final drive ratio's and where to look

[Ed Miller]

Ah, you have one of the pre-Carter speedometers.  Mine only reads to 85 and according to Snowbum they are very accurate.  I was calculating my speeds over that based on the tachometer; I can cruise quite happily at 6500 rpms but I will get a ticket, maybe even on our interstates which is insane.  

As for GPS accuracy, I run with a few people who carry those things.  We run the same 10? mile loop every Tuesday, and their distance varies from just under 10 to almost 11 miles for the same route.  I tell them it depends on the side of the road they run on....  

[NC Steve]

Around here, actual Interstate speeds run 75-85 mph, and the cops rarely ticket for speeding as long as you're riding/driving smoothly & sanely. I have an 80 mile daily highway commute and often lock in with other vehicles running 85-90 mph, well spaced apart and flowing smoothly, for 15-20 miles at a stretch.

When done properly, by good drivers, I honestly believe this is much less dangerous than the chaos, frustration and "road rage" created by the idiots who park themselves in the left lane at 64 (or 94, doesn't matter) mph and refuse to move or let anyone by. These same a**holes will let 20 miles of traffic get jammed up behind them on a 2-lane Interstate stretch, yet move into the middle lanes and actually speed up when a 3-4 lane section approaches!.

Even the big trucks have taken to driving like this. Is it not still taught in drivers ed that the left lane in a passing lane, and that slower traffic should always stay to the right?
If I'm ever crowned the King of the Highway Patrol, there'll be some big changes, by golly!  

[Ed Miller]

I'd vote for you.

[Jon_P]

how can you have a pre-carter speedo? the first year of our beloved r65 was late 78? right? he would have been in office for a couple years?

i dint get to my bike this weekend liked i hope. worked on the "new" home all weekend. i finally got the floors ready to seal, got the first two coats on and it looks nice.

so back to subject at hand i havent figured out what ratio i have.

[Rob Valdez 79 R65]

You are sure it is a BMW final drive??  Everyone I have seen look like this:


click for a different size


Of course, there is no guarantee that the gear set has not been changed from what was originally stamped on at the factory.

[Jon_P]

ok now i found it. looked to be sanded, polished or gound? down alot. took a peice of paper and a pencil and did a rub to see it. it tells me it is a 31/9. with a quick removal of the boot and some tire chaulk i started counting and it came out to 31 to 9.

[Bob_Roller]

If one wanted to alter the gear ratio of the rear drive to suit their particular riding style, would it be possible to replace ring or pinion gears ? Are the parts interchangeable between different ratio rear drives, or are they specific to a particular rear drive ?

[Jon_P]

i was thinking the same thing, i have a feeling it would be better to do it in the tranny. do something with 5th! and while i am there maybe 4th it could use a little more. or save my pennies and go get a big brother to the r65 and keep this for playing around town.

[Rob Valdez 79 R65]

I am about 95% sure (pure assumption  ) that the gear sets are interchangeable for similar years.

[Bob_Roller]

When I get my '81 R65 out on rural interstate cruising around 85 mph indicated, the tachometer is indicating about 5600 rpm ( it really doesn't sound like a happy engine at that rpm). My R1150R at 85 mph is indicating about 3500 rpm, and getting about 60 mpg while doing it ! It sounds like I need a sixth gear/ overdrive to get the rpm's down and increased fuel mileage.

[Rob Valdez 79 R65]

My chart from January when Steve wanted to know how fast he was going:
(these are speeds indicated on my Garmin GPSr)


3rd gear
30 mph (48.27 kph) = 3000
35 mph (56.30 kph) = 3500
40 mph (64.36 kph) = 4000
 
4th gear
45 mph (72.40 kph) = 3750
50 mph (80.45 kph) = 4000
55 mph (88.50 kph) = 4750
 
5th gear
55 mph (88.50 kph) = 4000
60 mph (96.54 kph) = 4500
65 mph (104.59 kph) = 5000
70 mph (112.63 kph) = 5500
75 mph (120.68 kph) = 6000

Above figures are on a 31/9 final drive ratio.


Someone mentioned they don't think a GPS receiver can be very accurate as a speedometer.  True, it depends on clear sky for optimal sensitivity, but I have ridden past those automated radar signs that the police park alongside the roadway.  Coming home from work at 1 AM with no other vehicles around.  I even turned around and came back on it a 2nd time just to verify.  It was a 40 MPH zone.  I was indicating 40 on the GPSr, and the radar showed me at 39.  I can live with that.

[Bob_Roller]

I go past one of those "INFO" only speed indicators put out by Phoenix police , at the entrance to Phoenix Skyharbor Airport, and both the R65 and R1150R speedometers indicate 1 mph faster than the radar indicator, from 30 mph up to 75 mph.

[NC Steve]

When I get my '81 R65 out on rural interstate cruising around 85 mph indicated, the tachometer is indicating about 5600 rpm ( it really doesn't sound like a happy engine at that rpm). My R1150R at 85 mph is indicating about 3500 rpm, and getting about 60 mpg while doing it ! It sounds like I need a sixth gear/ overdrive to get the rpm's down and increased fuel mileage.

Yep Bob, you're helping to reinforce my 2 Bike (minimum)Theory: thanks [smiley=thumbsup.gif]

Although 5-8 bikes would be ideal, we should all have at least our R65s for around town work, short hauls, and fun in the corners, and a higher hp/taller geared ride for highway work.
I've been counting my pennies carefully, and I think I'm just about to have enough to pick up a nice low-miles R100, or maybe an R1150R, sometime before next Spring...  

[Rob Valdez 79 R65]

Mine will definitely be another airhead.  Definitely an RS.  Probably a mono-shock.  My only concession to progress...

[Semper Gumby]

I've gone in a different direction....



Oo La la!