GPS Speed vs Speedometer Speed bg difference

[btreaves]

Recently I purchase a Garmin Geko 101 GPS unit at the local Radio Shack($85+tax).

Well last night I put this little bugger through it's paces.

First I took my car out. I have a 2003 Acura TL Type S. I got the thing up to 122mph on the GPS before I ran out of room. Not bad considering the thing has the worst 4th gear I've ever experienced in a "performance car". After 3rd gear it just falls on it's face. The cars speedometer was dead on though indicating just over 120mph. I was quite surprised that it was so accurate.

Then I took the BUSA out.

I took the bike up to 160mph (speedometer indicated) then shut her down. GPS maximum speed...141mph.

Then I took her up to 180mph (speedometer indicated) then shut her down. GPS maximum speed...161mph.

Finally I wound it out to a GPS speed of 167mph, however I neglected to look down at the speedometer. I hadn't even gone into 6th gear yet.

Anyway, it looks like the speedometer is off by 20mph on the big end at least...I haven't checked mere motal speeds yet. So keep this in mind the next time you think you're really hauling, cuz if it is off by 20mph that means you've got to get it to a speedo indicated 205mph to reach a GPS speed of 185mph and that still ain't 186mph. So how much does the restriction really matter?

I'll be doing more testing in the upcoming days, but I've got to find a better way to mount this thing. I've got it in a magnetic tank bag for now, but the tank bag doesn't want to stay stuck to the tank at those speeds. Any ideas of where and how I can safely mount this thing on either myself or the bike? It's always got to have an unobstructed view of the sky.

 

[WWJD]

sssshhhhhh! Let'em think they're going that fast. Probably safer if they THINK they're going light speed when really it's only SUB-light speed.

 

[Johnnycheese]

the only speed on a bikeThat I saw dead on was Harleys.
On a Busa rememeber tire size sprocket an air in the tire will throw the speedo off. in fact a 16/44 will read 220 mph

 

[Revlis]

Also, When the needle hits the 180 mark Indicated, the Busa will just keep pulling and pulling. When that speedo hits the peg at 180 there is a lot left, all you need is the room, the bike doesn't care that the speedo has topped out, it'll keep going. Also make certain your GPS is tracking a good number of satelites as well. To few can interfere with it's ability to track speed or location accurately...

SO yeah, the 186 MPH "limit" does come into play..

 

[Dr Geekenstein]

I have a GPS, have "mapped" some of our rides so they can be shared when newcomers want to know the good routes. Been meaning to calibrate my speedo for the last month or so but never remember to bring the unit along. Next time I get out there though, I will definately bring it along and will report back here with results. Have heard that stock the speedo is off 6%. That is what I kinda believe thus far for my ride. 6% error at indicated 180 should show me 169. We shall see.

Peace

 

[super851]

btreaves, what I did with the same unit is purchased a pack of the the heavy duty velcro and mounted it to the top of my triple clamp. All it took was a velcro patch of 3/4 of inch wide by 1.5 inch long. Thus far never came off until I take it off and it is easy to look at the gps and your speedo to get your true speed. Hope that this helps.

 

[btreaves]

I finally decided to mount this little bugger to my clutch reservoir with some heavy duty velcro. It works great. The thing doesn't shake rattle or roll. And when I remove it you can't really tell that anything is missing since the velcro is black and the reservoir cap is black.

I took her up to a speedo indicated 200mph tonight.

GPS said 179mph. (I did notice that I have been inadvertently running the thing in the "batter save" mode, I hope that's not affecting the read out too much. The manual simply says that in "battery save" mode the receiver turns on and off alternatively to conserve power. Battery life is 12 hours in batter save mode.

I'm going to the track on friday, it'll be interesting to see what the difference is on the trap speed at the drag strip and the GPS maximum speed.

BTW, when I'm running the GPS unit it says that it is in 3D mode...which means that you're receiving signals from 4 or more satellites for greater accuracy I assume.

 

[Charlesbusa]

I think the 186 restriction matters!!! I'll never go that fast, ever!! But my baby can't be restricted!!! It's just the whole point of the matter.

 

[btreaves]

In my view the restriction doesn't even matter unless you're going to exceed it. I believe that I have on a few occasions over the last 4 years, but it's been very few. Most roads just aren't long enough or straight enough to take advantage of the 195mph.

My bike is an unrestricted 2000 model and it's nice to have for chit chatting and such, but the restriction really doesn't matter unless you're going to try and exceed it.

Most people just point to the numbers in the magazines, as if they could ever pull those numbers off.

I hate posers like that!

 

[dezzy7]

Dang you mean i wasn't really going 205

 

[jwcfbd]

I found my speedo to be about 10% off. At 80 indicated I'm only going 72 per GPS.