Nate (solo-x) said this somewhere else:

"spring vs. bar, the tires don't have any idea if the force pushing them is coming all from the spring, or some combination of spring and swaybar and shock. They just see how hard they are pushed down into the racing surface."

"Speaking specifically to the peculiar dancing elephant we call a FWD race car, the more rear biased you go with roll stiffness, the more sensitive the car becomes to changing levels in grip. IE, if we have two car's that have the same balance on low grip asphault and car acheives 100% rear LLT at .7g's and car B acheives 100% rear LLT at 1.2g's then car A will be significantly pushier when both cars move to sticky concrete. Put another way, the higher you lift the inside rear tire, the more sensitive to grip your car will be."



Nate - I hate to change my mind too many times. But not as much as I'd hate to change my mind one too few times. Yes, the tire doesn't know what is creating the sum of vertical forces. But the respective end of the chassis has some vague idea as to the relative proportion of the contributions, and it can speak up if antagonized by the setup. So all I'm saying here is that there's more to it, and it can be important, not that it always is, it isn't.

Then, that second paragraph... I know you wouldn't say it if you hadn't experienced it. And I'll give you the benefit of the doubt as far as your thinking it out. Share that thinking - Why is the more rear stiff fwd kaa pushier on the high grip surface than it's less rear stiff competitor?

Scott, who has some more questions for this other guy who was having some trouble on a really rough track and "solved" it by going stiffer...I don't doubt him at all since it probably resulted in some hundreds pounds more downforce...things aren't always what they seem...

 

Hey Scott,

In regards to the first part, the tire understanding the sum of the vertical forces. I'm not sure I get where you're going here. It seems like we agree that spring, bar, shock, or geometry, the tire only cares about the sum of the vertical forces. Are you saying that the "feel" of the car is different if the roll stiffness contribution is spring+bar vs. spring? If so, I would say I agree with you there as well (the post you quote is simplified as much as possible for the specific question/topic I was repsponding to) as roll center movement and geometric roll stiffness will change some depending on spring vs. swaybar. The ultimate point I'm trying to get to and what I'm trying to explain is that a swaybar isn't really responsible for all the evil it is given credit. It would appear that most people think a swaybar can increase TLLT for the entire car, rather then just redistribute the load transfer from one axle to another, just like changing spring rates would.

As for the second bit, that one is a bit more involved. I have indeed experienced this behavior, and I've spoken with several VERY successful FWD racers who've echoed my position. Mark Ortiz has even written as much in his newsletter. I'm not sure how to explain the theory in writing without making it insufferably long, or unacceptably simplified. I'll try for somewhere in between.

The reason the more rear siff car is affected by grip changes to greater degree then the less rear stiff car has to do with dynamic cg height changes and what you do with an alignment when you acheive 100% LLT at .7g's vs. the same at 1.2g's. Take my car for example. I run it so it almost lifts the inside rear at 1.2g's. I like a really loose car, so I set the rear camber to 0* and run about 50psi in the rear tires. If you changed my setup so it lifts the inside rear at .7g's, the car would be undriveably loose. I would have to increase rear camber and run a lower rear tire pressure to tighten the car back up to where it is now. Most of that extra rotation comes at the early corner entry phase. (The traditional FWD setup shoots for crazy loose on entry and pray to carry that rotation through to corner exit.)

Switching gears a little, if we know that the car is balanced at 1g and we have the inside rear off the ground already, what happens when we now try to get the car to corner at 1.2g's? Clearly the surface is capable of generating something more then 20% increase in grip, of which the outside rear will see a large majority of that grip increase. This is because there is no change in normal force across the rear axle as it was already at 100% LLT, so the decambering affects would be the only way the outside rear would loose grip. And if we're talking about a race car, under 2* of roll/g isn't unheard of, which would mean the outside rear would decamber .4* (and many cars have enough static rear camber that this decambering affect actually puts the tire into a happier place, allowing it to generate even more grip even though it "decambered").

At the front axle, the additional load transfer from cornering 20% harder all comes from the inside front and goes onto the outside front. This axle too sees an increase in cornering force capability due to the surface change, but since it results in additional load transfer, the grip increase isn't as great. So while the car might be cornering 20% harder, the surface may actually have been capable of increasing grip by 25%. Additionally, the outside front is decambering some as well (unless you're already on the bumpstop, then it is decambering at the same rate as the outside rear), so the natural freeing up of the car due to the outside rear decambering is lessened due to the outside front decambering as well. The end result is that the outside rear can generate something greater then 20% more grip, while the front can only generate an additional 20%. IE, understeer.

Going back to how my car is setup, with 0* rear camber, any additional roll will continue to free the car up. In other words, the harder the car corners, the less grip the rear axle makes relative to the front. The sweet spot to hit is one where the grip generated by the front and rear axle increases or decreases at the same rate. This is important for a Solo car, as having it "out of the box" and at 90% of its peak performance on 100% of the courses is significantly better then having it 100% of peak performance on only 70% of the courses, especially if one of those courses is at Nats and on a surface you don't get to see but once a year. Less chasing the setup = more time to figure out the course and get it done in 3.

My apologies if that didn't make my thinking seem any clearer. Feel free to challenge any logic that seems wrong.

 

Damn, are we going to go back to the old days of actually having intelligent discussions on complex suspension problems?

 

OMFG, let's hope so. H-T member Johnny Mac is usually good for a few tidbits of suspension info. I'll wait for him to hopefully chime in here. (insert smiley).

 

Well, not always especially when it comes to handling threads since I would be writing my response for hours. I usually wait until I can post a short response to one aspect of the equation rather than the large picture. Besides, Scott wanted a response from Nate and not from me anyways. Maybe we'll see you tomorrow at b.'s? I think I have your ice chest with the beer and ham (well, I found the ham today while I was taking my car to get dynoed) Anyone for some aged Ham from Willow Springs?

 

I have the same problem Johnny Mac! I haven't had a block of hours that I wanted to spend thinking and writing yet. I appreciate Nate's response, and intend to pick back up soon. Today what interfered was hanging out at the track for a test day. I heard things that would make a reasonably intelligent race engineer break their 0.7 pencil lead and say "Wat?"

Scott, who is pretty sure he's figured out how to solve all race car problems...Don't race cars...but that would be too impractical...

 

<-- haz a warm & fuzzy feeling

 

H-T is doomed if the mentality is to wait around for JMac to say something smart sounding.
Whatever happened to people trying to figure things out together, instead of calling out specific forum members? Worst case is that somebody will say something wrong, and nothing works better to attract smart people to forums like the desire to correct somebody on the interweb.

 

I don't thinks it's quite correct to say that H-T is doomed. It is and or was doomed and is at the terminus of doom. At least that's how I think of racing fwd cars.

Scott, who doesn't care what anyone thinks...except for Johnny Mac...even his cast off afterthoughts are like drops of rain in the desert...

 

Haven't you read the book "How to be Smart Sounding without being Smart," which details how to take advantage of the principle (and logical fallacy) "appeal to an unqualified authority." That way, I can con anybody who doesn't possess the requisite knowledge of the subject into thinking I really know what I'm talking about. Anyway, thats my secret for Honda-Tech, but unfortunately a much smarter guy than me known to the world only as "Beanbag" happened to be a member on H-T and ruin my guise.

 

is there a problem here?

b.

 

Are you enjoying your morning coffee?

 

...Mmmmm...both a Logical Fallacy AND a Principle...sounds like Politics...

Scott, who apologizes to the OP for going OT...

 

Scott, stop talking to yourself.

 

Very well then Johnny Mac, I will talk to You.

Do you surf the VitalMX MotoDrive Old School Moto Forum? And seen the Corley / Socalmxnews thread with the old trackside pics from CMC races?

Well last night I went with Mrs Adams to one of her associates customer appreciation events in their posh offices and within our little group there happened to be another drug along husband and guess who/what he is/was? The Moto-Photo guy around here from early 70's to the early 80's. The conversation was excellent and everything was going fine and then I had to ask, and he had to tell me the awful news...yep, all gone. He'd get a call every so often "Do you have a pic of bike number 864 at Washougal in 1981?" and he'd say "I've got a box labeled Washougal 1981, you're welcome to come by and spend 4 hours or so". Never got any takers. Nearby our wives are talking and notice that we're really hitting it off, and mine says to his "Oh, they've discovered a common past life", and his says to him while rolling her eyes "Tell me you're not gonna start Moto-Photo back up."

What a small world. One of these days I'm gonna run into somebody with a time machine and then Look Out!

Scott, who has to go get some metal so I can make a thing...

 

Oh, and while I was coming back from Thunderhill last weekend, I noticed a bunch of motocross transporters - you know the 18-wheel kind - coming back from the Hangtown National. I just watched the race on Speed Channel, and oh did that bring back memories. I'll never forget Johnny 'O on the most bitchinest bike evarrrr...The Mugen ME125WI or WII take your pick. Back in the day, the pros transporter was a camper with an open trailer, a van, or if you were really lucky a box van. My Saugus childhood friend Mike Kiedrowski had a box van when he was riding for Kawasaki "Team Green", then of course he won all those National Championships and got a transporter.

Oh, did I ever tell you the story of Donny Elmer of FMF fame pouring half of his beer into his rider's (Frank Pilato) gas tank before the second moto at an Ascot 125 pro race? Those were the days.

 

The passing vessel wasn't a threat, captain. No need to raise the Sarcasm Shields.

 

Sounded pretty clear to me, and I believe my beloved english professors from days past might agree with me.

 

johnny mac stop playing with your beanbags.

 

Some unemployed people have too much time on their hands.

 

its called "funemployment" now. you should know, you are the master at it.

in your honor, ill just tell ppl im studying for GRE's now. cuz i wanna be just like Johnny Mac!

 

Against Johnny O's Mugen, and without getting into white bell bottomed leathers, I'll pit the 75-76? Kawi KX125 raced locally by Mark Gregson (later 250 National top privateer in 79 or 80 on an LOP Yamaha). It was the rotary valve 125, with a case reed setup added on - so some pretty serious fab on the cylinder and cases. Without making any obvious value judgements, it was undeniably trick. Way tricker than a Maico with forks for shocks, probably even tricker than a Penton with a CR125 motor, and dare I say more practical than a Husky with ports so big the piston almost falls out - maybe on par with a Maico using the swingarm pivot for a jackshaft.

And as for Donny Elmer (sic - you did that on purpose right?) and the illegal race gas, all I got is my favorite flagman throwing the checkered in one hand with a beer in the other. Local racing. Those Were the days alright.

A couple of things - Griff's pants were the best ever, Billy Grossi's Suzuki outfit with the green and yellow pants was way cool, the 77 YZ125D taught alot about rake and trail and the value of a forward cg - even as a kid it took about a lap to understand what Ake Johnson was doing with that Yamaico, and yet on the other hand Husky's really were the ultimate berm machines - at McMinnville there was a large radius tree lined banked sweeper at the end of the main straight and the fast way was at the very top even though it got treacherously rough (it was a third or fourth gear crouched both feet on pegs kind of turn). But there would always be a muddy berm tight on the inside making a much shorter distance. One day, after I'd crashed out of position, I was lapping back in position our thereabouts, and was getting as much out of that berm as anybody was getting a gear higher on the outside. It was fast, exquisite, and honestly alot less terrifying.

Scott, who can never forget his first visit to the night races..."...Rick Burgett....Chuck Sun..." over the PA, it sounded like I had arrived where IT was happening...

 

Yeah, there were a lot of cool machines that the backyard mechanics and small companies used to build. For example, LOP, or Laurens Offner Products, a small hop-up company became famous for building Marty Moates' (RIP Marty) 1981 Carlsbad GP winning YZ490 against the world's best riders. Moto-X-Fox, DG, FMF, and many others helped riders like me to try making the big show. Most of us ended up getting injured and retiring from the sport while still in our teens. Some riders either didn't get injured a lot and raced for years while others like factory pros Darrel Schultz or Mike Bell had six or more knee operations before they decided enough is enough and moved on. I decided that a twice surgically repaired right shoulder, one compound fractured finger, and one obliterated knee was all I was willing to suffer before pulling the plug.

I remember racing at night at Indian Dunes on the somewhat dimly lighted International Track and not being able to see the back side of the course very well. Also at Indian Dunes Friday nights, Pro rider Chris Heisser would bring Heather Locklear to the races. I remember meeting her a few times there and never would I have realized she would become a big star. Chris's family had money and would always have the coolest equipment, like a full Mugen kitted CR125R and CR250R. Yes, those were fun times.

On that Vintage site where Ascot and Saddleback track photographer Tom Corley is now posting photos of races he shot from the 70's and 80's. I saw a few of Todd Peterson from '79 (Suzuki) and '80, '81 DG Yamaha at Ascot park. Todd and Ron Turner used to bang into one another with block passes and whatnot so often that they would get so pissed at one another and get into fist fights in the pits following the race. It was like a hockey game.

I'm sure Tom has plenty of photos of me, but I'll have to try contacting him soon. He only lives 13 miles away from me.

 

I miss Ascot park

 

Hi Nate,

Ok, sorry so long to take this up. I'm having avoidance issues. And I'm distracted by more serious life priorities. But this is bugging me.

I too have run skinny hard old crappy same sized tires and enjoyed the ride more than I do on fresh grippy bigger in front tires, and noticed that much.

Also, I've found definite limits to reducing rear grip with dynamic positive camber - cording the outside of a brand new tire in 30 minutes. The balance was superb btw.

But I've got nagging problems with this thesis, and it's similarity to the the fallacy of the argument that from the instant the inside rear lifts understeer increases. The conclusion to be drawn from both is that at peak load the inside rear should just barely but not quite lift off. The wrongness of the argument in the one case powers my suspicions about the other.

Your statement of your case is good, and has some attraction. But many roads to error are marked with signs that reassure us.

One of the key elements of my criticism is the treatment of what's happening at the outside rear. At whatever peak load, we want it to be saturated, and we normally want a three wheeled car to do this - if it barely lifts at peak load then what's it doing the rest of the time?

I'm inclined to be more interested in looking at your thesis backward - what does the car that's set up to perform well at 1.2g do at 0.8?

Scott, whose car is doing 0.0g and looks like it...