Change in Gear Ratio Specs Between R1100RT & R1150RT

[Woodstock400]

I'm confused about gear ratios and the change in the specs between the R1100RT and the R1150RT.

 

According to the official specs, the gear ratios for the 5-speed 1100RT are: 4.16 / 2.91 / 2.13 / 1.74 / 1.45

 

The gear ratios for the 6-speed 1150RT are: 2.05 / 1.60 / 1.27 / 1.04 / 0.90 / 0.77

 

The gear ratios for the 6-speed 1200RT are: 2.28 / 1.58 / 1.26 / 1.03 / 0.90 / 0.81

 

The ratios between the 1150 and 1200 make sense, but there is some mysterious change between the 1100 and the 1150 - the numbers are just not equivalent. There is an additional spec quote in the 1150 and 1200 data: "Primary Transmission - 1.88" (minor variations between the two models). If I multiple the 1150 and 1200 ratios by that, then I at least get numbers that make some logical sense relative to the 1100.

 

Can anyone explain the difference in the specs and what the underlying cause is of the change is?

 

Dan

First time poster

[Stan Walker]

Just goes to show that the 1150 is twice as fast.....

[Matts_12GS]

how about the difference in effective ratio if I were to use a 17" rear wheel and 1100S FD with my 5 speed RT transmission?

[ShovelStrokeEd]

The difference comes from quoting the transmission gear ratios plus the primary drive factor on the 5 speed. The 6 speed transmissions are quoted with just the transmission ratios. The primary drive is omitted.

 

Neither way is more accurate than the other, they just did the math for you in the case of the 1100.

[Woodstock400]

Thanks, Ed. Good to know the real answer.

 

Converting the latter to a net ratio, the gearing ratios between the bikes are (all relative to 1):

 

R1100RT - 4.16 / 2.91 / 2.13 / 1.74 / 1.45

R1150RT - 3.87 / 3.02 / 2.40 / 1.96 / 1.70 / 1.32

R1200RT - 4.29 / 2.98 / 2.37 / 1.94 / 1.70 / 1.52

 

Curious (to me at least) that the range from 1-6 on the 1200 is actually a lot closer to the range from 1-5 on the 1100 than it is from 1-6 on the 1150. The practical result on the ride is that the R12 will go slower in first gear than than the 1150 (at an equivalent engine speed), which means easier handling at parking lot speeds. And the R12 will rev a bit more in top gear relative to either of the others.

 

The really low sixth gear ratio on the 1150 has disappeared on the R12. At 70-75mph that is probably a good thing since you have a lot more torque in top gear if you need to speed up to avoid a hazard, but on the Autobon where speeds are in excess of 100, the 1150 looks like it has the best gearing ratio.

 

Of course the R12 also has a lot more engine than the 1100 so it has a lot more torque at any given ratio.

 

Enough engineering. Back to riding.

 

Dan

[ShovelStrokeEd]

Actually, you will need to factor in rear drive ratio's and tire sizes as well before you can make a real comparison.

 

The R12 comes with a different rear tire than does the R1150 and different yet again than the R11.

 

Once you know the tire circumference, final drive ratio, transmission gearing, primary gearing, if any, you can calculate mph/1000 RPM and draw some conclusions.

 

Looks like BMW responded, with the R12RT, with the need for more torque at startup to get the bike off the line and a more useful 6th gear for North American riding. I currently don't shift into 6th on my R1100S, which is geared just a bit taller than an RT until I'm going about 80. Tough to justify to the LEO's that I was riding that fast so I could use high gear.

[jrbldr]

Thanks for the exercise Dan, I also was wondering about that and never got around to figuring it out. Personally, I love the gearing on my R1100RT - it has the low first for excellent pull-off from a stop, and 2-4 seem well spaced, with 5th also perfectly geared for good running and roll-on at about 75-85, where she likes to run. Can't imagine the need for taller gearing, whereas with my K11RS, it always felt like it needed another gear.

 

john

[Eschelon1]

Not only that, but there's a slight difference in the tranny ratios between the RTs and the RTPs because of the additional weight the RTPs carry. I don't know the ratios myself but would be interested in hearing from someone who does...

[Woodstock400]

Not only that, but there's a slight difference in the tranny ratios between the RTs and the RTPs because of the additional weight the RTPs carry. I don't know the ratios myself but would be interested in hearing from someone who does...

 

Makes logical sense, but it is not true. I checked the RTP specs and while some other things are different, the tranny is not.

 

Ed has been teaching me a lot about gearing, all the way from engine to tire. I will post some more accurate info on the differences between RT models tomorrow.

 

Dan

[99RT-P]

Here are some numbers that are cut and pasted from Jeff Deans R1100RT-P page:

 

Rear-drive gear ratio of 31:11 (civilian RT has 32:11 ratio but R1100RS has 31:11 ratio)

Gear ratios: 1st - 4.16:1, 2nd - 2.91:1, 3rd - 2.13:1, 4th - 1.74:1, 5th - 1.45:1

Final drive ratio 2.81:1

 

Here's a link to his R1100RT-P specifications page:

RT-P Specs

[Global_Rider]

Actually, you will need to factor in rear drive ratio's and tire sizes as well before you can make a real comparison.

 

Exactly!!!

 

Thats why I put together a couple of Excel spreadsheets along with graphs for the Enduro and Sport transmissions before I bought my GS Adventure. The spreadsheets are available for download off my web site for those that want to plug their numbers into it.

 

http://www.ott.igs.net/~ace/Technical%20Stuff.htm