Physics Analysis

[Nathan Dunnett]

So, I've done quite a few laps the last couple of weeks getting a good feel for the sim and learning it's quirks, and I think now I am familiar enough to give a rundown of the physical models and post my thoughts.

Tyres
The tyre model is probably both most important and hardest to get right, making it the most critical component of any automotive sim. IMO the tyre model for KRP is pretty good but it isn't perfect. My primary issue is that there is way too much sidewall deformation before the contact patch breaks into slip, this can be demonstrated by driving a kart to half speed, then locking the brakes and flicking the kart sideways to get to 90 degrees slip angle and wait for the kart to slide to a stop. Once stopped you'll notice the kart slingshot back the other direction when the spring rate of the sidewall exceeds the lateral force. IMO the sidewall stiffness is both too low and too linear. At low lateral force it needs to be a bit stiffer, and at high lateral force it needs to be much, much stiffer. It also feels like the tyres are too load sensitive where they make lots of grip at high loads, but that might just be a by-product of the soft sidewalls.

Chassis
I'm not sure how complex the chassis flex modelling is, but it feels like the chassis are too stiff in the waist which doesn't allow enough twist in the chassis. This makes the rate of lift too fast which makes it much harder to carry the inside rear wheel unless you increase the mechanical jack a lot (more caster, ackermann, stiff front end, etc.) and use a really soft rear end to get off the corner (40mm soft or 30mm hard axle, loose side pods and rear bar).

Axles
I'm not sure how complex the axle modelling is either, but it feels as though they are only corner springs with spring rate being the only difference. If true, this is a critical flaw IMO as axles are very important to the way a kart handles. The axle makes a big difference in the way the rear end of the chassis flexes. Each different axle design IRL is separated by both the cross section and the grade of steel. It is generally not fully understood, but the different axle grades tend to have different damping properties and resonant frequencies which has a big effect the way they behave on track. Generally hard axles are made of high grade steel and soft axles are made of low grade steel, soft and hard axles with the same cross section feel very different even though according to Young's modulus they should have the same stiffness. Adjusting the hub size would also be good.

I have some ideas for the setup page but I'll post them another day in the suggestions forum.

[EVO]

Great write up. Knowledgeable analysis from karters  like  Nat here will really help development. plus its free.

[Leonardo Ratafia]

very nice sort of review,  thanks for the writing and for helping us non karters with setups and tips for making this great sim enjoyable.
i bet it's very hard to make a karting sim and i think piboso nailed so far with a great sim in terms of physics and tracks.
i dont think iracing would make a better kart if that's what they've in mind other than a good multiplayer and i've tried other mods for rfactor and they don´t come close to the real thing as KRP.

[maxrod]

when I first see this post I thought here we go someone going on about a load of s##t but as I started to read it it was some great information you have analysed this sim and give some good information thanks.

[Nathan Dunnett]

Thanks guys, any thoughts from anyone else?