Helping wife back on to bike after pregnancy

[WattsUp]

Sorry if this is covered elsewhere, but I'd like to convert my wife's mountain bike so that she can join me on rides. I'd really appreciate people's thoughts.

Background: We used to ride a tandem and go distances of about 20-30 miles calling in at a pub if possible. We did a 100 mile race, but that wasn't the norm. I'd like us to be able to go 50 miles though, but it is very flat around here. My wife gave birth to our daughter 18 months ago and we haven't been out cycling since her pregnancy. Her being able to get exercise on a ride without her getting weary would be great.

First pass at requirements:

• Speed: she'd like to get some exercise, but at an amount she can control and able to go up to 25mph on the flat whilst putting in a fair amount of effort herself. I have a road bike and can maintain this speed on the flat for a fair distance, so it would be a good match.
• Range: normally 30 miles, sometimes 50 miles. To avoid full discharge, I guess a full range of 65 miles would be a good marker. She would be contributing, but it would be good if the bike could do that range on the flat, 15mph and no assistance from her.
• Safety: really important for obvious reasons. That said, she isn't a scaredy cat.
• Child seat: we'd like to have a child seat on the bike to allow are daughter to come along and enjoy the views etc.
• DIYness: I'm an electrical engineer so not scared of getting involved and would prefer a DIY approach

My thoughts so far:

• Base bike: Specialized branded mountain bike (15 years old) with cantilever brakes
• Tyres: 26" slick type tyres for mountain bike rims. Gatorskins if they come in this size would be good as that is what we have on the tandem
• Motor: 250W hub motor. I don't know what 'brands' are OK, but I'm far from a brand snob and prefer the value a well made Chinese 'branded' product can give
• Controller: Powerful enough to cope with 500W for hills etc (holidays). A lever on the handlebars to control the amount of assistance and then a crank based speed sensor would seem a good starting point. I expect to upgrade to a crank torque type arrangement I have an idea for a DIY approach, but that is for later.
• Battery: Thinking of 2x 20,000mAh MultiStar LiPos in series giving 44V x 20Ahr
• Weight: Rider ~63kg, Passenger ~20kg (not yet)

What mistakes am I making with my initial thoughts. I'd love to have the opinions of others and any experiences they have had. I have no idea which motors are highly thought of.

Sorry for the long first post, but I think I have included everything and this could turn out to be a popular theme.

 

[Wicky]

"able to go up to 25mph on the flat" "65 mile range"

Above 15mphish she'll have to pedal with out assistance assuming its a legal pedelec , as there's no drain on the battery at that rate of knots then it will have unlimited milage.

I think you both need to take some test rides to get a better idea of what a legal pedelec is capable off. As your speccing moped type performance from a souped up mountain bike.

 

[WattsUp]

Hi Wicky, thank you for your response.

The 65 mile full range would be for a cruising speed of 15mph without her assistance and on the flat. The 880Whr battery configuration I mentioned would be enough to power 200W for about 3.5 hours at 75% efficiency. That would get near 50 miles. This calculator (http://www.electricbikerange.info/Electric_bike_range.html) seems to think it would be 190W at 15mph.

As for the speed, there is no way she could ride at 25mph unassisted, so I guess that becomes only theoretical then. Theoretically, 250W + 100W from her would manage about 22mph I think? Is that about right?

If we lived somewhere hilly I could be struggling up the hills at 15mph and she could be at full power keeping up.

 

[Woosh]

Hello WattsUp,

You may not save much money doing a conversion.
A 17AH battery (600WH) is about the optimum capacity, weight and cost at the moment compared to an 800WH battery.
I reckon at her weight (63kgs), on a lightweight road bike like the Woosh Karoo with 17AH, she can get 120 - 140 assisted miles.
http://wooshbikes.co.uk/?karoo
On a crank driven MTB like the Woosh Krieger (if your wife is less than 6ft tall) or the Woosh Bali with 17AH, she can probably get 70-80 assisted miles.
http://wooshbikes.co.uk/?krieger
http://wooshbikes.co.uk/?bali
The Krieger is slightly more expensive because it has a gear sensor fitted.
If you want to fit a child seat later, then take a look at the crank driven step through Woosh Santana CD.

 

[GLJoe]

25mph on the flat ... I have a road bike and can maintain this speed on the flat for a fair distance, .

Hi Chris. Its great to have you join this forum!
How's the tour going? If you have too many of those pesky yellow jerseys at the end of the comp, I'm sure a few of us here are up for a freebie ;-)

(although something tells me not many people here would actually be able to get one to fit!)

 

[Deleted member 4366]

Do you already have the lipo chargers and other equipment for them. If not, I wouldn't use them. They won't work out any cheaper in the long term and they're heavy compared with normal E-bike batteries.

You can make a very nice conversion with a Q128C motor and a PSWPower 20 amp controller. Using the 36V 201 rpm motor at 48V, you get fairly comfortable cruising at 22 mph on the flat. It maxes out at about 25 mph (26" wheel), but the power ramps down after 22 mph, so you'd have to work harder to go above that speed.

A 12Ah 48v battery will give about 50 miles at 15 mph if it's not too hilly and the rider isn't too heavy. Cruising at 22 mph, the range would drop to about 20 miles. These figures are a very rough estimate, because I have no idea how hard the rider wants to pedal, which makes a massive difference. If that range is a bit low for you, you can get bigger batteries, but then there might not be room in your triangle for it and you pay the penalty of the extra weight.

These people have some nice 48v batteries:

http://eclipsebikes.com/index.php?cPath=30_31&osCsid=df6cc21739e51866c3c20e188df9e13d

You get the Q128C from BMSBattery.com and the controller from PSWpower.com. BMSBattery have a range of batteries that include 18A and 20A controllers and the rest of the kit, which makes a very simple installation.

Other possibilities are the Bafang BBS01, BBS02 and BBSHD, depending on how much power you want. Their installation is very straight forward. I prefer hub-motors for road use. They're quieter and more user-friendly.

 

[Woosh]

is it not a bit of an overkill to select a 48V 20A system for someone who weighs 63kgs and could previously pedal at 25mph on a push bike?

 

[Deleted member 4366]

is it not a bit of an overkill to select a 48V 20A system for someone who weighs 63kgs and could previously pedal at 25mph on a push bike?

No.

 

[Woosh]

No.

I don't understand you most of the time.
This thread is in the legal EAPC section of the forum. I know that the law is more lenient with kits but do you have to help people breaking the legal speed limit?

 

[Deleted member 4366]

I help anyone that asks. I don't judge what they do.

 

[Woosh]

I help anyone that asks. I don't judge what they do.

I get that. The forum has a section for off-road vehicles for that reason, where legal speed limit is not an issue.

 

[Trevormonty]

My issue is donor bike, 15yr MTB with Vbrakes, front shock is likely to be shot. Kits are great if starting with good donor otherwise factory new eBike might be better way to go. Larger wheels 700c or 29inch will be better at speed than 26".

Test ride a few new ebikes with different drives and styles you or your wife may change expectations of what is needed.

 

[Deleted member 4366]

I get that. The forum has a section for off-road vehicles for that reason, where legal speed limit is not an issue.

I can't reply to a post fron this section of the forum in another section. How will he know that myreply is for him. All I do is reply to posts. I don't look what section they're in, neither do I care.

Seing as your post is not about electric bike kits, you should have stuck it in another section of the forum, or stick it in your pipe and smoke it.

 

[anotherkiwi]

If you really want to use LiPo it is best to use 4 x 12 Ah because if you want to look after them and charge to 4.15 per cell and discharge to 3.65 you need 24 Ah nominative to have your 20 Ah usable. And paralleling two 12 Ah packs then serial connecting will give you more oompf when you need it (20 C instead of 10 C). 44.4 V is definitely the way to go, I have 20 Ah 37 V at the moment. If you are investing for the long term I can't say enough nice things about Graphene which leave the Multistars in the dust (I have both).

I agree with @Trevormonty about the host bike (he is from NZ and so should know better English, donor gives, host takes...) at least swap out the front brake for a Magura hydraulic.

If you really want to go fast on the flat with a hub motor you need to up your voltage to at least 52 V, maybe 60 V. You could look at a mid drive like the 25 Amp 250 W Bafang BBS02 sold by em3ev, with that your top speed is just a question of gearing (and setting the limit via the LCD) and you can parallel a couple of 36 V batteries to get the Ah you need for the range desired.

 

[Woosh]

Seing as your post is not about electric bike kits, you should have stuck it in another section of the forum, or stick it in your pipe and smoke it.

I sell kits, for example the XF08C or BPM or SWX02 or BBS01B or BBS02B or GSM with 13AH or 17AH battery that are suitable for his bike but I thought he should also check out what is available ready built because the saving is not much and the donor bike is not perfect.

Hub kits;
http://wooshbikes.co.uk/?hubkits
Crank drive kits:
http://wooshbikes.co.uk/?cdkit

 

[Woosh]

If you have access to cycle to work schemes, consider buying a high end bike on the scheme and add a kit to it.
This is a brand new Cube fitted with a Bafang BBS01B kit. It has Rockshox Paragon Air suspension, SLX components etc.

 

[WattsUp]

Hi all, sorry for the delayed response but I have been away from home.

She was never able to do 25mph, but that is my top end on the flat for any meaningful distance so that is why I thought it would be a good upper limit. No yellow jerseys, but I used to have sideburns which added at least 2mph.

Whoosh: Thank you for the ebike suggestions, I prefer the DIY approach as I like to be hands on and I can then upgrade things without too much of a penalty. A nice looking Cube conversion.

Trevormonty & anotherwiki: Good points on the frame. The bike frame is fully rigid so no worn out shocks to worry about. I was thinking I'd have to upgrade the front to a disc brake. I'll see what cycle to work scheme might be available, but I could always move the bits over later.

d8veh: Thank you for the battery information. I have a quadcopter etc so can use the chargers etc associated with that. I like that the battery could be retired into a boarder range of options if it is a LiPo. I don't know what sort of cycle life to expect though from LiPos. The cost of a battery scares me unless it is something I'm more familiar with and could think how to use on something else.

A more general question. Should I be considering a front or rear hub motor. I think it is a six speed cassette at the rear.

 

[Deleted member 4366]

Definitely a rear motor. A front one will spin the wheel at the power you need.

6-speed is probably a free-wheel, but you need to check. Q128cis the cassette motor. Q128H is the free-wheel one, which is more powerful.

General consensus is 250 cycles from lipos, but I think most get bricked by user errors before they get that far. E-bike batteries are 500+ cycles, except heavy LiFePO4 ones go 2000 cycles and lithium titanate goes forever.

 

[WattsUp]

Thanks d8veh, very useful. That lack of cycles will be a pain with lipos, but a full cycle each week (which would be good going) would still last 5 years, if not bricked sooner.

I'd like to start with a 250W motor. I know the performance will fall short of what I had hoped for, but a good start. Can you suggest a compact but well regarded 250W hub motor?

 

[anotherkiwi]

Q128C with 12S LiPo would be my starting point.

Graphene packs are given for 600 cycles and so far I have no reason to believe that isn't true. Yes they cost more, yes they weigh a little more but they pack a punch, charge faster and are absolutely puff free in e-bike usage.