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Speedometer accuracy

Posted: Fri Sep 08, 2006 4:43 am
by KidDynomite
I've read a time or two where people believe the speedometer might be about 10% optimistic.

I passed a copper running radar on a little stretch of road with little traffic. So, I doubled back and asked him if he'd mind clocking me as I drove by at 40mph (speedlimit 35) and he said okay. (I could tell he was annoyed, but who cares.) So, I crested the hill doing between 39-40 as close as I could tell on the speedometer. Once I passed and circled back around, he informed me I was doing 33MPH............Now, I'm not certain this was scientic, because I didn't get a huge run and maybe his radar was further down than I gave it credit for.

But all in all, the "un-scientific" version of the test comes in about 15% off.

Anyone else run a test or have GPS? I'd be curious to know so when I'm in traffic, I know not to speed too much or make my speed unbareable for the cars behind me.

Love to hear some feedback.

Posted: Fri Sep 08, 2006 7:09 am
by ericalm
If it does come to 15%, that's a wider margin of inaccuracy than most others I've seen. It could explain some of the possibly exaggerated stories going around about Buddy top speeds.

So, yeah, who has GPS? Or a strecth where they can ride alongside a car at 60mph (still inaccurate, sure)?

Posted: Fri Sep 08, 2006 10:29 am
by bwilms
I hear what you are saying. You don't want to intentionally annoy the drivers behind you by cruising under the speed limit. You also don't want to get a ticket because you overcompensated.

I've tested my speed with a GPS on several occasions. My speedometer consistently shows 5 MPH faster than the speed displayed on my GPS. So, when the Buddy 125 reads 40 MPH, the GPS shows 35 MPH. The margin is the same at lower and higher speeds.

Posted: Fri Sep 08, 2006 12:41 pm
by Lagerhead
bwilms wrote:
I've tested my speed with a GPS on several occasions. My speedometer consistently shows 5 MPH faster than the speed displayed on my GPS. So, when the Buddy 125 reads 40 MPH, the GPS shows 35 MPH. The margin is the same at lower and higher speeds.
It's the same for me.

Posted: Fri Sep 08, 2006 2:27 pm
by KidDynomite
So we're in agreement that the speed is typically 5mph heavy no matter the level? ie. When I'm doing 35, I'm actually doing 30 and when I'm doing 65, I'm actually doing 60?

Thanks,
Brian

Posted: Fri Sep 08, 2006 2:38 pm
by bwilms
KidDynomite wrote:So we're in agreement that the speed is typically 5mph heavy no matter the level?


That's been my experience, yes.

Posted: Fri Sep 08, 2006 2:41 pm
by rajron
Yea I’m getting very similar results. I checked my speedo with a GPS over a 12 mile trip and found the correction error to be 0.92 which comes out to about 59.8 mph with an indication of 65 on the speedo. I checked the milage not the speed.

Posted: Mon Oct 09, 2006 4:09 am
by hangukhurley
If any of you have a GPS hooked up to your Buddy, which one you do own? I've been checking into the Garmin ForeTrex 201 and am strongly considering going with that make/model. Any other suggestions? I have the Garmin c340 for my car but don't know a way to strap that onto my Buddy since it's so much larger than the ForeTrex 210 model. Any suggestions for that, too? If I could do that, I could save myself about $140 and not buy the ForeTrex 201.

Thanks much for any input on this!
:D

Posted: Mon Oct 09, 2006 11:26 am
by bwilms
hangukhurley wrote:I've been checking into the Garmin ForeTrex 201 and am strongly considering going with that make/model.
I have the Garmin ForeTrex 101. The only difference between it and the 201 is that the 201 uses an internal rechargable battery and the 101 uses 2 AAA batteries (I use rechargables). Oh, and it's $20-40 cheaper. I like using AAA because if you run out of juice, you can easily carry and extra set or stop at a store.

I like it for a basic GPS - Trip, MPG, AVG MPH, Direction, etc. It doesn't have maps or anything. It's more of a "bread-crumb-trail" type of navigation. Unfortunately, I haven't gotten it to properly interface with my computer so that I can pre-load routes, which is probably the only downside I have for it.

I haven't mounted it to the Buddy. I usually just put it in the front storage when I use it (which isn't often). It does come with a bicycle mount and a velcro wrist strap, which could probably be retrofitted to work with the Buddy. Let me know if you have any more specific questions and I'll try to help.

Posted: Mon Oct 09, 2006 12:16 pm
by rajron
I have a Garmin GA00306 but I do not mount it in my car, or my scoot. Whenever I want to use it I either put it on dashboard of the truck, or it fits in the ashtray of my car. When I use it with the Buddy, I simply put it in the front-side compartment, or glove shelf, like bwilms, when I wanted to read it I just picked it up and read the data, if I park in a public area with the GPS I just put under the seat of the 4 wheeled vehicles and when using it on the Buddy I just put it in my pocket when I park. Needless to say I am not a hardcore GPS guy, I just use it when needed so I have no idea where the best place to mount a GPS more permanently, sorry.

Posted: Mon Oct 09, 2006 10:52 pm
by vitaminC
hangukhurley wrote:If any of you have a GPS hooked up to your Buddy, which one you do own? I've been checking into the Garmin ForeTrex 201 and am strongly considering going with that make/model. Any other suggestions? I have the Garmin c340 for my car but don't know a way to strap that onto my Buddy since it's so much larger than the ForeTrex 210 model. Any suggestions for that, too? If I could do that, I could save myself about $140 and not buy the ForeTrex 201.

Thanks much for any input on this!
:D
It probably would not be good to use your c340 with the Buddy. The main reason is that the c340 is designed to be used inside the car, so it is not even slightly weather resistent. It also might not cope as well with the much rougher ride of the Buddy vs a car.

Another option instead of the ForeTrex might be one of Garmin's hiking GPS's, like the eTrex models. The older mapping models are reasonably priced (i.e., see http://www.gpsnow.com/gmet.htm) and have lots of utility both on and off the scooter. For mounting, it should be possible to rig something up using the RAM mount system, as they have all sorts of options.

I am saving up for the 60CX...