Chassis Stiffening importance...?

[Norm Peterson]

don't be shy, this isn't a vendor thread.

How about the idea that cars having some claim to being sporty end up with rear sta-bars simply because the car mfr has learned that its customers expect to see one. So they put one there, but make it thin and ineffective. But the expected "look" is there, and because the average buyer only understands "it's there" or "it's missing" it's all good.

Remember, I'm talking about OEMs here. That's what they're doing to take advantage of the average customer not having an engineering outlook on things.


Norm

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[shogun32]

Remember, I'm talking about OEMs here. That's what they're doing to take advantage of the average customer not having an engineering outlook on things.

You can't possibly be suggesting Marketing is overruling Engineering in a shallow and crass bid to appeal to the ignorant masses with no domain knowledge.

 

[Norm Peterson]

You can't possibly be suggesting Marketing is overruling Engineering in a shallow and crass bid to appeal to the ignorant masses with no domain knowledge.

Not at all [/sarcasm]

I'm just the messenger from somebody who has inside knowledge to the people here who don't.


Norm

 

[TeeLew]

How about the idea that cars having some claim to being sporty end up with rear sta-bars simply because the car mfr has learned that its customers expect to see one. So they put one there, but make it thin and ineffective.

That's the same reason as some race cars.

 

[Norm Peterson]

That's the same reason as some race cars.

Real race cars could well be tuning the LLT balance close enough to where 15 - 30 lb/in could matter. I know of people actively looking for 18mm rear bars for S197 Mustangs when 20mm was more common. Others looking for a 20mm to drop down to from something thicker. This is on a forum pretty much dedicated to running on road courses.


Norm

 

[TeeLew]

I'm as guilty as anyone. I pulled my 24mm RARB because I lacked rear grip and was able to find a smaller (20mm) bar off an earlier V6 car. I may very well be better off to lose the bar altogether and get the balance a different way. My previous attempt at unhooking it was good for grip, but bad for transitional response. I've made enough changes that this might no longer be the case.

Once you're 'close' on car balance, it's much more of an exercise in satisfying driver preferences rather than the lap time optimization by tiny roll couple nudges one way or another.

 

[Grintch]

Real race cars could well be tuning the LLT balance close enough to where 15 - 30 lb/in could matter. I know of people actively looking for 18mm rear bars for S197 Mustangs when 20mm was more common. Others looking for a 20mm to drop down to from something thicker. This is on a forum pretty much dedicated to running on road courses.


Norm

Right. Adjusting anti-roll bars is a lot quicker and easier than having to change springs to adjust the balance. And adjusting the rear tends to be quicker and easier than the front. Making rear anti roll bars very handy for a race car, even if small.

While race car roll stiffness is always stiffer than a street car. I would bet the typical proportion of roll stiffness that comes from the springs verses anti roll bar is biased more toward the springs with race cars. Especially as aero is added. So comparing the size their anti-roll bars is not very useful. Plus the mountings, and specific geometry can make big differences in the effective stiffness.

Speaking of comparing the size of stuff, I think some people like to compare the size of their mod list to show how good their car is. Just because you have more mods doesn't make it better, especially as your goals/applications change. And a lot of the "must have" mods are anything but.

 

[Norm Peterson]

While race car roll stiffness is always stiffer than a street car. I would bet the typical proportion of roll stiffness that comes from the springs verses anti roll bar is biased more toward the springs with race cars. Especially as aero is added.

This ^^^

Especially the concept of looking at how roll stiffness divides up between the springs and the bars. I think I've only seen brief mention of it once in any of the softcover books (one of Don Alexander's, ca. 1991).


Norm

 

[TeeLew]

It's heavily dependent on the type of car. GT cars tend to run stiffer bars, because it's more of an advantage to run softer spring rates for mechanical grip. Open wheel & prototype cars can often find lap time by better controlling the aerodynamic platform of the car (particularly front ride height) at the expense of mechanical grip.

It's not terribly uncommon to find an IndyCar or similar running with both anti-roll bars removed.

 

[Grintch]

It's heavily dependent on the type of car. GT cars tend to run stiffer bars, because it's more of an advantage to run softer spring rates for mechanical grip. Open wheel & prototype cars can often find lap time by better controlling the aerodynamic platform of the car (particularly front ride height) at the expense of mechanical grip.

It's not terribly uncommon to find an IndyCar or similar running with both anti-roll bars removed.

"It's not terribly uncommon to find an IndyCar or similar running with both anti-roll bars removed." Says who? Rain is the only time I disconnect the antiroll bars. And I only disconnect the rear.

The first statement is somewhat true, but because open wheel cars and prototypes run more downforce, and more downforce requires stiffer springs if you don't want to bottom out the car. The mechanical grip impacts of springs vs anti-roll bar are similar, the biggest difference being that anti-roll bars impact the ride less (which is why a stiffer bar approach is better for street cars).

 

[TeeLew]

Says me.

 

[TeeLew]

No one of consequence.

There's little use in arguing. Whether you choose to believe me is up to you.

Grintch already explained the logic. If the springs are stiff enough to account for the aero, then additional roll-stiffness, at the expense of independence of wheel motion, might be unwanted (especially on a street circuit).

 

[Grintch]

Oddly enough he got the logic backwards. On a street circuit (or the street), you want less spring in favor of more ARB (better ride, important on bumpy street circuits). And race cars pretty much always want to run ARBs (for quick adjustability, especially something like a IndyCar, which has cockpit adjustable ARBs).

Says who?
Race car owner
Engineer
Race car driver
Student of race car design and tuning

Not sure how we got to this discussion, from "How important is chassis stiffining?".

 

[shogun32]

If the springs are stiff enough to account for the aero, then additional roll-stiffness, at the expense of independence of wheel motion, might be unwanted (especially on a street circuit).

you know, i'm surprised race teams don't use dual-rate springs for just this reason. At sub-whatever MPH the car is riding high on 'soft' rate springs but once the downforce gets to a certain point (cubed of speed?) the suspension gets into the higher rates to better counteract .

 

[Grintch]

Variable rate springs are more complicated to tune, and harder to make. The ideal is having rising rate suspension geometry to sort of achieve the same thing (achivable with push rod, pull rod, or rocker arm suspension designs). Street cars almost always have falling rate geometry. Thus explaining why rising rate spring are so popular with them (to help compensate for the undesirable geometry). Plus race car springs are designed to be semi universal (but with LOTS of options for rate and length), while street car springs are very application specific, with only a few options.

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