Effect of Chassis Stiffness on Vehicle Handling | How Stiff? | Racecar Engineering

I go into the effect chassis stiffness has on vehicle handling. I've seen the question "How stiff does my chassis need to be?" multiple times, but never saw an answer, so I decided to do some research into it.

[@calebpier7401]

Real solid and in-depth video. A few things that could be improved. But overall you did an excellent job at providing new information that I have to seen on other videos on KZbin. If you are planning on making the car on your own or as a college project, i can't overstate how beneficial it is to read up on other teams published research. One of the best papers i have read on chassis stiffness for a fsae car stated there were no perspective improvement in vehicle handling after the chassis was 7 times stiffer than the suspension. Apart from that, if you are looking for a cheap way to test your various setups, i would look into assetto corsa. There you can change the car setting to see how much of a transient delay you or your teams driver can reliably handle without reducing lap times.

[@j.e.f.eGarage]

I graduated 11 years ago, so unfortunately, I don't have the schools money to support test lol 😅 Do you happen to remember what paper that was? The only ones I found were similar to what I did in excel, with no physical testing. Putting drivers in a sim could be beneficial for sure, the only downside is not knowing the model it is using. But, I assume it's not terrible and a lot cheaper than physical testing. Thanks for the input! I purely went into the vehicle itself and didn't talk about drivers even being able to exploit 100% of the vehicles performance.

[@manu217]

Could you reference me to the paper you mentioned?

[@pjay3028]

Very interesting, thanks. On the assumption that increased chassis stiffness will require more tubes and therefore greater weight, what is the minimum factor of chassis stiffness to suspension stiffness you would think is acceptable to achieve good handling and response whilst minimizing weight? Just a ball park suggestion would be appreciated. (I'm guessing around 10-15?) Thanks

[@j.e.f.eGarage]

The added weight is factored into the chassis natural frequency. Remember natural frequency is 1/2pi*(sqrt(torsional stiffness/rotational inertia)). The issue would be efficiency of the added tubes, as in the ratio of added stiffness per weight of the tubes. I've heard chassis stiffness should be 4-6 times stiffer than the suspension roll stiffness, but no data to back it up. That's what initially sent me down this rabbit hole haha. I really want to test at what theoretical rise time is above the drivers ability to exploit it.

[@pjay3028]

@j.e.f.eGarage thanks, that's extremely interesting. This is a really helpful topic, it's something I've often thought about but I don't have the skills or knowledge to do what you've done here so I really appreciate the video and your replies 👍👍

[@pjay3028]

In respect of road cars that have rubber bushings in the suspension giving significant compliance in the suspension mounts, does the chassis stiffness really have much impact? Thanks

[@j.e.f.eGarage]

Yes it does! Think of the bushings as just another spring in series. Just to put things into terms of this video, you could think of a squishy bushing reducing the suspension natural frequency, meaning a less stiff chassis could be used to meet a specific frequency factor. But, bushings are usually much stiffer than the suspension springs, and without modeling it, my hypothesis would be they'd have minimal impact (compared to suspension springs)

[@pjay3028]

@j.e.f.eGarage thanks. I can't quite get my head round it to be honest so sorry if this is a stupid question! Don't the bushings effectively mean the chassis is much less torsionally stiff than it would be without them? The bushings on the inside suspension mounts aren't in series with the road springs and must create a significant reduction in response times, don't they?

[@j.e.f.eGarage]

@@pjay3028 Not a stupid question! These systems are complex. It depends on where you apply load and how you're measuring the torsional stiffness. Bushings make the *system* less stiff, yes. Correct, they're not in series with the road springs, and do reduce response times. Look at my video on jacking force, and imagine a bushing inline with the suspension link. That bushing would change the rise time of the ride-height and normal-force-changes. Also, if you look purely at lateral force, that bushing would affect lateral acceleration rise time. With these mathematical models, I start simple (Like this one were I only have the chassis, suspension springs, and dampers), then at a later time you can add components such as bushings. Best advice I have for modeling, make it useful first, then add complexity

[@pjay3028]

@j.e.f.eGarage thanks very much 🙏 that's awesome

[@pedroarmando221]

Very nice and informative video! Loved it! How do you evaluate the YZ angular displacement? You evaluate it at the Roll Axis? I've always had that question.

[@j.e.f.eGarage]

Thank you! It was at the CG. But you bring up another topic, the effect of the true roll axis. The inertia would change as the roll axis changes, since you're effectively changing the radius of gyration. I went over true roll axis in my having force video, if you're interested.