I keep reading and re-reading my Carroll Smith, Allan Staniforth, and Neil Roberts books.
There are two things that give me pause with regard to all of them.
One is that especially Smith and Staniforth's books were written before radial tires became widespread in racing.
The other is that it's easy to forget that they most deal with Real Race Cars (read: open-wheel or club racer types that never ferried anybody to work or the shops). Smith's Tune To Win even has one chapter singled out for "The Peculiar Case of the Large Sedan", by which he refers to any production-based car.
I know that most of what is in there still applies. Spring rates still have the same relative behavior, roll resistance balancing front to rear still has the same effect... OTOH, occasionally he'll give something like a specific recommendation on rate of camber gain or sway bar size, and I have to wonder which of these thing (any? all?) goes out the window with changes in tires over the years.
If nothing else, it seems likely that what bias-plys and radials want in terms of camber gain would be different given radials' increased need of negative camber and increased tolerance of static camber relative to a bias-ply (as I understand it).
So, for anybody not already put to sleep by rambling so far, how do you make sense of How Stuff Works when the most favored titles are starting to show their age?
This also reminds me that I still don't own Milliken, which IIRC is probably the oldest of the books mentioned, but is still held in high regard.
No, I don't have a specific question. I just wonder what others have made of this dilemma, whether it's a concern, and what other sources they might turn to...
The fact remains that the tires are their own independant spring system. One which attaining the exact technical specifications and dynamic behavior of from the manufacturer is probably NOT going to happen.
The tire IS the most misunderstood part of the system, also one which you are reduced to guesswork on. Yes, if you were part of a large manufacturer with lots of money you might be able to approach it in computational terms. Problem is, as I said, good luck getting, what is in most cases, protected information from the tire manufacturer.
When I was with FSAE, I saw some stuff on a rig that tested the tires in different slip angles, forces, force directions, and a number of other things. It was a multimillion dollar rig. Even if you GOT the data, you would have to figure out how to intrupret it. (think big engineering teams like F1 has)
Even then, it comes down to testing and improving, as all engineering does.
I do think there is room for a text addressing the unique problems placed by tires taking into account the large advances in construction. Compounds? Any text would probably need changes within 5 years of publishing.
(and I DO have a copy of Milliken, I need to read it again soon)
Actually, I have been looking into the possibility of getting/running an F500/600 car in a few years. Looking at the problems presented by those cars gets my noodle cooking. (car that pretty much rides on bumpstops and uses tires as a large part of the compliance)
I was next to a F600 guy in the paddock @ Summit a couple weeks ago. I really like the idea of this class - SCCA has so many classes based on stuff that hasn't existed for years, or that was supposed to be simple a long, long time ago, that things like FB (formula continentals w/ 1000cc bike engines) FF where the second F is Ford ~or~ Fit, F600 where old F500 2-strokes get 600cc bike motors - is the way forward.
I race a CSR powered by a Suzuki Hayabusa engine and can attest that bike engine cars are much, much fun.
The F600 finished in front of the FV/F5 bunch by about 15 seconds all weekend.
I've never noticed specific recommendations on camber or sway bar size. The books give you the tools you need to set up your own vehicle and how to determine what's working - and those haven't changed with tire technology.
In Racecar Engineering sometime within the past couple years, they had an article about a guy who had developed a relatively inexpensive device for testing the effective spring rate of a tire. Apparently sanctioning bodies FREAKED and worked to ban it nigh immediately.
A quick googling isn't finding anything, but I still have the magazine in the house somewhere. I'll see if I can find more info and post up.
I have been told that the higher performance you go in radials, the more the construction looks like bias ply. I don't know how true this is.
Keith Tanner wrote:
I've never noticed specific recommendations on camber or sway bar size. The books give you the tools you need to set up your own vehicle and how to determine what's working - and those haven't changed with tire technology.
They are few but extant, though in re-reading it sounds more like sanity checking (e.g. and paraphrasing: "people run too much springs; I've never needed a front rate over 1000 lb/in" or "I've never been able to use a sway bar over 1.06 inch, usually more like 0.88...". I suppose I'm really borrowing trouble to ask what to do about the 1% of these books that does recommend anything specific when as you say, most of it still applies as principles.
I guess one other worry I can cross off is the recommendation of about 1 degree of camber gain per inch of travel (also from the "sedan" chapter), which sounds IIRC, like how you described the Miata in another thread just earlier today?
That's roughly what the Miata has. It's not a straight 1:1 relationship, it's a curve (of course). That's just what I use as a rule of thumb for how much the alignment will change with a change in ride height. Seems to work fairly well, but I suspect the Miata's secret is well-located and stable roll centers.
Keith Tanner wrote:
...I suspect the Miata's secret is well-located and stable roll centers.
That's another thread I'll start when I have a bit more time!
I'm not convinced that "big spring, big bar" has many disadvantages. If the tire can kinda tolerate a 1000 lb/in rate from the bumpstop, why can't it tolerate a 1000 lb/in rate from the spring? Same goes for the "solid-axle conversion kit" type of swaybar.
I'm gonna be buying a set of springs and bars for the CRX pretty soon. I think I'll set the rates like it's a ground-effect aero car: 5 Hz spring rates, .25 deg/g.
Smith does discuss radial tires a bit in "Drive to Win", but its only a page or so. IIRC he discusses a difference in required camber gain and plain camber requirements.
Had to check that in the reading room this morning.
There are more modern books. But they aren't written as primers like the evergreen favorites of Smith and Staniforth.
chaparral wrote:
I'm not convinced that "big spring, big bar" has many disadvantages. If the tire can kinda tolerate a 1000 lb/in rate from the bumpstop, why can't it tolerate a 1000 lb/in rate from the spring? Same goes for the "solid-axle conversion kit" type of swaybar.
I'm gonna be buying a set of springs and bars for the CRX pretty soon. I think I'll set the rates like it's a ground-effect aero car: 5 Hz spring rates, .25 deg/g.
Why would you want a big bar with big springs? Stiff enough springs you should be able to get rid of the bars. The big disadvantage with stiff springs comes if the surface isn't perfectly smooth. It doesn't allow the suspension to do its work and keep the tire in contact with the surface.
