What's the Best Placement for a Car Battery - Chassis or Axle?

[guitarrc6]

ok, i know about weight bias, and how its better to have a 50/50 weight distrabution on a car, for best handling in turns and junk. My question is, is it better to have unsprung weight or weight on teh chassis? This is mostly in regards to the battery, since its somewhat easy to move around and is a good amount of weight. I was wondering if it would be more beinficial to mouunt the battery to the back of the back axle, or just throw it in the trunk? If its better to mount it on the back of the axle, would the regular road vibration shorted the battery life substancially?

thanks, brian

 

[Cliff_J]

The more unsprung weight, the more work the shock absorbers must do. Also being unsprung means that the tire's workload is increased also as it will be the initial damper for this extra weight (instead of the suspension) for each and every bump on the road. Yes the battery life will also shorten, by how much depends on how well dampened everything is. Not a great idea.

50/50 isn't necessarily the only criteria. The height of the center of gravity and the polar moment of inertia (mid-engine pundits cheering) and a whole lot of vehicle dynamics play into this. Why else would the old 911 with its 40/60 weight distribution be such a force to reckon with even though its numbers seem poor on paper? Also why would open wheel racers use carefully placed ballast to tune their cars if 50/50 were the pinnacle?

Cliff

 

[guitarrc6]

i know that there is a lot more than just 50/50, but general rule of thumb is about 50/50, i mean i don't make cars for a living, and any car i would make would be street driven, so i don't need any balasts for better weight distrabution, i was just trying to find an easy way to get better preformance. I have another question, why would the tires have to do more work? the actual axles never touch the battery, so its not like you are adding weight directly to the wheel, and wouldn't any weight on the car effect the tires? how come unsprung weight would affect them but not sprung weight. Thanks for the help with the shocks, for that reason alone i don't think its worth it, i hadn't even thought about shocks and springs!

 

[Cliff_J]

Think of it this way. You have a couple of masses that are connected with a damping system, and one of those masses contacts an immovable object via another damping system. The second one I'm referring to is the tire and while it may be a secondary concern in most cases (except F1 where its the excuse for any victory/defeat) it is a factor.

So if you watch slow-motion video of any tire at work you'll see it flexing a little as it hits bumps and dips. The suspension system is also at work and helps bring this under control. But if the mass (and let's use lots of example) is moved from the suspended side to the non-suspended side the shocks are still doing their job (except their settings may be off) but now the tire is sharing more of this since its not separated from this additional mass by those shocks. In the end the tire supports the same average weight, but the in-motion numbers change.

How terribly important this is falls into another category except that those in pursuit of higher performance generally go for the least unsprung weight possible, whether they have good reason to do so or if they are simply being sheep. I do know that guys who try to build a dual duty strip/roadcourse f-body GM cars are very adamant that they do not like the Ford 9in rearend because they can feel the additional unsprung weight causing the back-end to step out on tight bumpy corners. I haven't amassed the budget to pursue such things yet, so I'm only repeating what I hear...

Cliff

 

[guitarrc6]

thanks, yeah i hurd that the nine inchers aren't as good ffor road courses. But people like them because they are strong. There is a company that makes dana 60s that are shaved down to save weight. I would probably pick something like that, or to smaller axles, and make it a four wheel drive car, but yea money is a problem