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Watt$ a tire worth?
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Trying to wrap my head around how much benefit there is in the tires.

When Bicycle Rolling Resistance (BRR) says that a tire will save you 5+ watts, do they mean one tire saves you 5+ watts and since we ride on two tires it makes a total of 10+ watts difference?

https://www.bicyclerollingresistance.com/...ed-turbo-cotton-2016

Also, is this a reliable watts calculator for cycling?

http://bikecalculator.com/examples.html

If so, when we say that a tire "saves" us 5 watts do we then input that as adding 5 watts (even though in reality our engines aren't creating more watts). In other words, if my current average watts is 150 would my average go up to 155 or 160 if I bought watts saving tires?

$$$:

When BRR rates a tire, one of the values is price. It seems like they might be using full price for rating and not the price that I can really buy the tires at. For example, I wouldn't pay $40 for a 15W tire. Yet a 15W training tire with good puncture resistance for under $20 works well for training in an urban area. For me this distorts the rating/recommendation scheme. Take price out?

Rear tire / front tire. My rear tire by far gets the brunt of wear and tear. The rear wears out faster and gets FAR more punctures than the front. Perhaps because on a road bike I have far more weight - 100lbs on the rear versus 50lbs on the front. And I can't really see what my rear tire might be running over.

By the way, how can we measure how much watts the difference of 100lbs of weight versus 50lbs of weight makes to each tires rolling resistance?

We like our tires to match. So we usually buy the same tires for front and back. If we follow Sheldon Brown's wisdom we place the better tire on the front. In my case, that means rotating the front tire to the rear when my my rear tire wears out or blows out.

However, if I looked at the front tire as being independent of the rear tire choice would it make sense to "save" 5 watts by having a really great tire with a latex tube on the front and just replace the rear tire with butyl tube as needed?

Thank you in advance for your worthwhile thoughts on tires and watt$.

Indoor Triathlete - I thought I was right, until I realized I was wrong.
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Re: Watt$ a tire worth? [IT] [ In reply to ]
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It is per tire as I understand it so its 5+5=10 watts total saved.

2019 T-Rex Tri Series
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Re: Watt$ a tire worth? [IT] [ In reply to ]
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Random thoughts:

You don't "gain" 5W. What it means is it would take 5W less power to maintain the same speed.
But assuming you ride to effort not speed, the actual effect is that for your 150W input, you'll go slightly faster (because less power is being wasted in RR, and hence more is being used to propel you)

As above, yes it's 5W per tyre.

I'm unclear in BRR's test whether the test includes a driving torque. e.g. as you described with tread wear, it's not just due to the vertical load on the wheel, the rear gets much more torsional load to propel you forwards which causes the friction and wear, the front wheel just passively rolls. And second to that, I'm unclear how driving torque is related to rolling resistance.

You can measure the effect of weight load on the tyre by just adding more weight on the rolling resistance test rig. I have a feeling BRR has done this, but at a guess it would be linearly proportional.
Last edited by: MattyK: Apr 21, 19 6:05
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Re: Watt$ a tire worth? [MattyK] [ In reply to ]
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MattyK wrote:
You can measure the effect of weight load on the tyre by just adding more weight on the rolling resistance test rig. I have a feeling BRR has done this, but at a guess it would be linearly proportional.

BRR seems to have their weight set at 42.5 kg or 96.4 lbs for testing. They also have speed set at 29kmh / 18mph (now I'm wondering if a change of speed would make for a change in watts???)


So if it's 5+5 less watts needed to go the same speed, that's good to know. So my average watts won't increase, I will see the benefit in overall speed.

It might not be linear on weight. BRR numbers don't seem linear in regards to watts when they reduce tire air pressure.

So if I'm putting 50lbs of my weight on the front tire at 70 psi (for deflection purposes) my watts could be at for 15 that tire.

And if I'm putting 100lbs of my weight on the rear tire at 100 psi my watts could be at 15 for that tire.

Too bad we have to pay a price for the value derived from deflection or we could all be riding on solid rubber at a low resistance without flats - like our first tricycles.

Indoor Triathlete - I thought I was right, until I realized I was wrong.
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Re: Watt$ a tire worth? [MattyK] [ In reply to ]
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MattyK wrote:
I'm unclear in BRR's test whether the test includes a driving torque. e.g. as you described with tread wear, it's not just due to the vertical load on the wheel, the rear gets much more torsional load to propel you forwards which causes the friction and wear, the front wheel just passively rolls. And second to that, I'm unclear how driving torque is related to rolling resistance.

No, there is no driving torque in the test.

I'm pretty sure high torque makes a difference, as I can hear my rear tire making noise on a climb. It won't be very high on the flat though.
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Re: Watt$ a tire worth? [IT] [ In reply to ]
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IT wrote:
now I'm wondering if a change of speed would make for a change in watts???

As speed increases air resistance increases requiring even more power to (go faster. Hence why reducing your drag & rolling resistance is so very important

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Re: Watt$ a tire worth? [desert dude] [ In reply to ]
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desert dude wrote:
IT wrote:
now I'm wondering if a change of speed would make for a change in watts???


As speed increases air resistance increases requiring even more power to (go faster. Hence why reducing your drag & rolling resistance is so very important

Air resistance increases. Where is it that rolling resistance increases at higher speed? Couldn't lift actually impact rolling resistance favorably?

Indoor Triathlete - I thought I was right, until I realized I was wrong.
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Re: Watt$ a tire worth? [IT] [ In reply to ]
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IT wrote:
Air resistance increases. Where is it that rolling resistance increases at higher speed? Couldn't lift actually impact rolling resistance favorably?


Tom Anhalt’s Crr spreadsheet illustrates weight and speed applied to Crr. https://docs.google.com/...BOeFmO3-_8/htmlview#
Last edited by: SummitAK: Apr 21, 19 13:14
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Re: Watt$ a tire worth? [SummitAK] [ In reply to ]
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SummitAK wrote:
IT wrote:
Air resistance increases. Where is it that rolling resistance increases at higher speed? Couldn't lift actually impact rolling resistance favorably?


Tom Anhalt’s Crr spreadsheet illustrates weight and speed applied to Crr. http://Link

The link didn't work for me. Tried looking on my own and didn't find anything that was speed only, it was a combination of air/rolling. The speed on the charts that I found was 40kmh without variance.

Indoor Triathlete - I thought I was right, until I realized I was wrong.
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Re: Watt$ a tire worth? [IT] [ In reply to ]
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Sorry. Blew the link in iOS post. It should work now. It is also available in hist Blather ‘bout Bikes blog where he has some related articles on testing methodology and results.
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Re: Watt$ a tire worth? [IT] [ In reply to ]
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In the opposite direction: I'm really thinking about running gatorskins in sprints. Sure I'll probably lose a little time, but having flatted in a sprint and losing all kinds of time, the peace of mind of extra protection may be worth it.
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Re: Watt$ a tire worth? [IT] [ In reply to ]
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IT wrote:
(now I'm wondering if a change of speed would make for a change in watts???)
Yes, power loss due rolling resistance is linearly related to speed and weight. A 10% increase in speed requires 10% more power for rolling resistance.
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Re: Watt$ a tire worth? [gregf83] [ In reply to ]
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This is why we use Crr which is a dimensionless coefficient designed by engineers to make the math easier!


Crr multiplies times weight and times grade/100, so a 6% grade becomes 0.06. The effect of this is that we can think of Crr essentially as being the same as gradient. So those Gatorskins with Crr 0.0065 compared to a GP5000 with Crr 0.0025 means that the riding the Gatorskin is essentially the same as climbing a 0.4% grade ALL THE TIME


If you only have one slow tire that tire will only be climbing the additional grade for the weight that is applied to it.. but still, this stuff is very real, and makes a big difference over distance. In a 100km flat race, the rider on Gatorskins will have spent energy equivalent to climbing 400 meters compared to the rider on GP5000.


Coincidentally, this topic is covered quite extensively in the MarginalGainsPodcast.cc which goes live at midnight tonight, along with some additional insight from Robert Chung on this effect.


The formula looks like this, G is grade in %, W is weight in Kg:

Frolling
=9.8067⋅cos(arctan(G/100))⋅W⋅CrrFrolling=9.8067⋅cos⁡(arctan⁡(G100))⋅W⋅Crr

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Re: Watt$ a tire worth? [joshatsilca] [ In reply to ]
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joshatsilca wrote:
This is why we use Crr which is a dimensionless coefficient designed by engineers to make the math easier!


Crr multiplies times weight and times grade/100, so a 6% grade becomes 0.06. The effect of this is that we can think of Crr essentially as being the same as gradient. So those Gatorskins with Crr 0.0065 compared to a GP5000 with Crr 0.0025 means that the riding the Gatorskin is essentially the same as climbing a 0.4% grade ALL THE TIME


If you only have one slow tire that tire will only be climbing the additional grade for the weight that is applied to it.. but still, this stuff is very real, and makes a big difference over distance. In a 100km flat race, the rider on Gatorskins will have spent energy equivalent to climbing 400 meters compared to the rider on GP5000.


Coincidentally, this topic is covered quite extensively in the MarginalGainsPodcast.cc which goes live at midnight tonight, along with some additional insight from Robert Chung on this effect.


The formula looks like this, G is grade in %, W is weight in Kg:

Frolling
=9.8067⋅cos(arctan(G/100))⋅W⋅CrrFrolling=9.8067⋅cos⁡(arctan⁡(G100))⋅W⋅Crr

Thank you!

Saying that "If you only have one slow tire that tire will only be climbing the additional grade for the weight that is applied to it." is gold to me. The conundrum is that the most likely tire for me to flat is the rear tire where I place two thirds of my weight.


For training purposes, it's probably fine to run Gatorskins, Krylion, Lithions, etc on the rear because that's where I would encounter the wear and tear of glass etc.



However in a race where the course is much cleaner, it would be a significant penalty to not use a race tire.


PS good example and explanation of the benefit of using Crr


Indoor Triathlete - I thought I was right, until I realized I was wrong.
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Re: Watt$ a tire worth? [vonschnapps] [ In reply to ]
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vonschnapps wrote:
In the opposite direction: I'm really thinking about running gatorskins in sprints. Sure I'll probably lose a little time, but having flatted in a sprint and losing all kinds of time, the peace of mind of extra protection may be worth it.

With sprints the negative would be less because the duration is much shorter. A flat in a sprint would pretty much be race over - DNF for me.

What caused a flat in a sprint? Wasn't it a clean course? Hate that for you.

Indoor Triathlete - I thought I was right, until I realized I was wrong.
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Re: Watt$ a tire worth? [IT] [ In reply to ]
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IT wrote:
vonschnapps wrote:
In the opposite direction: I'm really thinking about running gatorskins in sprints. Sure I'll probably lose a little time, but having flatted in a sprint and losing all kinds of time, the peace of mind of extra protection may be worth it.


With sprints the negative would be less because the duration is much shorter. A flat in a sprint would pretty much be race over - DNF for me.

What caused a flat in a sprint? Wasn't it a clean course? Hate that for you.


I think it was a piece of glass, but that wasn't the worse part. I've practiced changing a flat, using a co2 cartridge, etc., but under race conditions everything changes. I fix the flat, then what seemed like a few minutes later...flatted again!!! WTF!!! Already used my spare tube, and was running on 650c wheels at the time, so while many people offered me a tube, no one had a 650 tube. (it was unbelievable how many people offered assistance during the race, while they were also racing, triathletes are the greatest!). Had a few miles to go, and walking in bike shoes and pushing a bike seemed worse than just riding on the flat tire. Was going to DNF, but it was a memorial race for athlete who died, and his mother gave a speech before the race about how he never quit, so I ended up getting to T2 and went out for the run. On examining the tire it turns out that I botched the new tube installation and had a twist in the tube. I've lost races, or a place, by under a minute before, so hate to give up time due to tires, but a flat just ruins your day!
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Re: Watt$ a tire worth? [vonschnapps] [ In reply to ]
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As I was reading through your post I was thinking he probably installed it wrong... and it appears you did. I bike tech for a large event company and I've seen it... some even go through more than one tube.

I like to pull the tube and see if I can find the hole really fast and then check the tire in that spot. I can visually tell if a hole is a pinch flat... often tends to be two holes, referred to as a snake bite. Single can be a piece of glass in the tire. Gentle pass through the tire with my finger if I can't find anything to see if I feel anything rough.

FYI, you can put a 700 tube in a 650 wheel... fold it over on itself as neat as you can. Not ideal but will work for a Sprint for sure and you'll want to get the right tube after the race installed.
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