Is this enough suspension travel?

So I have coilovers on my double wishbone car. (It's a first gen Lexus IS300).

Because I have stock suspension uprights, the limiting factor on this chassis up front is the distance between the upper control arm and the shock towers of the chassis. When it makes contact - and I have made it do so - it is a very harsh, metal to metal bang. Not wanting a repeat of that, I have made it my mission for the coilover/shock to bottom out before said upper control arm smacks the shock towers.

But because the solution to that is a fairly stiff unyielding puck of sorts, I still need a bumpstop. Luckily, I have a progressive bumpstop that's just the perfect length of not being too short it's useless, and not being too long it's constantly engaged.

Anyway, here are my numbers.

Total shock travel from droop to metal-on-unyielding puck contact is 94mm.

The shock compresses 35mm from droop to that static ride height. That's about 59mm of Wheel travel from droop to static ride height.

At static ride height, I have about 19mm of compression travel before bumpstop contact. That's about 34mm of wheel travel.

The bumpstop is 40mm ish btw. I don't think the car can compress it to zero thickness, but I want whatever thickness it is as it turns incompressible
 to be there to keep distance between UCA and chassis (with only the unyielding puck it juuuust has that slight bit of clearance).

I guess the question is, how do these numbers look? 19mm of shock travel or 34mm of wheel travel before bumpstop contact seems very littIe. If the bumpstop can be compressed in half before it starts increasing the rate massively and upsetting the front end, that means I have 66mm of wheel travel or 39mm of shock travel total.
 

Solid height on the bump stop is probably 10-15mm. Personally I'd reduce the puck thickness by at least 5-10mm to squeeze as much travel as possible out of it. Worst case if it does still bottom out it'll be a pretty soft hit since the bump stop will have taken up a bunch of load. Can you increase spring preload to shift the ratio of bump to droop travel? The total amount of travel you have there is plenty, but you really want at least 2:1 bump to droop travel.

The height where the bump stop turns solid can only be found through testing if it wasn't specified on the packaging, but a rule of thumb for today's conical bump stops is that they will compress to 40% of their full length which would be 16mm for these.

If you don't want to engage the bump stop sooner than necessary then it sounds like you don't really want it to be that progressive. So you could trim down the bump stop at the pointy end which will give you more travel before the bump stops engage and make the bump stop less progressive. If you end up going too far you can add a solid shim/packer which will again make the bump stop action less progressive.

Questions:

Exactly where does the control arm hit the tower and what part of the control arm hits?

How much has this car been lowered relative to the standard ride height?

What angle is of the lower control arm at static ride height?

Finally; are you going for a look or performance?

Tom1200 said:

Questions:

Exactly where does the control arm hit the tower and what part of the control arm hits?

How much has this car been lowered relative to the standard ride height?

What angle is of the lower control arm at static ride height?

Finally; are you going for a look or performance?

Where control arm hits


You can see the crescent shape of the upper ball joint assembly on shock towers. Are you getting at solutions to lessen the contact via clearancing? If so then yeah, already searched that. People have cut that section of shock towers. Some people just leave a hole (dumb) and some people weld a box section (better).  People also more commonly  have shortened spindles (cut and reweld) + balljoint spacer/roll centre adjuster. Effectively a lowered spindle. But the more extreme cuts offered by shops who offer this as a service (which to me is a clue that this car does indeed dislike lowering) need very low offset tires OR mad stretch.
Photo stolen online:

Not my thing. I think with the sensible offsets and sizes I run, I can get away with 17mm shortening at most. That's definitely in the future. 

How much lowering do I have?
25mm or about an inch. That's with the springs already feeling like they're preloaded by a lot. I can honestly say I can't go any higher than this. In fact, that's why I went to ask the original questions: Coilovers where the height can be adjusted independent of preload will be in my future, and had the answer to "is this enough suspension travel" is "no, that's dumb. It's too little", then I would have had these coilovers replaced over the winter. Stiffer springs at the very least. But, it's not a priority, and for what its worth, I'm sprung and damped not unfavourably, so I'll just use these until they start failing.

Which  is perfect segue to another question:

are you going for a look or performance?
This car was originally owned by someone who just needed a decent looking daily driver. Only mods when I got it were said coilovers and pretty damn good looking staggered Enkei NT03+M's. As a daily, it's fantastic. But when I got it I thought I'd make it a dual duty car and have since added Eibach swaybars for added roll stiffness, SS brake lines, G Loc R10 Pads for track, and various bushings being replaced by poly. Some holes in the fender liner for brake cooling.  Lots of maintenance too.


There is a track in my province (not the one pictured above) where there's a frost dip and heave right where the right front suspension is most loaded and that's where I make contact. I have to take dumb funky lines just to avoid it. Eating up more and more inside curb than ideal, which btw does not induce said contact - simple bumps don't do it, need loading to really get on it.

What angle is of the lower control arm at static ride height?
Inner lower control arm bushing to lower balljoint is level, in case you're worried about an overlowered car. I'm not. At least I don't htink so. It's really just that travel I'm curious about. After having put on an incompressible 'puck' the leftover travel I have is the travel I must live with. As mentioned, if the answer was "no, that's a dumb amount of travel" then I start looking for replacement. Right now, the puck is a pretty decent solution.

At least I hope it is.

My son's LS has the aforementioned hole for clearance; it was done fore the whole VIP look.

We've since raised up the car because the suspension geometry was wrong with it that low.

As for clearance as long as the control arm is the only thing that hits I don't have a problem with cutting the sheet metal and welding in a new piece of metal that gives the control arm clearance.

19mm or 3/4" isn't much bump travel. If your local track is bumpy I would think it would limit the car a lot. 

dps214 said:

...but you really want at least 2:1 bump to droop travel.

I've long seen this generalization thrown around. I don't think anybody knows exactly where it came from at this point, but I'm confident that it was regarding one specific set of circumstances and never intended to be latched onto the way it has been outside of that. I know of exactly zero sporting cars that achieve this from the factory, and see no reason we should be shooting for it either. The closest I can come up with is that perhaps that 1/2 of the available 'bump' should also be the bump stop in that situation, such that free bump:droop travel is 1:1, but even that looks to be overly conservative based on the real only world examples I've found. I'm guessing part of that comes down to damping also resisting motion, not just the spring. Consider that the natural droop travel of a stock Miata would be 6+" if not constrained by preload. I know they used the bump stops as part of the suspension, but the only reason even a stock Miata could need even ~6" of free travel, let alone 12", would perhaps be with a lift and some all-terrain tires...And it's not going to pass the sniff test any better with any other sports or sporty car either. Sure, when you've got the room to spare, the more the better. But when you don't, every little bit matters.

So now that we've got that out of the way, what is reasonable? I had to grapple with that when spec'ing coilovers for my 128i. The E8X/E9X platform is substantially travel limited suspension. There simply wasn't enough room to give the amount of bump vs droop travel I ideally wanted without going insanely stiff. Let me clarify that when I say 'droop', I mean the 'natural' from static ride height to the spring coming loose, not just the shock running out of droop travel (preload). What I was finding though, was that even among the best regarded (least-bottoming) coilovers were running 'free' (before the bump stop) bump as low as just over 50% of natural droop. They were also only running ~20mm bump stops, that were perhaps progressive, but also aggressive. Playing with body length, shaft length, and preload, I was able to get 'free' bump that was  nearly 60% of 'natural' droop while also using softer springs than any of the off-the-shelf options. I only know of one time, in an unintentionally extreme circumstance, that I knowingly hit the bump stop, and couldn't have been happier with how that turned out and worked on the street.

Your wheel travels looks to be right in the real-world range I've found and experienced, and with a longer travel (presumably softer and/or more progressive) bump stop. So assuming your measurements are reasonably accurate, that seems good enough that I'd send it for now and see how it works on that car in that situation.

You're right, I was generalizing for simplicity. And nobody can agree on the exact "ideal" number either. Most all stock vehicles are around 1:1 because super soft springs mean they have a bunch of travel overall. Of course the more total travel the less it matters where the midpoint is. What I really meant was "when dealing with significantly limited travel you really want noticeably more bump than droop travel". Looking at it again I may have misinterpreted the information in the original post a bit. But we also don't have complete details. Given sufficient spring rate (which we don't know) the current ~2.75" of wheel travel may very well be sufficient. But I'd still want more if reasonably possible. Especially considering we know that the car will happily use all of the available stroke and then some absent the extra bump stop.

In reply to randedge :

Re-reading this, I see the mention of there being significant preload already... If the droop travel in the first post is including the preload, then it'll be in the bump stop a lot more than I was thinking in my previous post. It's also means the droop travel number is no real help in determining just how much bump travel is needed without knowing either the amount of preload or the corner weight vs wheel rate.

However, with the 'right' bump stop, that setup may still be worth a try.

Most stock cars that I'm aware of, including plenty of perfectly trackable ones, have significantly limited (especially bump) travel and noticeably less bump than droop travel. Despite this, they also frequently both ride and handle quite well. Manufacturers get away with this by relying heavily (sometimes even engaged at static ride height) on the bump stops... Or as BMW has called them, 'auxiliary springs'.

It may not be an ideal solution, but it can be a functional one.