[marig]

For years, I have always used the Bolink-style body posts, with the large plastic nut that threads to the post.

I have also, for years, mounted the front body posts where the front bumper attaches to the chassis plate. This results in needing a slightly taller post than if I were to mount the posts further forward, on the bumper, where they normally go.

I have also, for years, always had a noticeable, high-speed push. I could make adjustments to improve it slightly, but it never goes away. Could mounting my front body posts in the "wrong" location be causing this high-speed push? I say high-speed because the more the car slows down for the corner, the more the push goes away. This has been true for 2 or 3 different chassis and body combinations I've had over the last several years.

Does everyone mount the front body posts on the bumper? Has anyone run with them mount further, like I mentioned?

Thanks.

 

[KLUPI]

That could be a possibility, I personaly think it is very important on how you mount the body. I use a Proto Charger and the body slopes from right to left. If you are lazy you could just cut the body at an angle around the bottom to eliminate the slope. I take the time and adjust the body mounts so the body is sloped as designed and the bottom of the body is straight as it should be. LefthanderRC has some great threaded adjustable body posts that really let you fine tune how the body sits.

 

[swtour]

marig,

Do you have any body support from a foam front bumper or anything? If not, on high speed tracks the nose of that body is probably flexing quite a bit (I'm suprised it's not dragging)

I mounted my bodys at the bumper mount years ago, because it seemed to be a good common place and was consistant regardless of which type of front bumper I ran...and I've always liked playing with several cars and this let me change bodies from one to another. I felt this mounting caused bodies to crack at the wheel wells to easy (even with a center support mount) and just allowed to much body flex.

I'm not one of them supersonic guys, but I do beat the hell out of my equipment...and bodies last much longer for me with the mounts in the bumper...and the use of a center mount...and a FOAM Bumper (LIKE THE BEEFY ONE)

 

[burbs]

The further forward your body mounts are, the more downforce you wil have in the front of the car.. I have tried both, and the bumper always seems to work best.. You dont get as much body flapping either..

 

[marig]

swtour, I didn't mention it, but I do have the foam front bumper supporting the very front of the body. I also have a custom piece of lexan, bent and servo taped to the top of the steering servo, acting as a support for the hood of the body, just about where it meets the windshield. I'm running only on short carpet ovals, so the speeds aren't very high, compared to bigger tracks. Just pushing down on the front of the body seems to confirm that the support is good.

burbs, that's what I wanted to confirm - thanks. It doesn't seem like a big difference just thinking about, it but I've eliminated every other possibility I could think of. I have another car that I inherited from someone, which seems to definitely enter the turn better than the one I built, and I've been trying figure out why by process of elimination. I've noticed that the other car does have the front body posts mounted farther forward on the bumper, so it made me wonder.

 

[MIKE VALENTINE]

Marig, do you run a graphite bumper under the foam? Does the foam cover or enclose the entire area from the graphite chassis to the body? By enclosing this area of the car you will decrease front down force at high speed. try running a graphite bumper with the post in the same locations you have them know and only a small piece of foam at the vary fron portion of the graphite bumper in front of any cutouts in the graphite bumper.

 

[marig]

Mike, you're right - the foam covers most of the center section of the graphite bumper, going back toward the chassis, covering the cutout in the graphite bumper. The outside edges of the bumper are not covered, but it's no more than an inch on each side.

Wow - that's something I hadn't thought of - thanks for the tip. I will let everyone know how it goes next time I run the car.

 

[IndyRC_Racer]

Let's not forgot the obvious reason that more weight forward on the car should result in more steering. Having the body mounted on the bumper will mean what little weight the body posts/hardware will be more forward on the car and should have more leverage on the steering. I'm not sure how much of an affect this would have, but I'm sure it does make some difference.

BTW, my latest car has the body posts non on the bumper and the car seems to be working well.

 

[pmsimkins]

Let's not forgot the obvious reason that more weight forward on the car should result in more steering. Having the body mounted on the bumper will mean what little weight the body posts/hardware will be more forward on the car and should have more leverage on the steering. I'm not sure how much of an affect this would have, but I'm sure it does make some difference.

BTW, my latest car has the body posts non on the bumper and the car seems to be working well.

It may be counterintuitive, but the exact opposite is true. Moving weight rearword loosens the car up. That's a fundamental principle of the handling of any vehicle.

Moving the body posts forward creates more of a lever for the downforce to act on the front wheels.

Downforce and actual mass sitting on the chassis don't act in the same way.

 

[MIKE VALENTINE]

I'm not sure that the lever comes into play if the body is properly supported. I think about it this way, you move the rear wing for or aft and you never move the mounting point to the body and it has an effect. So if te body doesn't move and your just moving the body post, I don't see why it should efect the down force on the front wheels, as long as the body isn't messed up.

 

[pmsimkins]

I'm not sure that the lever comes into play if the body is properly supported. I think about it this way, you move the rear wing for or aft and you never move the mounting point to the body and it has an effect. So if te body doesn't move and your just moving the body post, I don't see why it should efect the down force on the front wheels, as long as the body isn't messed up.

First, we could be making a big assumption that the front of the bodies even make downforce. I did some wind tunnel stuff way back when I was in school and found that the bodies made varying degrees of lift. that could have been purely the result of how i ran my tests though. So, for the sake of argument we'll accept that the body does actually make downforce on the front.

That said, the force is transferred to the chassis through the body posts and then is transferred to the wheels through the suspension. For the sake of argument lets assume the car has no suspension, it is fixed. This simplifies things. Now if you mounted the post exactly in the plane that the suspension would pivot in and applied a pound of force you would see 1 pound increase in force acting on the ground through the front wheels and no change in the force on the rear wheels. Now if you put that post in front of the plane of the suspension and applied 1 lb of force you would see >1 pound increase in force acting through the front wheels and a corresponding decrease in the force acting through the rear wheels, so that the total force balanced out. If you placed the post behind the plane of the front suspension you would see an increase of <1 lb on both the front and rear wheels. How the pound would be distributed depends on how far behind the front wheels the post is.

Hopefully you see what I am saying. The same principle is in play for moving the wing forward and back.

 

[marig]

Just for followup:

I finally had a chance to run the car per Mike's suggestion of cutting away the foam bumper from the area between the front of the body and the front of the chassis, so this area was now open. I did not move the body posts from where I had them. I ended up with just a small thin strip of foam glued right to the front section of the bumper, not covering any of the cutouts.

It made a noticeable difference on corner entry - the car was a lot better turning in and did not want to push nearly as much.

There was still a little push, but I later figured out that was because I had the front of the chassis a little higher than the rear. Once I lowered the front a bit, it was pretty much perfect.

 

[nickcacc]

It may be counterintuitive, but the exact opposite is true. Moving weight rearword loosens the car up. That's a fundamental principle of the handling of any vehicle.

Maybe you can 'splain this to me clearer....if you go with your 1lb example you had a little later in the thread...wouldn't the farther back you move this weight, the greater the rear downforce and the more likely the car is to being tight or pushing?

 

[jdearhart]

Nope, moving weight rearward will loosen a car up. You create a pendulem (SP?) effect, helping the rear of the car to come around.

Do a little experiment the next time when you are at the grocery store or Wally World (Wal Mart). Get one of the shopping carts, and have your wife or someone stand on the front of the cart and ride. The cart will be noticeably harder to turn with all of the weight on the front.

 

[vwal]

So why is it when Silver Crown cars start a race with 75 gallons on fuel they don't turn but later in the race they are sideways at the flagstand?

 

[pmsimkins]

Maybe you can 'splain this to me clearer....if you go with your 1lb example you had a little later in the thread...wouldn't the farther back you move this weight, the greater the rear downforce and the more likely the car is to being tight or pushing?

Downforce and weight on the chassis do not act in the same way. Downforce is always pushing down and does not transfer.

Think of it this way. When you're going around a corner at any instant in time the front wheels and the rear wheels are actually traveling in straight lines (vectors) out towards the wall. This vector continually changes direction as you proceed around the corner. If I could draw a picture this would be easier. Think of a tether ball swinging around. If you cut the rope the ball flies off in a straight line tangent to the circle at the instant the rope is cut.

Our tires are like the rope they are providing the force to keep our car going in a circle and not fly straight into the outside wall. The weight and speed of our vehicle determine the force that wants to overcome our tires and make the car go out. The more weight there is the greater the force is. So, if there is more weight on the rear of the car the rear tires will want to slide out more than the front tires and you have a loose condition. if there is more weight on the front the front tires want to slide out more than the rear and you have a tight condition.

Hope that makes sense.

 

[MIKE VALENTINE]

First, we could be making a big assumption that the front of the bodies even make downforce. I did some wind tunnel stuff way back when I was in school and found that the bodies made varying degrees of lift. that could have been purely the result of how i ran my tests though. So, for the sake of argument we'll accept that the body does actually make downforce on the front.

That said, the force is transferred to the chassis through the body posts and then is transferred to the wheels through the suspension. For the sake of argument lets assume the car has no suspension, it is fixed. This simplifies things. Now if you mounted the post exactly in the plane that the suspension would pivot in and applied a pound of force you would see 1 pound increase in force acting on the ground through the front wheels and no change in the force on the rear wheels. Now if you put that post in front of the plane of the suspension and applied 1 lb of force you would see >1 pound increase in force acting through the front wheels and a corresponding decrease in the force acting through the rear wheels, so that the total force balanced out. If you placed the post behind the plane of the front suspension you would see an increase of <1 lb on both the front and rear wheels. How the pound would be distributed depends on how far behind the front wheels the post is.

Hopefully you see what I am saying. The same principle is in play for moving the wing forward and back.

i have to disagree with you on this one.

 

[pmsimkins]

i have to disagree with you on this one.

Fantastic. Explain why I am wrong.

 

[98Ron]

///

Stiff springs to hold up all the gas? and then more weight % on the nose as the fuel is used?

 

[CBear3]

Or because by the end of the race they've worn the right rear tire out...was listen to some scanner chatter during the cup race yesterday and they were talking about only taking one can of gas on the late caution to tighten the car back up.