Aventador custom chassis drawings for 500 USD / 470 EUR

[SchulzeA]

Dang, you guys write a book. Ok, so how do you determine all 7" springs bind at 4.25" without first knowing the wire size and pitch? Picture below shows that not all springs are created equal. I built a spring winder and would like to know what formula you use to find compressed length. Knowing what to expect is much better than finding that I've made a mistake like your custom chassis you built. Doing it right the first time certainly is the best way when possible!

Secondly, what is the application for this DS301 shock/spring setup if it will not function correctly?

Not being rude here, just askin...

[plans4sale]

SchulzeA,
   Those are good questions and observations, let me see if I can address all of them. You are absolutely right about the stroke length, that is what I was talking about when I mentioned motion ratio. That wants to be as close to the ball joint as possible for other design considerations. The stroke length of that shock is 2 1/2 inches. As you say, that is shock stroke length, not tire travel.
   Both your response and the first response of P4S concentrate on the shocks, forget about them, they are not the issue, they could be 1 or 100 inch stroke, but there is a problem if a 7 inch spring is the longest that will fit.
   I also mention swaybar rating in my answer, something that P4S never mentions. I assume his calculations are without a swaybar, and THAT WILL NOT WORK either. This subject could fill another thread, but let me give this brief example more to show a concept than to be absolutely accurate. A 100lb spring and a 300lb bar gives a total rating of 400lb on that corner. A 300lb spring and a 100lb bar gives a 400lb rating on that corner. The debate over which is correct has been going on since the wheel was invented, but you must consider them together. When P4S says 400lbs on the front, that is as much as you would want to go for both combined, I do not care what the geometry looks like.
   Realistically, to get this rate you need about a 250 lb spring and a 150lb bar. A 7 inch spring coil binds at 4 inches, 4 1/4 to be exact. That leaves 2 3/4 inches of spring stroke, forget the shock. Place the 530lbs guess of P4S over it and it compresses 2 1/8 inches. That leaves 5/8 of an inch for suspension travel. Put a passenger in the car and you do not have even that. If he misses that guess by even 100lbs you do not have that. If the ride height is not absolutely perfect (which it is not going to be in the real world, only on paper) you do not have that. Change the air pressure in a tire and you do not have it. For that matter, what sized tire is this based on, will everyone use the exact same tire? When the spring settles, which it is going to do, you do not have it. All of these will leave it coil bound before the suspension ever has a chance to travel. It may look good on paper, but it is not reality. Go to a 225lb spring and now any slim remote hope is gone. 
   There is a second way I know this. I have a junk chassis sitting here that was the R&D test bed for the development of that very shock. We got almost the entire chassis done and the prototypes sent to production before either of us realized there was a problem.
   P4S,I am not trying to argue, just save the agony of another junk chassis being built, but if your numbers say it will work, go for it. At the risk of extending what has now become a debate, I have a few observations. Why change it to the shorter shock in the first place? This is the same question I asked when my problems arose. The shorter shock and smaller spring is less unsprung weight but the bigger spring that is now needed negates this, and it is much harder to make the geometry work with the short one. I do not find an upside to this change. Also on the downside, I understand you have two years of development using the Hardpoint for the longer shock, which is the first starting point of chassis design. You are going to lose every bit of your suspension analysis data. Again just my opinion but any chassis design that is changing Hardpoints after two years of development has more problems that the shock length.   

Thank you for your very long post, 76mx! I appreciate the time you spent writing all of this. I will be short: I already have an experience with taking part in designing two sports car suspensions that were tested and used successfully in real cars. Now I design a more advanced, complicated and uncommon suspension layout, and I'm pretty sure it will work properly. Why? Because I do it. Thanks!

[INSPIREcomposite (BANNED)]

stop, just stop it.

[76mx]

SchulzeA,
   Those are good questions and observations, let me see if I can address all of them. You are absolutely right about the stroke length, that is what I was talking about when I mentioned motion ratio. That wants to be as close to the ball joint as possible for other design considerations. The stroke length of that shock is 2 1/2 inches. As you say, that is shock stroke length, not tire travel.
   Both your response and the first response of P4S concentrate on the shocks, forget about them, they are not the issue, they could be 1 or 100 inch stroke, but there is a problem if a 7 inch spring is the longest that will fit.
   I also mention swaybar rating in my answer, something that P4S never mentions. I assume his calculations are without a swaybar, and THAT WILL NOT WORK either. This subject could fill another thread, but let me give this brief example more to show a concept than to be absolutely accurate. A 100lb spring and a 300lb bar gives a total rating of 400lb on that corner. A 300lb spring and a 100lb bar gives a 400lb rating on that corner. The debate over which is correct has been going on since the wheel was invented, but you must consider them together. When P4S says 400lbs on the front, that is as much as you would want to go for both combined, I do not care what the geometry looks like.
   Realistically, to get this rate you need about a 250 lb spring and a 150lb bar. A 7 inch spring coil binds at 4 inches, 4 1/4 to be exact. That leaves 2 3/4 inches of spring stroke, forget the shock. Place the 530lbs guess of P4S over it and it compresses 2 1/8 inches. That leaves 5/8 of an inch for suspension travel. Put a passenger in the car and you do not have even that. If he misses that guess by even 100lbs you do not have that. If the ride height is not absolutely perfect (which it is not going to be in the real world, only on paper) you do not have that. Change the air pressure in a tire and you do not have it. For that matter, what sized tire is this based on, will everyone use the exact same tire? When the spring settles, which it is going to do, you do not have it. All of these will leave it coil bound before the suspension ever has a chance to travel. It may look good on paper, but it is not reality. Go to a 225lb spring and now any slim remote hope is gone. 
   There is a second way I know this. I have a junk chassis sitting here that was the R&D test bed for the development of that very shock. We got almost the entire chassis done and the prototypes sent to production before either of us realized there was a problem.
   P4S,I am not trying to argue, just save the agony of another junk chassis being built, but if your numbers say it will work, go for it. At the risk of extending what has now become a debate, I have a few observations. Why change it to the shorter shock in the first place? This is the same question I asked when my problems arose. The shorter shock and smaller spring is less unsprung weight but the bigger spring that is now needed negates this, and it is much harder to make the geometry work with the short one. I do not find an upside to this change. Also on the downside, I understand you have two years of development using the Hardpoint for the longer shock, which is the first starting point of chassis design. You are going to lose every bit of your suspension analysis data. Again just my opinion but any chassis design that is changing Hardpoints after two years of development has more problems that the shock length.     

[plans4sale]

 I just took measurements from my front suspension design to make sure I talk with exact numbers. Here is what I have for you:

- In a neutral position, the car will usually have a ground clearance of 100 mm (actually, it's 110 mm from bottom of chassis, but I consider 10 mm for underneath protective panels) and the coil-over is expected to be compressed about 30 mm. The latter is always a variable number since it depends on the spring ratio and owner's preferences for the right height.

- Using the 10" QA1 coil-overs with 7" springs, and assuming that the compression of the coil-over in a neutral position is 1.181" / 30 mm from the extended height (extended 11.125" / 282.585 mm minus 30 mm is about 9.944" / 252.575 mm neutral) due to the car's own weight, my suspension setup will allow the front wheel to go up by 1.531"" / 38.89 mm before it reaches the coil-over's maximum compressed height of 8.625" / 219.075 mm. This is just the perfect coil-over size for my Govedo chassis, as the front wheels must go up by no more than 40-45 mm. Of course, in extreme conditions such like heavy braking after very fast speed, the tyres will also get compressed a bit, so the actual movement of the tyre's road patch will be at least 45 mm if the rim is moving with 38.89 mm.

-  I suppose that the front end will weight approximately 1060 lbs, or 530 lbs on each front wheel, hence the 1.181" / 30 mm compression that I suggest as a realistic number for a neutral ride height. In order for the wheel to go up by 1.531" / 38.89 mm, which makes the coil-over to be fully compressed after an additional stroke of 1.319" / 33.5 mm, a 450 lbs spring must be loaded with over 688 lbs on each front side (1376 lbs for both springs) on top of the aforementioned 1.181" / 30 mm.

- However, that number of 688 lbs is a theoretical spring weight compression in ideal conditions where the mass is directly forced vertically on top of the spring. Since the coil-over is tilted in a certain degree and the front lower A-arm is longer than the distance between the inboard pivot point of the latter and the lower coil-over mounting point, the actual mass force that is required to fully compress the coil-over is slightly lower than 688 lbs. So, maybe 600 lbs. Also, we must not forget that the QA1 coil-overs come equipped with a poly bushing buffer to soften the impact before the full compression of the shock absorber. This will further require more force to be used for the coil-over to be compressed, so in the end of the day the mass force may be about 650-680 lbs on each front wheel.

[SchulzeA]

MX, how can you determine the shorter shock will not work without first seeing the actual suspension blueprint? The stroke length will depend on how far the shock is from the inboard pivot point of the lower control arm.
The picture attached shows a murci with a very small travel ability. +/- 1" max on the front AT the tire? So what's the stroke length of the shock? Idk but I doubt it's over 2.5" like the shock Plansforsale is suggesting for his suspension.

[plans4sale]

 Thank you very much for your valuable opinions! 

[Tusabes]

I doubt any car will ever be built using these plans since it's been many years of excuses and changes without a set of finished plans

[76mx]

I will stick with my opinion, best of luck with that design.

[plans4sale]

P4S,
   I have had this discussion on various other threads before but short stroke shocks like that WILL NOT WORK. It is not a problem with the shock, it is with their springs. The longest spring that will fit is 7", and it coil binds at 4", so you have at best 3" of spring compression available. It will take a 250lb spring (+ or - 50lb depending on motion ratio and swaybar rating) so when you put 750lbs of car over that corner you use up that 3" and you are coilbound before the suspension ever has a chance to travel. A suspension bottoming out is the most dangerous and scary experience in a performance car that I have ever had. You do not need the extra travel of a longer shock, but you need it in order to get at least a 10" spring on it.

Thank you for your opinion, 76mx. Small compression for the coil-overs is a typical limitation for sports cars. Even the original Diablo or Murcielago had very limited space there. For example, the front wheels of K-1 Attack could go up no more than 40 mm.
 On my Govedo chassis, when the tyre is in normal position (i.e. not turned sideways), the free room for it to go up is no more than 65 mm. However, this is not the real usable number, because in a real-life usage there are other factors that determine how much the tyre could be raised from neutral position. For the FLT kit, the projected front tyre motion from neutral to up position is 45 millimetres, which is about 1.771648 inches. This is slightly less than the actual free space in this area, because the FLT kit will have dedicated composite mounting panels over the chassis, plus mudguard panels protecting the chassis from water and those tiny rocks thrown by the tyres. If there is no mudguard and no mounting panels installed (as if the Govedo chassis is used for Aventador replica), the front tyre can go up about 50 mm or 1.968498 inches. When I talk about tyre up movement, I take into consideration a fully functioning  left tyre turned to the left side with an angle of 36 degrees. In real life this will never happen, of course, because most likely the front suspension will take load under hard braking in nearly straight direction or in a high-speed cornering when the front tyres will not be turned sideways more than 15 degrees. Note that I mention tyre motion to up direction, not coil-over compression, because the former will be slightly longer than the latter. This means that the spring compression distance will be even shorter than the numbers relative to the tyre's rising. Also, the springs used for the front suspension will be lost likely 450 lbs each. Anything below 400 lbs is not recommended. The suspension motion will be limited in both, going up or down, by an adjustable limiter in the sway bar itself. There will be zero chance to hit the tyre into the chassis. Thanks!

[76mx]

P4S,
   I have had this discussion on various other threads before but short stroke shocks like that WILL NOT WORK. It is not a problem with the shock, it is with their springs. The longest spring that will fit is 7", and it coil binds at 4", so you have at best 3" of spring compression available. It will take a 250lb spring (+ or - 50lb depending on motion ratio and swaybar rating) so when you put 750lbs of car over that corner you use up that 3" and you are coilbound before the suspension ever has a chance to travel. A suspension bottoming out is the most dangerous and scary experience in a performance car that I have ever had. You do not need the extra travel of a longer shock, but you need it in order to get at least a 10" spring on it.

[plans4sale]

UPDATE:

- There is a change in the front suspension's coil-over. Previously, my Govedo chassis was supposed to use 14" QA1 coil-overs (part #DS502, Poly bushing). However, after taking exact measurements from various actual coil-overs, and considering that poly bushing mountings are nearly impossible to replace by builders with no special equipment, I figured out that the 10" QA1 coil-over with bearing mountings (part #DS301, Bearing bushing) is a lot better solution for this application. It also has a very limited travel from compressed to extended height, which is also important since the front wheels must not go too deep into the wheel wells. Here, you can check the specifications of the DS301 QA1 coil-overs:
 http://www.qa1.net/suspension/street-performance-racing-shocks-struts-and-pro-coil-systems/custom-mount-shocks/proma-star/proma-star-single-adjustable
 Having that said, I recommend use of the QA1 DS301 coil-overs. Of course, other brand for coil-overs could be used, if modifications to the chassis and suspension mounting points are made.

- For European customers (and everyone who use Metric system), there is the option to use QA1 rod ends with Metric size thread instead of Imperial size thread which is used in the US chassis plans. I do additional plans for the machined parts that will use rod ends in either thread measurement systems. In a future update, I will post links to the exact model of EU thread size QA1 rod ends. The US model is QA1 XMR10-12: http://www.summitracing.com/int/parts/hal-xmr-10-12/overview/

- I made improvements in the four metal plates that will hold the roof roll-cage tubes. Also, the B-pillar will now be attached 10 mm further towards the front end, in order to allow better visibility through the rear quarter window.

- The current progress of the EU and both US chassis plans is as follows:
A - Floor level [fully completed]
B - Bumper [fully completed]
C - Engine cradle [fully completed]
D - Door frames and hinges [not yet started]
E - Engine bay [fully completed]
F - Front end [fully completed]
R - Roof roll-cage [half completed, near finishing]
S - Sides of the cockpit [fully completed]
T - Central Tunnel [fully completed]
W - Firewall [fully completed]
M* - Metal sheets and plates [half completed]
MP - Machined parts [half completed]
SP - Suspension tubes [front completed, rear not yet ready]

[plans4sale]

UPDATE:
 
 - The MP (machined parts) drawings for the EU version of the chassis are now fully completed, the US ones are next to do;
 
 - All front suspension mounting points and lower A-arm were modified to match the recent changes in the frontal chassis reinforcement;
 
 - Ready with the list of approximate lengths of all tube types used in the chassis (except for the moving parts like suspension arms and door frames; these are still not finalized). It's worth mentioning that you should consider a bit more material, because tube profiles are usually supplied in common lengths of 6 metres in Europe or 20 feet in USA, hence several pieces cut from such a long profile will leave some waste material. For example, if you need two pieces of 2900 mm each, that will leave almost 200 mm unused (6000-5800=200). After I complete all tube plans, I will probably create a more detailed list where each piece is set roughly 10-15 mm extra long and nested in the most appropriate way, so that you can use quick straight cuts to divide any large tube profile into the desired number of smaller pieces, then use the latter to cut the final shape of the respective chassis tubes with the necessary cut angle and shape. Recommended tube wall thicknesses for the square and rectangular tubes are 2 mm for the EU chassis and 0.83" for the US chassis; round tubes have different wall thicknesses depending on the usage and placement. Lengths for the EU and US chassis tubes by tube type are as follows:
 square tube 20x20 mm / 0.75x0.75" - 37.2 metres / 122 feet total;
 square tube 40x40 / 1.5x1.5" - 30.1 metres / 99 feet total;
 rectangular tube 40x20 mm / 1.5x0.75" - 50.9 metres / 167 feet total  (1.5x0.75" could be replaced with 1.5x1", depending on which one is available);
 rectangular tube 80x40 mm / 3x1.5" - 4.5 metres / 14.8 feet total;
 round tube 41.3x6.8 mm / 1.625"- 5.6 metres / 18.4 feet total (most appropriate US tube wall thickness not yet considered);
 round tube 33.7x2.65 mm - 5.2 metres / 17 feet total (most appropriate US tube wall thickness not yet considered).

[plans4sale]

UPDATE:
 
 - The front bumper have been redesigned to increase the structural strength. There are five new tubes and lots of metal plates added to secure the frontal impact members. This also makes the front bumper stronger for when skid beam rollers are installed underneath.
 
 - Six tubes in the feet and dashboard area were slightly redesigned to simplify the tube cutting, and two extra tubes were added to the engine cradle.
 
 - The ST (suspension tubes) plans are renamed just SP (suspension), for easier understanding while reading the abbreviations.
 
 - Metal plates for the A2 roof pillars (before the door glasses) were improved with fixed mounting holes, hence the positioning and welding of these should be easier.
 
 - Due to the recent big changes in the currency exchange rate between the falling Euro and stronger US Dollar, the cost of Govedo chassis plans is updated as follows: a) Pre-order is 400 US Dollars or 380 Euros; door hinge 3d CAD file is included for free. b) Regular price is 500 US Dollars or 470 Euros; door hinge 3d CAD file is optional for extra 100 USD or 80 EUR.

[plans4sale]

UPDATE:

1. After some improvements on key areas I'm revisiting certain old tube plans that were slightly affected of the new changes. In the following days I will send update with a whole new set of plans to chassis builders.

2. The lower engine cradle mountings were completely redesigned to increase the strength, and use shorter screws now.

3. There are a few changes with the naming of the chassis plans, where the part's main letter helps to better understand the position of the respective tube, sheet or machined part. The new names are as follows (I also include the progress on them I made, marked in the [] brackets):
A - Floor level [fully completed]
B - Bumpers [half completed]
C - Engine cradle [fully completed]
D - Door frames and hinges [not yet started]
E - Engine bay [fully completed]
F - Front end [fully completed]
R - Roof roll-cage [half completed]
S - Sides of the cockpit [fully completed]
T - Central Tunnel [fully completed]
W - Firewall [fully completed]

M* - Metal sheets and plates [half completed]
MP - Machined parts (mostly made with a turner machine) [half completed]
ST - Suspension tubes [half completed]

*The "M" sheets or plates will consist one or two additional letters, depending on the position relative to the section of the chassis. For example, a metal plate used for suspension A-arm will be named like MST, whereas a metal sheet used in the firewall will be named MW.