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Rolling resistance

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Rolling resistance

Old 05-30-21, 02:13 AM
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spilot101
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Rolling resistance

My new bike came with 25mm Conti GPs and I'm contemplating whether or not should upgrade to Pirelli P Zero Velo (I also have a set of 25mm Velo 4s, hence why they're featured in the comparison chart)

https://www.bicyclerollingresistance...o-velo-4s-2017


GP's rolling resistance is 14w vs. Velo's 12.5. That doesn't sound like a huge difference to me, or am I wrong here? The biggest appeal is that the Velos are 28mm (the ones that I'm looking at)... which might be enough of a reason, but I'm curious if I'll see any gains performance-wise?

PS. I'm realizing that this data is for 25mm tires.... I'm not sure how significant is the difference between 25 and 28 mm, but I don't see a way to choose the 28mm option.

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Old 05-30-21, 05:33 AM
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You will notice the bigger tyre volume - more comfortable. You will not notice any difference in rolling resistance. Any minor difference will be totally swamped by changing wind conditions and road surface. The rougher the roads, the better the 28s will feel.
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Old 05-30-21, 08:44 AM
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Unless you have an overwhelming reason why you need that extra little bit of savings, then just wait till you need to change tires due to wear.

The differences will be slight for rolling resistance. You might notice that you can use a lower pressure and get a slightly smoother ride with the 28 mm's but I doubt that much either.

Besides, if you change them without even trying the current tires for a couple thousand miles and gather some data then how will you really know if the change was a good change and worth it?
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Old 05-30-21, 09:03 AM
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Why are you worried about minute differences in rolling resistance?
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Old 05-30-21, 09:05 AM
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If you really do have Conti GP, they are 2 generations old and at least 7 years. GP5000 is the latest. I would ditch the old tires and mount GP5000 with latex tubes, myself anyway. You will be down around 9 W
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Old 05-30-21, 09:28 AM
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Comfort, flat protection, grip, durability and dare I say it price are equally important metrics to consider as rolling resistance, - unless you race for money :-)
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Old 05-30-21, 09:14 PM
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Originally Posted by Iride01 View Post
Unless you have an overwhelming reason why you need that extra little bit of savings, then just wait till you need to change tires due to wear.

The differences will be slight for rolling resistance. You might notice that you can use a lower pressure and get a slightly smoother ride with the 28 mm's but I doubt that much either.

Besides, if you change them without even trying the current tires for a couple thousand miles and gather some data then how will you really know if the change was a good change and worth it?
True. Actually, I rode the very same tire for about a year on my previous bike. Then I put the 28 Contis 4 Seasons and realized what difference can the tires make (even though the 4 Seasons are very slow). I've also tried P Zero 4s (25mm) and found them to be more comfortable than the 25mm GTs - which feel rougher.
This is how I've arrived at my original question. There's quite a bit of difference in speed that I've experienced between Conti GT (14w) and the 4 Seasons (19w)... so I asked myself, "is the rr really that big of a actor?", because, quite clearly, I was much faster on the less comfortable and twitchy GTs...But as Dan pointed out (and what I've gathered from my post-post research), the fact that there are other factors at play than just the rolling resistance still holds true. So even though there's not much difference in rr between the GTs and P Zero, I'm pretty sure the comfort here will win out big times... so I went ahead and bought the 28mm P Zeros (and will try to sell the GTs to get some $ back).

Last edited by spilot101; 05-30-21 at 09:20 PM.
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Old 05-30-21, 09:15 PM
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Originally Posted by Racing Dan View Post
Comfort, flat protection, grip, durability and dare I say it price are equally important metrics to consider as rolling resistance, - unless you race for money :-)
That's exactly what I've gathered as well. Cheers!
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Old 05-30-21, 09:21 PM
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I ride Conti 4 seasons and GP5000s. Yes, the GP5000s roll better, but under most circumstances, the quantifiable difference in performance is very small.
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Old 05-30-21, 10:24 PM
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Comfort and RR should be correlated, BTW - they both depend on suppleness.
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Old 05-30-21, 11:46 PM
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Ditto the suggestion to keep the Conti GPs and try latex tubes.

I've tried several road tires in 700x23 to x25, with rolling resistance rated from 12-14, and can't say I felt or measured any consistent differences. Getting more aero made more difference. But latex tubes feel much better and are a little bit faster or demand a little less effort for the same speed.

Mostly I switched to latex after all our roads were repaved with the worst, coarsest chipseal I've ever seen. It's like the just glued a bunch of railroad ballast gravel together with epoxy. Latex tubes and decent tires made it pleasant to ride again.
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Old 05-31-21, 12:26 AM
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Originally Posted by canklecat View Post
Ditto the suggestion to keep the Conti GPs and try latex tubes.

I've tried several road tires in 700x23 to x25, with rolling resistance rated from 12-14, and can't say I felt or measured any consistent differences. Getting more aero made more difference. But latex tubes feel much better and are a little bit faster or demand a little less effort for the same speed.

Mostly I switched to latex after all our roads were repaved with the worst, coarsest chipseal I've ever seen. It's like the just glued a bunch of railroad ballast gravel together with epoxy. Latex tubes and decent tires made it pleasant to ride again.
Cool. Any recommendations on the latex tubes?
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Old 05-31-21, 12:40 AM
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Originally Posted by spilot101 View Post
Cool. Any recommendations on the latex tubes?
I use Silca and Vittoria, which I think makes latex tubes for Silca to their specs. The valves are a bit different.

Prices have varied over the past couple of years from $11-$20 per tube, but usually closer to $11. Seems pricey but the ride is so nice it's worth it to me.

And I was able to repair the single puncture I've had using an ordinary self-adhesive patch, a Lezyne, I think.
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Old 05-31-21, 01:15 AM
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Originally Posted by spilot101 View Post
Cool. Any recommendations on the latex tubes?
Vittoria.
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Old 05-31-21, 06:20 AM
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Pressure lasts longer in Vittoria and Silca compared to Challenge, Michelin, and Vreidstein
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Old 05-31-21, 07:22 AM
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Originally Posted by spilot101 View Post
I was much faster on the less comfortable and twitchy GTs...
How much faster? It's very hard to measure objectively since ambient conditions change so much and rr is not really dominant in the overall list of variables. Tyres can certainly "feel" fast or slow, but when you are talking about a couple of Watts here and there (at speed) it all gets lost in the noise of other variables. I ride with a power meter on local loops and day to day difference in average speed can be as much as 2-3 kph over 100 km for the same average power on the same bike/tyres. If I changed tyres I wouldn't be able to measure whether or not they were quicker/slower. So I do rely on test data from the website you mentioned. But I don't stress over tyres that are within a couple of Watts on their tests. I actually pay a LOT more attention to their puncture resistance as that's what really slows you down out on the road!
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Old 05-31-21, 08:50 AM
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Originally Posted by PeteHski View Post
How much faster? It's very hard to measure objectively since ambient conditions change so much and rr is not really dominant in the overall list of variables. Tyres can certainly "feel" fast or slow, but when you are talking about a couple of Watts here and there (at speed) it all gets lost in the noise of other variables. I ride with a power meter on local loops and day to day difference in average speed can be as much as 2-3 kph over 100 km for the same average power on the same bike/tyres. If I changed tyres I wouldn't be able to measure whether or not they were quicker/slower. So I do rely on test data from the website you mentioned. But I don't stress over tyres that are within a couple of Watts on their tests. I actually pay a LOT more attention to their puncture resistance as that's what really slows you down out on the road!
I hear you on the puncture resistance (which is why I actually decided to change for 4s). I'm not too concerned with 2-3 watts, however, 5~6 watts (per tire) is starting to get quite significant... 10-12 watts is pretty noticeable. For me, it translated into about 0.2/0.3 off my avg kph (I race against myself on a very similar track and it's been very consistent, under same conditions, so it's the average speed on any given segment that I pay attention to), or a slightly greater effort to maintain the same speed. It is something that I noticed before I even knew what watts were, in relation to cycling etc... so I doubt it was some sort of a self-fulfilling mental hangup.
Perhaps the bigger question I should ask myself, "why in the hell does any of this matter?", since I'm not getting paid or race on any level for that matter haha.
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Old 05-31-21, 08:57 AM
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It is not hard to measure a difference of 5-10 watts.

An average recreational cyclist moving at 17 mph could see an increase to 17.5 with small changes in tires with same power input. Large improvements could see upwards of 1 mph improvement.

What is often erroneously assumed is the Crr published on various websites represents the actual Crr experienced on the road. Real world Crr is much, much higher and the incremental improvements are not trivial.
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Old 05-31-21, 09:31 AM
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Originally Posted by GhostRider62 View Post
It is not hard to measure a difference of 5-10 watts.

An average recreational cyclist moving at 17 mph could see an increase to 17.5 with small changes in tires with same power input. Large improvements could see upwards of 1 mph improvement.

What is often erroneously assumed is the Crr published on various websites represents the actual Crr experienced on the road. Real world Crr is much, much higher and the incremental improvements are not trivial.
it is actually incredibly hard to measure a difference of 5-10 watts when you are outside in the elements. Even the slightest of breeze will swamp that kind of difference out. It's not even a constant 5-10W either. It varies with both speed and how rough the road surface is. There are plenty of roads where a wider tyre with a much higher lab test rr result would actually be faster in the real world. All that road buzz you feel through your bars is lost power. Anyway the OP was talking about lab test differences of only 2-3W, which is basically next to nothing.
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Old 05-31-21, 09:34 AM
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Originally Posted by spilot101 View Post
I hear you on the puncture resistance (which is why I actually decided to change for 4s). I'm not too concerned with 2-3 watts, however, 5~6 watts (per tire) is starting to get quite significant... 10-12 watts is pretty noticeable. For me, it translated into about 0.2/0.3 off my avg kph (I race against myself on a very similar track and it's been very consistent, under same conditions, so it's the average speed on any given segment that I pay attention to), or a slightly greater effort to maintain the same speed. It is something that I noticed before I even knew what watts were, in relation to cycling etc... so I doubt it was some sort of a self-fulfilling mental hangup.
Perhaps the bigger question I should ask myself, "why in the hell does any of this matter?", since I'm not getting paid or race on any level for that matter haha.
I see more variation than that riding the same tyres day to day. Wind conditions are never identical. My power output varies too depending on fatigue, form etc. Too many variables to isolate rr. My mtb tyres are slower though!
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Old 05-31-21, 09:48 AM
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Originally Posted by PeteHski View Post
Too many variables to isolate rr.
If only there were some way to measure actual Crr on real roads.
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Old 05-31-21, 10:04 AM
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Originally Posted by RChung View Post
If only there were some way to measure actual Crr on real roads.
The best you can do is make assumptions based on more controlled testing - like the lab drum test and tests from indoor velodromes etc. where you have some control over the other variables. You could safely say that a super-light road race tyre is going to be significantly faster than a heavy gatorskin tyre on smooth tarmac. But once you start comparing very similar tyres across a wide range of real roads, it soon becomes pretty inconclusive. For that reason I tend to choose tyres that are more puncture resistant, while still performing reasonably well on the simple drum rr test. I'm currently running 32c Pirelli Cinturato Velo (the current benchmark for puncture resistance). I have no doubt that there are faster tyres in ideal conditons, but riding them in 100 mile Sportives over a wide range of crappy road conditions has confirmed them to be a sound choice i.e. I don't get any flats while many others do!
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Old 05-31-21, 01:10 PM
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Originally Posted by GhostRider62 View Post
Pressure lasts longer in Vittoria and Silca compared to Challenge, Michelin, and Vreidstein
The Michelin latex tubes donít have removable valve cores. I wonít buy them again.
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Old 05-31-21, 01:36 PM
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Originally Posted by terrymorse View Post
The Michelin latex tubes donít have removable valve cores. I wonít buy them again.
Michelin does make really wide latex tubes that can be cut down for wide 584 tires, other than that, I am with you. Not a fan

My preference is either Silca or Vittoria but Challenge does make a wide one for tires up to 38 mm, so, I use them too. Sealant works reasonably well inside latex tubes but eventually you are wasting a tube because the sealant dries and buggers it all up.

Today I pumped my tires up to 95 pi, 5 psi over optimum and they will be 85 psi tomorrow. About 10 psi loss per day for those two. In effect, I pump them up every other day. If I was doing some sort of timed event, I would be more concerned but it takes me under a minute to top them off. Even if I run butyl, tire check is something I do on every ride.
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Old 05-31-21, 01:46 PM
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Originally Posted by RChung View Post
If only there were some way to measure actual Crr on real roads.
I remember reading of a method by a Professor.

What you do is find windless day, a loop or a halfpipe road with elevation changes. You carefully ride say the loop several to many times at one speed. Then, you repeat it at another speed. You input it into his computer algorithm. You recursively line up the virtual elevations using Crr and CdA as inputs. When the slow and faster virtual elevations are aligned with the same CdA and Crr, you know both your CdA and Crr, it is almost like magic. The algorithm is widely available free.

I'll see if I can find his paper. Identifying 10 watts of rolling resistance difference at 17 mph is easy with his method.
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