Tomm Willians

What depth difference would there need to be to observe any gains with this ? Assuming a 38 front, would you need to use say a 50 on the rear? Is this a very discipline-specific application like time trials or might there be something to be gained in an endurance event ?

Koyote

As I understand it, the idea of running a shallower rim in front is to accommodate high crosswinds, which can cause problems with handling and stability. The gains are not really in speed, but stability, and will be highly dependent on whether you live in a windy area.

tempocyclist

I sometimes swap out my 60mm front for a 35mm rim when I know strong crosswinds are going to be an issue.

Aerodynamics are important across pretty much all disciples apart from all-out hill climbs, so yes there would be some advantage to running a deeper rear in an endurance event (I am assuming speeds are high enough). The front wheel has more of an effect on aero though, so if you have the opportunity to get deeper front and rear wheels, do that rather than just a deeper rear.

greatscott

Technically it's better aero wise for a deeper dish wheel to be on the front instead of the rear...but, a deep dish wheel in the front will make the stability of the bike to the point of being dangerous in wind. Just as why some people put skinner tires on the front and wider ones in the front.

Why is that true you scream? because the dirty air is actually hitting the front of the bike, and not so much on the rear because the bike frame and the person riding blocks some of the wind from the rear. I hope I explained that right! Oh well, I'm sure someone will correct me.

Lombard

FIFY. Wheels are not pizza.

Theory is all correct.

rsbob 

The doors to the raging debate have now been opened. May the gladiators enter and commence!

Koyote

There’s not really any debate about it. This is all rather well understood.

asgelle

Really? Because I've always understood clean air hits the front of the bike and gets disturbed as it travels back.

urbanknight

tFUnK

Shallow up front is for stability in cross winds. You used to see pros doing shallower front with deeper rear a few years ago for this reason. More recently, however, the shaping of the rim profile has presumably improved such that even the pros regularly run same depths front and rear.

rsbob 

New here?

DangerousDanR

My experience from living on the upper plains is that riding into gusting and variable cross winds sucks, and they are worse with deeper wheels. The best solution is to have some shallow wheels for days when the wind speed is above 25 MPH.
The front wheel is worse because it is out in the main air flow, while the rear is in the disturbed air.

Also, strong enough winds can overpower some riders and put even more disturbance into the bike by twisting it side to side.

Koyote

And it's worse because most of the weight is on the rear wheel, leaving the front more prone to buffeting by winds. That's why a shallower rim up front is desirable.

veganbikes

Also deep dish is not pizza but a very delicious and hearty pizza flavored pie. Pizza comes from Wooster St. in CT. You have Frank Pepe Pizza Napoletana and then some other places which I have been told make something edible

jgwilliams

You don't even have to live on high plains. I had some Vision Team 35 wheels with a relatively deep profile and I found the effect quite noticeable riding in London. I therefore determined when I replaced them that I wouldn't go for deep rims. Interestingly, the Fulcrum wheels that I now use have a slightly deeper profile on the back wheel than the front, but it isn't enough that you can really see the difference. As an aside, I think riding in London was sometimes worse than in more open country because the tall buildings could channel the winds in unpredictable ways.

ZHVelo

I did because it saves some weight (which brought my bike down to exactly 8.0 with pedals), because of winds, and because it actually looks quite cool with deeper back wheels.

KerryIrons

In perfectly calm conditions this is true. In the real world we more often ride in, the bike and rider serve to straighten things out, but just a bit. Whether things are smoother in the front or the rear will depend very much on the specifics of the wind conditions. Cross-wind stability is the primary driver for using a shallower rim in the front.

asgelle

Is there a source for this?

KerryIrons

There have been a lot of articles published over the years, many of them relying on wind tunnel tests where the air flows are straightened by the fan and louver systems. Beyond that I'm relying on my undergraduate and graduate courses in fluid dynamics plus many years of (non-bicycle) field experience.