Physics behind 60-ft times

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Jan 14, 2009 | 03:30 PM

Torlow

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From: Tyler TX

Physics behind 60-ft times

Experienced drag racers -- can you answer this question: How do you get 60-ft times in the 1.8 second range and better on stock tires?

I ask because I don't understand the physics. If your car accelerates at 1 G your 60-ft time will be 1.93 seconds. Many performance cars have tires/suspension that approach (and slightly exceed) 1 G in lateral acceleration. This should correlate to the traction potential of the tires. A 1.8 second 60-ft time is accelerating at 1.15 G's.

I know when you acclerate the car weight distribution transfers to the rear, but even if you lift the front end, only the full weight of the car (or 1 G) is over the drive wheels.

So how does it do it? Drag radials I understand are stickier, but stock tires? Does momentum temporarily increase the force on the wheels beyond the weight of the vechicle? Do the tires have an adhesive force independent of a pure frictional component?

Jan 14, 2009 | 03:44 PM

jkheit

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Quote:

Originally Posted by Torlow

I ask because I don't understand the physics. If your car accelerates at 1 G your 60-ft time will be 1.93 seconds. Many performance cars have tires/suspension that approach (and slightly exceed) 1 G in lateral acceleration. This should correlate to the traction potential of the tires. A 1.8 second 60-ft time is accelerating at 1.15 G's.

I know when you acclerate thow does it do it? Drag radials I understand are stickier, but stock tires? Does momentum temporarily increase the force on the wheels beyond the weight of the vechicle? Do the tires have an adhesive force independent of a pure frictional component?

I am not an experienced drag racer, but, I'll speculate a bit. First, the reports of 1G are on a skid pad (if I recall). I think the straight line Gs the tire can handle will be a bit different from the lateral measurement on the skid pad.

Second, even the lateral measurements, are likely an average at specific conditions. I imagine the std.dev. from that avg on even that very same pavement will be rather high based on the driver, not to mention when the conditions (humidity, temp, how much the car was driven before the test, etc.) vary. You will get very different characteristics when you burn out the tires to get them warm, and when you are on a stick dragstrip pavement.

Also, I think the warp of the tire on a straight line, bunches the tire in a way, at the right speeds, that it actually can increase the overall frictional force/surface area, which is quite different from when youre experiencing lateral frictional force as the tire distorts rather differently under those conditions.

That's just my speculation. Would be curious to hear from the experts.

Jan 15, 2009 | 10:07 AM

FloydSummerOf68

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From: Missouri City Texas

There is also a lovely combination of VHT and sticky rubber from other slicks/drag radials all over the first 60 feet.

If you walk out onto the track your shoes will literally feel like they are sticking to the floor.

Massive traction is possible on well prepped tracks with VHT and heat.

Jan 15, 2009 | 02:23 PM

c6 batmobile

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From: Middle of No where AK

lowering your tire pressure helps to so you can increase the surface area getting traction. As far as the g force the tires hold I dont know much about that im sure heat and the torque ratio of your gears and conveter is going to play a large role in that. I can tell you Ive personally attained a 1.83 60' on street tires at 24psi and a very light burn out to get the water off. Too heavy and youll actually make the tires slick. Launched at about 1800 rpm.

Jan 20, 2009 | 05:43 PM

siffert

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From: Makena, Maui & NM

Quote:

Originally Posted by c6 batmobile

I can tell you Ive personally attained a 1.83 60' on street tires at 24psi and a very light burn out to get the water off.

You got a stall, right? That had to help a lot

My best on runcraps was 1.96 near bone stock 25 psi with just catback and "free air" propped shroud. Still, I know others with 1.8x's bone stock so it can be done. Most of those is with the great help of VHT and -DA.

Jan 20, 2009 | 06:16 PM

jpee

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From: Somers NY

Lowering the air pressure does little IF anything on Runcraps.. because they have VERY stiff sidewalls...

The reason for lowering air is to let the tire "twist" a little on the launch.. The bigger sidewall you have the better traction you will get..

I run 265/40x18 Mickey Thompson... I could run a wider tire 275/35/18 BFG but I get better results with MORE sidewall.. I run 22 lb of air..

If I run my Runcraps I run them at 28... my best 60' with runcraps is 1.852

With a higher stall converter, and GOOD Drag Radials, I'd had 1.65 60' times..

If you HAVE to or plan to run on the stock tires 26 lb of air is as low as you should go... go AROUND the water, no need for a BIG burn out, just a quick spin to clean them off...

I used to leave the line at 1100 RPM with stock tires..

Jan 20, 2009 | 07:40 PM

siffert

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From: Makena, Maui & NM

Quote:

Originally Posted by jpee

Lowering the air pressure does little IF anything on Runcraps.. because they have VERY stiff sidewalls...
If you HAVE to or plan to run on the stock tires 26 lb of air is as low as you should go... go AROUND the water, no need for a BIG burn out, just a quick spin to clean them off...

I find the traction sweet spot of runcraps around at 25-26 lbs of air pressure both at the strip and on the street. Does make a difference than running at 30 lbs. I agree no burn is needed for them and just a quick spin to clean.

Jan 20, 2009 | 08:11 PM

ramrodw30

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From: Vista CA

If you HAVE to or plan to run on the stock tires 26 lb of air is as low as you should go... go AROUND the water, no need for a BIG burn out, just a quick spin to clean them off...