How many G's does a car pull under acceleration?

[ewenm]

monthefish said:

grahamr88 said:

jon- said:

Worth noting those "G apps" on the iphone are pretty useless. The GPS only runs at about 1htz, so only updates once a second and then has to calculate the mean G.

Do they not use the accelerometer?

Are all i-phones equipped with an accelerometer just in case someone downloads a G app?

I'd have thought it would be a fairly useful device for the games that use the movements of the phone as the inputs so they probably all have them.

Edit: Anyway, average G is pretty simple maths to work out from distance and time figures. Only peak G needs an accelerometer of some sort.

Edited by ewenm on Wednesday 16th June 11:04

[jon-]

ewenm said:

monthefish said:

grahamr88 said:

jon- said:

Worth noting those "G apps" on the iphone are pretty useless. The GPS only runs at about 1htz, so only updates once a second and then has to calculate the mean G.

Do they not use the accelerometer?

Are all i-phones equipped with an accelerometer just in case someone downloads a G app?

I'd have thought it would be a fairly useful device for the games that use the movements of the phone as the inputs so they probably all have them.

Edit: Anyway, average G is pretty simple maths to work out from distance and time figures. Only peak G needs an accelerometer of some sort.

Edited by ewenm on Wednesday 16th June 11:04

They might well use the built in accelerometer, but that becomes useless on a motorbike. The most accurate way is to use a high frequency GPS device like the racelogic stuff. Their base entry runs vbox at 10htz.

[McSam]

doogz said:

Why is it useless on a bike? 10Hz isn't exactly that quick. When the i-phone records at what, 100hz?

Because tilting an accelerometer produces a reading, so it must be mounted absolutely firm and steady to be any use for acceleration recording. In cars, data loggers' accelerometers must be calibrated to include a "tilt factor", reducing the reading automatically given how stiff the car's suspension is to compensate for squat under acceleration and braking. On a bike, with an iPhone in your leathers, you have no chance of getting anywhere near this accuracy

[RobM77]

doogz said:

McSam said:

doogz said:

Why is it useless on a bike? 10Hz isn't exactly that quick. When the i-phone records at what, 100hz?

Because tilting an accelerometer produces a reading, so it must be mounted absolutely firm and steady to be any use for acceleration recording. In cars, data loggers' accelerometers must be calibrated to include a "tilt factor", reducing the reading automatically given how stiff the car's suspension is to compensate for squat under acceleration and braking. On a bike, with an iPhone in your leathers, you have no chance of getting anywhere near this accuracy

Suppose, it would only be any good if you had a seperate device that recorded the attitude of the bike seperately.

Either that or mount it on a gyroscope!

Not forgetting that bikes pitch about an awful lot more than a car. It's not just the fact that the phone's in your trouser pocket (which is a rubbish way to do it, even in a car), it's the fact that the bikes leaning not just from side to side, but also pitching in acceleration and braking a lot more than a car.

GPS dataloggers are quite affordable now, and all budget club racers that I know run these rather than accelerometer based systems. It'd be easy to mount the unit and sensor on the back of a bike, or for bikes without pillion space the unit in a small tank bag and sensor on the back.

Actually, doesn't an iPhone have GPS? I'm surprised that there isn't a datalogging app that uses that.

[ewenm]

RobM77 said:

Actually, doesn't an iPhone have GPS? I'm surprised that there isn't a datalogging app that uses that.

There are running/cycling apps that use the iPhone GPS (possibly only on the iPhone 3GS?) so probably a car app too although the data record rate may be too slow (if the 1Hz claims above are true).

[Kozy]

Would I be right in thinking that the G you can pull is linked to how much torque you put out at the road surface divided by the weight of the vehicle?

So G = ((T x FD x R)/TR)/W

Where:

G = er... G
T = Torque
FD = Final drive
R = Gear ratio
TR = Tyre radius
W = Vehicle weight

That was how I figured it out for my car anyway.

Edited by Kozy on Wednesday 16th June 12:12

[RobM77]

ewenm said:

RobM77 said:

Actually, doesn't an iPhone have GPS? I'm surprised that there isn't a datalogging app that uses that.

There are running/cycling apps that use the iPhone GPS (possibly only on the iPhone 3GS?) so probably a car app too although the data record rate may be too slow (if the 1Hz claims above are true).

Oo, I hadn't thought of looking. Do you reccomend any particular iPhone apps for that? I'm about to buy a GPS enabled heart rate monitor to do this like Garmin produce (I normally don't carry my iPhone running or cycling because it's too big), but it might be fun to experiment with an app in the meantime.

[ewenm]

RobM77 said:

ewenm said:

RobM77 said:

Actually, doesn't an iPhone have GPS? I'm surprised that there isn't a datalogging app that uses that.

There are running/cycling apps that use the iPhone GPS (possibly only on the iPhone 3GS?) so probably a car app too although the data record rate may be too slow (if the 1Hz claims above are true).

Oo, I hadn't thought of looking. Do you reccomend any particular iPhone apps for that? I'm about to buy a GPS enabled heart rate monitor to do this like Garmin produce (I normally don't carry my iPhone running or cycling because it's too big), but it might be fun to experiment with an app in the meantime.

I don't have an iPhone but a colleague recommends MapMyRun but says the GPS is quite battery-intensive.

[otolith]

monthefish said:

Are all i-phones equipped with an accelerometer just in case someone downloads a G app?

All iPhones have a built in 3-axis accelerometer - it's how the phone knows to flip the display from portrait to landscape when you turn it sideways, or to disable the touch screen when you put the phone to your ear or to shuffle the next music track when you shake the phone, etc.

[twazzock]

MX5 Withdrawal said:

G-forces can be felt in all planes of movement.

It is a comparison to gravitational force, hence why astronauts pull 5g or so going straight up to escape the atmosphere.

The easiest way to generate g-force is by turning tight circles quickly hence the training in a centrifuge undertaken by astronauts.

I seem to remember a big hoha associated with a car pulling 1g in straight acceleration but cant remember which one....

http://www.pistonheads.co.uk/gassing/topic.asp?h=0&f=23&t=765003&mid=0&i=0&nmt=RE:%20700hp%20Caddy%20Dials%20%27SOS%27%20After%2011sec%201/4%20Mile&mid=0

This?

[RobM77]

ewenm said:

RobM77 said:

ewenm said:

RobM77 said:

Actually, doesn't an iPhone have GPS? I'm surprised that there isn't a datalogging app that uses that.

There are running/cycling apps that use the iPhone GPS (possibly only on the iPhone 3GS?) so probably a car app too although the data record rate may be too slow (if the 1Hz claims above are true).

Oo, I hadn't thought of looking. Do you reccomend any particular iPhone apps for that? I'm about to buy a GPS enabled heart rate monitor to do this like Garmin produce (I normally don't carry my iPhone running or cycling because it's too big), but it might be fun to experiment with an app in the meantime.

I don't have an iPhone but a colleague recommends MapMyRun but says the GPS is quite battery-intensive.

Great, thanks.

[jon-]

fluffnik said:

jon- said:

Probably about the same for a fast car, up to about 1.2G under braking.

Worth noting those "G apps" on the iphone are pretty useless. The GPS only runs at about 1htz, so only updates once a second and then has to calculate the mean G.

That would be true but for the fact that they use the phones accelerometer...

Those who have tried report that phones and drag strips tend to agree to a good level of accuracy.

As discussed above, that's equally as useless on a bike due to all the pitch changes.

[Slinky]

http://www.drcreview.com/news.asp?art=107

A good number of Gs, constant uninterrupted acceleration too..

[anonymous-user]

The data logger in my last rally car recorded a peak longitudunal G of just under 16g, although, to be totally honest, that was after approx 100m of travel on the cars roof after i clipped a gate post........ ;-)

[Sicob]

I got 0.9g acceleration in the Elise with iphone app and 1.2g braking. Probably more accurate me guessing than the figures though!

[jon-]

Sicob said:

I got 0.9g acceleration in the Elise with iphone app and 1.2g braking. Probably more accurate me guessing than the figures though!

That's not too far off. This is a trace from a performance box in my track MR2 (tyres listed on image)

[Gad-Westy]

Kozy said:

Would I be right in thinking that the G you can pull is linked to how much torque you put out at the road surface divided by the weight of the vehicle?

So G = ((T x FD x R)/TR)/W

Where:

G = er... G
T = Torque
FD = Final drive
R = Gear ratio
TR = Tyre radius
W = Vehicle weight

That was how I figured it out for my car anyway.

Edited by Kozy on Wednesday 16th June 12:12

Acceleration = Force/mass fundamentally so you're not a million miles away but it doesn't factor in rolling resistance, air resisatnce or limiting friction between road and tyre.

[brickwall]

www.vimulator.com

Gives a rough indication of G forces under acceleration for various cars.

[BriC175]

otolith said:

monthefish said:

Are all i-phones equipped with an accelerometer just in case someone downloads a G app?

...or to disable the touch screen when you put the phone to your ear...

Actually - I believe that's the proximity sensor

Edited by BriC175 on Wednesday 16th June 13:47

[otolith]

BriC175 said:

Actually - I believe that's the proximity sensor

So it is, it works with the phone horizontal if you cover the top of the screen. Didn't know that.