I have been corresponding with a fellow Honda CRX enthusiast about an upgrade to his car's suspension. He is very happy to have found a relatively rare set of front torsion bars to replace the stock items in his car, and he is looking forward to installing them for a stiffer ride. I am happy for him and I know that he will get plenty of enjoyment from the new parts, but I also told him that in order to get the maximum benefit from this set of front torsion bars, he is going to buy and install a whole host of other parts that are necessary to facilitate the new torsion bars working to their top potential.
Torsion bars are used rather than coil springs in some cars to provide a cushion for the car's suspension. The greatest difference between a torsion bar and coil spring is that the torsion bar is a straight piece of spring steel that gets twisted to provide the spring action rather than compresses as a coil. Air-cooled Volkswagens and Porsches, most Chrysler products from the 1950's until the 1980's and a variety of racing cars used torsion bars instead of coil springs for their compact size and unique packaging advantages that reduce unsprung weight in a car's suspension.
The 1984-1987 Honda Civic and its sporty brother the CRX all came with torsion bar front suspensions with a conventional spring suspension mounted over a solid beam axle located by trailing arms and a Panhard bar in the rear. Although not as sophisticated and adjustable as some other more complex suspension systems, the torsion bars served these cars well. The supply of stock replacement parts for these cars is very good, but the supply of performance parts sold by aftermarket manufacturers and retailers is slim and getting more scarce with each passing day. For my friend to score a set of 27.5mm thick torsion bars for his CRX is a real coup.
The CRX came with 19mm torsion bars and Mugen, the factory performance parts outlet, sold torsion bars as thick as 25mm so the 27.5mm variety made by torsion bar maker Swayaway are VERY stiff. Maybe too stiff for anything other than a racing application. I have a set of 23mm torsion bars on my hobby car, a 1987 Honda CRX Si, and I think that is plenty fine for street and track.
Nothing happens in a vacuum with automobile performance improvements. Even my thicker than stock torsion bars required a flock of other part improvements to fully realize their potential and so is the case with my friend's car. Stiffer springs (or torsion bars in this case) in front mean that stiffer rear springs are in order to balance the handling of the car. In my car I have upped the rear springs from a stock rating of about 200lbs. To 350lbs., the guy with 27.5mm torsion bars will need rear springs in the range of 500lbs to match the stiffness of his new torsion bars.
With all that stiffness in the springs, he will also need stiffer shocks and struts to manage that rigid ride; the stock dampers will be overwhelmed by the new ride dynamic. And if he has not replaced his suspension bushings (a series of rubber "donuts" that locate and insulate the various parts of the suspension) the new stiff ride will demand that they be replaced. And understeer, the basic flaw of nearly every street car as delivered from the factory, will need to be addressed by adding a rear sway bar to his car’s suspension.
It seems like every major sub-system of an automobile requires a group of new parts to make one new replacement upgrade part work to its best potential. In the engine, a new cam helps to make a ported and polished head breath at its best potential, new brake rotors will not be much better improvement until you upgrade the quality of the brake pads, and a car's stereo upgrade will require better speakers to get the full effect of the new system.
The bottom line is that if you budget for a single new part or set of parts, be prepared to also buy and install all of the supporting parts that will be necessary to make that first part work to its fullest potential.