Help! Mid-drive conversion, losing those front gears.

[Brent533]

Hi guys. I am looking at converting my friends mountain bike with a mid-drive conversion. However they are concerned about going from 3 chain rings down to 1 and therefore 21 gears down to 7.

Anyone who has done this; how do you get on with less gears? What size chain ring do you run at the front?

Thanks

 

[guerney]

I've only ever had 8 gears on my (bbs01b converted) bike, and with a 52T chainwheel to 32T-11T rear cassette, it copes with all of the steepest hills I have found so far... but that being said, it was a light bike before conversion (10.7kg or 12kg, unsure) plus endless extra bits, and I now only weigh 10 stones; having lost over 2.5 stones (through slow jogging, not cycling), therefore a much heavier rider might not manage without a 42T or even smaller - I've heard tale somewhere of 38T and smaller Bafang chainwheels.

 

[Nealh]

I am terrible on hills and usually have a very low 36 or 42t gear at the back and also have used a double front ring set up, 32t is lowest that is acceptable on a bbs.

 

[guerney]

I really couldn't ride my bike if it wasn't electrified, not for long even on the flat - just 5 miles would exhaust me, hills were impossible but 16wh per mile defeats every incline. Suddenly I have superpowers

 

[Nealh]

The chain line with a bbs or tsdz isn't always good so even with a double one may not be able to use all gear options, on a mtb I converted cross chaining wasn't an issue.

 

[matthewslack]

Hi guys. I am looking at converting my friends mountain bike with a mid-drive conversion. However they are concerned about going from 3 chain rings down to 1 and therefore 21 gears down to 7.

Anyone who has done this; how do you get on with less gears? What size chain ring do you run at the front?

Thanks

Unless the target terrain is extreme mtb, then it should be fine by choosing the lowest low gear setup that will gracefully fit.

For example, a cassette with 46T low end, smallest chainwheel and the secret weapon if the wheel allows, is chuck the 7 speed and go to 9 speed.

 

[flecc]

However they are concerned about going from 3 chain rings down to 1 and therefore 21 gears down to 7.

They'll be ok so long as the territory isn't extreme. No-one actually has 21 gears since many of the sprocket pairings are just duplications.

The gears chart below I produced using a common front chainwheel setup of 32-44-52 teeth and a Shimano 8 speed cassette. The the sets of green bars are a horizontal graph of the gears ratios for all three chainwheels. The outcome wouldn't have been much different for any other choice of chainwheels and cassette.

Look how many of the R/H ends of the green bars are the same on all three chainrings, 5 sets of 3 lined up,all duplicated or triplicated gear ratios, leaving far fewer than 24 actually different choices: (click it to enlarge)

 

[georgehenry]

I still have a 3 chain ring set up on my acoustic hard tail mountain bike. With such a set up I was taught to keep the chain in the middle area of the cassette where ever possible to reduce wear on the chain and use the three front chain rings to accomplish this.

My hard tail electric mountain bike has a single narrow wide front chain ring paired to a nine speed cassette, 12/36, and with the extra power of the electric crank drive this gives a wide enough range for the off road routes I use and a good turn of speed on the road when I think I need it.

I have discovered that with my current 42 tooth chain ring I do not have low enough gearing in my 36 tooth bottom gear for the steeper/technical more demanding mountain bike routes in my area.

I have been contemplating swapping out the 42 tooth chain ring for a 38 tooth one in tandem with swapping out the 14 tooth and 12 tooth top gears with 13 tooth and 11 tooth ones. Using a gearing chart from the internet, an invaluable tool of reference when playing with your gearing, this would give me me 10% lower gearing for climbing and retain the ability to occasionally hold speeds in the 20 to 25 mph range on the road.

If I need wider gearing still, then my 2015 Yamaha motor allows for a double front chain ring. Though I do like the simplicity of my narrow wide single chain ring set up.

I also have two rear hub electric bikes from 2011, still working well and really good work horses for hauling shopping back up a steep hill from town. One of those has a 7 speed/ 52 tooth chain ring and unrestricted throttle and works really well.

 

[TJS109]

Hi,
I fitted a TSDZ2 with 42T chain ring to my old Dawes hybrid going from 21 gears to 7.
Hills are not a problem, it does have a wide ratio low gear but I rarely have to use it.
Originally I overrode the max speed limit to about 20Mph and you have to pedal quite fast to achieve this so max speed might be a problem. I have set it back to the legal limit now as I only potter about and it is fine at this speed.

 

[guerney]

Fast was far to frantic a pedal with 42T, so I tried a 48T then settled on the 52T because it's an all rounder on my particular bike. I should sell the 42T and 48T (got the 42T as part of the kit and 52T for free). I stick to the legal limit - I just like the leisurely cycle feeling of the 52T at 14 to 15mph.

 

[egroover]

I run a 42t front and Sunrace 9 speed 11-40t rear cassette on my bbs01 250w 36v Boardman conversion, never had to get off and push yet and I've been up some very steep hills including off road
Chainring here

Lekkie Bling Ring alternative 42T for Bafang BBS01/2 - £31 del.

Hi all In the quest to improve the chainline and to give a lower gearing compared to the stock Bafang 44t chainring, I have been looking for a cheaper alternative than shelling out £70+ on a Lekkie Bling Ring and found this on Aliexpress for £31 delivered inc VAT...

www.pedelecs.co.uk

 

[guerney]

I run a 42t front and Sunrace 9 speed 11-40t rear cassette on my bbs01 250w 36v Boardman conversion, never had to get off and push yet and I've been up some very steep hills including off road
Chainring here

Lekkie Bling Ring alternative 42T for Bafang BBS01/2 - £31 del.

Hi all In the quest to improve the chainline and to give a lower gearing compared to the stock Bafang 44t chainring, I have been looking for a cheaper alternative than shelling out £70+ on a Lekkie Bling Ring and found this on Aliexpress for £31 delivered inc VAT...

www.pedelecs.co.uk

I was wondering how you were getting on with that egroover, good to hear it's working well for you - I might try to find a 60T of the same if I can, for a bit of occasional extra speed after the PAS stops at 15mph. There aren't too many very steep hills where I live, mostly avoidable.

 

[egroover]

I was wondering how you were getting on with that egroover, good to hear it's working well for you - I might try to find a 60T of the same if I can, for a bit of occasional extra speed after the PAS stops at 15mph. There aren't too many very steep hills where I live, mostly avoidable.

Wow 60T chainwheel! Step aside Chris Hoy there's a new kid in town lol

 

[guerney]

Wow 60T chainwheel! Step aside Chris Hoy there's a new kid in town lol

Lol for some reason I've retained the unhealthy mental mentalness of my younger days when I was last cycling on my racer in the 1980s, the pandemic forced me back to cycling and now I'm hooked - I literally got withdrawal symptoms when I killed my controller and had to await delivery of a replacement, but I've got a spare controller now in case it happens again to avoid all that lack of sleep and pacing about exhibiting nervous ticks. I shouldn't look too hard at the 80T either, but it's this totally pristine recently resurfaced "A" road which runs downhill completely straight for 2 miles near whereI live, that every time I cycle down at 33mph+ I think "I could be doing over 50mph! If only I had a bigger chainwheel..." On the other hand I don't have a deathwish, and I really shouldn't look at this for too long:

Alligt chainwheel 60 BCD (Bafang Motor)

 

[jimriley]

I have 7 speed 13 / 34 on the back, with 42t on front. Bbs01b came with a 46, not enough low end grunt for some bits of local bridleways and tracks. It can fly along at 25mph top if I up the speed limit. Altering other settings like Keep Current and setting the throttle to Current Control made a big difference, using more ah but a better ride. Editing the settings needs a special usb lead and a program for n a Windows laptop, or the Speeed app on an Android phone.

 

[vidtek]

@Brent533
I use an aluminium frame Specialized Crossroads 1980's vintage fitted with a mid-drive TSDZ2. The 42 chainring that comes with the kit replaced the original three chainring setup.

You don't say what sort of rider your friend is.
He could be:

1) A 9 stone lean lycra lout, head down over the handlebars oblivious to his surroundings concentrating on getting the last little bit of speed from his bike​

2) A middle of the road fit person about 10-11 stone enjoying the downhill runs and just wants help up the hills.​

3) A 19 stone fattie sorry politically incorrect slip-up there....​

4) An old fart like me that poodles along at 6-12mph and looks at the views and just enjoys his bike ride, never going much over 15mph.​

​

The single 42t chainring is adequate for flat propulsion up to 15mph. Much more than that and your feet are flying round like a demented mouse on a treadmill. I've just fitted a 9 gear cassette, new chain and shifter/cables and it's as smooth as silk.​

​

You need to tell us about your friend and his peccadillos!​

​

Cheers, Tony.​

​

​

 

[AndyBike]

Mine is 12 speed 11-51 on a single 34t chainring. But to be honest ive yet to use any more than about 6 gears. usually about 13-24t,maybe 28t on the cassette cogs.
Be losing the bigger chainset, plus the front derailleur plus the front shifter you'll also shed a fair bit of weight, which is good for battery range(I think)
So if you set up you're mates bike for as Vidtek says to a usual usage, you wont overdo its capabilities,and capitalize weight savings overall.

Because of the usage mine is getting after 6 months of use, Im changing the rear cassette from a 12spd 11-51 to a 10 spd 11-36, which for my shopping runs and pottering about quiet roads etc is more than enough.
Plus with the change of mechs from XT-290grams to a Sram OX-190 grams, and the 10spd XT cassette 294grams from the Shimano Deore 593 grams. Im making a weight saving of about 400grams thats over 3/4lb just on losing 2 cogs, which ill probably never notice.
Admittedly im more high end spec which is usually lighter, but by losing those extra rings and all as mentioned you could be making a good weight saving too. And if my experience is anything to go by, i doubt he'll notice the loss. The motor makes up for removal of the lower speed gears.

 

[georgehenry]

Not completely prompted by this thread as I have been contemplating it for a while, but I have just put an order in for a new narrow wide 38 tooth chain ring.

This will lower my gearing by 10% and it will be interesting to see what effect this has in the steeper more difficult routes I have available in my area.

By replacing the two top gear cogs. 8 and 9, with ones with one less teeth respectively on each I will retain the ability to travel as quickly as before on the road which every now and again is useful.

So win, win, 10% lower gearing at the bottom and the same gearing as before at the top.

However as we all know there is no such thing as a free lunch and those two higher gears with less cogs will wear out real fast if I shove too much power through them for too long.

If I decide I need still lower gearing, Sunrace do 9 speed cassettes with bottom gears with up to 50 teeth on them.