Rollers and tire width - Need some math help!

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JackRussellRacing
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by JackRussellRacing

I freely admit I'm not the sharpest knife in the drawer.... so here goes,

(1) I ride rollers for training. Although the model probably is not relevant, they are Elite E-Motion B+ which are ANT+ FE-C controlled by TrainerRoad.
(2) I have two very similar bikes that I put on the rollers with identical frame geometry, saddle height, pedals, etc.

    (a) Pinarello GAN RS with RED Etap 11/28 and (temporarily) Vueltra Ultra Light wheels, wearing Gatorskin 700x25 @ 95psi
    (b) Pinarello GAN RS with Di2 11/32 and HED Ardennes Plus SL, wearing Continental GP 4000s II 700x25 @ 95psi.

Now, the meat of the question:

If I ride the exact same TrainerRoad program but swap the bikes, "Pinarello B" with the 11/32+Ardennes+GP4000 allows me to produce significantly higher watts for a longer period of time. Why?!? Is it the gearing of the 11/32 ? Doesn't make sense because I'm never in the 32 on the rollers. Is it the rim width of the Ardennes? Doesn't make sense because the rubber on both bikes is 25mm. Is it the rubber compound of Gatorskin vs. GP 4000 ?

Dozens and dozens of roller rides over the past year have confirmed this feel, and the TrainerRoad data backs it up --- I'm riding (no b.s. here) roughly 30 watts higher on a 1-hour workout when using "Pinarello B". Full disclosure, 5'9" 66kg, FTP 260

Educate a dummy. I don't understand.

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mattr
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by mattr

Just the base tyres have a 10W CRR difference between them (per pair), if you add in rim width (wider = lower CRR) and different tubes plus a bit of drift/measurement error in the equipment and some slight errors in things like tyre pressure and position (though it's effectively the same bike by the looks of it) you won't be far off your 30W.

Also, doing slightly different sessions might affect the measured power output.

icenutter
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by icenutter

I agree. You could work it out for sure by swapping wheels, then tyres, and maybe even cassettes.

You could get a more precise wattage by working out your virtual speed for a set power with different setups.

Marin
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by Marin

Rolling resistance is my bet too. It's exaggerated by the roller because the tire deforms more.

On my free rollers, the difference between already-good open tubulars at low-ish pressure and my fastest tire set - Turbo Cottons with latex tubes - pumped up hard - is absolutely massive, really hard to pedal vs. almost no resistance.

JackRussellRacing
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by JackRussellRacing

Wow... I never would have expected the difference between tires to be *that* noticeable on rollers, but clearly it sounds like that's the culprit. Tonight I'll put some new GP4000 rubber on the crappy Vueltra Ultra Light wheelset and see how it behaves. (The Gatorskins are great for long rides on lousy roads, but maybe that's the only place they're worthwhile)

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ms6073
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by ms6073

Marin wrote:Rolling resistance is my bet too. It's exaggerated by the roller because the tire deforms more.

While I now have a Tacx Neo direct drive trainer, my experiences with Kreitler Compact with hot dog rollers (2.5" diameter drums with 10" width) a number of years back seemed to support higher pressures yielding lower rolling resistance. I would even go so far as to say, assuming a radially true wheelset, training on the rollers is one of the times were super high tire pressures> 100 psi (6.5 bar) actually make since.
Last edited by ms6073 on Thu Dec 01, 2016 8:09 pm, edited 1 time in total.
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icenutter
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by icenutter

JackRussellRacing wrote:Wow... I never would have expected the difference between tires to be *that* noticeable on rollers

http://www.velonews.com/where-the-rubber-meets-the-road-what-makes-cycling-tires-fast
http://www.bicyclerollingresistance.com/road-bike-reviews
According to the second link there's about 10w difference between a 4000s and gatorskin. Probably compounded because it's on a small roller.

AJS914
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by AJS914

Isn't there some kind of calibration? Can you have two different calibrations for each bike?

11.4
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by 11.4

Everyone understands that SRAM simply isn't as fast as Dura Ace. Haven't you heard?

Kinesthetic sense on rollers can cause quite a difference -- one tread feels different from another and you simply put out more or less energy because you're rocking it or hating it. Those two tires are pretty close to opposite ends of the spectrum, but not thirty watts worth. Put the same tires on both bikes and see if the differential goes away. I have a feeling it won't. Somewhere I suspect you have a setup or calibration difference that's throwing a tweak at you.

JackRussellRacing
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Location: USA

by JackRussellRacing

11.4 wrote:Those two tires are pretty close to opposite ends of the spectrum, but not thirty watts worth. Put the same tires on both bikes and see if the differential goes away.


Well I'll be a monkey's uncle! Tonight I put some fresh GP4000 tires on "Pinarello A" while retaining the same latex tubes and crappy Vueltra wheelset. The difference was indeed massive -- and the now the two bikes feel almost identical. GP4000 FTW :)

I'm stunned. I obviously knew that tire selection on the road was important, but blissfully ignored the role good rubber can play on rollers or a wheel-on trainer. I'll relegate the Gatorskins to my commuter. Thank you for everyone who responded.

mentok
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by mentok

Just to clarify, you don't have a powermeter on either bike do you? power numbers are reported by the rollers, right?

Similarly, I run soft gatorskins and heavy wheels when on my rollers and can ride at or above FTP no worries. I recently did a warm down with nice wheels and wasn't really able to get far past 75% FTP. I also lost ~10kg over the last season and I had do reduce the pressure i normally run to hit the same power numbers.

Rubber, but i guess more importantly friction can make a significant difference on the rollers...

mattr
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by mattr

TBH, for roller use it doesn't really matter, power is power, speed is of no importance whatsoever. And i'd not use anything fragile on rollers. The extra deformation caused by the small diameter roller, and the potential for extra heat in the carcase won't do the tyre any favours. Not as bad as a turbo though!

Jsut get some cheap nasties for rolling, or a couple of turbo tyres at £15 each.

And aren't trainer road programs based around power anyway? So you should be putting the same power out irrespective of how much mechanical losses the bike has.

JackRussellRacing
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by JackRussellRacing

mentok wrote:Just to clarify, you don't have a powermeter on either bike do you?

Power number is being reported by the Elite e-motion B+ rollers only.

(But, to answer your question -- both bikes *do* have a Quarqs. One has a DZERO and the other has a Red GXP. My full thread is about the power being reported to TrainerRoad from the rollers themselves, not the PM's on these bikes)

Delorre
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by Delorre

JackRussellRacing wrote:
mentok wrote:Just to clarify, you don't have a powermeter on either bike do you?

Power number is being reported by the Elite e-motion B+ rollers only.

(But, to answer your question -- both bikes *do* have a Quarqs. One has a DZERO and the other has a Red GXP. My full thread is about the power being reported to TrainerRoad from the rollers themselves, not the PM's on these bikes)

In that case, my guess is that YOUR power remains the same, but, as the GP4000s have less roling resistance, you manage to reach higher speeds, and the e-motion 'thinks' you put out more power. That's a pure calibration issue, and a limitation of rollers showing power rather than a crank based system.

11.4
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by 11.4

Delorre wrote:
JackRussellRacing wrote:
mentok wrote:Just to clarify, you don't have a powermeter on either bike do you?

Power number is being reported by the Elite e-motion B+ rollers only.

(But, to answer your question -- both bikes *do* have a Quarqs. One has a DZERO and the other has a Red GXP. My full thread is about the power being reported to TrainerRoad from the rollers themselves, not the PM's on these bikes)

In that case, my guess is that YOUR power remains the same, but, as the GP4000s have less roling resistance, you manage to reach higher speeds, and the e-motion 'thinks' you put out more power. That's a pure calibration issue, and a limitation of rollers showing power rather than a crank based system.


I'd basically concur with this. This is about where roller-based resistance and roller-based power systems don't work as well as drivetrain alternatives such as a Kickr. I would have been comparing crank arm power measurements all along.

Use the heavy tires for training. Why not? Save the nice tires for use on the road.

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