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post #1 of 32 (permalink) Old 08-02-2018, 04:03 PM Thread Starter
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Weight vs Traction

Racing theory question-

Say I have a 4,000 pound car that has 10" wide rear tires and is on the edge of traction while accelerating. I then remove 500 pounds from the car (while leaving the weight distribution equal for sake of discussion). Will the car need a wider or a narrower tire to be at an equal level of traction? Or will the 10" tire continue to be my optimum size?

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post #2 of 32 (permalink) Old 08-02-2018, 04:49 PM
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The shift in mass distribution is more important than the standing weight to a point; i.e. the weight shift to the rear when you dump the throttle.

The shift is proportional to the 500 lbs less mass, but the weight on the tires is way higher than the resting weight.

This is also why you want the weight off the front; there's more of a shift proportionally front vs rear weight distribution.

See what I mean?
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post #3 of 32 (permalink) Old 08-03-2018, 05:17 PM
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There are multiple reasons why traction is an issue. Tire size, track traction, suspension, weight, weight transfer, and a multitude of other things.

Not just tires. It takes seat time, track time and driver experience along with the rest to get the most traction under various situations and set ups. Bottom line there is no definitive answer. Just changing a tire for no reason is not justifiable in my opinion until you've exhausted all the rest of the issues.

Just my thoughts.
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post #4 of 32 (permalink) Old 08-03-2018, 07:30 PM
No, Mr. Lemmywinks, No!!!

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Quote:
Originally Posted by 1MTNCAT View Post
There are multiple reasons why traction is an issue. Tire size, track traction, suspension, weight, weight transfer, and a multitude of other things.

Not just tires. It takes seat time, track time and driver experience along with the rest to get the most traction under various situations and set ups. Bottom line there is no definitive answer. Just changing a tire for no reason is not justifiable in my opinion until you've exhausted all the rest of the issues.

Just my thoughts.

Those are good thoughts, Steve; the hardest part of racing is "Doing the Absolute Best You Can, With What You Have."

Then, when you rip and drag every last iota of performance you can, THEN you upgrade the worst thing you have, Rinse, and Repeat.

OP, Unless the tires are complete trash, use them until they die.

That doesn't really take long for me, lol.

.
The biggest thing to watch for on our cars is Wheel Hop; it breaks Axles, Right TM?

(I don't think yours bounced, did they? I think you just twisted them off...)

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post #5 of 32 (permalink) Old 08-03-2018, 09:49 PM
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Oh yea. I didn't break mine but when we took them off one had a nice crack in it! I did have some issues with wheel hop.

I looked briefly for the picture (it's buried here as well) but couldn't find it.

I now use drag bags to keep the wheel hop down.

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post #6 of 32 (permalink) Old 08-03-2018, 11:32 PM
No, Mr. Lemmywinks, No!!!

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I seem to remember...

Damn Memberberries, lol.

https://forums.tccoa.com/13-drive-tr...eys-axles.html


TM, I seem to be thinking of another set of pix; I swear I thought they were yours.

Was there someone else that inspired the inspired the aftermarket with 1200 hp?

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post #7 of 32 (permalink) Old 08-04-2018, 06:57 AM
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Well I've snapped quite a few of them over the years and the last time broke both at once at MIR years ago. Bounce breaking and hook breaking are two different things as well. Most of the breakage on Drag radials is bounce. Most of the breakage on slicks is hook. Depends on suspension action, tires, etc.

But it does make a difference on how much power is being put down. 28 X 10 slicks and 500+ft lbs of torque on a well prepped track can and will make pretzels out of our halfshafts.

Steve
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Nitrous 11.75 @ 114 MPH

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post #8 of 32 (permalink) Old 08-05-2018, 04:49 PM
No, Mr. Lemmywinks, No!!!

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You've seen the 31 spline 'upgrades' that are bigger, right? It's ~.060 bigger dia.

It's either custom assembly, or exxpensive aftermarket, it seems; if we want to make big power with the irs...

I guess I understand why the 9 second guys abandon the IRS.

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post #9 of 32 (permalink) Old 08-06-2018, 05:14 AM
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In theory is tire grip independent of the weight of the car.
The formula for the friction force is dependent on the coefficient of friction and the normal force, which in turn is dependent on the mass of the car. However, the maximum lateral force when cornering is also dependent on the mass of the car, so they cancel each other out.
That's why downforce works so well. You increase the normal force without increasing the lateral forces.

In practice however, there is something called tire load sensitivity, wherein this relationship is not linear but gives diminishing returns the more weight you put on the tire. So wider tires will always give more grip (under dry conditions). Or in your case, you can use narrower tires for equal grip.

The rule of thumb we used when racing was: use the narrowest tire possible (lower rotational and overal mass), for the intended amount of use (how long must they last), plus a slight margin of error.
It might also be necessary to alter the width slightly dependent on the tire temperature. If the driver has problems bringing the tires up to temperature, use narrower tires. If they overheat, use wider ones.
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post #10 of 32 (permalink) Old 08-06-2018, 03:47 PM
No, Mr. Lemmywinks, No!!!

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I like your post, and it is very good advice; but the only turns these guys are making is at the end of the dragstrip, to come back to the line.

The gold standard in this type of racing is 15" wide floppy drag tires; that would break our cars to pieces, IMHO.

I think the guys with 15"w tires here have swapped to a real drag axle setup, and have long since abandoned the IRS setup, that makes these nice for curvy roads.
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post #11 of 32 (permalink) Old 08-07-2018, 07:22 AM
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For drag racing, a taller tire is just as important as a wider tire. One the launch, the weight is transferred to the rear, making the contact patch grow from front to rear. This is one reason why guys switch from 26's to 28's, for the larger contact patch. Lowering the air pressure from 32 to 18 also increases the contact patch.

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post #12 of 32 (permalink) Old 08-07-2018, 03:28 PM
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Oops , silly Europeans with all their stupid corners at the track
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May the downforce be with you.

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post #13 of 32 (permalink) Old 08-16-2018, 08:47 PM
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Quote:
Originally Posted by ErwinN View Post
Oops , silly Europeans with all their stupid corners at the track
That was pretty good advice, although very technical for your average reader. But you summed it up pretty well as it applies to road racing vs. drag racing, apples and oranges. Not all of us are using our cars as dragsters, some of us prefer a more sporty approach to driving.
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post #14 of 32 (permalink) Old 08-16-2018, 09:22 PM
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Quote:
Originally Posted by dDUBb View Post
That was pretty good advice, although very technical for your average reader. But you summed it up pretty well as it applies to road racing vs. drag racing, apples and oranges. Not all of us are using our cars as dragsters, some of us prefer a more sporty approach to driving.
Agreed; the actual Racers currently active here that are doing Handling-Based racing are S4Gunn, from San Francisco, and Mad Martigan from Ohio.

The rest of us are apparently Anarchists, and would lose our license so rapidly in the EU that you might as well think of us as Mad Max refugees.



My last infraction: The guy that wrote me for 74mph in a 40mph was SO Pissed; I'm amazed he didn't kick my ass. (I passed a car, it was totally clear; he had radar as he came into view, mid-pass. Not great timing on my part.)

Don't get me wrong, I like Europe, but your rules are effective, and expensive, lol.

I worked with a bunch of people from Europe; good peeps, every one of them. (Except for Maciej; he epitomized "Euro-Douche" to a lot of us. )

I managed to insult the Swedish guy by asking where in Germany he was from, the Belgian guy by asking about France, and the South African guy for asking about his English accent.

I also asked the Austrian guy if he was German, but that's not so bad in comparison, lol.

To really piss someone off, in my experience, you ask the Polish guy if he's Russian, lol. He was a judo expert, lol. Not good.

The easiest thing to me was telling the difference between the Chinese guys and the South Korean guys.

Best thing I learned from my German friends: Don't move rapidly in a 9 Tesla magnetic field, lol.
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Red '96 Cougar XR-7 240k mi. '02 4R70W, PST DS : '03 PI engine, 04 maf, 24lb injectors, 2.5" exhaust, '02 4r70w + Jmod, DirtyD0g TC + cooler + 3/8" lines, 255 walbro fp. Alpine system.
Black '96 Cougar XR-7 (Lazarus) 210k mi PI Intake, '02 4R70W, Jmod, PST DS, GrogTune, Konis, Mark LCA+Poly, racecougar Custom Engine Chain, and JL and racecougar Bracing.
Black '97 Tbird Limited Edition, '02 4R70W, 255 walbro, PST DS, PBR Brakes&SS lines, Toicko Blues & Springs, GrogTune.


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post #15 of 32 (permalink) Old 08-16-2018, 09:31 PM
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There are also rumors here that somebody may or may not be setting up their SC for a run at Laguna Seca, but that's just a rumor.

I was at the Sonoma drag strip last night and got to talking to this older guy - he got pulled over speeding in Mexico a few months back. The federales said, Senor .. today you have two choices. Ticket or no ticket. He said no ticket. The federales wrote on the tail light .. 100.
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post #16 of 32 (permalink) Old 08-16-2018, 09:41 PM
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I like corruption, when it's well known, and even.

And I have the cash, lol.

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Black '96 Cougar XR-7 (Lazarus) 210k mi PI Intake, '02 4R70W, Jmod, PST DS, GrogTune, Konis, Mark LCA+Poly, racecougar Custom Engine Chain, and JL and racecougar Bracing.
Black '97 Tbird Limited Edition, '02 4R70W, 255 walbro, PST DS, PBR Brakes&SS lines, Toicko Blues & Springs, GrogTune.


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post #17 of 32 (permalink) Old 08-16-2018, 10:06 PM
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I love reading posts with real physics in them.

At one point I had pondered the effects of given coefficients of friction (static and dynamic) with varying object mass and, correspondingly, normal force. E.g. whether a heavier car gets more grip, enough to offset the drawbacks of additional mass and required forces to overcome said inertia. I had (and do) suspect[ed] that adding mass is actually a step backwards, but it would be nice if I had some data...

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post #18 of 32 (permalink) Old 08-16-2018, 10:16 PM
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You did see the launch this week to the sun?

That should be really informative, as it will actually travel into the corona.

(The white stuff outside the eclipse, for those that don't know.)

The view of that, and the solar prominences thru your 8" scope during the eclipse was a Bucket List item, btw. Thanks!!

It's apparently layers of plasma, trapped in magnetic fields, that make it hit 20 million degrees.

If that spacecraft flies into a 20Mk temperature field with any heat capacity, it will look like a moth in a flame, or a bird flying by that solar tower out west, in the Mojave.


I really want to know what the deal is, because it doesn't neatly fit ANY of the models.

Did you get to see the meteor showers?



Quote:
Originally Posted by theterminator93 View Post
I love reading posts with real physics in them.

At one point I had pondered the effects of given coefficients of friction (static and dynamic) with varying object mass and, correspondingly, normal force. E.g. whether a heavier car gets more grip, enough to offset the drawbacks of additional mass and required forces to overcome said inertia. I had (and do) suspect[ed] that adding mass is actually a step backwards, but it would be nice if I had some data...
F=m*a, adding mass for a given energy input is going to go slower, less a.

But, it's not a simple relationship; years of racing have shown that accentuating the mass transfer to the traction wheels maximizes the acceleration, as does larger contact area to the ground.

Easy way to see that is that Front wheel drive cars suck at dragracing.

Red '96 Cougar XR-7 240k mi. '02 4R70W, PST DS : '03 PI engine, 04 maf, 24lb injectors, 2.5" exhaust, '02 4r70w + Jmod, DirtyD0g TC + cooler + 3/8" lines, 255 walbro fp. Alpine system.
Black '96 Cougar XR-7 (Lazarus) 210k mi PI Intake, '02 4R70W, Jmod, PST DS, GrogTune, Konis, Mark LCA+Poly, racecougar Custom Engine Chain, and JL and racecougar Bracing.
Black '97 Tbird Limited Edition, '02 4R70W, 255 walbro, PST DS, PBR Brakes&SS lines, Toicko Blues & Springs, GrogTune.


"War Is Peace. Freedom Is Slavery. Ignorance Is Strength." - George Orwell.
Truth Isn't Truth. - Rudy Giuliani, 2018 Award winner, “Most Outrageous Diversion” by MSNBC for this quote

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post #19 of 32 (permalink) Old 08-17-2018, 02:16 AM
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Quote:
Originally Posted by theterminator93 View Post
I love reading posts with real physics in them.

At one point I had pondered the effects of given coefficients of friction (static and dynamic) with varying object mass and, correspondingly, normal force. E.g. whether a heavier car gets more grip, enough to offset the drawbacks of additional mass and required forces to overcome said inertia. I had (and do) suspect[ed] that adding mass is actually a step backwards, but it would be nice if I had some data...
Like Collin Chapman said: "Add lightness"
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May the downforce be with you.
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post #20 of 32 (permalink) Old 08-17-2018, 02:49 AM
No, Mr. Lemmywinks, No!!!

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That's a nice graph, but our cars weigh 3800lbs, so the number on the rear wheels, during launch, is likely to be over 1000lbs.

Each.

Take that, Toyota! (lol)

Red '96 Cougar XR-7 240k mi. '02 4R70W, PST DS : '03 PI engine, 04 maf, 24lb injectors, 2.5" exhaust, '02 4r70w + Jmod, DirtyD0g TC + cooler + 3/8" lines, 255 walbro fp. Alpine system.
Black '96 Cougar XR-7 (Lazarus) 210k mi PI Intake, '02 4R70W, Jmod, PST DS, GrogTune, Konis, Mark LCA+Poly, racecougar Custom Engine Chain, and JL and racecougar Bracing.
Black '97 Tbird Limited Edition, '02 4R70W, 255 walbro, PST DS, PBR Brakes&SS lines, Toicko Blues & Springs, GrogTune.


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Truth Isn't Truth. - Rudy Giuliani, 2018 Award winner, “Most Outrageous Diversion” by MSNBC for this quote
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post #21 of 32 (permalink) Old 08-17-2018, 02:49 AM
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Originally Posted by Grog6 View Post
I managed to insult the Swedish guy by asking where in Germany he was from, the Belgian guy by asking about France, and the South African guy for asking about his English accent.
LOL, so true! In Belgium there are two main language groups; Dutch (the majority) and French. We both refuse to speak each other's language .
Instead we chose to speak English as a neutral language .
That's how we prevent conflict over here.
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post #22 of 32 (permalink) Old 08-17-2018, 11:13 AM
No, Mr. Lemmywinks, No!!!

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The really funny thing to me is hearing two people having a technical discussion in their native language; it doesn't matter what it is, but you'll hear a nice, flowing conversation, and boom, there's an english word, usually technical, dropped in the middle.

That sounds really strange in Chinese, lol.

Red '96 Cougar XR-7 240k mi. '02 4R70W, PST DS : '03 PI engine, 04 maf, 24lb injectors, 2.5" exhaust, '02 4r70w + Jmod, DirtyD0g TC + cooler + 3/8" lines, 255 walbro fp. Alpine system.
Black '96 Cougar XR-7 (Lazarus) 210k mi PI Intake, '02 4R70W, Jmod, PST DS, GrogTune, Konis, Mark LCA+Poly, racecougar Custom Engine Chain, and JL and racecougar Bracing.
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post #23 of 32 (permalink) Old 08-17-2018, 10:54 PM
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I like that graph; as I suspected, the tractive effort function is anything but linear - sure, you get more traction with more weight but it seems pretty insignificant past a point given the additional inertial you need to overcome. E.g. an additional 25% load factor only gets you ~10% more traction - nowhere near enough to offset all that extra mass! Doesn't take a physics degree to see why racecars have wide tires, lots of aerodynamic downforce, and the lightest chassis possible.

So a bunch of extra weight in the car for better traction in winter will net you worse acceleration/cornering and longer stopping distances than no added weight...
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post #24 of 32 (permalink) Old 08-18-2018, 01:11 AM
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Adding weight to a car for traction is like completely opposite of the whole F=m*A rule.

Unless you need to weight a car to stay under 10 seconds, or to fix radical handling F/r balance issues, or other rule; you're pissing up a rope, wondering why it raining.

Remove 10% weight, Acceleration goes up 10%, all else being equal. (F is horsepower, in a very general way, after losses, etc. But, a lighter car will have a different tune, as the advance curve related stuff will want to be different.)

The opposite is even more true; Adding it always works, unlike the removing weight.

You need to know "Contact patch force" vs suspension compliance, because you ride that number as the the suspension dips, and the mass transfer to the rear happens.

At the maximum weight transfer to the rear, That's your maximum traction point; that's where you see all the lines in the sidewall of the big drag wheels. (I have not seen that on an MN12; please send pic, it will become my wallpaper.)

Weight balance is more important in Lemons racing; for drag, it's pull everything you can out, Especially out front. See The sticky...

Our cars are too long to wheelie, although anything's possible with enough boost and nitrous, lol. Again, send pix.

Red '96 Cougar XR-7 240k mi. '02 4R70W, PST DS : '03 PI engine, 04 maf, 24lb injectors, 2.5" exhaust, '02 4r70w + Jmod, DirtyD0g TC + cooler + 3/8" lines, 255 walbro fp. Alpine system.
Black '96 Cougar XR-7 (Lazarus) 210k mi PI Intake, '02 4R70W, Jmod, PST DS, GrogTune, Konis, Mark LCA+Poly, racecougar Custom Engine Chain, and JL and racecougar Bracing.
Black '97 Tbird Limited Edition, '02 4R70W, 255 walbro, PST DS, PBR Brakes&SS lines, Toicko Blues & Springs, GrogTune.


"War Is Peace. Freedom Is Slavery. Ignorance Is Strength." - George Orwell.
Truth Isn't Truth. - Rudy Giuliani, 2018 Award winner, “Most Outrageous Diversion” by MSNBC for this quote
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post #25 of 32 (permalink) Old 08-23-2018, 11:48 PM
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Hmmm
Attached Images
File Type: jpg 1mtncat Launch 2.jpg (12.8 KB, 29 views)
File Type: jpg 1mtncat Launch 1.jpg (8.3 KB, 30 views)
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post #26 of 32 (permalink) Old 08-24-2018, 08:20 AM
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Originally Posted by 1MTNCAT View Post
Hmmm
I hope you'll see those "Glory Days" again soon! Cheers buddy. Cheers.


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post #27 of 32 (permalink) Old 08-24-2018, 01:30 PM
No, Mr. Lemmywinks, No!!!

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Hmmm
I stand corrected, lol.

That rear wheel is fully involved; I can't tell if the wheel is in the air tho.

I need bigger pix for wallpaper, tho

Red '96 Cougar XR-7 240k mi. '02 4R70W, PST DS : '03 PI engine, 04 maf, 24lb injectors, 2.5" exhaust, '02 4r70w + Jmod, DirtyD0g TC + cooler + 3/8" lines, 255 walbro fp. Alpine system.
Black '96 Cougar XR-7 (Lazarus) 210k mi PI Intake, '02 4R70W, Jmod, PST DS, GrogTune, Konis, Mark LCA+Poly, racecougar Custom Engine Chain, and JL and racecougar Bracing.
Black '97 Tbird Limited Edition, '02 4R70W, 255 walbro, PST DS, PBR Brakes&SS lines, Toicko Blues & Springs, GrogTune.


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Truth Isn't Truth. - Rudy Giuliani, 2018 Award winner, “Most Outrageous Diversion” by MSNBC for this quote
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post #28 of 32 (permalink) Old 08-24-2018, 02:15 PM
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Quote:
Originally Posted by Grog6 View Post
Our cars are too long to wheelie
I’ve seen quite a few 60s GM A bodies and Chrysler B bodies at the drags that would dispute that, all of which are longer than MN12s by a fair margin.

-Matt
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post #29 of 32 (permalink) Old 08-24-2018, 03:06 PM
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I stand corrected, lol.

That rear wheel is fully involved; I can't tell if the wheel is in the air tho.

I need bigger pix for wallpaper, tho

Maybe this will help LOL!! The last year EECDOC and I had our cars running and out together. Watch JP's Lincoln as well.

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1996 Cougar XR7 Special Edition (Street & Strip)
"There's a bad, built NA 4.6L COMING Spring-Summer 2018"

Elite member of the Halfshaft snapping, Auburn eating, Tranny crunching, Piston Melting, Tire lifting, 500+ lb ft Torque Club.

Cougar ET-Stock 4.6 shortblock/Stock PI headswap Bullitt NA 12.94 @ 105+
Nitrous 11.75 @ 114 MPH

2008 Ford Powerstroke 6.4 TT F250 4X4 Supercrew: 12.82 @ 105 MPH

"IN MEMORY OF MY FRIENDS JOEL BENDER 1979-2006", JOHNNY LANGTON 1975-2011, and MICHAEL VIVERETTE 1953-2013"

Last edited by 1MTNCAT; 08-24-2018 at 03:15 PM.
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post #30 of 32 (permalink) Old 08-24-2018, 08:53 PM
No, Mr. Lemmywinks, No!!!

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Thanks, Steve!

That's an awesome video!

I stand completely corrected.

Red '96 Cougar XR-7 240k mi. '02 4R70W, PST DS : '03 PI engine, 04 maf, 24lb injectors, 2.5" exhaust, '02 4r70w + Jmod, DirtyD0g TC + cooler + 3/8" lines, 255 walbro fp. Alpine system.
Black '96 Cougar XR-7 (Lazarus) 210k mi PI Intake, '02 4R70W, Jmod, PST DS, GrogTune, Konis, Mark LCA+Poly, racecougar Custom Engine Chain, and JL and racecougar Bracing.
Black '97 Tbird Limited Edition, '02 4R70W, 255 walbro, PST DS, PBR Brakes&SS lines, Toicko Blues & Springs, GrogTune.


"War Is Peace. Freedom Is Slavery. Ignorance Is Strength." - George Orwell.
Truth Isn't Truth. - Rudy Giuliani, 2018 Award winner, “Most Outrageous Diversion” by MSNBC for this quote
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