1/4 Mile Times

[jordak]

I was wondering if there was some correlation between 1/4 mile and acceleration times.

Using PSI's recent result of 13.64 with a trap speed of 100mph . If I can get from 0-100mph in 13.64sec could I expect a similar result on the strip. Alternatively if I can reach 100mph in 12 sec what could this equate to on the strip.

Given the number of variables that can effect 1/4 mile runs I'm sure no such correlation can be drawn however just interested to hear from the more mathematically minded amongst us on the subject.

[Adam]

I'm not sure mate.

But I can tell you that the last 3 PB's I have run have all decreased in MPH regardless of the ET being quicker.

[gogo]

jordak,

the basic equation for calculating distance covered under acceleration is

s = u*t + 1/2*a*t*t

where:

s = distance covered in metres

u = initial velocity in metres per second (for 1/4 mile this is zero) (divide kms/hr by 3.6 to get m/s)

t = the time period under consideration in seconds

a = the rate of acceleration in metres per second squared

Now, having just spelt that out - in the real world this is moderately useless unless you broke it down into much smaller intervals AND have some very good detailed information - in which case you probably would not need to be playing with sums!!!!

Having just said that - with enough empirical data and a few assumptions you could probably get something that might be roughly accurate.

Basically the issue is a car accelerating - particularly a turbo car will do so at variable rates, highest when at peak torque, then slowing (particularly for the manuals) when changing gear.

The only way to get any sort of approximation would be to look at the the average rates of acceleration in each gear (which will be quite different because of different mechanical advantage factors through the drive train ignoring traction issues), factor in a change of gears time and see how you go...

If you would like me go further let me know and I will repond further or knock up a little spreadsheet to have a crack at calculating it from peak power/assumed torque and known gear ratios...

Cheers,

Ben.

[Phils XM]

The equation to get an accurate figure would involve some serious calculus, and a lot of spare time.

Much easier to get your hands on a program called 1/4 Jnr.

Just plug in weight of car, gear ratios, final drive, frontal area and a couple of other details and presto. You get 1/4 mile times and MPH

also gives you 60", 330", 660", 1000" times and speed.

[Lawsy]

Phil is correct, it requires more calculus, with more multi variable intergrals, more 2nd order differential equations and more partial derivatives to correctly model it with any accuracy, than a year or two of an engineering degree... That is, to get it 'perfect'...

Instead, by using some of these equations plus realistic human constants, these calculators can come up with relatively accurate times (to within half a second I guess) so long as the information you instert is correct.....

[Turbo6man]

  Lawsy said:

these calculators can come up with relatively accurate times (to within half a second I guess) so long as the information you instert is correct.....

<{POST_SNAPBACK}>

Half a second??? You call that accurate? What kind of an engineer are you? Geez mate, tell me the weight of the car and the power and I'll guess to within half a bloody second.

:spoton:

[Adam]

  Turbo6man said:

  Lawsy said:

these calculators can come up with relatively accurate times (to within half a second I guess) so long as the information you instert is correct.....

<{POST_SNAPBACK}>

Half a second??? You call that accurate? What kind of an engineer are you? Geez mate, tell me the weight of the car and the power and I'll guess to within half a bloody second.

:spoton:

<{POST_SNAPBACK}>

He has a point!

[F6 UTE]

  Turbo6man said:

  Lawsy said:

these calculators can come up with relatively accurate times (to within half a second I guess) so long as the information you instert is correct.....

<{POST_SNAPBACK}>

Half a second??? You call that accurate? What kind of an engineer are you? Geez mate, tell me the weight of the car and the power and I'll guess to within half a bloody second.

:spoton:

<{POST_SNAPBACK}>

So, A day at the drags consisting of 6 runs, would you suggest that joe amateur's times wouldn't vary by 1/2 second??

[Turbo6man]

  F6 UTE said:

  Turbo6man said:

  Lawsy said:

these calculators can come up with relatively accurate times (to within half a second I guess) so long as the information you instert is correct.....

<{POST_SNAPBACK}>

Half a second??? You call that accurate? What kind of an engineer are you? Geez mate, tell me the weight of the car and the power and I'll guess to within half a bloody second.

:spoton:

<{POST_SNAPBACK}>

So, A day at the drags consisting of 6 runs, would you suggest that joe amateur's times wouldn't vary by 1/2 second??

<{POST_SNAPBACK}>

We weren't talking about driver ability - the discussion was about the potential time any given vehicle could achieve ... DO try to keep up.

[Lawsy]

I was giving some margin there for human error. Not everyone is as brilliant or as perfect down the quarter mile as you are, mate.

Some of those calculators say the T should do a 13 flat, some say it should do a 14.5.

So I'd say half a second (as in, + or - 0.25) is relatively fair.

Also, example.

You have a dyno day. 2 cars with almost identical power curves with the same driveline, same factory wheels with roughly the same tread and fuel...

Yet they run 0.5 second differences down the quarter, and both drivers stalled up to roughly the same rpm at launch, and have roughly the same weight....

Timeslips for similarly powered cars in similar conditions vary around about 1 whole second in this forum alone.

So sometimes a bit of leniency wouldn't go astray turbo6man.

Talking power and dimensions you can quote decimal places, but when it comes to real life performance, factory differences and the like, you simply have to give a little here and there.

  Turbo6man said:

  F6 UTE said:

  Turbo6man said:

  Lawsy said:

these calculators can come up with relatively accurate times (to within half a second I guess) so long as the information you instert is correct.....

Half a second??? You call that accurate? What kind of an engineer are you? Geez mate, tell me the weight of the car and the power and I'll guess to within half a bloody second.

:msm:

So, A day at the drags consisting of 6 runs, would you suggest that joe amateur's times wouldn't vary by 1/2 second??

We weren't talking about driver ability - the discussion was about the potential time any given vehicle could achieve ... DO try to keep up.

I thought we were beyond theory and got onto what it should be like in practice...

Oh well, you can't please everyone...

And I didn't say it was MY calculator. It has nothing to do with me, I said one of those calculators that can be readily found on the net. Like I said up there, some vary around a second. So don't attack me.