New E-Bike Conversion - 26" vs 29"

[Vonkrumm]

Hi guys,

I'm about to purchase either a 26" or 29" MTB, each one with a 68mm bottom bracket.
And I'm not sure whether to go hub or mid drive just yet.
So I guess the question is, can I just purchase the bike and figure it out later?

I want the 26" to avoid issues, but it's not in yet.
The vendor I'm looking at doesn't have 29" hub motors (em3ev), but I'm sure I can get one right?

I'll post pictures after for anyone who is interest, but in the meantime I just need a god damn bike

 

[Chalo]

I'm about to purchase either a 26" or 29" MTB, each one with a 68mm bottom bracket.
And I'm not sure whether to go hub or mid drive just yet.
So I guess the question is, can I just purchase the bike and figure it out later?

26" bikes are inherently sturdier and cheaper, all else equal, than 29" bikes. There is a better selection of e-bike appropriate tires and rims in 26" than in 29". Getting the best motor efficiency and performance is easier with a 26" wheel than with a 29" wheel.

As for advantages of 29" bikes: They offer a nicer ride quality, all else equal, than 26" bikes. They are very, very slightly faster, all else equal, than 26" bikes. They look and fit better for tall riders.

I'm 6'8" tall. For me, there is no question that I prefer 29" for a pedal bike, and also no question whatsoever that 26" is better for an e-bike.

 

[Sunder]

I'm 6'8" tall. For me, there is no question that I prefer 29" for a pedal bike, and also no question whatsoever that 26" is better for an e-bike.

Can you explain why 26" bikes are better for eBikes?

Is it just because they're sturdier?

 

[arkmundi]

It doesn't matter that much anymore. I'd get a bike based on how much you like riding it under the conditions you expect ride it in. Lots of choice these days. Go to http://www.trekbikes.com/ and see their offerings, even if you don't buy a Trek. They've put together a very nice web site to make choosing from the plethora easier. Has to fit your riding style and budget.

That said, I ride a 26" Trek Comfort bike - a Shift 3, recently purchased, specifically to take an EM3ev MAC 10T hub. But if you prefer a 29'er, then get that. EM3ev will mount a hub on an Alexrim for you, making it very easy. I'd get the DX32 rim because its the most rugged rim Alexrims makes. Paul used 13 gauage Sapim spokes, which are as good as it gets. Be sure to get extra spokes cut at the same time, for future breakage.

Larger wheels spin faster, so all things consider, a 29'er should be a faster ride.

 

[Chalo]

I'm 6'8" tall. For me, there is no question that I prefer 29" for a pedal bike, and also no question whatsoever that 26" is better for an e-bike.

Can you explain why 26" bikes are better for eBikes?

Is it just because they're sturdier?

Sturdier wheels, cheaper to buy equal or better wheel components or forks, easier to find fat tires and big rims, easier to get appropriate reduction ratios (electrical or mechanical). Less leverage on the fork, making the system stiffer and stronger from the same thicknesses, diameters, and materials.

 

[Sunder]

Sturdier wheels, cheaper to buy equal or better wheel components or forks, easier to find fat tires and big rims, easier to get appropriate reduction ratios (electrical or mechanical). Less leverage on the fork, making the system stiffer and stronger from the same thicknesses, diameters, and materials.

Got you. Thanks.

Because I came from a road riding background, I always preferred light, thin tyred, efficient geometry road bikes over mountain bikes - or even hybrids. The riding position just felt more "natural" if not actually more comfortable, the bike just felt like it could glide along instead of needing to pedal all the time.

However, my opinion has changed somewhat in the last few months after I swapped to the MAC motor, going a little faster, and the roads here getting worse, because of a high number of new constructions occurring on the road to work. (I see huge trucks and bulldozers there every morning).

Because I've spent so much on the bike to date, I'm loathe to switch to a mountain bike right now, but I'm think when these parts start wearing, the next one may actually be a high quality mountain bike will broad tyres.

 

[Chalo]

Well, one of the advantages of a 29er bike is that you can have fat tires and high ground clearance when that's appropriate, or skinny tires and lower ground clearance when you want to turn up the speed. It's all 700c, and 29er bikes fit all the tire sizes.

You can get racy 25mm tires for 26" bikes, but that combines the ride tradeoffs of small tires with those of small wheels. It's efficient but harsh, and the range of skinny tires in 26" is poor.

 

[Sunder]

Well, one of the advantages of a 29er bike is that you can have fat tires and high ground clearance when that's appropriate, or skinny tires and lower ground clearance when you want to turn up the speed. It's all 700c, and 29er bikes fit all the tire sizes.

You can get racy 25mm tires for 26" bikes, but that combines the ride tradeoffs of small tires with those of small wheels. It's efficient but harsh, and the range of skinny tires in 26" is poor.

I have been wondering what the widest tyre I could fit on my 700c x 19mm rim is.

It's not just the rim though, is it? It still needs to clear my frame.

Oh well. I guess I'll put up with it in part by running the lowest recommended pressure for the time being.

 

[Raged]

I disagree. 26" is more appropriate for ebikes maybe 1-2 years ago, but for a commuter (road/park/light duty bush) a 29er is more suitable with a geared hub motor. It's just the difference in manoeuvrability between wheel sizes and what you're comfortable riding at the end of the day. As a commuter, you don't need the agility of navigating tight switchbacks but you want the increased stability to roll over small bumps that a fat tire gives you - due to the increased weight of the bike. A 29er is the best compromise for a hybrid with the strength of an MTB and road speed close to a road bike.

A 29er rim is the same as a 700c rim with the difference in frame clearance. So you can swap to road tires easily if you really wanted to. That said, I'm am biased as I have a 29er =) I literally spent 2 months comparing the pro's and cons of both for commuting (coming from a carbon road bike) and ended up with a hardtail 29er with lockout front suspension so I could swap between and get the road bike stability when I needed to.

 

[dogman dan]

Used to be a 29er limited your selection of bikes. Still does, if you are shopping 5 year old used bikes.

No particular need to go 26", especially if you are a big tall guy.

Cheap walmart bikes will usually be too small in any wheel size. They are intended for 14 year olds in most cases.

 

[melodious]

1:9 ratio of 29er tires to 26er tires, if we're strictly talking wide MTB choices. There are 29er tire choices for every situation but you have to look for them. 26ers are practically shoved in your face. I'd have went with a Surly Troll in my Ebike choice than the Ogre. It's just easier in the long run, less thinking & planning. :wink:

 

[Vonkrumm]

Thanks guys, really helpful information.

I'll have one last look at getting the 26" but if it fails i'll go the 29". I'm 6'2" so probably sounds better anyway.

 

[Raged]

FYI : the 29er wheel from EM3EV is the 700c rim with Alex DM24 Disc. I was one of the first to get it and got it laced from them with Sapim Spokes (should have gone black instead of silver). If you get it laced from him, make sure you tighten the spokes before use. Theres usually 3-4 that get loose during transit.

Also, you need the DNP freewheel, grin torque arm and the disc brake spacer.

 

[Vonkrumm]

So I bought a bike.
Get it out the store, realise it has quick release drop outs



FML.
I was so happy. But I think I've done it now.



What are my options? Take it back?

 

[Chalo]

QR skewers are a feature of the wheels, not the dropouts. Nutted axles fit in the same slots.

If you use a hub motor, it will most likely have a nutted axle. And if you use a mid drive motor, QR wheels work fine for that.

 

[Vonkrumm]

So I'm all good for a rear hub?
That was my first choice, being a bit easier and a bit cheaper.

The only reason I stress is because I've read somewhere that as an alloy frame, you want pretty solid drop outs. Hence the concern with the vertical release slots.

(Sorry for the ignorance in cycling jargon and expertise, only learning).

 

[Vonkrumm]

Ok so maybe I've miss understood. Apparently the forks have nothing to do with the "QR skewers" ?

Sorry, wow crisis adverted. For some reason I thought that was so. All good

 

[Chalo]

You'll need close-fitting torque arms. That's independent of the dropouts on your bike. Even if the slots are infinitely strong, the motor axle will tear itself up without good torque restraint.

Remember that a 29er will put 10% more hurt on the axle/frame interface for any given amount of thrust at the tire, compared to a 26" bike. Another way to think of this is 10% less push from the motor for any given set of power components.

 

[Vonkrumm]

You'll need close-fitting torque arms....Remember that a 29er will put 10% more hurt on the axle/frame interface for any given amount of thrust at the tire, compared to a 26" bike.

Wouldn't there be less moment on the fork, because there is a larger distance between the axel and the wheel contact point (for a given torque/power rating)? :|
Probably wrong but.

Anyway, the torque arm. Got it, Thanks a bunch mate. Really appreciate your help.

Josh

 

[Raged]

Theres more torque because the distance is longer. Think how a breaker bar works and the only thing holding it in is an open ended aluminium plate. Thats why you need a torque arm.

 

[Vonkrumm]

The distance from the force on the ground (Thrust), to the fork/wheel fastening point, is larger.

Therefor for a motor with, say 500w, you'll have say 40nM of torque, say.
Then for a 29" wheel, you'll have 311mm radius (rim), so approximately 129 N Thrust.
For a 26" wheel, " " 279.5mm radius (rim), " " 143 N Thrust.

The reactive force on the fork will be roughly the same as the thrust on the ground, in the opposite direction. There will be other forces from the rider/gravity ect., but equal.
Yes I understand that a longer fork will increase the bending moment, but that is a matter of frame size.

Right?

 

[Raged]

I think you're mixing up the bike jargon. Fork length doesn't matter. The point of contact is the dropout (gap where the wheel goes into the fork). putting a hub motor in will put forces on the dropout that it wasn't designed to handle (the torque is big and the point of contact is small) which is why a 500-1000w geared hub motor will shred the dropouts (not the fork).

Either way, you're over-thinking it.

The question is whether you're doing trails or purely commuting? Flat road vs hills?

 

[MadRhino]

Mounting a motor on a suspension fork is not only about dropout strength, it is about fork function and maintenance. Even if you can make it strong enough to hold your motor, it will not function properly and will wear its seals quickly. I say if you want a motor on the front you should use a good quality rigid fork. If you want suspension on the front, build with a rear motor.

Wheel size makes a big difference: Larger wheels are using a lot of energy to accelerate and are weaker, but they ride good on the rough. Smaller wheels are robust, on a 26" rim you can easily find 2.7 wide tires that will make it 28" OD and that rides just as good as a 29er on the rough. Yet, it is a 24" wheel with a 3" tire that is making the best compromise for performance: Efficient, robust and riding fairly good on the rough.

 

[Vonkrumm]

When I say fork I mean the hardtail, A-Frame thing, like on the front, but on the back.

That pretty much confirms the 26 vs 29 thing. 29ers are "stronger" because they have a larger leverage for the fixed power/thrust to work from.

Yes the frame shouldn't have much to do with it, unless a failure mode existed half way along those four truss', that was weaker than the torque at the drop out.

If that's not the case, then frame size is irrelevant and it's a matter of the reactive moment at the drop out.

 

[Chalo]

That pretty much confirms the 26 vs 29 thing. 29ers are "stronger" because they have a larger leverage for the fixed power/thrust to work from.

The opposite. The same torque from the motor becomes less push (slower acceleration, less climbing ability) when you use a larger diameter wheel. The larger wheel diameter results in higher speed, but only if you have enough power to support that speed. Otherwise it could have both slower acceleration and lower top speed with the larger wheel.

That's one of the reasons I think 26" is better for e-bikes, even though I prefer 700c for pedal bikes.