| Author | Message | |||
     P3newbie |
so i'm on the hiway last nite coming home. according to my speedo, i was doing 80 mph. i passed a honda civic w/ a digital speedo, and she was doing 72. my problem is i wasn't passing at an 8 mile per hour pace. which brings me to my question: in rpms what is my speed? ex: (my bike 07 9R) about 4200 = 80 mph on the speedo. i'm just curious. yes i realize tire wear, etc... create other variables. just looking for some idea. don't want to have to calculate speed all the time. i did look in the kv, couldn't find. | |||
| Xl1200r |
The XB speedo's are not very accurate. When I run my GPS, I typically see a 4-5 mph difference on my bike. | |||
| Greenlantern |
The XB speedo's are not very accurate. When I run my GPS, I typically see a 4-5 mph difference on my bike. Yeah, most bikes I have owned have been off 1-2 mph @ 60 mph, 4-5 mph @ 80 mph and 30-40 mph @ 120 mph.  One of the constants that ties modern bikes to their ancestors?  | |||
| P3newbie |
soooo then if i'm @ 120 on the interchange minus the 30mph math i wouldn't be breaking the law. i like it. my gps bit the big one somehow, gotta send it in, then i'll check it. thanks. | |||
| Hammer71 |
I've put my speedo up against a freshly calibrated radar unit and it was dead on, 83 in a 30. Most have found that for some reason or another the Buell speedo is very accurate. Either way I dont look at it much. | |||
| Mnbueller |
4200 RPM / 1.676primary = 2505.97 2505.97 / 2.407secondary = 1041.12 RPM Final drive 24.8" dia tire = 6.49 feet circumfrence 1041.12 * 6.49' = 6756.86 feet per min 6756.86 fpm / 5280 = 1.279 miles per min 1.279 mpm * 60 = 76.78 MPH 4200 engine RPM = 76.78 MPH | |||
| Mnbueller |
I was a little bored after I ran those calculations, so I whipped up an excel spread sheet to do all the calculations. Here it is if anyone is interested.
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| P3newbie |
thanks for that. my rear tire is nearly due to be replaced, so that should change things a bit, but the calculations simplify things.  | |||
| Iamarchangel |
Still working on the picture of you pulling up beside some lady in a Honda Civic and then you leaning over to read her speedo... cool. | |||
| P3newbie |
i was on the hiway @ nite, those dashes are a bluish color with giant numbers, all i did was move to the right and look in, did seem like her civic was low. we were going up an incline while i was moving up on her. i was also checking for hotness. not. worth a look though. just in case.  | |||
| Bigredwood |
Mnbueller, You have too much time on your hands. I have an old TI-85 if you get sick of scribbling all that math.  Or maybe you professors needed you to show all your work. Thanks for the spreadsheet though. It helps with the 9 primary project I have in mind. | |||
| Punkid8888 |
Saved to computer  | |||
| Court |
Keep going and introduce the coefficient of thermal expansion and the reduction in tire loading, therefore sidewall profile and tire height due to lift. You'll soon be ready for Bonneville.  | |||
| Mnbueller |
I don't need to show all my work, I do it for 2 reasons. 1. To educate those who may not know how to do it. 2. It allows others to notice mistakes I have made And yes I do have too much time on my hands. I run engineering tests on generator sets. And once the thing is up and running, its a whole lot of sitting behind the computer watching it run, hopeing nothing exciting happens. | |||
| Gentleman_jon |
Speedo's are notoriously in accurate. Not to worry if your GPS is down. Simply download Speed, a free app by Stephan Troughton Smith, on to your iPhone, and bada-bing: GPS speedo. Looks like this:  Also reads in MPH, of course, for all you mid westerners out there. Don't have an iPhone yet? No problem, they are in stock at almost every Apple store right now. Don't have an Apple Store nearby? No problem: just move!  | |||
| Xl1200r |
Don't have an iPhone yet? Don't tempt me... I have 2 buddies with iPhones and I want one in the worst way... | |||
| Court |
I'm jumping on the iPhone the minute they have decent service in Manhattan. | |||
| Xl1200r |
I'm jumping on one the minute my Verizon contract expires and I can justufy an $80/mo service plan. | |||
| Xbrfirebolt |
Saved here also. Thanks Mnbueller | |||
| P3newbie |
so 1 hand riding the other checking the i-phone? sounds like a safe plan, especially at hiway speeds. you'll fit right in with those observant soccer moms.  | |||
| Firebolt020283 |
you could always duct tape your phone to the dash or something like that. | |||
| P3newbie |
i heard pink duct tape is the best for bike mount gps. |
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