NOR-CAL General Chat.

[Thizzelle]

just to clear it up you youngsters
Theory = a system of ideas intended to explain something. so yes it is a theory even though it is proven, as you can see it's very vague, it means too many things at once.

[Wh33lhop]

Sears Point

idk what org is putting it on, usually they will have helmets to loan out at the event

i have a shitty old hand me down beat up helmet you can use if there are no loaners and you want to pick it up. i'm in mountain view

[Wh33lhop]

just to clear it up you youngsters
Theory = a system of ideas intended to explain something. so yes it is a theory even though it is proven, as you can see it's very vague, it means too many things at once.

I have a theory that you are a douche

[Bimmerman325i]

Wouldn't the pivot point of the rear trailing arms and the force applied by the weight of the car, plus resistance of the spring bring both torque and torsion into play here?

Touche, makes sense about the law, not a theory.

If you were modeling suspension articulation under load, yes.

Motion ratio does not depend on springs, it is measured with the springs removed and car in the air. You measure the distance between the spring perches when the wheel is more or less where it is when the car is on the ground (i.e., use a jack to simulate ride height). Then move the jack up or down a small amount of measured distance, then measure the change in distance between the spring perches. Divide distance change in spring perch by distance changed at hub, and you have your motion ratio.

Springs and dampers and all determine how much the suspension will articulate with a vertical disturbance. They don't change the motion ratio, or the motion ratio curve (e30 rear suspension being special and all).

[Bimmerman325i]

Not sure...so many to choose from...

Why Rs vs street tires? For the M5?

Sears Point

Which group are you going with?

[mbonanni]

If you were modeling suspension articulation under load, yes.

Motion ratio does not depend on springs, it is measured with the springs removed and car in the air. You measure the distance between the spring perches when the wheel is more or less where it is when the car is on the ground (i.e., use a jack to simulate ride height). Then move the jack up or down a small amount of measured distance, then measure the change in distance between the spring perches. Divide distance change in spring perch by distance changed at hub, and you have your motion ratio.

Springs and dampers and all determine how much the suspension will articulate with a vertical disturbance. They don't change the motion ratio, or the motion ratio curve (e30 rear suspension being special and all).

I'm not going to argue anymore because my knowledge is limited to one year of AP Physics in high school..

Buuutt I would say motion ratio does depend on the spring, when under load... To my understanding we were talking about when the car is under load, hence why spring rates, camber, etc where also taken into play.



Wh33lhop has me crackin up.

[YosemiteSam]

idk what org is putting it on, usually they will have helmets to loan out at the event

i have a shitty old hand me down beat up helmet you can use if there are no loaners and you want to pick it up. i'm in mountain view

It's with Trackmasters. BlackbirdM3 told me about it. I asked him and he told me I'd need to source one. I'd appreciate it a lot, thanks for offering. On the website the organizer says that helmets need to be SA2005 certified. I just want to make sure that the helmet is certified to that so I'm not SOL on Saturday.

[Wh33lhop]

I'm not going to argue anymore because my knowledge is limited to one year of AP Physics in high school..

Buuutt I would say motion ratio does depend on the spring, when under load... To my understanding we were talking about when the car is under load, hence why spring rates, camber, etc where also taken into play.

Basically you two are kind of getting caught up in technicalities

What he is saying is that you MEASURE motion ratio based upon geometry (in this case, leverage) which torque can be closely related to, and the spring DOES put a torque on the control arm... but you don't measure motion ratios using any sort of torque or force. Just a ratio of distance displaced. So it is just geometry.

That said, when you do actually have a spring in there, it does put a torque on the trailing arm, and that can help you understand why it is less effective.

[Wh33lhop]

It's with Trackmasters. BlackbirdM3 told me about it. I asked him and he told me I'd need to source one. I'd appreciate it a lot, thanks for offering. On the website the organizer says that helmets need to be SA2005 certified. I just want to make sure that the helmet is certified to that so I'm not SOL on Saturday.

I use it for autox. It's an SA, and IIRC it's still valid so that means it's '05 but I will double check when I get home.

Let me know when you want to pick it up. I'll be around Palo Alto/Mountain View most of the week.

[mbonanni]

I was never talking about motion ratios, which is where I think we both got off track..

[PorscheH6]

Why Rs vs street tires? For the M5?

Not for DD, just for auto-x and track use. Not a lot of choice w/ stock staggered sizes though, might have to go w/ a square setup.

[Bimmerman325i]

I'm not going to argue anymore because my knowledge is limited to one year of AP Physics in high school..

Buuutt I would say motion ratio does depend on the spring, when under load... To my understanding we were talking about when the car is under load, hence why spring rates, camber, etc where also taken into play.



Wh33lhop has me crackin up.

No, motion ratio under load will be the same. All the motion ratio is is the proportion between wheel movement and spring perch movement as a result of a constrained linkage. Adding springs and shocks in does not change the motion ratio, as that is a function of how the trailing arm (e30 case) moves on its own. The trailing arm sweeps the same path regardless of if it has a spring or not, and it is this path that defines the motion ratio.

Think about it. The rear trailing arm is located by four points: the inner/outer subframe mounts, the lower shock bolt, and the upper shock bolt. The trailing arm therefore has a very rigidly defined path that it can move through. At every point along this path you can define the motion ratio as I've done so above, and it will never change regardless of what spring rate you choose. Springs will just require more force before movement occurs. Does that make sense?

[Wh33lhop]

Not for DD, just for auto-x and track use. Not a lot of choice w/ stock staggered sizes though, might have to go w/ a square setup.

It's hip to be square

unless you like understeer

[YosemiteSam]

I use it for autox. It's an SA, and IIRC it's still valid so that means it's '05 but I will double check when I get home.

Let me know when you want to pick it up. I'll be around Palo Alto/Mountain View most of the week.

Cool, thanks. I'll PM you so we can work out when I can pick it up.

[Ian Bowers]

Understeer is where it's at. Makes all the girlies scream.