15T and Other Sprocket Sizes FAQ

Compiled & edited by Kristian #562
Updated 22 Feb 2003 by Spakur#1117
Please read the Disclaimer before attempting any work in this FAQ.
Last Updated: 20 September 2005, by Winter #1935

For other FAQs related to this topic:

Section 2: Introduction

Some people find the stock sprockets on the F650 are unsuitable for their requirements. The most common change is to drop the front counter-shaft (C/S) sprocket from 16 teeth to 15 teeth. This makes the bike more suitable for off-road usage, and makes slower speeds around town much easier. There are many things you need to consider when selecting the sprockets. This FAQ provides the theory and the tables that should help you work out what you are after.

Remember: The most important thing about wear of the chain and sprockets is: KEEP THEM WELL MAINTAINED

Section 2: Modification and Theory

The 15 Tooth Sprocket Modification

Maralan Hutchins, John Stock and Peter #233

If you would like to make a simple and inexpensive improvement to your F650, try changing the countershaft sprocket from 16 teeth to 15.

When we first purchased one of these bikes we found the gearing to be annoying, especially in traffic and also at 50 miles per hour. This modification does not noticeably change top speed. Our bike still do an honest 100 miles per hour at 7000 feet in elevation. They run like scalded cats! Of course, the largest improvement comes with off-road riding. The machines run great at low rpm; no more stalling and lurching. By the way, this modification does not affect vibration at cruising speeds. the bikes are just as comfortable at 70, 80, and 90 miles per hour.

We got the idea after reading an article in Owners News. We got the part from California BMW Triumph in about three days. It cost about $26 and it took about 15 minutes to make the change. There is no need to break the chain and you can switch back to stock at any time.

Thanks to Inmates for this Tech Tip.

Peter did some calculations and came up with the following tables of information for those contemplating the sprocket switch suggested by Maralan and John. Peter's calculations look correct.

Note the stock 16T C/S sprocket has a rubber washer-like feature that I did not expect. Both sides of the sprocket have a think rubber piece glued to it. Not sure, but maybe it provides some sound or vibration dampening. The new one is plain steel.

Gear Ratios 16/47 final 15/47 final
2.94 3.13
1 2.75 8.08 8.62
2 1.75 5.14 5.48
3 1.31 3.85 4.10
4 1.05 3.08 3.29
5 0.88 2.59 2.76

Table: Gear Ratio Table

Stock (16/47)New (15/47)Change

Table: RPM

14 3.433.503.573.643.71
15 2.872.933.003.07
16 2.692.752.812.88 2.943.
17 2.532.592.652.702.762.82 2.882.943.003.06
18 2.392.442.502.552.61 2.672.722.782.832.88

Table: Ratios

FrontRearRatioFunduro / STGS / Dakar
17T47T2.76112 confirmed
(possibly 110)

Table: Chain links suggested - check on your own bike!

Chain Wear - The Theory

by Francois, November 2001
GS / Classic clarifications by Winter, September 2005

About Chain Wear: This is about the impact of sprockets number of teeth on chain / kit wearing.


The wear of the chain depends on the frequency the same link hits the same sprocket tooth. The more often the hit, the faster the wear.


We must calculate how many chain revolutions are necessary for a given link to hit a given tooth.

A chain link can hit a given sprocket tooth from once per chain revolution (higher wear, a given link always hits the same tooth at each chain revolution) to once per a number of revolution equal to the number of sprocket teeth (lower wear, a given link hits the another tooth at each revolution and it takes "number of teeth" chain revolutions to hit aga the given tooth).

Example: Faster wear - the same links always hits the same tooth at each chain revolution
Tooth:123123123 1st rev (tooth 1 hits links 1,4,7 during the fist chain revolution)
Tooth:123123123 2nd rev (tooth 1 hits the same link during the second revolution
Example: Longer wear - it takes 'number of teeth' revolutions to hit again the same tooth
Tooth:123412341 1st rev (tooth 1 hits links 1,5,9)
Tooth:234123412 2nd rev (tooth 1 hits links 4, 8)
Tooth:341234123 3rd rev (tooth 1 hits links 3,7)
Tooth:412341234 4th rev (tooth 1 hits links 2,6)
Tooth:123412341 5th rev : equal to 1 rev : it takes 4 rev to hit again the same tooth


The same tooth hits the same link at revolution number R when R x [number of links] is divisible by [number of teeth]

Alternatively, using a spreadsheet, the following will work: Teeth / GCD(Links, Teeth), where GCD is the Greatest Common Denominator


Links Front Sprocket (teeth) Rear Sprocket (teeth) Comments
14 15 16 17 18 43 44 45 46 47 48 49 50 51 52
108 7 5 4 17 1 43 11 5 23 47 4 49 25 17 13  
110 7 3 8 17 9 43 2 9 23 47 24 49 5 51 26 Classic Stock (16/47)
112 1 15 1 17 9 43 11 45 23 47 3 7 25 51 13 GS/Dakar Stock (16/47)
114 7 5 8 17 3 43 22 15 23 47 8 49 25 17 26  
116 7 15 4 17 9 43 11 45 23 47 12 49 25 51 13  
118 7 15 8 17 9 43 22 45 23 47 24 49 25 51 26  
120 7 1 2 17 3 43 11 3 23 47 2 49 5 17 13  

Table: Number of revolutions necessary for the same tooth to hit the same link

Color Meaning
  Worst Possible Score
  Best Possible Score


Detailed Observations: Here are some more detailed observations based on the table above...

A help to make the kit last longer (on a classic) could be to manually shift the chain along 1Tooth every 1000km! On the GS you are probably better off using a 15 or 17T sprocket.

The other thing that always springs ot mind is the number of teeth. Even numbers of teeth have stress patterns across them that let the wheel flex as it turns (gap opposite gap). Odd numbers of teeth avoid this, but can sort of ripple on the way round (divisible by 3, gap opposite tooth on each pair of 3 tooth groups). Prime numbers of teeth avoid even this. Flexing and rippling let the side-plates of the chain contact the teeth with more force, rather than the rollers. 47 is a prime number so BMW got their sums right. 16 is even. 17 would be better.>

F650 Gearing: More Theory

from Advrider

  Classic GS/Dakar (37kW) GS/Dakar (25kW)
Rear Tire Size 130/80-17
Primary Transmission (37/72) 1.946:1
First Gear Ratio 2.75:1
Top Gear Ratio 0.88:1
Stock C/S Sprocket 16T
Stock Rear Sprocket 47T
Bore / Stroke 100/83mm (3.94/3.27in)
BHP Peak 6500rpm 6500rpm 5500rpm
Torque Peak 5000rpm 4800rpm 4000rpm

Table: Some basic numbers

Average piston speed in feet per minute ([6/stroke (in)]*rpm). Generally, it is accepted that 3000-3500 FPM (feet per minute) is a good all day, all night, ride-it-around-the-world-four-times piston speed. 4000 FPM used to be the accepted upper end. 4500 FPM is not that unusual today, and a lot of racing engines push 5000 FPM. So what do these numbers look like for the F650?

OK - So our torque peak of 5000 rpm is comfortably under the 3000 FPM threshold. So let's see what road speed this works out to be. See the Gearing Calculators for neat links to do this sort of stuff.

5th Gear

Let's see how slow we can go without slipping the clutch. Well, Idle is 1400 rpm, so 1600 rpm seems reasonable

1st Gear

So what does it mean? Well, I always like bikes that cruise near the torque peak. Easy roll-on passing, holds speed on grades, etc. So if you want to cruise at 75 mph, stock gearing is probably your best bet. But the Dakar is no RT (thank God), so I will gladly trade the 4.5 mph you lose from dropping from a 16T C/S Sprocket to a 15T. Now, my optimal gearing may be the 15/49 combination, but you will need a 114 link chain for this (stock is 112) and that is good and bad. If, like me, you live where people do not drive by all night lobbing D.I.D. VM chains out the passenger window, the chain is not cheap. And if you want a riveted Master link, you need a $90 tool to go with the chain. The good news is the stock chain is worth exactly f-all, so no great loss if you get rid of it. And I am thinking a 14T C/S sprocket might be the "Dog's" for the woods. I plan to find out. Front sprockets are @ $34 USD. Cheers.

Little Sprocket Vibes and Wear

by Jinx on Advrider

Probably the best way to treat this tech stuff is like a free buffet. Take what you want, leave the rest. There is a lot more to life than numbers. But for those who care about this stuff:

Why do chains wear faster on a smaller sprocket? Well, it is not just from being pulled. You can nail a good chain to a barn, strap a big old weight on it, and it will not continue to grow after it takes an initial strain. Ever. So it is a dynamic issue. Moving parts are what are wearing, and that is why lubrication is critical. Because chains don't really "stretch". It's just the pins and rollers wear and get smaller, and the bushes wear and get bigger, and all that additional clearance (112 links = 224 pins, rollers, and bushes) makes the chain, when you pull on it, "longer".

Sprockets may look round, but they are not. Chain links are straight, so they can only approximate a curve. They form polygons. And how much each link has to rotate is determined by the number of teeth (which equate into the number of sides in our polygon). Specifically, each link will have to rotate 360 deg/ #teeth. So our 16T will rotate @23 deg, our 15T @24 Deg, and our 14T @26 Deg. So we would expect a chain looping around a 14T sprocket, at the same rpm, to have approx. 10% less life than one looping around a 16T sprocket. This is far less than the effects of dirt and lack of lubrication, but just so you know.

Now for the vibration bit. Chains looping around sprockets do not run at constant speed, even when the rpm of the sprocket is constant. Bummer. Why? Same reason as above. A polygon can only approximate a circle, and the cruder the approximation (less teeth) the greater the speed variation will be. So there is a variation in effective radius depending if you are "points" up ar "flats" up. This is known as the Height of Engagement. And it will result in some vibration in your drive train.

Figure: Tsubaki diagram showing change in Chordal Height.

Tsubaki also stuffed up. The diagram above right should say "Minimum" Chain Speed.

Figure: Tsubaki Chart for Speed Variation

So how big a deal is it? Well here is the Speed Variation of a chain rolling over our three C/S Sprockets.

So what about our big rear sprocket?

So big sprockets are good? Well, maybe. They weigh more, get in the way of other things, and chains skip much more easily on big sprockets than small ones. Which means while your chain may wear a bit less, it's allowance for wear is also a bit less. So you may be packing all that weight around for stuff-all in gain. But really small sprockets start to develop some pretty significant speed variations, which are of course transmitted to the rear wheel and back into the entire drive train. At some point we are not going to be happy with these effects.

Section 3: Questions and Answers

Q. What is the stock setup for the F650?

A. Both the Classic and the GS/Dakar have a 16T C/S and a 47T rear sprocket. The Classic has a 110 link chain, and the GS/Dakar has a 112 link chain. See also the Basic Numbers table

Q. Where can I find gearing calculators?

Q. Will my mileage increase or decrease when I use different size sprockets?

A. Some riders have noticed a slight decrease in their Gas mileage as a result of higher rpm's others an increase, due to being in the power band for the bike.

Q. Yeah, yeah, so what about the theory... does it really make that much difference?

A. The theory probably does make some difference, but the biggest difference is probably to CLEAN and LUBRICATE your chain regularly.

Q. Is there a sprocket puller to get the C/S sprocket off?

A. The F650 is the only BMW which can do a quick gearing ratio change. It is inexpensive as well. A puller is used for the quick removal of the countershaft sprockets. See photo.

Editors Note: There is at least one example of a sprocket puller being used to remove the C/S sprocket from and F650.

Q. Is there any other way to lower the stock gearing? Can I replace the stock engine gears?

A. You might be able to try using the gears (1st-5th) from a Bomberdier DS650 or may be a Honda Transalp. But no one has ever tried it to see if it would even work. If you do try it, please let us know!

A. Team Pami offer alternative gearing... From an email to Team Pami:

the standard ratio, for exsample for the first gear is 2,75 - we can offer you 2,077 or extreme 1,75. This is exactly then the ratio of the second gear!!! Such changes require a new main shaft and several gears. In the end the gearbox is complete different from it`s standard ratios, only the fifth gear ratio is the same.

Q. Which gearing should I use?

A. This will depend on multiple factors:

Some people actually carry a second sprocket with them so they can change while away on a trip. Generally the slower the speeds you are likely to require, the higher the ratio needs to be (see the Ratios table). If you want better fuel consumption, lower ratios may be better, but this will be dependant on your riding style and which power-band you ride in. If you care about the theoretical optimal wear, read more on the theory, and have a look at the Revs Table.

Example: The most common change
Start simple. Change to a 15T C/S sprocket if you want better control at slower speeds. You should change the chain AND sprockets at the same time. The stock chain length of 110links (classic) or 112links (GS) should be okay. Re-read this FAQ, and start thinking about what other options you might try.

Q. Do you have an idiots guide to explain all these numbers?

A. Your bikes speed depends on the ratios between gears. If you have a small gear with 10 teeth (10T) driving a big gear with 50 teeth (50T), the small gear will need to turn 5 times before the big gear will have complete one revolution. Conversely, each time you turn the big gear once, the small gear will turn 5 times.

Generally you divide the number of teeth on the big gear by the number of teeth on the small gear (on our motorbikes anyway). So 10T:50T will result in a 1:5.00 ratio (1 tooth for every 5 teeth on the big gear). The bigger the ratio, the slower the larger gear will go. In other words, the higher the ratio, the lower the range of gears OR the more suitable the bike will be for slower speeds. Most people just change to a front 15T sprocket.

Regarding the optimal wear pattern, all you need to understand is that some sprockets have a better theoretical wear pattern than others. The Revs table shows you which sprockets are better combinations with which chains.

Q. Why can't you have a chain with an odd number of links?

A. Lets consider a chain to have 2 types of links: The ones that are sorta on the inside, and the ones where the side parts are on the outside (yes I know there are other joining links, but we will ignore those). Consider a chain that is not looped end-to-end and number the links 1,2,3... etc. If you start with 1, you will find it might be an "inner" link, 2 will be an "outer" link, 3 inner, 4 outer... etc.

Now you can only link an inner link to an outer link - you can not link an inner link to an inner link, and you can not link and outer link to an outer link. In order to loop the chain around, assuming the 1st link is an inner link (odd number), the last link on the chain MUST be an outer link (an even number) to join to it. By deduction the final link that connects to the 1st link MUST be an EVEN numbered link.

The short answer: Try it yourself after a few beers... ;-)

Q. Are there any clearance problems with a 17T C/S sprocket?

A1. There have been reports of the the protective arm / slider on the swingarm being in the way. You may need to trim the plastic a little.

A2. There's no problem with the clearance of the slider piece on the swingarm, BUT the lower half is riding on the cylindrical slider piece. With the larger sprocket there is no longer a straight shot from the front to rear sprocket - it's deflected slightly upward on top of the cylinder... It was just barely resting on the roller but it made the clearance once I sat on it. socal timbo

Check the clearance when the bike has its normal rider on it. It may be that with the weight of the rider and bike in a normal position, the clearance is fine. Also be sure to check the "roller" is still rolling. Too much Chain Wax or off-road stuff it might eventually quit rolling and rub through the roller into the pivot bolt.

Q. Does the 17T C/S sprocket made starting in first difficult?

A. Yes, it does make it slight more difficult. You just need to slip the clutch a bit more.

Q. With a 17T/47T, what RPM are you doing at highway speeds (65/70mph)?

A. Roughly 5800rpm @ 80mph in 4th, and 4800rpm @ 80mph in 5th.

Q. What kind of response dows the throttle have in fifth gear with a 17T?

A. Twist until it hits the stop, maybe a little more vibration, very little acceleration - that's what 4th is for.

Q. Does the 17T affect gas mileage / highway ride comfort / anything else?

A. One report of gas mileage down slightly, if anything - ligging 5th or revving 4th; comfort is the same; have to shift between 4th and 5th more than stock. [ed note: This is probably due to the engine ability to maintain the revs in 5th is much harder]

Q. What chain length should I use with a 17T?

A. You should measure it on the bike to make sure, but the stock chain length might be okay. If not, two more links should be enough.

Section 4: Opinions

The following tables lists people's opinions in order of the ratio they have. Thus at the top are really low gearing (harder off-road riding), and at the bottom of the table are the high gearing (faster more highway cruising oriented).

Gearing Change: Mileage and Performance Opinions

Note: The rear Sprocket on the GS is the same as classic F650.

C/SRearRatio Comments
14473.36 I have been running the 14/47 combo for over a year. I like it !! I'm turning big Dunlop 606 knobs. A 70 mph cruising speed is about 5300 rpm and good for about 55 to 60 mpg. The lowered gearing really rocks on the gravel backroads. IMHO 15/47 is a nice combo/all-around setup and the stock 16/47 is good for freeway only. BIG FUN dirt performance can be yours with the 14/47 setup. CascadeThumper
14473.36 Earlier this summer, I ended up doing 300 road miles with the 14t on. The revs are pretty high, but I still managed 80+ for the duration of the ride. But when you are offroading that 14t is the best (except maybe a 13t!). Some will say it wears a chain and spockets faster and that may be. But my chain looks great and is wearing just fine after 16K miles. Then again I saw the light and surrendered my soul to the ATF God 2 years ago. My 17t and 14t look good and I still have not found any appreciable wear on the rear sprocket.
15493.27 15T front or 51T rear? You won't be hitting 3rd at fifteen, use that redline, they put it there for a reason. I don't have my bike here yet so I can't give you a gear by gear, (I wrote it down somewhere for a FAQ that I never got around to writing, but I can't find it now), but I have a 15t/49t set up and because of the mechanical advantage this gives me over the stock ratio, I can putt around at 1500-2000 RPM all day off road, climb hills and everything, rarely getting out of 2nd gear. On the road around town I shift 1-2 about 3K to avoid hurting my neck, 2-3, 3-4, 4-5 all close to redline. If I remember right, the 2-3 is about 40 MPH, and in most cases, (trying to stay legal) third or fourth is all I ever use in town. On the highway, going to and from a good dirt ride, it cruises COMFORTABLY at 65 (4800-5K RPM), and will do 90 if needed. (88GPS,IIRC). David#476
15493.27 I'm using a 15/49 combo. Fine for shorter rides and good off road but I'd like to find a 17 to switch back to near stock gearing for longer road rides. (BradG)
16523.25 For my '99, if I remember correctly: 1 front tooth roughly equals 3 rear teeth, either roughly equals changes of ~4mph or (maybe) 500rpm, compared to stock gearing. If you go to a 15t front, you will lower your top speed by about 4 or 5mph. Or if you add 3t to use a 50t rear, you will lower your top speed 4 or 5 mph. If you add teeth, make sure you order the 120 link chain. btw, I ride off-road often and I'm running an OEM 16t with a 52 rear, and quite like the gearing. It runs up to 80mph effortlessly, cruises at 70 reasonably, at 50 it's at the bottom of the power band in 5th. But now in First it will chug along at a very slow pace and can actually idle up a slight grade under it's own power, with a fully closed throttle. I'd love a 6th gear too, but I really shouldn't go that fast! Todd #389
16513.19 My mileage increased also when I went to the 15T C/S sprocket. This time I went to a 16/51, which should be a bit easier on the chain with negligible difference in ratio. FWIW, for the newer folks, my speed at 5K rpm with the 16/47 and 130/80 tire was71/71; with a 130/90 tire 76/77; with the 15/47 69-70, so there is no great difference there and, as noted above, the bike is much more tractable in traffic. Hal#15
15473.13 I like the effects of the 15T in slower riding, particularly dirt and around town. I don't like it on the hwy at all. Bike needs a 6th gear with the 15T sprocket. Mark #403
15473.13 At my 600 mile service I decided to change to the 15 tooth C/S. I can honestly say the change is subtle. Accelerating is much crisper and the bike is much more responsive to throttle inputs at all RPMs. On the highway at 70-75 mph the roll on acceleration seems to make the bike pull harder. Yes the speed/rpm did decrease/increase. But not to a point where it becomes an issue. Off road/highway/pavement/in the dirt/whatever the low end makes the bike much more responsive at low speeds and up inclines. Makes a big diff! I have found the change to a 15 tooth C/S to be an excellent mod. and at $29 it sure is easy to do. K12RSSteve, Advrider.
15473.13 I changed the front sprocket to AFAM 15 tooth. Dropping that tooth makes the bike a lot more fun to ride, especially when shifting up. Run it up to 5000 to 6000 RPMs, and the next gear will already be about 4000 RPMs (in the power band). Instant response and no lag. Colorado Bob #1297
15473.13 I am very happy with going from the stock 16t sprocket to a 15t. More power on all gears, which makes for easier city driving and more fun on the dirt. You will lose some RPM speed on the freeways. Before I was making 75mph at 5k RPM, now I get 70mph at 5k RPM. This will affect your gas mileage too, but I prefer shorter dirt/pavement trips over the long pavement-only ones. First gear on my 2001GS is very short and not very smooth from 1st to 2nd. Lately I have been taking off on 2nd gear and it feels right. (The new sprocket might have something to do with this). Is anyone else out there taking off on 2nd gear? If you do it right you will not eat too much of your clutch. Dan #802
15473.13 15t - I find I have to think too hard about not slipping the clutch with second gear starts. I've not noticed a drop in mileage. What I have noticed is the mileage needs to be checked over several tanks of gas. Too many variables. I've been getting an average of 52 based on indicated miles for the last few thousand. BradG #1002
15473.13 If you ride much at speeds above 65mph (105 kph) you won't want to gear the bike down lower than the 15t C/S sprocket. That plus dropping another 2 on the rear is going to make you wish you had 7 speeds. Now, if you ride off road a lot and your highway riding is limited to slower, smaller secondary roads it might be a kick. You could probably start from 2nd like it was 1st. However, I might wonder if that begins to defeat the purpose of having such a large bike in the first place. Now I'd be thinking of getting a more single purpose bike (light weight dirt machine). By just doing the C/S sprocket you have the option of switching back and forth without needed a new chain. BradG#1002
16503.13 When I changed my chain I went to 16/50 rather than the stock 16/47, which gives you the same ratio as 15/47, plus with more teeth and a few more chain links this setup should last a bit longer (although it may be marginal). I agree with Mark, at highway speeds (75+) it's rather buzzy, but in the city it's much more comfortable. Swapping to 16/49 may be a bit nicer, but 15/49 would be for off-road only, I would think. If you're changing your sprockets and considering re-gearing, you may want to go to a larger rear sprocket rather than a smaller front; the chain will bend less and the sprockets (having more teeth) will last longer. I went to 16/50 (same ratio as 15/47) and ended up using 116 links. Purchased from onoffroad.com, no extra charge for different sized sprockets or 120 link chain. Mason #631
16503.13 If you want to go high end (max wear life for more $ up front), get the DID 520VM, the stock BMW 16t sprocket (with the nice big rubber shoulders), and the carbon steel rear sprocket from the classifieds. I didn't bother and went with the less expensive combo from onoffroad.com, but if you do high mileage and find chain/sprocket changes very annoying, then you may decide otherwise you can probably do without the replacement rivet pin. it would probably only be needed in a shop, where the tool is being used over and over. I went from stock 16/47 to 16/50 for the reasons you mentioned (less chain bend/wear and less sprocket wear), which is almost identical in ratio to 15/47 which most people use. I ended up needing 116 links. To echo Flash's advice, measure the chain ON THE BIKE. If you cut it one link too short, you'll be sorry. BTW, re-gearing was the best change I made to the bike by far. Mason #631
16493.06 I recently replaced the sprockets and chain on my '97 ST and wanted to share some thoughts on the swap. I upgraded to a 520VM DID chain, very nice. Stock front sprocket and lock ring. The rear sprocket is now a 49 tooth aluminum cog from Sprocket Specialists. I decided on the 49 tooth cog since the engine has always seemed to labor in 5th gear .... 5th gear was essentially unusable unless operating at super-legal speeds. A 15 tooth front sprocket is cheaper but rougher on the chain and the sprocket due to the tight radius. The difference is remarkable. At 55mph the engine is right in its sweet spot at about 4250. I am a little concerned about the wear on the aluminum cog; any thoughts on that? When the time comes for the next switch give a larger rear sprocket some thought. I am sold on it. Unknown
16493.06 I have the 16/49 combination on my 97ST, I recently replaced a 130/90-17 rear tire with a 130/80-17. At 70 mph it runs at about 5000 rpm vs. about 4500 rpm with the 130/90. The low speed (0-60 mph) drivability is great and well worth the swap. A 6th gear would be nice for extended slab running, but since I try not to spend a lot of time on the super slabs it is okay. I am running 112 links for the chain, and I got the rear sprocket from Keith #714 (one of the steel ones) a great product well worth the time and money. Overall I like the 16/49 combo, but I live in a hilly area so the trade off of better gearing for climbing vs. highway was the main reason I changed the rear sprocket. The down side is at a steady 70 mph I am turning about 4800 rpm. I got my rear sprocket from Keith in Alaska , It is one of the steel ones from the Chain Gang in Aus. Peter Jensen #233
16493.06 I had a 15t C/S for a long time on a GS. Just as mark #403 says, works well off road and is acceptable on. When I needed a new chain I went to a 49t rear like Art #884 has done and restored the 16t C/S. I find this better for the longer highway trips I was doing. It is right in between the 15t and 16t ratios (check out the spreadsheet to confirm). Now I have the option to use either a 15t for short or off road trips and the 16t for road tours. BradG#1002
16493.06 I ride about 450 miles a week on my commute, and a hundred or so extra for fun. I started with the stock 16-47, switched to a 15-47 and am now at a 16-49. I have gotten up to 90 mph on the speedo with all three combinations without noticing it, to 100 with some effort, and did not miss the extra 5 mph or so I lost on the 15-47 combo. If you are somewhere where you can actually do 90 mph on the highway consistently, a higher-gearing combo like what you are talking about may help. My experience on crowded LA freeways is that you are far more likely to be doing 50 (or 30) than 90, and that the extra oomph from 30 to 60 is much more important than additional acceleration from 60 to 90 or 80 to 100. Going to the lower gearing ratios (15-47 or 16-49) lets the bike cruise more smoothly in neighbourhoods and makes it more fun in the twisties. My $0.02. YMMV. (danieljmccarthy)
16493.06 When I went to a 49t rear last summer ('00 F), when the Service Mgr. test rode the bike his comment was "it should have come this way......, really great". I love it and do no really high speed highway. Really nice to take a corner in 3rd, and stay in third. The purpose for this post is to mention that because of the change, I had to go for a new chain. Not technical, but I think that will always apply when you get a bigger sprocket. Also....., my understanding is that Sprocket Specialists (.com) will make whatever you want....., 2-3 weeks. (Art 884)
16493.06 Installed a new rear sprocket and chain. Titbits that may be of interest:
  1. Aluminum 49T with Titan (hardened) option took 4 weeks to get from Sprocket Specialists. Color is light grey (the 'no' color option).
  2. DID 520VM (x-ring) chain came with one master link. I now have three because I ordered two along with the chain.
  3. The new chain when laid side by side with the OEM I removed (9,000 miles on it) was actually slightly longer, link for link. I'll assume my OEM chain did not shrink and that the new one is slightly different pin to pin. The new one is nearly a 1/2 link longer over 112 links.
  4. The combination of a 49T rear, 16T front and DID 520VM chain required 114 links. This put the axle about mid way in the swing arm slot. I can now switch between 15 and 16 tooth C/S sprockets depending on the ride I have planned. On the GS model this is a 30 minute job (maybe less if you're in a hurry).
17513.00 I went to a 17/51 on the new sprockets - essentially the same as the 16/47, but easier on the chain. Hal #15
16472.94 Stock Ratio
16452.81 I went to 16/45, much happier now. NormJ #473.
1747?2.76 I recently swapped out the stock counter shaft sprocket for a 17 tooth and running 85-90 MPH is much nicer. The engine RPM's dropped about 500 or 800 (can't remember the exact amount) and the transmission requires a bit more churning on hilly twisty roads but I think the drop in RPM at high speed is worth it. There's less vibration and the engine feels more comfortable at those reduced RPM's. Richard #424
17472.76 I put a 17-tooth (Sprocket Specialists) on the front...you'll need to trim the swingarm "slider" a bit to make clearance. I would have preferred a 45-tooth rear, but was unable to locate a STEEL one. I find that the 17-tooth is geared too high for hills, headwinds, etc. Of course, a downshift solves that. I will shoot for the 45-tooth solution when I NEXT need a change (and am considering getting a 16-tooth front meanwhile, which may be a problem since I installed a 2-link longer chain). May not be a problem with the HIGHER HORSEPOWER FI models. Marty #436
17472.76 Actually, a 50T rear would be closer to a 15T front, since they are about a 3 to 1 ratio (47/16, R/F). A 15T sprocket can be had from sprocket specialists for about $35 and you won't need a new chain. And "experts" say that a 15T sprocket wont cause any problems. There are a lot of dirt bikes that actually use a 14T, stock. I've been using a 15T for several thousand miles now. i like the better off-road performance, but the classic carb'd bikes dont like the higher rpms....motor is fine, but mpg suffers a lot. Front c/s are easy to change, even on a trip. Not so with the rears if you need a new chain. mark #403
17472.76 I have gone with 17/47 (virtually the same ratio...cheaper to replace the front sprocket (Sprocket Specialists) and you can use the stock steel 47-tooth and chain). I push a lot of wind with the bike (tall windshield, Jesse bags, etc) and usually carry lots of weight. In my opinion, I find that the gearing is too tall, and has no MPG gain. I'll live with it for now, but will be going back to the stock configuration when the time comes for replacement (I'll just downshift as needed for now). If you are lightly loaded with less air resistance, you may well like the lower RPMs. Can't speak of off-road, but the bike is rideable in town (although starting out takes a bit more slipping of the clutch). Marty #436
17472.76 I replaced both sprockets and chain at 16,000 miles. 17 front (There is no problem with clearance at all.) 47 rear (stock steel) and VM 520 Chain. This is the third best mod I have done. My bike pulls wonderfully all the way to 100 MPH and cruising at 90MPH is at 5,500 RPM. Used to be 6,000. I ride a lot on the freeway. I highly recommend this change. Take off is great also. I'm now at 18,000 miles and couldn't be happier! Andre
16?442.75 I changed my chain over the weekend. A much easier task looking at it from this side. I changed the rear sprocket all the way down to 44, and love the new gearing. Dan #667
16432.69 At 27,800 miles my sprockets were needing to be replaced. The front was pretty shot, although the rear could have lasted through another chain. I spend a fair amount of time in the above 75 indicated range when I travel. I wanted to be able to cruise 80-85 indicated (75-80 GPS) and keep my RPM's at 5000 or below. Using a spreadsheet I picked up at The Chain Gang, I figured out that a 16/43 combo would work out just about right. So, I went shopping. I checked several websites and called a couple of places and found that some places don't carry sprockets for the F650 and others only carry the stock gearing. I finally called Kiernan Racing Supplies and they told me they do carry the sprockets I wanted. They updated their website as I spoke on the phone with them, to reflect more accurately the sizes available. I now have my 16/43 set-up and I really like it. I can now cruise 82MPH indicated (78 GPS) at 5000 RPM. Very little difference at low speeds. At 1800 RPM in 1st gear stock speed is about 8.6 MPH and my current is about 9.4 MPH. With a 15/47 it's about 8.1 MPH. Grt W
17452.65 I have made the gearing taller on my bike (the opposite of what most folks do) and I love it. I've done a few mods to my bike to make it necessary and easy, but I'd still do it if the bike was stock. On a stock bike, I'd try 16/46 or 16/45. I think you'll find the bike revs out easier, gives better mileage, and a greater top speed. I know why folks shorten their gearing, and I don't argue with that, but if your like me, and never go off road, you might consider taller gearing. The ratios on our Rotax motors are quite even between 2nd and 5th, with a big gap to the lower first. 1st isn't low enough for some folks, but my experience with changing gearing is, you notice it most at high speeds, not at low speeds. Think about it a 10% (big) gearing change can drop you from 100 to 90 at a given rev in 5th, but would only drop you from 10 to 9 mph at a given rev range in 1st. Mods to my bike include a 150/60x17 rear tire (3.3% shorter than stock) and 36mm Team Pami race carbs (more HP). I currently run 17 front and 45 rear, which would on a stock bike be 10.4% taller (too tall), but on mine works out to 7.1%. I can still lift the front wheel in first, no problem (well ok maybe not with a full gas tank). mtiberio (cugino pegaso).

Wear on a 15 Tooth Countershaft Sprocket - Opinions