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Everyone has their own approach, mine is reduce weight as much as possible and account for weight imbalance with suspension tuning. 10lbs less is 10 less lbs the motor has to try and push, the brakes have to stop and the shocks have to dampen.
If you have to add weight, add it near the polar center. Dont increase MOI by adding weight further back to try and fix weight balance. I know it sounds good to have the rear loaded harder to lift the front but that really doesnt do what you think it does. All that gets you is less force on the front tires but the same amount of mass that needs to shift laterally for angular position change.
So yes, move battery off the front, but dont move it behind rear axle. Keep it inside the axle if possible.
Since were posting pics and talking batteries and weight I'll join in. Personally Im on the camp of pull whatever weight you can, but also within reason and take priority as to where the weight resides. Also depends on if I see the expense as necessary or not. In the case of the battery I said, well I have to buy a new one so I mind as well get something that is nice and light. On the flipside something like the BR mustache bar is good bang for the buck weight wise but its in one of the least describable spots so I havent bothered.
Now, back to batteries. I seemed to have missed the bulk of this thread but Im shocked to see you guys having issues with the Shorai battery. Perhaps I've been lucky but oh well rather be lucky than good. I've had my Shorai since 2013 and its still working great. Car was my DD up until 2017 so perhaps the car not sitting for long periods of time helped my case? But since then the car has sat for what seems like forever after the recent engine build and I purchased the Shorai charger and kept it on that for a year straight. Went to use the battery again and it worked mint and is still trucking along to this day.
So yes, move battery off the front, but dont move it behind rear axle. Keep it inside the axle if possible.
Interesting input Dallas. If Im understanding you correctly what youre saying is that if you put the car on scales with the battery as far back as possible the F/R balance would mathematically be superior but in reality, forget the math and get the weight as low and close to the center as possible?
Interesting input Dallas. If Im understanding you correctly what youre saying is that if you put the car on scales with the battery as far back as possible the F/R balance would mathematically be superior but in reality, forget the math and get the weight as low and close to the center as possible?
Yes. Think of the extreme case, put the battery on a rigid post 20 ft behind the axle. That's going to take even more weight off the front. Front still has to move its same amount of mass around the pivot of basically the rear axle. Now you just have less load on the front axle to do that work.
Its a similar thing in how if you add a rear wing, the aero load and drag can work to by leverage lift the front. If you had a scale under the tires, you'd think you were lighter. But still the same finite mass to move just less grip now to do it.
Last edited by Dallas J; Jan 10, 2019 at 01:01 PM.
If you have to add weight, add it near the polar center. Dont increase MOI by adding weight further back to try and fix weight balance. I know it sounds good to have the rear loaded harder to lift the front but that really doesnt do what you think it does. All that gets you is less force on the front tires but the same amount of mass that needs to shift laterally for angular position change.
So yes, move battery off the front, but dont move it behind rear axle. Keep it inside the axle if possible.
So, everyone should put their ACD pumps that are mounted behind the rear axle back up from where Mitsubishi put it?
Everyone has their own approach, mine is reduce weight as much as possible and account for weight imbalance with suspension tuning. 10lbs less is 10 less lbs the motor has to try and push, the brakes have to stop and the shocks have to dampen.
I'll just turn the boost up 2psi... lol
I have a lot places to lose weight on the car before I choose to fight with a small battery and the constant issues they seem to present with not starting the car in less than ideal conditions.
So, everyone should put their ACD pumps that are mounted behind the rear axle back up from where Mitsubishi put it?
Technically, would be better to mount it in front of the axle but perhaps behind the driver. Obviously thats not super practical so of course have to take that into account. I decided not to move mine cause I use the car to hold tires/tools and rear seat area or trunk but full. So 2.8lbs of Lithium up front works perfect.
That's fine for a racecar, but I drive my car- on trips, to places its really cold, and to places it's really hot, sometimes remote places where there are no services. And I don't want to deal with the small battery BS. And to keep what little trunk space we have more useable, behind the drive rear tire in the trunk seemed like the best spot. I don't want it in the car because I occasionally have passengers, and I've also seen optimas vent before, so in the passenger compartment is completely out for that reason. And my car corner balances really nicely, so I'm happy with it.
I'm not questioning your reasoning, if my car saw any remote amount of normal street use I'd probably use a larger battery too. But alas, track car = remove all the weights (within budget)
That's fine for a racecar, but I drive my car- on trips, to places its really cold, and to places it's really hot, sometimes remote places where there are no services. And I don't want to deal with the small battery BS. And to keep what little trunk space we have more useable, behind the drive rear tire in the trunk seemed like the best spot. I don't want it in the car because I occasionally have passengers, and I've also seen optimas vent before, so in the passenger compartment is completely out for that reason. And my car corner balances really nicely, so I'm happy with it.
The only parts Austin and I were disagreeing with was the part where people seem to think adding weight behind the axle will unload the front and make the car turn better. Its just a common misunderstanding. Functionally, definitely do what you gotta do. No qualms there!
That's fine for a racecar, but I drive my car- on trips, to places its really cold, and to places it's really hot, sometimes remote places where there are no services. And I don't want to deal with the small battery BS. And to keep what little trunk space we have more useable, behind the drive rear tire in the trunk seemed like the best spot. I don't want it in the car because I occasionally have passengers, and I've also seen optimas vent before, so in the passenger compartment is completely out for that reason. And my car corner balances really nicely, so I'm happy with it.
I used a normal large optima, placed horizontally in the spare tire recess (no spares on eudm e9)... and that worked flawlessly trough cold winters and cold summers.. A more track friendly solution might be in the trunk, right behind the passenger space, and use the smaller optima..
Having said that, there is a point in having the lowest moment of polar inertia and for that reason a lot of race cars, rally cars especially, will tolerate even 60/40 weight distribution just to keep MOI low..
What's funny is that my battery did better as a DD then it did sitting. I never tested parasitic drain but I've seen a few cases that evos for whatever reason seem to kill batteries that sit for extended periods of time. A few years back I had surgery on my hand and my car sat in the garage for about 2 weeks. When I went to start the car the battery was drained so we can assume the car has something like a 100miliamp draw which is excessively high. I had to get to work so I jumped it and went on my merry way. Its been 3 years since then and battery has still been working fine.
Like I said I now keep it on a maintainer but I have yet to fully kill the battery. I was also successful starting my car in 0 degree weather after sitting outside all day at work running on e85. All in all for a 5# battery I've had great luck with it and didnt feel the need to go big battery or relocate to trunk.
I did however move my ACD to my trunk, mainly to keep it out of the elements bc I already seized one. Was happy to pull the weight out off the front but perhaps backseat area might have been preferred...Oh well at least its tucked away. My accusump however is located in back seat area so I guess that was good placement but was merely put there so I can easily reach the ball valve from my seat.
I would certainly caveat my post on weight position to be, I would rather have weight behind the rear axle than in front of the front axle, but if possible get it all inside the axles.
If we think about how a car turns, it pivots around roughly the center of the rear axle. If we want to make the weight a small of an impact as possible, it would be centered there and as low as possible. Obviously you cant cause there's a funny thing called the differential in the way. But Zack did it right by cutting the fuel tank in half and putting the ~300lbs of ballast next to it.
The other method of a car turning is back end rotating, which then it pivots around I think a virtual point that intersects two lines orthogonal to the tires traveling direction. Which in any case is forward of the rear axle. So more rear mass will make the pendulum of a car swing that much harder (think Porsche).
everything on this car's set up is ultimately gonna be a compromise between how the car is designed and between how much money, time, resources, and how far you're willing to go.
Jan 10, 2019, 12:44 PM
