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Old 02-11-2015, 07:10 AM   #5446
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So b20btec, which Combination have you found best then?
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Old 02-11-2015, 07:37 AM   #5447
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Originally Posted by Wacker1 View Post
So b20btec, which Combination have you found best then?
Indoor Carpet, medium to high traction (blinky 17.5)
Aluminum Chassis
Standard shocks and towers - Black bladder, dual orings
Standard motor mount position
Shorter arms when traction is up
Front arm sweep (even 3.9 blocks up front)
Less rear toe (2.0 to 2.5 stock racing)
X brace on up front
X brace off rear

I could be completely wrong but i'm not investing anymore time on the short shocks and FMC. The X brace made the biggest difference so far on chassis adjustment.
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Old 02-11-2015, 07:47 AM   #5448
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The FMC makes a big difference on higher-bite carpet if you don't have the aluminum chassis. With the aluminum chassis you can run the normal motor position and regain some of the steering you lose with the FMC.
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Old 02-11-2015, 07:56 AM   #5449
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I will test a excellab chassis and after i'm done i will have two bd7 2015 up for sale. Complete with 2 aluminum chassis, factory chassis, and tons of spares. All raced on carpet.
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Old 02-11-2015, 10:54 AM   #5450
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I know this is going to be a silly question what is a fmc. Sorry don't know what it means
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Old 02-11-2015, 10:58 AM   #5451
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I know this is going to be a silly question what is a fmc. Sorry don't know what it means
Forward Motor Conversion

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Old 02-11-2015, 11:00 AM   #5452
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I know this is going to be a silly question what is a fmc. Sorry don't know what it means
Forward Motor Conversion. ... motor mount moved forward or backwards using different belts and top deck..
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Old 02-11-2015, 11:20 AM   #5453
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Thank you
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Old 02-11-2015, 09:15 PM   #5454
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I've noticed more and more drivers are using heavier weight oil in the rear dampers? What are the benefits to this setup and under what conditions would you use this?

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Old 02-11-2015, 11:10 PM   #5455
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It mostly used when running mod motors, it can make the rear a little less responesive under acceleration. So the rear end have less tendensy to spun out.
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Old 02-12-2015, 04:54 AM   #5456
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guys, what is it about the blue vs black bladders and the single vs double o-rings? What did you feel? i felt nada...


thanks
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Old 02-12-2015, 04:56 AM   #5457
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howcome the FMC would take steering away all the time? I was thinking only when the car is drifting, but not when it is planted... am I thinking this wrong? Thanks, Paul
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Old 02-12-2015, 05:46 AM   #5458
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howcome the FMC would take steering away all the time? I was thinking only when the car is drifting, but not when it is planted... am I thinking this wrong? Thanks, Paul
Something I wrote a few years ago:


1. Static weight distribution.

The effects of changing a car's fore/aft weight distribution is probably the most commonly misunderstood adjustment in all of motorsports. It sounds simple enough, want more steering, move weight forward right?

Nope. It's the exact opposite of what you think. Let me see if I can explain it. There are two reasons for the effect.

When you add vertical load to a tire, it gains traction. But if you put them both on a graph, you will see that the traction goes up less than the load is going up. For example, take a tire with a 1 pound vertical load on it, let's say it can also take 1 pound of lateral load before it slides. Now double the vertical load to 2 pounds. Does it now take 2 pounds of lateral load to make it slide? No, it will slide at a lesser lateral load, let's say 1.8 pounds.

Secondly, if you move static weight forward in the car, you are putting more vertical load on the front tires but you are also moving the center of gravity forward. Obviously I am talking about the fore/aft position of the cg, not the height. The cg is the point on the car where centrifugal force pushes on it to try and push the car towards the outside of the corner. Let's see an example of how this might affect things.

Imagine a 1 pound car. It has the exact same tires all the way around and its weight distribution is exactly even, 1/4 pound of weight on each tire. Its fore/aft cg position will be right in the middle of the car between the tires. Now let's say skid pad tests show this car can take a 1 pound lateral load before skidding, meaning it can corner at 1g and it's perfectly balanced handling wise so when it skids, it's a four wheel drift out of the circle, not a spin out or an understeer out of the circle. If you doubled the car's weight to 2 pounds, the tires will gain more traction but not as much as the weight will increase the lateral load so the car will now skid with a 1.8 pound lateral load which is LESS than 1g with a two pound car.

Now let's go back to the one pound car but let's move some component forward so that the front tires now have more weight on them. This would initially seem to increase front traction so now this car will spin out when it skids instead of a nice, balanced, 4 wheel drift right? No, that's wrong. Remember, traction goes up more slowly than the vertical load does. So what happens is that the now more lightly loaded rear tires have lost less traction than the fronts have gained. But this alone is only part of the story since we are still seeing a loss of rear traction and a gain in front, even if it isn't an even trade.

That's where fore/aft cg location comes in. Imagine the original, balanced car is stationary on the skid pad and you are in the middle of the skid pad with a pool cue to use to try and push the car from the side out of the circle. The end of the pool cue is placed right on the cg (middle of the car) and the tires and load are the same so when you push on the cue, the car just slides all four tires. Now move the weight forward. The cg moves forward so you have to move the spot on the car that you push with the cue forward. This means you are now pushing harder on the front tires than on the rear. This would be balanced out by the increase in front traction and the decrease in rear traction resulting in another perfect, four wheel slide except that as I said before, the rears have lost less traction than the fronts gained. So the front tires are going to slide first. The car will now understeer.

I hope that makes sense. I am not the best at clearly explaining complex concepts of vehicle dynamics but I have studied it extensively and this is the basic consensus of ALL well informed engineers on the subject. This is why nose heavy front engined cars fight understeer issues while tail heavy rear engined cars like 911s fight with oversteer.

Also, this subject can get even more confusing due to another effect. As I described above, moving the weight to the rear should make the car oversteer but there is a situation where this could be backward. Moving the weight back will make the car looser in a steady state corner but with a rear wheel drive car, the increase in rear weight could reduce wheel spin under power, improving rear traction. This is why offroad dirt cars have such a high rear weight distribution. So in this situation, moving the weight to the rear could result in more steering off power but less on power. Especially when powering off of a slow corner, but might have even MORE on power steering exiting a fast corner. And if that wasn't confusing enough, having that motor slung out in back also gives the car a high polar moment of inertia, making it less responsive. Moment of inertia is a whole different subject to be addressed later.
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Old 02-12-2015, 07:16 AM   #5459
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Excellently described wingracer! Maybe this is a bit over the top, but:
Would you agree with me that a modern TC setup with a spool up front tends to have better steady state and transition performance when it has a bit more rear than front statical weight?
Reason i think that: While steady state the spool creates a yaw decreasing torque and let the car understeer. With a rear-heavier car and same tyres you need to increase front roll stiffness to get the same handling. So the wheel load alteration on the front is higher which in turn will have the spool to create less of the unwanted understeer because the inner front wheel will have just less vertical load!

And to bring the argumentation to an end: I think, that when using the FMC, and therefore more statical weight at the front, you should start thinking about a gear diff up front. Because the negative side effects with the spool will become more apparent while ALSO the advantage in traction, so longitudinal performance, of the spool diminishes!

Would you agree?
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Old 02-12-2015, 07:23 AM   #5460
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Understood (yes, really). thanks
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