Ride height with coilovers

Hello,

Just finished watching "Adjusting Ride Height Using Coil Over Suspension" video. And still can't understand why we should change height using only lower spring perch. As I understand, it will reduce possible bump travel of shock absrober. And it can be significant if shock absorber has a small total travel?

For example travel of front MacPherson shock absorber is 108mm. From full bump to full droop. Bump stopper height is 36mm. So we have 72mm of shock absorver travel. Right corner of the car weight is 500kg. Even if we have 10kg/mm spring - we will loose 50mm of travel by car weight. (it will be droop travel). So we have only 22mm of bump travel. If we want to lower a car for 20mm using lower perch - we left only 2mm of bump travel?

But if we use lower hub mount for lowering - we still have 22mm of bump travel,

Where is my mistake? )

Thank you.

I understand that this is a tricky topic to get your head around. First of all it's important to understand that there are two parts to this - First is the ratio of bump to rebound movement of the coil over which is set via the bottom mount. This still needs to be taken into account from your desired ride height though. Next we have the ride height which needs to be set so that we can actually use the available travel. This time we want to set the ride height using the spring perch, so the two adjustments are related but very different.

In most instances we would adjust the base platform so that we reach the bump stop prior to the wheel/tyre contacting the chassis and then leave it well alone, making ride height adjustments via the spring platform. If you're in a situation where you've done this and you've got 22 mm of bump travel from ride height my first point would be that you're running the car too low in the first place and due to the constraints of the tyre to chassis clearance, no matter how you adjust the coil over you won't create additional bump travel. The same goes for lowering the car further, you end up in the same position - If you lower the car by the spring perch you'll end up with 2 mm clearance to the bump rubber, however if you lower the car by the bottom mount then you need to wind this up until you also only have 2 mm clearance to the bump rubber. Neither will work but in the second instance you've also compromised your rebound travel (which in reality is going to be the least of your worries if you're constantly riding the bump stop).

Check out this video from MCA which I think does a great job of showing you how this all works - [url=https://www.youtube.com/watch?v=jjsocJxdlYA]https://www.youtube.com/watch?v=jjsocJxdlYA

Many thanks again for your answer, Andre. I will try to understand it all in depth :)