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|Subject: Review #1 - "Throwing Your Weight Around"|
|Gus||Posted on 7/18/2001 10:54:58 AM|
(Click here to read the article review)
OK, folks, let's hear it! Please help me out with my questions listed in the article. Or if you have additional questions, ask away, and we'll try to get some answers for everyone.
Thanks for your help!!!
|3xRacing||Posted on 7/19/2001 3:54:11 AM|
Great questions, but they are EXTREMELY difficult to give an exact answer to.
First, I think Gore's theories can be applied to both dirt and asphalt. Obviously you can get more grip(side and forward bite) with the car using all 4 tires to their fullest ability, but this really depends on the class of car, or more importantly, the horsepower of the car compaired to the weight of it and the size/compound of the tires.
We've all seen the super late models carry the LF tire coming off the corners. This is caused by the amount of forward bite these cars can produce. Once the driver begins to pick up the throttle, the car has so much bite, its would pick up both front tires if not for centrifical force holding the RF to the track(the car's force turning the corner).
On heavier cars like the pro-ams or hobbys, the power to weight ratio, or the tires 'stickiness' isn't great enough to pull the front end off the track. In this case your better off using more static weight to help plant the LF tire to the track to aid in the steering necessary to come off the corner.
As for the side bite, I personally don't think more weight on the right side of the car is the way to go. The static weight of the car (the way it sits sitting on the scales) should always favor the left - somewhere around 53% depending on the size and banking of the track. I have found that side bite becomes less important when you get the entry to middle of the corner working good and the car is fast here. A good example I once heard a very winning SLM driver give of this is as follows:
'Suppose your driving on a gravel road in your regular street car at say 20 MPH, now floor it and see how easy it is to spin your tires....now try to do it going 60.'
This is a very exaggerated example but the point being if you can get into a corner alittle faster and carry that MOMENTUM into the corner, you'll find your car had more sidebite and forward bite than if you ride the brakes and slow way down getting in.
The spring comment is accurate given the car still rolls over in the corner. Meaning that if you have 3 inches of suspension travel on the RF with a 500 lb. spring, and you switch to a 600 lb. spring and STILL have 3 inches of travel, then it took 300 lbs. more of weight transfer to the LF to give you that result. Stiffing up the RF spring adds dynamic cross weight, softening the RF spring removes dynamic cross weight. (The opposite is true of the LF spring)
Edited on: 7/19/01 5:05:53 AM
|Rusty Nutz||Posted on 7/23/2001 12:55:24 PM|
You bring up some very good points. I do have a question for you regarding what you say about side bite being less important when you get the car working good through the middle of the corner - Isn't it side bite that is responsible for GETTING it working good through the middle of the corner?
Where's the WD-40?
|3xRacing||Posted on 7/23/2001 3:59:27 PM|
Rusty Nutz, (great name)
What I actually said and meant was, get the cars entry through the middle good, meaning 'turn 1 and turn 3', if you can get the car into the corners faster, without using a ton of brake, the shock to the rear tires when you try and pick up the throttle will be lessened just by the fact the car is moving faster. I also stated that the size and banking o fhte track your running will affect how true this is. A high bank track can be run with less rear weight and side bite than can a flat track with tight corners.
|warrior5||Posted on 7/23/2001 11:45:56 PM|
How about the front weight. On a late model what split should a person have across the front. I can never find a solid answer. Many times people responde with I never look at the front. I feel there has to be some solid answer. As far as not looking at the front. What do ya do all race. Its the first thing the flag stand.
Edited on: 7/24/01 12:08:08 AM
|3xRacing||Posted on 7/24/2001 1:53:39 AM|
Believe it or not warrior, most guys I know DON'T look at the front weight when scaling a late model chassis. The left weight, rear weight, and left rear bite seem to be the important numbers here. I personally think that cross weight is extremely important no matter what class of car you run. Once you get your left, rear, and left rear numbers you want, the only way left to adjust your cross is by adjusting your front split(which will affect the left weight so you'll have to chase these 2 back and forth alittle). I like about 49% cross weight for the way I drive and the feel I want out of a car. For a 2400lb. late model, that usually results in about 50 - 60 lbs. of split across the front tires.
Edited on: 7/24/01 2:49:44 AM
|3xRacing||Posted on 7/24/2001 2:55:56 AM|
I think the first thing that needs to be said is that there are MANY ways to set up a car. NO answer given by anyone here is the tell all truth for every car out there. It needs to be a COMPLETE set-up. I like certain things in my car for the way I drive, the way I scale a car, the springs I use, the shocks, the stagger, the wheel offsets, the lead placement on my chassis, etc etc. Unless everything about your car is exactly the same as whoever is giving advice, it may or may not work, but it should get you going in the general direction. Anyway, take what you read with a grain of salt.
|ProAm17||Posted on 7/24/2001 9:57:58 AM|
I agree with 3x's last statement. First you have to have a good, sensible starting point, then learn the car and how to adjust from there.
In my ProAm, I started with 53% left, 57% rear, and crossweight depended on track. Eagle was 48% - 49%, Sunset was always right at 51%, and I-80/NRP was around 49% - 50%. Primarlily 50% at NRP I-80 towards the end of last season. That was mainly due to running a lower gear (6:50), which resulted in a quicker throttle response which would loosen the car. So I increased the cross by 1%.
Another biggy in the ProAms is track width. Your front end should track roughly
1 1/2" (or so) wider than the rear. This adds to the front stability, and makes the rear "follow" the front better. Utilize the wheel offsets as much as possible, plus, you can use a 1/2" wheel spacer (1 per wheel) to accomplish the desired track width, plus make adjustments. START WITH SOMETHING BASIC THOUGH! Don't throw some goofball set up under the car that doesn't make sense, and you don't know what it'll do!
In the ProAms, start with a basic shock set up too. I usually had a LF7600, RF7700, Left and Right rear 9500. Those were ProShock numbers. The first digit indicates the length of the shock rod. The second digit indicates the valve or softness/hardness of the compression and rebound. If the last two digits are "00" that means it is an equal amount of valving on compression and rebound. If the last two digits have a number, then its a split shock. As a beginner, avoid split valves until you under stand them. I would somtimes put a 7630 on the right front for the feature. Due to changing my right rear offset (pulling 1 more inch under the car) I would need to loosen my corner entry since I was tightening my corner exit. Without confusing or going into more detail, trust me, it worked!
I used 17 lbs of tire pressure on both lefts, and 19 on both rights for the heats. Then I'd drop to 15 and 17 for very dry conditions. I'd also adjust a couple of pounds here and there for minor adjustments.
The Pro Am rules never addressed air pressure relief valves for the tires. So I ran one on the right rear. The nice thing about it was as the right rear stayed at my designated tire pressure, the left rear would grow a little. Then as fuel burned off and lightened the rear a little, the gain in tire pressure in the left rear would tighten the car enough during the race, I didn't notice the loss of weight so much in the rear and the car stayed consistent throughout the race.
3x is right, this stuff worked great for me, but it might not work perfectly for you. It never hurts to try something though. I experimented with several set ups and finally got to one I liked.
In Pro Ams, don't think your car has to be low to the ground. If you have it too low, or the front end itself sits too low, you'll have problems. Make sure the suspension has room to go through a full range of motion. The front should sit up a little so it doesn't bottom, and the rear should sit up around 1 - 1 1/2 inch higher than the front. I usually tried to go with the right rear my highest point, then the left rear 1/2 lower, then the right front 1/2 lower than left rear, and then the left front 1/2 lower than the right front. You kind of made a "Z" pattern going 1/2" lower at each corner starting at the right rear. Didn't always work perfectly with a leaf spring car, but usually got close.
More to come if anyone needs it. Gotta go for now.
Edited on: 7/24/01 10:01:33 AM
|Gus||Posted on 7/24/2001 12:36:53 PM|
When ProAm17 was describing how his pressure relief valve in his right rear kept the car tight as the race progressed and he lost rear percentage due to fuel usage (less fuel later in the race), he seems to indicate that his car would normally otherwise get looser with less rear weight as fuel is consumed. In contrast, during last week's Winston Cup race on TV, Benny Parsons was describing how a car gets TIGHTER at the end of a fuel run as the fuel is consumed. I have also read this concept in technical articles as well, how the end of the car with the higher weight is the end that will slide out first due to the centrifugal force acting greater on that end than on the lighter end. In other words, if the center of mass is closer to the rear than the front, the centrifugal force pulling out on that center of mass in the middle of the corner will pull the rear out farther than the front, resulting in a loose condition. But yet, for years, I hear local racers talking about always ADDING more rear weight to TIGHTEN their cars! Is this possibly an example of something that works opposite on asphalt vs. dirt and maybe Benny and the technical articles are referring only to asphalt? Or is it possible that the apparently conflicting ideas are referring to two different parts of the race track? For example, maybe adding rear weight would loosen a car in the middle of the corner but tighten it coming off?
The Rookie Wrencher
|3xRacing||Posted on 7/24/2001 3:37:24 PM|
Great question Gus,
When you see local racers on dirt adding weight to the rear, they are actually adding the weight to the LEFT rear. This adds more bite to the car which tightens the rear of the car all the way around the corner, but especially coming off while on the gas.
As far as 17's deal with the bleeder valve, I think what he was doing (and I'm sure he'll correct me) was letting the LR tire build up during the race while kepping the RR at the softer pressure. This will tighten the car in 2 ways.
First, it will add cross weight because the LR tire will carry more weight the harder it gets, and second by making the RR seem softer in compairison to the LR it will seemingly have more grip. I would just have to assume his fuel cell was set to the left so he was loosing that LR weight that keeps the car hooked up.
|racer31x||Posted on 7/24/2001 5:50:40 PM|
Not sure what tires the ProAm's run, but allowing the left rear to build pressure as the race progressed while the right rear stayed constant would also decrease rear stagger, tightening the car as the race went on as well, right?
|ProAm17||Posted on 7/24/2001 6:26:12 PM|
The tank was indeed a 16 gallon, and as far left as I could get it. So the guess work had to begin when I was experiencing a "loose" condition at the end of an A feature.
Fuel was burning off at the left rear, and I need to correct something. I feel that I lost forward bite, in combination with the loose off condition. Two things were happening. Left rear weight decreased, causing less crossweight as the race progressed. Secondly, it decreased rear percentage, taking away some forward bite. Also, and as usual, the right rear was usually the hottest tire, therefore gained the most pressure, therefore decreasing the crossweight percentage (LR/RF). This all spelled trouble in the A.
My answer was to keep the right rear tire pressure consistent, then letting the LR build. Second, was to pull the right rear in 1" with wheel offset. On my car this didn't necessarily do much to the crossweight, but had a profound effect on the leverage point of the rear end, and, got the right rear tire to "dig" in more, better utilizing the edge of the tread. Next was the right front shock. I used the split valve as described earlier, to let the weight of the car transfer quicker from the RF to the LR, causing the LR to have more bite coming off. The decrease in compression valving on the RF helped to keep from being too tight going in.
Now I agree with Gus' theory on the heavier end will go out first, as a pendelum(?). But the question I have is the forward bite? Wouldn't a lighter rear cause you to lose forward bite as the fuel burns off? Just wondering. I think my car was more apt to become loose because of the fluctuation in tire pressure, and losing weight from the left rear due to the fuel cell location. Could these condition outweigh the "pendelum affect?"
To clarify something, I do not believe in "adding weight" for anything. Once a car is set up, weight should never be added, only moved around. But I don't even believe in moving weight around. My opinion is that using shocks, tire pressure, wheel offset, etc.
Gotta go quick here,
|3xRacing||Posted on 7/24/2001 6:57:39 PM|
we're getting deep here now..(not in s**t! lol just theory).
the LR, RR thing is kinda like on a car with adjustable rear springs, cranking turns into the RR loosens the car because you are taking weight away from the left rear and adding it to the RR (your doing the opposite to the front but we'll just talk about the rear for now). The pendelum effect really only holds 100% true if the weight is 50/50 on the tires, meaning same weight on the LR as the RR, and same weight on the LF as the RF. When you start to make the LR heavier, the car has to 'drag' that heavier wheel around the lighter RR to use that pendelum effect, thus making the car tight. The opposite is also true. A heavy RR can easily 'drag' a light LR around with it to make the car loose.
17's car became loose as he burned off fuel because he was loosing that weight off of the LR, making the balance shift to a heavier RR. The way to get around this is to add weight to the left rear (like Gus says he sees the local guys doing) to make it alittle too heavy at the start of the race, but once that fuel burns off about half way in the race, the car will be balanced the way the driver likes it.
One other thing that could have loosened 17's car is the split valve shock on the RF. A 6-3 shock will compress as a 6, and extend as a 3. So going in to the corner, the harder compression will help keep the LR planted to the track, so the braking effect from that tire is helping turn the car alittle more than if using a 50/50 shock. You could achieve the same using a 3-6 shock on the LR. To help tighten 17's car getting in, either a 50/50 shock on the RF, or that same 6-3 shock from the RF moved to the LR to let that tire unload alittle quicker to take some of it's braking effect away would have helped tighten the car getting in.
|ProAm17||Posted on 7/25/2001 8:39:10 AM|
Just to make sure, I purposely wanted to loosen the entry with the split valve shock, due to doing so much to the car to tighten the tighten the exit.
Hey! We're all pretty much on the same track! Imagine that.
I think it would be safe to say that the "pendelum" effect is not something we put a lot of trust in, but it does exist. I agree with you analogy of the LR vs. RR weight and the pendelum effect.
I could of easily moved more weight to the left rear, but my car was real touchy, and I didn't want to lose any rear percentage AT ALL! I liked that feeling of having the rear grab and go! Plus, the way my car was designed, it would of taken a lot to bracket the rear end to mount the weights. I had my car built brand new from K9 in 1993, and we hit the track with it in 1995. I never changed anything in John's design, ever. The car was the same in 2000 when I sold it as it was brand new. Only a few more very small reinforcement bars in the front bumper area.
John also did the original set up on my car, and those numbers were very trust worthy. I had to figure out the rest, such as shocks, tire pressure adjustments, etc.
One great point you made 3x was to have the car the fastest at the end of the race. My theory was, as the fuel burned off, the car became a little bit lighter, therefore the horsepower had more of an effect at the end than at the beginning. That is why I cut my end of race weight so close. Theoretically, if the set up was right, as others were slowing down, I was speeding up. It happened sometimes, but you had to hit it just right.
Wonder when some of our Rookie friends, and Hobby stock gentlemen will start joining in? Lots of great info here.
Blah blah blah, yadda yadda yadda.
|Rusty Nutz||Posted on 7/25/2001 8:55:30 AM|
PA17 touched a bit on tire temps, which brings up another question I've had for a long time. When a tire gets hot, what exactly does that mean? Does it mean it is working really well and sticking to the track or does it mean it is sliding and/or spinning on the track and NOT working well? For example, if you take tire temp readings right after your race and the right rear is quite a bit hotter than the left rear, does that mean that the right rear is working/sticking BETTER than the left rear (which I would think would indicate a loose condition if the right rear is sticking and the left rear is spinning) or does it mean the right rear is being overworked in relation to the left rear and its extra heat is coming from spinning on the track surface (indicating a tight condition if the left rear is sticking and the right rear is spinning)?
Where's the WD-40?
|ProAm17||Posted on 7/25/2001 11:11:47 AM|
RN: Someone else can probably give you a better answer than I can, but the only thing I can tell you is this.
When I brought up this very issue with a VERY well known SLM and GN driver, he said, "Who's right rear tire doesn't get got?"
I can say that after I made the adjustments for super dry A features as I described earlier, such as the RR pressure relief, wheel offset, shocks, etc., that the rear tire heat equalized a little bit more. In other words, it seemed like the LR got closer to being as hot as the RR. I should point out however, that I was going according to feel, and not a temp guage. It lead me to believe, and I could be wrong, that the more traction a tire is getting to the track, the more heat it builds. I could be wrong. It also seemed that when the RF felt like it was stuck down pretty good, the RF would feel hotter.
The other thing about tire temp is alignments and proper pressure. You can tell how well your front alignment is in the ballpark is to check the tire temp in three spots across the width of the tire. If the temperature is even across the tire, that means you're getting good traction from you alignment, and your tire pressure is right. If the tire is hot in the middle only, you might be running to high of pressure. If it's the same temp on the outside and inside, but cool in the center it might not have enough air. You get the picture!
Rear stagger will change the camber of the rear end. Obviously, if the right rear tire is bigger in circumfrence than the left rear, the rear end will "tilt" slightly to the left. So you can adjust a little bit in the rear using stagger to get the proper traction through the tire temps.
Hopefully 3x will have some more for you. This was the best I could do for now. I think with the Pro Ams and Hobby's, the cars are big and heavy, and you're going to get tires hot.
The absolute perfect race car would have precisely the same tire pressure on all 4 corners, and the temperature would be exactly the same across the tire on all 4.
If anyone has been able to accomplish this, you are now an official racing god!
See y'all later,
P.S. If you can afford to have a nitrogen bottle on hand, use the nitrogen to fill you tires and maintain the pressure. Nitrogen doesn't heat up and expand as bad as regular ol' compressed air.
|3xRacing||Posted on 7/25/2001 2:00:52 PM|
If you have 3 tires that are all about the same pressure and only 1 that is really hot ,like the RR for example, the hot tire is LOOSING traction and the extra friction from it spinning is making it hot.
A good example is the drag cars, The all do this big smokey burn out before they stage to heat up their tires so they get better traction. The tires spinning builds heat in them. Now the dragsters use a rubber compound that is designed to get 'sticky' as it gets hot so the heat is good for them.
Oval track tires need to wear to keep cool. If you have a tire that is getting hot, it probably is loosing traction and spinning faster than the car is moving, OR you could be unloading that corner of the car so far that the tire really isn't doing much but skimming along the track. Either way, this friction is causing heat build up.
When you see guys getting out of their car and putting their hand on the tires to 'measure' tire temps, they are finding out which tires are hot. If you find a hot RF, you know your car was pushing alittle or you were using alittle too much steering input. A hot RR would indicate that you were spinning the rear tires either with the gas or the rear of the car was skating out and heating up that RR tire. You then could make your adjustments based on what your tires just told you.
PA17 is on the money about the front tires and reading across them for camber/toe adjustments.
|ProAm17||Posted on 7/25/2001 2:34:05 PM|
3x's analogy of why the tire heats up actually sounds good after I gave it more thought.
If the LR is getting a whole bunch of bite, and the RR is a bigger circumfrence tire, that would lead me to believe the RR is experiencing some "slippage" or spin to try and keep up with the smaller tire, thus resulting in more friction heat. If this was an extreme condition, it would also result in the RF getting hot due to a push. Makes sense.
Blah blah blah, yadda yadda yadda.
|Rusty Nutz||Posted on 7/25/2001 5:10:00 PM|
So is it ideal on dirt to try to have as equal of temps as possible across all the tires? For example, if the left rear is cooler than the right rear, does that mean the chassis needs to be adjusted (more leftside static weight perhaps) to even them out? Or is there some advantage to having the right rear be warmer than the left rear? I've always read in technical articles that the closer you can get all four tires to being equal temp, the faster you'll be, but one critical part always seems to be lacking from those articles - they are usually asphalt oriented articles and never really specify whether the same applies to dirt tracks. Is it possible that somewhat UNBALANCED temps are faster on dirt? Or should you still aim for equal temps as much as possible?
Where's the WD-40?
|3xRacing||Posted on 7/25/2001 6:27:51 PM|
It's really hard to say RN, of course no matter what you do, your RR will always be alittle warmer than the LR just from turning the corner. (unless your pushing so bad you dented the front of the car off the wall!) Banking and speed of the track play into this so we'll have to assume we're talking about NRP here. The banking of the track abuses the outside tires more than the inside because of the force the tires 'hit' the track. Therefore on a high banked track, you need to adjust your car off of what your but tells you. ('seat of your pants') Don't put quite so much stock into this tire temp thing, it's a good 'ballpark' adjustment, but you really need to just pay attention when driving the car to whats happening when your off the gas, on the brake, off the brake, steering into the corner, steering into the slide, picking up the thottle, etc..,. If you just get out of the car and say 'It's pushing', then your in for a long night. But if you can get out and say ' It's pushing when I'm on the brakes but is OK once I let off them', then you know you have too much front bias dialed in and you can fix the problem. Pay close attention when driving to whats happening INSIDE the car as well as where your going, and you'll find making adjustments to the car much easier.
|ProAm17||Posted on 7/25/2001 8:55:17 PM|
Just to give you a "ballpark" figure, I started with a 50 pound split on the rear. The LR was 50 pounds heavier than the RR. My temperatures improved as I increased the LR weight a LITTLE bit. In other words, either the LR temp increased, or the RR decreased, as the split in weight across the rear increased.
For some reason, and considering all the stuff earlier in this thread that I made for adjustments, made the temps improve. They were a little more even, but the RR was always hotter.
As 3x said, don't get too hung up on this thing. Concentrate on the "easy to do" stuff first. And document EVERYTHING!
Edited on: 7/25/01 8:56:02 PM
|3xRacing||Posted on 7/26/2001 11:52:09 PM|
OK, i think we covered that one pretty well, let's see your next question Gus.
|Gus||Posted on 7/27/2001 8:45:41 AM|
Workin' on it as we speak, 3xRacing!
Thanks to everyone who participated in the discussion above. If anyone has any more to add or any more questions about the topics mentioned above, fire away and we'll continue this discussion while we prepare the next one.
Also, if anyone sees a specific article in any of the racing magazines (Circle Track, Stock Car Racing, Speedway Illustrated, etc.) that they'd like us to tackle as an upcoming topic, please let us know. Or if you have any other ideas to add to this section of the site, please share them with us. We appreciate your feedback!
The Rookie Wrencher
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