20" vs 26" bike wheel, what's best?

[Chalo]

It turns out my local bike shop does not carry axles, he said too many types they just special order them.

That's poppycock. 9 and 10mm hollow axles and 3/8" solid axles are common, cheap commodity items that fit 90+ percent of hubs out there. There's no excuse for a bike shop not to keep them on hand. The same goes for bearing cones.

Anyway, I reiterate that cassette hubs don't bend or break axles like freewheel hubs do.

 

[sendler2112]

Looking around Walmart yesterday to see if they happened to stock a V2100, I see many of the cheap mountain bikes are now.... 27.5"

 

[spinningmagnets]

On trash day after Christmas, there will be thousands of 26-inch BSO's on the trash heap, waiting to be picked up. If you happen to need parts for a project. Also BMX's with 20-inch wheels (for a trailer?)...

 

[John in CR]

I don't know if anyone will build a standard axle and torque control that will work for really high power. Frame mounting must be stronger too.

If you're talking about mid-drive, use motorcycle parts on the drive wheel. As far as hubmotors go, mine has a 1" axle with 15.5mm between the flats. For motor mounts of mid-drives, if you're using a compliant bicycle suspension, then the motor has no place being on the frame. The torque should be anchored to the swingarm with the ideal being in the pivot point. With the motor in the frame you get excessive squat on acceleration and brake dive with regen, but anchored to the swingarm you get anti-squat on acceleration and some rear squat to fight brake dive on regen. It feels different enough that it is strange at first, and the effect increases as the height of the pivot point increases.

 

[slowhands]

It turns out my local bike shop does not carry axles, he said too many types they just special order them.

That's poppycock. 9 and 10mm hollow axles and 3/8" solid axles are common, cheap commodity items that fit 90+ percent of hubs out there. There's no excuse for a bike shop not to keep them on hand. The same goes for bearing cones.

Anyway, I reiterate that cassette hubs don't bend or break axles like freewheel hubs do.

It sounded odd to me. It was Rick the owner, too. Maybe they just want to sell me a whole bike if a part breaks, huh? No matter, I just tore into a junker and got what I needed. I'm new at this, but it's fun to put stuff back on the road, err, trail.

I can see why Freehubs are sturdier. The drive side bearing is closer to the end of the shaft, instead of in the middle, yielding a much shorter bending moment. Shimano did a nice design change, too bad they trademarked the term Freehub and patented the bearing design. I guess you have to license from them.

 

[slowhands]

On trash day after Christmas, there will be thousands of 26-inch BSO's on the trash heap, waiting to be picked up. If you happen to need parts for a project. Also BMX's with 20-inch wheels (for a trailer?)...

I notice all the homeless types here seem to cruise around on mountain bikes. Maybe they will get new used ones for XMAS. My fav is the guy with a kiddie trailer for his dog. They go everywhere, and the dog seems to like life on the road. Hope they are warm this year... It's a tough life.

 

[Ohbse]

Some very interesting discussion going on in here. I do not have any hands on experience with 20" hubs, however I have just purchased one of Justins 3d drilled rims to re-lace my HS3540 from my first bike into. I imagine I will be picking up one of those trashed BMX frames post christmas and putting together something cheap and cheerful out of the various spares I've accumulated just to try it out (and practice my wheelies)

One thing I see mentioned a number of times though is a bit of a pervasive myth that's not just limited to the Bicycle realm. Bigger tires do not increase the size of your contact patch. All things being equal, a 20" rim and a 26" rim will produce the same amount of rubber touching the road. Chalo nailed it when he mentioned casing distortion being less on a larger wheel to achieve the same contact patch and that's actually one of the key disadvantages IMO of the smaller wheel. You have to run higher pressure at a given load to achieve acceptable performance. If you run too low the physical tire distortion can lead to flats, overheating etc. The larger rim has the opportunity to run lower pressure if so desired, but even at equal pressures the shape of the contact patch will be longer rather than wider. Same total area, just shaped differently. This should result in better braking, straight line stability and potentially better handling as the casing distortion could result in some unwanted behavior. That might go some way towards explaining why the bigger wheels are better in the specific areas previously called out.

Bigger wheels are better on bicycles, that much is apparent after significant R&D by many people. What's also just as clear is that hub motors in small wheels are significantly better than in large, as far as producing useful thrust efficiently. In there somewhere is a happy compromise for all of us. For some, that thrust is the key driver - for others the performance as a bicycle. Like many things, there is no right answer here for all situations.

 

[dogman dan]

Assuming that the use is street, and the rider will not be pedaling up any more than 10% of the wattage, Perhaps there's good reasons why a moped uses this size?

http://www.monsterscooterparts.com/2-25-17-scooter-tire-tread-3108-innova.html

17" is the actual rim size, so not far from bike 20" I'd think. Eventually I'll be lacing up my 5304 motor for this moped rim. Or an even more powerful muxus, if money should fall from the sky.

But a completely different set of requirements, when the bike is low power, the rider will provide more than 50% of the wattage. Or, you need a big tire to roll over logs, or good size boulders easier.

 

[sendler2112]

The main reason motorized scooters and such use small wheels is cheap price and packaging to fit under seat cargo in the rear.

 

[MadRhino]

17" is the actual rim size, so not far from bike 20" I'd think.

Actually it is right in between a 20 and a 24. A good compromise for the street, dimension wise. The weight is another story, but I guess that when one decides for heavier wheels he knows the pros and cons. I would probably like the motorcycle tires myself, if I was living where tires can catch a hundred thorns a day. :wink:

 

[dogman dan]

Maybe the 16" then. A more durable tire would be nice for a bike I'd tend to ride 35 mph on the street. Not so many thorns there, but plenty of sharp rocks, chunks of random metal, the usual glass.

Off road, always 50-100 thorns in my tire, but sticky knobbies only last at most summer riding season. I want that ride to have a light 26" wheel. A 10 pound hub motor bad enough already.

 

[thundercamel]

I am choosing to revive this thread instead of starting a new one. My interests are purely from an electrical efficiency standpoint, since my bike pictured below has both a 26" and 20" wheel anyway.

My Lynx recumbent and my friend's bikeE recumbent currently have an identical ebikeling 11.6Kv motor, and identical power meters. I have a 40 amp square wave controller, while he has a 26 amp sine wave controller. Also more obviously I have a 26" rear wheel vs. his 20" rear wheel. The simulator shows that at cruising speed the efficiencies and power draw differences are negligible. On the trails we ride there are enough crossroads (start and stop) to make his energy consumption about 80% of mine. You could argue that I'm getting out of shape :lol: and the 40 amp controller doesn't help, but thankfully the upright bikes we've road many times before always had similar power consumption. I think the real game changer is just the 20" wheel.

I originally planned my recumbent with a 20" front motor so that I could use an internal geared hub, similar to solarEbike's setup. The 26" rear 11.6Kv motor is in place because that's what I already had available to use. The first simulator image below suggests that a 4T 13.16Kv 20" front Leaf motor would be more efficient throughout at full throttle. Taking this concept further, a Mac 6T would be even more efficient yet, if they're even available with a 100mm front axle.

My question for Endless Sphere is can the Mac be more efficient than the Leaf even with the geared reduction sapping some of that efficiency? I may purchase a front motor and have a 2WD setup to test with, but I don't like the thought of geared reduction maintenance and noise. Also we keep finding broken 80mm spokes broken on the 20" radial bikeE setup. I assume we just aren't getting them tight enough...

My Lynx:

My friend's bikeEbike:

Current 26" ebikeling vs. Leaf 4T 20":

Leaf 4T 20" vs. Mac 6T 20":

Current 26" ebikeling vs. Mac 6T 20":

 

[neptronix]

Having had both, the leaf is gonna be significantly more efficient all around.. and more powerful.

In a 20" wheel, the loss of watts to rotating gears scales faster than the eddy current losses of a motor that wasn't particularly designed for a 20" wheel.

To reduce the eddy current losses of a DD in a 20" wheel, you can simply pick a smaller motor if you don't need a big leaf.. a 30mm leaf or 27mm 9C will have very impressively low eddy current losses.

I like the idea of using a 22" BMX rim ( 18" moto size ) as a wonderful compromise between the two wheel sizes.

 

[MxusMick]

Hello, I have 2 ebikes, both have a larger front wheel and smaller rear hub motor. I love the ride! The first has a 26" rear hub motor and 29" front wheel, full suspension. My other ebike has a 20" rear hub motor and 26" front wheel, also full suspension. On a 36v battery the smaller 20" is slightly faster than the 26" on flat ground at top speed with better exceleration. Honestly, the nimble handling of the 20" rear/ 26" front is much like an Ewok flying carpet!

 

[MxusMick]

Dudes, I scored a full suspension Motobecane DS 700 off the curb today, I love 'Heavy Trash' week! I removed the rear wheel 26" and slapped on a rear DDhub20". I am thrilled it pedals well with enough clearance, super mushy frame, I needed a bike for the wheel(1000w 20"). Cant wait to get a controller and throttle hooked up. It still has the 26" front wheel, I love the posture and ride with smaller rearwheel and larger frontwheel.

 

[Voltron]

If you go fast enough, the people staring because it looks funny will all be behind you.

I liked mine enough that it evolved like a Pokemon where everything changed except the motor! Managed to squeeze a 55 tooth front sprocket on, so could still pedal up into the 30s....