Best Pure Speedometer For Sports Car Challenge

May 4, 2006

Greetings! First time poster here.

I am co-organizing a 7 event charity performance challenge (www.wingedwarrior.net) next month and one of our events has presented us with a few scoring challenges, the 100mph-0 brake test. We need a good way to assure that drivers are maintaing 100mph with an in-car official. To avoid speedometer error, we chose GPS.

Now the question is which one....

Our Wants:

1) High Refresh Rates (i know most are 1hz max, but we need one that works as fast as possible so that the speed at the brake point is an accurate representation)

2) Affordable (we'll need 3-4 of these and they're really only speedometers, so a good price would be nice)

3) Large Speed Display (these will be in loud shaky cars running at 100mph, and it'll be nice if the speed display can be large)

4) Potential for External Antenna or Window Mount (in case signal reception is holding units by hand)

I'm looking at the Garmin eTrax, but was wondering if something cheaper that is a pure speedometer exists.

Thanks in advance!

2k · May 4, 2006

I would think that a Garmin 60CX might fit your needs. You would have to set it up with the display you want, but I have mine setup with a large display and it is easy to read. It allows for an external antenna, about $20. You can get several types of dash mount either permanent or temporary. Not cheap though, around $450.

May 4, 2006

That sounds good on everything but price, which is probably a deal breaker. $450 x 3-4 = Ouch. I think we're hoping to shop in the Sub $150 range since we'll only use one feature on these.

5.3k · May 4, 2006

A 60cx is enormous overkill for this application. Everything you desire is available on far, far cheaper GPS units. A plain-vanilla Sportrak from Magellan would work just fine; it has a couple of large-format display modes that would be perfect. You can still get nice dashboard mounts for them for < $20 each. Main problem is that they are no longer manufactured by Magellan, so you'd need to buy them used.

I don't know of any handheld units that can be configured to report faster than 1 Hz.

May 4, 2006

That looks like a fun way to thrash your tires! I'm going to be a GPS wet blanket and suggest that there's probably a better and/or cheaper way to do this. A cheap radar gun and 2 walkie-talkies comes to mind. You might also contact your local Sports Car Club of America chapter/club, and see what they'd use for such an application.

May 4, 2006

i have 2 initial suggestions, neither of which involve gps that may interest you.

1)you could use a pace car if there are no safety concerns, space becomes an issue. for our event we were using an abandoned amercian air force base and the space/safety issue wasnt a concern except that we were traveling at 250 km/hr. <_<

2)local law enforcement. here, for similar type of events, weve been able to get local law enforcement to 'donate' their radar guns for use by a retired member of the force. by 'donate', it did tale a donation to a local charity for them to agree, they also provide some very good safety seminars for the contestants and they also got the opportunity for an off duty officer to liason with public in a fun event.

my suggestion for a gps unit wuld be nearly any basic unit. my experience with gps primarily involves magellan/thalles unit (though a new member is the garmin 276c). the magellan units as notes contain a large display screen feature with 3/4" high digits specifically designed for use while driving. otherwise my reccomendation would be to research your purchase and buy what unit you feel youd like---im sure youll find other uses for it. i dont really think it would be necessary to have identical units as the data being feed into the units is the same and the computation process varies very little between manufacturers. gps may pose some troulbes as some vehiciles have metallic laminated glass which may impair signal reception.

May 4, 2006

We'll have a radar gun as well, but you need in-car feedback from an official so that guys with inaccurate speedometers (it's common) know their true speed. It also helps avoid guys trying to fudge their speed a little. Remember, guys who have to redo their pass will need to drive 1/2 mile to restart...we don't have time for too many errors. I don't think a pace car would be very safe if a car has braking pull. There other logistical issues with this as well. I've gibven this quite a bit of thought, and we always come back to GPS.

So Back to GPS...

Is this the Magellan unit with large digits that has been mentioned here?

May 4, 2006

Its not a GPS, but I think its what you are looking for.Performance computer Or this link for a cheap radar gun.

http://www.opticsplanet.net/radar-guns.html]RADAR GUN[/url]

Edited May 4, 2006 by HOGCAT

May 4, 2006

I have used my old etrex legend in the car as a passanger quite frequently. If the judge is the person watching the speed on the gps all they have to do is hold the gps near the window side of the car and they will likely be fine. and if these are throuw away units I would get something like the legend (has dta cable included in package) and use them as prizes at the end of the day. Garmin also has a large text size option

just my 2 cents.

bwmick

Edited May 4, 2006 by bwmick

3.8k · May 4, 2006

The Explorist 300 would work. I think used Sportraks would be better. Not the Map or Pro version. Just the plain jane Sportrak. Try ebay or Amazon.

Some screen shots here.

Edited May 4, 2006 by Sputnik 57

May 4, 2006

Lower end eTrex and I think the Geko's would give you cheap GPS with readable speed display. No external antenna, but that shouldn't be an issue with a decent dash mount. Buy them on eBay.

May 4, 2006

We'll have a radar gun as well, but you need in-car feedback from an official so that guys with inaccurate speedometers (it's common) know their true speed. It also helps avoid guys trying to fudge their speed a little. Remember, guys who have to redo their pass will need to drive 1/2 mile to restart...we don't have time for too many errors. I don't think a pace car would be very safe if a car has braking pull. There other logistical issues with this as well. I've gibven this quite a bit of thought, and we always come back to GPS.

So Back to GPS...

Is this the Magellan unit with large digits that has been mentioned here?

safety is a definate issue for a pace car. if safety for brake pull is your concern, maybe you misunderstood my thought...i was thinking more along the lines of a lead pace car as in a horse/car race, safety is definately a concern regardless.

May 4, 2006

As mentioned, we have a gun already. A GTech would definitely not work, and make us a bit of a joke (they're not taken seriously by most experienced drivers).

Let's keep this conversation to GPS.

So it would get a decent signal just holding it out/nearly out the window? I'm concerned at 100mph that might be a challenge.

The explorist does look pretty good for this purpose. Does it have good refresh rate? Can you get a larger speed display with the eTrax, as it's still a little cheaper to purchase.

May 4, 2006

Would a radar gun IN the car, pointed at a fixed object give a useful reading?

Failing that, how about a radar gun in a fixed location driving a 4 foot high external display, or something, that the driver can read from 1/2 mile away.

May 4, 2006

(Beats Head Against Wall....)

Let's keep the conversation to GPS options.

May 5, 2006

I use an Explorist 500 on my dash and it is extremely accurate for a speedometer. I actually refer to it more then I do my regular speedometer. My only worry would be on the refresh rate. You could have the finish set as a waypoint, and have the screen set at Speed and Distance to the waypoint and get an accurate reading at certain distances from the waypoint. Ex. 120 km @750 m. from Waypoint, 160 @500 m. from waypoint, 210 @250m. from waypoint,etc.

You definately wouldn't need an external antenna if it is mounted on the dash. I would check the Explorist 100 or 200 series if you don't need mapping capabilities and want it strictly for the stated use.

Have fun!!!

May 5, 2006

Any of the basic GPSs will work as a speedometer. Someone mentioned an ETrex Legend, it'll work fine. The unit can be set up to record a tracklog, recording a point every second (best it gets). This tracklog will include current speed and bearing - proof of your driver having done the exersize properly in case there is any question. The large digit screen in the trip computer is more than big enough to be seen when the unit is on the dash, it can be configured to show current and maximum speed.

5.7k · May 5, 2006

Where do you purchase cheap radar guns?

May 5, 2006

(Beats Head Against Wall....)

Let's keep the conversation to GPS options.

LOL I feel sorry for you, you've walked into a den of nitpicking (but wonderful) geeks!

I drive a 2000 Z3 and when my speedometer says "100" my Magellan eXplorist 210 says "96".

I've been trying to figure out which is right... I'd hate to think one of them has a 4% margin of error. Or maybe each has 2% in opposite directions...see? Nitpicking geeks!

I got my 210 a couple of weeks ago at http://kidwell.biz/ for $163 shipped. As someone pointed out, it would make a great prize at the end of the day.

Where are you having your contest? If you're in the Southeast USA I might attend.

DconBlueZ

3.8k · May 5, 2006

Speed is not a factor in keeping a lock. I get good signal in an aircraft by holding the GPS near the window and get speed readings in excess of 500 MPH on a routine basis. The GPS does not measure your speed using distance over time. It measure the doppler effect on the signals it receives. Signal thru a windshield is not a problem except those few models that have metalic coatings. If it blocks an EZ tag toll tag, it will block a GPS.

As far as I know, virtually all handheld GPSrs refresh at 1 hz. The etrex does. Here are some screen shots.

3.8k · May 5, 2006

I drive a 2000 Z3 and when my speedometer says "100" my Magellan eXplorist 210 says "96".
I've been trying to figure out which is right... I'd hate to think one of them has a 4% margin of error. Or maybe each has 2% in opposite directions...see?

Most spedometers over-report your speed on standard sized tires. GPSr speed readings are accurate to +/- .1 mph. Yes, this means that your warranty will run out 4% ahead of time too.

May 5, 2006

lol at DconBlueZ's post....I've found my C5 was always 1mph off. After reprogramming the speedo (i have a standalone engine tuning setup) for a new diff install it has been dead on since then. I think it was tire related error. The competition is about 30 miles north of Indianapolis. We have a few drivers coming from the southeast.

It seems the Explorist 100 costs more than the 200? any rationale for that? The etrex still seems to be a good option as well. Which of these units can make the largest speed display?

May 5, 2006

Speed is not a factor in keeping a lock. I get good signal in an aircraft by holding the GPS near the window and get speed readings in excess of 500 MPH on a routine basis.

Yep. Considering the satellites could be going over 3000 kph in relative velocity to you, your car speed is kind of trivial in relation.

The GPS does not measure your speed using distance over time. It measure the doppler effect on the signals it receives.

Some do, some don't, some use both.

Another thing to worry about is to test to make sure that pointing a radar at the GPS receiver doesn't jam it. (Or melt the antenna element at really short range.)

May 5, 2006

These guys mount the antenna inside the back window and don't have any problems*:

But I guess they have a fiberglass shell to receive through instead of metal (or do they?).

Considering it's for charity, have you called local marine/survey dealers for loaners or demos?

*Edit to say that it's more of a minimal problem compared to their other problems (high fences & grandstands, calibrating the cameras, radio telemetry, lots of turns, etc.).

Edited May 5, 2006 by GPSlug

May 5, 2006

These are on sale for $134. I put this in my jeep after a larger tire install. It was actually less expensive than the correct output gear.

http://www.cpperformance.com/detail.aspx?ID=5909

Sorry I didn't realize that they don't give you the receiver anymore,

Edited May 5, 2006 by flattie

May 6, 2006

Where do you purchase cheap radar guns?

Believe it or not; Mattel is offering a mail in promo right now for a radar gun. Apparently, it really works with decent accuracy, both for 1:1 vehicles and 1:64 toys.

Go Figure?

May 6, 2006

Speed is not a factor in keeping a lock. I get good signal in an aircraft by holding the GPS near the window and get speed readings in excess of 500 MPH on a routine basis. The GPS does not measure your speed using distance over time. It measure the doppler effect on the signals it receives. Signal thru a windshield is not a problem except those few models that have metalic coatings. If it blocks an EZ tag toll tag, it will block a GPS.

As far as I know, virtually all handheld GPSrs refresh at 1 hz. The etrex does. Here are some screen shots.

I understand that part, however, if you are trying do use the speedometer feature on a GPS to record speed at certain intervals, it won't be correct. The speed of the car can decrease/increase more rapidly then the GPS can refresh. I've stopped my vehicle to a dead stop from a reasonable speed and it takes my Explorist at least three to four seconds to catch up?

6.4k · May 6, 2006

(Beats Head Against Wall....)

Let's keep the conversation to GPS options.

Everyone else is also beating their heads against the wall because a GPS really isn't the best solution for what you want to do. They don't refresh fast enough for one thing. Another is MPH is pretty much just a nice little afterthought in a GPS. It calculates speed based on time between postions. the cachers here will tell you that despite the theoretical accuracy of a consumer GPS (9-12ft for most units) in the real world it's not uncommon to see 20-50ft errors, or even more. Some days/times you can be standing still and the GPS will jump 50-100ft all over the place. These jumps can be averaged out to get a decent fix on position, but they totally screw with the MPH readout. One many occasions my GPS has claimed my car has hit a max speed of 900mph or more!

The G-tech is a bit of a toy, but there are other non-gps solutions to your problem.

Maybe your group could beg/borrow/buy/get donated a Vericom? I own an older model and it does exactly what you want. It would signal the driver when he's reached the preset speed, and then calulate braking time, distance, and G-forces from the time he applies the brakes.

It's no toy like the G-tech, and is used by many racers, automotive magazines and govt test centers.

Edited May 6, 2006 by Mopar

6.4k · May 6, 2006

BTW, here are the accuracy specs for the Vericom VC3000 ($1000 MSRP, might find it cheaper):

Speed: .36 mph (.58 kph)

Distance: .65 feet (.20 meters)

G-force: .01 G

Time: .001 second

The following information applies to the VC3000 firmware, version 2.14, released September 15, 2004.

The VC3000 version 2.14 has been is tested and proven to be accurate within 1 % for G-force, speed, time and distance. The testing was conducted in October 2004 at the Minnesota Highway Safety Center, St. Cloud State University, Minnesota.

A calibration certificate will be issued at the time of purchase.VC3000.

Hey, it's accurate enough for the FAA to use it to inspect braking systems on airlines, and the DOT uses them to check trucks and mass transit.

May 7, 2006

If all the cars are OBDII compliant I would suggest www.scangauge.com. Nice little scantool has quite a few functions.

May 7, 2006

Why not use G-tech??? They are deadly accurate on the MPH side if set and leveled in properly. Try using two at a time and do an average and you will see how close they are.

They might not be perfect for a recorded record run for the record books, but they will work perfectly for an arbitrary comparison.

It'll tell you when to start braking after hitting 100.

The GPS will never work, on my 0-100-0 runs with a 5th wheel I'm at 100 for less than 1/10 of a second.

Edited May 7, 2006 by SKYWLKR

May 11, 2006

Which GTech tells you your current mph? Our brake point is marked, so we would need to use our brake point, not what a GTech said.

My GTech Pro was consistently 4-5mph off at the drag strip, even after leveling.

May 11, 2006

The MPH is "off" due to the G-tech being more acurate.

The reason is, the strip calculates the average speed of the last 30 feet.

The G-tech Is within ~one mph of your actual radar verified Trap speed.

There is a 0-100-0 mode on the G-tech, I'm not sure if was carried over to the G-tech Pro.

it sense when you hit it and then tells you when you hit 100 and then sense when you are at a full stop.

May 12, 2006

I doubt I gain 4mph in 30ft pulling 4th gear at 120mph.

If you hit 100 and hold that speed, will the GTech continue to flash, or will itsense the throttle lift and start considering you as braking?

Best Pure Speedometer For Sports Car Challenge

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