B6 vs B8 – Only One Difference
There is only one difference between the B6 and the B8 and that is the length of the shock (damper). Bilstein B6 shocks are the same length as the original dampers, the B8 are shorter than the original dampers.
Which one to use?
Assuming you are using sport springs/lowering springs which do not require shortened dampers, you can use either. The majority of the lowering springs from H&R and Eibach are designed to work with the original dampers.
If you are using springs which need shortened (sport) dampers then you will need the Bilstein B8. Check the H&R/Eibach catalogues, it will tell you in the product notes if the springs need “sport” dampers. If it doesn’t saying anything about dampers, you can use the original dampers.
Why have shortened shocks?
When the car is lowered you lose some suspension travel because the damper is slightly more closed than it is with the longer original spring.
However the loss in travel is partially offset because the sport/lowering springs are stiffer so will compress less.
In terms of performance, I think most people will not understand the difference, they won’t know if a car has shortened or standard length Bilstein sport dampers.
Which one would we use?
We would only use sport dampers with sport/lowering springs and seeing as the B8 shocks are usually the same price as the B6 shocks, we would use the B8. We do not see any reason to use the B6.
When not to use Bilstein B6 or B8?
If we were using the car’s original springs then we would not use the B6 or the B8 dampers, we would use Bilstein B4, the standard replacement damper.
Using Bilstein B6 or B8 dampers on standard springs will make the ride stiffer with very little benefit in stability and performance (compared to sport/lowering springs)
Claims by Bilstein
For the B6 they say this
Bilstein B6 vs B8 Summary
While the B6 is the same length as the standard dampers, we do not see any use for them.
If you are looking to improve the stability of your suspension, fitting stiffer dampers on/with the stock springs will be a far inferior solution (and much more expensive), compared to fitting sport/lowering springs on stock dampers.
And while fitting shorter dampers (Bilstein B8) with lowering springs is usually not required, there is a very slight benefit in doing so, in terms of suspension travel. Couple this with the fact that the difference in price of Bilstein B6 vs B8 is negligible, we would fit Bilstein B8 dampers with our lowering springs, not the B6.
We do not see any circumstance where we would fit the Bilstein B6 to a car.