Sprockets and Mods for High Altitude Trails
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Thread: Sprockets and Mods for High Altitude Trails

  1. #1
    Junior Member WildernessAU's Avatar
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    Hey guys, I'm new to the forum and have already spent a good deal of time reading many of your great posts.

    I'm new to the TW and am really loving it!

    I live at 9,400ft in the central rockies of Colorado. I mainly will be riding on steep rugged single tracks and fs roads between 8,000 and 12,000ft. Id like to optimize my 2006 TW for high altitude steep trail riding. The bike will hardly ever go below 5,000ft in altitude or venture on big highways but still being able to putter around town is semi important.

    I spend a great deal of time prospecting up in the mountains and essentially want to use the TW as a pack mule to areas that I don't want to or can't get my truck into.



    My first issue is to address any re-jetting or air box mods that might be necessary. It sounds like most do just fine with leaving the stock jetting and simply adding holes to the airbox cover. If I'm spending most of my time this high in altitude, do I need to change out the jets or make other adjustments?



    Horse power loss this high up is near 30%. I might be dreaming but in the end I'd like to be able to climb 60% grades at this altitude. I image that I would need to re-jet and change the sprocket gearing at the very minimum???

    Would changing the sprockets give me noticeably more torque or climbing ability? What sizes are recommended and safe to run without risking damaging the motor or other components?

    I am open to any and all realistic suggestions.



    Right now, I'm stock. Hand guards, rear rack and skid plate on the way.



    Thanks for all of your help!

  2. #2
    Senior Member small's's Avatar
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    I read somewhere on here that a feller drilled small holes in the air box lid and used rubber grommets to plug them. When he would get in higher elevation he would start pulling out the plugs. I dont know what size jett to start with? Maybe around a 124-125 and go from there. If i was gonna be in the mountains all the time at higher elevation and wasnt concerned about running 60mph i would try around 55-57 rear sprocket. My bike ran ok up to around 9-10,000' before it started studdering but im sure it was still a bit rich at thoses altitudes but it made it the top of imogene pass which was all i was asking for with the stock jetting and 14/47 sprockets. Not ideal but we made it. Are you down around silverton, ouray, telluride area?

  3. #3
    Member eskermel's Avatar
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    I bought a new TW in Alamosa this spring, and the dealer had installed a 118 jet for use at the high elevations surrounding the San Luis valley. This appears to yield a leaner mixture than some of the forum users are comfortable with and I have not yet had the time to ride at 10-13k feet. I will keep you posted.
    WAGmore likes this.

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  5. #4
    Junior Member WildernessAU's Avatar
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    I live up in Summit County. All of the paved roads are above 9,000+ft!

    Small's, I think I saw your pics from your Telluride trip...beautiful place. A buddy of mine lives in Silverton which I hope to visit soon and ride some trails with.

    I'll call some local shops to see if they can suggest jet sizes. The thing is, I like to research and try to get everything dialed in on the first go around.

    I sorta understand gearing but don't really know if changing sprocket sizes will affect the motor or carb settings?

    From the sprocket calculator it looks like I can get good results by just changing one of the sprockets. I like this idea because it would be easier to swap back to the stock sprocket if I head to lower elevations or want to do a road trip.

    Looks like more torque gain from changing the front sprocket compared to changing the rear.

    If I go 12front 50rear, I get a 20% torque gain. 15/57, I get 12.3% Is this much gearing difference safe for the bikes mechanisms? can I go higher?

    Is the front sprocket much more difficult to change than the rear?



    Would I be able to keep the same/stock chain for these set ups, or would I need the stock chain for stock gears and a different chain for my climbing gears?

    Lotsa questions I know...thanks for all your help!

  6. #5
    Senior Member small's's Avatar
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    You have to take the shifter, foot peg and side case off of your motor to change the front sprocket. You also have to drain your oil or lay the bike on its side if you dont want to change the oil. That small of a front might wear your chain slide faster. I would start with getting it jetted right.

  7. #6
    Senior Member B-dub's Avatar
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    If I were in your situation and had the money to play with I would jet it lean and install a Dial-A-Jet. The Dial A Jet compensates for altitude and temperature variations and helps to ensure you don't end up too lean when you make a trip to lower altitudes. It also gives you more flexibility. More information here.



    I would also go with a dual sprocket set up on the back, and would probably start with a 55/60 combination. If you find that is not enough you could bump it up to 60/65, etc. More information on dual sprockets here. Bigger sprockets on the back shouldn't affect the motor or carb settings, they effectively just reduce top speed, and increase torque or climbing ability. It's good practice to get a new chain when installing new sprockets because a worn chain will quickly wear new sprockets, and vice versa. The exception, of course, is if your chain and sprockets are fairly new and in good condition.



    Most people consider the front sprocket more difficult to change because you have to pull the engine side case, etc. This entails getting an impact driver and correct size bit or risk stripping the screw heads. Some people have also had trouble pinching the wires when going back together.
    My handle is B-dub, I ride a T-dub, and drive a V-dub.

  8. #7
    Junior Member WildernessAU's Avatar
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    The dial a jet sounds pretty awesome and at $78 it could very well be worth it.

    A dual dual sprocket like Qwerty mentions in the dual thread would be amazing:

    "My opinion is that chain alignment with a single/dual setup would not satisfy me. I would prefer a dual/dual setup to widen the ratios with the same length chain, and use an inch of adjustment to allow a wider ratio. If memory serves, I did some calcs that revealed one could run a 15/50 and a 13/68 dual/dual setup within the limits of the stock chain adjustment slots without changing chain length. That would be a fairly extreme difference in final drive."

    but I think this might be beyond me? unless someone in CO would be wiling to help and I'm not sure that it would really work safely?

    I'm thinking of leaving the 14 front and going with a 65 or so in the rear. I'm definitely looking for a noticeable torque difference and can always change back to the 50 if needed. Guessin I'd need a new longer chain too.

  9. #8
    Senior Member B-dub's Avatar
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    Mr. Gizmow, who to my knowledge pioneered the dual rear sprocket idea on the TW ran with a single front sprocket/dual rear sprocket set up successfully for awhile before he went to the dual/dual setup. Even then he went dual/dual to get a greater spread between gear ratios, not because he had any real problems with the single/dual setup (correct me if I'm wrong, Gerry). There are others on this forum who run a single front/dual rear sprockets and I've not heard of a problem with this setup. It's very easily done using darnold's tutorial on the before mentioned thread. I just did dual sprockets on the rear of mine, but don't have any miles to speak of on it yet. I believe with the span between front and rear sprockets the misalignment is small and abnormal wear would be slight as well. The advantage of single/dual, of course, is it's much simpler, but still effective. To change gearing you simply loosen the axle nut and adjusters, roll the wheel forward, reposition the chain on the desired sprocket, re-tension the chain, then tighten the axle nut and install the cotter key. It can be done in 5 minutes. But, you should do what you feel comfortable with.
    My handle is B-dub, I ride a T-dub, and drive a V-dub.

  10. #9
    Senior Member lizrdbrth's Avatar
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    The shoulders on the front sprockets prevent using two ratios up front. The chain will not drop down onto the smaller sprocket without riding on the taller shoulder of the larger. Not an issue in the rear.



    JT will reduce the shoulder on one side of the larger sprocket if you custom order.



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  11. #10
    Senior Member Gerry's Avatar
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    "The shoulders on the front sprockets prevent using two ratios up front."

    As my JT (front) sprockets had no shoulders, my use of duel front sprockets has not posed any problems. As a general statement, you will not be able to use a 12 or 13 tooth front sprocket in a "duel/duel" set-up. The reason being, the smaller sprockets do not have enough room (diameter) to have, or allow the drilling of screw holes needed for attaching the two front sprockets together. Perhaps this is what Russ meant (?). A 12 or 13 tooth sprocket is held to the primary shaft with a clip. The 14, 15...... use a plate that is held in place with two bolts (not present on 12/13 sprockets).





    In my opinion, the slight misalignment on a single front, duel rear affords way more convenience as to offset the accelerated wear of a modestly priced chain and sprocket. Gerry.





    Take care my Friend.........

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