Path: news.eternal-september.org!eternal-september.org!.POSTED!not-for-mail
From: Frank Krygowski <frkrygow@sbcglobal.net>
Newsgroups: rec.bicycles.tech
Subject: Re: Getting old is not for sissies
Date: Sun, 2 Mar 2025 14:38:40 -0500
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On 3/2/2025 12:16 PM, AMuzi wrote:
> On 3/2/2025 10:10 AM, AMuzi wrote:
>> On 3/1/2025 8:06 PM, Frank Krygowski wrote:
>>> On 3/1/2025 4:39 PM, Jeff Liebermann wrote:
>>>> On Sat, 1 Mar 2025 13:55:50 -0500, Frank Krygowski
>>>> <frkrygow@sbcglobal.net> wrote:
>>>>
>>>>> IIRC, hydrostatic transmissions are standard features on zero turn
>>>>> mowers. But as you noted, the mechanical efficiency is lousy. 
>>>>> That's not
>>>>> a concern if you have a big enough engine and low enough use hours. 
>>>>> It's
>>>>> a huge concern for a cyclist.
>>>>
>>>> True, but the huge concern is mostly for racing.  If you're using the
>>>> bicycle as a moving exercise machine, the added weight and increased
>>>> friction might even be considered beneficial.  It's like the weights
>>>> on barbells where light weight is not a concern.  For competitive
>>>> fixie racing, maybe the governing organization should specify a
>>>> minimum allowable bicycle weight, which might inspire technical
>>>> innovation instead of shaving grams off the bicycle weight.
>>>
>>> I think that level of inefficiency would be a concern of most 
>>> cyclists, and very few actually race. It would take a lot of fun out 
>>> of riding.
>>>
>>> I once worked on a bicycle belonging to a friend that had a quite 
>>> rare (at least, at the time) 5 speed Sturmey- Archer geared hub. 
>>> IIRC, there were two shift cables, one going to each side. Anyway, as 
>>> I remember when shifted to its lowest gear it seemed extremely 
>>> sluggish. Unlike the equivalent low gear on a derailleur bike, it 
>>> really didn't seem much easier going uphill in that gear. Instead it 
>>> just seemed slower. And as I recall, that was a not uncommon 
>>> complaint about that particular hub.
>>>
>>> I understand the desire for exercise. But I think almost everyone 
>>> prefers to get their exercise while moving farther or faster, not by 
>>> slogging along slowly. If that were acceptable, we'd all be riding 
>>> solid tires.
>>>
>>>
>>
>> Odd symptom and no logical reason for it IMHO.
>>
>> The S-5 gearbox (went through several variants) is basically an AW 
>> three speed design with dual sun gears. With no left side change, it's 
>> a three speed (+26.6% high, direct drive, -21.1% low).
>>
>> When the left side is changed, the sun gear clutch slides over to the 
>> other gear set, giving -33.3% super low, direct drive and +50% high.
>>
>> The gear sizes being different from an AW (-25% low, direct drive, 
>> +33% high), the five model notably gives a faster high gear but not a 
>> lower low gear.
>>
>> Since everything is in the same oil bath* and rolling on the same 
>> bearing adjustment*, overall efficiency should vary only in the 
>> relative losses of gear diameter which is a small difference.
>>
>>
>> * can be correct or deficient
>>
> 
> edit: 'not a much lower low gear'

It was probably about 1984 or so, meaning memory is dim. I was asked to 
fix it by a dear friend who lived far away and brought it here on a 
visit. The complaint wasn't inefficiency; it was that the bike was balky 
responding to the left shifter. I never had time to, say, open the hub 
gear. I just played around with cable adjustments.

I thought it might have been John Allen or John Schubert who described 
it as an inefficient device, but I don't recall any explanation. If the 
output of one planetary stage became the input of the next, the losses 
would sort of compound, but it seems odd that would be detectable while 
riding. I'd guess maybe 95% efficiency for each stage, so ~90% overall.

-- 
- Frank Krygowski