Determining Ratio

[AnnapolisAirhead]

Does anyone know how to positively determine what ration your gear set is? I can pull the stock specs for my bike, but the PO pulled a trailer and made numerous mods to the bike so I'm wondering how to identify the ratio by inspecting the bike.

[sumran]

It should be stamped on the flat surface where the drive shaft enters the final drive. It is in fraction form. Mine is 32/11, if I remember correctly.

[tghsmith]

the ratio is set by the final drive, has the numbers stamped on it, very very doutful that someone changed the gear set in the housing, would have just swapped out the complete unit, and the speedo if they wanted that to read correctly.

[AnnapolisAirhead]

It should be stamped on the flat surface where the drive shaft enters the final drive. It is in fraction form. Mine is 32/11, if I remember correctly.
So, what's the translate to? 1:3.21 ??

[AnnapolisAirhead]

the ratio is set by the final drive, has the numbers stamped on it, very very doutful that someone changed the gear set in the housing, would have just swapped out the complete unit, and the speedo if they wanted that to read correctly.

Good to know that's what it would take, and he probably didn't. I just recalled speaking with him and him mentioning that he pulled a trailer and then was going about why most Harley's weren't good for long trips at 75+ MPH because of the gearsets and that he's run into a guy who changed his.

In the end, I am just looking to understand and doubt that he did change it. Now I know how to verify it.

Thanks! :drink

[PAGoldsby]

So, what's the translate to? 1:3.21 ??In automobile terms, it would be a 2.91. Personally, I like the explicit form used by BMW as you know exactly what the pinion (11) and ring (32) are, individually.

[AnnapolisAirhead]

In automobile terms, it would be a 2.91. Personally, I like the explicit form used by BMW as you know exactly what the pinion (11) and ring (32) are, individually.

Not that I have any interest in changing it, but I'll be using the bike to commute daily from Annapolis to Bethesda and then weekend trips to PA, Deep Creek, Blue ridge, etc. Is there one ratio better than the other or highway speeds/travel? I'm no speed demon, but the bike seems to have a lot of torque. Probably just my airhead-newbie-ism.

[PAGoldsby]

Not that I have any interest in changing it, but I'll be using the bike to commute daily from Annapolis to Bethesda and then weekend trips to PA, Deep Creek, Blue ridge, etc. Is there one ratio better than the other or highway speeds/travel? I'm no speed demon, but the bike seems to have a lot of torque. Probably just my airhead-newbie-ism.The 32/11 is generally the "lowest" ratio available for BMW road bikes, and is best suited for highway speeds. I think I have the 32/10 on my '77 R75/7. You're good to go, it would seem!

PhilbeRT

[20774]

One can "confirm" the gear ratio by counting the rotations of the 4 bolts under the rubber boot at the back of the tranny for each rotation of the rear wheel.

Here's a nice little program that Anton has on his website to get a sense of what different gear ratios provide in terms of RPM at given speeds, etc. It basically uses the "math" associated with all of the various factors, including transmissions, final drive, and rear tire size. It shows a MPH at 5K RPM. Obviously using a taller final drive will get you mire MPH at 5K RPM, or conversely, lower RPMs at given MPH, say 65 MPH or other typical cruising speed.

http://www.largiader.com/articles/gearing/

[sumran]

Not that I have any interest in changing it, but I'll be using the bike to commute daily from Annapolis to Bethesda and then weekend trips to PA, Deep Creek, Blue ridge, etc. Is there one ratio better than the other or highway speeds/travel? I'm no speed demon, but the bike seems to have a lot of torque. Probably just my airhead-newbie-ism.

The stock 32/11 drive was made for highway speeds. It puts you in the sweet spot in 5th gear at 70 mph. Some riders like to change the final drive to get quicker acceleration. It is common on the cafe racer projects. Mine is plenty quick for my taste and the gearing is just right for those times I get out on the road.

[The_Veg]

The stock 32/11 drive was made for highway speeds. It puts you in the sweet spot in 5th gear at 70 mph. Some riders like to change the final drive to get quicker acceleration. It is common on the cafe racer projects. Mine is plenty quick for my taste and the gearing is just right for those times I get out on the road.

Right- my R100R has 34/11...STUPENDOUS acceleration, can pop wheelies if the carbs are lean enough, but sucks gas touring and won't get over 105 MPH without at least a gale-force tailwind.

[Jeff488]

Speaking of the Batbike, how's the rebuild coming?

[The_Veg]

Speaking of the Batbike, how's the rebuild coming?

Hi Jeff! :wave

Stalled due to lack of budget (no progress in nearly a year). I've got the bike pretty much disassembled and it will get a frame-up total refurb at some point. At this point I'm leaning more toward starting over with another engine than trying to repair this one, since I have totally destroyed top-end and a questionable bottom-end. Once the budget improves I'm gonna give Airhead Salvage a call and see if Mike's got a good engine lying around. I am also thinking of doing some basic and discreet frame-stiffening. Nothing as radical as Old Cro, just some gussets here and there. I've got lots of small ideas, and the end result will be a pretty lean & 'sorta mean' bike with a cafe-racer flavour to it.

[sumran]

Right- my R100R has 34/11...STUPENDOUS acceleration, can pop wheelies if the carbs are lean enough, but sucks gas touring and won't get over 105 MPH without at least a gale-force tailwind.
:laugh
Is it to late to reconsider my vote for the board position? I thought you were responsible and respectable. :stick I guess that is the risk of only knowing people online.:D

[AnnapolisAirhead]

So when cruising, I've been riding by the tach and not so much the speedo. In light to moderate traffic I try to keep my RPMs at 3000-3500. Cruising I'll slip into 5th gear at 70 but still around 2800-3200. Does that sound right?

In light traffic (30-50mph), if I get into 5th it lugs waaaay too much and does it in 4th too. I'm probably just getting used to a boxer engine. This was my first weekend on the bike after bringing her back to life...so I haven't checked the mileage (Bing 40s, removed the EGR and its dual plugged) and not sure what to expect if I ride sanely.

Any thoughts?

[AnnapolisAirhead]

So when cruising, I've been riding by the tach and not so much the speedo. In light to moderate traffic I try to keep my RPMs at 3000-3500. Cruising I'll slip into 5th gear at 70 but still around 2800-3200. Does that sound right?

In light traffic (30-50mph), if I get into 5th it lugs waaaay too much and does it in 4th too. I'm probably just getting used to a boxer engine. This was my first weekend on the bike after bringing her back to life...so I haven't checked the mileage (Bing 40s, removed the EGR and its dual plugged) and not sure what to expect if I ride sanely.

Any thoughts? :dunno

[20774]

So when cruising, I've been riding by the tach and not so much the speedo. In light to moderate traffic I try to keep my RPMs at 3000-3500. Cruising I'll slip into 5th gear at 70 but still around 2800-3200. Does that sound right?

Those RPMs at that speed doen't seem right. On my /7 with a 3.0 rear drive, I'm going 65mph at 4K RPM in 5th gear. Did you go to this site http://www.largiader.com/articles/gearing/ and select the infomation to get an idea of what the RPMs should be for your configuration?

You'll get a wide variety of input on RPMs and what you should be using. Some say ride it like you stole it (whatever that means!!) and others say these bikes like to wind the gears out. I'm a sedate driver and tend to keep the RPMs between 3K and 4K RPM...shift at 4K and it drops down to the low to mid 3Ks as I accelerate to the next shift point. I don't whack the throttle or accelerate hard...just smooth acceleration. Driving around at 3K RPM or lower constantly is probably not the best for the engine. At those kinds of RPMs, I can really feel the pulses of the engine more in the pegs, so I usually downshift a gear, to get the RPMs more up in the 3750 range....my engine really likes this range.

[lkchris]

Not that I have any interest in changing it, but I'll be using the bike to commute daily from Annapolis to Bethesda and then weekend trips to PA, Deep Creek, Blue ridge, etc. Is there one ratio better than the other or highway speeds/travel? I'm no speed demon, but the bike seems to have a lot of torque. Probably just my airhead-newbie-ism.

Very good to assume that BMW provided a VERY GOOD ratio for the bike you have, which means the engine you have. Changes by owner usually produce negative results.

FWIW the term "gear set" is seldom used to describe the final drive but rather the "set of gears" in the transmission. This isn't so important, however, as every five speed has the same set.

[AnnapolisAirhead]

Very good to assume that BMW provided a VERY GOOD ratio for the bike you have, which means the engine you have. Changes by owner usually produce negative results.

FWIW the term "gear set" is seldom used to describe the final drive but rather the "set of gears" in the transmission. This isn't so important, however, as every five speed has the same set.

Ok, I don't think the gearing was changed. These bikes are new to me and I am intrigued to learn as much as I can.

Fair enough on the terminology. My inner newbie/noob is showing, unashamed.

I guess my unfamiliarity with the bike makes some sense in that my only other experience was with a 1981 CB750K--pretty good torque but an entirely different machine all together. I had been dreaming of an old airhead for a couple years and now that I have one, the thrill is beyond what I'd imagined. Simplicity and even the areas that I haven't fully understood are never so dauntedly complicated that I'd consider getting rid of it for a newer bike. While I do appreciate them and have enjoyed a couple test rides, they scare me. The airheads have some kind of an allure that is hard to describe.

Maybe I worded my previous post obscurely. What I was trying to say was that the bike feels happiest at around 3500-3750 rpms (regardless of which gear I am in). My natural inclination was to shift up to at least 4th, but that's not always the gear that keeps the bike in that range. I too noticed that much below 3000 and I can feel vibration, etc. I was initially worried that something wasn't right, but realized I am just in too high of a gear for the speed I was traveling.

Since these are new to me, my dual-plugged, electronic ignition monster feels great but I'd liken it to a John Deere that can actually hit higher speeds. Torquey and it feels capable and the bike seems perfectly balanced, inspiring confidence although I remain an ultra cautious rider. I don't ride it like I stole it either. Slipped an old Van Morrison tape (yes, cassette tape) in the deck and had a great ride around southern Maryland's backroads until 10:30 last night (deer whistle intact). Couldn't have been a better night.

This one is a keeper, a bike to love. Thanks for the advice, much obliged. :p

[tkpinsc]

Ok, I don't think the gearing was changed. These bikes are new to me and I am intrigued to learn as much as I can.

snip

Maybe I worded my previous post obscurely. What I was trying to say was that the bike feels happiest at around 3500-3750 rpms (regardless of which gear I am in). My natural inclination was to shift up to at least 4th, but that's not always the gear that keeps the bike in that range. I too noticed that much below 3000 and I can feel vibration, etc. I was initially worried that something wasn't right, but realized I am just in too high of a gear for the speed I was traveling.

Since these are new to me, my dual-plugged, electronic ignition monster feels great but I'd liken it to a John Deere that can actually hit higher speeds. Torquey and it feels capable and the bike seems perfectly balanced, inspiring confidence although I remain an ultra cautious rider. I don't ride it like I stole it either. Slipped an old Van Morrison tape (yes, cassette tape) in the deck and had a great ride around southern Maryland's backroads until 10:30 last night (deer whistle intact). Couldn't have been a better night.

This one is a keeper, a bike to love. Thanks for the advice, much obliged. :p

A large carb r100 (your 83) is much happier over 4k and even over 5k then under 4k. If you get on the throttle you will notice the vibration in your mirrors present at 4k will disappear at 5k if your carbs, valves and timing are correct. At 6k it will feel as smooth as a 4 cylinder. If you are feeling the engine pulses at 3k you are seriously lugging the engine which is bad for the engine and drive train. Try to be over 4k if you are putting any load on your engine, It won't hurt the milage and the drive train will thank you for it with a longer lifespan.

[tkpinsc]

So when cruising, I've been riding by the tach and not so much the speedo. In light to moderate traffic I try to keep my RPMs at 3000-3500. Cruising I'll slip into 5th gear at 70 but still around 2800-3200. Does that sound right?

In light traffic (30-50mph), if I get into 5th it lugs waaaay too much and does it in 4th too. I'm probably just getting used to a boxer engine. This was my first weekend on the bike after bringing her back to life...so I haven't checked the mileage (Bing 40s, removed the EGR and its dual plugged) and not sure what to expect if I ride sanely.

Any thoughts?

No its not right. Your speed is reading to high for the indicated rpm.

It sounds as if your speedometer is ready 10mph or so fast at 70mph. This is very common for this vintage airhead. What you should do is use a chart like the one suggested to you to tape a speed to expect on your tach in a certain gear at a certain rpm for reference. Usually the tachs and odometers are accurate.

[The_Veg]

:laugh
Is it to late to reconsider my vote for the board position? I thought you were responsible and respectable. :stick I guess that is the risk of only knowing people online.:D

This ain't the Goldwing club! :nyah :burnout

[AnnapolisAirhead]

No its not right. Your speed is reading to high for the indicated rpm.

It sounds as if your speedometer is ready 10mph or so fast at 70mph. This is very common for this vintage airhead. What you should do is use a chart like the one suggested to you to tape a speed to expect on your tach in a certain gear at a certain rpm for reference. Usually the tachs and odometers are accurate.

Ok, I think this is all due to my lack of experience on an airhead. I did try it out at higher revs and yes, vibration stopped. So commuting to and from work (37 miles each way) will be a lot of stop and go on the DC beltway...but when it does open up, it seems happiest at 70-75 in 5th. If I need to accelerate a shift down to fourth should do it.

I thought about a F650GS to commute, but I love the way this bike feels. Solid, tractor like and easy. Thanks for the help. :bliss

[Jeff488]

My bike is the same as yours, and I get about 66 mph at an indicated 4000 rpm.
4000 to 4300 seems to be a sweet spot for mine.
You could check your speedo and/or tach if you have a gps.
That's what I did when the speedo lost its mind. Sent it off to the psychiatrist(Overseas Speedometer in Austin, TX) and it came back sane and quite accurate(1 to 2 mph higher than actual).

[lkchris]

A large carb r100 (your 83) is much happier over 4k and even over 5k then under 4k. If you get on the throttle you will notice the vibration in your mirrors present at 4k will disappear at 5k if your carbs, valves and timing are correct. At 6k it will feel as smooth as a 4 cylinder. If you are feeling the engine pulses at 3k you are seriously lugging the engine which is bad for the engine and drive train. Try to be over 4k if you are putting any load on your engine, It won't hurt the milage and the drive train will thank you for it with a longer lifespan.

Everything stated above is simply incorrect.

There is NO SUCH THING as an engine that requires high revs to live and there is NO SUCH THING as an engine that gets better fuel mileage the higher it's revved.

But, it does make you feel manly.

Everything will last longer and you'll get better fuel economy the sooner you get it into 5th. Not in city traffic, obviously.

PS: Lugging in 5th gear on the subject R100 occurs around 2500 rpm. Higher if you really get on it. Just don't--this is not rocket science it's simply how to drive--anything.

[tkpinsc]

Everything stated above is simply incorrect.

There is NO SUCH THING as an engine that requires high revs to live and there is NO SUCH THING as an engine that gets better fuel mileage the higher it's revved.

But, it does make you feel manly.

Everything will last longer and you'll get better fuel economy the sooner you get it into 5th. Not in city traffic, obviously.

PS: Lugging in 5th gear on the subject R100 occurs around 2500 rpm. Higher if you really get on it. Just don't--this is not rocket science it's simply how to drive--anything.

Extreme lugging occurs when the bike is shuddering and you feel the engine pulses travel through the drivetrain. In this case he described the sensation at 3k on the highway. You can make most any engine lug at any rpm by applying a load approaching the power the engine is producing at that rpm. Reducing the gear is one way to apply less load to the engine. Producing more power by increasing rpms is another way to limit lugging.

The sweet spot for mileage is the same as the engines most effcient operating rpm - where the engine converts fuel and oxygen into energy with as little unburned fuel as possible. You may notice that it can take less throttle to maintain travel speed in a lower gear then a gear that is to high for the engine at that speed/load. This excess throttle is another sign of an engine that is being lugged. Detonation is also usually present when an engine is being lugged.

Each engine designs sweet spot is different depending on cam timing, ignition timing, intake tract and carburation, exhaust system, compression, stroke, displacement, combustion area design, valve size and placement and a host of other factors.

As far as everything living longer in 5th, the straight cut 1st - 4th gears will transfer loads better and with less wear on the gearbox then the helical cut 5th, although 5th is quieter.