Bilstein Science Experiment

[foodtruck]

Not strictly on subject, but since we're on the topic of B14 I had a pretty surprising experience with them today when I went out to the first autocross with the car since I installed them.

For the first run, I set the pressures to my usual F40/R40 PSI and almost spun out in the first sweeper. Compared to stock, the rear was Loose with capital L. The reason why I say it was surprising is both setups have similar front/rear spring rate ratio of about 1.2 but the difference in balance was massive. Over the day I ended up with F40/R30 PSI which made the car manageable but still notably more tail happy than stock even when tires were up to temp.

What gives?

 

[Fusion Works]

Something isn't right. The Bilstein spring setup is basically the same as OEM balance wise, just stiffer. Now the B14 damper has a LOT less rebound than the OEM dampers and even the B6/68, so its possible that lack of low speed control allowed the car to rotate better. I kinda doubt it though as that would mean Bilstein is liable every time some clown goes off backwards into the ditch.

 

[foodtruck]

Oddly enough, here are the pressures for UK(or Euro?) Fiestas: https://www.fiestastoc.com/threads/tyre-pressures.327870/>

For V<190km/h 1-3 persons, 36F/26R which, if we add 4 PSI, is bang on where I ended up with my pressures. I wonder if NA cars have different suspension tuning and B14s were made to match UK specs. Or is it because they are 2 doors short? Surely a door doesn't weigh that much more than the equivalent body section?

 

[Fusion Works]

Since I put the stock rear dampers back on my car with the 1in rear roll bar, when I switched to my "winter tires" I had to drop the rear pressures way down, probably into the low 30s, high 20s. Of course I don't run my normal tires at the OEM pressures. Ride quality is much better LOL.

Have to wonder if the US engineers just put the max pressure for the potential load cases to avoid having the customer make the decision themselves. Theoretically, you should adjust your tire pressures to suit your conditions. Chalking the tires can be helpful to determine proper tire contact patch and loading.