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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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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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West Virginia Chapter Director /, MA Drag Race Te
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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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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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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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West Virginia Chapter Director /, MA Drag Race Te
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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.
 

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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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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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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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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.

Al
 

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Oops :xpshame:, silly Europeans with all their stupid corners at the track :D
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. :wink2:
 

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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. :wink2:
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.

:rofl:

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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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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I like corruption, when it's well known, and even. :)

And I have the cash, lol.
 

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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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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?



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. :)
 

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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... :(
Like Collin Chapman said: "Add lightness" :thumbsup:
 

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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)
 
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