoyen mentioning the above.
As I am used to slippery tracks, it could be the reason I couldn’t follow you. So, I am more familiar to the situation below:
The quote below is aligned to my understanding and linked to my previous comment about two tires generate more traction than just one.
But the quote below confused me again.
Are you saying that weight balance does not change from read-end to front-end (vice-versa) when you change ride height in just one end? Or you are saying that changing ride height in one end does not affect load transfer?
If you meant the first option, I believe you can’t see differences in the scales because the center of mass has marginal moves in the horizontal axle when you do small height changes in one of the ends.
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.
So, 2 different philosophies, which is correct?
2 Likes
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.
2 Likes
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.
Not exactly. I’m not talking about axles.
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.
2 Likes
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.
Lightheartedly… you just described KartKraft build 3. 
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.
Note: Will be putting new tires on the rims once decided.
1 Like
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.
Thanks all!
Some of this discussion I have been struggling with recently. So I’ll appreciate responses that should be rolling in.
1 Like