Spinoff of the nose dive thread

[NJSHO]

I’m trying to figure out how and if bias plugs could actually help the car brake flatter? I don't think they do, but I can see it 2 contradictory ways. If you can explain it please do, because I’m confusing myself:

1. Plugs don’t do anything to prevent nose dive or weight transfer, only springs and suspension design can prevent weight transfer. Rational: Newton’s first law, a body in motion stays in motion. Since the car is moving forward, when a braking force is applied (no matter from what point front or rear) the mass of the car wants to keep moving forward. Since the mass is constrained by the suspension, it causes the front suspension to compress. Even if you did all the braking from the rear of the car (relative to the direction of motion) the car would still nose dive. The only way to conteract this force is to have front springs that apply a force that is equal but in the opposite direction.

2. When riding on a bike, if you grab the front brake hard, you will most likely go over the handlebar, not very "flat braking." If you grab each the front and rear brakes with a force equal to the amt of forced used on the front brake only stop, the bike tends to keep both wheels on the ground. This isn't a very scientific explanation and it’s done on a bike with no suspension.

I’m siding with Newton on this one but can anyone explain the difference?

Edit: Another thought popped into my head. If bias plugs really did provide flatter braking, then the reduction of weight transfered to the front of the car would allow for more rear traction during braking. This is contradictory to what people are experiencing when they get squirly or activate the abs on hard stops after bias plugs.

 

[shomesomesho]

They lead to the perception that the car brakes flatter. Under mild to moderate braking with limited weight transfer, the bias plugs actually help braking because the rears are actually doing some work to supplement the fronts. As this requires less pedal effort, the car seems like it brakes flatter.

It's a different story under hard braking and increased weight transfer, when traction threshold is reached. The rears lock up first, ABS operates all 4 brakes, and braking distances are increased compared to proper threshold braking. This is why I no longer use the bias plugs in my autocross car.

With the stock bias plugs, under hard braking the fronts always lock up first.

 

[Shoaz]

I’m trying to figure out how and if bias plugs could actually help the car brake flatter? I don't think they do, but I can see it 2 contradictory ways. If you can explain it please do, because I’m confusing myself:

1. Plugs don’t do anything to prevent nose dive or weight transfer, only springs and suspension design can prevent weight transfer. Rational: Newton’s first law, a body in motion stays in motion. Since the car is moving forward, when a braking force is applied (no matter from what point front or rear) the mass of the car wants to keep moving forward. Since the mass is constrained by the suspension, it causes the front suspension to compress. Even if you did all the braking from the rear of the car (relative to the direction of motion) the car would still nose dive. The only way to conteract this force is to have front springs that apply a force that is equal but in the opposite direction.

Yup. And the changes in suspension stiffness, etc., don't change the amount of weight transferred, they just change what happens as a result. A 500 lbs/in spring only deflects one inch when 500lbs is transferred onto it, while a 250 lbs/in spring deflects two inches. They're both reacting to the same weight transfer, but the stiffer front springs result in less nose dive. There are a lot of reasons that stiffer springs are desirable on a performance car.

2. When riding on a bike, if you grab the front brake hard, you will most likely go over the handlebar, not very "flat braking." If you grab each the front and rear brakes with a force equal to the amt of forced used on the front brake only stop, the bike tends to keep both wheels on the ground. This isn't a very scientific explanation and it’s done on a bike with no suspension.

One difference here is that that relatively huge bike wheel means that the brake can exert enough torque to lift the rear of the vehicle. That can still be true even if the bike has suspension, both front and rear. Having no front suspension just means that it can happen more quickly than it might with a soft suspension.

I’m siding with Newton on this one but can anyone explain the difference?

I don't think there is a difference other than in the extreme case you can flip the bike, where you can't flip the car.

Edit: Another thought popped into my head. If bias plugs really did provide flatter braking, then the reduction of weight transfered to the front of the car would allow for more rear traction during braking. This is contradictory to what people are experiencing when they get squirly or activate the abs on hard stops after bias plugs.

I've never used the bias plugs because I never thought they'd do anything useful. I -want- the rears to get less brake as the tail rises and that little doohickey does just that for me. Why on earth would I want to eliminate that feature?

Having said that, right now on the Pumpkin I have the bias valve wire-tied fully open, mostly because I haven't gotten around to modifying the bracket to fit on the BMR arms (like I had on the silver car). I havent' been in too much hurry on the Pumpkin because it has the battery in the back and the fuel cell all the way back against the bumper cover, which helps. Nevertheless, I still get some rear lock-up (ABS activation) under trail braking.

In the silver car I could actually tell the difference between right and left-hand trail braking. Because the bias valve is on the left side, trail braking into fast right-hand corners would sometimes result in the right rear getting intermittent lockup (and ABS activation). Never had it happen in left-hand corners, though, because the inside rear would lift, the bias valve would reduce rear pressure, and I could sail through the corner with no ABS activation. What I got from that was that I had the valve adjusted just about right for best compromise.

There is no perfect system.

 

[93rev2sev]

The only way to limit the TENDANCY of the car to nosedive is to lower the center of gravity so that less of the cars mass is "higher" than the axle and more of it is below the axle.

You can potentially offset the TENDANCY with stiffer front springs but eventually, the mass of the vehicle that is relatively "higher" than the COG will want to force the top of the car over the front axle.

The latest way to lower the COG is with very large wheels as the axle gets farthur from the ground, the relative COG goes down.

If you can run 22s and still have the same ground clearance, nosing over will deminish greatly.

I'm not sure I spelled everything right but whatever....LOL

 

[Shoaz]

The only way to limit the TENDANCY of the car to nosedive is to lower the center of gravity so that less of the cars mass is "higher" than the axle and more of it is below the axle.

You can potentially offset the TENDANCY with stiffer front springs but eventually, the mass of the vehicle that is relatively "higher" than the COG will want to force the top of the car over the front axle.

The latest way to lower the COG is with very large wheels as the axle gets farthur from the ground, the relative COG goes down.

If you can run 22s and still have the same ground clearance, nosing over will deminish greatly.

I'm not sure I spelled everything right but whatever....LOL

Actually, the lever arm which the CG is trying to rotate against is the distance to the tire contact patch on the ground, not the axle. Putting the CG below the axle may reduce nose dive, but it won't eliminate weight transfer. Lowering the CG is effective against reducing weight transfer, but you really just want it as close to the ground as you can get it. Making the tires taller won't help that, it'll likely make it (and other things) worse.

One of the things I find fascinating about F1 cars is that the chassis are routinely built significantly lighter than the minimum weight allowed by the rules. The difference is made up by bolting a cast slug underneath the undertray of the car, where it is as low as possible and can be positioned as desired to optimize weight distribution.

I don't think I've heard of a better way to manage CG height.

 

[shobote]

The only way to limit the TENDANCY of the car to nosedive is to lower the center of gravity so that less of the cars mass is "higher" than the axle and more of it is below the axle.

You can potentially offset the TENDANCY with stiffer front springs but eventually, the mass of the vehicle that is relatively "higher" than the COG will want to force the top of the car over the front axle.

The latest way to lower the COG is with very large wheels as the axle gets farthur from the ground, the relative COG goes down.

If you can run 22s and still have the same ground clearance, nosing over will deminish greatly.

I'm not sure I spelled everything right but whatever....LOL

Got to be kidding me; 22 inch wheels ... your car will be much slower and handle much worse (huge unsprung weight increase) with these plus the ride will be simply untolerable; all for show; typical too much hot dog and not enough mustard.....

 

[JEM]

Got to be kidding me; 22 inch wheels

Yeah, when I see these idiots riding around on that garbage it just amazes me more of them don't fall off or just wobble off the road

 

[DemonNeno]

Yeah, when I see these idiots riding around on that garbage it just amazes me more of them don't fall off or just wobble off the road

Are you talkin about the drivers or the cars??

One of the worst things about working in a tire shop is dealing with this crap. 22" wheels add far more reciprocating weight then most OE brake systems are intended to work with. Not only do they complain about high speed vibrations (Yeah.. uhm.. the average 22" wheel requires around 7-10 ounces of weight...) and "shaking" when stopping. Hmm..

Off topic, but needed to rant!

 

[K-Dawg]

In the silver car I could actually tell the difference between right and left-hand trail braking. Because the bias valve is on the left side, trail braking into fast right-hand corners would sometimes result in the right rear getting intermittent lockup (and ABS activation). Never had it happen in left-hand corners, though, because the inside rear would lift, the bias valve would reduce rear pressure, and I could sail through the corner with no ABS activation. What I got from that was that I had the valve adjusted just about right for best compromise.

Stock rear brakes on the silver car? And what front brakes?

 

[Shoaz]

Stock rear brakes on the silver car? And what front brakes?

Stock rears with Porterfield R4-S pads, Baer 12.5" kit with R4 pads on the front.

Same setup on the Pumpkin.

 

[JEM]

One of the worst things about working in a tire shop is dealing with this crap.

I know it'd be chasing away money, but I'd think tire shops ought to be concerned about the liability implications of hanging so much more mass on the bearings and suspension than it was designed to handle.

 

[drivinhard]

One of the things I find fascinating about F1 cars is that the chassis are routinely built significantly lighter than the minimum weight allowed by the rules. The difference is made up by bolting a cast slug underneath the undertray of the car, where it is as low as possible and can be positioned as desired to optimize weight distribution.

Info I read said that the top teams at the end of the V10 era were putting close to 200 lbs on the undertray as ballast. Which means when you take away that, and the fluids and driver away from the car, you're talking about a ~875 lb machine. Staggering.

I always wondered if the CG approached, or was (heck, is) actually below the axle centerline.

 

[Shoaz]

I always wondered if the CG approached, or was (heck, is) actually below the axle centerline.

I wouldn't be at all surprised if it is.

Took these at NAB last week:




Especially with a 200lb slug on the bottom of that dude, and as low as the drivetrain mass sits, I could easily imagine the cg being near or below the axles.

Got a good look at the CF suspension with no hinges. There was an IRL car in another booth, which had steel spherical joints everywhere. It was a really interesting contrast in the technology levels for what are otherwise visually similar cars.

 

[SHOspazz92]

Stock rears with Porterfield R4-S pads, Baer 12.5" kit with R4 pads on the front.

Same setup on the Pumpkin.

And they work VERY nice


-Sam

 

[Jonny Cash]

I remember when Kirk had the white+ raked big time for a track setup. Slightly lower in the front than in the rear. Nose dive was non existant. I cant say I know much on physics, but I know shorter, stiffer springs in the front make a huge difference. I can show you a pic of the setup if interested.

 

[drivinhard]

It was a really interesting contrast in the technology levels for what are otherwise visually similar cars.

LOL an F1 car at NAB.

I'm in that field and I would have probably ignored the other booths and looked at the F1 car all day

 

[Shoaz]

LOL an F1 car at NAB.

I'm in that field and I would have probably ignored the other booths and looked at the F1 car all day

It did seem a little out of place, but I wasn't complaining.

There was a Vietnam-era tank in the outdoor exhibits, too. Never did figure out what that was all about.

 

[DemonNeno]

I know it'd be chasing away money, but I'd think tire shops ought to be concerned about the liability implications of hanging so much more mass on the bearings and suspension than it was designed to handle.

In all honesty, there isn't much money to be made on sets of rims. Especially with the market taking such a globalized (like everything else..) twist. Profit is down as is value.

The bearing situation isn't actually that big of a deal. Although you are adding weight, you generally don't double the weight of the assembly compared to the stock wheels & tires. Also, the biggest bearing-killer is entirely different offsets. When we install these wheels, the offset is actually closer to what the vehicle requires compared to the guys that lift their truck and use far more negative offsets / smaller backspacings to clear body panels. They, of course, have solid axles and much more durable hubs that can withstand the added load, however it does shorten the life of almost all wearing parts.

Long story short, the most ill effect a larger wheel has mostly involves vehicle performance. At a immensely large size, the vehicle's abilities are greatly lessened to practically the point where it's only good for cautious cruising.Which is what I don't get. Why not lower your vehicle more, use 20" at the largest and run at least a 50 series tire? You drastically increase the ability of a truck. Cars should wear nothin' larger than 18s IMO... 19s are totally unrealistic in daily driving. And if you can deal with it, you must have a mob of angry drivers waiting for you to cut it slow over tracks, weavin around the lines between lanes and (my favorite) on someone's ass when your tryin to stop... which you do poorly (since the average big-wheeled vehicle has extremely underpowered braking).

Ahh, now i feel better.