NASCAR physics questions

<<1) In the NASCAR game manual, under Rear Bias, it says (and I'm paraphrasing) that the more weight there is in the rear of the car, the more it tends to get loose. Also, under Fuel, it says as the tank gets empty, (thus lightening the rear weight) the car tends to push. Ok, so far so good.>> Interesting... I've found my experience with the game to be just the opposite of what the manual says. My car gets looser as the tires die and the fuel load lessens. I'm pretty sure the real cars are similar to that. Look at it like this... what do you do to keep the rear tires of a truck from getting "loose" in the snow? You add weight! <<However, when the manual talks about downforce, it suggests that to CORRECT a loose condition, you add MORE rear downforce.>> There are a number of different ways. That is just one suggestion. For example, are you getting loose entering a turn or exiting? <<2) When I watch NASCAR races on TV, cars tend to 'pair up' (the announcers always call it finding a 'dance partner'). I would assume this is so the car behind gets a draft, but how does it benefit the car in front?>> The are drafting each other. Neither car has to work as hard to run at speed. The car in front is in the cleaner air, though. It gets more air to the motor. One of the long-term effects of drafting is if you follow for too long your motor has a tendency to run a little toasty. The fuel mileage will increase also, probably for all cars involved. <<And if it doesn't, why doesn't the car behind just slingshot past? I would think they might just keep slingshotting past each other, but instead it seems they maintain their order.>> Some cars just don't have the power to stay in front. Look at Sterling Marlin. The cars ran faster when he was leading at Talladega recently than when he wasn't. It all depends on which cars work best together. Say you have two cars drafting off each other... cars A and B. They may run faster, for whatever reason, with car A in front. Car B may not lose any ground when he is following, but it may be apparent that car B doesn't have enough intestinal fortitude to pull car A along and force him to follow. Nick ______________________________________________________________________ #6 (will he be #28 in '97) & #94 in the *real* quest for the Cup My home away from home... http://www.annihilated.com/~ntotoro/ ______________________________________________________________________

Yes, that makes sense. It also helps explain why it's so hard to pass the car that I'm drafting! :) --Tim

The aerodynamics was explained, so just a little to add about the racing aspect. When 2 cars are drafting, they run faster dividing the wind flow, so they need less horse power, and in turn, burn less fuel. Two cars who 'team up' and draft for a while will run faster and last longer (because they conserve fuel) than a single car, or two cars who keep slingshotting past each other. Tire ware also plays a roll. Casual drafting doesn't melt them as quickly as aggressive racing does.

: 1) In the NASCAR game manual, under Rear Bias, it says (and I'm : paraphrasing) that the more weight there is in the rear of the car, the : more it tends to get loose. Also, under Fuel, it says as the tank gets : empty, (thus lightening the rear weight) the car tends to push. Ok, so : far so good. : However, when the manual talks about downforce, it suggests that to : CORRECT a loose condition, you add MORE rear downforce. : My question: Why do "weight" and "downforce" have opposite effects? I'm : confused. I've read several explanations of this, so let me put in my 2 cents worth. Downforce is created from wind resistance such as on the rear spoiler. The wind acts in two directions (recall your statics and dynamics here), opposite to the forward direction of the car (drag) and downward (downforce). There is no force that acts to the side of the car (ie. perpendicular to the forward motion of the car). However, when dealing with weight, the term "weight" is actually a misnomer. The correct term would be "weight distribution", because all the cars weigh the same (about 3400 lbs). But, the teams distribute the weight in the car to get the desired effects of speed and traction. This is how it works: When a car is travelling at a constant speed, there is no weight shifting. However, when the car accelerates, the weight shifts to the rear, and when it slows, the weight shifts to the front. Everyone has witnessed this in their own cars when stopping at red lights. Also, when a car turns left, the weight shifts to right, and when it turns right, the weight shifts to the left. Now, imagine a car racing at Martinsville. The car accelerates out of turn 4 across the start/finish line. The weight is shifted backward (I'm neglecting shocks, tire pressure, etc. I'm only dealing with weight bias here). When it reaches turn 1, the car slows and turns left. Naturally, the weight is shifted forward and to the right (ie. mostly to the front right tire). If I have my car set up so that there is more weight distributed to the front than to the back, then the action of braking and turning will accentuate this and it is very likely that the car will push going into turn 1. However, to offset this effect, if I had more weight in the rear, the car would probably not push into the turn. Then as I ease off the brake and coast through the apex of the turn, there is no longer a difference in weight distribution between the front and rear. However there is a difference between the left and right side of the car. As I'm turning left, the weight is shifted to the right. I want to lessen this as much as possible because I don't want to be thrown to the outside wall. Therefore, usually the the maximum amount of weight is placed on the left side to counterbalance the car. Then as I get back on the gas to exit the turn, the weight is once again shifted to the rear (and I think that this is where your question lies). The shifting weight does not create a downward force as the wind acting on the rear spoiler does; instead it acts to the side. In other words, if you had too much rear weight, when you accelerated out of the turn, the lateral force would be greater than the friction of the tires and you would slip. Conversely, if more weight was on the front, you would push into the wall. Try to imagine a shopping cart at a grocery store. If you load all you groceries on the very front of it, it's hard to turn. It's the same way when you exit a turn. This may not have helped much, but here's one more tip. The best way I've found to find to correct weight distribution is to look at the right side tire temps. Depending on the track, I like my car either neutral, neutral - tight, or neutral - loose. I first learn my driving style for a particular track and then I move the weight around so that if I want the car a little loose, the rear tire will be a few degrees hotter than the front tire or if I want it a little tight, the front tire will be a little hotter than the rear tire. Then as the tires wear, the setup will change depending on the track. For example, at Bristol, I set up a little loose, and the car gets looser as the tires wear. But at Loudon, I set up a little tight, and the car gets tighter. Then at Atlanta, I set up loose, and it tightens up later. So you must know you driving style at a track to be able to adjust the weight. Again, remember that I only spoke on weight distribution. It becomes more complicated when all the other factors are added to the formula. -- Danny Fe***an

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>1) In the NASCAR game manual, under Rear Bias, it says (and I'm >paraphrasing) that the more weight there is in the rear of the car, >the more it tends to get loose. Also, under Fuel, it says as the tank >gets empty, (thus lightening the rear weight) the car tends to push. >Ok, so far so good. However, when the manual talks about downforce, it >suggests that to CORRECT a loose condition, you add MORE rear >downforce. >My question: Why do "weight" and "downforce" have opposite effects? d. >2) When I watch NASCAR races on TV, cars tend to 'pair up' (the >announcers always call it finding a 'dance partner'). I would assume >this is so the car behind gets a draft, but how does it benefit the car >in front? And if it doesn't, why doesn't the car behind just slingshot >past? I would think they might just keep slingshotting past each other, >but instead it seems they maintain their order. > Thanks, > Tim

re: 1) I hope this makes some sense. More weight on the back of the car may provide some downforce but, when the car is rolling thru a turn centrivugal force tends to try to throw this weight into the wall which more than offsets any benefit gained from downforce created by the weight. Using a spoiler to get down force is great because it does not add mass that is effected by centrifugal force. It's not free either, spoilers catch air to produce downforce therefore causing drag which can slow you down. You must balance these effects. re: 2) A car running alone at speed must punch a hole in the air (increased pressure at the front of the car) then when the hole in the air closes behind him there is actually a vacuum created which kinda sucks him back (negative pressure at back of car). Also, when the air goes over the roof and hits the spoiler drag is created (downforce too). When a car comes up behind him two things occur (actually more than two but I gotta get to work) A)The air hole is kept open. no more vacuum behind the lead car. B) Not as much air hits the spoiler on the lead car which means less drag. Oh, and C) if the lead cars gets bumped that helps too. The main benefit for the aft car is that he doesn't have to punch a hole in the air. It's already open. I'll let someone else deal with the dirty/clean/turbulent air issue. I don't type so good. Hope this helps, Mike Radler

> Any thoughts about giving bonus points for doing well at the short tracks like Bristol when assigning skill ratings? At 'Dega if you can > make it through the inevitable major crash at the start which wipes out half of the field it is pretty easy to finish high. At Bristol or > other short tracks the racing is much tighter and it takes more skill to finish high. That would make it a bit unfair to us on leagues where we cannot really choose which track we will be running on that given week. For instance, if I am running a league race at Pocono I will be racing/practicing that week at Pocono, not Bristol or Martinsville. Whos to say winning at Dega is more difficult than winning at Bristol or visa-versa?? Sure everyone can run Dega, but it is sooo dang touchy there, that its not that easy to run thoses consistant 197s that I am seeing...(without the draft) I am sure people like Irvan & Martin would consider a win at any track equal victory If you are worried about skill level points, run on a league. I was all concerned about my skill rating when I first jumped on Hawaii.....Now I concentrate on being a safe, patient, consistant driver. League racing forces you to do that. ::stumbling off the soapbox:: ----------------------------------------------- vetteracer (on hawaii) http://www.geocities.com/MotorCity/1726 If you wanna Finish First, you have to First Finish -----------------------------------------------

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>1) In the NASCAR game manual, under Rear Bias, it says (and I'm >paraphrasing) that the more weight there is in the rear of the car, the >more it tends to get loose. Also, under Fuel, it says as the tank gets >empty, (thus lightening the rear weight) the car tends to push. Ok, so >far so good. >However, when the manual talks about downforce, it suggests that to >CORRECT a loose condition, you add MORE rear downforce. >My question: Why do "weight" and "downforce" have opposite effects? I'm >confused. >2) When I watch NASCAR races on TV, cars tend to 'pair up' (the >announcers always call it finding a 'dance partner'). I would assume >this is so the car behind gets a draft, but how does it benefit the car >in front? And if it doesn't, why doesn't the car behind just slingshot >past? I would think they might just keep slingshotting past each other, >but instead it seems they maintain their order. >Thanks, >Tim

The physics are such that two cars drafting can actually go faster than one car alone. And, add to that a bump from the car in the rear, and the effect is compounded. Rick

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>1) In the NASCAR game manual, under Rear Bias, it says (and I'm >paraphrasing) that the more weight there is in the rear of the car, the >more it tends to get loose. Also, under Fuel, it says as the tank gets >empty, (thus lightening the rear weight) the car tends to push. Ok, so >far so good. >However, when the manual talks about downforce, it suggests that to >CORRECT a loose condition, you add MORE rear downforce. >My question: Why do "weight" and "downforce" have opposite effects? I'm >confused.

I'm not really qualified to answer this part, but I'll at least try. Downforce plants the rear end of the car, keeping it from getting loose. Weight distribution is a completely different issue, and I'd rather someone answer it that knows what they are talking about. When a car is running by itself, a large area of turbulence is created at the back of the car, causing a good bit of drag. If a car is drafting behind this car, it smooths the airflow behind the car. This allows the two cars, together, to go faster. Hope this helps. Pat ----------------------------------------------------------------------------- Pat Campbell The Chevy Monte Carlo 6,94,88,16,4,25 Lexington, AL NASCAR's Wide Load War Eagle!!! Home Page: http://fly.hiwaay.net/~pscampbe/pscindex.html NASCAR Stats: http://fly.hiwaay.net/~pscampbe/nascstat.html -----------------------------------------------------------------------------

[snip -- since my mechanic isn't here to help on on #1)] : 2) When I watch NASCAR races on TV, cars tend to 'pair up' (the : announcers always call it finding a 'dance partner'). I would assume : this is so the car behind gets a draft, but how does it benefit the car : in front? And if it doesn't, why doesn't the car behind just slingshot : past? I would think they might just keep slingshotting past each other, : but instead it seems they maintain their order. I hope I get this right.... The car behind gets the benefit of the draft. But, as the air flows over the back of the rear car it will begin to flow over the top of the car behind. This actually has the effect of lessening the drag on the lead car. Therefore the theory goes both will go faster. It also seems that due to aero changes over the last few years it is harder to get the slingshot effect of old. Also having two cars side by side disrupts the clean air flow over the cars, thus causing more drag on the 2 cars -- slowing them down. At times you will see one car passing another and then "teaming up" again in reverse order. This is because the one car can actually go faster than the other and thus increase the "pulling" effect. The longer they stay in order, the faster they will be compared to the cars that haven't caught up to the draft. Yeh, I know I've stated it all too simplistic, but then I'm not a Rocket Scientist :) -- **************************** Michael E. Carver ************************* Upside out, or inside down...False alarm the only game in town. =-=-=-=-=-=-=-=-=-=-=-=-=-=-=<[ /./. [- < ]>=-=-=-=-=-=-=-=-=-=-=-=-=-=

1) In the NASCAR game manual, under Rear Bias, it says (and I'm paraphrasing) that the more weight there is in the rear of the car, the more it tends to get loose. Also, under Fuel, it says as the tank gets empty, (thus lightening the rear weight) the car tends to push. Ok, so far so good. However, when the manual talks about downforce, it suggests that to CORRECT a loose condition, you add MORE rear downforce. My question: Why do "weight" and "downforce" have opposite effects? I'm confused. 2) When I watch NASCAR races on TV, cars tend to 'pair up' (the announcers always call it finding a 'dance partner'). I would assume this is so the car behind gets a draft, but how does it benefit the car in front? And if it doesn't, why doesn't the car behind just slingshot past? I would think they might just keep slingshotting past each other, but instead it seems they maintain their order. Thanks, Tim

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> <<1) In the NASCAR game manual, under Rear Bias, it says (and I'm >paraphrasing) that the more weight there is in the rear of the car, the >more it tends to get loose. Also, under Fuel, it says as the tank gets >empty, (thus lightening the rear weight) the car tends to push. Ok, so >far so good.>> > Interesting... I've found my experience with the game to be just >the opposite of what the manual says. My car gets looser as the tires >die and the fuel load lessens. I'm pretty sure the real cars are similar >to that. Look at it like this... what do you do to keep the rear tires >of a truck from getting "loose" in the snow? You add weight!

I believe you're right ... I just checked the IndyCar manual, and it says just the opposite of the NASCAR manual ; i.e. that as weight transfers to the rear, the rear grips better and the car tends to 'push'. Now, I know Indycars and Nascar cars (Nas-cars?) are different, but I'm pretty sure they don't have different laws of physics :) So I'm concluding the NASCAR manual is wrong, and that you and the IndyCar manual are right. Perhaps they'll fix that in the NASCAR 2 manual (like it's a big priority :) ). On the short ovals, I tend to get loose entering a turn, and tend to push on exiting (ouch, that wall hurts!). Any suggestions? --Tim

One other thing to add to this. The original poster asked why the second car in a draft doesn't just slingshot past the front car. Well, it used to be that way. Cale Yarborough won two straight Daytona 500's in 1983-'84 by waiting till the last lap to slingshot past the lead car on the backstretch. Darrell Waltrip, and Buddy Baker were the victims. Before restrictor plates, it was possible for the second car to run at about 3/4 throttle in the draft (this according to the late Neil Bonnett). All that driver had to do to pass was lay back a little, floor the gas, pull out, and shoot right by the lead car. But, the plate takes away all the top end acceleration from the car. Consequently, all the top cars are running wide open in the draft. It takes an extremely strong engine for anyone to pass by themselves. So far this year, only Sterling Marlin has shown an ability to do this with ease, thanks to Runt Pittman. Pat ----------------------------------------------------------------------------- Pat Campbell The Chevy Monte Carlo 6,94,88,16,4,25 Lexington, AL NASCAR's Wide Load War Eagle!!! Home Page: http://fly.hiwaay.net/~pscampbe/pscindex.html NASCAR Stats: http://fly.hiwaay.net/~pscampbe/nascstat.html -----------------------------------------------------------------------------

>to that. Look at it like this... what do you do to keep the rear tires >of a truck from getting "loose" in the snow? You add weight! I think this is only true for such an extreme situation as power oversteer in the snow, a transitional condition. if you try to corner with this snow in the back at a decent speed, you'll find the pickup gets loose. Gregory Fung Vancouver, B.C., Canada

>I believe you're right ... I just checked the IndyCar manual, and it says >just the opposite of the NASCAR manual ; i.e. that as weight transfers to >the rear, the rear grips better and the car tends to 'push'. Now, I know What you are describing is weight transfer backwards during acceleration. What he's asking is how weight distribution affects handling. Both manuals are correct, it's just that both are taken out of context. Look up the part in Indycar manual about cornering weight transfer, then think about this: The grip available at each axel is about the same with a small change in weight (this simplifies the analogy), so with more weight over an axel, it will stick less than the other axel. Please see another message in the thread regarding weight/grip ratio. This is rather natural of weight transfer. You move weight forward under braking (going in), causing looseness. Weight moves backwards under power, causing push. Personally, I counter the latter by using small amounts of power oversteer. You can change your driving style to minimize the effects. Gregory Fung Vancouver, B.C., Canada

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> >I believe you're right ... I just checked the IndyCar manual, and it says > >just the opposite of the NASCAR manual ; i.e. that as weight transfers to > >the rear, the rear grips better and the car tends to 'push'. Now, I know > What you are describing is weight transfer backwards during acceleration. > What he's asking is how weight distribution affects handling. Both > manuals are correct, it's just that both are taken out of context. Look > up the part in Indycar manual about cornering weight transfer, then think > about this: The grip available at each axel is about the same with a > small change in weight (this simplifies the analogy), so with more weight > over an axel, it will stick less than the other axel. Please see another > message in the thread regarding weight/grip ratio.

======= Hmmm. They're close, but not quite right. Friction increases as vertical load increases, but not linearly. This is adequate to explain why rear drive performs better than front drive in straight line acceleration. For cornering, the question is one of lateral weight transfer. It's important to point out that aerodynamic down force contributes nothing to weight transfer. Thus, increased rear wing can help control oversteer. Sprung weight, however, transfers when cornering. Lateral friction increases with vertical load, but at somewhat less than 1:1. That is, adding 100 lbs vertical load will increase friction somewhat less than 100 lbs. Weight transferred off the inside tire decreases the lateral resistance at that corner a certain amount. The corresponding load increase on the outside tire raises the traction there some amount, but always less than that taken from the inside tire. If this imbalance brings the total traction available at the rear below that required, oversteer results. I hope this was clear. I'm rushing this because I'm connected via long distance. ====== Try adjusting the rear shocks to get a gentler weight transfer under acceleration. The problem here is weight transferring from front to rear weight when you roll on the power. And yes, stomping the gas abruptly will definitely worsen the conditon. Mike.

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>1) In the NASCAR game manual, under Rear Bias, it says (and I'm >paraphrasing) that the more weight there is in the rear of the car, the >more it tends to get loose. Also, under Fuel, it says as the tank gets >empty, (thus lightening the rear weight) the car tends to push. Ok, so >far so good. >However, when the manual talks about downforce, it suggests that to >CORRECT a loose condition, you add MORE rear downforce. >My question: Why do "weight" and "downforce" have opposite effects? I'm >confused.

This seems to be an error in the physics model. In everything I've read about vehicle dynamics, increasing the load on a tire increases the amount of lateral (turning) and longitudinal (brake/acceleration) force available. However, it is not a linear function, so generally you want to distribute the weight evenly. In other words, two tires sharing an equal load will generate more lateral/longitudinal force than say 60/40 distribution. I assuming you're talking about restrictor plate racing (Talladega and Daytona). The primary reason for not constantly slingshotting past another car is because it slows both cars down. If you're in the lead pack, you want to hook up to drive away from the rest of the pack. If you're behind, you want to catch up. Also, when two cars pit together, they can draft back up to speed much more quickly together. You'll see a lot of shuffling go on in the last 10-20 laps of a restrictor plate race, as drivers try to set themselves up for a run to the front. A lot of action is going on in the pits as the teams send runners down pit road to figure out who they can hook up with to make a dash. But on the white flag lap, all bets are off. Dave "davids" Sparks Sequoia Motorsports

> >2) When I watch NASCAR races on TV, cars tend to 'pair up' (the > >announcers always call it finding a 'dance partner'). I would assume > >this is so the car behind gets a draft, but how does it benefit the car > >in front? And if it doesn't, why doesn't the car behind just slingshot > >past? I would think they might just keep slingshotting past each other, > >but instead it seems they maintain their order. When two or more cars are drafting the front car does benefit, but the rear car benefits more. The leading car benefits from the lack of air closing down behind his car, which will create drag. The trailing car suffers from this "vaccuum" behind his car, but the forces pulling from the leading car prevail. Terry

> Question: Do you guys on HAWAII mind if someone 'bump-drafts' you? Add a note about Bump drafting to your hotkeys (F1-12) Its tough in pickup races when you don't know everyone quite so well. Join a league, you will get to know all the drivers and the trustworthy-ness of their driving... Last night on my league I was only gettin 196s alone at 85 degrees, got in a bump draft and was seeing 202 going into turn 3. What a rush!! vetteracer http://www.geocities.com/MotorCity/1726

>Subject: Re: NASCAR physics questions >Date: Tue, 23 Jul 1996 19:08:59 GMT >The physics are such that two cars drafting can actually go faster >than one car alone. And, add to that a bump from the car in the rear, >and the effect is compounded. >Rick Question: Do you guys on HAWAII mind if someone 'bump-drafts' you? ________ Eldred Pickett I am NOT paranoid. And why are you always watching me?!?

I don't since it only slows the one doing the bumping. Assuming it is not in a turn and he isn't going twice my speed. -- Chuck Stuart - Mesquite TX USA VBTrace 96 is a runtime Procedure Trace, XRef, Debug, Profiler and much more. Shareware $49. http://www.apexsc.com/vb/ftp/coop/cstuart