Components of a High Speed Fat Tire Electric bike

[thetimmy]

I currently have a the SSR Sandviper, a 350W fixed frame 26x4 Fat Tire bike and I love using it to ride to work at 18MPH. I love it so much that I want to build a faster and safer Fat Bike.

I’m looking for anyone who has experience building electric bicycles that go over 25MPH, in fact going 35MPH is my goal, and I’ll address the legal issues of that speed once I learn more from the community here.

I know downhill speed bikes are safe to operate at over 45MPH, but those components are mostly not compatible with Fat Tire Electric Bikes, so I’m curious to know what components people here have used or what they recommend.

The bike should be under 60lb not including the battery, controller & hub motor (currently 48V 500W 8Fun/BaFang)

 

[thetimmy]

(Reserved for the component research)

Frame:
I am looking for a dual suspension frame that can withstand the impact of hitting a standard pothole or road elevation change while traveling at 35MPH. I’m not looking for anything extreme, essentially I would just want to be able to follow a scooter or lightweight motorcycle down the road and have my bicycle be able to handle the same type of road conditions.

Downhill frame

There are not so many fat bike suspension frames on the market yet. Best I've seen was a mod of a DH frame, with custom swingarm to accomodate 4".

Rims & Tires:
Does anyone have experiance with Fat Tire rims and Tires that are designed for such speeds?

Gears:
I currently have a 44T chainring that runs a 14T freehub, allowing me to go 19mph @ 80RPM cadence. A 53T chainring on a 11T freehub would allow me to go 28MPH at 80RPM.
I could hit my target goal of 35MPH by pedaling at 120RPM, but the 53T chainring reduces my ground clearance, so any alternatives would be welcome.

One way to pedal at higher speed is with a Schlumpf Drive (can multiply the chainring by a factor of 2.5). Disclaimer: I haven't used one yet.

The price of this component alone is $700, which makes it too expensive, but otherwise excellent.

 

[wesnewell]

https://www.google.com/search?q=dual+suspension+fat+tire+bike

 

[2old]

One way to pedal at higher speed is with a Schlumpf Drive (can multiply the chainring by a factor of 2.5). Disclaimer: I haven't used one yet.

 

[thetimmy]

https://www.google.com/search?q=dual+suspension+fat+tire+bike

My post made it very clear that I was aware that dual suspension fat tire bike frames existed.
My question pertained to the frames ability to handle standard road conditions at 35MPH, a speed that a only racing bikes are built to handle.
My initial reaction was that you were trolling, but perhaps my initial post wasn't clear

 

[markz]

Downhill frame

 

[John in CR]

It's not the other components so much as the tires that are the weak point. Fat bike tires are fine on a fat pedal bike or a low power low speed electric fat bike, but regardless of how many step in to say they use theirs at speed doesn't make it any safer. The right size moto tires can give you the same look with safety at speed.

 

[wesnewell]

I' have no experience with DS fat bikes, but I've had my hardtail fat bike above 35mph. and my other non fat bike (except with me on it) over 60 mph. I thought you were looking for DS fat tire bikes. good luck.

 

[MadRhino]

There are not so many fat bike suspension frames on the market yet. Best I've seen was a mod of a DH frame, with custom swingarm to accomodate 4". John is right about fatbike tires being thin and weak to be safe at higher speed. I prefer to ride on a 3" that is good, than on 4" that is not safe to hit. A good 4" tire is a trial motorcycle tire, and I find it too heavy to build on motorcycle wheels.

A good fat bike with 45NRTH tires can ride 40 MPH safely with the extra weight of ebike components, that would be the max speed that you should target with a fat bike IMO. On good 3" tires I ride above 60 Mph everyday, and much safer than a fatbike at 40 Mph.

 

[thetimmy]

I' have no experience with DS fat bikes, but I've had my hardtail fat bike above 35mph. and my other non fat bike (except with me on it) over 60 mph. I thought you were looking for DS fat tire bikes. good luck.

My SandViper is a hardtail 18in fatbike with 4x26 wheels and I've gotten it to 43kmh and felt very safe with the major limitation being gearing and the fact that i'm 6'1 @ 226lbs.
My thoughts were that front suspension would absorb the impact of hitting a pothole at 35MPH, as I don't believe Fat Tire bicycle rims were designed to go faster than 17MPH (based on the gearing I see on Surly's).
What safety enhancements did you add to the frame or other areas of your bike?

 

[thetimmy]

It's not the other components so much as the tires that are the weak point. Fat bike tires are fine on a fat pedal bike or a low power low speed electric fat bike, but regardless of how many step in to say they use theirs at speed doesn't make it any safer. The right size moto tires can give you the same look with safety at speed.

The task of fitting motorcycle rims to a Fat Tire bike frame and lacing in a hub motor seems like a considerably amount of custom work with special tools, or is the process less complicated than I'm anticipating?

 

[thetimmy]

There are not so many fat bike suspension frames on the market yet. Best I've seen was a mod of a DH frame, with custom swingarm to accomodate 4". John is right about fatbike tires being thin and weak to be safe at higher speed. I prefer to ride on a 3" that is good, than on 4" that is not safe to hit. A good 4" tire is a trial motorcycle tire, and I find it too heavy to build on motorcycle wheels.

A good fat bike with 45NRTH tires can ride 40 MPH safely with the extra weight of ebike components, that would be the max speed that you should target with a fat bike IMO. On good 3" tires I ride above 60 Mph everyday, and much safer than a fatbike at 40 Mph.

What I'm looking to build is very similar to the photo you posted, but I intend to make my bike look as much like a regular bike as possible, using a kit similar to this https://bmsbattery.com/ebike-batter...-panasonic-battery-torque-sensor-battery.html. Do did you write a post on your build?

 

[jimw1960]

I'm sure something like the new Salsa FS fat tire bike would handle a pothole at 35mph. Kinda pricey at $5,000 though.
http://dirtragmag.com/first-impression-riding-salsas-full-suspension-fat-bike-the-bucksaw/

 

[wesnewell]

None to the frame. It's much stronger than a regular bike and rated for 300lbs. I used this rim for the rear simply because I didn't won't to use the original rear wheel in case I wanted to go back to a normal bike with it.
http://www.weinmanntek.com/Products/CHOPPER/DHL101.htm
And the original tires aren't thin. In fact they are a lot thicker than a regular bike tire. I'd have no trouble with running them over 40 mph all day long.

 

[MadRhino]

What I'm looking to build is very similar to the photo you posted, but I intend to make my bike look as much like a regular bike as possible, using a kit similar to this https://bmsbattery.com/ebike-batter...-panasonic-battery-torque-sensor-battery.html. Do did you write a post on your build?

That is my street bike, built on a Trek Session 10 Large DH racing frame. 3" X 24" tires on 65mm rims are fat enough and very reliable at high speed. You can't have a fat bike that is coming close to handle like that bike, I can put my hands in my pockets and let it coast at 50 Mph, even on a rough street. It beats motorcycles on a start, corner and brakes much shorter than anything I've seen in 40 years of riding.

 

[Drunkskunk]

A normal bike frame isn't designed to handle 35mph. Light motorcycles are built much heavier duty than a normal bicycle. Even a light weight moped designed for 30mph uses frame tubing many times thicker than a bicycle frame. That's not to say a bicycle can't go 35, but if you're going to use it like a light motorcycle, standard bike parts aren't going to cut it. You might start considering a custom frame. Either buying one of the various Ebike frames out there now, or building your own.

My bike floats down the road like a motorcycle. It can handle hitting potholes, bumps, curbs, logs, small cars. Having a suspension fork isn't enough for potholes. That will save the front wheel, but all your weight is over the back wheel, so when the rear tire hits, it impacts harder than the front wheel would have with or without the suspension fork. While a rear suspension is the best way to cure the problem, you can partially mitigate it by using a longtail frame that leaves your weight more centered on the bike.

Fatbike tires don't handle speed very well. MadRhino is having luck with 3" tires, but on the 4" 45Norths I tried, they were blistered and worn out in 100-150 miles at 40mph. That's only slightly faster than the other dozen or so other tires I've tried. Fatbike tires are made from extra thin rubber and soft sticky compounds. Very good for traction and braking, but very bad for surviving the road or lasting very long. I haven't tried any of the 26x3.5" Street tires like the Vee Speedster or the Boa yet. They might last a little bit longer, but they would be tiny on my bike.

There are more forks available now for fatbikes, but the list is still short and they're all expensive. You'll have even more options if you go down to 24" rims and use a 3" tire, or go for a 19" motorcycle tire. Many DH forks can handle a 24x3" tire.

 

[spinningmagnets]

Personally, I would not run a 4-inch fatbike tire over 30-MPH (50 KPH). These days, we can find 3.0 and 3.5-inch bicycle tires (along with a bigger selection of the 4.0-inch "fatbike" tires).

For 35-MPH on the street (and potholes), I would go immediately to 19-inch moped rims and tires.
https://www.electricbike.com/moped-rims-tires-hubmotors/

 

[MadRhino]

...

My bike floats down the road like a motorcycle. It can handle hitting potholes, bumps, curbs, logs, small cars.

Hehe, with a Super Monster T you can ride over much smoother than hitting them small cars. 8)

 

[markz]

I dont understand the people who want to go 60mph on a bicycle, it boggles my mind it really does.
I understand the need to blend in and be able to ride bike paths without heads turning.
I agree you need moto rims/tires, but at that speed just get a motorbike/scooter/moped that is built for it, otherwise I think a downhill frame is the next best thing.
I never really looked at fat bikes, but when I posted get a downhill frame I thought they sold them in fat bikes, but thinking back on it now I doubt they do.
Its easy enough to swap out the front fork, then theres the rear linkage which would have to be custom made.

Thats what you should do, custom fabricate a new rear linkage that is wide enough for your needs and put on a fat bike front fork

 

[MadRhino]

Thats what you should do, custom fabricate a new rear linkage that is wide enough for your needs and put on a fat bike front fork

Yep, but this can be some fancy fabrication on some bikes...



For the fork, I would definitely find an old Monster T. With the most common "M" lower clamp, it does clear a 4" tire and it is a much better fork than any fatbike specific.

 

[thetimmy]

None to the frame. It's much stronger than a regular bike and rated for 300lbs. I used this rim for the rear simply because I didn't won't to use the original rear wheel in case I wanted to go back to a normal bike with it.
http://www.weinmanntek.com/Products/CHOPPER/DHL101.htm
And the original tires aren't thin. In fact they are a lot thicker than a regular bike tire. I'd have no trouble with running them over 40 mph all day long.

Did you post a link to your build? What frame did you select?

 

[wesnewell]

No, I didn't post a build thread. Here's a pic of the rear wheel.

 

[thetimmy]

Thank you all for the great information!

I'm impressed with the different eBikes several people have built and shared with on the forum.
It appears that almost all of the bikes that meet my performance guidelines required serious modification as a matter of necessity not desire.
Does anyone here want to post an estimated cost-to-build for their eBike?

 

[thetimmy]

Dual Drive HIgh-Torque & High-Speed: Why haven't I seen this?

My initial thoughts for building an electric bicycle was to build a dual drive system.
The front wheel would be high torque but with a low speed, activated by a PAS only and it would max out at about 15MPH.
The rear wheel would be high speed, low torque and would be activated in addition to the front wheel drive system when high speed was appropriate.

I have not seen any builds like this and I was wondering why that was. I know there are significant downsides, such as having to duplicate several components, but it would appear that having two different motors would have some advantages. I have seen several dual drive eBikes that utilized the same motor for the front and rear, like like this https://www.youtube.com/watch?v=bvo5557cX48

 

[MadRhino]

2 WD bikes are typically made to ride extreme loose terrain at lower speed. On snow, mud and sand they can do better than a RR motor alone, yet that is a very different situation when it comes to proper handling and cornering at high speed.