how much load transfers to one side under HARD cornering?

[NSX_GTR_LM]

I was just wondering the load transfer on a celica with hotchkis competition sways and Tein HA coilovers. The reason I ask is because the HA's have a 5 kg mm spring rate in the front, and it is more for dimensions in rubbing issues on the outside fender well and how much the car can safely be lowered without rubbing. Anybody know a way to calculate the load during cornering of say 1 G?

[Chui]

Unfortunately, I don't have nearly enough information to make an educated guess. Sorry.

[NSX_GTR_LM]

you bastard :D

You are the one i was hoping could give me an answer. I guess I will have to use the old guess and check, hehe. Thanx anyways chui.

[lost808]

Just a guess..mebbe half the car weight?? At 1G the human body weighs about 2x the normal weight right?? so instead of the usual 1/4 weight transfered to the corner...This is just a WAG(Wild Ass Guess)

[NSX_GTR_LM]

i dont think it can be that much. Imagine how much body roll you would get if that were the case. if 700 lbs transferred to the right front tire, thats about 325 Kg, which with the spring rate on the teins woul;d mean the car would dip 6.5 cm. That seems like alot to me. I could be wrong though.

[chris1zz]

i belive that you need to know the wheel rate and the suspention rate before you can figure out how much the spring compresses. or something like that. i got a good book on the subject, i'll get back to you on this.

[RedNOSceli]

1g would be= to 1X the earths pull, so 2g would be double

[NSX_GTR_LM]

I am talking about the vertical load on the springs. I am trying to figure out how much the fender will dip under excessive cornering.

[robertsp]

There are a lot of variables that fit into that equaiton. You have the spring rates of the tries. rims, springs, body flex, and how much body roll your car has.

[NSX_GTR_LM]

the body roll is what i am trying to calculate. Another major problem is i do not know the quantitative numbers on the hotchkis competition sways. I do know that HA's are 9 KG/mm rear, 7 KG/mm front.

[ap1f20c]

Hey cool thread, I missed this one first time around.

You can make some very basic assumptions and calculations.

Lateral weight transfer is a function of cornering force, track width and center of gravity height.

The equation is:

(Lateral accelertion x vehicle weight) x (Cg height/track width)

So, let's say you're capable of pulling 1 g in a particular corner. Your vehicle weighs 2700 lbs with you in it. Track width is 60" (I don't know exactly what it is) and Cg height is 24" (again a guess, but not unreasonable for a low car like the Celica).

This would give you:

(1)(2700)(24"/60") = 1080 lbs transferred.

If you assume that the side to side weight distribution is 50/50, you have a static weight distribution of 1350 lbs/side. So, at 1g you'll be transferring 80% of the weight from one side to the other side.

There are some other variables involved including body roll, etc., but they are an order of magnitude smaller than the primary forces I just described.

Now, if you're concerned about rubbing at the front, let's consider that. Your car normally carries about 60% of its weight at the front. That means that of the 1080 lbs transferred, 648 lbs will be transferred at the front - assuming the roll rates are matched front and rear. On a car like the Celica, I'm betting they are not. So a little less weight may be transferred. Let's say 600 lbs.

Now, you have 5 kg/mm spring rates up front. That's equivalent to 280 lbs/in. Next we need to know the wheel rate. This can be determined (approximately) be measuring the distance from the lower control arm inner link to the bushing where the strut bolts on, and then from that bushing to the wheel hub, the ratio of these distances gives you a good handle on calculating wheel rate. On Honda's, that ratio is about 1:1. That means if you move the wheel 1", the spring compresses 1/2". That means that it only takes 140 lbs of force to compress the spring that much. And when applied from the wheel, you have leverage ratio of 2:1, so the effective wheel rate is only 70 lbs/in.

But there is one more thing - the anti-sway bars! They act like a giant spring when cornering and will limit the body roll substantially. The equation for determining the effective spring rate of a solid sway bar of spring steel is:

K = 500,000D^4/(0.4244A^2B + 0.2264C^3)

A = Length of one sway bar arm (from the "straight" part of the bar to the link - the L part at the end of the bar)
B = Sway bar length
C = Length of other arm
D = Diameter of bar.

So, a 1" thick bar with 4" arms and a length of 36" would have a spring rate of:

K = 1930 lbs/in

However, the wheel rate contribution is somewhat less, again because the sway bar link is located inboard of the wheel hub. If it were located in the same location as we estimated for the strut bushing, it would have a wheel rate of 480 lbs/in.

Now, I happen to know that even Hotchkis' bars aren't that stiff (they use 1" hollow). Let's say that you've got a rate of about 400 lbs/in at the wheel for the sway bar. That plus the spring would give you a wheel rate of 470 lbs/in. So, in a 1g corner, you'd see the wheel move up 2.2".

This is all, of course, a very, very, very rough estimate based on a lot of assumptions. In reality, I bet the sway bar link is a little further in than the strut bushing. That would reduce the swaybar wheel rate contribution by up to 50%. If that were the case, you'd see wheel travel in a 1g corner go to 3" or more.

And finally, once you get too much travel, you hit the bump stops, which will raise your effective spring rate - a lot. I don't know how much travel the Celica strut has before it hits the bump stops, but its probably less than 4".

Wheew, hope that helped a little bit. Now go take some measurements on your suspension (control arms, sway bar lenght, etc.), call Hotchkiss and ask them for the dimensions on your sway bar (thickness, hollow/solid, etc.). Run some calcs and see what you come up with. Or, just go run the car in a hard corner and see what happens :-)

If anyone who designs suspensions for a living would comment, I know I'd appreciate it. Also, if I made any errors, please point them out (anyone) - I won't be offended.

SC

[autxr]

Just a note...

In a macpherson strut setup (like the celica), the wheel rate is basically equal to the spring rate.

Scott

[ap1f20c]

Indeed, strut suspensions usually have their pivot point closer to the hub. But how close? 80%, 90% of the control arm length?

I haven't been able to find any pictures to allow a reasonable estimate.

SC

[NSX_GTR_LM]

wow, thanx alot dude. This is great info. I really appreciate it.