Help with the 30% Rule

[0meridian]

I am planning my conversion and wanted some input on the so called 30% rule.
I want to have a 24 kwa ( or higher ) 144 v pack that weighs just over 1000 # but this gives me between 34% and 37% of total vehicle weight. This happens to be from slightly under to 180 # over Gross Vehicle Weight depending on battery selection..
I am not afraid of exceeding the weight since brakes and suspension will be upgraded.
However I am worried about a possible degradation of performance.
Any thoughts from those who have been down this road before would be greatly appreciated.
Thanks,
Justin

[madderscience]

My battery-weight to curb-weight ratio is 37%.    I have 21 Trojan T-105s stuffed in a 1985 toyota MR2.    The car's original curb weight was about 2300lbs.  It weighs about 3400lbs now.

Handling is still decent but I'm sure it is a lot less nimble than it originally was.

Near as I can figure, THE MORE BATTERIES THE MERRIER.   You just need to do what you have already stated:  Ensure the chassis, brakes and suspension are up to the challenge.   Its all easier to do with a truck, but you will get more range out of a small car.

I figure my car is about maxed out even with suspension and brake mods.  I could get one more battery up front but the rear is at the maximum safe weight without significant chassis reinforcement.    (In terms of pure volume, I could  get 24 T-105s in the car if I sacrificed most of the remaining trunk space)

As for range, well last night in sub-40 degree weather (without battery heating)  I drove 42 miles:   8 miles to downtown seattle, 12 miles home including a detour with two stops in (very hilly) west seattle, then home to charge from 120V for 1h:45m (which put back about 7 miles of range) then another 22 miles to north seattle and back.   It was getting low (probably 65-70% DOD), but still safe when I got back home.   These batteries are about 15 months old and have about 3500 miles on them.

Good Luck. 

[0meridian]

Thank you Brian.
I have been wrestling with this 30% thing like it's some kind of sound barrier.
See you tuesday I hope.

[madderscience]

I think the 30% rule came about for a couple of reasons:

First, That 30% will get most people enough range that the car is useful.    (30% battery-to-curb weight with lead acid will give about 40 miles of range under good conditions)

Second, it does start getting more difficult to cram in the batteries (for cars anyway) once you start getting past that ratio.   I could have fit 15 T-105 batteries into my car with zero chassis modifications but to get up to 21 (and still have a trunk) I had to modify bulkheads, redesign and move engine mount brackets, and cut big holes in things and do a lot of welding to make everything fit.   

So its a level of effort versus performance thing and 30% is at least the low side of the sweet spot.

Brian