Weight distribution

[electrabishi]

Alright race car fans. Got a question to run buy you guys that have been doing this a while. So the Pinto weighed 3200 lbs with the lead acid batteries. The 850 lbs of batteries was distributed evenly, half in front of the rear axle in the back seat area and half behind the axle in the old exploding gas tank area

So now I have some new fangled lithium-ion batteries that will weigh a total of ~316 lbs. The question that I'm trying to get a first impressions answer to is where do I put the new batteries. The car was launching pretty failrly balanced with moderate front end lift (didn't need wheelie bars yet). I don't want to have to split the pack if the answer is to make the distribution the same and put half the weight in the front box and half in the back box. My first inclination is to put them all in the back box to keep the weight more on the rear axle. However I don't want to transfer too much weight back on the launch if I can hook with that much torque but with less weight.

So my second thought would be put them in the front box and that enough weight would transfer back on launch to keep the Hoosiers planted.

Whatdya think? First impression answers
I'm going to have to find my old drawings of the chassis set up so I can see some angles. But a lot of my stuff is still packed up from the move.

Mike

[candyman]

Put the weight in the back...............Weight behind the axel will act as "leveraged" weight and impose more down force on the suspension. If the car for some reason wants to do crazy wheel stands because of this change, I would sugguest one of two options. Limit front wheel travel via shock adjustment (rate of rise) or by installing limiters. Poor man's solution, take a fat girl for a ride where the back seat used to be. Both will have the same effect. You should be around .5 quicker due to weight loss alone. Benifits other than weight loss with the new fangled batterys? More HP?

[electrabishi]

Thats what the roll bars are for is to keep the fat girls out of the car ;-) It might not be as cheap either if you have to feed her. Maybe just fill the front box with jelley donuts or something instead ;D

But I hear ya. As the car gets faster too it will hard for me to meet the containment regs with batteries in the front tray. If they are in the back I can close the trunk area back off easily enough.

Think I might have to go in with some wheelie bars. Keep meaning to get some 90/10 shocks up front.

But as to the additional power, after we switch to parallel wiring on the motors about half track it necessarily limits my power from the controller to 1/2. Since these new batteries won't sag down near as much I can keep adequate voltage up on the motors while they are in series to pull all the way down the track. So the additional power will from just short of the 1/8th to the end will be 2x what we were seeing. I'm hoping another 0.5 on that as well.

But its the weight placement right now that I'm worried about . Don't know if I can get it balanced well enough not to need wheelie bars

Mike

[White Lightning]

Hi Ya Mike! Welcome back to the forum....missed ya input.
A good rule of thumb is 49% weight on the front wheels and 51% on the rear when you got a leaf setup like yours. Where ever that puts the batteries.......

[White Lightning]

Mar 7, 2010 13:38:18 GMT -9 candyman said:

Put the weight in the back...............Weight behind the axel will act as "leveraged" weight and impose more down force on the suspension. If the car for some reason wants to do crazy wheel stands because of this change, I would sugguest one of two options. Limit front wheel travel via shock adjustment (rate of rise) or by installing limiters. Poor man's solution, take a fat girl for a ride where the back seat used to be. Both will have the same effect. You should be around .5 quicker due to weight loss alone. Benifits other than weight loss with the new fangled batterys? More HP?

What Candyman is talking about here is called "Moment of inertia", the farther UP and or BEHIND the axle it is in the chassis the more the leverage effect changes as it rotates up and back (transfers weight faster and sometimes isn't controlable). Look at the 60's drag cars....tall cars with engines placed high in the chassis. When they launched the moment of inertia moved weight rearward and placed it on those hard azz bias ply tires trying to make them stick. But also look at how out of control they were, in part because or their high roll center. With your suspension limitations my sugestion would be to keep the weight as low in the chassis as possible and strive for the 49% front and 51% rear weight bias.
Rob