It seems like you are missing a few things in these calculations. First off, where are you accounting for the force the shock absorbs? Shock force is proportional to speed, so a 5G bump in the road will create more force in the shock than in the spring. Second, where is the motion ratio of the suspension? Without seeing your calculations, I can't tell without doing the math (and I didn't do that). The force the wheel sees is not the same as the wheel because they aren't traveling the same distance.

I think the practical answer to your question is to use some known geometries and rates and then test it on the street. Put some travel indicators on the shocks and see if you are bottoming them out.

Ken

I would say that 95% of all Seven style suspension systems only have about half the travel of your current design.
As already mentioned you need to look at jounce loads of 2G, along with a vectored braking of 2G, using the 1/3 to 2/3 travel ratio.
The only time you see 5G's is when you missed the corner and end up in the ditch. [Structurally design for 5Gs]
DaveW

So you inherently have "1G" worth of available droop from rest, which appears to be ~2.2 inches. While I have not tested this out for myself yet, from my research I believe that an additional 1G of bump (~4.5 inches total from full droop) before hitting the bumpstop should generally be sufficient.

Another way I've seen people look at it is that your at rest droop should be 1/3 of your total available travel, while 2/3 of your total available travel should be reserved for bump travel. This method does not include the reduction of available travel from the bumpstop in the analysis, so the ultimate result is it typically seems to end up relatively close to the first method I mentioned once the bumpstops are factored back in.

I went through this about 5 years ago. I ended up with springs a lot stiffer than necessary. But it turns out that when you hit a bump, the suspension doesn't soak up the full height of the bump. Not by a long shot. The chassis takes up easily half of it (i.e. you get jarred), so the suspension only sees half the compression you'd expect, or less. I have about 4" of travel in front and 2" in back. I have never hit the bump stops. Not once, not even close, in 45K miles. And I've been down some seriously bumpy roads at speed over the years. My springs are 340#/140# F/R.

My understanding of why you want the chassis to be stiff is so that it will force the suspension to do it's job, namely absorb forces and respond to the road in such a manner that maximum control and traction are maintained.

Cheers,