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post #1 of 12 (permalink) Old Nov 13th, 2006, 3:25 pm Thread Starter
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Question Overall gear ratio

How do you calculate the overall gear ratio from engine to back wheel?

The K1200R and the K1200S have different final drive ratios and first, second, and third gears have different ratios.

It would be helpful to compare the bikes across the board for all six gears.

Last edited by Larry; Nov 13th, 2006 at 6:13 pm.
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post #2 of 12 (permalink) Old Nov 14th, 2006, 2:54 am
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First you need the gear ratio:

(K1200S)

1. 3,93
2. 2,87
3. 2,27
4. 2,01
5. 1,78
6. 1,582

the ratio from the shaft drive is 2,82

than you need the distance for one round of the tire: 1,920 mm (Meter).

1000 revs = ? km/h

1000/ (2,82*1,582) * 1,92 * 0,06 (time factor) = 25,82km/h

V/max = 11 (rev-limiter) * 25,82 = ~ 284 km/h = 178 mph
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post #3 of 12 (permalink) Old Nov 14th, 2006, 7:57 am Thread Starter
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post #4 of 12 (permalink) Old Nov 14th, 2006, 10:46 am Thread Starter
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Question

Quote:
Originally Posted by OSM62
First you need the gear ratio:

(K1200S)

1. 3,93
2. 2,87
3. 2,27
4. 2,01
5. 1,78
6. 1,582
Another question. How did you arrive at the gear ratios above. The BMW site lists a ratio of 1.01:1 for sixth gear. You have 1.582. Does that include the primary drive ratio of 1:1.559?

Dividing the sixth gear ratio by the primary drive ratio: (1.01/1)/(1/1.559) = 1.574

I have no idea if the above corresponds to a correct equation, but it's the closest I could come to what you listed.

Last edited by Larry; Nov 14th, 2006 at 10:59 am.
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post #5 of 12 (permalink) Old Nov 14th, 2006, 12:02 pm
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Quote:
Originally Posted by Larry
Another question. How did you arrive at the gear ratios above. The BMW site lists a ratio of 1.01:1 for sixth gear. You have 1.582. Does that include the primary drive ratio of 1:1.559?

Dividing the sixth gear ratio by the primary drive ratio: (1.01/1)/(1/1.559) = 1.574
Exactly 6. gear= 1,559 * 1,015 = 1,582

i have the data up to the 3rd. place behind the point "." (bei uns Komma ",") .
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post #6 of 12 (permalink) Old Nov 14th, 2006, 6:26 pm Thread Starter
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Thanks again.

It appears that the K12R engine spins about 3% faster in sixth gear than the K12S.

You could deduce that the gas mileage is about 3% less on the R for super-slab travel, disregarding aerodynamics and probably some other factors I'm unaware of.

Putting more air in the tire would increase the weighted outside diameter and circumference of the tire and decrease this effect. It might also decrease rolling resistance of the tire.
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post #7 of 12 (permalink) Old Nov 14th, 2006, 8:43 pm
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The final drive on the K12R is 1:2.92 with the Primary and gears 1-6 the same as the K12S.

6th gear gets me 15 mph (gps) for each 1,000 for a theoretical top speed a tad over 165.... haven't got there yet, but been close enough to believe it possible.

K12S and K12R gear ratios:
1= 2.521
2=1.842
3=1.455
4=1.287
5=1.143
6=1.015
Primary Drive ratio 1:1.559


K12R Final drive ratio 1:2.92
K12S Final drive ratio is 1:2.82

Bill "Omaha"

"Life may have begun at 44, but it didn't get thrilling until I shot past 100"

'06 K1200R "Wolfgang" White Aluminum Metallic, FB 6/7/05
'04 K1200LT "Dieter" Titan Silver, FB 4/23/04
RCB, AMA, BMWMOA, Booze Brother "in training"
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post #8 of 12 (permalink) Old Nov 15th, 2006, 10:12 am
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Okay, here is the official "skinny" on the gear ratios for the following K-bikes.

K-S and K-R are the same except for Final Drive.

K-R-Sport is the same as K-R except for gears 1-4.

K1200S
Primary 1:1.559
1st gear 2.52
2nd gear 1.84
3rd gear 1.45
4th gear 1.28
5th gear 1.14
6th gear 1.01
Final Drive 1:2.82

K1200R
Primary 1:1.559
1st gear: 2.52
2nd gear 1.84
3rd gear 1.45
4th gear 1.28
5th gear 1.14
6th gear 1.01
Final Drive 1:2.91


K1200R Sport
Primary 1:1.559
1st gear 2.40
2nd gear 1.87
3rd gear 1.53
4th gear 1.30
5th gear 1.14
6th gear 1.01
Final Drive 1:2.91

I added a chart of "calculated" speeds. I think I got it right, but a second pair of eyes are welcome.


I am more than a little curious as to why the different 1-4 gears on the K12RSport :wtf I wonder if they are going to make the change for the other two next model year :think:

Attached Files
File Type: pdf k1200s.pdf (19.5 KB, 147 views)
File Type: pdf k1200r.pdf (19.4 KB, 122 views)
File Type: pdf K1200RSport.pdf (22.5 KB, 184 views)
File Type: doc K-bike gearing.doc (73.5 KB, 261 views)

Bill "Omaha"

"Life may have begun at 44, but it didn't get thrilling until I shot past 100"

'06 K1200R "Wolfgang" White Aluminum Metallic, FB 6/7/05
'04 K1200LT "Dieter" Titan Silver, FB 4/23/04
RCB, AMA, BMWMOA, Booze Brother "in training"

Last edited by BillyOmaha; Nov 15th, 2006 at 12:10 pm.
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post #9 of 12 (permalink) Old Nov 15th, 2006, 4:55 pm Thread Starter
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Quote:
Originally Posted by BillyOmaha
I added a chart of "calculated" speeds. I think I got it right, but a second pair of eyes are welcome.
The egine to wheel revs look correct.

It would appear that the RSport has a taller first gear than either the R or the S. This would allow a higher speed for a given engine rpm. It then drops to shorter gearing than the other two except for 5th and 6th with the R.

Does anyone know how weighted and spinning tire circumferences would affect speed? Seems that weight makes the circumference smaller and spinning would have the opposite effect except during hard acceleration.

Last edited by Larry; Nov 15th, 2006 at 6:44 pm.
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post #10 of 12 (permalink) Old Nov 15th, 2006, 6:01 pm
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Quote:
Originally Posted by Larry
The egine to wheel revs look correct.

It would appear that the RSport has a taller first than either the R or the S. This would allow a higher speed for a given engine rpm. It then drops to shorter gearing than the other two except for 5th and 6th with the R.

Does anyone know how weighted and spinning tire circumferences would affect speed? Seems that weight makes the circumference smaller and spinning would have the opposite effect except during hard acceleration.
Howdy Larry,

I believe the terms you're referring to are "loaded, unloaded and deflection".

On our bikes, the tires are "high speed" rated and will not significantly increase in diameter at the max speeds we can attain.

I'm going to "go out on a limb" and say that if our tire pressure is up to maximum specification you would see not more than a very minor difference in the deflection. Maybe a 1% increase in the revolutions of the tire per mile travelled. It's something, but not very much.

What the tire does experience when going faster is an increase in the rate at which the sections of the tire are "loaded" and "unloaded", or "deflected". That event puts stress on the tire that would be better avoided. By running at slightly higher psi. during high speed runs the deflection is minimized. This would only be necessary on sustained high speed runs, such as on the autobahn, or across the great state of Nevada

.

Bill "Omaha"

"Life may have begun at 44, but it didn't get thrilling until I shot past 100"

'06 K1200R "Wolfgang" White Aluminum Metallic, FB 6/7/05
'04 K1200LT "Dieter" Titan Silver, FB 4/23/04
RCB, AMA, BMWMOA, Booze Brother "in training"
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