I was wondering if there is an aftermarket product that would give me the same effect as putting 250lbs of sand in the trunk of my car but without the weight.

 

try air bags or LCAs

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ICON Motorsports
1st & 3rd

 

Just lug the Ole' Girly around

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60 Ranchero - Project ( Money Hole )
85 Sport Coupe LG4 - Daily Driver

Livin' the Stereotype

 

Traction bars might help. When the wheels spin, the bars lift the rear end of the body up, which in effect pushes the wheels into the ground.

(I'm assuming that's what you're going for.)

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89 iroc-z 305 tbi
everything stock, except for a mirror that fell off

 

If you're talking about winter traction, good tires will be your best investment by far. Then, added weight.

As far as suspension mods like ede and Enkil proposed, they won't help because the traction bars or LCAs are "reacting" to the traction you start with and adding to the force being applied to the tires - on ice, no dice.

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82 Berlinetta, orig V-6 car, now w/86 LG4/TH700R. 2.73 unlimited slip. Cat-back from '91 GTA, Accel HEI SuperCoil. AMSOIL syn lubes bumper-to-bumper. Daily driver, work-in-progress (LB9 w/ZZ3 cam, TBD heads, exhaust, paint, etc.).
57 Bel Air, my 1st car. 0.030 over 396, Weiand Action+, Edelbrock 1901 Q-Jet, Jacobs Omnipack, 1-3/4" headers, TH400 w/TCI Sat Night Special conv & shift kit, 3.08 10-bolt, AMSOIL syn lubes bumper-to-bumper. Best 15.1 @ 5800' Bandimere. Daily driver while Camaro was being put together.