cghstang
cghstang HalfDork
7/29/13 7:07 a.m.

Let's say that one wanted to maximize the rear weight bias of an NA or even NB Miata.

Without moving the engine back or doing any altered wheel base shenanigans, about how much rear weight bias is realistically achievable given the following:

OEM hardtop required

AC/PS/all power amenities/air bags/etc can go

radiator could be relocated to trunk

front end crash worthiness not a concern

minimal or no purely ballast weight added

still looks like a Miata (bumper cover/hood/fenders all present)

full oem fuel tank okay for weight calculations ('wet weight' with driver)

Could 45% f / 55% r be reasonably attained? Is 40/60 possible?

GameboyRMH
GameboyRMH UltimaDork
7/29/13 7:17 a.m.

I think you'd be lucky to hit 45/55. That would require moving ~120lbs from the front to the rear, so with the battery and radiator moved to the rear, and maybe some bodywork lightening up front, you might just hit it without adding ballast.

EvanB
EvanB PowerDork
7/29/13 8:00 a.m.

Battery is already in the rear.

iceracer
iceracer UberDork
7/29/13 8:21 a.m.

How about explaining why you want to do this .

GameboyRMH
GameboyRMH UltimaDork
7/29/13 8:23 a.m.
EvanB wrote: Battery is already in the rear.

D'oh, forgot...Only other thing you could move to the rear, if you're a real masochist, is the AC compressor - by getting an electric one.

GameboyRMH
GameboyRMH UltimaDork
7/29/13 8:23 a.m.
iceracer wrote: How about explaining why you want to do this .

In preparation for a front-heavy engine swap I'd guess.

v8exocet
v8exocet Reader
7/29/13 8:25 a.m.

well, you can drop 30ish lbs id say pulling all the AC, Airbag sensors, all the wiring you dont need, etc etc etc.

if you hack up the front like i did and make a new bash bar/rad hoop i dropped around 60 lbs and added 17. http://www.flickr.com/photos/yokotas13/7022600117/in/set-72157623946703386 http://www.flickr.com/photos/yokotas13/7014868037/in/set-72157623946703386 http://www.flickr.com/photos/yokotas13/6260684141/in/set-72157623946703386 but you can get away with just a bashbar and one or two more welded supports also FRP fenders and bumper saved around 10lbs over stock stuff and fasteners. FRP hood was a 2lb savings pull the gas tank, and throw a 20gal fuel cell in the trunk along with the rear radiator and without a DOUBT you will be where you want.

EvanB
EvanB PowerDork
7/29/13 8:26 a.m.
iceracer wrote: How about explaining why you want to do this .

Traction/better weight distribution for what the car is used for.

cghstang
cghstang HalfDork
7/29/13 8:26 a.m.

Iceracer,

http://www.youtube.com/watch?v=M3ot0JPj1_0

I would like to know if a rear weight bias can be achieved without extravagant effort. Think Stratos. 911. Lancia 037. MR-2. Renault Apine A110. There is a theme.

When you have the opportunity to accelerate from 5-30 mph on a loose surface more than once per run and every run counts, maximizing rear traction would be nice. And before Knurled gets here: it's not getting a solid axle swap!

iceracer
iceracer UberDork
7/29/13 8:44 a.m.

do you need the headlights ?
Pull the bumper cover and see what you can remove. keep tract of how much front weight you remove and add ballast to the rear.

v8exocet
v8exocet Reader
7/29/13 8:51 a.m.

headlights are heavy also, if you go with a fixed mount with stock headlights and eliminate the motors its like 5 lbs i think?

with the stuff i listed you can already get to 150lbs moved/removed

tpwalsh
tpwalsh Reader
7/29/13 9:29 a.m.

Do you have a minimum weight in mind? There's LOTS of stuff that you can remove or lighten up, but unless you start putting weight back IN, you're never going to get to 55% rear weight bias. My miata is about 1640lbs, and it's currently 52/48. I'm sure that I could get to a 55% Bias via adding in ballast but the car would have to weigh almost 2000lbs again. I think I've got another 30lbs I can take off the nose of the car if I really tried. (CF fenders, hood, lightweight clutch, etc), but that's still in the 1950 range.

Keith Tanner
Keith Tanner MegaDork
7/29/13 9:29 a.m.
cghstang wrote: I would like to know if a rear weight bias can be achieved without extravagant effort. Think Stratos. 911. Lancia 037. MR-2. Renault Apine A110. There is a theme.

Stratos: mid-engine
911: rear engine
Lancia 037: mid-engine
MR-2: mid-engine
A110: mid-engine

Yup, there's a theme all right.

If I was looking for maximum acceleration on gravel at the expense of all else, I'd set the car up with a tall ride height (high CG for high weight transfer), drag race style shock valving and an OS Giken differential. It is easier to pull weight off the front of the car than the rear which is good in this case, but I'd be more interested in overall weight loss than just trying to take it off the front.

cghstang
cghstang HalfDork
7/29/13 9:35 a.m.

In reply to Keith Tanner: I was aware of that theme as well

Also, none of those other marques support our activities to the extent that Mazda does.

Thanks for the input Keith and everyone else.

EvanB
EvanB PowerDork
7/29/13 9:38 a.m.

More info on the specific Miata:

No A/C components or P/S

All airbag system parts have been removed with the exception of the wiring behind the dash.

Most of the stock bumper support is intact.

EvanB
EvanB PowerDork
7/29/13 9:39 a.m.

In reply to Keith Tanner:

So what you are saying is we need to swap the Miata to a mid-engine?

v8exocet
v8exocet Reader
7/29/13 9:43 a.m.
tpwalsh wrote: Do you have a minimum weight in mind? There's LOTS of stuff that you can remove or lighten up, but unless you start putting weight back IN, you're never going to get to 55% rear weight bias. My miata is about 1640lbs, and it's currently 52/48. I'm sure that I could get to a 55% Bias via adding in ballast but the car would have to weigh almost 2000lbs again. I think I've got another 30lbs I can take off the nose of the car if I really tried. (CF fenders, hood, lightweight clutch, etc), but that's still in the 1950 range.

did you rear mount your radiator? that alone has to be 50-60 lbs all said and done

tpwalsh
tpwalsh Reader
7/29/13 9:46 a.m.

No, Not sure if it's legal for my class(Solo DP). I don't think it's worth 60lbs anyway. I'm running a stock radiator. I'd call it less than 30lbs with water, and it would require more weight for all the piping.

v8exocet
v8exocet Reader
7/29/13 9:52 a.m.

but WHERE the weight comes from is a huge diff. that plus removing the stock fuel tank and putting a fuel cell where the spare tire would be would make a HUGE weight change also

tpwalsh
tpwalsh Reader
7/29/13 10:25 a.m.

Not sure if you're talking to me, or the OP, but yes a fuel cell is on the list. Should drop 10-12lbs with that, but it would be from the rear of the car, where the OP wants weight ON the rear, and not the front. I'm looking at a 3G cell.

v8exocet
v8exocet Reader
7/29/13 12:21 p.m.

have you looked at the location of your gas tank? almost directly over/fwd of the rear axles. put a fuel cell BEHIND the axles that is larger and you not only added more weight but moved it further back thus increasing overall ratio.

tpwalsh
tpwalsh Reader
7/29/13 12:53 p.m.
v8exocet wrote: have you looked at the location of your gas tank? almost directly over/fwd of the rear axles. put a fuel cell BEHIND the axles that is larger and you not only added more weight but moved it further back thus increasing overall ratio.

True, though depending on the application, that might not be ideal. For autocross for instance, I'd much rather have the drop in rotational moment vs weight balance.

v8exocet
v8exocet Reader
7/29/13 1:23 p.m.

he isnt doing autocross lol.

for me. i put a 15 gal tank in the back mounted directly on the subframe (cant go any further back) and keep it totally full at all times haha

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