specialized sirrus

Electrically assisted bikes, trikes, etc.
theballboy
Posts: 6
Joined: 2 Jun 2020, 10:25am

specialized sirrus

Postby theballboy » 2 Jun 2020, 12:18pm

Anyone converted a Specialized sirrus hybrid?
I have that as an option for donor bike (but not sure of bottom bracket size if anyone can signpost)

Im looking at a bafang mid motor 1000w with 52v 17ah - frame is steel but forks carbon
Would have preferred suspension in the forks but maybe could upgrade at some point

Hard to get hold of seemingly at the minute unless anyone can signpost who is selling/ shipping quickly

Thanks in advance all

stodd
Posts: 296
Joined: 6 Jun 2018, 10:24am

Re: specialized sirrus

Postby stodd » 2 Jun 2020, 12:59pm

Don't forget that any motor over a nominal 250w makes a bike illegal to ride on road without plates, insurance etc, and illegal to ride in any off-road public place such as a bridleway. Good 250w motors can actually generate up to 750w for short bursts.

theballboy
Posts: 6
Joined: 2 Jun 2020, 10:25am

Re: specialized sirrus

Postby theballboy » 2 Jun 2020, 2:01pm

Yeah, thanks . I was aware of that
I know they are switchable though so can operate at legal limit when on road and at full limit off

stodd
Posts: 296
Joined: 6 Jun 2018, 10:24am

Re: specialized sirrus

Postby stodd » 2 Jun 2020, 5:35pm

It remains illegal on the road if switchable, even with the switch on low. And remains illegal off road in public places. But you are very unlikely to be caught if you ride sensibly.

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philg
Posts: 526
Joined: 7 May 2009, 12:13pm
Location: Porlock, Somerset

Re: specialized sirrus

Postby philg » 2 Jun 2020, 9:40pm

I know zilch about mid-motors, but I understood that the 500+ Watt hub motors are pretty useless apart from high speed burn ups due to lack of low speed torque, i.e. great for speed but useless for hills. Is this correct?
Does the same apply to mid-motors?
And does being able to use the bike's gears mitigate this to some extent?

hemo
Posts: 784
Joined: 16 Nov 2017, 5:40pm
Location: West Sussex

Re: specialized sirrus

Postby hemo » 2 Jun 2020, 9:57pm

philg wrote:I know zilch about mid-motors, but I understood that the 500+ Watt hub motors are pretty useless apart from high speed burn ups due to lack of low speed torque, i.e. great for speed but useless for hills. Is this correct?
Does the same apply to mid-motors?
And does being able to use the bike's gears mitigate this to some extent?


As wrong as you can be.
Any geared hub motor can be high torque if the rpm winding is low enough, typically 160 - 201 rpm.

stodd
Posts: 296
Joined: 6 Jun 2018, 10:24am

Re: specialized sirrus

Postby stodd » 2 Jun 2020, 10:41pm

I think you are talking a little at cross purposes.
Many (?most, especially the cheap ones) 500+ watt hub motors are direct drive, and have the issues philg mentioned.
But, as hemo points out, the geared hub motors do not generally have those issues, especially if suitably wound and geared.

I'm pretty sure any 500w mid motors would be geared.

You'll get more specialized advice at https://www.pedelecs.co.uk/forum/forums ... ussion.42/

theballboy
Posts: 6
Joined: 2 Jun 2020, 10:25am

Re: specialized sirrus

Postby theballboy » 3 Jun 2020, 12:33am

Obviously a total noob question but if I purchase a bafang - and opt for a 42t, I lose use of my 32t chainring? and thus the left microshift correct?

stodd
Posts: 296
Joined: 6 Jun 2018, 10:24am

Re: specialized sirrus

Postby stodd » 3 Jun 2020, 9:04am

theballboy wrote:Obviously a total noob question but if I purchase a bafang - and opt for a 42t, I lose use of my 32t chainring? and thus the left microshift correct?
Some mid drives will accept double chainrings, varies with details of the spider and chainline. I've not heard of one that takes a triple.

I'll repeat my comment above: You'll get more specialized advice at https://www.pedelecs.co.uk/forum/forums ... ussion.42/

hemo
Posts: 784
Joined: 16 Nov 2017, 5:40pm
Location: West Sussex

Re: specialized sirrus

Postby hemo » 3 Jun 2020, 8:13pm

theballboy wrote:Obviously a total noob question but if I purchase a bafang - and opt for a 42t, I lose use of my 32t chainring? and thus the left microshift correct?


The Bafang and Tongsheng both will accept 2x chainrings with a mid drive 5 hole spider adapter chain line will be compromised for some gears, 32t is the smallest you can get away with.