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From: Roger Merriman <roger@sarlet.com>
Newsgroups: rec.bicycles.tech
Subject: Re: Patching TPU innertube
Date: 30 Dec 2024 12:51:43 GMT
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Frank Krygowski <frkrygow@sbcglobal.net> wrote:
> On 12/29/2024 7:58 AM, zen cycle wrote:
>> On 12/28/2024 6:25 PM, Frank Krygowski wrote:
>>> On 12/28/2024 12:32 PM, cyclintom wrote:
>>>> On Thu Dec 26 22:10:15 2024 Frank Krygowski  wrote:
>>>>> On 12/26/2024 5:32 PM, Roger Merriman wrote:
>>>>>> 
>>>>>> The issue for me is that while Gravel tires absolutely do feel more 
>>>>>> supple
>>>>>> with TPU tubes, these are tires while some claimed sidewall 
>>>>>> protection,
>>>>>> these aren?t like Trail etc MTB tires which have reinforced noticeable
>>>>>> stiff sidewalls is aren?t floppy, each tire is 1kg or so.
>>>>>> 
>>>>>> Hence I wonder if a upgrade to TPU tubes would be noticeable...
>>>>> 
>>>>> 
>>>>> I'd be interested in people's personal measurements of differences. If
>>>>> someone here had access to some long, gentle downhill and kept track of
>>>>> terminal coasting speed using different tires, different tubes, but
>>>>> otherwise identical equipment, terminal coasting speeds might be good
>>>>> information.
>>>>> 
>>>>> It would be best to test in consistent temperatures and with negligible
>>>>> wind, of course.
>>>> 
>>>> Frank, what do you believe the difference in terminal velocity would 
>>>> be with 1/2% decrease in rolling resistance on a 5% slope which is 
>>>> almost entirely set by the tires? For crying out loud, you claim to 
>>>> be a mechanical engineer! Aerodynamic drag would be 100 times the 
>>>> rolling resistance.
>>> 
>>> I'm breaking my recent resolution to skip responding to you, Tom. It's 
>>> normally a futile endeavor.
>>> 
>>> But as to your question: Aerodynamics was the specific reason I 
>>> specified a _gentle_ downhill. I think the best might be one that 
>>> would give a terminal speed of 12 to 15 mph, since at those speeds 
>>> aero drag is at least roughly the same magnitude as rolling resistance.
>> 
>> I question this: I suspect resultant drag at 15 MPH is significantly 
>> higher than the resultant drag from rolling resistance, but since the 
>> resultant drag 15 MPH in terms of watts is likely in the low single 
>> digits, the difference between that and a few tenths of a watt from 
>> rolling resistance is imperceptible.
> 
> True, the slower the terminal speed, the better for judging rolling 
> resistance, or attempting to separate it from aero drag.
> 
> Part of my thinking was to test at the rider's typical riding speed. I 
> suspect almost all of us here typically ride faster than 12 mph. In any 
> case, results of tests at one's typical riding speed would give the best 
> indication of the difference tires, tubes, etc. would make for that rider.
> 
>>> And yes, I expect the differences would be difficult to detect. Which 
>>> raises the question: If the differences are difficult to detect, are 
>>> they really worth worrying about? Are they really worth the expense, 
>>> and the hassle of changing one's equipment?
>>> 
>>> If you're racing, perhaps so. Otherwise, it seems not.
>> 
>> Even if you're racing, the law of diminishing returns applies heavily. 
>> For a pro, certainly it matters. For us amateur age groupers, benefits 
>> from tire selection get lost in the noise.
> 
> Agreed. Assuming one stays away from really terrible tires, that is.
> 
> 
Kinda depends on folks intended use, cheap road tires are okay, as dry
weather commute/training tires tend to be heavy and maybe a bit sluggish,
but also fairly robust.

They loose on rolling resistance and grip but then some premium winter
tires like the Gatorskins are similar lack of wet grip, to the extent
“Skaterskins” is one of their nicknames!

I’d say that a tire upgrade makes the biggest difference on any bike, off
road it’s particularly important and noticeable, and fairly cost effective,
though off road or MTB it is a more complicated than road, or even gravel
tires.

Roger Merriman