Lighter Wheels: Climb vs Descend Benefits
 

I have a set of Axis 1.0 Wheels which weight about 2000g+ and I'm lookng to get a new wheelset. Something in the 1500g range.

Now I know reducing rotational weight will help improve speed and climbing but does the same increase on climbs decrease the speed on my descending because theirs less weight going down the hill?

Yes.

For descending, you need these.:thumb:

Tech: HED launches descending special | Cyclingnews.com

So why in this case do people say wheels should be the first upgrade if the benefit are only on climbing and you have reduced speed on descending?

Math - w/out getting too detailed you spend more time climbing than descending.

your tuck and line choice i.e. descending technique plays a bigger part in downhill speed than wheels.

also most people get a higher sense of reward dropping time off a climb than a descent.

Need to clarify if we're talking acceleration or max speed.

I built a set of wheels recently which I didn't weigh, not having a suitable scale, but the parts sum = 1450g. They're Kinlin XC279 23mm X 28mm rims, 460g, 20H and 24H, CX-Ray spokes. Parts cost was $340. I run 23mm Conti 4KIIs on them. I did a non-technical 3000' pass descent with a group this past Sunday. I had to wait a good minute at the bottom for the next rider, another minute or so for the 3rd guy, then more waiting. I'm a short-legged 145 lb. guy on a 52 with a slammed stem, so my bars are only 5cm below my saddle. I was doing 35-40 mph most of the way. They were even further back on the preceding pass descent.

The right lightish wheel and tire combo descends just fine.

I often brake going downhill. Not too often when climbing. Yes, I know, but folks are fessing up to all sorts of flaws on BF these days....

Possibly because you are doing hard work to climb, and doing very little work descending.

if the descent is long or steep enough, you might not even be pedaling.

But if you don't pedal, you don't climb.

Obviously if you had a 400-lb bike you would have a lot more momentum on the downhill. Of course, it would take a pretty long hill to get up to speed, but it would overcome as Lot of wind resistance with inertia.

Of course, you probably wouldn't be able to ride the thing on the flats, hardly, and forget climbing.

Also ... no matter how fast you go on the downhill ... the next climb is just as steep and hard. You might climb at 10 mph for an hour, zip down the other side at 50 mph and get there in 12 minutes .... and have another hour climb at 10 mph. And then, another.

With a heavier bike, you might climb a six mph for an hour and 40 minutes, zip down the far side at 60 mph and finish in ten minutes ... and now have to haul that heavy bike up that hill and it might take you two hours this time. And ... you get two minutes less recovery. ;)

By the third hill, you might say "Eff it." You have already spent two-and-a-half hours climbing and have a huge hill left.

Meanwhile the guy on the lighter bike has climbed for three hours and is heading on that long final downhill. He will only hit 50 mph ... but he will be home soon. You will be out in the middle of the mountains, exhausted, trying to find cell phone reception so you can get a ride.

But yeah, your heavier bike might go a little faster on the downhills.

I think aerodynamics are more important to descending.

I don't see the light wheels being an issue on decent. They still have to spin up and heavier wheels are going to spin up slower even going downhill.

The extra little bit of weight of a heavier wheel is not going to help you much going down hill. It adds a little more potential energy but this is lost to the increased rotational energy being sucked up by the wheel.
On the climb, the reduced weight helps a tiny bit in the (less weight in general is better when climbing) and the reduced rotational energy is a positive too.

Bottom line, don't worry about the affect on the downhill. I don't think you will be able to see any difference.

Who said that?

On a straight, low wind buff, un-braked decent, go aero. But most descents are twisty. Handling matters, as does aero. You have to figure it out, but if you are thinking brakes will be involved, use the lighter better handling wheels.

You don't have reduced speed on the downhill if you're riding with others. No one's going to drop you on a descent because your wheels are too light. On the other hand on a long steep climb saving a couple of pounds of weight could make a substantial difference in your time up the hill.

The new wheels weigh about a pound less than the old ones. 500 grams is the weight 17 ounces of water. Can you tell the difference on a climb if your bottle is full or mostly empty? It'll cut a couple of seconds off your climb, perhaps.

Light wheels that spin up quicker also spin down quicker, so the net effect is quite tiny. But they seem faster. My replacement wheels went from 2000 grams to 1550, and I noticed a quicker steering response. And they felt faster, but was that a real effect or just expectations?

This is the real answer. Your speed going up a hill is limited by your fitness; going down, it's limited by your skill, by traffic, road and weather conditions, etc.

About 13 seconds on a 40min climb. Whether that's important depends if you're racing or riding in a competitive event where you're trying to maintain contact with faster riders. A 13 second gap could mean the difference between staying with and being dropped from a group. If you're dropped the ultimate time difference will be far greater.

People generally suggest upgrading wheels because A.) a lot of bikes come with soft, heavy wheels, and B.) it is a much more meaningful upgrade for most bikes than the ones people do.

If you can save a pound of rotating weight you are improving your bike's performance potential a lot more than the almost imperceptible change of going up one level in group set, and way more than a new stem or seat post with a flashier logo.

Strong, stiff, light wheel waste less energy. Every time you speed up and slow down they offer a small benefit.

Will you be able to feel that benefit? Maybe doubtful, maybe imaginary ....

I swap between a CF climbing bike (not super light but pretty light) and a pair of aluminum endurance/tourers which weight 25 or 26 lbs ... 8-10 lbs more.

When I first climb onto the different bike I can tell ... for at least the first 20 yards.

Then it is just another bike ride.

If light wheels are better climbing and heavy wheels are better descending ... this isn't rocket science. Climb on light wheels, swap to heavy wheels at the top. Problem solved.

Or... https://en.wikipedia.org/wiki/Jean_Robic

Only actual weight affects climbing and descending. So getting wheels that are 500 gm lighter is the same as reducing some other component by 500 gm. Rotational weight affects acceleration/deceleration. Lighter wheels accelerate a little faster and but lose speed faster, so you might surge and lag compared to heavier wheels which tend to even out your speed a bit, but the overall speed comes out the same.

500g on wheels <> 500g on bike.
There is a huge amount of side to side movement (change in velocity = acceleration) even when the bike is going the same speed.

Who said that?

Light, aero wheels is your best choice.

Many options available in the 1500-1600 g range.

In any case, do you sprint at the top of every descent until you reach max speed, then go into a full-on top tube tuck with your chin on the stem, hitting the apex of every turn with reckless abandon? If no, this is a completely useless question.