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Checking clearance to bodywork

Motorsport Wheel Alignment Fundamentals

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Discussion and questions related to the course Motorsport Wheel Alignment Fundamentals

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I've been fighting setting up the suspension on my Integra DC2 for quite some time and tried several times with different ride heights, spring rates etc. I've setup several other vehicles for friends and even my daily driver 99 EK Civic using the bump, droop and ride height adjustment methods suggested in the course and have actually just finished watching the worked example on the DC2, which was extremely helpful.

I thinking I'm close to having the suspension optimised for my specific circumstances but I have a few questions;

1). When checking tyre and suspension clearance to the chassis (with the spring removed) on the front of the vehicle. I am presuming clearance should be checked through the full range of steering angle from lock to lock? I only ask this as it isn't specifically mentioned in the course, and the video shows the adjustments only being made with the steering set straight ahead.

2). Much like the worked example, I found I ran out of threads on my damper before I could stop the tyre hitting the chassis (I left 20mm of threads on the damper in the lower mount). I've since installed a set of bumpstop packers (front & rear) to limit the damper travel before the tire hits the chassis and a helper spring which was required on the front. Obviously this isn't totally ideal, and my question is that would the correct way to actually remedy this issue would be to use a damper which is physically longer?

3). Using these methods to measure and adjust the bump, droop and ride height has left me with the car looking somewhat ridiculous at the minute. At the ideal ride height from the calculations (1/3 of available damper travel rule) I have a car which honestly has more of an arch gap and ride height greater than the OEM suspension! Even using a 50:50 ratio of available damper travel the car is too high at static ride height in reality. I presume this is just the nature of how these settings are made? My compromised damper travel available due to needing bumpstop packers probably isn't helping either I guess?

Any help or advice to the questions above would be greatly appreciated.

1/ Yes, also a good idea on full droop as the suspension, steering, and even brake components may move closer to the wheel/tyre assembly.

2/ I'm not sure how to read that - are you using a limiting stop over the damper/strut shaft? Not familiar with the car, or don't remember, but there isn't a chassis/suspension bump stop used? You may need to review your main spring length and/or rate?

3/ That's a recommendation - different applications may be quite different, and you may need to take a step back, especially regarding spring rates, lengths and, I suspect, pre-loads.

Thanks for the reply. I'll continue to keep the numbering system going as it's easier to refer to which question I am answering.

1). Thats good then as I made sure I have clearance at all times from lock to lock

2). When checking for tyre clearance, I could no longer wind my damper out of the lower mount any further as I had the minimum thread engagement on the damper body. At this point I still had roughly 30mm of bump travel remaining on the damper. In line with the course recommendation, I am using a delrin spacer under the damper bump stop, on the damper shaft in order for there to be no tyre to chassis contact.

3). I under stand it's a general recommendation in essence to obtain more travel in bump than rebound from static ride height. However, at a relatively reserved ride height I would be faced with minimal bump travel remaining;

For my example, I have 118mm of total available damper travel. At full droop my wheel to arch gap is around 640mm and full compression is 522mm (I understand these value are arbitrary). From those measurements and ideal ride height would be around 600mm (1/3 of the total travel at static ride height).

However, the car sits far to high at this ride height and I find a reasonable height is around 555mm. This obviously only leave me with 33mm of compression available, compared to 85mm of droop.

1/ forgot - don't run it too close, you also have to allow for tyre distortion as the sidewalls are pulled out of shape when cornering. If you're going to be using drag race slicks, you will also need to make allowance for the tyre growth at speed - with drag radials this shouldn't be such a problem.

2/ just to confirm, is this the suspension you have?

DC2

3/ It would seem you have the wrong length, and probably rate, spring for what you want to do. I would expect a spring 2/3rds the length and 50-100% more rate would be around what you need, and you may still need to use those spacers for the 'bump stops'.

Hopefully someone more experienced in these can come in and comment.

Hi Simon, sorry for the slow reply to this thread. Some additional input on your questions:

1. This really comes down to practicality and personal preference. The question I would ask myself is 'How likely is it that you're going to be at full lock and full compression simultaneously?'. In my view, that's almost never going to happen, so if you do in fact set your suspension to guarantee clearance under every possible condition, you're probably going to end up with your ride height jacked up well beyond what would be normally accepted. On the other hand for an OE manufacturer this is exactly what they want to achieve but their ride height and wheel offsets are obviously much less aggressive.

I take a slightly more pragmatic view and aim to maintain clearance with maybe +/-180 deg of steering lock. Remember that if you do in fact find issues with contact/rubbing on track you can always come back and revisit this step.

2. It sounds like you're using a strut that's not ideally designed for your application (it happens though) and the correct/ideal solution would be a longer strut/strut body to allow the correct travel to be achieved. Given what you've explained a solid packer for the bump stop will work but of course compromises your available travel.

3. With a generic damper that is possibly less than ideally selected for a vehicle, compromise is going to be the name of the game. While the 2/3, 1/3 bump/rebound ratio is a great starting point, you have to also consider that it's not just the ratio of bump to rebound that's important - really it's the specific amount of travel that we really care about. The amount of bump travel you can get away with is going to then depend on the spring rate and surface condition of the track. You can also test with a cable tie around the strut to see how much of the shock travel you're actually using (if you're doing this test try and stay off any curbs as an aggressive curb is almost certainly going to run you into the bump stop which isn't necessarily an issue.

Hi Andre, no problem and thanks for the reply. I have been doing a few tests and checks in the interim.

1). That's a fair point actually, I think even on the tightest hairpins on the UK circuits I very rarely have to input much more than 180 degrees of steering wheel angle. It does have a relatively short ratio steering rack anyway at 2.8 turns lock to lock. I think I'll revisit this and make some checks again with slightly less steering angle input to see if I can alter the coilover positioning at all.

2). I think I proved that I required a longer damper to myself a few days ago actually, I have a set of fixed length Koni dampers which are a good few inches longer than the coilovers are maxed out, and with the spring removed they actually measured to have the perfect tyre to chassis clearance and enough droop travel to have a perfect ratio of bump and droop travel on the rear of the car. The ride height was also perfect however, the only downside is they can only use a progressive style lowering spring which is really too soft a spring rate. I think the main issue for the coilovers not being long enough comes through the use of front and real roll centre correction kits. On both ends, it lowers the lower control arm mounting point by about 25mm. My civic, which uses the same suspension design without roll centre correction and also the same coilovers, doesn't have any of the issues laid out here.

3). Yeah I understand the 1/3 rule is a good guidline if the coilovers don't come with any recommendations etc I was just finding I have more like a 1/4 ratio where 1/4 of my remaining travel was in bump and 3/4 in droop. When using a cable tie on the damper shaft, I presume removing the dust boot is necessary for viewing it? Also, would you put the bump stop and packers to the bottom of the damper shaft and the cable tie above them and measure how much the cable tie has moved up the shaft from static ride height after driving?

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