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From: zen cycle <funkmasterxx@hotmail.com>
Newsgroups: rec.bicycles.tech
Subject: Re: Patching TPU innertube
Date: Sun, 29 Dec 2024 07:58:32 -0500
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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.

> 
> 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.

> 
> If you get to your coffee shop fifteen seconds earlier, do they give you 
> a prize?   ;-)
>