Changing tyre sizes...

[TheNissanMan]

Getting technical for me but if it helps strava believes my avg energy usage to be 165w

[thelawnet]

BRR hasn’t tested low-end Kenda tyres as fitted to new bicycles, but the two Kenda tyres they did test (here and here) had staggeringly high rolling resistance, which matches my perception of the Kendas that came on my girlfriend’s city bicycle – unbelievably draggy things.

Hmm, they do seem to perform consistently badly

http://www.mckramppi.com/en/bike04renga ... alyysi.htm
https://www.englishforum.ch/sports-fitn ... tires.html
https://roadbikeaction.com/tire-test-ke ... nd-maxxis/

[thelawnet]

Getting technical for me but if it helps strava believes my avg energy usage to be 165w

Well what does it say is the difference between the previous ride and the current one?

The wattage calculation is based on assumptions, e.g., a 'typical' pair of MTB tyres on a MTB, but it should be roughly accurate.

[horizon]

Getting technical for me

No, you started it.

By sharing each stage of your preparation in detail, it has allowed a lot of interesting stuff to emerge. I've really learnt something in this thread.

[TheNissanMan]

The last two rides before the new tyres recorded 144kwh so power output has increased...

Have had the bike service and would never have found the clicking or gear issue. Apparently when bikes are built they use a link on the chain that makes it easier to fit the chain on the bike which was overly stiff and not sitting straight which was rotating slightly diagonally. This has now been replaced with new link and gear cable also re tightened. Will get out on Tuesday and see how it goes.

[thelawnet]

The last two rides before the new tyres recorded 144kwh so power output has increased...
.

Presumably that is an average output of 144w, rather than a total output of 144kwh

[Samuel D]

So there you go, Strava thinks the tyres saved 165 W minus 144 W equals 21 W. Sounds about right although Strava is famously bad at power estimation (the problem being unsolvable without a power meter).

[TheNissanMan]

The last two rides before the new tyres recorded 144kwh so power output has increased...
.

Presumably that is an average output of 144w, rather than a total output of 144kwh

Yes, Avg 144/165 claimed...

[TheNissanMan]

So there you go, Strava thinks the tyres saved 165 W minus 144 W equals 21 W. Sounds about right although Strava is famously bad at power estimation (the problem being unsolvable without a power meter).

I have the wahoo cadence and speed sensors fitted to the bike, stupid question but is there another sensor to measure power as the power meters I can see look to be exactly the same.

[thelawnet]

So there you go, Strava thinks the tyres saved 165 W minus 144 W equals 21 W. Sounds about right although Strava is famously bad at power estimation (the problem being unsolvable without a power meter).

I have the wahoo cadence and speed sensors fitted to the bike, stupid question but is there another sensor to measure power as the power meters I can see look to be exactly the same.

cadence is just measuring the number of times the pedal passes a certain point, the speed sensor measures the number of times the magnet on the wheel passes a point on the frame, while a power sensor is inherently more complicated as it has to measure the power (which depends on the terrain, gradient, etc)

[TheNissanMan]

Would it not be possible to calculate as the revolutions vs the speed with gps giving elevation must give a close estimation to power or is that what strava is already doing?

[Samuel D]

Power meters use strain gauges to determine the torque at some part in the drivetrain and then multiply that by the speed of that part of the drivetrain to get power. There is no getting around the requirement for strain gauges. Strain gauges themselves are not very expensive but their calibration is difficult and not susceptible to mass-scale, automated production. That is why power meters cost around €500 and up.

Strava gives a tolerably good estimate of power on climbs if it knows your weight and that of your bicycle accurately. The steeper and longer the climb, the better the estimate.

However, you can do this calculation yourself, since power equals work done divided by time, and the main work done on climbing a hill is increasing your gravitational potential energy. Multiply your all-up weight in kilograms by the height climbed in metres by acceleration due to gravity (9.8 m/s/s) and you’ll get your potential energy in joules; divide that by the time in seconds it took you to climb between the two points and you’ll get an estimation of your power. Add about 20 watts for rolling resistance and drag at climbing speed to increase the accuracy of your average power estimate during the climb. Strava just automates this.

On flats or descents, speed is mainly determined by wind and aerodynamics, things that Strava knows nothing about for individual cases. The estimates are therefore pretty useless.

Power is not an interesting metric for beginners anyway. It can be useful for advanced training and pacing after you’ve done a whole lot of work and tests to establish your curve of sustainable power versus time.

Concentrate on getting comfortable on the bicycle over a period of hours, drinking and eating while riding, and not overdoing it at the beginning of long rides. That’ll take you far.

[TheNissanMan]

Just as a quick further update, yesterday I did a 30 mile (suffering today) cycle trying new tyre pressures at 75R 55f, although the bike felt as comfortable as the lower pressures from Sunday looking at the energy useage and avg speed over various Strava segments the lower pressures definitely look as if they respond better and provide a quicker ride.

Will be lowering them on Friday ahead of Sundays ride, getting closer now!

[NetworkMan]

Since all threads on the site eventually turn into chat about Vic. Hypers I have a couple of points:-

1. If you do indeed pump them up to crazy pressures there is a real danger that the rim may get damaged since the force on the rim from a fat tyre is higher than form a thin one at the same pressure.

2. As I'm very light I've been looking for light, inexpensive wheels for the 35/37 mm Hypers on my steel Spa Touring. I've just found Mavic Aksium:-
https://www.sigmasports.com/item/Mavic/ ... -2018/F1AE
These are really light, inexpensive, and perhaps surprisingly are 17mm internal width. Mavic only recommend them for up to 32mm tyres but using the rule of 2.2 times internal width they should be OK for up to 37+mm. Any reason why I shouldn't use them with my Hypers? I, bike, and luggage are far, far less than the quoted 120 kg.

[TheNissanMan]

So feedback after a longer ride (l2b), what a difference, I was still slow uphill but then I’m unfit but downhill I found quite amusing, with the Hypers I was just coasting down at a rate of knots without peddLing and sitting up to have a rest, it was amazing how many people I was cruising past comfortably which were trying to sit down into the bike and still peddling.

An only really put that down to the rubber below as I’m a rather large wind break and was rather pleasant looking at what looked like expensive machinery rolling at a much slower speed