added weight, possible issues?
 

Hello

I'm a new RX-8 HP owner, and so far very pleased with this wonderful car:)
English is not my main language, so please bear with me

I am planning to build a large stereo-install (more than you need for daily drive, mostly for show and competition)

My concern is issues with added weight and how this will affect the car. What I am planning will probably add about 3-400lbs. (batteries,subs,amps,enclosures,sound deadning)

Obviously the performance will decline, wich is fine, I dont plan to race with it anyways.

Will I expirience serious issues with handeling? Will the mpg be far worse or just minor?

Also, would harder springs be a good idea? I have seen that if I sit down on the trunk, the car would sink down considerably, wich could cause issues with height(and looks)

I understand that I have to do some trade-offs here, but I dont want a car that is undrivable.

If you don't plan of racing the car, I don't see a problem. Just get some adjustable coilovers to level out the ride height and call it a day.

I dont think it will be a big issue but you may have issues with space in this car =/, Door panels are very thin. Goodluck though.

Ok. Thanks for quick feedbacks :)

I know the space is very limited. But compared to my to my last project (a toyota MR2) this is a big SUV :P

Some fiberglassing helps a lot with space, and it saves some weight too.

I'm not sure about coilovers, since there is some special law about US imported cars in my country. They cant be modified from their original state.
Is there any normal springs that is just harder/longer? If so, where can they be bought?

Id say putting in a huge stereo and changing the springs to accommodate the extra weight qualifies as "changing the original state" Might as well do it somewhat right.

The added weight would be at the back, i assume, because of the speakers and the amp. I think lower the front more than the back to have the level look and feeling of the ride...that is just a suggestion.

Yea, I guess you are right, but with normal springs it would not look as obvious. Some coilovers would indeed be the best solution. I might just take a chance on that.

Any suggestions where to buy a decent set that will ship internationally?

I allready have issues with hitting the ground (poor roads around here) So lowering the car more is not an option :)

If you really want to find out, find 2 fat guys to sit in the back of the car.

If most of that weight is going in the back of the car, it will increase oversteer. You may want to purchase some "street" lowering springs for the front only. That will both stiffen the front to reduce the oversteer, and lower the front to match the back end which will ride lower due to weight.

You should also check out the gross axle weight rating (GAWR) displayed on the sticker on the front edge of the driver side rear door. That is the maximum load on each axle that the car is designed to carry, including passengers, luggage, and thumping subwoofers.

Thanks for good advices. I think I will be within the legal specs, unless I got those two fat guys in the back seat whose mentioned earlyer :)

No, it will increase understeer!

then why did the 911 get the reputation of being very tail happy?

i dont know, maybe because the 911 was designed with extra weight in the rear. If you add weight to the rear you get more grip on the rear tires, you lighten the front and get less grip on the front tires. Less grip on the front tires equals understeer.

What an interesting way of looking at it....

Maybe because it has a lot more torque causeing the tires to break loose thus creating oversteer?

The amount of weight that you are going to add is no more than having one to two adult size passengers. If you only plan on driving normally and not racing and you rarely have passengers in the back seat then, you should be fine. If you plan to also carry passengers frequently, a suspension upgrade should be considered.

I'm rarely having passengers, but when I do I allready have issues with the back bottoming out at uneven roads.

If I sit down on the trunk opening (weiging about 200lbs), I have measures the car drops about 4cm (about 1,6 inches) If we are two sitting down it drops even more, about 2,5 inches.
So I think I will need a new suspension anyway.

Ah, the "road hugging weight" theory of handling. Adding weight to the rear does increase grip on the rear tires. However, it also increases the mass that the rear tires have to guide through the turn.

A tire with twice the weight on it produces less than twice the grip. But doubling the mass of the rear of the car does exactly double the force required of the rear tires to hold a given turn.

This is not really the place to discuss this, but feel free to try it out, far away from anything you can hit.

I have decided to get a set of coilovers, but I'm not sure wich one. I see that the majority of coilovers have a minimum lowering. I want to mantain stock height (or atleast not lowering much), and possibly need heigtening at the back end to compensate for the added weight.

Does anyone have a suggestion for wich set of coilovers I should buy? As mentioned, I want comfort more than performance, but still want some that handles well.

I see that tein has some coilovers that have the possibility for adding height, but theese are kinda expensive. Is this the price i should expect to pay for some overall good quality coilovers? Remember this is mainly for street use, daily driver. Not looking for track usage.

I got my coilovers (bought some BC BR coilovers) and is in the process of installing them.

As I understand, the height is adjusted by adjusting the lower adjustment nut and moving the entire dampener body up and down. The upper is the spring preload adjustment.

I am trying to get the car close to stock height, but I'm unsure how high i can adjust the dampener body. If I adjust it too high I will run out of threads. How far down the threaded socket does it need to be to ensure it is firmly attatched?

I see that usually the preload should only be tightened a bit, but I wonder if with my added weight I should add a bit more preload to compensate. This will also mean that I dont need the dampner body to be adjusted so high.

Hope this is explained clear enough, english is not my first language.