SPROCKET change?

Discussion in 'Parallel Universe' started by Metalsapo, Apr 23, 2013.

  1. Metalsapo

    Metalsapo R.E. Ordoñez

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    I will make a story to explain myself, i dont speak perfect english so i must ask a little patience and basic english words please, the technical stuff is something im still learning.
    Hi for a F650GS twin i am thinking the following...

    The problem is that i am not an expert in off road and still practicing allot of it, im starting to feel really confortable with it and always careful in strange paths, specially in downhills, and here comes the story.

    When first gear is selected, the terrain is off road downhills with some curves.
    I let go the front brake because of the curve, and suddenly infront of me appears a pickup going in my same direction full of people trying to get somewhere (In Guatemala public transportation is limited and pickups do the job in off road terrain in far away small villages) and in the opposite lane another car appears so i must reduce the velocity very fast, without skidding the back wheel so the bike does not turn with the wheel blocked and the engine brake is to loose to make me brake, so this complication could make me react with my Survival Reactions with fear and could make me brake harder and loose control, fall off the cliff,
    crash with the back of the pickup or killed by the oposite lane transport, so, the sprocket configuration will help me with this?

    This is one of my three crashes off road, learned allot this time.

    [​IMG]

    So, been there and done that, jajajja, to the left side the nice guy who helped me a little later to put the bike up.
    So what will the sprockets do in the motorcycle?
    It will make it less efficient with gas?
    Torque?
    What can i do to have a little more of engine brake to make me go downhill a little slower and in control.

    Also is good to mention that the crash happened because i was afraid of the speed in the moment, and the terrain, the curve is like 50 feet away from me and the downhill was getting steeper, so i think that first gear would do its work and brake me little by little with back braking help, and just having guts to let the bike go down and counter balance in the corner and problem solved. This is a 100km off road next to a little lake called Ayarza, anyway the important thing here is: what do you think? thanks.
    #1
  2. Indy Unlimited

    Indy Unlimited Long timer

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    Learn to use your front brake going downhill!
    Engine breaking on steep hill will just lead to losing stability and it will not slow you down enough.
    You got ABS so go for it on the front brakes!!!:wink:
    #2
  3. Metalsapo

    Metalsapo R.E. Ordoñez

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    No Abs for my bike, first model in Guatemala. 2008 show room bike.
    Yes i do use the front brake in straight downhill paths, anyway, first answer
    score is.
    Sprocket
    No change 1
    Change 0
    Thanks, i will practice more.
    #3
  4. BlueLghtning

    BlueLghtning Riding is my passion

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    I don't own an F650/800GS so I don't know specifics on this bike how its geared stock and playing off road, but generally speaking if you are doing a majority of your riding off road or slow going, a sprocket change to give you lower gearing can really help. A lot of how a change affects the bike depends how big the gear spread between each gear is to begin with. One advantage of using a sprocket range with over all lower gearing is it puts the gears closer together which can help in off road where gear changes aren't such a huge change.

    Sometimes there's enough room to play to get a bit lower gearing without sacrificing road performance. Other guys that own these bikes can chime in on what they have found works for them in their scenarios to give you some ideas.

    So what I gathered from your story was that while you are in 1st gear, you are not finding that low enough for your liking with enough engine braking? Do you ever get out of 1st gear while playing off road or what gears do you use the most? In optimal dirt bike world, you try to get where 1st gear where it can be a really crawl gear and 2nd gear can be good to use from almost a crawl on up and sometimes into 3rd gears and higher depending on the terrain. You still have 4-6th gears for pavement and faster dirt sections, although they will overall be lower gears.

    Of course the downside of doing a drastic gearing change is it is going to make your overall 6th gear lower so that when you are on faster road sections, the bike will be revving more. However, if you generally aren't going faster than 55-60mph, this may not be a big deal if at all affect you?

    I do agree that you should practice more efficient braking while off road. Regardless of gearing, you should be comfortable in coming to a stop off road in steep terrain, but with that said, overall lower gearing would help keep your speed down to begin with. You just have to find the right gearing combination that works for you, but if you are focusing on mostly off road riding, then I don't think you can go wrong going lower in the gearing.
    #4
  5. Indy Unlimited

    Indy Unlimited Long timer

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    Even without ABS you need to learn to pull in the clutch and use the brakes
    #5
  6. epicxcrider

    epicxcrider Been here awhile

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    Practice and slow down a little bit until you get more confident :)
    #6
  7. JRP

    JRP Old guy

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    Changing the rear sprocket enough to do any good would cut your top speed WAY down. Using the rear brake along with the front one will accomplish the same thing. Just get lots of practice, you want all the braking you can get before the wheels lock.
    #7
  8. Kiwi Tinkerer

    Kiwi Tinkerer Ross

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    I went from R1200gs to a 650 x-challenge so I could learn to ride off-road. (140kg dry weight) A lot comes down to confidence. For me, that came down to practice.
    Once I found out how hard I could push the suspension, the better it was for me. Then I learned what is slippery and what is not. Good tyres help to. (Tires?)

    I now have an F800gs. I am not going to take it in the mud, but I have had it down some reasonably rough tracks. The F650 twin should be better in some ways. Lower to the ground.

    I would stick with standard gearing. Unless you want to do more technical riding.
    I would not so it for engine breaking. I learned to pull in clutch and use brakes.

    Good luck
    #8
  9. P@vlos.B

    P@vlos.B Stuck in an Island

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    practise, practise & practise!Learn to use the brakes and the sliding of the rear wheel. And as epic said, go a bit slower till you get more confident! ABS ain't gone help you in the dirt.. all dirt bikes don't have them..
    #9
  10. itsatdm

    itsatdm Long timer

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    Buy the counter sprocket for a F800gs. It is 1 tooth smaller than the F650( 16 teeth vs 17). That is about a 6% reduction in the gearing.

    You can go smaller, but it does effect rpm at speed. I think maybe your issue is really lack of experience? You can use both brakes in dirt. You just need to modulate the amount and that takes practice.

    Touratech will probably be cheaper than BMW.
    #10
  11. Reaver

    Reaver Outta Here

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    If someone can tell me how easy it is to ship to Guatemala from Canada, I can send a good used 16T to Metalsapo for shipping cost or less. Then he can see for himself!
    #11
  12. Loutre

    Loutre Cosmopolitan Adv

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    I'm starting to believe that you are a serial mugger having all spare parts in the world hanging around in your garage

    :hide
    #12
  13. Reaver

    Reaver Outta Here

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    See my ads in "Tent Space" and "Couch Surfing".


    Also have many items in the Flea Market.

    Don't make me post pics Loutre. :eek1
    #13
  14. bdx

    bdx Wheeeee!

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    Metalsapo: You may know this already. If you are new to off road here are a couple of tips that may help on down hills. Shift your weight to the back of the bike. Get more weight over the back tire. It give the back more traction making its braking more effective. If you are standing or up on the tank while going down steep hills most of your weight is on the front wheel which makes it really "grabby" when you try to apply front brake because it has all the traction. Shifting your weight to the back improves engine braking, rear braking and makes the front brake easier to apply gradually.

    Of course someone on here will disagree with this.
    #14
  15. Loutre

    Loutre Cosmopolitan Adv

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    A whole cartel? Dear goodness, Canadians are cheeky bstrds after all :lol3
    #15
  16. Metalsapo

    Metalsapo R.E. Ordoñez

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    Yesterday i got my answers, i went to the BMW and asked to the mechanic manager (i hope you understand this) what i could get from a sprocket change, if it is good or not?
    He said that is a very common modification (back or front)for 800 parallel twins, and it is done in the process of competition to get more control and torque response to the off road technical conditions, and when the motorcycle is on the pavement and the upper gears (6th' 5th) are used is when the gasoline use is not efficient.
    With that said, i made my choice, and i choose to practice more.
    Im a new rider, scince November 2012, just 4500 km of experience and about 1300 km off road until today, so i am very rookie and the practice i have is just in the ride to work and a couple of other small trips like the picture is showing, i do 12km or a little more off road and the rest is bad pavement and the city cahos every 3 or 2 days, also the offroad course i assisted was limited in this area of downhill so i do more than i learned there, i have crashed once after the course and twice before, your advice is correct and i must place my body correctly to help traction, braking, and balancing the bike, i am very honest about it, and it is very scary for me sometimes when terrain is too dry and loose in downhill sections, i think is normal to feel fear, and fear is telling me like a good friend to be carefull, fear inside of me must be trained to back off a little bit to let me do what im learning to do, so if i do feel that i could modify the sprocket (available from touratech or original BMW) in the future i will, but meanwhile i will do my practice.
    Thank you all. (Sorry for spelling, ipad is not that easy for this)
    #16
  17. itsatdm

    itsatdm Long timer

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    It is a fairly common mod. The mechanic is correct if you mean it will raise the bikes rpm vs speed on pavement. On a F800gs, 128 kph is about 5,000 rpm. I would guess on yours, with its gearing it would be around 4,700 rpm. Am I close?

    You have to keep in mind that the transmission is supplying its own multiplication of the gearing. In other words a 6% gear reduction overall, is more in the lower gears than the top gears.

    It is also simple to do. Take the cover off the sprocket. 1 bolt holds the sprocket on. The same chain works with either, you just have to adjust it.

    Counting stock I have 3 sizes. I detect little difference in mileage with the various sprockets.
    #17
  18. Avner

    Avner Not noob anymore

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    I posted it on another thread, but you can read the short version:

    Switching the front sprocket from the stock 16 to 15 tooth is something anyone who ever leaves the pavement should do, because in my opinion the stock should be the 15-tooth sprocket; it does much better on and off-road. It will only cost $32 or less and takes less than 15 minutes to replace. However, it is just an improvement and not a game-changer, and you will still have to slip the clutch a lot in technical terrain.

    If you really want to have good control and high torque off-road, then replacing the rear stock 42-tooth sprocket with a 47-tooth one is the way to go:

    Last night I installed the 47-tooth rear sprocket in addition to the GREAT 15-tooth front sprocket mod from last week, so now I’m running 15/47.

    The chain was too short after adding the 47-tooth sprocket, but I didn't feel like spending $145 on a new chain because all I needed was ½" more. The only thing limiting the rear wheel from moving forward was the chain-tension screw. I fastened it all the way in, but it was too long and it was sticking out and not being able to go all the way in. Since I’ll never need the full length of the screw (my 15-tooth front is permanent because it has the best balance for road/off-road), I just cut it off and everything now fits perfectly. I even had to give it a few turns, because the chain was too loose with the screw all the way in.

    Two major improvements I felt right away when I visited my "private" off-road area last night:

    1- The bike can crawl on 1rst gear with no throttle added. It was very useful when I was going down a steep hill without touching the clutch or the brakes, and it is harder to stall the bike even in low RPM.
    2- I know I’m only gaining about 10% of torque with this setup, but when I tried climbing up a familiar steep hill I felt as if I got 50% more torque – it was almost effortless!

    The down-side is obviously more buzz because the RPM is now “living” in the 5,000 range (which I like doing anyway), and long highway hauls would be tiring with an estimated 6,000 RPM at 80MPH. I never checked my MPG, so I won’t be able to compare, but I’m sure it will be affected as well. However, I’m very happy because my main concern is the low-end anyway, and this $122 modification completely transformed this bike into a mud-craving bitch!
    #18
  19. Metalsapo

    Metalsapo R.E. Ordoñez

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    Abner, thank you, i will purchase the sprocket very soon and re thread you with my modification results, i take notes of the KPG i do with the bike, and average is doing 90 KPG, and the modification will be for the back sprocket using a 42, and i feel better to have your same problem and that the solution is easy, my sporcket will be from touratech for $84, so i let you know. :evil
    #19