azza_333

I am looking into building up a new wheel set, using DT Swiss 240 disk centre locking hubs 32 hole, DT aerolite (buddle butted and slightly bladed), Brass nipples

Consider a cruising speed of 25km/h (15.62mph), and another cruising speed of 30km/h (18.75mph). at each of these speeds how much difference in watts or km/h (mph) would the 38mm rims make over the 18mm rims


Carbon, 38mm deep, 430g
VS
Alloy, 18mm deep, 417g

RobbieTunes

No clue. At those speeds, build what looks good.

Drew Eckhardt 

14/17 gauge aero spokes like Aerolites save 1-2W at 30 MPH compared to round ones like Revolutions so that's 0.25 - 0.5W at 18 MPH.

Rims vary. Vaguely aerodynamic shapes only give up about 2W to a 38mm carbon wheel at that speed. Box section rims like Open Pros are somewhat worse.

Half that at 15 MPH.

GeoKrpan

You have disc brakes, go carbon.

azza_333

Thanks for the info, for such a minimal gain I guess I will stick with my current alloy rims. I was hoping for at least a 10w gain.

fietsbob

thats when you put the "mechanical doping" motor on the bike.

Drew Eckhardt 

If you want to go faster with equipment and still ride a human powered diamond frame bike with road bars, your two most effective choices are

1. Tires. Gatorskins and GP4 Seasons are about 20 and 15W less efficient at 20MPH compared to GP4000SII tires. With power overcoming rolling resistance linear with speed you still save 15 and 13W at 15 MPH. I never noticed a difference in flat rate between the three, although the GP4 Seasons lasted half as long as the others. OTOH, the GP4000SII tires lack sidewall protection and would not do well on gravel. There's a regular Grand Prix with better side-wall protection that's supposed to share the GP4000 tread, although I've never seen measurements. Power lost due to rolling r

2. An aero jersey (or skin suit). The meat bag on top of the bike is responsible for about 75% of total drag.

StanSeven

Drew consistently has good input and his tire comment again is right on the mark. Tires has a huge impact.

Even though the carbon aero only saves a couple watts at your cruising speed, don't forget sprints, hard efforts, and downhill. You may not see 10 watts difference, but it will be more than two.

milkbaby

Basically the difference is also enough that nobody participating in this forum should care. LOL

In a recent interview, the road bike manager for Felt bikes said the cyclist accounts for about 85% of the drag in the system. Then of the remaining 15% due to the bicycle, a huge amount is from the handlebars. Pretty amazing considering Felt was one of the earliest companies to push the road aero bike.

fietsbob

Bladed spoke You can hold the flat part while you turn the Nip so wont have spoke wind Up.

Drew Eckhardt 

Windup is reasonable with round spokes provided you properly lubricate their threads - on the order of 1/4 turn with 14/17 gauge (like DT Revolutions) at 130kgf. Zinc anti-seize is the "correct" lubrication because it corrodes before aluminum by virtue of being more anodic in the galvanic series, although grease works fine - the alloy nipples still turned like new in a wheel I rode for over 10 years mostly in Colorado which has road salt, and even oil works for building although it's less likely to keep water out.

Sharpie dots on each spoke or a tape flag on representative samples (after the valve hole, plus the next spoke in rear wheels) let you undo that completely with no negative effects.

PepeM

If watt savings per cost is what is important to you, wheels are one of the last places to look. As already mentioned tires and aero clothing are important. Aero helmet is another decent option, as are aero shoe covers (I assume, can't recall any solid data on this but I am sure it is out there.)

Elvo

Get the skin suit, aerobars, and aero helmet before you get the wheels:

StanSeven

Except the OP is probably just a road rider looking to go a little quicker. While skin suits, aero helmets and shoe covers help with tt's, they aren't for daily road riding. The same likely applies with aero bars