johninar

I've been reading a lot and I'm fairly confused about what GPS data logger to get. I have run across quite a few posts on other forums about GPS drift and general inconsistancies when comparing lap after lap. Is this a real issue? Any brands to stay away from?
Any brand really stand out now? I don't want to spend a grand on a fancy lap timer.


TIA,

John

autoxer6

GPS drift is inherent to the global gps satelite system. This will happen with all gps units. Some software programs will try to auto align laps or runs. It can help or hurt the data depending on what you are looking at.

Satelite drift occurs over hours, not minutes. So an AM run may not line up with a PM run but lap 2 will be a good match to lap 3. Keeping the unit on over the on keeps the satelites locked in the same order. This seems to help minimize the impact of drift but doesn't fix the issue.

davidfarmer

I agree with above, non-military GPS simply has it's limitations.

Have you looked at the RAceChrono?? http://mh-motorsports.com/lap_timers.shtml
Demo'd it at the end of last season.....VERY impressive!

put "DFarmer2011" in the order notes for a $25 discount!!!

rbl

You're talking a few MM and perhaps a 1/00th second error occasionally. Seems you'd have to be mighty good to really notice that.

You may get an error occasionally, like mine will miss a fix then it skews two laps, but that is so obvious in the times that it is just dismissed without consideration.

johninar

Thanks for the replies. I think some of the complaints that I was reading was really not drift, but inconsistancies in mapping during a session.

What I want is to see how I am attacking turns and what works and what doesn't. I want to be able to examine a session and see the different laps and be able to trust what I'm seeing. Are the lap by lap mappings really accurate?

Black_Mamba

So what Loggers would you consider accurate and reliable. I am hearing godd things about traqmate but someone told me the "exact track mapping" of the DLC unit is better. This is a cool but very confusing toy to shop for. How about VBox?

johninar

Yes, exactly what I am trying to figure out.
Found one the other day that was over $4K!!!

Still researching

autoxer6

The accuracy is based on two main things:
1. Inherent GPS accuracy which is independent of the model you buy.
2. GPS Sampling frequency which does depend on which unit you buy. They generally range from 5 to 20 Hz. I find that 10 Hz with accelerometers works well.

The main difference you should compare between units is the software. Some have limited features but are easy to use, some have lots of features and are difficult to use. Some have accelerometers which helps.

It may also be good to buy the system your friends are using so you can compare data. That is the most usefull aspect of data acquisition for me.

Also remember that the GPS antenna needs to be visible to the horizon to get a good signal. The GPS satellites overhead dont do much good. It's the ones on the horizon which give it the angle to triangulate speed and position accurately. So the roof of the car is the best place to put it.

ScaryFast

The lower buck GPS units may not have accurate "absolute position" on the planet, but they have adequate postion in relation to previous position. In other words, your data may be inaccurate based on where the system thinks you are in the world, but all of your laps will have that same offset and you can get the results you are looking for, which is comparing different lines, etc. Most single antenna GPS units have a positional accuracy error of up to 10 feet. The pricey ones (Oxford tech, etc) have an accuracy of 10 cm.

I'm with autoxer6, it's the SW you want to compare, in a given price range most units have comparable GPS hardware performance.