The DR-Type coilovers from BC Racing use digressive valving, this means they rely on high flow pistons and preloaded shim stacks in order to get high, low speed damping forces(~2 in/sec). The pistons flow enough oil that the shims control the valving profile, and at high shaft speeds oil flow through the piston is not restricted. This provides decent force ramp up from about 20 in/s and higher, but less than linear and progressive valves. "Cornering" happens at ~2 in/sec so the digressive shock will have better feel and control in most road racing applications. Refer to the comparison below:
With the technical points out of the way, lets talk about my experience with these on the Toyota Yaris. When you order a set of Yaris DR-Type coilovers from BC Racing you can get the standard 5K front/ 3K rear spring rates, custom BC rates, or the SWIFT spring upgrade with custom spring rates. The INSTALL for this suspension upgrade is straight-forward and only requires basic set-up for most. We tested the standard spring rates first to see how they perform, then made changes. Check out the DR damper dyno graph below:
On The Street...
On the street these spring rates were perfect. We started with the dampers right in the middle at 16 clicks, but the ride was very harsh. I turned them down to 10 clicks and the ride quality was nearly identical to my previous Tokico damper feel. If you want coilovers just to slam your car and maybe attend an occasional autocross, the BR-Type and standard rates may be more suitable for you
At autocross these rates were not so great. The 5K front was fine, but the 3K rear had us completely maxed out on the dampers to get some rotation. We went to a 5K rear swift spring to try a square setup, and the car starts rotating perfectly around 5 clicks front/16 clicks rear. Then we tried adding a UR BRACE to the rear of the car to be sure we weren't losing spring performance due to chassis flex. There was just a bit more rotation after the brace so we decided to stay with the square 5K spring set-up.
At the track this square setup felt amazeballs, but I turned all of the dampers down to 5 clicks to be sure the car stayed nice and predictable. Even at this low setting the car did great and you could still get some rotation with a little flick of the wheel. I have no doubt a more talented or fearless driver could crank up the damping and toss the car around this course faster than I did.
Why Swift Springs?
When you order a set of coilovers from BC Racing, you will have the choice of; Standard spring rates, Custom BC spring rates, or the Swift spring upgrade. Now I can imagine you are curious like me as to what the difference is between the BC and Swift springs, so I'll drop in a description from the Swift website below:
...So you see, It's about getting the absolute best performance out of your suspension. The Swift springs are extremely light, holding them in comparison to the BC springs will make you wonder how they hold the weight of the car. The evenly spaced coils and linear spring design results in more predictability and control through transitions, unlike the increasing rate of a progressive spring. If you're like me and do an excessive amount of research and planning, you will always have the thought in your head that your leaving time on the course because of that "one last thing". For me it was not having Swift springs or corner balancing, but now we're finally there. For the front you need the 8", 60mm ID. The rear is a 6", 60mm ID.
Do you really need to corner balance?
The answer to this question is based on how you use your vehicle. If your're never going to do any type of racing, then odds are you dont need it. But if youre racing like me and want to ensure the suspension is operation at its absolute best, to squeeze every tenth out of your tires requires a properly balanced car. A drivers weight ballast is placed in the car with the race tires on and fluids at their normal levels, then the spring perches are adjusted to achieve an optimum 50/50 cross weight balance. Suspension geometry, ride heights, and rake are all verified at the same time. Once this procedure is complete, a wheel alignment is performed, resulting in a 100% optimized suspension. I was able to notice the difference right away after the corner balancing, a smoother ride and easier slide recovery being the main benefits.
The main take-away here is that you should consider the intended use and future plans for your vehicle before deciding on a suspension system. I thought I never really "needed" coilovers until I started doing WEIGHT REDUCTION and changing the cars balance, but I'll tell you you...that was a miscalculation. The ability to fine tune the suspension has been one of the most beneficial upgrades to this car, and I'm still impressed to this day. BC Racing Coilovers AND Swift springs....highly recommended. Then when you're ready to get serious, get that corner balancing done.
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