C2 suspension analysis Mitchell "Racing By The Numbers"

[Bill H.]

Re: C2 suspension analysis Mitchell "Racing By The Numbers"

Question Jerry, Where does the oversteer happen? Corner entry, mid-corner or corner exit.
I assume the .003 was front bump steer.
What is the measurement on the rear from ride height to full bump?
You don't want the rears toeing out in bump.

[Jerry G.]

Re: C2 suspension analysis Mitchell "Racing By The Numbers"

It happens from apex through exit as power is applied. The car is square in that it has the same size tires front and back.( It's part of the rules.) I haven't retaken the rear numbers yet. They are alway bad its just how bad. The big deal is to NOT let it go into toe out under bump. So far thats about the best I've been able to do at the back.

[Duke W.]

Re: C2 suspension analysis Mitchell "Racing By The Numbers"

It may be that the rear tires don't have enough traction to deliver full power, so you just have simple power oversteer. That's why most race cars, even front engine with near 50-50 weight distribution have higher load capacity tires on the rear, but rules are rules, and all you can do to find balance is play around with tire pressures.

I recall from the SAE paper on the '63 Corvette (I'm pretty sure it's floating around the web somewhere.) that the rear toes in under jounce, and since the rear suspension has poor anti-squat geometry, applying power should increase rear toe, which helps stability.

The biggest problem I have with the C2/C3 rear suspension is trailing throttle oversteer due to the rear suspension's poor anti-squat geometry. If you are accelerating through a steady state corner or encounter a decreasing radius corner, both of which require throttle reduction, squat is reduced, which reduces toe-in, and the rear wants to go the opposite direction.

Duke

[Jerry G.]

Re: C2 suspension analysis Mitchell "Racing By The Numbers"

I would dearly love to see that SAE paper. They are really pretty good information sources. Do you recall the title?

[Duke W.]

Re: C2 suspension analysis Mitchell "Racing By The Numbers"

It turns out that what I have is an old, faded photocopy. I've probably had it for decades. The paper number is 630064. It's still available to SAE members as a 43MB download or mailed CD for about 15 bucks:

http://papers.sae.org/630064/

but an even better deal is that it appears to be a part of a book that includes a whole bunch of SAE papers on the Corvette than anyone can buy for 20 bucks:

http://books.sae.org/book-pt-118

The paper has graphs of toe and camber change for both front and rear suspensions. I suspect they are "theoretical" in the sense that they likely don't take into account bushing deflection.

It turns out that rear toe is fairly constant in jounce, but goes into increasing toe-out in rebound. Toe change is more dramatic at the front and the fast steering setting has more toe change than the standard steering ratio setup.

BTW the front/rear roll centers are 3.25/7.56" and the CG is 16.5" above the ground plane.

This paper is a very interesting explanation of the 1963 Corvette chassis and body technology that I'm sure would be of interest to all technically inclinded NCRS members.

It would be great if NCRS could cut a deal with SAE to make the book available to member via the NCRS Store.

Duke

[Jerry G.]

Re: C2 suspension analysis Mitchell "Racing By The Numbers"

It's on its way to Boulder...thank you

[Duke W.]

Re: C2 suspension analysis Mitchell "Racing By The Numbers"

Yeah, I just spent about and hour on the SAE website. When I realized that shipping cost of the book was half its price I decided to add a few other things to the order - a couple of other books and SAE papers on the Vega and LT1 engine and ended up putting about a 200 dollar dent in my credit card.

Non-members can order, but pay "list price", and you have to register a user ID and password on the site.

I reviewed all the various Corvette specific SAE papers, and most are in the PT-118 book.

I'll write a review on the book in a month or so, and I have a hunch it will be great!!!

Duke