Rolling resistance while climbing, should I care?

Triathlon Forum
1

Does rolling resistance make a notable difference on long steady climbs?

I ask because I’m planning to make an Everesting attempt this week. I’ll be on my road bike which currently has GP4000 S2 tires and butyl tubes. I’ve got some lightly used GP5000 tires and latex tubes on my tri bike. Is it worth swapping the 5000s and latex tubes to my road bike just for the attempt? I’m not looking to set any records, just looking to finish. Still, it’ll be a loooong day and I’m curious if better tires and latex make an actual difference. I’ll take any help I can get.

Thanks!

2

On long steady climbs, rolling resistance and gravity play a major role, so I’d say yes. Just because the roads slope up doesn’t mean better tires and latex tubes become less efficient.

3

See the diagram at 10:41 here: https://youtu.be/wShmwzp5XZY?t=641

The difference in rolling resistance between GP4000 and Gp5000 is equivalent to >500g at 10% climb.
Would you get rid of 500g on the bike if you could?

4

Well this’ll be a short thread. GP5000 w/latex it is. Thanks!

5

Your looking at a decrease of about 7-8 watts with the better tires and latex tubes. I would imagine that will add up quickly as you attempt 29,000 feet of climbing. So would you rather climb at the same speed while saving 8 watts or climb faster while hitting your wattage goal?

6

I nerded out a bit on the physics here.

According to the internet the coefficient of rolling resistance (Crr) varies from ~0.004-0.007 for typical tires (lower is better). The power you have to produce to overcome rolling resistance is:

Proll = Crrmg*v

m = mass of rider + bike
g = gravitational acceleration
v = speed of bike on road

If m = 80 kg then “good” tires save you a little over 1 W/mph. So depending on the hill, probably about the same power savings as shaved legs on a flat TT! Over an Everest-length effort I think you’d be very happy to not have to put out those extra 10-15 W on the last few climbs.

7

I nerded out a bit on the physics here.

According to the internet the coefficient of rolling resistance (Crr) varies from ~0.004-0.007 for typical tires (lower is better). The power you have to produce to overcome rolling resistance is:

Proll = Crrmg*v

m = mass of rider + bike
g = gravitational acceleration
v = speed of bike on road

If m = 80 kg then “good” tires save you a little over 1 W/mph. So depending on the hill, probably about the same power savings as shaved legs on a flat TT! Over an Everest-length effort I think you’d be very happy to not have to put out those extra 10-15 W on the last few climbs.
Given the option, i would go for the 5000, but dont expect miracles, it’s probably a matter of seconds/minutes - it won’t feel easier

8

Don’t forget the descent. Rolling resistance will be hugely important on the descent.

While my road bike was getting major carbon repair done, I used my gravel bike as my daily road bike for a few weeks. I had no problem staying with people, except on descents. Tires made a huge difference on the descent. (And I’m fairly confident it was the tires, and not aero differences.)

9

Time savings are more difficult to estimate (host of other factors with a big influence) but I estimate it’s in the neighborhood of 20-30 minutes of climbing time for an effort of this length. Everest is ~5.5 miles of climbing, even a small increase in speed can save quite a bit of time in an absolute sense. And that’s just on the climb, less RR would also save OP a bit on the descents too.

10

Put an extra 5-15 psi in the rear tire to compensate for the extra weight on rear when climbing. For hill climbs I put a lot extra in so that there is no extra tire scrub or wallowing and crr tends to increase at lower speeds. You’ll be descending a lot so don’t compromise handling on the way down.

11

Put an extra 5-15 psi in the rear tire to compensate for the extra weight on rear when climbing. For hill climbs I put a lot extra in so that there is no extra tire scrub or wallowing and crr tends to increase at lower speeds. You’ll be descending a lot so don’t compromise handling on the way down.

I’ve never heard this before. You’re saying the extra psi for the rear is to help reduce rolling resistance? I’ve been following the FLO studies that suggest running too high of pressure causes the tire to bounce more, wasting energy/watts. But if crr increases at lower speeds then maybe that makes up for it??

12

While my road bike was getting major carbon repair done, I used my gravel bike as my daily road bike for a few weeks. I had no problem staying with people, except on descents. Tires made a huge difference on the descent. (And I’m fairly confident it was the tires, and not aero differences.)

Well sometimes the opposite it true - I’ve been dropped plenty of times by gravel riders while riding a tri bike in the jungle on Zwift 😁

13

I’ve never heard this before. You’re saying the extra psi for the rear is to help reduce rolling resistance? I’ve been following the FLO studies that suggest running too high of pressure causes the tire to bounce more, wasting energy/watts. But if crr increases at lower speeds then maybe that makes up for it??

Ideal pressure increases with weight. And when you climb, more weight tends to shift to the rear wheel (on really steep climbs you have to work to prevent doing wheelies). So if you had perfect psi on the flat, it’d probably shift to a bit less in the front and a bit more in the rear for climbs.

14

Yes, for change in weight distribution, lower cadence ( higher peak force deforms tire more) and crr change with speed. Don’t compromise the handling for the descent though.

15

Does rolling resistance make a notable difference on long steady climbs?

Thanks!

It’s slightly complex calculation to pull out the CRR on the climb, but you can get ball park figure if you know your climbing power (or speed) here: https://www.cyclingapps.net/...mb-speed-calculator/ (see image in row 30). If you need to estimate your climb power as well look for “climb power calculator” under calculators . Good luck with your everesting!

16

I nerded out a bit on the physics here.

According to the internet the coefficient of rolling resistance (Crr) varies from ~0.004-0.007 for typical tires (lower is better). The power you have to produce to overcome rolling resistance is:

Proll = Crrmg*v

m = mass of rider + bike
g = gravitational acceleration
v = speed of bike on road

If m = 80 kg then “good” tires save you a little over 1 W/mph. So depending on the hill, probably about the same power savings as shaved legs on a flat TT! Over an Everest-length effort I think you’d be very happy to not have to put out those extra 10-15 W on the last few climbs.

Except we’re talking “good tires” vs “great tires.” A 25c GP4000 with butyl tubes has .crr of ~.004 @ 90psi. A same-size GP5000 with a latex tube has a .crr of ~.003. So more like ~0.4W/mph difference.

You can nerd out scenarios to your heart’s content on the Gribble Cycling Power Model. Using all the default values except .crr and grade, it showed the difference in speed between the two tires on a 7% grade at 200 watts was .09mph (7.19mph vs 7.10mph). If you prefer a watts:watts comparison, it would take ~202.7W on the GP4000’s to hold the same speed as the GP5000’s @ 200W. On a less steep grade of 3.5%, it would take 204.4 watts on the GP4000’s to maintain the same speed (12.03mph) as the Gp5000’s @ 200 watts.

OP, I’m going to assume (maybe incorrectly) that on an “Everesting” attempt, you’ll be soft pedaling or coasting on the descents to recover. So the higher .crr will cost you a bit of time on the descents where you’re freewheeling, but won’t have any metabolic cost. How much time is more difficult to quantify. Descents are harder to model as .cdA is a significant factor, and that can vary considerably from person to person, bike to bike, and position to position. Using the default values other than .crr, the model predicts a difference in terminal velocity on a 7% descent of less than 1%; 37.11mph vs 36.84mph. That percentage doesn’t vary a lot even if you assume a pretty slick (for a road bike) 3.0CdA.

So back to the question at hand. Is it worth it? I’m going to assume that your effort’s going to be the same on either tire. So it’s not a matter of saving watts, but saving time. Best I can figure, changing tires will save you roughly 5-7 minutes on an ~8 hour ride (1-1.5% faster). Maybe 3-5 minutes of that time would be under power; the rest lost while coasting descents. If this were a race, the 1-1.5% would undoubtedly be worth the effort. For a personal solo effort? If it were simply a matter of swapping wheels, I’d do it just because. If I had to change a cassette as well? It’s a toss up. Dismounting and mounting a set of 4000’s once and wresting a set of 5000’s with latex tubes off and on a set of rims twice?* I’d much rather pedal another 5 minutes.

*(once to go on to the road bike, and then again to go back to the TT bike)

17

Maybe with all the braking on the descent, faster tires vs fast enough tires makes minimal difference, but for the ascent the lower metablic cost is likely worth it and then pump up the rear so is deforms less, but can also hold enough traction on downhill. I don’t think you need to pump it up “much” compared to optimal PSI to avoid the deformation from out of the saddle or even high crank torque sitting climbing. What do you guys think? 10psi? maybe 15 psi?

18

Maybe with all the braking on the descent, faster tires vs fast enough tires makes minimal difference, but for the ascent the lower metablic cost is likely worth it…

As this is a solo effort, and not a race or group ride where you’re trying to keep pace, the “metabolic cost” is only time. Roughly 5 more minutes of effort on an 8 hour day. That’s not nothing, but neither is the effort to dismount and mount 6 Conti GP tires, 4 with latex tubes! People will undoubtedly have different opinions on whether the effort to change tires is worth it. I’ve at least given a reasonable objective estimate of the actual cost to base that opinion on. Many in this thread have greatly overestimated the cost.

19

That is very interesting. I hadn’t thought about those points. Thanks for bringing them up in this thread.

20

@OP

Let us how those last 5-7minutes of the attempt felt like :slight_smile:
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