Old SStroker

You meant reaction load from the anti-squat designed into in the rear suspension, right? Weight transfer comes from 1) vehicle weight(mass), 2) height of the center of gravity (CG), 3) wheelbase and 4) acceleration.

Be careful asking questions like "Am I making any sense?"

hammertime

iTrader: (1)

Your trap speed is an indicator of HP, which will only change marginally. The ET is an indicator of traction, and it looks like you are doing ok there.

Now it's up to you to make more power and chip away at the 60 ft time while pushing the MPH up. Looks like you have the setup to take advantage of it.

Good luck!

Gannet

#1, you are correct, this was a cut & paste error. The torque computation was done with a 3.42. #2 is certainly true, the only point I was trying to make is that the car is not massively over-tired with the PS2s. For #3, yes, 120 was a bit of hyperbole, but you get the idea.

For an example of how I am using this in practice, look at this graph:




This is the output of the spreadsheet, for 4 different combos. We are assuming torque output is constant over the rpm range, and that's obviously not the case, but since we're interested in traction we can use "worst case" in each gear and it suits our purposes. For the purple one, no N2O is used in 1st or 2nd, and then we add it in 3rd. In real life we'd use a progressive controller or something. Also, for all the combos except the light blue (baseline), we assume a G-Force overdrive set with .83 and .70 5th and 6th gears.

This should make clear what I'm trying to do. Examine fairly disparate but streetable combos, in this case a strong blown 346, a NA 481, and a 427 with N2O, and try to semi-predict their relative performance.

For example, I know what 1st gear in my present ride feels like, at about 3300 ftlbs to the wheels. Can I then assume that acceleration in 2nd gear with the 481/3.15 combo will be about the same as what I presently have in 1st gear? If so, I can predict that I will, indeed, be able to hook the 481 in 2nd, and also predict what the neck-snapping effect of nailing the 481 in 2nd should be like. I can also predict that 1st with the 481 will be smoke city and that I might as well assume I will be short-shifting out of first as soon as is practical.

Does all this make sense, or am I kidding myself?

dochall22

iTrader: (6)

Without taking time to read the posts, I'm just replying to the initial question - so If someone has already said what I say, Sorry to be a copy cat!

I'd say that traction would decrease because with the higher velocity of the tires the tires would expand in diameter, leaving less rubber to be on the ground. Look at a dragster, for instance, when it is going down the track the tires are much taller, and have less contact area than when at rest. Thats my story, and I'm sticking to it...haha haha...get it...sticking? haha traction?? lol have a good'un

Doc99SS

iTrader: (2)

Old SStroker, are you still on this thread? I took a break. Above, I do mean load transfer,,, on a road course we get load transfer to the front axle when braking,, load transfer to the rear axle when accelerating. And load transfer left and right in the corners. I dont care where it comes from or what causes it, I get load transfer which changes my mechanics of the tire.

For those who talk about dragsters, forget about dragster tires, who runs those things on the street or even at the dragstrip, I sure dont!

Anyway I am digressing abit. The traction of a tire does not change with speed. Because the total contact area barely changes at all, your favorite steel belted UHP tire will maintain the same traction all the way down the dragstrip. However, the traction will increase at launch due to load transfer to the rear axle (this is due to a slightly larger footprint), and goes quickly back to steady state as the load transfer diminishes. I would say that the traction does not change from the 60 ft line to the traps.

Old SStroker

I guess if you don't know or care where load transfer comes from, you would make the last statement. Load transfer comes from acceleration, so if you stop accelerating after the 60 ft mark, you would be substantially correct.

We tend to confuse traction with tractive effort or force. More downforce (normal force in physics terms) equals more tractive force (parallel to the road) with the same tire...up to a point.

I don't think it's time to get into how tires actually "grip", do you?

Stang's Bane

iTrader: (22)

On asphalt the tire doesn't do the "gripping", the road does.

dochall22

iTrader: (6)

Traction decreases, for many reasons. Another I was thinking was the fact taht the faster you go, the more wind under your car, and techincally your car would be lighter and have less force to push down onto the road, so i'd say less traction.

Old SStroker

Isn't it a cooperative effort, especially at the molecular level? It's not a simple thing, although it may initially seem so.

OKcruising

It's actually the surface roughness on both parts that gets the friction, if something is infinitely smooth along its plane(impossible) then there would be absolutely no friction, no matter the interface. This is kinda hard to visualize, but when you do, it'll make sense.

There are a bunch of other variables that rarely get considered when you have a single contiguous contact patch, like the twisting along the axis possibly tearing molecular chains, non-uniform loading becomes a bigger issue (unlike the rubber blocks that kind of act on their own in their own little domain)

As you increase the weight (force) on a tire, it's traction increases. Hence giant wings and massive downforce on lightweight cars.
*You don't want a heavy *** car however because of the myriad of inherent inertia, momentum, etc. and other considerations. That's why you can visualize downforce as a quasi-linear tire load increaser-thinger hahaha.


Tire stickiness(synthetic compound property) is also a factor. When the tire is "sticky" you notice that it picks up many objects. This moldability in combination with the load allows the compound to "expand" if you will, into the tiny surface cracks, gaining traction.
However, if the tire becomes to "greasy" it's because it's own internal cohesion forces are being overcome by greater external forces.


I'll give you an example:
Look at the dyno vids of the supras with all those fat people chillin' in the hatch.
They are there for a reason, more weight->more load->more traction for when they reach boost at 7Krpm

Stang's Bane

iTrader: (22)

I look at it as the tire "deforms" to the road, the road doesn't deform to the tire. Maybe I should say "conform".

That is all I can wrap my simple little mind around. Anything more than that, I get confused!!!!

Jakes Dad

Before I finish I also want to talk about the 19# of air pressure in the tires.

Tires do grow as speed increases. The illustration of watching a drag tire grow as it's driver goes through the water box is a good example. Because they grow, during the run, is the reason top fuel cars have wings so high above the car to force air back to the car ie rear tires to keep traction.

The comment about 19# of tire pressure. Normally thats taken in the staging lanes. Sometimes it's the first thing you do when you get into the lanes. Then you sit, perhaps even cooling the tire off more. Guess what? Now perhaps your pressure has dropped more. Before your run, even with street tires, most hot rodders go through the water box burning the hell out of their tires. Guess what? You have now heated both street tires and drag tires up - dah! Does anyone want to bet if the tire pressure has changed? If it has changed has it increased or decreased? No for you smoking street tire folks. Because most street tires have tread. You have thrown water from the box up into your fenders. You stage, where do you think the water goes as it drips? The best traction and cornering on street tires is achieved when? At normal driving temperatures! So, what have you street tired folks done when you heated your street tires up by burning rubber? You've changed the traction of the tire because now it's hot, or hotter. Does it grip more or less in a hot condition?

Does traction increase the faster your go around a corner. Only to the capability of the tires, the side wall height, weight of car etc.etc.

Original poster, aren't you the same guy that last week you said your 60' times got better but your fell on your face after the 1/8 mile? I said your tires were too tall or you had the wrong gear. Then you posted you had a 3:23 gear.

Why do you think the manufacturers have added so many gears to transmissions over the years? Well silly because you can take a small cuin engine and keep it in it's power range, better O.A. performance, if you provide more gears. If a car dies on the top end it's easy to figure out why. Same as if someone says. Why don't I get more trap speed when I add another 50 hp. to my Nitrous shot? Just the reverse silly. Instead of the 4:10 gear the guy learned was the best to run on the street and before Nitrous. Today, the person needs to go backwards in gearing like a 3:73. The added Nitrous isn't increasing his trap speed because the engine can't spin any higher of an rpm. dah!

Old SStroker

Yes, the rear wing on a TF car is to produce downforce, perhaps 2 tons @ 330 mph. The reason the wing is so high up is to get it into the free airstream where it its most effective at producing (negative) lift. The airflow around and over the wing stays prety much away from the tires which are generating some fairly wild airflow patterns themselves.The negative lift (aka downforce) is transfered directly to the chassis by the superstructure which holds the wing.

One of the reasons the TF (and FC) tires grow so much is so they act like gears in the TF and FC with only one "gear". The more they grow the numerically lower the effective rearend gear. Remember these tires are most definitely NOT belted construction. Drag radials really don't change their rolling radius much at all. Neither do most of the slicks used on cars running under a buck fifty in the quarter.

Dad, You probably shouldn't be getting into cornering forces generated by a tire. That's way off topic, and not necessarily what you seem to have said.

Another Old Dad.

CaribooLou

iTrader: (1)

With any steel belted tire traction absolutely increases because the affect of down force is much greater than tire expansion. Friction = normal force x the coefficient of friction. That coefficient can be as high as .8 with a "perfect" tire and a fresh road. Another concern is lift from air moving underneath the car. If you look at your car from the side you will see it resembles an airplane wing. At high speeds the air moving over the curved body of the car has to move at a much faster rate then the air that passes against the flat underside of the car. The fast air moving over the top pushes the car down to the road with a force that is greater than the cars weight at rest. Physics 101 people

Alvin

iTrader: (2)

umm.. the top side of the car has much more of a curve to it..

the reason why your car might stick to the road better (it doesn't btw).. Is because of the negative angle of attack it has. don't trust me.. compare your car at 55mph to 155.. at 155 it will feel like it handles as good as a school bus.

The available amount of torque is cut by huge with each upshift.

CaribooLou

iTrader: (1)

yes curved, so the air moves faster, its the Bernoulli Affect

http://en.wikipedia.org/wiki/Downforce

And as far as the crappy handling at 155mph is because of air turbulance, not because there is no traction

Alvin

iTrader: (2)

If air has to speed up pressure drops.. High pressure on bottom, low pressure on top car.... car is lifted.

CaribooLou

iTrader: (1)

Well **** you are correct on that aspect of it, explains the floating affect at high speeds, still air resistance and down force stick the car to the ground. If traction loss at high speeds is true explain how in nascar when a driver is drafting another air flow is affected and both cars become real loose...

Old SStroker

I highly recommend the book New Directions in Race Car Aerodynamics, Designing for Speed by Joseph Katz, published by Robert Bentley Publishers.

No offense Lou, but real aerodynamics is much more complex than your somewhat simplistic comments.

In a two car draft both cars don't necessarily become "loose" (exhibit oversteer). One can become "tight" (exhibit understeer) and the other loose. It is often described as "taking the air off the spoiler" of the leading car. That, too, is simplistic, but paints a good basic visual picture.

FWIW "air resistance" aka aerodynamic drag generaly creates forces mostly parallel to the ground and pointing backward, not down. That is part of the whole aero thing.

Most production cars create noticeable aero lift, not downforce, because of their profile shape as you and Alvin noted above. That aero lift subtracts from the load on the tires (called the "normal force" meaning downward) which is due to the vehicle's mass. Lower normal loads on the tires decrease their ability to generate side forces (to resist or aid turning) so the car may feel like it is wandering around. It is.

CaribooLou

iTrader: (1)

Sounds like a good read, I'll definitely check it out.