AMGkobez

Where are you guys moving the battery too? I was thinking the passenger side of but am not sure if the seat will get in the way. I don't usually run a passenger seat but every now and again my wife likes to ride along. I was thinking the spare tire area but that kinda seemed to be adding weight to the wrong place, any suggestions would be greatly appreciated.

dirty19

iTrader: (1)

Why do you want to relocate it?
If there is no real reason then leave it where it is.

Pompiuses

If weight distribution is a concern put it as far as you can in the rear right corner of the car.

Usually people put it in the spare tire area. I don't see why that would be so bad. Civics and FWDs in general are nose heavy, so getting the battery in the back of the car is a good thing.

JBrettHowell

http://www.pebblemotorsports.com/img...bble_Hatch.JPG

Although I will probably back this out and just put a lightweight battery as low as possible in the engine compartment at some point.

Voodooboy520

Behind the passenger seat - low, and keeps the PMOI down. Plus, you want all the right side weight you can get.

TunerN00b

I've never understood that line of thought. The front does all the work, why move weight/traction to the rear? With only 62% of the weight on the front tires, I think my Integra is too tail heavy.

Voodooboy520

The short version - You want 50/50 weight distribution.

The long version - The max force the tire can react (aka how much force it "outputs") is not linearly proportional at the vertical loads seen on a car at its limit. More simply, tire reaction force suffers from diminishing returns as you increase the vertical force. Thus, you want to keep the tires as evenly loaded as possible to maximize the (vertical force) : (output force) ratio.

Remember - Tires can only react to being pushed on, and by a limited quantity. Total cornering ability is limited by the tire that gives out first, so if you overload the front end of the car it will, in turn, understeer.

slammed_93_hatch

typically on a FWD car you want a Front to Rear weight distribution of 60% front and 40% rear.


I know my car isn't/wasn't to entirely happy with its 64% front and 36% rear, for me at least.

redciv4u

behind dash, in center!

mc-integra111

This is something I have always wondered about myself. I am not convinced either that putting as much weight in the rear is the "for sure in all circumstances" thing to do for front heavy front drivers. I would love to do a bunch of testing with setups and weight distribution and learn more about this, but I don't have the time or the budget (or for that matter the skill and consistency to create useful data).

AMGkobez

I am going to move it for more weight distribution, with the car totally gutted all the weight seems to be in the front of the vehicle. Ideally I need to get the car corner balanced, and go from there.

Linh.

Isnt it not safe to keep the battery inside the cabin?

AMGkobez

I think it has to be covered and its recommended for it to be a variable lead acid (vrla) battery.

dirty19

iTrader: (1)

What race series are you wanting to run in?
I have a gutted EG, so does Slammed 93 hatch, and I left mine under the hood.
For my class i have to have an OE size and weight battery anyway.

AMGkobez

I race EP in auto-x

drewbie

Braile makes a regular battery that weighs 6lbs. why not run that and save the trouble of relocating?

civicgsr

I've been eyeballing the braile batteries as well. I though the 6lb battery was really tiny?

I agree whole heartedly that you need to keep the battery inbetween the front and rear wheels. Having extra weight in the back increases the polar moment which would cause for more tail happy situations during oversteer situations. I experimented with the concept and after removing everything from the back of my hatch along with the stereo bits, I noticed that the car was much more predictable while autocrossing. I was able to call on oversteer when I wanted it and if I lost traction it was easier to regain control.

Hemix

+1

You may be getting a better "weight distribution" but the larger polar moment will make it harder for the car to rotate and make it harder to correct when it does rotate. Put it as close to the firewall and as low as possible, IMHO...

drewbie

i have a friend who races an EVO VIII with the braile 6lb

sackdz

Awesome!!

beanbag

I dunno, I think the polar moment argument is overrated. larger PMOI tends to make a car more stable. The MR2 is a low PMOI car and it spins out kind of easily. What you wrote above is true, however, the extra weight hanging off the back of the car also improves rotation, since it is pulling the back outwards and pushing the front inwards.

The MOI is mr^2
The additional torque during cornering from the weight hanging off the back is mr*(lateral accel)
The resistance to rotation is I dw/dt or mr^2 dw/dt (w is angular velocity in radians)

So just plugging in some basic numbers like r = 2 meters behind cg, and for cornering at 0.5g, you can figure out the point at which the two torques become equal

rm*0.5g = mr^2*dw/dt

This comes out to dw/dt=140 degrees/sec^2 of rotational acceleration.

What this means is that unless you can basically pull a u-turn in about two seconds, the added benefits of having the weight hanging further backwards outweighs the additional PMOI.

There's probably additional factors I didn't take into account, but I hope I made my point.
In practice, I've located my battery in the spare tire well mainly for the lower CG, and because it doesn't take up any additional passenger space in the car.


update: while taking a nap, I thought of one of these "other factors". Namely, that by shifting weight backwards, you take weight off the front wheels. However, because of the sub-linear grip vs weight of tires, in general there is a net gain on cornering grip by doing so. Therefore, this, that, and the other thing having to do with the blah blah blah means that moving the weight wayyyyy backwards isn't as good as I initially said. But still better than not.

civicgsr

I think you are missing something. First, the MR2 has most of it's weight in the back. That weight contributes to the inertia that helps it spin out.

Think about this. A light weight flywheel. You can increase angular rotation and decrease it quickly (rev up and down). Add 10 lbs to the outside edge and with the same angular effort, the flywheel with rev up and down more slowly. Take the same 10 lbs and move it to the center. It will not have much of an impact as compared to the un-weighted flywheel.

Back to your MR2. I really need a diagram for this Picture this: MR2 enterin a turn. The natural tendency of an object is to go straight or follow the tangent from the circle. Your MR2's mass is in the back. Your force diagram will show that the mass in the back of the MR2 is going to want to go straight while the rest of the car is trying to turn ->oversteer.

Bottom line, when I had 70 lbs worth of stereo in my hatch...which sat behind the rear axle, when I lost control, it was much harder to regain it. I did have a harder time initiating rotation which would support your argument about a larger polor moment increasing stability. With the stereo out (and out for good) I could initiate rotation much more easily, but then it was also much easier to stop that rotation.

Make sense? I really need a drawing for all of that

beanbag

The distinction I wasn't too clear on is the difference between steady state turning vs. initial turn-in and trying to stop once you are already spinning out. If you already have so much oversteer as to spin out, then reducing the pmoi is good. By removing your stereo, you also probably reduced steady state oversteer.

The porsche is a car that has a lot of weight in the back, and probably a larger (relative) pmoi than a mr2. Thus it would tend to have more steady state oversteer. I have seen videos where a porsche is minding it's own business going thru a wide sweeper, and then suddenly it spins out.

In my case, I don't make such rapid transitions such that the PMOI is a big deal. I could use a bit less steady state (mid corner) understeer. Maybe it is different for you...

Anyway, the stuff you wrote makes perfect sense. I was just trying to say that minimizing pmoi is not necessarily the only goal when shifting weight around.

Egezzy

iTrader: (2)

no need. do the ol rock on a string visualization. a simple but great tool for inertia.

Hemix

Just to add to that, the MR2's engine placement is more to get the weight towards the center of the car, not the rear. Porsche for instance puts the engine in the actual rear of the car which makes it hard to get a Porsche to rotate and when it does, it really starts rotating. That is why a lot of people like the handling characteristics of the Cayman over the Carrera.