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supercat1
Flying Brick Rider
Joined: 11 Aug 2009
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Location: Hoboken, NJ
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 Posted: Mon May 17, 2010 12:32 am Post subject: gear ratios ... were there multiple? |
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so my brother has a 93 k11rs and i have a 93 k11rs. he says his is at 5k rpm when he is at 75mp. i don't hit 5k rpm till 85ish (maybe a little higher). were there multiple gear ratios for the bikes? just curious. not much that can be done about it before the two of us set off for hm3 here in a couple days.
thanks!
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tmarshall57
Mad Brick Rider
Joined: 07 May 2007
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Location: Tottington, Bury, Lancs, UK
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| Posted: Mon May 17, 2010 4:55 am Post subject: |
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On my K1100 the rev counter needle is in exactly the same position as the speedo needle in top gear.
I adjusted my speedo to take out the 10% built in optimism. My speedo reads 80MPH at 5KRPM - before adjusting the speedo it would have read approx 88MPH at 5K
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drikko
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Joined: 20 Nov 2009
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Location: Brisbane, OZ
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| Posted: Mon May 17, 2010 9:46 am Post subject: |
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Funny you should mention it, I fitted my brand new Garmin Zumo 220 (awesome BTW) for the run to the Budgie last week and discovered that mine was reading about 10% too high as well. So my posts about noticing a vibes at 110k really meant 100k! So now I don't worry about it!
Next time I take the cluster off I'll adjust it. There's a trimpot in there to adjust it, you'll find instructions on IBMWR.
Cheers
Derek
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Flying Duck
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RobWheatley
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| Posted: Mon May 17, 2010 3:11 pm Post subject: |
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Got to de different ratio's, My LT is nearly at the redline doing 130mph while my RS did 145mph and was still under it, Mine is and LTIC so the plod might have had it played with, The FD is the correct ration as i did check it.
Rob
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drikko
Flying Brick Rider
Joined: 20 Nov 2009
Posts: 1966
Location: Brisbane, OZ
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| Posted: Mon May 17, 2010 7:04 pm Post subject: |
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| Flying Duck wrote: | | http://smithduck.home.comcast.net/~smithduck/bmw/tech/speedocal/speedocal.htm |
Will that work with a gas soldering iron 
It's OK, just being stupid.
The K100 LT and RS definitly had different final drive ratios, I would have thought they continued that through to the K11's. I just looked through my Cymer and there doesn't seem to be any mention of ratios excpet the gear box!
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K1100RS '97
Laverda RGS 1000 '84
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Flying Duck
PsyKotic Waterfowl
Joined: 27 Jan 2005
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| Posted: Mon May 17, 2010 10:30 pm Post subject: |
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LT - 32:11
RS - 31:11
Someone may have put an LT final drive on to drop the revs a tad. Klinker did that when the seal went on his final drive.
Stamped into the final drive near the breather cap is the gear ratio. That would confirm it.
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mtnroads
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Joined: 29 Mar 2005
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Location: West Linn, OR
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| Posted: Wed May 19, 2010 1:25 am Post subject: |
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| Flying Duck wrote: | LT - 32:11
RS - 31:11
Someone may have put an LT final drive on to drop the revs a tad. Klinker did that when the seal went on his final drive.
Stamped into the final drive near the breather cap is the gear ratio. That would confirm it. |
32:11 is lower gearing than 31:11, probably because the LT has more work to do. So revs would be a tad higher at any given speed on the LT.
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lrome48
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Joined: 30 Jan 2006
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Location: Northridge, SFV,Southern California
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| Posted: Wed May 19, 2010 9:10 pm Post subject: |
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| mtnroads wrote: | | Flying Duck wrote: | LT - 32:11
RS - 31:11
Someone may have put an LT final drive on to drop the revs a tad. Klinker did that when the seal went on his final drive.
Stamped into the final drive near the breather cap is the gear ratio. That would confirm it. |
32:11 is lower gearing than 31:11, probably because the LT has more work to do. So revs would be a tad higher at any given speed on the LT. |
Tall gear ratio (high speed, low numerical ratio)
Short gear ratio (low speed, high numerical ratio)
The LT typically has the tallest gearing. Usually the final drive ratio is 33:12, or 2.75:1. The LT cruises faster at lower RPM but does not accelerate as fast as the RS. The RS ratio is typically 32:11, or 2.91:1.
K100RS 2 and 4 valve used 31:11 gears. (2.81:1)
Shorter gearing makes for quicker acceleration. I have seen some LT's with RS (and visa versa) final drive ratios so the difference is not that much between them, maybe 5-8 MPH either way at 5000 RPM.
I put 3.00:1 slightly shorter than stock K75 gears (R1100GS) in the cream K75. Standard for the K75 is 3.20:1/3.36:1. Many K75s's used the shorter 3.36:1 to be more competitive with other 750cc bikes of the era.
The cream K75 splits the difference. The fifth gear on the K1100 trans is slightly taller than the K75 trans ratio (1.61:1 to 1.67:1) Using the K1100 trans makes the cream's final output slightly taller, even so, the cream cruises at 80 MPH and spins 5200 RPM. The LT cruises at 80 MPH and spins 5000 RPM. Tire diameter needs to be factored in for really accurate measurement. The stock K75 spins nearly 6000 RPM @ 80 MPH, which is OK because the motor is so smooth anyway.
The first K75 paralever conversion I did was from a 4 valve K100RS, and the final was 2:81:1. Straight line aceleration was fine as long as you got on the pipe a bit, but top gear @80 MPH spun 4800 RPM. Carol and I rode it two up loaded with gear from LA to Sonora with no performance issues. The bike handled the hills and dales OkeyDokey.
Regardless there were multiple final drive ratios used throughout the K line, so it's all a crapshoot.
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K75
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Last edited by lrome48 on Thu May 20, 2010 3:59 am; edited 1 time in total |
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mtnroads
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Joined: 29 Mar 2005
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Location: West Linn, OR
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| Posted: Thu May 20, 2010 2:09 am Post subject: |
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Wow, thanks for the great info Larry. I just wish I could drop the r's on the LT by 500 rpm at 75 -it's smooth up to ~4400 rpm (68 mph on gps), then buzzy until 5000 (79-80) when it smooths out again. Positively silky smooth at 85 mph actual... so the bike is buzzy in the zone I prefer to drive - 70-78mph. Driving 80+mph requires too much concentration (for cops) to relax and 68 mph is just too slow.
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lrome48
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Joined: 30 Jan 2006
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Location: Northridge, SFV,Southern California
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| Posted: Thu May 20, 2010 4:04 am Post subject: |
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| mtnroads wrote: | | Wow, thanks for the great info Larry. I just wish I could drop the r's on the LT by 500 rpm at 75 -it's smooth up to ~4400 rpm (68 mph on gps), then buzzy until 5000 (79-80) when it smooths out again. Positively silky smooth at 85 mph actual... so the bike is buzzy in the zone I prefer to drive - 70-78mph. Driving 80+mph requires too much concentration (for cops) to relax and 68 mph is just too slow. |
That's the standard buzz range, ~4500-5000. You could drop the RPM down by 500 or better with a hybrid ratio, say 31:12 which would give you 2.58:1. Assuming your rear tire size is stock 17", you would therumrectally..er theoretically turn 4000 RPM @71 MPH, and 4500 RPM @ 80 MPH. The tradeoff would be the buzz zone would move to between 80-89 MPH approximately.
I don't think you would notice too much difference in acceleration unless you were racing against a stock geared LT, and even then the difference would only be a few MPH slower.
It would also make looking for the phantom 6th gear a less frequent exercise in futility. 
Disclaimer: These are theoretical approximations, because too many factors affect the accuracy of the calculaions. Barometric pressure and altitude all contribute to a variable air pressure that affects the external pressure on the tire, reducing its size and reducing the vehicle's velocity. The tire size is also affected by other factors like temperature, humidity, bike weight, bike weight distribution, weight shifting caused by acceleration, and rotational speed (centrifugal force). Gravitational forces from the earth, moon, and sun also affect the pressure on the tire and its size.
Even so, the numbers are good for estimating, and are not too far from the empirical values.
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Larry
K75
97 K1100 LT Specialk under construction
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robleyd
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Joined: 23 Jul 2009
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Location: Murbko, Australia
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| Posted: Thu May 20, 2010 6:14 am Post subject: |
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| Quote: | | Gravitational forces from the earth, moon, and sun also affect the pressure on the tire and its size. |
Presumably there would also be some effect from the planets between here and the sun?
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lrome48
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Joined: 30 Jan 2006
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Location: Northridge, SFV,Southern California
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| Posted: Thu May 20, 2010 10:43 am Post subject: |
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| robleyd wrote: | | Quote: | | Gravitational forces from the earth, moon, and sun also affect the pressure on the tire and its size. |
Presumably there would also be some effect from the planets between here and the sun? |
Just covering the bases mate. Well spoken Bruce, time to ask the Padre' for a prayer.
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Larry
K75
97 K1100 LT Specialk under construction
87 SpecialK75 Carols done!
2004 K12 Special the 'Beast' delivered
K1100 Standard Custom Gone but not forgotten |
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mtnroads
Flying Brick Rider
Joined: 29 Mar 2005
Posts: 281
Location: West Linn, OR
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| Posted: Fri May 21, 2010 1:05 am Post subject: |
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[Quote ]That's the standard buzz range, ~4500-5000. You could drop the RPM down by 500 or better with a hybrid ratio, say 31:12 which would give you 2.58:1. Assuming your rear tire size is stock 17", you would therumrectally..er theoretically turn 4000 RPM @71 MPH, and 4500 RPM @ 80 MPH. The tradeoff would be the buzz zone would move to between 80-89 MPH approximately. [/quote]
Sounds good - wanna' build me one? It's my only real complaint with the bike. Actually when I do the math I get about a 5 mph shift upwards at 4500rpm (70 mph x 2.75/2.58 = 75 mph) but that would be enough. Should help the mpg some too. A 31:13 would be perfect.
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lrome48
Flying Brick Rider
Joined: 30 Jan 2006
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Location: Northridge, SFV,Southern California
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| Posted: Fri May 21, 2010 1:47 am Post subject: |
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Right, @ 2.58 4500 would be 76.1 MPH, not 80 MPH. Forgot to factor in the gravitational pull of the Tea Party.  
31:13 would be 2.38:1. 4500RPM would be close to 83 MPH.
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Larry
K75
97 K1100 LT Specialk under construction
87 SpecialK75 Carols done!
2004 K12 Special the 'Beast' delivered
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mtnroads
Flying Brick Rider
Joined: 29 Mar 2005
Posts: 281
Location: West Linn, OR
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| Posted: Fri May 21, 2010 2:55 am Post subject: |
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| lrome48 wrote: | Right, @ 2.58 4500 would be 76.1 MPH, not 80 MPH. Forgot to factor in the gravitational pull of the Tea Party.
31:13 would be 2.38:1. 4500RPM would be close to 83 MPH. |
Ha ha - no kidding. Actually, working the numbers, a 2.38 rear would probably be a bit high, but with 32:13 it would be 2.46 - a 12% reduction in rpm and about perfect. Now who can build me one? I don't have a garage right now (sucks).
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