SPD Tuning Service

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Why do so many people speak so highly about the Prodrive Bilstein Eibach suspension kit?

Prodrive is a contract race car developer in the heart of England's Formula One country. All Subaru World Rally Championship Group A cars (hand built from a bare shell and almost as trick as a Formula one car) and many regional Group N Championship cars  (Stock based rally car conversions) have been developed by Prodrive for over eight years. The Prodrive kit has been very carefully developed to get the most out of the suspension by optimizing the front and rear roll center relationship, the proportion of front to rear spring rates and most important, the shock damping, again, with special attention to front to rear proportions. The Bilstein shocks have been evaluated at different velocities, travel positions, separately for jounce and rebound and tuned to give the car an amazing combination of ride and handling qualities.

In 1999 STI began producing a regular production version of the Prodrive suspension for the WRX STI ver 5, using a Bilstein licensed inverted strut. The are minor differences in shock valuing, due to the Japanese driver's taste for stiffer damping than is really necessary for good performance. The two sets, Prodrive or STI, are about the same in performance, with the ride quality still going to the German made Prodrive kit. Note that wee only have one or two "take-off sets available of the Japanese made STI suspension each month. What are these take-off suspension sets replaced with? Prodrive Bilstein/Eibach rally suspension! 

These are  not the fastest suspension setups we sell. However, for faster lap times you have to sacrifice ride quality due to stiffer spring rates and shock rates used in track biased suspension kits.  The Prodrive setup is not about the fastest lap - It is road suspension intended for everyday use with the grip, and most important, the balance for keeping the car on your side of the road in most any sensible driving situation.

With that said, Prodrive has taken the STI V6 shock and made a special spring set for the Impreza P1 currently on sale in England. We have been given 50 sets of this suspension in excess of the 400 made for the P1 production run. It is a very firm, no holds barred sport suspension for a 280 hp WRX. The price makes it a special bargain for those who what a powerful, yet balanced setup.

The roll centers on the Impreza are a function of ride height and thus the car is lowered by only a certain amount in the front  and a only certain amount in the rear (about 3/4") best suited to optimum handling. The long and the short if it is, if the car were lowered more, the chassis would not work as well. The ride height/roll center equation is combined with properly proportioned spring rates front/rear. The car has much less dive under braking, and is much quicker to respond to steering inputs with a fine turn-in balance that neither the RS or the WRX have in stock setup.

The heart of the Prodrive suspension system is the several years experience the staff at Prodrive have put into the valve settings of the special make Bilstein shocks. Bilstein damping rates are both velocity and position dependant. These settings have been tuned by the same engineers that won the World Rally Championship three years in a row. The suspension is remarkable in that the car has a perfect balance on turn in and the ability to come off of corners under power with minimal understeer. This is accomplished be careful balancing of the rebound and compression rates of the shocks at the appropriate velocity and ride position. Quite a trick to get right, as any dirt track racer knows, and Prodrive has it just right!

These are the reasons, aside from unquestioned build quality, that this suspension is so important. Many owners ask what the difference is between our suspension kit for the car. The answer is the shocks valving is just not as refined and the less expensive suspension's ride height needs to be higher to work with standard length struts! What you will find is that you can lower the car with other company's springs and make it stiffer and lower, but discover that the car only has a much rougher ride than it did before and has poor or even unpredictable handling.

A well sorted suspension is a very special issue and at present only Prodrive has anything that works really well for a road suspension setup. All the Japanese coil-over setups seem to be way off the mark, too high a spring rates and always over dampened shock rates that are great on a smooth track and just impossible in all other conditions.. That is why we have stayed with the European units.

Send mail to mshields@spdusa.com with questions or comments about this web site.
Last modified: May 23, 2000