marcparnes
Active Member
It has no effect on the gear ratio but it will decrease the pedal speed, ie: how fast your feet move and therefore will increase your effort in a given gear.
Marc
SuperDelite pedals too close to ground :-/
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Marc
FlatSix911
Well-Known Member
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None... no effect on gear ratios.
Crank length: Forget leverage and power, it’s all about the fit | CyclingTips
For example, Inbar et al. (1983) measured the mean and peak power output for 13 subjects during a seated 30s effort using crank lengths 125-225mm.
While the authors identified an optimal crank length of ~165mm for this kind of effort, there was no significant change in power when cranks were as long as 200mm or as short as 150mm.
Martin and Spirduso (2001) essentially repeated this study with 16 trained cyclists for a 3-4s effort and five crank lengths (120/145/170/195/220mm) with very similar results.
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marcparnes
Active Member
Empirical trumps theoreticalNone... no effect on gear ratios.
Crank length: Forget leverage and power, it’s all about the fit | CyclingTips
For example, Inbar et al. (1983) measured the mean and peak power output for 13 subjects during a seated 30s effort using crank lengths 125-225mm. While the authors identified an optimal crank length of ~165mm for this kind of effort, there was no significant change in power when cranks were as long as 200mm or as short as 150mm.
Martin and Spirduso (2001) essentially repeated this study with 16 trained cyclists for a 3-4s effort and five crank lengths (120/145/170/195/220mm) with very similar results.
Marc
AbeK
Active Member
I just got my brand new Superdelite Rohloff HS on Saturday and on its maiden voyage yesterday my Shimano pedal scraped the ground on a high speed turn. It left only a minor scratch on the pedal, but it certainly made it clear to me how important it is to pay attention to pedal position on turns with this bike!
Alaskan
Well-Known Member
Pedal strikes can be very dangerous. The very best way to avoid them is to cultivate the habit of pushing and holding down on the outside pedal when moving through a turn. None of us are in a race so there is no need to pedal through a sharp turn and risk a pedal strike.
Yeah, but to be honest mine occurred also on uneven surfaces. Of course my sag setting might be too low, but there's an evidence in a low design... As I have written, the dealer told me he was experiencing this on his first rides and this was the reason why he shifted selling only GX models.
I may be wrong but i think this has to be changed in the Bosch configuration too via dealer portal?
marcparnes
Active Member
No, it wouldn't. Computer keeps track of cadence among other things which isn't affected by the crank arm length.
Marc
Torque calculations?
Nycturne
Member
Not sure that would change much, based on the study FlatSix911 shared. If human power output doesn’t vary much based on the crank arm length, it is safe to assume the torque applied to the pedals isn’t varying much either. Assuming it’s actually measuring torque applied.
Bosch has a torque sensor at the other end of the crank from the pedals which it uses to determine how much energy the user is applying to move the vehicle and with calculations it in turn delivers more or less power to the motor/engine. It may be a small portion of the formula/algorithm.
Nycturne
Member
Yes, I'm aware of the basics involved here. It's more that I'm not 100% familiar enough to say that the sensor actually measures strain from torque applied, or some sort of analogue that can be assumed to be akin to torque. I'm assuming they are using something like a rotary torque sensor which should be fine, but when cost is involved, I hesitate to trust my assumptions.
But the point I made still stands. If the torque sensor is a small portion of the algorithm, then the small variation that exists based on the crank arm length matters even less. It's not got a lot of inputs into the system it can even use, and so far all the ones I'm thinking of don't really care about the crank arm length. Torque is about the only one where crank arm matters at all, but in the bike use case, it's not a big factor.
I rest my case
2019 Bosch Electric Bike System Updates – e-bikeshop.co.uk
For 2019 Bosch offer new features for its eMTB community based on rider feedback. Let's look at the new features.
www.e-bikeshop.co.uk
Bosch drive and min/max gear ratio parameters
I'm looking into having easier unassisted climbing (that's just how I roll, I'm not interested in losing a tiny bit at the fast end nor do I care about tuning the drive to assist faster) with my Performance Line CX equipped bike. The bike now has a 15t chainring/sprocket and XT 11-42 in the...
www.pedelecs.co.uk
And come to think of it more, the Bosch ebike torque sensor, i imagine plays a major part in the whole system's dynamic feel, with i presume fine granularity & precision coupled with cpu & high sampling rates.
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Nycturne
Member
I rest my case
2019 Bosch Electric Bike System Updates – e-bikeshop.co.uk
For 2019 Bosch offer new features for its eMTB community based on rider feedback. Let's look at the new features.Bosch drive and min/max gear ratio parameters
I'm looking into having easier unassisted climbing (that's just how I roll, I'm not interested in losing a tiny bit at the fast end nor do I care about tuning the drive to assist faster) with my Performance Line CX equipped bike. The bike now has a 15t chainring/sprocket and XT 11-42 in the...
I'm not seeing anything related to your original question about updates required about crank arm length. So I'm left asking: what case?
Open your eyes.
McCorby
Well-Known Member
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- USA
Easy webcurl......
Kaiede, this is what webcurl is referring to in the first article they linked.
Quoted from linked article:
New Update For Short eMTB Crank Arms
Most riders run regular length cranks (170-175mm) but on an eMTB you tend to tackle harder climbs and the electric mountain bike allows you to navigate up rocks/obstacles etc.With full-length cranks, pedal strikes become more apparent. This means many riders have been fitting short Bosch eBike crank arms (165-150mm) which allows more ground clearance for more adventurous riding.
The trouble with just swapping the cranks is that it alters the feedback the drive system gets. Which in turn alters the output of the motor assistance feel, torque curve and in particular the characteristics when in eMTB mode.
For 2019 Bosch introduces software updates via a Bosch eBike dealer, who can program each bike to suit the preferred crank length. This adapts the progression curve in eMTB mode and also offers increased support in Tour mode, offering maximum power up-hill.
marcparnes
Active Member
Surprise for me as well. I would imagine it only applies to bikes with eMTB mode but the description doesn't specify.
With full-length cranks, pedal strikes become more apparent. This means many riders have been fitting short Bosch eBike crank arms (165-150mm) which allows more ground clearance for more adventurous riding.
The trouble with just swapping the cranks is that it alters the feedback the drive system gets. Which in turn alters the output of the motor assistance feel, torque curve and in particular the characteristics when in eMTB mode.
For 2019 Bosch introduces software updates via a Bosch eBike dealer, who can program each bike to suit the preferred crank length. This adapts the progression curve in eMTB mode and also offers increased support in Tour mode, offering maximum power up-hill.
New Update For Short eMTB Crank Arms
Most riders run regular length cranks (170-175mm) but on an eMTB you tend to tackle harder climbs and the electric mountain bike allows you to navigate up rocks/obstacles etc.
The trouble with just swapping the cranks is that it alters the feedback the drive system gets. Which in turn alters the output of the motor assistance feel, torque curve and in particular the characteristics when in eMTB mode.
For 2019 Bosch introduces software updates via a Bosch eBike dealer, who can program each bike to suit the preferred crank length. This adapts the progression curve in eMTB mode and also offers increased support in Tour mode, offering maximum power up-hill.
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