Right this one has bugged me for 24 Hrs now and I think I have close to the best way to test the OP’s question in the real world:

First you need to find our two hypothetical, similarly performing, similarly built, ~10Lb different riders, before any test could be performed I think you need to try and “harmonise” their fitness as much as possible/reasonable, force the two poor buggers to live under the same conditions for lets say 48hrs, eat and drink the same, exercise the same, rest the same, basically maintain their weight difference (48hrs shouldn’t be long enough for a significant change), take on the same nutrition/hydration, and match each other on training and rest.

Next the bike, all this talk of different bike configurations is beside the point, we are trying to quantify the effect of body mass and bike mass, so the test bike has to be a fully rigid single speed machine, the bike plus each rider will be weighed. The difference in weight will be added to the bike by strapping weights (probably in some sort of bag) to the frame when the lighter rider is using it, preferably within the front triangle and as close to the BB as possible, this means that wheel's rotational mass is the same for both, suspension effects are as minimal as humanly possible and COG is affected as little as possible.

Both riders will be equipped as identically as possible, i.e. same helmet, clothing, hydration pack or water bottles, shorts, jersey, shoes, hair gel, socks, everything… Remember we are trying to minimise variables.

A Short XC course will be laid out, one which gives approximately the same distance of climbing and descending, the riders will alternately do a lap each, between each lap the bike will be wiped clean of as much Mud as possible, each rider will be given the exact same amount of water and food for each lap/rest period, and the weight pack added/removed from the frame depending on which riders lap is next, this will be done for say 5 laps each, every lap being timed, and also timing key climbing and descending sectors of the lap…

What we’re looking for in the sector times is peak speeds, which rider is able to climb/descend fastest, both in a single lap and averaged out over the whole day, the lap times again we are looking for fastest lap times but also for drop off in performance over the whole 5 to see who tires fastest, again using the sectors to see where that drop off is most pronounced…

The reason for using the same bike and not making the two riders race each other is simply so that neither rider can gauge their speed from the other, and they won’t be tempted to race each other directly, there should be no bar mounted computer or watches allowed to indicated speed or time and riders will not be given any timing information until the experiment is completed.

If you wanted a real world test of Rider Vs Bike weight I reckon the above is about the best way to go about it… :nerd:

you log your commuting times and bikes that you've used.

That IS dedication.

Your just too polite to use the word anal???

I keep a log of all my rides – one way of motivating myself to ride regularly.

It also works on another level…… In discussions with my wife, x miles per year commuting = £y saved in fuel and £z in car running costs (typically £100-200 in fuel, £500-600 in typical ppm running costs) Very useful in bike budget discussions!!!

As an environmental professional I also find it interseting to equate bike commuting mileage to CO2 saving etc…

I have logged my commuting times for the past 2 and a bit years..

I don't log my other rides, I simply treat the commute as a baseline indicator of my general fitness and endurance, it's useful as it's a set distance on the same bike on the same roads, so other than traffic lights and weather the variables are minimal…

you log your commuting times and bikes that you've used.

That IS dedication.

Your just too polite to use the word anal???

My daughter's nappy needs changing so I'm trying to avoid thinking about bum stuff as much as I can.

The flaw in this question is that realistically, if someone turns up looking a bit of a chubber, on a fancy lightweight bike, you would almost always expect them to be slower than the person who turns up looking super skinny and fit, but riding a hire bike.

The only question that is relevant to any actual rider, is whether they'd be better off losing 10lb off the bike, or off them. Now in reality, for most people who aren't super skinny and fit already, that'd probably involve riding more, eating more healthily and generally getting a lot fitter.

Personally I think the answer to that question for most riders who don't ride tons already is that if they have the time, they'd be better off riding. If they don't have the time, maybe they should spend some money to compensate.

Joe

Anyway, you've proved that a lighter bike is quicker than a heavier bike on that particular journey. Well done.

Thinking about this over lunch, and I don't think I have proved the lightest bike is quickest – despite that being my intuitive position on light vs heavy bikes.

What I think I have shown is that the stretched out XC race type frame geometry is quicker than the shorter more modern / upright geometry of the Pace / Reign

The light race hardtail is quickest, yes, but there is only a pound or two difference between that and the Pace. There is approx 8lb weight difference between the Pace and the Reign, yet both their quickest and average times are almost identical….

If advantage was based only on lightest weight, there should be a much bigger gap between the Pace and Reign. Whereas comparing geometry, both of these feel like hard work on the climbs, whereas the stretched out position on the race HT is a real advantage on climbs.

…ETA… and in terms of "that particular journey", it does have a good mix of terrain and gradient. Approx 4 miles of country lanes with undulating 10-20m climbs / descents, a 150m lane or forest singletrack climb, followed by another mile of lanes, a 200m woodland / quarry descent and flat riverside cycle path