Nice! I'm a year or so into my BSME...quite a ways to go...
Regardless of the technical benefits, I still hate driving CVT cars. The modern ones are getting good at sort of simulating gear-changes to comfort the ear, but I still get the feeling I'm driving a go-kart or a snowmobile. I suppose you likely get used to it.
An interesting case where the captain cares all about torque and HP is only a figure of academic interest is the PT6 (or probably about any turboshaft/constant speed prop setup) captain pays attention only to torque. Since his prop turns (more or less) at a constant speed, torque is all he needs to know. Its also the only thing that can be easily directly measured, which is probably why they have a torque gauge and not a power gauge.
Yes, but you need the WHOLE thing, not just one figure from it. Thats the disadvantage of talking about torque. Uber torque at weaksauce rpms will not get the work done. Sure, if you have uber torque at macho rpms, you will get the work done in a hurry.
The best way to express a torque curve in a single figure is horsepower. This is why you see horsepower figures quoted versus weight, not torque versus weight.
500hp/ton ALWAYS results in a predictable acceleration over time, regardless of the actual torque curve...assuming we have decent gearing. So a 500hp electric motor with 5000lb-ft of peak torque will get from a>b in about the same amount of time as (opposite end of spectrum) a 500hp gas turbine making 80 or 90lb-ft of torque.
If you made the absurd statement that the 5000lb-ft/ton car is going to be faster than the 90lb-ft car, you better not be betting big money. You could very well be wrong.
Bob made these statements:
"Power to weight is irrelevant, I'd say it's the most useless statisitic you can have about a car IMO."
Obviously its not irrelevant. Fairly simple physics can show with the single hp/weight figure results nearly as accurate as his torque/gear model...which requires a LOT more knowledge of the way the system works. It would be very bad to assume the electric motor's torque curve would be similar to a gas motor and plug it into a torque and gear calculator.
"Power to weight tells you nothing really."
In fact, it tells you quite a bit. Knowing weight and something as seemingly unrelated as fuel consumption can give you fairly a fairly accurate representation of of the acceleration available at a given speed. What it doesn't give you a clue about is the gearing you'll need to achieve that. Thats a rather critical part of the setup, and thats why a gear calculator is indispensible.
Outside of the automotive world there are plenty of places where torque is as seemingly irrelevant as horsepower is here. Your typical airbus captain doesn't much care about the torques the turbines are producing, but the simple power to weight calculations are absolutely vital to getting off the ground at the appropriate speed and distance. If you think about it for half a second, the rate of acceleration that massive airliners achieve at a max performance takeoff is mind boggling given their mass.
It'd be nice if there were some big conspiracy to that effect....but thats just not the case.
A given acceleration over a given period of time requires a given amount of work to be done. This work cannot be done without power. All the torque in the world is nice, but means absolutely squat if the torque can't be produced far enough to the right of the graph.
I can give a very realistic and very obvious example which proves this point.
" torque/weight is directly analogous to force/mass which equals acceleration."
So I've got this electric motor that produces 2000lb-ft of torque at 1 rpm. It produces 300lb-ft at 1000 rpms. This is not an unrealistic torque curve for an electric motor.
Although it will smoke the tires even in fourth gear from a stop, no amount of gear swapping in the world will make it accelerate faster over any reasonable time period or distance than a 160hp gasoline engine making about 150lb-ft of torque.
By stating this:
Torque/effective wheel radius = delivered linear Force at contact patch.
you are implying that you don't understand the function of a gearbox. Bob did a good job of explaining its torque multiplication duties.
If torque to weight were a better indicator of performance than power to weight (obviously false with a basic look at physics) the izzy Celica would be faster/quicker than the duzzy Celica. Its not. Same goes for ZO6 vettes, which really don't make more torque than stock vettes. They move the torque curve further right, increasing the PRODUCT of torque and RPM......horsepower.
Right on, and thats exactly why the figure given is hp/weight, not torque/weight. Given non-silly gearing you can get pretty much the same result of calculation from hp/weight as you can by plotting torque available at a given engine speed/gear combo over time. Its a lot less labor intensive too, unless you have something cool like the tool Bob is using.
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Yeah I agree totally. That kind of setup is popular on front engined sedans in order to minimize power on oversteer to get good grip on the way out of the corners. On something with the engine behind the rear axle, its only more necessary.
I think if you look closely at that pic you'll see the thing really is all twisted out of shape. Look at the plane of the rear spoiler and that of the front bumper. :O Could probably use better a beefier cage, but stiff isn't always fast and that setup looks rather vintage anywho.
:huh:
Perhaps if your gearing is off...
Power limits the acceleration of the car. Not torque. 1500Nm of torque does you little good at 400rpms.
Last I checked, F1 cars get off the line in a serious hurry despite a tall first gear, an on/off clutch, and less torque than my road car. 200-250lb-ft
The venerable PT6 is another great example. The little PT6a produces
(depending on rating) 675ish hp and more than 1600lb-ft of torque at the output shaft at 2200rpm. At 30000 rpms at the input shaft of the planetary reduction box, its producing 118lb-ft of torque. Honda territory.
Unless fuel efficiency or ultra-longevity is important, engine speed doesn't much matter. Therefore, torque doesn't matter. The only thing that matters is the product of torque, a constant, and engine speed....horsepower.
So I would say that it is torque to weight thats an unbelievably useless figure. Its rarely published, perhaps because its pointless.
Ours was like that for a long while.
Recently, both Comcast and Adelphia have added it to basic cable. I don't know if Time Warner has yet. Sucks that you get no choice with the cable companies.
That link is awful. Man. Please note we aren't all that clueless, lol.
...err...lets not give them more ammo.
Nope, its not. If it were "racing" about crossing the line first, there would not be such Pro Wrestling style moves as "free pass" and "green white checker". Its a spectator sport. Pro Racing, if you will. WWE and NASCAR are very similar in both conception and fanbase.
Now you're talking about me.
But it is. NASCAR is the 800 pound gorilla, and although Hollywood isn't bad I think WWE is a better comparison, as WWE and NASCAR both lack class.
Remember Speedvision? Man, it kicked some ass. Guess what killed it?
Yeah, and there are some people in France that love NASCAR.
I think you are kidding yourself to believe real road racing has a long term chance in America. Series like ALMS tend to come and go every 10 or 15 years. Outside of wealthy niche activities like club/sportscar racing, real racing in America isn't going to be prosperous. Real, honest, fair competition just isn't that attractive to most Americans.
Ahh, so its perfectly on-topic for you to bring it up and verbally excoriate someone for, but not OK for anyone to suggest that perhaps you are full of it.
Perhaps you should have sent a PM in the first place, Einstein. Who do you think you are?
edit: I reserve the right to make fun of Southerners, Californians, or any other silly group of people, and I don't particularly care what you think about it.
Do you have any idea how uncommon that much snow is in Maryland? Maybe a once a year thing.
Anyone dumb enough to do that DOES set a bad example for the rest of us 'muricans.
Whats wrong with someone pointing out when an American does something particularly dumb?
Yes, its a common towstrap that no one should be without. That looks like a Wal Mart cheapie, probably rated for 8000lbs or so. Good ones can be as much as 30,000lbs.
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Yeah, behavior of wings at varying angles of attack is a lot more complicated to model than LFS uber-simple current method.
But yes, its always the z-axis, and it would hold the vehicle on the roof if we had a corkscrew... lol
I own a wheel. I also live in a teensy dorm room and play LFS on a damn laptop. No room for a wheel here.
(6 seconds faster than you on WE Int'l with FV8...mouse and all. 4 seconds faster SO Town FOX...with mouse.)
Maybe you got rammed in the ass because you were in the damn way.
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Again, that may be true NOW for most new cars, but it certainly wasn't the case 10 years ago. Examples like the BMW M engines show it can still happen today.
Tell that to the 15.4 inch LCD I'm looking at in 1280x800.
It depends on the monitor only if your monitor is uber-cheesy.
Also, anyone else note the irony of calling them "non square modes"? I mean, I understand it means the pixels aren't square, but none of the modes are actually "square" anyways.
yeah, I said:
"Tire adhesion available is not linearly related to the vertical component of force on the tire (twice the force doesn't result in twice the grip), so less weight transfer is always better."
which is not nearly as thorough and well defined as your explanation above.
That link really is cool, I had some fun reading about that RFH LeMans hydraulic suspension.
Can't recall from the dash what that is. Mark II VW of some sort?
In real life, a street car motor like that either wouldn't really rev that high free, or it would break into little-bitsy pieces.
Not all road-car motors behave like that. I can think of one in particular that has a 7500rpm fuel cut but makes peak power at 5600 rpms. Little point in pulling past 6200 rpms in any gear but first.
Lots of vehicles really run out of steam before the redline. Pretty much any American built stock motor prior to 1990 or so exhibits that.
Really good info, hadn't heard that about that failure.
Can't seem to find anything saying so at the moment, but I'm 99.999 percent sure its a dry sump. For it not to be their engine would have to needlessly be raised several inches in the chassis, thats the primary disadvantage of wetsump in a racing car. Also, I don't think you could make any wetsump live through an F1 race. Its hard enough to make wetsump engines last in racing use with street tires. The dry sump uses vacuum to accumulate the oil, defroths it, then pressurizes it.
I can find various places mentioning other team's engines are dry sump.
The problem you mention doesn't automatically mean its a wet sump. Even in a "dry-sump" oil is constantly draining to the bottom of the engine. If its lifted by G-loads into the path of the crank, things could get very interesting. It'd be neat to know what part of that interaction made the engine fail....was it the 19000spm pistons bashing through liquid oil drops (which would be like little rocks at that speed) or was it through some other mechanism? "Interfere with the pistons" is a bit confusing, because I'm also reasonably sure they have oil-sprayers pointed at the bottom of the piston to keep it cool.
edit: another thread that makes passing mention of the oiling issues in eau rouge.
http://www.templeofvtec.net/fo ... -message?message_id=45261
It would make more sense to me if it were as this gentleman suggests an issue of the oil actually in use, rather than an oil pressure problem as one would expect without a drysump. As noted, there is still a bunch of oil in an engine with a drysump.
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My prob with airport tracks in sims/games has always been finding my turnin point. Soooo much concrete and such a narrow field of view.
I like the idea though. Would definitely be cool to have.
I think its odd that two people both not living in the US think a Route 66 track would be cool. I didn't know the Route 66 legend extended past our borders. Cool.
I live uh, about .3 miles from a section of that road.
I've got a TJ, which comes with the "modern" coil live-axle suspensions front and rear.
I too have driven it like piss without flipping over, and spun it more than once on wet pavement. Oops.Of course, its a lot more LIKELY to roll over than my Mazda, given the appropriate set of circumstances. Stickier tires would be the biggest one, followed by a bump at the inside wheel in a turn, like a curb you were too close to.
Stupid Consumer Reports thought that was a safety issue. Silly worrywarts.
Lots of performance oriented RWD cars lift inside fronts.
Yeah. I'd note that MULTIPLE mx6.com members, some with lowered cars, have managed to roll them. 2nd gen MX6/Probe lowered is at least as low as a 240sx and a lot harder to get sideways. Goes to show the right set of circumstance can flip anything. There are also a good number of Miatas that have rolled over, I wouldn't drive one without a good rollbar.
With the appropriately screwy setup, and the appropriately sticky tires, you could almost certainly flip a real life GT wth some careful slalom-like maneuvers. Realistically non-silly setups would make it very unlikely without curbs/other stuff.
Lots and lots of trucks SUVs and vans even on road tyres if handled improperly. Cars...not that many, though I've seen it done.
I haven't driven GTi much in S2, but my setups (just as in S1) still lift or come close to lifting the inside rear, noticeable with the locked inside rear on corner entry in replays. Real-life FWD racecars do this as well.
Is it really that easy to flip a GT without a bizarre setup or a big kerb? I think I need to go play with that. Hadn't noticed it before to be honest. I flip the XFR constantly.
edit: remembered during testing a HUGE factor in rollovers that I didn't mention: locked or very effective limited slip differentials. Allows the outside rear wheel to drive the vehicle right over. Not only does your typical road car not have sticky tires, it doesn't have a LSD that can provide meaningful torque to the outside wheel if the inner is off the ground. Most real street LSDs are like a LFS one set to 10-25 percent.
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Excellent link, all sorts of nifty rare stuff. Thanks.
Dry-sump system is used on piston stuntplanes. Very similar to what modern racecars use. I think you'd find a modern single seater type car would run for quite a good bit of time inverted without running out of fuel or oil. Simple mods could make it work indefinitely I would suppose. The fuel tank might need some additional baffling or another pickup, but those cells are already often really well baffled with multiple pressurized "accumulators" that can hold a good bit of fuel. 6.2 kilos in BAR's case. :lol:
The corkscrew seems really feasible, driving around an upside down track not so much. The upside down track would need LARGE radius curves, as you need enough speed to have the downforce offset one G, plus enough for the grip needed to overcome drag with forward force, plus the grip needed to do that while turning. Probably no turns at less than 250kph or so. Suppose it depends a lot on how meaty your wings are.
Remember Stunts 4D racing? Had that tunnel.
Except, it will change this, because the CG doesn't stay in one place. That axis its rotating isn't where the CG is, or else things would be rather ugly.
Agreed.
Yes. As it likewise would if you magically removed the rear ARB. Where was I wrong again? Increasing the roll stiffness at one end makes that end transfer more load and produce less grip.
This isn't true in all cases. If there is enough available grip and a high enough CG, both inside wheels will lift without any outside input like a curb. (umm, a variety of examples exist, karts are a common one, its becoming more common at FSAE events where the cars have to be tilt-tested to almost 2Gs to pass tech) This will happen regardless of ARBs, but stiff ARBs don't help. Maybe I'm wrong on that point, but I don't think so. They certainly don't help if there is an outside force like a curb, but thats a different issue entirely.
In the case you describe (FWD racing car it seems) I agree totally. Many RWD touring cars are setup just the opposite, lifting the inside front for much the same reason.
Its really important that 5th Earth reads this carefully. The larger ARB does effectually decrease grip at its end of the car.
If the movement of the CG was minute and unimportant, that may be true. The mere act of preventing the CG from moving away from the center of the circle the car is traveling in can/does have a noticeable effect. It was for this reason that "sway bars" were initially used. Not for tuning of handling characteristics. Cars that have a high CG and lousy suspensions tend to run brutish ARBs at both ends. As in, the crap Detroit produced in the 50's/60's when they started including "sway bars" as standard equipment.
Its a great tuning tool, isn't it?
None of this changes the facts that real racecars abide by in contrast with LFS:
-They don't have infinitely adjustable ARBs, blade types are more or less stiff or soft. Slider types are better and more adjustable.
-Adjustable ARBs have limitations and aren't used when not necessary.
-Need independent action of the suspension. LFS tracks (it seems to me) have some big bumps across the track, but few pothole type bumps that effect only a wheel. For instance, it seems at BLGP that there is no bump driving onto the concrete at T1, just a change in grip. Most real racetracks aren't all that smooth. Maybe they are in Europe? Wouldn't surprise me, some of the roadcourses here look like rural roads in comparison to the beautiful european tracks.
5th Earth, the "live-axle" for offroad is a good debate. You nailed that one, except I tend to think given the appropriate cash a live-axle would get stomped by an appropriate IFS/IRS system even in rockcrawling. Off-road racing has some of the coolest and most bizarre suspension designs out there. Rockcrawling is brutal on parts (two u-joints last summer just barely picking through rocks with my silly D33) and beefy as heck live-axles are readily available. Any mass-produced independent suspension is going to suck for rockcrawling, but let it not be said that it would be at a disadvantage to a live-axle if properly designed.
Here's a bit of silly trivia: No matter where a car is built, you'll find the engineers specify the "swaybar" size in mm's in the specifications sheets. However, few examples I've found are built to an actual "metric" size. 25.4mm (one inch) swaybars are rather common, as are various sizes in 1/8th inch increments expressed in mm. One has to wonder why this is.
I still stand by my statement that if you could get the CG very close to the road and the track wide enough, the swaybar would do you more harm than good. I think some examples of that exist. I hate driving FV8 with beefy ARBs, same for FOX.
Last edited by skiingman, .
Explained at length above, but long story short, the uber-antiroll bar will lift the inside wheel straight off the ground. 'Nuff said. If you transferred much more weight than that, you'd roll the feck over. :lol:
I would hope I could, or else I had better not make those statements.
1) Stiff springs keep the rollcenter (or centre, if you will
from moving around as much. For a variety of reasons this is beneficial, all of which are rather complex and not worth discussing in such a forum. More to the point, when the body rolls it invariably increases weight transfer from inner to outer wheels. This isn't a good thing for obvious reasons, and since "a few percent" less weight transfer might mean a third or a half more load on the inside wheel, I don't think its worthless enough to simply write off. Note that all of this is more or less equally true for "stiff springs" as well as stiff ARBs, with the exceptions explained below.2) Any antiroll linkage incearses the weight transfer from the inner to the outer wheel. This should be intuitively obvious. Stiffer rear bar = less rear grip -> more oversteer or less understeer. The actual action is dead simple to understand, but probably less so in words than in pictures or demonstration. The stiffer the bar, the more resistance there is to droop of the inboard suspension while the outboard suspension is being compressed. A simple torsion bar of some sort is the usual way to effect this action, racecars in LFS have magical ideal torsion bars with infinite adjustability.
If you could get away with it, no roll bar would be great. You'd minimize the weight transfer between the wheels, and you'd make testing/tuning a lot simpler. For a variety of reasons, that isn't usually possible. For one, my point number one above is often a big factor. Despite the increased transfer due to a big bar, its better to keep the body from rolling too much for a variety of other reasons. Not the least of which is transient response. Also, the weight transfer due to a high CG allowed to roll can yield worse effects than the same system prevented from rolling. Ergo sedans with very big bars on the non drive wheels lifting inside wheels in corners. Guess what, drop the bar, and the inside wheel will get back on the ground. This should be more obvious proof that rollbars increase weight transfer, to the point of pulling wheels right off the ground. That requires more than 100% weight transfer.
As it is, rollbars are a great tool. Since most cars don't have third-spring setups, the wheel rates need to be soft enough to absorb road inconsitencies AND stiff enough keep the rideheight in the appropriate place with sometimes large downforce. This as well as low CG and big track leads to small bars for singleseaters.
On the other end, look at a big sedan. High CG, lots of unsprung weight. Stiff springs will be liable to prevent the wheels from staying on the ground over bumps. Big anti-roll bars can keep the transient response tight with softer springs and also keep the thing from nailing the bumpstops when in cornering. If it rolls enough to hit the bumpstops, the springrate is no longer soft, it is near infinite. Sedan suspension design is usually far from ideal in camber control and modern camber sensitive radials really suffer if they get positive camber dynamically. Keeping the body flat with big antiroll bars is one effective, if not ideal, way to do this. Longer (and often better designed) suspension links and a lower CG would be better, but thats often not allowed in the rules and is obviously more development and cost intensive.
Carroll Smith has been quoted as stating at FSAE competition that ARB rate should be no more than 10% of the wheelrate (both measured in force/degree of roll) in a situation where the design is not very limited. Current FSAE competitors have often disagreed with this logic, but I don't know how wise that is.
The main thing is to understand that there are advantages and disadvantages to increasing rollbar stiffness. If you can increase springrate instead, its probably a better idea. Obviously, sometimes you can't.
I know the LFS differential modeling currently means people driving fast drive locked-diffs, but try this out for kicks: Grab the stock F08 (or FOX) setup. Select, say, the viscous diff, set to a low rate. Turn downforce down to reduce the masking of mechanical grip. Try this setup with both front and rear bar set to maximum. Note the massive wheelspin when attempting to put power down on corner exit. Retry with bars set to just about nothing. Note the better power put down on corner exit.
Since everyone uses locked diffs now, that kind of effect is somewhat masked. When locked diffs start giving the disadvantages they should to the extent they should, I think you'll find that setups change quite a bit.
FGED GREDG RDFGDR GSFDG