Open Source Racecar

Post here information about your own engineering projects, including but not limited to building your own car or designing a virtual car through CAD.
Tim.Wright
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Joined: Fri Feb 13, 2009 5:29 am

Re: Open Source Racecar

Post by Tim.Wright » Sat Nov 09, 2019 1:54 pm

maunde wrote:
Sat Nov 09, 2019 1:12 pm
Hey Tim, that all seems to make sense to me, however, given that you will already be having a large proportion of understeer due to your COG, would you not want to reduce this at low speeds?

All valid points as far as road-car practicality from what I understand.

May I ask what your experience has been like working in Europe and moving there from Aussie?
The rearward CG creates (dynamic) oversteer tendencies not understeer. With such a large rearward bias, the compromise is always between dynamic stability and mid-corner understeer. In this battle stability always wins because it's simply more important (for a human driver at least. Robot drivers are another story) and that's why rear-heavy cars often have a reputation for mid corner understeer. Not because of the weight distribution directly, but because of the actions you need to take to keep the car dynamically stable (roll balance, roll steer, camber recovery) all induce steady state understeer.

Additionally, a reaward weight bias will also introduce delays into the reponse of the lateral acceleration and yawrate build-up which drivers interpretate in many different ways but understeer is one of them. My guess is that this is the reason why front tyres appear to be typically "oversized" for vehicles with large rear weight distributions - to increase front tyre cornering stiffness to try to mitigate these delays.

Regarding moving from Aus - it was pretty much the only option if I wanted to work in the automotive industry. I had zero contacts in Europe so it was a slow process to build up experience and contacts but it all seems to have worked out ok for me.
Not the engineer at Force India

maunde
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Joined: Sat Nov 02, 2019 11:36 am

Re: Open Source Racecar

Post by maunde » Sat Nov 09, 2019 9:41 pm

Tim.Wright wrote:
Sat Nov 09, 2019 1:54 pm
maunde wrote:
Sat Nov 09, 2019 1:12 pm
Hey Tim, that all seems to make sense to me, however, given that you will already be having a large proportion of understeer due to your COG, would you not want to reduce this at low speeds?

All valid points as far as road-car practicality from what I understand.

May I ask what your experience has been like working in Europe and moving there from Aussie?
The rearward CG creates (dynamic) oversteer tendencies not understeer. With such a large rearward bias, the compromise is always between dynamic stability and mid-corner understeer. In this battle stability always wins because it's simply more important (for a human driver at least. Robot drivers are another story) and that's why rear-heavy cars often have a reputation for mid corner understeer. Not because of the weight distribution directly, but because of the actions you need to take to keep the car dynamically stable (roll balance, roll steer, camber recovery) all induce steady state understeer.

Additionally, a reaward weight bias will also introduce delays into the reponse of the lateral acceleration and yawrate build-up which drivers interpretate in many different ways but understeer is one of them. My guess is that this is the reason why front tyres appear to be typically "oversized" for vehicles with large rear weight distributions - to increase front tyre cornering stiffness to try to mitigate these delays.

Regarding moving from Aus - it was pretty much the only option if I wanted to work in the automotive industry. I had zero contacts in Europe so it was a slow process to build up experience and contacts but it all seems to have worked out ok for me.
Thank you for enlightening me in regards to oversteer vs understeer, I was always of the impression that more highly loaded rear tyres tends to result in more understeer and vice-versa. Would you suggest any good resources for further learning VD?

Cheers!
A kiwi looking to fly like McLaren.

Tim.Wright
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Joined: Fri Feb 13, 2009 5:29 am

Re: Open Source Racecar

Post by Tim.Wright » Sat Nov 09, 2019 9:45 pm

maunde wrote:
Sat Nov 09, 2019 9:41 pm
Would you suggest any good resources for further learning VD?
Milliken or Guiggiani are the best by a long way.

Avoid any motorsport based stuff if you want to learn VD stuff properly.
Not the engineer at Force India