Why doesn't the XR4 and Madone have a protected rear wheel?

[Shrike]

Not sure what you call it, like an aero flangey thing to stop turbulence between the seat tube and the rear wheel. Seems to be a design trait in aero bikes, so I'm assuming it's common knowledge and uncontroversial that it's more aerodynamic? But even recent aero gen bikes seem to flout it. Is there a reason for this? Some competing design philosophy?

XR4


Madone



Compare with
Aeroad


S5


VIAS (kinda)

[ichobi]

It's called rear wheel/ seat tube cutout? Providing trek/ bianchi and others can make the overall frame drag competitively low, i dont think it's nexcessary to have. Also Trek has that semi suspension thing in their seat tube, so they probably make the wheel cutout while accommodating those bits?


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[GambadiLegno]

They cut the tube, I agree. Although my bike has this geometry in the rear wheel, I don't really like it and I don't believe in aero arguments in this case, especially talking about a road bike and not a TT bike. IMO, Trek, Bianchi and other brands simply prefer to focus on other parts than cutting the tube.

[grumpier]

The Madone and I believe the Canyon and Merida seat tubes are Kahn tails, so there is a virtual airfoil that extend off the back of the tube. A clue to how important this area is to overall drag would be to look at the Speed Concept white paper. Trek list wattage saving for the draft box and the fin that shields the rearr wheel under the bottom bracket. I don't remember the savings for the draft box, but the lower fin saves 1 watt at 30 mph. My guess is the added material and loss of tire clearance doesn't make up for the savings.

[kgt]

They do or don't because these design choises have practically zero impact on the performance of the bike.

[victorduraace]

^^ this

[jbaillie]

kgt knows what's up.

It probably winds up having a larger impact on handling (shortening wheelbase) than it does on aerodynamics.

[naambezet]

The XR4 does have it, it is only a bit smaller than the most frames