When it comes to stock (for the most part) R53 mini’s….what kind of G’s will they pull on a skid pad? From what I’ve seen in the Road & Track magazines….when cars get up around 1G, they are doing darn good. I’ve got a stock ride-height R53 with no real suspension upgrades except IE Fixed Camber Plates, and KONI FSD shocks, and poly LCA and front sway bushings. With a set of decent G-Force Pro tires…..just out of curiosity, what kind of G-force numbers would my car be able to pull on a skidpad? It would be cool to have some sort of idea when looking around at what other cars can do whenever I’m flipping through all of those car magazines.

Any ideas?

 

I'm betting your in the .9x range at this point. Tires make the biggest difference.... put some track day tires on it and you'd probably break 1g.

 

btw: stock is .87g

 

a bit over 1.1 on street tires, and a bit over 1.2 on slicks

graphs are in my gallery

cheers,

Charlie

Arrgghh: I am too slow to read, and too quick to boast - these are obviously not STOCK numbers. </stfu>

 

An old 2004 issue of Road & Track tested a stock R53 and they got 0.87 G. That would be on the runflats.

Get dynolicious for your smart phone and have fun measuring it yourself.

 

Have you verified the accuracy? Most smart phone apps derive G from velocity and curvature of travel. These can be very inaccurate. The testing I have done shows G about 50% off.

And if it uses the phones's accelerometer they will likely be even further off.

Alan

 

The accelerometer would in fact be the ONLY way it would measure Gs. (What do you mean by "it derives G from ... curvature of travel"? It only "knows" you are turning from its sensing of lateral Gs, which is exactly what you want to know!) What are you comparing the smart phone's measurements with (what other device)? A known source of error for the smart phone measurements is if it is not mounted properly.

There are a couple of tests floating around (I can find them if needed) that have shown that the Gs measured by a properly mounted smart phone are indeed quite accurate---the derived HP numbers are within a few percent of HPs measured on a dynomometer.

Edit: Sorry, I did not answer your first question: You can very easily test the accuracy of dynolicious by, after pressing the 'calibrate' button. turning the phone on its side. This is, in effect, imparting a lateral force of exactly 1 G.
The accelerometer is perhaps too sensitive, so if it is not mounted well and if you are driving on a bumpy road, it will detect any "unwanted" movement.

 

Your phone doesn't have GPS? If you know the car's position through a corner you can calculate:

http://answers.yahoo.com/question/in...4111251AAK3zR6

This is the method all smartphone "track" apps use, cause the accelerometer in the phone is not accurate.

And you can see why the derived G is not that accurate either, cause you have to assume all corners are constant radius.

And your calibration method is total crap. I don't know how else to put it.

I was gonna ask for the references you mentioned but after reading your edit I thing it would be a waste of time.

Alan

p.s. You really need an external bluetooth GPS if you run a track app. The GPS is the phone is good for lap times, but not too much finer analysis.

A bluetooth GPS has a much better antenna and can take up to 10 samples/second, while a phone's GPS runs at 1 sample/second and the antenna is compromised to fit the form factor of the phone.

 

Hello Alan,

Although you could calculate the lateral Gs knowing curvature of the path and the car's velocity, that is not how the iPhone does it. It simply uses the accelerometer combined with its internal clock. It does not use the GPS (which would be highly inaccurate in plotting such a small curved path over a short period of time). Is that what you did to calculate your lateral G? (Sorry, you didn't explicitly say if that was your basis for comparing the iPhone's lateral G reading.)

The resolution of the iPhone's accelerometer in its standard setting, according to Apple, is better than 0.02G (i.e. it can measure accelerations larger than 2% of a G), which is fine for the Dynolicious app. Here is one test that was done when the app first came out (sorry, you will have to bear some ads and distracting characters :

http://www.youtube.com/watch?v=0-DFb...eature=related

Regarding the simple test I suggested to see if the iPhone's accelerometer is accurate by turning it on its side and seeing if it reads a lateral pull of 1 G, no, not crap at all, actually. By turning it on its side, the phone is now experiencing a pull of 1 G on it side. That is a perfectly good way to test the phone. As Einstein inferred in his "thought experiment", you wouldn't know if the elevator you are in were accelerating upwards at 1 G, or if you were in a gravitational field pulling on you with 1 G. Both scenarios would feel exactly the same to you

I hope that helps!

 

iPhone - ahh I live in the Android world.

I'm not sure what turning a phone has to do with 1G. An accelerometer at rest relative to the Earth's surface will indicate approximately 1 g upwards. So you only check calibration at one value and declare victory? You could check 0G a simple way too.

I did a little digging and I think this is the accelerometer used in the iphone.

Don't know how it is configured in the iphone, but if it is set for +/- 8G range and the iphone is setup to read all three axis (which it should be) at a decent sample rate and you orient it correctly, it should work very well. But you should calibrate all three axis and at more than just one value. Unless you just use it for straight line testing as in the video, then you only need to calibrate that axis.

And as you can tell from reading some of the comments to your video, this method would not work with most Android phones, thus the need for GPS derived G.

Alan

 

Most iPhone aps which do gs require a calibration which involves a lot of turning this way up and that way up. You eventually get 1g in each direction on 3 axes, which is enough to calibrate it on each axis. I'd guess they use the 2g range, I don't think I've seen an iPhone read over 2g.

 

I'll try to explain it one more time below ...

Exactly!

So, the accelerometer needs to be calibrated in all three directions (i.e., the three axes at right angles---up/down. left/right, forward/back). To calibrate it, one needs to impart a known gravitational pull or a known acceleration to the phone in each direction. To do this the phone is placed in three different orientations so that the Earth's gravitational pull of 1 G (the known calibration value in this case) acts on the phone in those directions. Now the phone is ready to measure accelerations (in a car, say) or changes in gravity (if you could take it to the Moon!).

Once it is calibrated, you can test to see how well it does by telling it to measure Earth's gravitational pull (1 G!) as an unknown. The phone is "zeroed" (in the upright position) to essentially tell it that it is ready to measure any changes. Then by turning it on its side the left-right axis (which is now vertical) will be experiencing Earth's downward pull of 1 G. It is now measuring that pull as an unknown. So, the reading you get is a valid test of the accelerometer's accuracy. When I do this, it always reads within a percent or two of 1 G, which is exactly the performance that Apple claims.

Conclusion: the accelerometer is indeed very accurate.

So ... if you are getting readings that are "50% off", either

(a) It is getting readings of accelerations that you do not want it to maybe due to improper mounting (it moves around, perhaps), or driving on a curve that is too bumpy, or the driving is too erratic. Or,

(b) Whatever you are comparing the reading to (a GPS-based curvature calculation, say) is itself, erroneous.

Cool?

 

So, you check calibration at two values (+/-1G). Not a bad way to go if you have the V/G curve of the accelerometer and there is not a lot of variation between accelerometers.

Can you confirm the accelerometer is set at +/-2 G rather than +/-8 G? It would of been nice if you had superimposed G on the video. I would think a car with slicks could pull more than 2 G at launch?

At the track (my word for road course) +/-2 G would be acceptable. You could max it under braking. Have you tested the accelerometer's ability to accurately report all three axis simultaneously?

Oh, and as far as the criticality of the mounting position goes, the correct way must be the way the phone is oriented to be used as a camcorder. My phone video records each lap as well as collects data.

 

I think we've answered the OP's question and also given some options to test his own car if he wishes. Dynolicious for the iPhone and Dynostorm for the Blackberry work fine if used properly. For $13, it's really not bad.

 

This thread is so hijacked that even a Somali pirate would be embarassed, so I started thinking that smartphone apps might be a real heartbraker to GTech. Here's their take on the question, from their website:

" Phone apps are another way to test the performance of a car. While the new generation of phones is pretty amazing, their accelerometers are not factory-calibrated for precision measurements. They are intended to detect the orientation of the device. There are calibration procedures, that a user must perform, in order to use these devices. This helps with the accuracy somewhat, however it depends on the ability of the user and the temperature, so the results vary widely. You might get lucky and get a good measurement once in a while but consistency, which is most important, is just not there. "

Obviously they're in the business of selling their product, but AM inclined to do buy their logic. If you'd like a measure of what you can do on a skidpad or in an acceleration run or whatever Dynolicious is sure gonna beat "seat of the pants" by a mile, but I don't know that I'd count on it to evaluate performance modification expenses, and I don't see Dynolicious making big inroads at track days, where, as GTech points out, "consistency...is most important."

 

Oh what the heck - here's some Somali data...

 

Well, I disagree. The original poster asked how many Gs a MINI can pull. An entirely relevant question is "how can you measure Gs yourself on your own car?". People have different tires, suspension setup, so a number determined by Road & Track would certainly not be applicable to your own car. What to do? Measure it yourself. How? Using either GTech, Dynolicious, or, the most accurate way, measuring out a circle and timing your run.

We are unfortunately at an impasse, because there is no study---at least I have not found one---that does an independent and statistically valid test comparing the different devices. I stand by my claim though that the iPhone and Blackberry accelerometers (apparently the Android uses something less accurate) are very good and their measurements are quite reproducible.