Weight...how much does it really matter?

Slim wrote:"Not so much the time as the effort" Ok, same parameters and speed fixed at 5 mph, I get 211 W for the 18 lbs bike and 216W for the 23lbs bike, so 5W effort for the heavier bike. Where a 5 lbs bike will make a huge difference is when you have to carry it on your shoulders.

drwelby wrote:There are a bunch of calculators on the web that do this. I ran some quick numbers at bikecalculator.com using the following values:

Rider: 200 lbs, putting out 200 watts.
Hill:5 miles at 8% grade.

On an 18 lb bike it should take 59.68 minutes
On a 23 lb it should take 59.97 minutes.

So five pounds on the bike saves you 18 seconds over about an hour. 

I'm not sure if 18 seconds is important to you. Note that losing 5 lbs from your body would accomplish the same result, and probably more if the weight loss is from training.

namdoogttam wrote:

But also remember that you don't start from a stop at the bottom of every hill....in the real world, you often carry momentum from a previous downhill. So if your route consists of shorter rolling hills, you're less likely to incur the 'cost' of bike weight (when compared with a long climbing to get up over a mountain pass). Just another factor to consider.  

Call me a weight weenie, but… weight does matter.  

The crude estimate that I’d heard was about 1% extra effort climbing per kilo (or 1% slower speed or 1% longer time).  That’s roughly 0.5% per pound.

drwelby’s numbers in Post #2 suggested an 18 sec penalty for an extra 5 lb over a 1 hour 5 mile climb on a 8% grade, or ~0.1% for each extra lb.  This struck me as being too small an effect, so I ran some numbers on the bikecalculator.com web site reflecting what I might encounter on a mountain bike. Please check the results to see that I did not make a mistake! 

A 170 lb rider on a 30 lb. mtb riding a 7.5% grade for 4 miles would require 200 watts output to maintain 4 mph and complete the climb in 60 min.  The same ride on a 25 lb. bike would only require 195 watts output to complete in an hour, a 2.5% drop corresponding to 0.5% less effort per pound.  If the rider put out 200 watts on the lighter bike the speed would increase by ~0.1mph and time would drop by ~90 sec, both equivalent to a 2.5% drop or 0.5% per pound.  The time penalty for the heavier bike is thus ~18 sec per pound. For heavier riders, such as the 200 lb example, the effect will be slightly less.

In terms of distance:  the 4 mph speed in the above scenario corresponds to apx. 5.9 ft/sec, so the 30 lb bike would lag behind the 25 lb bike by about 528 ft (0.1 mile) after 4 miles. Again, this corresponds to a 2.5% difference, or 0.5% per pound.

The differences in time, speed, effort, and distance covered are not huge, and as drwelby said you have to decide if it’s important to you.  I also agree with drwelby’s other comments: “Note that losing 5 lbs from your body would accomplish the same result, and probably more if the weight loss is from training.”   As pointed out by Bsfdivder fit and comfort are also key to performance and may compensate for weight increases.

Re wheel/tire weight:  Have to disagree with namdoogttam.  Unless you’re riding a steady pace on smooth roads with minimal terrain changes (e.g., a road bike time trial) this is where weight is most important.  Whenever your speed changes you have to reaccelerate the bike each time it slows (rotational inertia).  It does not have to be from a complete stop. The real world benefit is easily recognized, especially in off-road situations where speed is constantly changing.  The maneuverability of a lighter weight spinning wheel/tire combo is also easily recognized

Bottom line:  Weight matters.  How much it matters is up to you - are you most concerned with speed? with handling? with comfort? with durability?

drwelby wrote:There are a bunch of calculators on the web that do this. I ran some quick numbers at bikecalculator.com using the following values:

Rider: 200 lbs, putting out 200 watts.
Hill:5 miles at 8% grade.

On an 18 lb bike it should take 59.68 minutes
On a 23 lb it should take 59.97 minutes.

So five pounds on the bike saves you 18 seconds over about an hour. 

I'm not sure if 18 seconds is important to you. Note that losing 5 lbs from your body would accomplish the same result, and probably more if the weight loss is from training.

drwelby wrote:You can do the math - wheel weight is worth about double. You have to accelerate the wheel sideways at it's weight, and then you also have to spin it. Since most of the weight is at the edge, you can count the weight a second time.

namdoogttam wrote:The emphasis on rotational weight (wheel weight) is a nice theory, but it's waaaay overplayed and it's been largely 'debunked': https://youtu.be/vhhLUA7kG5A?t=2m3s.

As usual, most of the weight-weenie discussion in this thread centers around ideas, concepts, and theories that do have a kernel of truth to them but fail to actually produce any decipherable results in the real world. The supposed benefits are so negligible - fractions of percents - that they're almost irrelevant. I'd wager that the majority of members of "The Riding Gravel Forum" (myself included) waste far more time pissing in ditches than they could ever make up with a $15k bike budget. 

But...to each his/her own. "You can spend as much as you want".