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Discussion Starter #1 (Edited)
My TW came stock with 14/49 gearing. I like the ultra low first gear and being able to putt along at 3 mph without slipping the clutch. But, I'm one of those people that thinks that wringing out a 4 stroke at high RPM's for long periods causes premature wear and I felt like 40-45 mph was as fast as I wanted to go with stock gearing so as to not be revving the motor like crazy. I need to be able to cruise at 50-55 mph in order to get to some of the trails I like, so I did the dual rear sprocket mod by adding a 45 tooth rear sprocket. The 45 tooth sprocket only raised my 1st gear putting speed to ~4 mph, but raised my comfortable top end to 50-55 mph. Even with 14/45 gearing, 1st gear is so low that I rarely use it, even on hard single track trails.

I then changed my stock tires out for the 26x8-14 Duro Power grip in the rear and a 120/100-18 Kenda Trackmaster up front. The circumference of the Duro tire is 85'' and the stock Bridgestone tire circumference is 77''. This equates to a 10% increase in speed at any given RPM. That bumped my 4 mph putting speed to ~4.4 and bumped my comfortable top end cruise to ~55-60 mph, with 14/45 gearing. Running a Duro rear tire with 14/45 gearing is essentially the same as running the stock tire with 14/42. Likewise, running the Duro with stock 14/49 gearing is like running the stock tire with 14/45. I had not considered the difference in tire circumference between the Duro and stock when selecting my gearing, so I'm posting this as an FYI.

With the stock tire, you can have a 5 tooth spread in rear sprocket teeth for your dual sprocket setup, without changing the chain length. The Duro tire is so big that you can't slide the axle all the way forward in the adjusters because the tire will hit the swing arm. Because of this, you can only have a 4 tooth spread in rear sprocket teeth without the need to add or subtract extra chain. To me, not needing to change the chain length is key to the dual setup because it makes the swap so much easier to do when on the side of the road.

On my un-calibrated, cheap, bathroom scale the Duro Power Grip weighs 24 lbs. The stock Bridgestone only weighs 15. That's a huge increase in rolling weight. Because of the extra weight and the larger tire circumference, the Duro makes the bike noticeably slower and less responsive.

Since I love the 14/49/45 dual sprocket combo with the stock tire, I'm going to go with a 14/49/52 combo with the Duro, to maintain the same speed/RPM's as I had before. You could go with an even bigger rear sprocket to 'feel' more power, but I really don't need to go be able to go any slower in 1st gear and like to keep cruising RPM's down. With the Duro tire and 14/49 gearing, I can ride the gnarliest, rockiest, steepest, single track trail and have plenty of traction and power at the speeds I need it. (Power is relative - this is a slow bike designed to be ridden slowly, so keep that in mind here.)

You can keep the stock chain guard when running dual sprockets with the Duro too! Just bend both of the guard mounting points to align the guard over the two sprockets while keeping it away from the tire.

Here's what everyone wants to know: Seating the bead of the Duro is hard to do. I've probably mounted 50 motorcycle tires, and this was by far the hardest. It sat in a cage at 90 PSI for 3 days and didn't seat. I removed the tire, trimmed the bead on both sides (trim the inside edge of the bead, to increase the diameter of the 'hole'), remounted it, and the bead seated at 40 PSI. SAFETY NOTE: The Duro tire is only rated for a MAX of 20 PSI. Over inflating it could cause a huge explosion, ruin your wheel, and hurt you.


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Even 14 x 52 sprockets seems like pretty tall gearing considering the typical TW Duro sprocket mods encountered out west tend to feature a 12, 13 or 14 tooth front sprocket and 55, 60 or greater teeth on the rear sprocket. As you note 14x52 w/ a fully inflated Duro approximates stock gearing but you have much more rotational inertia with the heavier tire. My 13X55 Duro @ equipped bike @ 12 psi pulls 55 mph w/o issues up to 8,500 feet elevation or so, then comfortable top speed falls off as elevations increase.
While circumference is a handy metric what your bike sees as a final drive ratio determinate is the loaded tire radius which is a function of tire pressure. This is the measurement to consider. Lowering a 26x6x14 Duro’s pressure to 6 psi or so reduces to loaded rear tire radius to approximately that of a stock tire @ 14 psi. This is a good trick in the nasties. Low pressure not only creates greater ground contact surface area but reduces driven radius and thus lowers overall final drive ratio facilitating greater torque at the rear wheel.
 

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Discussion Starter #3 (Edited)
Good trick about lowering the pressure to reduce the tire diameter. I always drop my tire pressure when I get to the trails anyway, but hadn't considered how it impacts the diameter/circumference.

I'm on the east coast, so most of my riding is from 0-3000 feet. I have a jetted carb with high flow filter and a cut airbox. It breathes and moves ok with the tall gearing and Duro tire, but it is a bit slow. I also only weigh 155 lbs, my friend weighs ~225 lbs and he reports that the bike struggles to pull him up hills that I ride up without needing to downshift. I bet it would struggle at your higher out west elevations.

I have a street legal TTR-250 for when I want to be able to ride trails faster. I like the 'relaxed' feeling the taller gearing and lower RPM's give me. Your mileage and speed/RPM's may vary though.

I didn't see very much info about how the taller tire effects gearing before I did the mod, so I posted this thread as an FYI for those interested. A bigger rear sprocket will definitely allow you to feel more power. When I had the stock tire and 14/45 gearing, I was perfectly happy on rough trails and on the road, so I'm trying to emulate that same gearing with the Duro. If you like different gearing, just know that the bigger duro tire will give you +10% in mph at any given RPM, and that you really can feel the extra weight of the tire. With that knowledge, you should be able to calculate the right ratios for you.
 

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Of note is the effect of the taller, heavier tire and any sprocket changes on fuel mileage. My fuel consumption has fallen from about 70 mpg to an even 50 mpg with the Duro @ 10 psi.
Have others noted a similar decrease? On some longer road orientated rides I have raised Duro pressure to 16 psi without much of an observed increase in range.
 

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On my un-calibrated, cheap, bathroom scale the Duro Power Grip weighs 24 lbs. The stock Bridgestone only weighs 15. That's a huge increase in rolling weight. Because of the extra weight and the larger tire circumference, the Duro makes the bike noticeably slower and less responsive.




View attachment 137282 View attachment 137290

Good reminder about the tire beading issues with the Duro. Many have succeeded but there are lots of reports here on the forum of Duro Tires exploding during the bead seat process.


I have played the gearing as well. It's fairly subjective as I can tell what is not comfortable for you with higher RPM's is fine for me. That's the beauty of it all, like Burger King, "we can have it our way" in regards to the gearing we feel comfortable with.

For trail riding I use 13x60 gearing through the aluminum sprocket I was using wore out in about 6 months of use. Right now I'm using 13x54 which "sounds" close but not exact to stock gearing. I think I tried 13x50 but it was pretty weak in 5th gear.


Here are rear tire weights TW-Brian provided when he did the ATV tire/Trailer Rim Mod.

For comparison purposes, I weighed the following:

Stock TW wheel and tire - 32.8 lbs
Stock TW wheel with Duro Power Grip 26x8x14 - 37.8 lbs
Trailer wheel and Sedona Rip-Saw 25x8x12 - 46.4 lbs


This is what my Ceros Trailer Rim mod weighs. My wife uses a 25x8x12 which is noticeably smaller than mine but I haven't weighed it yet.

Stock TW wheel with Ceros 26x9x14 - 44 lbs


 

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Wow that’s a beefy tire. How does that thing feel at 55 mph? So do you have two master links and add a chain section at the trailhead? Good write up and good thread. Cheers
 

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I was surprised how well the Duro Power Grip does on the highways. I figured it would really cut down on cornering speeds yet hoped the enhanced off-road traction would make for an acceptable trade off. Turns out that it can be a win-win. If one can adapt to the squarish profile it can have nice road manners. Mine corners well enough but it does take a bit of getting used to, usually notice the difference only when changing from my non-Duro to the Duro equipped TW.:p

A section of chain plus a second master link is indeed the commonly selected solution to the chain length issue when going from one sprocket to another involving more than a few teeth. However not too many dual sprocket owners report using them frequently. Handy for changing seasonally varying conditions, or any ride with a different pace than normal I guess. Certainly nice to look at.
Gerry carefully built a dual front and dual rear sprocket combo on the Mr.Gizmo bike he sold me. It permits going from 15x47 to 13x55 sprocket combinations without need for a chain length alteration. However that is a one-off creation that may lose some reliability with chain stretch over time as the snail cams have only so much adjustability before a link removal is neccesitated. I need to build a trip with a lot of 70 mph followed by a lot of 7 mph riding to really enjoy it beyond it’s novelty and elegance.
 

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Discussion Starter #8
I'll echo Fred's opinion of the Duro at high speed: it's surprisingly stable. It feels better than most 'normal' dirt bike knobbies at 55 mph.

If you keep your two rear sprockets within 4 teeth of each other, you DON'T need to add chain to swap between the two with the Duro tire (with the smaller stock tire, you can get a 5 tooth spread). If you spread is more than 4 teeth, you'll need to add chain. I keep mine at a 4 tooth spread, so I don't have to mess with adding chain, it makes the gearing change so much easier and quicker on the side of the road.
 

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I ran 47/55 for quite a while and found it a good combo street and moderate fire roads. Then I started going crazy with 60 and 66 tooth rear sprockets, etc. It just depends on the type of riding that you plan to do.
 

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I run 14/55 and only a few times found I might want lower gearing.
On the dunes lower gearing may allow the TW to pull 2nd gear on more hills. The bike needs to be in at least 2nd gear or it digs down.
As Fred indicated, it takes a bit to get use to the squareish Duro when cornering on the pavement.
 

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Discussion Starter #12
Just got the DURO with stock sprockets (14/50).
Should I go for 46/54 ?
Mount the tire and ride the bike before you order sprockets. The tire height makes the bike faster at any given RPM, but the extra tire weight makes it noticeable slower. The balance how much power you want to feel vs how many RPS's your turning is up to you.

The Duro definitely makes the bike feel different from stock, so I'd ride it before ordering sprockets. I wish I had, it would have saved me $30. IMO, 46/54 with a 14 front sprocket would be perfect. The 14/46 will do everything but the nastiest trails, and that's where the 54 will shine. You'll have to carry an extra length of chain to make the swap though, since there isn't enough adjustability in the axle slot to accommodate that large of a spread.
 
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