But the OP asked about "speed".

You are probably right, I will measure the rims. It was a nice fantasy while it lasted. If I have a flatter tire profile it may explain why the bike feels really different on turn in to fast corners when I lean it over. The wheels are different but I really couldn't put my finger on why the bike feels like it does on turn in.

I think it is more interesting to look at the performance of a bike that is being ridden than how far you can throw a wheel.

Air flow across wheels on an actual bike with a rider interacts with the rest of the bike in complex ways. The down tube drafts the front wheel and the rear wheel drafts the seat tube. Meanwhile, the rider's legs are churning the air all around the wheels and frame, and the rider's body, compared to the wheels and frame, is basically a parachute.

MIT wind tunnel testing with a bike and rider shows that "... wearing gloves in a time trial will slow you down more than using a nonaero front wheel." "The drag difference between a vented road helmet and an aero-helmet is 2-4 times larger than the difference between a good aero-wheelset and a 32-spoked wheelset."

And those comments are based on the rider in a time-trial position. A rider on the drops of regular road bars, or worse yet, on the hoods, has such a big affect on aerodynamics that your choice of wheels (from an aerodynamic perspective) is even more trivial.

In addition, low-spoke-count wheels require heavy rims to distribute the stresses, so they accelerate more slowly.

For the 400-watt pro, a second or two in a time trial matters, but for the rest of us, aero wheels are jewelry.

Refences: https://www.pezcyclingnews.com/defaul...lstory&id=3574

https://www.bicycling.com/article/0,6...4995-1,00.html

Whew, I only wear gloves if it's 45 degrees Fahrenheit or below, saving money on gloves AND wheels! Wonder if I should shave my arms and hands this summer.

Those are interesting tidbits, sluggo!

There are a hopeless amount of variable but this is a good field test.

Well, that's not really a good test since there were so many variables that weren't controlled. The only way to measure the difference in wheel-performance is to at least maintain constant speed or constant power-output. And control all other variables like air-temp, wind-direction and speed, relative-humidity, as well as air-density (same course on different days will have different air-density due to varying atmospheric conditions). You MAY be able to compensate for those variations if you measured all those conditions, but they weren't recorded. And the rider's fitness-level and recovery-state will be different on two different days as well. Way, way too many variables to narrow down the performance differences between two wheelsets.

Well, I'd like to answer the OP's question anyway since this is such an academic discussion. First, let's use the Kreuzotter site to calculate bicycle-speed given various aerodynamic positions and power-outputs: https://kreuzotter.de/english/espeed.htm. I used the following changes from the default settings:

1. roadster
2. hands on drops
3. air-temp = 70F for STP
4. height above sea-level = 0ft for STP
5. blank out watts box in lower-left
6. enter 31mph in speed box in lower-right
7. hit CALCULATE

And we get 565 watts required to push that bike at 31mph in the drops at sea-level. Al1943 is correct in that using steady 50kph is an unrealistic test-speed as most riders won't be able to output 565-watts for long. However, let's use that speed since that was one of the few instrumented tests with data we can use. And it may closely match the sprint of an average rider and he'd want to know how much faster he can beat his friends if he upgrade his wheels.

Let's use the 18-watt difference between the "slowest" Mavic R-sys wheel used in that test versus the "fastest" Zipp-808 and plug that difference into the model:

8. blank out speed box in lower-right
9. enter 583 in the watts box, basically 565 generated watts + 18 "free" watts from "faster" wheels
10. hit CALCULATE

and we get an increase of 0.4mph to 31.4mph when upgrading to the "fastest" Zipp-808 wheels or 1.3%. Of course this is only from the Mavic R-sys wheels. Depending upon what wheels you originally had, your speed-increase will be more or less than this.

Danno;

Thanks, the best post of the whole thread IMO. It actually provides a quantitative comparison and shows the amount of difference in performance likely with a change of wheels, very minor for the average road rider.

I would expect tires to make a bigger difference than wheels as far as the average rider is concerned. The general rule for tires seems to be narrower and higher pressure is the way to go though it also seems subjectively that rolling resistance varies considerably with construction. By reputation it seems in a given size the most puncture resistant tire is going to have the highest rolling resistance. Apparently no such thing as a free lunch.

Do you have a link to information on tire rolling resistance data by tire make, model and size?

Well.... tyre rolling-resistance is measured in grams of drag (or milli-Newtons). Not much of a milli-wattage difference between the fastest and slowest tyres in terms of rolling-resistance. Their aerodynamic profile is a bigger contributing factor to speed and narrow tyres block less wind, and weigh less for hillclimbs. Jobst Brandt, the granddaddy of biking physics did a study on rolling-resistance decades ago. As well as Damon Rinard. I'll look for some graphs somewhere.

Meanwhile, power-required to overcome rolling-resistance remains fairly constant relative to speed due to the low-RPMs of bike wheels, while power-required to overcome wind-resistance goes up to the 3rd-power of speed. What this means is that the grams of rolling-resistance doesn't really increase much when you double your speed. However, aero-drag is measured in kilograms of drag and you need 8 TIMES more power to overcome aero-drag at twice the speed (or use Newtons pushing you back):

Check out this site where Damon Rinard graphs rolling-resistance versus aero-drag relative to speed:

https://www.sheldonbrown.com/rinard/aero/formulas.htm


Basically the faster you go, the less and less drivetrain/rolling-resistance contributes to total-drag while aero-drag becomes much, much more important. For beginners who want to get faster, the most dramatic increases will come from learning an efficient pedaling-motion and getting the flexibily to generate high-wattage while tucked down in an aero position with flat back and horizontal forearms. This will easily give you +5-7mph or more for the same power-output.

DannoXYZ, your avatar's demeanor doesn't match your intellect.