Hello, I need to stiffen up my rear suspension, as I have a big sub box with two heavy subs, and I put two amps, capacitor, and want to carry a few tools, and I always end up packing my car with crap I buy, or go to deliver motorcycle parts, or car parts...so my car squats a bit in back...what is the best way to get it a little stiffer? All I ever see anywhere is stock springs and lowering springs...not interested in lowering..car is low enough as it is...cant even get my floor jack under the front frame rail unless I drive up on a board on the one side I am going to jack up...I dont believe it is lowered...it is a 135,000 mile 03 sedan that was owned by an older person(not that I am young, but they were older than me)...thanks in advance!! oh yes I just put new struts all the way around-just stock replacements...so they have less than 5000 miles and work great..also new tires same time and are a touch larger than stock...

Higher spring rates and stiffer dampers of equal length to your current suspension sound like a good idea. You may need to find a similar sized, but much heavier car to get swap-able parts. I don't know what that specific vehicle is. You may have to do some trial and error. How much do you think all your stuff weighs? Have you asked a suspension shop?

No I havent asked anybody except right here..just thought of it late last night and figured I would post it, sure there are some g35 experts on here, that can tell me which springs to use..

Okay, I gotcha. Yeah, someone may notice this thread and have the knowledge you're looking for. I wasn't suggesting you redact the question here, just that you ask a suspension shop in addition to asking here. Like looking around in more than one place. Anyway, how much weight do you think you've added? 500 lbs? 800 lbs?

If you switch over to Bilstein struts it will stiffen it up. Not cheap, but it was worth it.