Dumb question for automotive racing gearheads

[230RN]

OK, so I'm retired now, with plenty of time on my hands to pursue a lot of things, including a bunch of annoying little dumb questions I have accumulated over the years.

Here's one:

I came across this fascinating little picture-rich site about engines a couple of years ago: 

http://fastjeff57.tripod.com/

This picture of the Mario Andretti Indy 500 winning race car appears in it:

http://fastjeff57.tripod.com/marioindy.jpg

(You may have to load the whole page to see this picture.  Apparently "Tripod" does not like deep links.)



OK, now for the dumb question which has been bothering me all this time: 

How do they keep the tire treads flat against the surface of the track?

I can "see" it with passenger car tires, but these things seem to be 16-18 inches across the treads.

Do they mold the tires such that at a given pressure the tread surface just "comes out flat?"  (I note that they will change tire pressures during pit stops to match track conditions, etc, so this doesn't seem likely.)

Do they have steel (or other) rods inside the tire which resists the "bowing out" of the tire tread as it is inflated?  (That is, with higher pressures, the tire surface would seem to be convex, and with lower pressures, it would tend to be concave.)

Or are there other methods?

See, I told you it was a dumb question, but I'm not all that familiar with automotive racing concepts.

(Incidentally, this is a really interesting site on unusual internal combustion engines.  Just to whet your appetite, it has details on such things as the deltic 3-crankshaft 2-cycle 36-piston locomotive diesel engine, and the world's biggest monster marine engine: 1,556,002 cubic inches [25,480 liters].)

Terry, Chief, Dumb Question Dept, Colorado Division, 230RN

[dogmush]

Short answer: Racing slicks =/= the Goodyears on your F-150

Long Answer:  They're built that way.  Racing tires tend to have super stiff (and short) sidewalls and a big sticky tread patch.  So think less of a donut being inflated, but more like a sheet hung between two walls.  There's not much bowing out available to the tire.  Also as you've guessed things like tire pressure, and even the camber are frequentlly adjusted so that when the car shifts weight in a turn the outside tire tread comes to full contact with the track.  If you get a chance take a look at the right front tire of a NASCAR car at rest.  The camber is usually visable.

If you really wanted you could get tires for your car that do that.  I run 315 series Drag Radials on the back of my Cobra, and 275 Toyo R1r's on the front.  Tread with is 11.5" and about 10.5" respectivlly.  They stay nice and flat due to the sidewall design of the street/strip tires.  Downside:  bumps are more ......noticable.  But that's the price you pay to go fast. 

[230RN]

"more like a sheet hung between two walls"

Ah, thank you!  That 'splains a lot. As I said, that's been in the back of my mind for a couple of years.

Terry, 230RN

[Tallpine]

Racing tires tend to have super stiff (and short) sidewalls and a big sticky tread patch.

That pretty much describes the wheels/tires on many new cars now.

Including our 2006 chevy - the tires must be 2-3 inches tall and 8-10 inches wide.

And they are damn expensive 

[Brad Johnson]

Plus, racing tires have belts running continuously around the tread just like your belt runs continuously around your waist.  Lots of them.  Strong ones.  They keep the tread from ballooning under centrifugal force.

The problem with racing tires isn't one of keeping the tire from ballooning, it's one of keeping the tread attached to the rest of the tire.  Incredible amounts of heat are generated at the tread (or lack thereof depending on track and conditions).  Materials technology struggles to keep the tread and tire body from parting ways. 

Goodyear petitioned, and got, top fuel rules changed in order to limit speeds because they simply could not make a tire that would stay together at 350+ mph.  A drag slick that expands to an effective 45 in diameter is spinning an incredible 2600 rpm at 350 mph.  That may not sound like much, but keep in mind that a 30" car tire is spinning a leisurely 673 RPM at 60 MPH.  The centrifugal forces on a racing tire are measured in multiples of tons per square inch.  That does not include the torque that's trying to tear the sidewalls to shreds as entropy and enthalpy wage a loud, violent war.  That tires stay together at all is a testament to manufacturer's ingenuity and the properties of modern materials and construction methods.

Really want your head to spin?  Keep in mind that a Formula One engine spins to a redline of twenty thousand RPM.  That mean each piston is transiting the cylinder, coming to a full stop, then reversing direction, twice (top and bottom), at a rate of three hundred thirty three times per second.  If that doesn't blow your mind then consider everything that has to happen for a complete firing cycle, and it's happening in one 165th of a second.  Continuously.  For hours.
Brad

[230RN]

Holy crap, this is fascinatinger than I thought!

I hadn't even considered centrifugal forces... and "belts around the tread" makes sense.

Thanks!

"as entropy and enthalpy wage a loud, violent war"  I like that one.  I used to parallel that with the entropy-enthalpy equilibrium between my picking up the kid's toys off the living room floor versus them scattering them around.  I'd put in energy (enthalpy) and they'd distribute it to the universe (the entropy part).

And sometimes that process got a little loud --but not violent, unless I tripped on a teddy bear or something.

Terry, 230RN

[Tallpine]

I'd put in energy (enthalpy) and they'd distribute it to the universe (the entropy part).

Now I know where all my energy went... 

[drewtam]

http://www.youtube.com/watch?v=If5t783NZFY

For road racing, the treads don't stay perfectly flat to the road. Camber is the angle a tire has to the road. 0deg camber is perfectly straight up, 90deg is a tire laying on its side on the ground.

As suspension travels, the camber changes. So as the tire goes over a bump, or the car rolls through a corner, the camber is constantly changing.

The sidewall flexes some to keep contact, but the pressure is not evenly distributed across the tread.

In a passenger car, if the camber is not set right, the inside section of the tread will wear faster (too much camber setting) or outside section of the tread will wear faster (too little camber setting).

Camber settings are usually between 0deg (better for drag racing) and 4deg (oval track racing).

Race tires are difficult to make and are expensive. Old racing hands recommend checking dimensions of tires before accepting delivery (once they are on the car, there are no returns). They recommend checking runouts and profiles.

[rcnixon]

Racing suspensions are also very stiff and do not have a great deal of travel in jounce and rebound (vertical travel above and below the standard position.  This, combined with extraordinary chassis stiffness means that the camber doesn't change that much and thus, more of the tire stays in contact with the road surface.  This is why you can see rear-engine, rear-drive cars lift the inside front tire off the road during cornering while braking and front-engine, front-drive cars will corner on the outside fron tire with the other three in the air.

Russ

[sumpnz]

Really want your head to spin?  Keep in mind that a Formula One engine spins to a redline of twenty thousand RPM.

Nope.  They're rev-limited for 2010 and 2011 to 18,000rpm.  If not for that, they probably would be turning 22-23krpm.

[Brad Johnson]

The Suzuki Hybitoomisakimotoitsybitsywhatheheckever redlines at 20k so I amend my previous statement to include it instead.

I yield the balance of my time... but reserve the right to revise and extend.

Brad

[230RN]

Wow, 20,000 RPM.  No wonder they sound like mosquitos going around the track.  The main attraction for me in televised races is watching the coordination of the pit crews.  An incredible technical "ballet."

Yeah, I'll watch the race for car-passing technique and a few other things, and I know, in my naïveté, that I'm missing a lot, but I really dig the pit stops.

[Perd Hapley]

OK, these tires are real impressive and everything, but how good are they in snow?

[griz]

OK, these tires are real impressive and everything, but how good are they in snow?

You need tires like this for racing on snow and ice:

[230RN]

^ Hm.  Grain-of-salt "photoshop time?"  Or is this a real picture?  I don't have enough of a background information pool on racing in general to judge.

However, I automatically suspect any "unusual" pictures on the 'net.

Terry, 230RN

[griz]

It's real.  They are Rally cars and they race on pavement, dirt, snow, pretty much anything.  And it's done on real roads (closed to traffic).  Really awesome car control.  Google "WRC" to see more.  I was going to post a link to a video but there are enough that you can pick and choose.

[sumpnz]

That is certainly believable, and if it's not real I'd be very, very surprised.  The rally car drivers pretty much define insane death wish driving.  100+mph on a dirt/gravel/snow road with a steep, forested drop off on the outside of the curve kind of insane death wish driving.  

 

[230RN]

Gee, to me, a "Rally" means a non-race to determine expertise in time/distance/driving speed control.  I did some navigating and driving in some of them in the late '50s, and they were never as hairy-#$$ed as that unless you had to make up time real bad because of tire-changing or whatever other delays might occur.  All the legs of the race between checkpoints involved legal speeds, etc.

Are these "olden days" matches now obsolete --perhaps because of GPS equipment?  Or is this a pic of the same thing except the driver had to make a long pit stop or something?

My google abilities are limited by a sloooow connection, and, to repeat myself:

See, I told you it was a dumb question, but I'm not all that familiar with automotive racing concepts.

Terry, 230RN

[drewtam]

There are still some who participate in the time/distance/ speed control challenges you described.

World Rally Championship (WRC) is different. It is a partially solo event on staged sections of treacherous roads. Rules require a race vehicle based on a typical road going car. Popular models include Fords, Subarus, Peugeots, Renaults, Mitsubishis, etc. These are typically ~2L turbocharged, all wheel drive vehicles. Older versions of the race had competitive classes for rear wheel drive cars (BMWs etc).

Grab some popcorn and watch...
 
http://www.streetfire.net/video/wrc-craziest-moments-part-1_143594.htm

Final note: The WRC fans are more dedicated and crazier than any other group of sporting fan I can think of.

[HeroHog]

The rallies 230RN spoke of sound like S.C.C.A. club rallies. Those ARE a ball! I especially liked the unsanctioned club runs like ScotchBrite and Lime rallies! In those rallies you had a known destination with the objective to arrive there exactly on time and with the exact mileage as if you drove the mapped run perfectly. The catch was that certain intersections were "decision" intersections and you had to decide to go Left, Right or Straight. If you chose the right direction, you would see a verification marker within .5 miles of the intersection. No marker, go back to the intersection and guess again! This made for cars backing up up to a ½ mile to keep the odometer reading "right" and then driving like a bat out of hades to make up lost time. These were held at night on roads with low usage and you were supposed to drive legally as there were NO protection from the police involved (hence the unsanctioned run).

In a ScotchBrite run, a ScotchBrite reflective tape triangle pointed down meant it was a Decision intersection. Pointed up meant you were on course. Pointer Right or left meant you had to take that turn. In a Lime run, bags of quicklime were thrown on the road prior to an intersection indicating a decision. When seen .5 miles After an intersection, it meant you were on course. GREAT FUN!

[French G.]

Sometimes rally needs no wheels. What do you get when you have bored Aussies, an empty field, a backhoe, some race motors, a few hapless rally co-drivers, a whole lot of water and a boat? Yep, sprint boats. most insane crap ever, no tires required.

http://www.youtube.com/watch?feature=player_detailpage&v=GnNRMbBhjbU

I might go into all that I don't know about race tires later. Suffice it to say that if F1 doesn't always know, we probably never will either.

[HeroHog]

THOSE guys are driving some SERIOUSLY overpowered boats! I wonder how many G's they pull in a turn? It looks like you would need a pressure suit to stay conscious in that puppy!

[230RN]

The catch was that certain intersections were "decision" intersections and you had to decide to go Left, Right or Straight. If you chose the right direction, you would see a verification marker within .5 miles of the intersection. No marker, go back to the intersection and guess again! This made for cars backing up up to a ½ mile to keep the odometer reading "right" and then driving like a bat out of hades to make up lost time.

Yes, yes, yes!  That's what we did!  Gawd, it's been so long ago!  We did it in an Austin-Healey Sprite.  

http://upload.wikimedia.org/wikipedia/commons/b/ba/Austin_Healey_Sprite_Mk_I_red_vl.jpg

Looks like a TR-3 or 4 in the background.

I don't think they were "sanctioned," though.  Come to think of it, wasn't it spelled "rallye?"

[HeroHog]

Like this one?







Man I miss those days!

[230RN]

Yeah, that one.  I edit my posts forever, and I went back and linked to a pic of one.

Not sure I miss those days.  Just getting out from under the wings of (what I considered to be) an overprotective mother, and kind of overdid lots of things.  With my dumb luck, I never got in any real  trouble or got many injuries because of my rambunctiousness.

You sure couldn't call it smart luck.

When I think back.... wow.

I had a mild relapse about ten years ago when my sons got interested in 240Zs, so I bought one, too.   We kind of copycat off of each other.  At one point, between the three of us, we had five Zs.

I broke mine just before I would have got in any trouble with it, gave it to the boys for parts.

Terry, "Thinks back, wipes brow with forefinger, flicks off the sweat," 230RN