Traction question: Maybe this could apply to off road high traction situations?

[mbryson]

Curious who would have some knowledge of this and could be an interesting discussion? I've ALWAYS liked muscle car type acceleration. Above is a great example on a racetrack (as safe of an environment as can be made for this type of racing). The red '68 is obviously hooking up HARD enough to pull the front wheels but likely has enough acceleration that it doesn't end up like the gold '69 below. The black '71 has a little wrinkle on the slicks and might be dialed in slightly better than the '68? To those that have raced (@lhracing or ???), would you rather be the black car or the red car here? (maybe something in between?).

 

[mbryson]

The gold '69 has obviously "hooked up". Enough that all 4 tires are off the ground and it's riding on the bumper for a short time.

Would the red '68 "stepchild" and ESPECIALLY the gold '69 "stepchild" be better served by a taller differential gear? Would that increase acceleration enough that the torque wouldn't be turned into altitude? I have no idea what happened to this car as it's landing but there's some pretty impressive chassis flex.

I don't know the specs on either car but they are both Buicks with likely 455 based engines. Likely over 600 lb ft of torque at peak but the below is a solid chart for a stockish type engine 455 Buick. Olds, Pontiac, Chrysler, Ford and Chev engines can all have similar characteristics.

http://www.westernbuicks.org/buick-gsx-engine-rebuild-alan-haime-wa-buicks/

I'm sure there's a magic combination for every powertrain and rear suspension design. Generally speaking, you need the right gearing, clutch action/converter, and effective rear gear ratio (tire size relating to diff gears) to have a successful launch. What's the most effective place to start "tuning" and dialing in from the gold car's results to get something slightly tamer than the red car results?


How could this apply to 4 link rear suspensions and effective gear ratio on a 4x4?

 

[Pile of parts]

I think you're absolutely right in the fact that it's a combination of "tuning" multiple components that all work hand in hand. I won't pretend to understand or be knowledgeable on the topic. I love the link suspension in my jeep. I followed some basic rules and let the rest fall where it had to. It seems to work well, to me. However, someone in the know, or on a competitive level, may not feel the same. The same holds true in the racing world. How much knowledge, or budget, do you have???

Judging from the pictures alone, I would say the black car has the ideal setup/"tune". All tires are planted and energy is moving forward. Now, that is based on the picture and what I would think would be best.

 

[UNSTUCK]

Suspension is key, or at least a major component I think often overlooked. Watch linked rear ends of a jeep climbing something steep. Sometimes the tires start to hop vs some that don’t move at all. Dialing it in just right will cause the body to lift a bit which is forcing the tires down, increasing grip. At least that’s how it seems in my head.
The last thing a race car wants to do is remove power in order to prevent lifting.

 

[mbryson]

Suspension is key, or at least a major component I think often overlooked. Watch linked rear ends of a jeep climbing something steep. Sometimes the tires start to hop vs some that don’t move at all. Dialing it in just right will cause the body to lift a bit which is forcing the tires down, increasing grip. At least that’s how it seems in my head.
The last thing a race car wants to do is remove power in order to prevent lifting.

Good point. One of the reasons I chose those particular cars was they all (factory) had the same suspension. These particular cars may or may not have upgraded control arms (lowers are likely) or even rip/replace full on drag race 4 links.

I wondered if gear ratio adjustments alone would prevent lifting. Not sure.

 

[Cody]

Judging from the pictures alone, I would say the black car has the ideal setup/"tune". All tires are planted and energy is moving forward. Now, that is based on the picture and what I would think would be best.

I don't know the answer, but my gut says this is the correct line of reasoning. The energy being used to lift the front of the top car would be better spent propelling the car forward instead.

 

[Pile of parts]

I wondered if gear ratio adjustments alone would prevent lifting. Not sure.

Don't forget to factor small things like tire pressure into the equation... (and the list goes on)

 

[mbryson]

Don't forget to factor small things like tire pressure into the equation... (and the list goes on)

Honestly, that is a HUGE factor on "slow" (15-13 second) muscle cars and how they hook up. I do hear of pressure adjustment on nitro cars though so I think it's real for the big guns as well. Hooking up 10-14k hp is definitely a balancing act. Multi-stage clutches and direct drive

 

[Corban_White]

According to these 2 videos, if the front tires are on the ground you are leaving some grip on the table. But if they are too high off the ground the torque is not appropriately translating into acceleration.

However, since these are tractors pulling a sled on dirt, I'm not sure how much translates to cars pulling nothing on asphalt. And since they don't have suspension I'm not sure how much translates into rock crawling. However, they are cool.

 

[mbryson]

I would think in an ideal dialed in situation you would pull the front about 1"ish for a few feet?

 

[Hickey]

I would think in an ideal dialed in situation you would pull the front about 1"ish for a few feet?

Yes, because then you are using the leverage of the body weight to transmit force to the ground, without losing stability. If the front never lifts off at all, then there is power being wasted.

 

[bobn]

I would think in an ideal dialed in situation you would pull the front about 1"ish for a few feet?S

Yes, because then you are using the leverage of the body weight to transmit force to the ground, without losing stability. If the front never lifts off at all, then there is power being wasted.

Several decades ago, (maybe half a century) one of the car mags had a road (track) test of a funny car. The weight distribution chart, under power, showed: 50% right rear, 49% left rear, and 1% right front. With the left front slightly off the ground. I don’t know why I remember this but I always liked reading the data sheets of road tests.

 

[kmboren]

I don't have the answers but have been watching Cletus McFarland on YouTube and they drag race several cars. Go watch some about Leroy or Mullet and their 6 and 7 second passes. The blazer also which has big wheelies.

It is suspension geometry pushing the front of the car down under heavy acceleration, proper transmission set ups, adding or removing timing, and boost.

 

[lhracing]

In my opinion, if you have enough power you want the pull the front wheels 4-6 inches off the ground for the first 10-20 feet for maximum traction. This puts all the weight on the rear axle and the car is not putting too much energy in lifting the front end, it's putting the energy in moving the car forward.

 

[mbryson]

In my opinion, if you have enough power you want the pull the front wheels 4-6 inches off the ground for the first 10-20 feet for maximum traction. This puts all the weight on the rear axle and the car is not putting too much energy in lifting the front end, it's putting the energy in moving the car forward.

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That's usually the look I see on launch from the faster full bodied cars. (10.15 is no joke at all! Was that at elevation?)

Stock type rear suspension or custom 4 link? Love the wrinkle on the tires!

I'm assuming a T400 in the car? I can't imagine you didn't match the converter to the cam?

How often did you change diff gears to get the "right" combo? I'm curious if you finally settled on an "odd" gear just to tune it for your car? Maybe it was cheaper to make tire height adjustments than gear changes?

 

[lhracing]

That's usually the look I see on launch from the faster full bodied cars. (10.15 is no joke at all! Was that at elevation?)

Stock type rear suspension or custom 4 link? Love the wrinkle on the tires!

I'm assuming a T400 in the car? I can't imagine you didn't match the converter to the cam?

How often did you change diff gears to get the "right" combo? I'm curious if you finally settled on an "odd" gear just to tune it for your car? Maybe it was cheaper to make tire height adjustments than gear changes?

Elevation, typically at RMR the DA (Density Altitude) was about 6300 to 7800 feet, really good air was 5800ish.

Suspension, The car was a Ladder Bar rear.

Transmission, T400, the converter was a COAN matched to the car/engine combination. When I designed the engine I selected the heads and cam to put the car in the bottom 10's. In Vegas or Boise, I would have to slow the car down because it would have run about 9:75 which both car and me weren't certified to do.

Diff gears, Ford 9", when I first built the car I had a target speed of about 130 through the traps. I calculated the gear ratio of 4:56 based on tire height of 32" and RPM about 6500.

 

[Hickey]

That tire wrinkle is so cool.

 

[TurboMinivan]

All my serious drag racing experience involves front-wheel drive, so I don't have a lot to offer this thread... but I think this pretty much nails it:

In my opinion, if you have enough power you want the pull the front wheels 4-6 inches off the ground for the first 10-20 feet for maximum traction. This puts all the weight on the rear axle and the car is not putting too much energy in lifting the front end, it's putting the energy in moving the car forward.

RWD is gonna want enough weight transfer at launch to put virtually all the car's weight on the rear end--helping to maximize your traction--but not much more. It's a balancing act, to be sure.

Looking back, I could never get my 60-foot time below about 1.95 seconds. I now have a couple of ideas about how I might have improved that, but even after years of campaigning at RMR I never did better than this. That was a significant factor that kept my minivan from running faster than 13.50 ETs.

 

[Hickey]

Mah lord!

 

[Thursty]

I love watching their channel! This fight to get Leroy into the 6s is epic.