LP 640 Autopro

[76mx]

Doesn't that bother you when all of the pieces have to be stripped off of the frame to paint it? My least favorite part of a build. Taking parts off seems so counterproductive. Here is a picture of 5" travel shocks with tires selected. It is at ride height and there is 2-1/2" of travel either way.

Wow that is a beautiful suspension setup . I love those brakes and suspension arms, just lovely my friend.

You're right, I didn't like to have to tear down the car after I had all the mechanical parts and the body mounter and I was dreading to do it.  But now that I'm just bolting on parts and everything is nice and clean I'm really enjoying it.

By the way, I'm eagerly waiting for your next set of videos.  I really want to see you start on the body, keep up the good work Charley.

Doesn't that bother you when all of the pieces have to be stripped off of the frame to paint it? My least favorite part of a build. Taking parts off seems so counterproductive. Here is a picture of 5" travel shocks with tires selected. It is at ride height and there is 2-1/2" of travel either way.

Wow that is a beautiful suspension setup . I love those brakes and suspension arms, just lovely my friend.

You're right, I didn't like to have to tear down the car after I had all the mechanical parts and the body mounter and I was dreading to do it.  But now that I'm just bolting on parts and everything is nice and clean I'm really enjoying it.

By the way, I'm eagerly waiting for your next set of videos.  I really want to see you start on the body, keep up the good work Charley.

Pedro,
   Just for you I have recorded three more videos today, the first one just posted to YouTube.

[autopro]

I need more clearance because of the messed up roads here in Tijuana 

I bought this stuff from Home Depot that is the same as Peel & Seal so I  can use it as sound deadener.  It works amazingly well and it's the same as Dynamat, but a whole lot cheaper.  Thanks Dustin for letting me know about this stuff.   I started installing it under the dash so I  can install my A/C unit next.

[plans4sale]

Here we go again and sorry to temporarily divert your thread Pedro but let us see if we can learn something here. "A potential relocation of the coil-over's sweet spot will only happen if the spring is being manually set at a different compression length". What does that even mean? If a 10" and 200lb spring has 600lbs of car at that corner, it will compress 3" to be 7" when the shock is in the middle of the sweet spot at ride height. If the same shock and spring puts the sweet spot way too high at ride height, there is still 600lbs on that corner and the spring still compresses 3". If the same shock and spring puts the sweet spot way to low at ride height, there is still 600lbs on that corner and the spring still compresses 3". How do you "Manually set a different compression length?".

If you put 1" bigger wheels on a car, it's coil-overs will not change, but the car will simply get raised by half an inch which is basically nothing for a road car. In the worst case you get better roadability through speed bumps and half inch reduced distance from top of the tyre to top of the wheel well liner (presumably a properly designed suspension already has rubber bump stops set to stop the upwards movement of the suspension at least one inch before a potential collision between the tyre and the wheel wheel liner). It's not necessary nor critical to adjust the suspension to be half inch lower for the new 1" larger wheels, because this is not a Formula 1 car where the ground clearance is very important and is set at different level for each track.

 And, yes, I meant that large nut of the coil-over used to adjust the spring load and lenght.

[lp670mike]

This is why i just used an MR2 for a donor car lol
This stuff is over my head hahahaha

[76mx]

Can't be it, Coop. The sweet spot is determined by the shock mounts, not the coil-over adjustment. Once the shock is located with the car sitting at ride height (as Pedro did and explained), the coil-over adjustment is cranked to wherever it needs to go in order to maintain that correct ride height (and this will vary from spring rate to spring rate), and once that is done the sweet spot is exactly where it wants to be. The coil over adjustment sets the ride height, it has nothing to do with setting the sweet spot. You can crank it to change the sweet spot, but that will also change the ride height at the same time, and that is just not a good plan. Either way, it will not "Manually set a different compression length". The only thing that will change a compression length is changing the amount of weight it is supporting.   

[sisqocracker]

I think he's just talking about turning the threaded bit at the bottom of the spring to set the ride height.  Is this not what he means by manually setting a different compression length?

Thanks,
Coop

[autopro]

All good Bobby and Charley any information on this subject is good so please keep it coming,  I just wished I knew the answer to your question  . I just hope that how I set up my suspension and my shock and spring choices are correct, if you feel I need to change anything please point it out.

So continuing to work on the car I installed the brake booster and painted the closing panels.

[76mx]

Here we go again and sorry to temporarily divert your thread Pedro but let us see if we can learn something here. "A potential relocation of the coil-over's sweet spot will only happen if the spring is being manually set at a different compression length". What does that even mean? If a 10" and 200lb spring has 600lbs of car at that corner, it will compress 3" to be 7" when the shock is in the middle of the sweet spot at ride height. If the same shock and spring puts the sweet spot way too high at ride height, there is still 600lbs on that corner and the spring still compresses 3". If the same shock and spring puts the sweet spot way to low at ride height, there is still 600lbs on that corner and the spring still compresses 3". How do you "Manually set a different compression length?".

[plans4sale]

All true P4S and that brings up other important considerations. The aspect ratio needs to be as large as possible. If the shock is more than 25% in on the lower a-arm, there are big problems. The shock needs a fair amount of travel, the farther inboard the less it travels and that shorter travel is still handling the same big bump but the fluid is traveling much faster to do so and makes tremendous heat. This will kill a regular shock in no time, the only option is $4,000 worth of inert gas shocks. Also, the spring rate must increase or even double to compensate for the lever arm. Besides adding unsprung weight, a similar thing happens with the spring. A very heavy spring travels a very short distance to handle a big bump and it knocks your teeth out. The more the inclination angle, the worse all of this gets. The shock and spring should be as far out and as straight up as possible to optimize suspension design, which makes the tire travel and the shock travel close but not the same. Notice I said that if you change the tire diameter by one inch that it will change the sweet spot by ABOUT 1/2" (centerline of axle moves 1/2" for every 1" of tire size change). 

 Due to the aspect ratio I mentioned in my previous post above, the "sweet spot" (the recommended default length of the coil-over in relation to its stroke, i.e. difference between the maximum and compressed lengths) of the coil-over will change less than 0,5" should the tyre diameter is increased by 1". However, there is something important to remember. After moving the coil-over's upper mounting point to the chassis or after changing the tyre diemater, a potential relocation of the coil-over's sweet spot will only happen if the spring is being manually set at a different compression length. If these is no intentional change in this matter, the car will simply be raised or lowered a bit (same as the changed tyre radius or moved mounting point) while preserving the exact same sweet spot as before.

 As for the quote coloured in blue, according to my understanding, the shorter travel of a shock will result in a slower speed and lesser amount of fluid transfer inside if there is no manual change in the shock's adjustment valve(s) (and many shocks will even not have an optional adjustment, so they always work in the same way). This will generate less heat and less friction of the rubber sealing.

 Bobi

[76mx]

All true P4S and that brings up other important considerations. The aspect ratio needs to be as large as possible. If the shock is more than 25% in on the lower a-arm, there are big problems. The shock needs a fair amount of travel, the farther inboard the less it travels and that shorter travel is still handling the same big bump but the fluid is traveling much faster to do so and makes tremendous heat. This will kill a regular shock in no time, the only option is $4,000 worth of inert gas shocks. Also, the spring rate must increase or even double to compensate for the lever arm. Besides adding unsprung weight, a similar thing happens with the spring. A very heavy spring travels a very short distance to handle a big bump and it knocks your teeth out. The more the inclination angle, the worse all of this gets. The shock and spring should be as far out and as straight up as possible to optimize suspension design, which makes the tire travel and the shock travel close but not the same. Notice I said that if you change the tire diameter by one inch that it will change the sweet spot by ABOUT 1/2" (centerline of axle moves 1/2" for every 1" of tire size change). 

[plans4sale]

 There are a few important general rules to mention that some people may not notice:

1. The actual stroke of a wheel is not equal to the stroke of a coil-over. The same goes for the strength of the spring. Both parameters fully depend on the angle of installation of the coil-over and the aspect ratio between (a) the overall length from A-arm mount on the chassis to the bottom outside wall of the wheel and (b) the length from A-arm mount on the chassis to the coil-over mounting point. In some cases the aspect ratio is so big that the wheel gets twice as long stroke compared to the coil-over's own stroke;

2. Any properly designed suspension will have rubber suspension bump stops that will limit the stroke of a wheel before the minimum and maximum stroke of its coil-over and eliminating the possibility of a collision between the upper wall of a tyre with the car's chassis or inner wheel liner.

[autopro]

You certainly give a lot to think about, for the next chassis build I will definitely keep this in mind Charley.

Installing the pedals took a bit longer than I expected tonight and this was all that I was able to get done.  I decided to add a couple more supports to the panel that goes behind it and it took some time to weld the little brackets.  Only one pic for tonight maybe tomorrow I can mount the booster and master cylinder.

[76mx]

Thank you Pedro and you are welcome Rstaggs. Glad to help. Consider something. Most people logically think that a chassis design starts with the framerails and works outward. It does not. It starts with the tires and wheels, which is the first and only set of "Givens", and works inward. The height establishes the axle centerline and the offset determines the hubface. These things then establish where the outer a-arm mounts can be and need to be. From there, that will establish where the inner a-arm mounts need to be in order to get proper geometry. Then the framerails go wherever they need to in order to make it all work. Same way with the shock mounts. Once the locations are established, the frame is designed to accommodate them. A chassis plan is useless until you first know the suspension design.   

[autopro]

Thanks 76 and Auto. Great clarity! I welded my shock mounts acourding to blue prints. I found several errors on the prints, such as the front shocks don't lined up straight. When I get my wheels and tires I'll do the same as you guys suggest. Thanks again, greatly appreciate it!

You're welcome Staggs.  Another thing I did was make an extra set of upper shock mounts like the rear ones and use them up front and I placed the shock in a more vertical position.

[autopro]

Doesn't that bother you when all of the pieces have to be stripped off of the frame to paint it? My least favorite part of a build. Taking parts off seems so counterproductive. Here is a picture of 5" travel shocks with tires selected. It is at ride height and there is 2-1/2" of travel either way.

Wow that is a beautiful suspension setup . I love those brakes and suspension arms, just lovely my friend.

You're right, I didn't like to have to tear down the car after I had all the mechanical parts and the body mounter and I was dreading to do it.  But now that I'm just bolting on parts and everything is nice and clean I'm really enjoying it.

By the way, I'm eagerly waiting for your next set of videos.  I really want to see you start on the body, keep up the good work Charley.