How much bump travel is too less

Gday everyone,

I've watched the course a couple of times and like all the info.

I have installed my MCA coilovers as per instructions, and not having any issues. I measured my total coilover travel (from bump stop contact to full droop) and is showing as having 100mm of travel.

My current ride height is set to around 50mm(1/2) so droop and bump are both around equal. This is measured from the fender to edge of the wheel. So far, the coilovers don't bottom out but I only had it for a week or two.

However, I would like to go lower if possible, about 15-20mm more. This would make my bump travel to only about 30-35% of the total travel. Is this too less?

I can't adjust the bottom perch anymore as the tyre would hit the fender.

Uh, I'm confused - you want to lower the vehicle but at the same time you're saying you don't want to because of tyre to body interference?

Sorry I made it confusing.

What I was trying to say was, I'd like to lower it more but could not add any more bump travel because of tyre to body interference so adjusting the bottom adjustment ring is out of the question.

If I were to adjust using the spring adjustment ring, it would lessen my bump travel to 1/3.

That's my point - it's the tyre to body clearance that is limiting your ability to lower the vehicle - you NEED to address that first, before even considering changing the damper/spring setup to lower the vehicle.

If you don't understand that, have a good think about what you're trying to accomplish.

The only way you can further lower the vehicle without taking care of the clearance problem is to use a physical stop like a modified bump stop, significantly stiffer springs so the suspension compresses less on bump, damper bump stops*, or a combination of those. Depending on the vehicle, changing the width and/or overall diameter of the tyre/wheel combination and/or offset may give a little more clearance, but don't forget to allow for tyre and suspension deflection in turns, acceleration and braking.

*Like these - https://www.google.com/search?source=univ&tbm=isch&q=damper+bump+stops?&client=firefox-b-d&sa=X&ved=2ahUKEwiUhvCo5svpAhVxyzgGHXwhAksQ7Al6BAgIEDA&biw=2400&bih=1288

Thanks.

So the general rule of damper travel is 2/3 bump, 1/3 droop.

Will a 1/2, 1/2 or even 1/3 bump, 2/3 droop be okay if you compensated for it with stiffer springs? What will be the consequences?

Uh, the ratio between compression (bump) and droop is going to be dependent on the load on the spring and the spring rate. Where that lies will depend on the vehicle and it's requirements, but I would expect a bias towards having more compression travel. As I understand it, some applications may have NO droop when static - I understand that is/was not unusual for F1 front ends.

However, I still get the idea you have no idea what you're doing - have you actually addressed the tyre to body/chassis interference yet? You need to do that before anything else.

I'm sorry but I have to disagree. I, and many others I assume, have successfully adjusted the bump and droop ratio without changing spring rates - simply by adjusting the bottom mount adjustment collar and the bottom spring perch collar - so I do not think it is dependent to that. In fact, Andre even said that on the video?! 4:25 of the coilover setup video.

I would suggest you have a read through my first post again as I feel you don't really understand what I was trying to convey (I edited it a bit for you)... but to clarify it more, I'll try to extrapolate further which hopefully would simplify it.

Now I'm assuming here that you have actually watched the Racecraft video, Adjusting Ride Height Using Coil Over Suspension so I am going to refer to certain times in the video for your reference. I'll also reference the MCA video here.

Now let's pretend for a second that I actually know what I'm doing...

So I've setup my ride height to 350mm (measured from center wheel to the tip of the wheel arch) Refer to Video 6:35

Just like the video, I removed the springs for easy adjustment.

Next, I let the wheels droop down then I measured the droop to 420mm -Refer to Video 6:53

Going great so far. Next, I move the suspension to full bump but...

Uh oh... It is starting to hit the wheel arch BEFORE hitting full travel. - See MCA video 6:06- https://youtu.be/jjsocJxdlYA?t=366

To fix this, I adjusted the bottom mount collar by turning it like this - Refer to Video 8:04 and this https://youtu.be/jjsocJxdlYA?t=333 (MCA Video 5:33)

This allowed me to utilize all bump travel and avoid my car from blowing up like the one on the video (I know it won't blow up by the way)

Great, now the bottom collar is locked and there is no need to adjust it anymore... Hence my comment on the first post "I can't adjust the bottom perch anymore as the tyre would hit the fender"

But wait, my ride height is now 370mm?!? Oh yeah, because of the bottom collar adjustment. Easily fixed by turning the bottom spring perch collar.

Now to measure again...

350mm ride height...Check

400mm droop...Check

300mm bump...Check

That gives me a 50mm bump, 50mm droop (1/2, 1/2 ratio). It seems far away from the general rule of 2/3, 1/3...But I drove it around for a couple of weeks and it's not bottoming out. I wonder, can I lower my ride even more?!? To 1/3 bump, 2/3 droop perhaps? What would be the consequences if I did?Have other people done this? What were their experiences?

Hence why I have asked the mother question...

How much bump travel is too less? 2"? 1"? 10mm?

I hope this clears it up...

I may be mistaken, but it would appear you are simply moving the lower spring perch on the damper, and using that pre-load to reduce droop from the normal ride height? Then correcting it by moving the suspension mounting point?

If so, I don't think you've quite grasped it, and my previous comments stand - however, I have been wrong before and will be again...

There are two basic types of 'coil-overs' those with a single adjustment to the lower spring perch and a body with a fixed fixing point to the suspension - IIRC, this type is the only one discussed in the HPA video. Then there is a second type developed, I believe, by TIEN which as the spring perch adjust ment as with the first type, BUT it has a second threaded adjustment that is used for adjusting the ride height/corner weights - I believe you have this type. They are adjusted differently.

The correct proceedure for that, latter, type damper/coil assembly is to fit the spring and then extend the damper fully before bringing the lower spring perch into light contact with the spring - most recommend ~5mm (3/16") preload. This will give the maximum travel on the damper and minimise the abrupt change between the spring still working and the travel topping out, the more severe this is, the more unsettled the vehicle will be.

Then you use the lower adjustment between the body and the actual suspension to set ride height as desired.

If you do that and find that under full compression (bump) the tyres, or other suspension parts, make contact before the damper and/or spring is fully compressed, it doesn't matter - if you are really concerned and want to use it ALL, you will have to find some way of increasing the tyre-chassis/body clearance first. It is not actually a good practice to bottom out the dampers, though, anyway as it increases the chance of damage from overloading and can make the vehicle twitchy when the spring rate basically goes to infinite without warning.

Normal, and correct, practice for actually adjusting compression and/or droop is to use different spring rates and/or length springs.

Hmmm, technically, if you have the correct top spring perch (retainer) which has a higher location for the spring, you could compress a strut more if there was travel left, but that would simply be taking it away from the other end.

Getting back to your question, in practice, as much as the spring rate will give you without unseating the spring - there are only two ways to adjust that - pre-load which is BAD(!) or spring rate, which is good, but should be as a result of other criteria and not the reason for making a change, as such.

I'll leave it there, as I've said my piece - anyone else?

Ride Height adjustment is an irritating subject, because it affects just about everything else in your suspension. The simplest explanation is that the only correct ride height is whatever your suspension engineer designed around, but most of us don't have those on call. So we have to figure it out by testing. Wheel to body contact is game over, control arms colliding with something is game over. You have to prevent problems before you can tune the handling.

You don't need any more bump travel than you're capable of using, 2/3rds 1/3rds is a conservative, and likely safe estimate get you to a point where you can test the car and tune from there. The minimum travel required is vehicle dependent, and rather complex to calculate. Put a zip tie on your damper shaft, slide it all the way up, and test the car out. Then see how far down the ziptie has slid. Try to account for something like hitting a road reflector while cornering near the limit that will compress your suspension beyond the maximum expected compression.

If we think of a gokart(with no suspension) With a spring and damper attached, 0mm compression travel isn't an issue. It can't move to begin with. So the minimum travel is application specific. Nobody can answer that for you, and any experiences people have are wildly subjective because it depends on so many variables. Like gord said, f1 cars may very well have no droop travel, why would they. They have downforce from aero to compress their suspension enough to allow for rebound over bumps. They also get pitch and roll dampers for each of those motions which might fully bottom out or extend to keep everything within an expected range of travel.

You're asking a complex question, with no real answer. To help we'd need a ton of information about the car, and what your goal is. The downsides of getting it wrong is scraping an oil pan, cutting grooves into your tires from wheel wells, blowing dampers, maybe a strut tower, or who knows what. With those in mind, most advice you will get will be trying to keep you from breaking things. Test the vehicle for yourself(I would start at say 370mm that you had it at) and be mindful of how much more your suspension may compress beyond what it's expected max compression is. Cornering force is where the most suspension travel will be used(for most cars).

I have roads in my area that look like https://i.imgur.com/XHhKBQ7.jpg which have a nasty habit of slamming me into my bumpstop. So my ride height is more than what my minimum would be. Road conditions will have a massive influence on what the correct ride height is. It may not be as low as is possible.

@Finalreqy

Thank you for the tip about the zipties. That would really help me gauge it.

Yes, I somehow agree that it is a complex question and is a case by case basis. I have installed 4-5 of these coilovers and don't normally have a problem with it sitting on a ratio of 2/3, 1/3 - even when lowered. The problem with the current build I am doing is the wheel offset is too much and could not tuck in under the fender arches - limiting the bump travel geometry. I was hoping someone out there might shed some insight/experiences - even a magic number but alas, I guess it would have to be trial and error for me then.

I forgot to mention this, lower ride height quite often results in a low roll center, and thus lower roll stiffness. If you see 20mm on the ziptie spare, and lower the vehicle 19mm, you'll probably bottom out if you preform the same test again.

@Gord

Ah, now I know why we seemed to be having this misunderstanding. I somehow get the impression that you actually have not seen, or maybe grasped, the video Adjusting Ride Height Using Coil Over Suspension of the alignment course. I highly recommend watching it as it enlightens on a lot of the points you brought up.

Now please don't feel that I am here to argue with you. I am just clarifying it for everyone, as it seems you have mentioned this to multiple people already and you have given them advice that contradicts the point the video was trying explain. The fact that I find the irony in this situation a bit humourous - seeing that in your words, I know nothing - is beside the point.

That video, specifically discusses the proper way to adjust a DUAL adjustment coilover, similar to TEIN's design. The coilover example on the video (MCA Red) is actually a DUAL adjustment type (Similar to mine). To clarify, the older SINGLE adjustable coilover design (aka Bilstein B14/16, KW v1-4) was never discussed on that video. (Personally, I don't think you need to make a video about those as it only has one adjustment collar.)

It also addresses the antiquated and wrong way of adjusting it - that most people have become accustomed to. The antiquated way that I am referring to, and I quote, is this:

"The correct proceedure for that, latter, type damper/coil assembly is to fit the spring and then extend the damper fully before bringing the lower spring perch into light contact with the spring - most recommend ~5mm (3/16") preload. This will give the maximum travel on the damper and minimise the abrupt change between the spring still working and the travel topping out, the more severe this is, the more unsettled the vehicle will be.

Then you use the lower adjustment between the body and the actual suspension to set ride height as desired."

The Racecraft video explains that in detail, as well as the MCA video here - https://youtu.be/jjsocJxdlYA?t=286

I'll just chime in with the little knowledge(or should I say, speculation) I know/or I think I know...

On a DUAL adjustment coilover, the bottom adjustment affects the BUMP, DROOP & RIDE HEIGHT.

The spring perch adjustment affects RIDE HEIGHT & DROOP. The only time this affects BUMP is when you adjusted it too much, past the solid height threshold of the springs - but this means you are using the wrong springs and it won't be covered.

Now of these 2 components (Bump, Droop), the most dangerous one when not adjusted properly, is the BUMP. Why? because it has the tendency to hit parts of the vehicle ABRUPTLY (aka fenders, etc). A tyre rotates to around 1000+ RPM at 120kph. When it contacts, game over. This is prevalent especially on McPherson designed vehicles as most don't have external bump stops (bump stops are mostly integrated on the shaft of the suspension)

Bilstein, KW and others knew this so they made the bump travel FIXED. That is why they never adapted the lower adjustment collar (not fully anyways). This is well and good, but the problem is production cost. This would mean they would have to produce hundreds, if not thousands of different shock bodies specific to the countless chasis types out there. Being a solid non-adjustable design, this means that they would have to mold/weld the mount to the shock body. This would mean added cost, which equates to higher parts.

Enter TEIN... They came up with their own smart way to actually make the bottom mount removable and adjustable as well. It allowed us to alter the position of the hub, in relation to the shock body. This then opens up more avenues of adjustment, PROVIDED you know what you are doing. Another advantage to this is, they could just make generic shock lengths, and produce the mounts specific to the vehicle. I actually recall an old forum thread that someone made/modified custom mounts so they could fit the TEIN Monoflex to their E36 (TEIN didn't have one for those back then). TEIN's design is actually not new. If I recall correctly, they were making them as far as 2006.

Due to this, manufacturing can be streamlined and production cost lowered. Other manufacturers saw the angle to this as well so started their own brand. That is why we are seeing an influx of cheaper (not necessarily nasty) coilovers now, utilising TEIN's design. Enter BC Racing, MCA, Pedders, Shockworks, HKS, Stance, etc... Even the generic Ebay ones!

ADJUSTMENT DEBATE:

Now for some reason, TEIN's instruction notes that when adjusting the ride height, you must turn the bottom collar as supposed to the spring perch. Their reasoning behind it is by adjusting the spring perch up (preloading), you will limit damper travel. This is true and there is no arguing this. They also mention that this will damage the dampers - though this remains to be seen as I've seen 5 year old bilsteins that have lived its life with no spring preload. It could be limited to their design, I don't know.

There is one caveat to this... By adjusting the lower collar, you inadvertently relocate the hub higher in relation to the shock. If you go low enough, you will experience tyre-body contact. This is the compromise of the two methods. On one hand, you will limit damper travel. On the other hand, you will allow the wheels to contact the body. Now I don't know about you, but I'd rather have limited damper travel, than having tyre-body contact. Most people will do as well hence why TEIN's method is considered the antiquated way of adjusting coilovers. Why they haven't updated it? I do not know. One thing I know though, they have recommended ride height values when you purchase one. If you stick to those values, you should be good...but what is the use of having adjustable coilovers when you can not lower it past those values?

Wow I just noticed how this thread evolved... I think I grab a beer now.

From that, it seems you do have a general understanding of the process for each type, so I would surmise it just comes down to the wording we were each using. However, not an understanding of why the process I mentioned early is still the best, and correct, way of adjusting them. That will maximise the damper travel, which you apparently want, and the ride height, that you apparently want. That there is then tyre to body contact is down to YOUR choice of excessively low ride height, too low a spring rate, wheel offset (as mentioned) and tyre size and the bump stop not preventing excessive suspension compression. Your best option may be to modify the bump stop, especially if it is a bolt on that can simply be replaced or, if you're lucky, can be spaced out as an alternative tot he more correct offset correction.

As I said a couple of times before, if your compression travel under bump at your desired ride height causes tyre to body interference, you CANNOT physically change the suspension, alone, to gain more clearance in bump and/or for lowering the ride height.

As Robbie said, though, you will be making other compromises and I would also suggest also checking the steering linkages have clearance and aren't binding.

Change the offset, or whatever, to gain clearance and THEN you can adjust the coilover for a lower ride height as you will have the clearance required.

BTW, I used "TIEN" because that was the first brand I came across using it - 40+ years ago they didn't exist, as far as I am aware, we were lucky to get the most basic coil-overs...

I don't think either Gord or myself particularly cares what a manufacturer suggests. We just look at what the various parts do, and what changing them effects. If the manufacturer is right, great, if it's a sort of correct statement, intended for a specific setup, you need to take it with that in context, not an absolute. It's fairly easy to have a bunch of correct things, that work terribly on your setup.

With that in mind, I'm not sure what everyones issue with preload is. Seems like its a misunderstood, and possibly misused setting. I've never needed it on any of my cars, but I adjust it constantly on my motorcycle. If I take a passenger, well, me and a passenger weight as much as the bike itself so I adjust the preload to account for the additional weight, and ultimately stay in the same place once the bike is loaded. Obviously cars are significantly heavier so the value of this is greatly diminished.

Alot of the confusion seems to spawn from a difference in how people go about changing their suspension. I get all the information for the car, figure out what ride frequency, roll stiffness, and various other math related things to end up at whatever spring rate is required. Then order dampers, and springs at whatever length is required. If I end up at a half step in length that doesn't exist, I use a helper. From there ride height is set to whatever I set, without really touching the adjustments, preload or ride height, leaving that to corner balancing, or testing various roll center locations. The only reasons to deviate from this are cars too stiff to much suspension travel at all(a fair number of hardcore autoX), rally cars, or aerocars where your primary interest is in controlling down force, not disturbances from the road.

Working with your ride height, and spring rates predetermined, and a solid estimate of the travel that will be used, ride height largely solves itself. I might have to adjust +/- 10mm and corner balance the car, but not any major shifts. With all that being said, It's more often I target a roll center height than a ride height. If I had your coilovers to setup, I would barely even use them as ride height adjustment, the spring length was chosen to handle that, and adjust both upper and lower mounts together to position my compression and rebound. I do tend to run far softer, and higher ride than most people on my cars due to road concerns, so depending on the coilover range of adjustment, and damper length, there's atleast a possibility I would use preload to avoid running stiffer springs or bottoming out compression under normal driving. The only reason I would do this, would be because say... 2 inches of compression travel is simply not enough, and I'm perfectly fine sacrificing rebound to gain the compression.