johnc

> If the tire is in contact with the ground > and not sliding , and the ground is not > moving, the the tire patch in contact with > the ground would not be moving. Yes, the > axle is moving forward, but at that > instant the tire is in contact with the > ground, that patch is not moving. I think you're trying to compare apples and oranges. Is your point of refence the tire/road interface (called the contact patch or footprint) or the whole tire? I'm assuming you're talking about the contact patch. The tire is rotating around the axle shaft at a set rpm. The tread of the tire is always moving at a velocity determined by rpm and tire diameter. Given that: 1. The contact patch as a whole is also constantly moving because the tread surface and the sidewalls are constantly flexing. 2. 99% of the elastic forces (stresses) are built up and released through the contact patch area. 3. Longitudinal shear forces are built up in the contact patch due the radius reduction when the tread enters the contact patch area. 4. There is a reduction (compared to the tire tread velocity outside of the contact patch area) in the longitudinal velocity of the tread at the beginning of contact patch, but there is also an increase (compared to the tire tread velocity outside of the contact patch area) in tread velocity toward the end of the contact patch. In essence, the rear of the contact patch is always sliding. > This is why a turned tire makes a car go > in circles. Each part of the rotating tire > bites or sticks as the next or following > parts advances the car around the curve > and pull the car sideways more. No grip, > no turn, as the compound flexes each time. > I'm not sure of the term used for the > process, but a steel tire would not turn a > car because it cannot have that minute > flexing needed as the tire "advances" the > car around a corner. What you are describing are slip angles and yes, they are a significant reason why a tire can turn a vehicle. But they are not the only reason. Steel wheels work fine on asphalt/concrete at their lower traction limits. Steam rollers and guys out-running cops on just the rims are two examples. Solid rubber tires are another (remember your little red wagon?) Tires are very complex things. Much more complex than shocks, springs, engines, etc. There is no such thing as a general theory of tire behavior. You have lots of independent theories about one aspect (lateral force, longitudinal force, camber affects, aligning torque, slip angles, pressure, temperature, footprint, etc.) but no all encompassing algorithm.

Most people laugh, but JB Weld will work just fine. I've used it to fix a cracked cooling passages in a cylinder head. That engine is still running after 24 years.

You need more sleep. Your point of refernce for the term "rest" is wrong. A rotating tire is never at "rest." The tire is rotating around an axle at a certain rpm and contact with the road is incidental to that rotation. No part of the tire is ever at rest. In fact, the greatest stress point on a tire is the contact patch. Read Chapter 2, Tire Behavior in "Race Car Vehicle Dynamics" by the Millikens. Incindentally, this book will help you sleep...

Where the tension rods are attached to the frame is very strong laterally. The firewall is there to take the side loads. That area is weak longitudinally. The car bends like a hinge at the bottom of the firewall/tension rod attachment area. That's why connectors tying the top of the front strut towers to the firewall and through to a roll cage are so effective. Another trick is to weld the doors closed, but that makes getting in and out a real bitch...

Here's the roll bar in my 240Z. It ties in the rear strut towers very well.

Marc Jones of Datsun Alley fame ran a 400+ horsepower single turbo VG30 for 5 years in local SoCal SCCA ITE racing. Never once torn down the bottom end in all that time and he probably had 1,000+ racing hours on it. Steve Millen run a similar engine early on in his IMSA efforts and the block wasn't the source of any of their engine problems. You should probably talk with an engine builder that knows about such things. Try Jim Thompson at Sunbelt (770) 932-0160.

Erik Messley and I modeled a 2" crossmember drop on a computer simulation of the 240Z front suspension. Here is what got spit out: 1. The effect is the same as lowering the front of the car over 4", only worse. 2. The front roll center gets moved below ground level a significant amount (assuming no corrsponding rear suspension drop). This will cause the front end to "skate" on corner entry. Its like driving on ice. Because of the low roll center there is little load transfer to the outside tire so it doesn't "bite" into the turn. 3. The built in, OEM, camber curves are upset. The front suspension actually gains positive camber in bump instead of the factory (and much more desireable) negative camber gain. 4. The inherent bumpsteer in the 240Z is exacerbated. You would need bumpsteer spacers between 3 and 4" in depth to correct the problem. But, bumpsteer spacers of this depth would require a 19" wheel diameter to clear. A better alternative would be the correct oil pan or cutting, dropping, and rewelding the center of the crossmember.

Oops! I stand corrected.

Did you put spacers between the crossmember/frame mounting point? If you, did, you didn't "lower" the crossmember, you actually "raised" the car. Camber changes are the least of your concerns.

The rumors are true, but in a roundabout way. You can check the IZCC web site. From what I recall, the Prince Motor Company in Japan licensed the Mercedes SOHC 6 cylinder engine in the early 1960s. They were working up their engine design from the Mercedes license when they were purchased by Nissan in 1965. From there, the design effort continued and the results were the L4 and the L6 engine families.

http://www.ccwheel.com/

Brand new 27 spine (280Z) stub axles are ~$180 each from Courtesy Nissan. Worth every penny.

The book is $89.00 at Amazon http://www.amazon.com/exec/obidos/ASIN/1560915269/qid=999815893/sr=1-1/ref=sc_b_1/107-6869113-3129310 I have never seen any other style of wheel from CCW. That doesn't mean John has only one style. Richard Pilfold here in SoCal runs 16 x 8s on his 240Z and loves them. Most of the applications for CCW wheels are Corvettes and Vipers.

Longer vs. wider contact patch in braking (my cross post from and earlier IZCC discussion.) The same applies to acceleration. I've just spent some time re-reading Chapter 2 - Tire Behavior in Milliken's "Race Car Vehicle Dynamics." While all sections in the chapter are relevant, I think Section 2.3 - Longitudinal Force helps explains the issue above. There's a lot of fundamental information that's need as background, but I ain't about to type all that. Go buy the book and read Chapter 2 yourselves... A tire's footprint under braking (and acceleration for that matter) experiences shear stress. This is because the tire's radius is forced to change as the tire tread (and sidewall) elements enter the footprint. For a constant angular velocity, the linear velocity at the circumference of the tire decreases as the radius changes resulting in rearward stress. Under braking, the footprint is moved rearward relative to the axle centerline, compressing the elements in the rear half of the print and stretching the elements in the front half. As more and more elements enter the footprint (which occurs as braking force increases) and move aft under increasing load, the longitudinal shear force builds up linearly. As the footprint unloads toward the rear, sliding occurs between the tread elements and the road. In a tire with a long footprint, the longitudinal shear forces build up quicker and reach higher values than a comparable shorter tire with a wider footprint. Why? 1. The tires' overall radius change is greater so you get a higher linear velocity number. 2. The stress force distribution is more concentrated through the footprint. 3. The sliding velocity is higher in the rear part of the footprint. (you need to see Figure 2.14 on page 34 to see the velocity curves and the shear force distributions) Due the items 1, 2, and 3 above (and probably some other things that I don't understand), more of the taller, narrower tire's potential braking force is used overcoming the greater longitudinal shear force. So, even though both a tall narrow and a short wide tire put pretty much the same amount of rubber on the ground, the short wide tire uses less of its potential braking force overcoming longitudinal shear forces.

John Perner runs Complete Custom Wheel. He's very knowledgeable and also very opinionated. And, he's right. A 15 or 16" wheel works better on a 240/260/280Z. Look at all the racers who compete in classes (GT2, BSP, SM) with no wheel size restrictions. Almost all run 15 or 16" wheels even though custom 17" have been available from Bogart, Taylor, Monocoque, CCW, Kiezer, and others for years. I don't know the theory behind the "why." The previous owner of the 240Z I bought tried a 17" racing wheel and DOT race tires (Hoosier) and the car was very unpredictable. One minute it would understeer and the next it would oversteer. The problem was with the rear suspension and no amount of caster, camber, and toe adjustment could get it to be predicable. Swapping back to 16" rims and tires instantly cured the problem.

That's sweet. Let's see, the Solo Street Modified rules require retention of the stock suspension mountings, but...

I still see 10 to 20 240-280 Zs in junkyards here in Southern California. Most are fairly complete for at least the first couple days they are in the yard.

Scotty, A lot of tracks comply with NHRA rules as an insurance condition regardless of whether its an NHRA event or not. I don't know if that's the case where you run. I spend a bunch of time working with Viper guys and once they started getting into the 10's they were banned from pretty much any track here in the West coast until they swapped the diff for a solid axle. After a year's worth of work they were able to get an exception, specific to the Viper, to allow them to run at NHRA sacntioned tracks. That is the rule change you cite in your post. It could be (and has been) argued by a track official that the C5 rear suspension doesn't meet the upper/lower control arm requirement ("If the suspension utilizes both upper and lower control arms, the IRS may be retained regardless of weight or e.t.") because the upper arm is the halfshaft. I know of at least 1 C5 Corvette guy that got asked to leave an event at Pomona when he turned a 10.98. That may have been an isolated incident. I'm not trying to be an jerk about this. I would just hate to see you turn a 10.xx and then be asked to leave. Does anyone have a current NHRA rule book?

Scotty, Have you checked with your race sanctioning body about any limitations to IRS rear suspensions? I know with NHRA when you get down into the 10's you are not allowed to run an IRS that has the axles as a stessed member of the suspension. The C4 Corvette IRS is normally not allowed on vehicles going that quick becuase the axles are the upper locating links for the rear suspension.

Looking at the topic title I though it was a discussion about an AC/DC song. What's that rod pushing up on the left side of the rocker arm? Looks like something from the "vintage" era of automotive design...

But catalytic converters do do something. They convert hydrocarbon emissions to hydrogen and water with no horsepower penalty. That's a good thing for everyone. Unfortunately you have to have the engine control systems in place to keep the air/fuel ratio near stoichiometric. Without those controls the catalytic converter will overheat and fail because most folks run their engines slightly rich. When a cat fails, the internal substrate usually collapses and now you have a big plug in your exhaust system.

The best book I've found on the basics of EFI is: Bosch Fuel Injection & Engine Managment Charles O. Probst, SAE Robert Bently Publishers Time and time again I refer back to this book to solve problems or answer questions. [ August 27, 2001: Message edited by: johnc ]

Owen, You're OK with the older block in the car. The law says the vehicle has to comply with the emissions requirements in force for the latter of: 1) chassis or, 2) engine. Your car needs to comply with the emission requirements of the chassis if the engine is older. Unfortunately, the folks who swap in LS1s also need cats and fuel evaporative systems. Older is better...

Simmer down guys... Owen's post didn't say what year the car was and why it was impounded. California does not require retrofitting smog equipmet. All vehicles in California are subject to drive by sniffers/inspections. The pollutant limits for a 73 and earlier Zs are very forgiving and they are based a percentage of the total, not pounds per mile. If you're engine (even a V8) is tuned and running correctly you really don't have anything to worry about. If you do get stopped at one of those inspections, ask to see the measured emissions and the standards they are comparing them to before agreeing to any visual or tailpipe inspection. My friend did just that for his 1967 Porsche and the inspectors found that his car was way within the standards for that year so they had to let him go without any visual or tailpipe check. [ August 27, 2001: Message edited by: johnc ]

Lucas oil is really no different than STP. They both work the same, they both make the same claims, and STP used to have a display, year and years ago, where they showed how the stuff clung to an old wood drill bit that was turned in a contianer of the stuff.