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Discussion Starter · #1 ·
Hey all, I hope you'll chime in to help me get a sense of what's what on the 2005 K1200LT Hannagan trike conversion I bought last year. One thing certain is that I really don't know how fast I'm going based on the speedo indication All the usual queues from other vehicles on the highway over time and distance seem off. My sense is that I'm rolling slower than indicated on the speedo. (OR everyone is speeding allot more these days!)
For context, this conversion uses a Ford Thunderbird differential with 14 inch rear wheels. I know the good engineers at Hannagan did their best to meet/ mimic original BMW relationships between their drive train components and the original BMW specs so that the indicated speed would be reasonably accurate. But it sure seems off.
Here's my question: When I set the cruise control to 80 MPH, my tach is revving at ~4600 RPM. What indicated speed do ya'll see at 4600 RPM? 1000 thanks for sharing!
 

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Hey all, I hope you'll chime in to help me get a sense of what's what on the 2005 K1200LT Hannagan trike conversion I bought last year. One thing certain is that I really don't know how fast I'm going based on the speedo indication All the usual queues from other vehicles on the highway over time and distance seem off. My sense is that I'm rolling slower than indicated on the speedo. (OR everyone is speeding allot more these days!)
For context, this conversion uses a Ford Thunderbird differential with 14 inch rear wheels. I know the good engineers at Hannagan did their best to meet/ mimic original BMW relationships between their drive train components and the original BMW specs so that the indicated speed would be reasonably accurate. But it sure seems off.
Here's my question: When I set the cruise control to 80 MPH, my tach is revving at ~4600 RPM. What indicated speed do ya'll see at 4600 RPM? 1000 thanks for sharing!
That sounds fairly close....I like to stay just around 4K revs and for me that translates to around 75mph.
 

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2005 K1200LT
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If they have matched the ratios exactly you will hit the rev limiter at 62 MPH in first gear.
 

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I found my indicated vs. actual speed (GPS speed) to be off about 6 MPH before the Hannigan conversion. Since the conversion it’s much closer now, within 1-2 MPH. As for RPM at 80 MPH, 4600 sounds about right but I couldn't tell you for sure as I rarely dwell on the revs and mainly go by engine sound!......;)
 
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Discussion Starter · #9 ·
That sounds fairly close....I like to stay just around 4K revs and for me that translates to around 75mph.
Thanks Bob. Exactly what I was looking for in a reply. I was already aware that there is a bias to the high side in the indicated speed through existing thread(s) here in the forum. But the added visibility on the RPM at any given indicated speed would help me understand the overall affect that the conversion had on speedo accuracy. Cheers!
 

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Hey all, I hope you'll chime in to help me get a sense of what's what on the 2005 K1200LT Hannagan trike conversion I bought last year. One thing certain is that I really don't know how fast I'm going based on the speedo indication All the usual queues from other vehicles on the highway over time and distance seem off. My sense is that I'm rolling slower than indicated on the speedo. (OR everyone is speeding allot more these days!)
For context, this conversion uses a Ford Thunderbird differential with 14 inch rear wheels. I know the good engineers at Hannagan did their best to meet/ mimic original BMW relationships between their drive train components and the original BMW specs so that the indicated speed would be reasonably accurate. But it sure seems off.
Here's my question: When I set the cruise control to 80 MPH, my tach is revving at ~4600 RPM. What indicated speed do ya'll see at 4600 RPM? 1000 thanks for sharing!
My LT indicates 20 MPH for each 1,000 RPM. 4,000 RPM = 80 MPH for me. However, my speedometer is about 6-7% fast. 80 MPH indicated is about 76 according to my GPS.
 

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My LT indicates 20 MPH for each 1,000 RPM. 4,000 RPM = 80 MPH for me. However, my speedometer is about 6-7% fast. 80 MPH indicated is about 76 according to my GPS.
Same here exactly...when I said 75mph in my reply to MB1, that was not my indicator speed because like you at 4K I show 80mph. When it comes to the rubber meeting the road, the reality is 80 is really 75 (y)
 

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My '00 LT always runs about 10% over what I am actually running compared to my GPS... though it actually runs truer when I have new tires!
As the centre tread of a tyre wears a single rotation of the tyre covers slightly less road distance. Mathematically: Circumference equals two times pi times the radius (C=2𝝿r). As the distance from the centre of the wheel to the centre tyre tread (r) gets less and less, the road distance travelled by a single rotation of the tyre is a smidgen less. The speedo doesn't understand this, it thinks that a rotation is a rotation is a rotation. A speedo that reads over the correct speed with a new tyre will be even less accurate as the tyre wears.
(My apologies for the use of mathematical terms like "smidgen":))

Ian
 

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Discussion Starter · #16 ·
Thanks again for all the replies! From what I gather, the way everything stacks up with the drivetrain components of this Hannagan trike, I'm turning about 600 RPM more than y'all at the same indicated MPH. That's xactly what I was looking to know. Cheers.
 
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