you can use this page on analytic cycling to work this out for yourself, if you have a reasonable guess of your CdA on each bike:

http://analyticcycling.com/...LessWeight_Page.html

5% at your w/kg will tend towards the TT bike being a teeny bit faster if you make the same power on it. Depending on mass difference and such.

If you make 10 less watts, maybe not. run the numbers!

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Kat Hunter reports on the San Dimas Stage Race from inside the GC winning team
Aeroweenie.com -Compendium of Aero Data and Knowledge
Freelance sports & outdoors writer Kathryn Hunter

How much lighter is the road setup? Which one do you practice climbing form in more often?

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Run PR's: 18:05 - 36:58 - 1:22:59 - 3:07

I climb very little on either tbh, flat round here (road bike is a bianchi oltre xr2 which when I got it I was told is just under the UCI limit, TT bike is a heavier Argon18 E114, I would guesstimate the TT bike to be 1.5KGs heavier)

I am flexible with a strong core so can hold the TT position fairly well for long periods.

If it were me, I'd use a road bike with aero wheels, a tight fitting skinsuit and a TT helmet.

ta for link, well it looks fairly close if I take off 10 watts for the TT bike and the extra weight,,

there is normally a tail wind on the course so I'd lean towards the road bike..

Road bike with skinsuit, aero helmet, shoe covers, etc.

Sounds similar to Lookout Mtn here in Denver/Golden. Pretty sure I personally would go with my road bike on that over my tri bike.

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Colorado Triathlon Company, CO2UT 2021, Crooked Gravel 2022, Steamboat Gravel 2022

We have a very similar TT in our local stage race, but with a short downhill and a flat section at the end. Folks used to ride road bikes with clip-ons, but they got tired of the TT bikes beating them. At 12-13 mph there is still a substantial aero advantage to be had on the TT bike, if you can generate nearly the same power as on the road bike.

I ride it regularly on both road and TT bike in training, so I have a lot of data. The TT bike is 30-40 seconds faster on the hill alone, even more for the full course.

This if you can stay tucked and can still put out same power at ~12-14 mph. See US Pro Tour Challenge uphill section and Teejay or Uran at moderate hilly 1st TT of the Giro. A lot of riders though have power disparities on road versus tt (could be 20 watt difference from the data I've seen lately from the Pro Ranks). If that is the case back to the roadie.

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Founder: BestBikeSplit
Amazonian

Something seems off....30-40" is what most claims are for a TT bike in a 40k TT vs. a road bike. Seems like a HUGE delta for a 5 mile, uphill TT.

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Chicago Cubs - 2016 WORLD SERIES Champions!!!!

"If ever the time should come, when vain and aspiring men shall possess the highest seats in government, our country will stand in need of its experienced patriots to prevent its ruin." - Samuel Adams

40 seconds over 40k would only be a 10W difference (ROT IS 10W ~= 1s/km) in aero drag between the road and TT setups. That seems fairly low to me.

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http://bikeblather.blogspot.com/

I raced San Dimas Stage RAce TT and Joe Martin Stage Race TT this year on the pro NRC circuit. Both uphill at about 5-6% average and 95+% of riders were on road bikes with maybe only 20% using clip ons. And this with average speeds approaching 28-30kmh.

For the vast majority of pros it would seem uphill absolute power is compromised on a TT rig. So unless you know you can crank the torque and watts in aero I would stick to the roadie, especially considering your speed will be 8-10kmh slower.

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Professional Athlete: http://jordancheyne.wordpress.com/ http://www.strava.com/athletes/145340

Coaching Services:http://www.peakformcoaching.com/

Really? A TT bike is only worth 3/4 to 1 sec/km over a road bike? Not on this planet, where just putting clip-ons on a road bike saves 1-1.5 sec/km.

But thanks for making me re-examine my numbers. I'll grant you that my delta(road-TT) is probably larger than most. My TT position has pretty low drag (CdA .21-.22), but my road bike position is fairly upright. Also, the wheels that live on my TT bike are much more aero than the training wheels on my road bike, and have lower Crr.

That said, I'll still stand by the statements made above, particularly the underlined one. If you don't believe it, just go to analyticcycling and plug in the numbers. It's just physics!

TT bike. And disc. Always disc.

Joe Martin is 6.8% average according to one source I checked, and while almost everyone uses a road bike, it has been won on a TT bike before on the men's side!

I rode the course a few times this year and was thinking hell yes I would use a TT bike, if I had a light one...but I'm weird in that I lose no power.

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Kat Hunter reports on the San Dimas Stage Race from inside the GC winning team
Aeroweenie.com -Compendium of Aero Data and Knowledge
Freelance sports & outdoors writer Kathryn Hunter

Sorry....poor phrasing on my part. I was referring mostly to the frame, not the resulting change in position, as well. And with the speeds the OP was talking about (12-13 mph), I doubt many people are holding an aero position.

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Chicago Cubs - 2016 WORLD SERIES Champions!!!!

"If ever the time should come, when vain and aspiring men shall possess the highest seats in government, our country will stand in need of its experienced patriots to prevent its ruin." - Samuel Adams

Then something is wrong about their aero position...I can hold mine going up am 8% average grade! going ~9mph or so, ~20 minutes at a time...

Even so, depending on the road and TT frames being considered, it most likely is well more than 10W on the frame alone...heck, I saw more like 10-15W just between a P2K and a P3C.

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http://bikeblather.blogspot.com/

So because you can hold your position like that, everyone should / can?

What ever happened to "N=1"?

The reality is that at speeds higher than even the 12-13 mph noted by the OP, people start bailing out of their aero position. What was Rapp's "breaking point" where the data indicated he was better sitting up? IIRC, it was around 15 mph, and he obviously has a very slippery position.

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Chicago Cubs - 2016 WORLD SERIES Champions!!!!

"If ever the time should come, when vain and aspiring men shall possess the highest seats in government, our country will stand in need of its experienced patriots to prevent its ruin." - Samuel Adams

Jordan has a slippery position for a long course triathlete, I'm pretty sure he could get slipperier if he was concentrating on short TTs ;-)

In any case, you're getting off the point that the difference between a typical road frame of today and a TT frame is usually more than ~10W.

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http://bikeblather.blogspot.com/

Actually, my point was that it seemed unlikely that a TT frame on a 5 mile, 5% grade TT would yield a 40" difference.

By your own math, a 10w difference would only yield a 8" difference for a 5 mile TT. So in order to save 40", you would need a frame that saves you 50w.

Correct me if I am wrong, but the time savings of 10w = 1 sec / KM saved is also based on a 30 mph test (or maybe 40 kph?) The speeds for this uphill TT would be substantially less, correct? So doesn't your time saved / KM also drop?

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Chicago Cubs - 2016 WORLD SERIES Champions!!!!

"If ever the time should come, when vain and aspiring men shall possess the highest seats in government, our country will stand in need of its experienced patriots to prevent its ruin." - Samuel Adams

Well...that's where we start getting into the true differences between people's positions on road bikes and TT bikes...heck, I've seen my drag on my TT bike go up by the equivalent of ~20W just if my bar height is too high by 5mm.

The ROT is based on typical TT speeds, so yeah, it would be de-rated for this sort of TT...which just goes to show the best thing to do for these decisions is to model the whole thing up. It's not that hard ;-)

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http://bikeblather.blogspot.com/

That does seem unlikely. But nobody has made that claim, have they? The discussion is about TT bikes, not TT frames, no?

Anyone riding a TT who isn't holding an aero position at 12-13 mph is giving away time to the competition. In a short TT, the only reason to be out of aero position at those speeds is if you are one of those folks who can't generate power in the TT position. In a longer TT, 12-13 mph may be your opportunity to stretch and relax a bit - but you're still giving up time.

Thanks guys

Eb - ""My TT position has pretty low drag (CdA .21-.22), but my road bike position is fairly upright""


That's me as well (not saying anywhere near your CdA, just in comparison to road bike posistion) , I have a pretty good TT posisition I can hold, but roadbike is fairly upright, that's why I mentioned in orginal post that there is, more often than not, a decent tail wind.

On my road bike I would benefit more from that tailwind as will be presenting more surface area to get blown up the hill?

Ok - so I know with my weight I'm gonna be well towards the back of the field and much much slower than the top guys but was genuinely interested in getting the best performance for myself so thanks for all the replies.

Being more upright would be a benefit with a tail wind if and only if the tail wind is faster on average than your average speed. If the tail wind is slower than you, the TT bike is aerodynamically advantageous, although by less so than with no wind or a headwind.

Ah - cheers will have to google so I understand..

We can argue what people should do at what speeds all day, but the reality is what I described....most people are out of aero well before 12-13 mph.

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Chicago Cubs - 2016 WORLD SERIES Champions!!!!

"If ever the time should come, when vain and aspiring men shall possess the highest seats in government, our country will stand in need of its experienced patriots to prevent its ruin." - Samuel Adams

If you extrapolate down from tests done at 30 mph in a wind tunnel possibly, but on the road at those speeds, are you sure?

Only if you're traveling slower than the tailwind...think about it ;-)

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http://bikeblather.blogspot.com/

Really? In all situations? How much time?

Yes, I'm sure. Try analyticcycling.com if you don't believe me.

You, of all people ?! I really hope you're pulling my leg! Because if you truly don't get it, then you are leaving time on the table, and you of all people should not be leaving time on the table. If you were in my age group I'd tell you to go ahead and ride your road bike! ;^>

The answers are "Yes", "No", and "It depends". I'm only being the tiniest bit flippant.

Go to analyticcycling .com. There are several different calculators that would work - I tried http://www.analyticcycling.com/WheelsClimb_Page.html

Enter the following: Note: everything is identical except CdA ("Frontal Area" * "Coefficient Wind Drag"). You have to be a little careful with the calculator because it apparently rounds those two inputs to one significant figure. I used values of .24 (0.6*0.4) for a TT bike and .28 (0.7*0.4) for road bike. In most cases the difference in CdA between road bike and TT bike would be greater than .04, so this is a conservative estimate.

Data Parameters Parameter Standard Rider Test Rider
Frontal Area 0.6 0.7 m2
Coefficient Wind Drag 0.4 0.4 dimensionless
Air Density 1.226 1.226 kg/m3
Weight Rider 65.0 65.0 kg
Weight Bike 8.0 8.0 kg
Front Wheel
Weight 1.300 1.300 kg
Ic 0.0900 0.0900 kg m/s2
Cx0 0.0500 0.0500 Dimensionless
Radius 0.337 0.337 m
Rear Wheel
Weight 1.800 1.800 kg
Ic 0.1000 0.1000 kg m/s2
Cx0 0.0491 0.0491 Dimensionless
Radius 0.337 0.337 m
Rear Shelter 25. 25. %
Power 300. 300. w
Coefficient of Rolling 0.004 0.004 dimensionless
Grade 0.05 0.05 decimal
Initial Speed 0.0 0.0 m/s

(sorry about the format)

The results? "At the end of 8000m Standard Rider is ahead by 19.91s and 124.97 m."

Go ahead and run it yourself. That's a 5 mile, 5% grade climb. Speed ends up being a bit over 6 m/s (22 km/hr).

Any more questions?

"It depends" and "everything is identical" answers all my questions.

Ok - I did the hill this morning on my road bike, (I'm actually I'm 90KGs, plus the bike, probably 7.5KGs with water and seat pack.)


According to wko+, the gradient was 5.2% @ 4.92 miles


for 300 watts (301NP) I averaged 11.4 mph , 25:42, 117 place, (3rd on same hill with an actual powermeter is; 351 watts for 18:28, 15.8 mph)



http://www.strava.com/...50067?filter=overall


If I try TT bike I'll post result.

That's pretty similar to Bear Mtn near where I live.
Tri bike all day, every day, and twice on Sundays. There is a definite aero benefit, even at those speeds.
(like Jackmott, I don't lose any watts on my TT bike)

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float , hammer , and jog