Extreme Hill Climber Fat Tire MTB Project.

[commuter ebikes]

I have a couple of 170mm dropout standard length (as opposed to midtail) fat tire cargo frames that I rejected from my commuter bike project.

I rejected these frames because I could not obtain tall enough gearing for commuting. The largest chainring that I could fit was a 46t and I only had room for a 3-speed freewheel because I insist on using a 50mm magnet rear hub motor.

3-speed freewheels definitely suck. They can be very difficult to remove. Of all the 3-speed freewheels available, sixteen is the least number of teeth that you can obtain on the smallest cog. I geared them as high as I could and my pedaling spun out at 18mph--boring!

The commuter bikes that I have are perfect for high speed riding, but being midtails with tall gears and a rigid fork, they would be ridiculous on steep single track.

There are great MTB trails in my city which call for a standard length frame, low gearing and a suspension fork. I am taking a suspension class which requires me to buy a Fox suspension fork, so with two leftover standard length frames and 170mm dropout Cromotors, as well as a suspension fork, I want to take this opportunity to build a couple of very low geared eMTBs.

The main reason that I made this post is because the lowest available gearing of a 23t single speed freewheel (http://www.bikeman.com/WIND-FWENO23....LoUaAuSq8P8HAQ) and Vuelta 20t chainring (https://www.amazon.com/Vuelta-Mtn-fl.../dp/B007YH7YV0) has me wondering if having more teeth in the rear than the front is reasonable.

I am used to riding with a 14t rear cog and a 58t chainring and I spin out at about 33 mph (a 58 X 14 setup yields a cadence of 80 at 33 mph on my 31.5" diameter tires).

A 20 X 23 setup yields the following cadences:

[commuter ebikes]

Obviously this "Bicycle Gear Size and Cadence/Speed Calculator" is not made for riders wanting to build hill climbers, but I noticed that the cadence at 30 mph is twice the cadence at 15 mph, so I will assume that the cadence at 7.5 mph is half of the cadence at 15 mph.

If this is true, then the cadence at 7.5 mph with a 20 X 23 setup would be half of 172, or 86. So I would certainly be spinning out at 7.5 mph. This seems to be about what I am looking for, as walking speed is about 4 mph. So if my wife was walking up a hill at 3.75 mph, I could be pedaling along with her at a comfortable cadence of 43.

[commuter ebikes]

The formula for gear inches is:

[commuter ebikes]

I don't see any exponents in that formula, so I will assume that comparing two different setups in bikes [(58 X 14) and (20 X 23)] would be linear.

My 58 X 14 setup has functional pedaling for speeds up to 33 mph. It has 128.2 gear inches.

[commuter ebikes]

A 20 X 23 setup has 26.9 gear inches. So with the linear relationship, the "Hill Climber" MTB would have functional pedaling up to (26.9/128.2) = 20.98% of 33 mph, or 6.9 mph, certainly a very lowed geared bike.

So why even have a motor, you ask? With the extremely low gearing, I wouldn't need much assist going up a steep hill, and I wouldn't need any assist going down a steep hill due to the force of gravity. On moderate grades and level ground, however, I could clown pedal and enjoy the ride.

Spinning out at 7 mph, any pedaling at speeds above that is all clown pedaling.

The MTB trails begin 7 miles from my home, so I could clown pedal over there and not have to bother with transporting the bike in my wife's van (I don't have an automobile) and getting the interior all dirty or muddy.

Also, I could be really tough on the bikes because I don't need them to transport me to work.

[commuter ebikes]

This is the fork: https://www.probikesupply.com/produc...jKIaAhiE8P8HAQ



It fits up to a 2.4" wide tire which is unusual for me because I like fat tires. If I want to take advantage of the fat tire cargo frame, the bike will be a chopper.

I don't particularly like the look of choppers, but I currently weigh 290 pounds so I probably need the fat tire in the rear for suspension. Fat tires can provide up to 2" suspension depending on tire pressure, but it is not quality suspension because the rebound and damping is not regulated as it is with a shock.

[commuter ebikes]

I realized that using this suspension fork https://www.worldwidecyclery.com/pro...TRsaAqi78P8HAQ and this hub http://salsacycles.com/components/ca...rsion_rear_hub can fit a Vee Snowshoe XL (or Surly Bud) on a Clownshoe rim. The crown race is 40 mm so it fits my frame.

That would suck if I put it all together and the tire or fork crown hit the down tube upon full compression.

[Jasdidit]

You can always extend the lower headset bearing down further with a spacer or an oversized bearing. That gives more fork clearance. For 1 1/8" head tubes I like the Origin8 cartridge headsets, which have extended/oversize bearings. If you're taking a suspension class, why not build some rear suspension? You could widen the bottom bracket and rear dropouts at the same time. An extreme climber is going to need that fat tire in the back to climb steep hills. You can always lock down the forks to keep your weight forward, but having a small tire in back makes loose soil a hazard. Check out the Maxxis Minion FBR 26x4.8" tire. That is some hill-climbing tread. Another problem is what I call "steps" in the hill. A "Step" is where soil has fallen away from a rock or root, leaving a step, anywhere from 6" to 20" high. These are difficult to get over while climbing a hill. It takes practice. I pull a wheelie about 5' in front of the "step", almost going over backward before I hit the lip of the "step" with my back wheel. This brings my front wheel down, hard, I throttle back, and then I shift my weight forward over the bars, to lift the back wheel over the "step". Throttle back on, and up to the next "step". These are so easy to walk over, you don't even think about it, but they are hard to go over with a bike.

[fos'l]

Hope I understand this, but are you going to be happy spending an hour both getting to and from the trail? Does the frame have single speed capability or are you using some kind of tension device? Also, having played around with small front, bigger rear tires (extreme hill climber with maximum weight on front wheel), they don't ride well for most other purposes.

[commuter ebikes]

Hope I understand this, but are you going to be happy spending an hour both getting to and from the trail? Does the frame have single speed capability or are you using some kind of tension device? Also, having played around with small front, bigger rear tires (extreme hill climber with maximum weight on front wheel), they don't ride well for most other purposes.

Good call on the tension device. I had not yet recognized the need for that. The rear dropouts are vertical mount, so this frame does not have single speed capability. I will use a Surly Singleator.

The road to the trails is flat and paved, so I would use the motor and fake pedal so it would take about 15 minutes to get to the trailhead.

Some of the trails up there are very steep, so the low gearing is required so as to eliminate the need to get off the bike and hoof it.

With only one very small chainring up front and one large freewheel in the rear, the gearing on this bike is only good for pedaling up steep hills. All other times I would either be coasting downhill or fake pedaling on flatter terrain.

[commuter ebikes]

Here is the frame, ready for reconfiguration with a very low geared single speed setup, Surly Singleator, a Bluto suspension fork and narrow profile battery boxes hidden in the panniers which will hide the motor and somehow withstand a huge side hit without damaging the frame. I am also going to make a lightweight passive heat sink for the controller.

[commuter ebikes]

You can always extend the lower headset bearing down further with a spacer or an oversized bearing. That gives more fork clearance. For 1 1/8" head tubes I like the Origin8 cartridge headsets, which have extended/oversize bearings. If you're taking a suspension class, why not build some rear suspension? You could widen the bottom bracket and rear dropouts at the same time. An extreme climber is going to need that fat tire in the back to climb steep hills. You can always lock down the forks to keep your weight forward, but having a small tire in back makes loose soil a hazard. Check out the Maxxis Minion FBR 26x4.8" tire. That is some hill-climbing tread. Another problem is what I call "steps" in the hill. A "Step" is where soil has fallen away from a rock or root, leaving a step, anywhere from 6" to 20" high. These are difficult to get over while climbing a hill. It takes practice. I pull a wheelie about 5' in front of the "step", almost going over backward before I hit the lip of the "step" with my back wheel. This brings my front wheel down, hard, I throttle back, and then I shift my weight forward over the bars, to lift the back wheel over the "step". Throttle back on, and up to the next "step". These are so easy to walk over, you don't even think about it, but they are hard to go over with a bike.

I have this issue to resolve because the Bluto is for a tapered headtube and my frame has a 40mm headtube: https://electricbike-blog.com/2015/0...ered-headtube/. If, however, the compressed suspension fork hits the down tube after I test it, I will extend the lower headset bearing down further with a spacer as you suggested.

The suspension class I am taking is for servicing suspension forks and rear shocks. They are the suspension classes in these links: http://www.bikeschool.com/classes/me...ation-seminars and http://www.bikeschool.com/classes/me...ation-seminars.

I like the aggressive tread on that Maxxis Minion tire:

[Jasdidit]

If your frame comes with the standard, cheap, caged bearing, head set, then just replace the bearings with oversize bearings. then you won't need a spacer, and with the added benefit of a having a better head set to handle increased loads. Look at the Origin8 cartridge bearing headset for 1 1/8" head tubes. They are cheap, work smoother, and handle more load then simple 1 1/8" caged bearings. You could use a 20 x 4" wheel in front with a Chao Yang 20 x 4" tire on it. that would bring more weight to the front. It wouldn't work with the Bluto fork though, because of the brakes. It would work with the Luna Lander forks, because they are made for 135mm drop outs. If you are taking the wheel lacing class also, you could always lace up a 15 x 150 hub to a 20 x 4" rim. Just make sure it has 36 holes in the hub, because that's what most 20 x 4" rims come with.
Come to think of it, I have all the parts to make the exact same conversion. 20 x 4" fat wheel and tire, Luna Lander fork, I even have a 20 x 4" hub motor for AWD and more front weight. I just don't have a cargo frame though.

[commuter ebikes]

I am building two matching bikes like this. I just placed the order for two White Industries ENO 23t freewheels, two Vuelta USA 20t chainrings, two Surly Singleators (http://surlybikes.com/parts/drivetrain/singleator), and two Chris King NoThreadSet headsets (https://chrisking.com/products/20).

I also bought the headset removal and installation tools (http://www.parktool.com/product/head-cup-remover-rt-1 and http://www.parktool.com/product/bearing-cup-press-hhp-2 and), the crown race setting tool (http://www.parktool.com/product/crow...g-system-crs-1), the Chris King headset press adapter (https://www.amazon.com/Chris-King-He.../dp/B001GSMKUI) and the White Industries freewheel removal tool (http://www.bikeman.com/WIND-FWTOOL.h...SagaAl688P8HAQ).

Buying two of everything plus the tools made the order painfully expensive. I could not afford any suspension forks, so I will use the Surly Ice Cream Truck forks (http://surlybikes.com/parts/forks/ic...truck_150_fork) that I have on hand which will enable me to fit a 5.05" X 31.5" tire in the front. The largest tire I can fit in the rear is a 4.80" X 30.5", so the bike may have a reverse rake of 3/4". A reverse rake is disadvantageous to hill climbing, though, so we'll see how that works out upon testing the bike.

I was surprised to discover that the White Industries freewheel does not screw onto the freewheel threads as much as you may want. Because it is a removable freewheel, it has a metal area where the removal tool engages which prevents threading it down further. The photos below compare my old 3-speed freewheel and the White Ind. freewheel:

[commuter ebikes]

My buddy Alan B. wanted to use a White Industries freewheel on his 150mm dropout Cromotor, but this metal lip prevented the freewheel from screwing down far enough, necessitating the the height of the freewheel threads to be reduced.

My 170mm dropouts give me an extra 10mm to play with, so hopefully the metal lip (which is an obstacle at this point) is less than 10mm high.

A neat bike tip is that AR-15 flash suppressor shims (http://www.brownells.com/rifle-parts...prod42002.aspx) are the perfect size for use as bicycle axle spacers. The outer diameter of a .223 AR-15 barrel is about the same diameter as a standard 1/2" hub motor axle and the outer diameter of a .308 AR-15 barrel is about the same diameter as a 16mm Cromotor axle. These flash suppressor spacers are the only washers that I have found that are small enough to fit inside a freewheel. Using these spacers allows one to push out the dropouts to fit a taller freewheel.

A brass thrust washer (plumbing part from the hardware store) tops it off and you're in business as long as you still have enough threads remaining to fully engage your axle nut.

[commuter ebikes]

I anticipate having to use brake rotor spacers to get the rotor spacing right, as well as using freewheel spacers (the same thing as a bottom bracket spacer) to get the chainline right.

[Sneakers915]

If you're spinning out at 7.5 mph, you don't need a suspension fork unless you're descending at 20.

Maxxis Minions are the best mtb tires out there and are widely copied for a reason.