so many smart minds here, I’m curious what the house view is on what the consequence would be to how a kart would handle if you were able to take 5-10lbs off the nose of a kart?
I’ve seen some guys add weights up between the feet right on the nose, but then some other old experienced racers have said that putting weight way up front and out at the ends of the kart there is terrible because it makes the kart turn in more slowly/worse from worsened polar moment of inertia (having weight of kart farther away from the center of the kart making it harder/slower to rotate)
if one took 5-10lbs of weight off the nose of the kart would it make it handle better or worse? would the kart rotate better or would the weight on the nose cause the front tires to “dig” in better at the apex?
I was thinking about playing around with this but I’m sure some of you black belt drivers have already done this with best spots to put weight
and if the polar inertia of a kart matters why does everyone start by putting weights on the back of the seat and NOT in the crotch area of the seat where the weight would be exactly in the center?
The kart needs weight in the seat to flex the chassis and unload the inside rear wheel. That is priority when placing weight.
It’s impossible to say definitively that removing or adding weight to the nose will make the kart better or worse. It all depends on your situation. It will change the handling for sure. By how much and to what affect will depend completely on your class, tires, track, engine, driving style, and the rest of your setup. You cannot tune a kart in a vacuum, you can only fix the problems that exist in the current moment.
Taking weight off the nose will make the front lighter. Whether that contributes to under or oversteer would be impossible to say unless you were doing back-to-back testing. And even then, you have to drill down to figure out WHY the kart is reacting a certain way. Too much nose weight could make the kart oversteer because the force would be all on the front tires and the rear tires would be light. Too much nose weight could also make the front understeer, because you’re overworking the front tires immediately.
Very common to run 5-10 pounds on the front between the driver’s feet. Get the kart on the scales, set the seat to factory specs, and see where the weight distribution is. Aim for 41-43% front percentage. See how it feels in that range, and tweak from there. But get too far out of that range and the kart’s balance will start to fall apart and it’ll become un-tunable.
I’ve done big swings on weight distribution, like 2-4% changes. Loading up the front with weight makes the front feel heavier, but takes away how much pendulum weight you have in the seat working to flex the kart. It’s a give and take.
maybe let me ask it this way with a hypothetical example:
if you took two karts, both with identical front/rear weight % on the scales with 41-43% weight on the front
but then one kart got there with a 5lb weight right out at the nose between the feet, and the other kart got there with a +20lb weight in the crotch/front of the seat but also had lighter stuff out at the nose of the kart so that the weight was identical but more of the total kart weight was right in the middle of the kart
how do you think the two karts would handle differently?
I race in a class where you can run 375lbs rear brake only or 395lbs with front brakes, and when I took the -20lbs weight penalty off and went to rear brake only I was shocked at how much better the kart felt in the turns. Got me to thinking about polar inertia, as I’ve become more experienced driver I’m really surprised how much I can now feel even 5lb differences in how the kart handles
Polar inertia is definitely a factor, but it goes hand in hand with the other factors @tjkoyen mentions.
Going along with this example, it is always preferred to have the weight placed as close to the center of mass as possible. 5lbs on the nose isn’t the end of the world, but if you can place that ballast on the seat, and still maintain the proper seat position that is ideal.
Smaller drivers may run out of real estate on the seat, in which case you may need to get creative and mount ballast on the nose, or in other places.
20lbs is significant difference in total weight, and will absolutely affect the handling capabilities of the chassis. I’ll add that front brakes also affect the balance of the chassis due to the difference in braking force, and resulting weight transfer.
In summary, I usually try to follow these rules of thumb:
Mount the seat per the manufacturer’s recommendation (usually they have a range based on driver size)
Mount all ballast on the seat, starting at the crotch area, then front of seat, then rear of seat. You can then move weights to a more rearward position if you need a slight adjustment (and vice versa).
Mount ballast as low as possible. For smaller drivers you may need to raise to a higher position.
what is the impact to how a kart drivers or feels from moving the vertical center of gravity lower? I always understood that more weight higher helped with lateral bite at the apex (like raising kart ride height) so if you could magically take 5lbs off someone’s head and move it to their crotch (hahaha) how do you think that would change how a kart handles or performs?
Higher CoG = more side bite. Kart digs and wants to tip up on the sidewall more. Not always desirable, but sometimes very desirable.
I’m 5’7" and almost always run with my ride height up in the rear to get a higher CoG. For me changing the ride height from neutral to high in the rear makes the kart feel completely different. Almost like you bolted on softer tires. Tall guys don’t want that because the kart will totally over-flex and transfer too much.
interesting TJ - and you run the front ride height in the middle?
we run an 80 shifter class on evinco blue tires so is a fairly hectic little kart with decent power on not super soft tires, and our local tracks are pretty slippery (and bumpy) track surface most of the time
previously i was running higher ride height on an OTK chassis but it made it feel pretty sketchy in the braking zones but I feel like I need to experiment with ride height again a bit more next season
Experiment with it. We always are working between two major variables; keeping the inside rear unloaded and keeping the tire within its traction limit.
So depending on where you are in that window, you might find the adjustment has differing results. If you are already breaking traction on the outside tire, raising the rear ride height is only going to make that worse, since you’re just trying to put even more load on it. Sometimes, in certain conditions, the only way to get rear traction is to lower the rear ride height and get both rear tires working sooner in the corner.
The real trick comes in the driver feeling out where they are in that tuning based on how the kart is reacting.
Its an interesting concept but I think its effect is taken a bit out of proportion. If it was that important, we would have manufacturers trying to make bodywork and nerf bars ultra lightweight, but instead the aero advantage is more important (although thats widely debated too ). In theory, yes, you want all weight to be as close to the center of mass as possible and if you can get the kart to scale properly with all the weight on the seat, that’s ideal. But, mounting the seat in the correct spot and getting it to scale properly is more important, so if 5-10 lbs needs to be on the front, so be it.
). In theory, yes, you want all weight to be as close to the center of mass as possible and if you can get the kart to scale properly with all the weight on the seat, that’s ideal. But, mounting the seat in the correct spot and getting it to scale properly is more important, so if 5-10 lbs needs to be on the front, so be it.