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irish44j
irish44j PowerDork
7/10/14 11:08 p.m.

WARNING: This will be a train of thought, rambling commentary born of my complete boredom late at night. So....if you're gonna read it, just realize that I'm all over the place here, and I'm really just trying to spark some discussion of a topic I have interest in

Ok, so usually I just toss the SCCA rag in the recycling bin after a quick flip-through reveals no substantive rally-x content, but the latest one actually had an article with some analysis (by Jonathan Olschewski, who has an impressive MF Sentra as detailed here: http://www.sccabb.com/forum_posts.asp?TID=11810&title=buildmod-fnt-1991-nissan-sentra-jon-olschewski), so decided to read it.

The main gist of the article is that lightening a rallycross car doesn't help it win/go faster/etc. He states that there "aren't any facts to back the theory." He makes an exception for lighter cars in muddy conditions (which seems kind of an odd exception, seeing as rallycross frequently has muddy/slick conditions, at least in our region).

"In muddy or extremely slick conditions, lighter cars tend to be faster....in all other conditions those cars do not seem to have any advantage"

First problem here: ok....so they may not have any advantage in dry conditions, but do in muddy conditions. So I guess if you rallycross where it's always dry, that is a notable point. But every rallycross venue I've been to sometimes has muddy/slick conditions. So right from the start this would tend to argue that "lighter IS better", if it's good in some conditions and "equal" in other conditions, right?

His second piece of evidence was that after he lightened his car, it was losing to a heavier car, and by that logic reduced weight was not the key. He notes, to his credit, that it's just one anecdote and is subject to other variables.

But then goes on to state "the facts:" - at nationals, light cars only win in Mod FWD. And then not always. - a 3000lb car beat a 1700lb car at nationals, even though the 1700lb car had previously won MF at nationals. - all the cars that won MR and M4 were "stock weight."

Now, I'm a technical analyst for the government. I do analysis of facts for a living. And those data points do not constitute an objective analysis in my book. They're really just a series of anecdotes centered on one specific event: Nationals. Having never been to nationals, most of my knowledge is secondhand admittedly. But my perception is that nationals is usually on dry courses, for one. Does it rain much in Nebraska? IDK. Also this perception that "all the best drivers" are at nationals, which I don't necessarily agree with. I'd say many of the best drivers are. I'd also say there are a lot of great drivers in regions on the east coast, west coast, gulf coast, northeast, etc who don't go to nationals because of the distance, expense-per-seat time, etc etc. And nationals is on a specific surface. So I don't think that constitutes an substantive analytic method there. What if nationals were on a muddy course in Tennessee every year (like SE divisionals last year). What if it was on gravel (like NE divisionals will be this year)? Does that change the analysis? Probably.

"there is simply no proof that lighter cars are the ticket..."

But he doesn't seem to take into consideration that the heavier cars may have substantially more power as well as more weight. a BRZ is a hell of a lot heavier than a 1st gen RX7. And drivers and modifications being equal, the BRZ will almost certainly beat the RX7 in most cases. Is that because it's heavier? I disagree. It's mostly because it has more power, better chassis dynamics and suspension, better brakes, better steering, and the use of electronic nannies in muddy conditions. All of these are of course subjective.

It also doesn't take into account "where" weight is shed. SInce I know e30s, let's go with them first. If you have a 325i, your car is already nose-heavy. If you ditch the back seats, rear glass, spare tire well, etc....well yeah, that's not gonna help. It just exacerbated your problem. If you have a 318i though, your car is already well balanced. If you do all those things above, and then move your battery to the trunk, you've then lost weight while maintaining the good balance. So the weight reduction in the first case is bad for the car (especially since it has good power to start with so weight isn't as much an issue), while in the second case, it allows an under-powered car to gain p/w ratio relative to the 325 without sacrificing balance. The lighter weight allows a car to brake faster, and to accelerate faster (especially a low-powered car) to a certain point.

Are the heavier cars winning because they're heavier, or simply because they are better cars overall? WIthout a lengthly analysis of ALL the cars in all historical rallycross events, I don't believe that it can be determined. And with drivers being the biggest variable, the scientific way to prove this would be to have one good driver drive several cars of different weights and power and see which is fastest.

We just so happen to do this all the time in WDCR. I'll use my own example here: My car is the lightest in MR, and possibly the best set-up locally. I am NOT the fastest driver locally though. But I finish top-2 almost every event, mostly because of my car (IMO).

To test this, I've had the other top drivers (who I regularly beat) drive my car. They both drive heavier cars than I do, by a good margin (and also far more powerful). We all use fairly equal tires and have fairly equal experience.

Chris Nonack drove my car last season against me at an event. He has never beaten me (I don't think) in either his MR2 or his Mustang or his Celica. I don't think he ever won a WDCR event. Until he drove my low-power, very light car. He beat me handily in it, as well as the other 10 cars in the class.

Nick Drymalski has driven my car several times. He usually drives an e28 and puts up times very close to mine in that heavy tank. In my car he is equal to or faster than me pretty consistently.

Both of these guys are slower than me in heavier cars. Both of these are faster than me in my own light car. So they are faster in a lighter car. As I lost weight from my car, I won events by larger margins as well.

Again, these are anecdotal and at the "local" level not the nationals (though again I submit that many top local drivers are just as good as many national drivers - it's not like bad drivers aren't allowed at nationals.....anyone can enter). But it is evidence no less. And the amount of experience and car prep at our (and other) local events is no less than at any divisional or national events, in many cases.

So, sorry for the diarrhea of the keyboard here, but that article just seemed kind of silly to me. While I respect peoples' opinions regarding their own car prep and that of what they've seen personally, I think it's pretty ridiculous to claim that this limited evidence is proof of a "fact," just because it is a general trend at a small number of events.

In our local events, the lighter GC subies generally beat up on heavier STis and WRXs with drivers of similar experience and prep. Adam Kimmet's gutted 2.5 locally beats pretty much the entire (large) M4 class, other than Matt Berk's H6-swapped impreza - which is slightly heavier and WAY more powerful. They both generally beat up on any STis in the class (which are heavier and more powerful). So there's another anecdote that means nothing by itself.

One of these days, I'd love to do a full analysis of this using local and national results for the last decade and see how hit pans out (I'll never have the time to, but whatever).

Actually, would be interesting to see GRM put this to a test. Make a random rallycross car. Run it with a few drivers. Take some weight out (or add weight, if that's easier) and run the course again. Do it semi-scientifically if possible. WOuld be a real analytic comparison, rather than a comparison of a bunch of different cars with different prep and different drivers - which proves essentially nothing.

In any case, if the author is by any chance on here - don't get me wrong....I enjoyed the article. I just found that it was a bit weak on analytic method and thin on "facts."

There are a few facts about cars: 1. lighter weight results in increased acceleration (traction-dependent, of course). 2. lighter weight results in decreased braking distance (traction-dependent also) 3. lighter weight results in less lateral inertia during turns (which is a good or bad thing depending on where the car's balance is and what the driver's style is, of course).

None of these facts says that a car HAS to be faster if it's lighter. But I can't find any "facts" that support the case that a heavier car is just as fast, or faster. Worse acceleration. worse braking, more lateral inertia. Weight over the wheels helps to a certain point, and too light may not get enough "dig" for traction. Too heavy may dig in too much. Too much power can't be used in some conditions. Too little power and you're simply gonna be slow on any straight areas. All of these things are factors. The key is to find a balance. Taking weight off in the right areas is helpful, and hurts if in the wrong areas. Taking off "enough" weight is the key, but I can't see in any way how leaving a Mod-class car stock weight is an advantage vs. that exact same car with 200lbs removed from the appropriate area, that's all I'm saying.

and so on and so forth.

Thoughts from the peanut gallery? I know some of you guys rallycross light cars, and other heavy cars. I know we all have opinions on how much power is too much power (as we say in NONACKs mustang build thread), but haven't heard much opinions regarding how much lightness is too much lightness (or is any lightness good)?

GO!

irish44j
irish44j PowerDork
7/10/14 11:14 p.m.

The other notable point of the article, which of course IS factual, is that the driver skill is more important than the car setup. But I think they are complementary. Put a top rallycross driver in a stock crown vic and he's not going to beat up on a well-prepped lightweight car driven by someone of equal or slightly less skill, I wouldn't guess.

I'm proof of that. I win a lot of events. I fully admit that at least 2 drivers in my class are better drivers than I am. My car is better, mostly because it's lighter (it has way less power, and doesn't have any fancy suspension or other tricks). So I usually beat them because my car is faster. They'll say the same thing, I'd wager...

Also seems an odd article considering the author's heavily-prepped car that has GOT to be lighter than stock by my reckoning. I know he's talking more to people to say that they don't "have" to strip their interior to be competitive. But if you're building a race car, why not build it. If you race a DD, obviously your priority may not be to make it as competitive as humanly possible.

Or maybe it's late and I'm reading too much into the article and being defensive because I have a light car, lol......

NONACK
NONACK Reader
7/11/14 7:52 a.m.

Simply put, F=MA. Want more A? Decrease the M or increase the F. The guy is wrong on the most basic level. BUT...

In rallycross, suspension matters. Pull some weight and suddenly your spring, damping, roll rates are all wrong. Too much weight off one end, same thing. This makes the car hard to drive, and predictability is key. One could argue that, with anything but a perfect driver, the more predictable car will be faster, unless it is so horribly slow that it doesn't stand a chance when being driven at 100% against other cars driven at 70% (your Crown Vic scenario).

Your car is fast not only because it's light, but because it's predictable. I described this as "boring" I think . The takeaway from this article is probably that easy to drive trumps light weight- but if you can have both, that's even better.

I've had cars at all ends of this spectrum. The Celica is the mythical "easy to drive, horribly slow" car. The MR2 was very fast, and light, but on such a knife edge as far as handling (and reliability) were concerned that it was very hard to compete with. The Mustang was just insane and only had one mode (flying asshat) and therefore was impossible to drive fast without coning, mostly due to incredibly compromised weight distribution (and my lack of self control).

I have driven a LOT of different rallycross cars at this point, and I have never felt light weight to be detrimental to performance. No such thing as too much power, no such thing as too little weight- but there is such a thing as a system not tuned to function with those parameters.

NONACK
NONACK Reader
7/11/14 8:09 a.m.

One more thing- want proof that light cars are the ticket? I've stated before that I'd love to see 2wd and 4wd unlimited classes. I'd bet good money on those being the two fastest classes, and the cars being much lighter than those in the modified classes.

Mr_Clutch42
Mr_Clutch42 HalfDork
7/11/14 8:34 a.m.

I have zero experience in rallycross, but it seems like the author is mostly focusing on the fact that stripping the interior of your DD for rallycross isn't always the answer.

I didn't read the article in the SCCA magazine, but in his build thread, he is also trying to highlight that it is better to buy a cheap rallycross car to be able to experiment with stuff like weight, etc. He also reveals that him or any of his fellow rallycrossers aren't nice enough to drive each others cars to see how driving a lighter or heavier car helps or hurts someone's times. Also, the easiest way to add weight to a rallycross car is to have a passenger ride with you, as long as there's a passenger seat; He must not have had many passengers ride with him in rallycrosses, either. Lastly, he also reveals that him and is fellow rallycross drivers don't use fancy GPS or OBDII race datalogging systems to accurately measure every .001 of a second when they're on the course like top autocross guys do.

The topic is very complex, and like many things, people try to simplify it to either understand it easier or to strengthen their arguments, etc. This is my third season of autocrossing, and even though weight is extremely important, even top drivers aren't slowed down by a passenger riding along, especially if they have a hard suspension setup.

iceracer
iceracer PowerDork
7/11/14 8:38 a.m.

In our Street Legal ice racing class, we have cars weighing from 2400 lbs. to 3500 lbs.

So who wins ?

The driver with most experience and ability.

noddaz
noddaz Dork
7/11/14 10:05 a.m.
iceracer wrote: *SNIP* So who wins ? The driver with most experience and ability.

This...

wae
wae HalfDork
7/11/14 10:07 a.m.

I read that same article and have been doing some head-scratching ever since. I know that when a car is lighter (blah blah physics something blah blah) a change of direction requires less work, but I also know that a lot of the rules that apply to a hard smooth surface go totally out the window when you change to a soft loose surface. Right now I don't have much value to contribute to the discussion other than to agree with you that this is interesting and needs some more thought.

EvanB
EvanB UltimaDork
7/11/14 10:19 a.m.

Well at last nationals my light car was well ahead of a much heavier car when the surface was muddy. On the second day it was dry and he was consistently faster than me every run. That doesn't mean that it was the increased weight of his car that was the advantage, it was probably more about the suspension.

Maybe my next rallycross car will be a rolls royce so I can test the theory.

11110000
11110000 Reader
7/11/14 10:19 a.m.

It gets into semantics, but if you're familiar with statistical analysis you know that you are generally out to 'prove that x has a significant effect', or 'cannot prove that x has a significant effect.' I am not saying that there was any real mathematical rigor to this analysis, but it sounds like his statement that "there is simply no proof that lighter cars are the ticket..." is technically correct. There does not exist (to his knowledge) a definitive study which proves that lighter weight is better.

The essential problem with this finding is that there are so many other variables to consider in this casual observation of limited venues that the conclusion has little merit. More study is clearly needed, so let's all build some rally-x cars and generate data.

GameboyRMH
GameboyRMH MegaDork
7/11/14 10:22 a.m.
NONACK wrote: Simply put, F=MA. Want more A? Decrease the M or increase the F. The guy is wrong on the most basic level. BUT...

D'oh, beaten...

See also: My sig.

Knurled
Knurled PowerDork
7/11/14 12:42 p.m.

TL;DR

Heavy cars are at a massive advantage because their sprung to unsprung weight ratio is much more favorable, so the chassis does not get upset on rough sections.

Watch a super light car try to navigate a course, bouncing around and getting kicked this way and that, and then watch a heavy car just zip over like it was nothing. Really light cars are entertaining to watch because it seems like they are off the ground as much as they are, but a car that stays in contact with the ground is more controllable and therefore can put down quicker times.

Remember the goal is not "how fast", but "how quickly without making mistakes". A stable car is better than something that is constantly fighting you for directional control.

And Jon's Sentra sounds wicked when the flywheel falls off and it revs like an F1 car.

edit - Okay, i read it. And yes, when it is muddy lighter is better... because the course is more malleable and you're not going to be getting kicked around like you would is the course was bumpy and lots faster.

Knurled
Knurled PowerDork
7/11/14 12:50 p.m.
NONACK wrote: One more thing- want proof that light cars are the ticket? I've stated before that I'd love to see 2wd and 4wd unlimited classes. I'd bet good money on those being the two fastest classes, and the cars being much lighter than those in the modified classes.

Mod is already "unlimited". You just don't see wildly modified cars because it doesn't make sense to.

If you mean buggies, I have seen buggies at rallycrosses and they usually are fighting for DFL. Too much unsprung weight.

NONACK
NONACK Reader
7/11/14 1:00 p.m.

In reply to Knurled:

To cover both comments- a light car with a good sprung to unsprung weight ratio would be even faster. The fact that you have witnessed plenty of light cars with a poor ratio does not make that any less true. Same goes for buggies: a VW based desert runner is awful for this, but a purpose built vehicle WOULD be faster.

Something like this, but with a bit more power:

and:

Knurled said:

Mod is already "unlimited". You just don't see wildly modified cars because the arms race hasn't gotten there yet

FTFY. Rallycross will eventually go the way of autocross, just wait and see...

irish44j
irish44j PowerDork
7/11/14 1:04 p.m.
Knurled wrote: TL;DR Heavy cars are at a massive advantage because their sprung to unsprung weight ratio is much more favorable, so the chassis does not get upset on rough sections. Watch a super light car try to navigate a course, bouncing around and getting kicked this way and that, and then watch a heavy car just zip over like it was nothing. And Jon's Sentra sounds wicked when the flywheel falls off and it revs like an F1 car.

How upset the chassis gets of any car is more directly attributable to how appropriate the damping and spring rates are to the weight (and drivetrain layout) of the car. A blanket statement like that also assumes all other things being equal (like...does the car have a solid axle rear end, or a multi-link IRS?), which of course they rarely are. Also is this rough course full of tight turns, or is it basically just a big oval with high-speed sweeps?

IF the article is referencing ONLY a comparison of a stock car vs. that exact stock car with not changes other than weight reduction, I suppose the argument could be made that weight reduction has limited impact. But I don't know of many guys who rallycross a bone-stock car where they just gut the interior. Gutted interior and weight reduction pretty much land a car in Mod class, where other mods are unrestricted. So at that point I would have to imagine the majority of top drivers are doing suspension modifications, tire pressure changes (and tire type changes), etc. These changes are there to compensate for things like weight reduction. I run a softer progressive-rate spring (with spacers) to compensate for the lighter weight.

I expect you to show up at nationals this year in a Lincoln Town Car. You would be a lock to win by a mile with all that weight, power, and long wheelbase resulting in so much general rallycross awesomeness. I mean, it'll zip around the course so fast that the other competitors will probably just give up and go home. Also make sure to carry a full load of passengers (preferably in business suits) and their luggage to improve your victory margin.

NONACK
NONACK Reader
7/11/14 1:07 p.m.

In reply to irish44j:

NO NO NO, a Town Car has too much power- you can't use that kind of power on dirt! It needs a rotary

irish44j
irish44j PowerDork
7/11/14 1:14 p.m.
Knurled wrote:
NONACK wrote: One more thing- want proof that light cars are the ticket? I've stated before that I'd love to see 2wd and 4wd unlimited classes. I'd bet good money on those being the two fastest classes, and the cars being much lighter than those in the modified classes.

Mod is already "unlimited". You just don't see wildly modified cars because it doesn't make sense to.

If you mean buggies, I have seen buggies at rallycrosses and they usually are fighting for DFL. Too much unsprung weight.

I'd say you don't see wildly modified cars because people with the cash to wildly modify their cars have moved on to stage rally or baja (ala Caswell). I know that's what I'd be doing if I had the finances to support it.

Rallycross has always been the ultimate "budget" motorsport for people to bring cheap beaters out to play in. If people are dropping $10s of thousands on crazy mods (like some Solo people at the top levels do), that doesn't really fit with the ethos that most rallycrossers seem to have: keeping it cheap, grassroots, etc. because you're just going to beat it up anyhow. Sure there are some guys who show up with full-built cars here and there, but they are the minority who are willing to spend big-bucks for what is basically bottom-rung motorsport in terms of typical budget. The big spenders out there either do solo (if they're scared to hurt their cars) or do rally/wheel-to-wheel racing (if they don't mind destroying their car).

irish44j
irish44j PowerDork
7/11/14 1:22 p.m.
Knurled wrote: edit - Okay, i read it. And yes, when it is muddy lighter is better... because the course is more malleable and you're not going to be getting kicked around like you would is the course was bumpy and lots faster.

That was kind of my point though. Conditions change in rallycross. Our old courses at Summit Point on baked red clay in the summer weren't slick or bumpy. It was almost like tarmac. And the cars that were both light and high-powered constantly were fastest (in all classes), much like they'd be on a paved course. Rallycross doesn't have to be a bumpy grass field. It can be anything. Making blanket statements about car setup as a panacea doesn't work, because the conditions, course style, or surface that YOU run in or HE runs in is not necessarily the same as the guy in California or Maine or Florida.

If lighter is better on slippery, and "no different" on dry, and (according to you) worse on bumpy, it all comes down to where your events are held and what surface you're on. Seems like some venues are ALWAYS muddy and slick. Our venue is always bumpy, but always very loose surface. So lighter there is better and worse.

Dammit....so this is what happens when I haven't actually gotten to rallycross in 6 weeks. Thank God we'll be racing for the next two days so I can start doing it and stop talking about it, lol.........

eastsidemav
eastsidemav Dork
7/11/14 1:25 p.m.

One other possible point. If you lighten your car up (without doing anything to weaken it), it should be more durable, since the impacts will be acting on less weight.

Whether or not its enough to make a difference in a typical rallycross season, I don't know.

I second some of the above comments, rail jobs are generally not built to deal with a rallycross. If I could be sure I could get away with it, I'd be tempted to grab up one of those cheap off-road go-karts, and see if I could rebuild it as a rallycrosser. Or just do a custom build, with a much better suspension and weight distribution than a typical VW-based buggy.

MadScientistMatt
MadScientistMatt UberDork
7/11/14 1:36 p.m.

It seems like a good way to test this would be to take a reasonably well prepped light weight rallycross car, make a few runs, and keep adding ballast while checking lap times.

NONACK
NONACK Reader
7/11/14 1:45 p.m.

I know how to prove my purpose-built vehicle theory AND be MR legal!

This plus this plus a lot of work and a welder. Someobody give me the funds and I'll do it.

irish44j
irish44j PowerDork
7/11/14 2:39 p.m.
MadScientistMatt wrote: It seems like a good way to test this would be to take a reasonably well prepped light weight rallycross car, make a few runs, and keep adding ballast while checking lap times.

I fully intend to do this at an event later in the season if I can build up enough of a points lead that I'm safe (or at a test-and-tune, try to do it with my car and 2-3 different drivers and different weights).

Will definitely do a write-up of the results if/when I do it. I love analytic comparisons :)

irish44j
irish44j PowerDork
7/11/14 2:43 p.m.
eastsidemav wrote: One other possible point. If you lighten your car up (without doing anything to weaken it), it should be more durable, since the impacts will be acting on less weight. Whether or not its enough to make a difference in a typical rallycross season, I don't know.

also anecdotal, but a couple of the stock-class e30s (6cyl) cars this and last season have had severe cracking problems in both the front and rear suspension towers. My car (4cyl, and a lot of weight reduction) has had none of these problems in 3 seasons, even though it's the oldest e30 of the group. Obviously this could have to do with the cars' previous lives, rust, and the fact that one of those 6cyl cars has had 3-4 drivers per event for 4 seasons. But it's another data point. I feel the "slams" in big ruts and dips much less in my car than I do when driving one of the sixers....

Knurled
Knurled PowerDork
7/11/14 4:50 p.m.
NONACK wrote: FTFY. Rallycross will eventually go the way of autocross, just wait and see...

Well, it all depends. When guys in super modified AWD turboBOOOOOOST machines get bested by some guy in a stock Neon on worn out all-seasons, people realize that the car isn't as big a deal.

Part of it, too, is people modifying their cars in all the wrong ways. Like making the car super light then sticking 60lb of wheel and tire on every corner.

Knurled
Knurled PowerDork
7/11/14 4:51 p.m.
irish44j wrote: I expect you to show up at nationals this year in a Lincoln Town Car. You would be a lock to win by a mile with all that weight, power, and long wheelbase resulting in so much general rallycross awesomeness. I mean, it'll zip around the course so fast that the other competitors will probably just give up and go home. Also make sure to carry a full load of passengers (preferably in business suits) and their luggage to improve your victory margin.

SR was traditionally won in Detroit by someone in a Crown Vic.

I am still *this* close to running an E36 M3 in SR, and BMWs are kinda like Town Cars, lots of leather and cracked interior plastic.

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