How many G's does a car pull under acceleration?
Discussion
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?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
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?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
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 accuracydoogz 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 accuracyEither that or mount it on a gyroscope!
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.
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).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.
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
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).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).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.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=0It 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....
This?
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).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...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.
Those who have tried report that phones and drag strips tend to agree to a good level of accuracy.
http://www.drcreview.com/news.asp?art=107
A good number of Gs, constant uninterrupted acceleration too..
A good number of Gs, constant uninterrupted acceleration too..
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.
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.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
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...Edited by BriC175 on Wednesday 16th June 13:47
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