Affect of cross wind on aero wheels

BugsBunny · Postby **BugsBunny** » Wed Mar 11, 2015 9:05 pm

Hi guys

I am looking at a bike with Reynolds Strike SLG aero wheels. They are 62mm in depth but the marketing spiel and some reviewers say it's not all that susceptible to cross wind. Can someone explain how this can be given their depth and also why some older design and shallower wheels get poor reviews on cross wind handling

MattyK · Postby **MattyK** » Wed Mar 11, 2015 10:13 pm

Crosswind sensitivity is caused by an unequal side force on the front and rear edge of the wheel. More force on the front edge (in front of the axle) than the trailing edge causes the wheel to steer away from the side the wind is pushing from.

Older rims did this a lot, because the round front edge (tyre) was shaped differently to the trailing edge (usually a pointed V).

The newer wheels on the market try to balance the side force at the front and rear edges. This is done by making the trailing edge round and blunt and wide, just like the leading edge (which is the tyre). You still get a side force overall, but it's not twisting the steering and making you change direction.

http://flocycling.blogspot.com.au/2014/ ... orial.html" onclick="window.open(this.href);return false;

BugsBunny · Postby **BugsBunny** » Thu Mar 12, 2015 12:10 pm

Thx Matty. Very helpful. And that tutorial is brilliantly written also.

Cheers.

Dr_Mutley · Postby **Dr_Mutley** » Thu Mar 12, 2015 12:24 pm

U will soon realise if u ride a few different deep rimmed carbon wheels that this isn't all just hype... Albeit some manufactures do falsely claim their particular wheel is so stable in the winds... Shen it's just as crap as the $500 chinese carbon wheel u could buy and save a $1000...

For example.. I used to ride the 1st incarnation of the DA C50 50mm wheels and thought they were fantastic... Like VWD them! I thought how much I got blown around, even at my then, heavy body weight (90+kgs) was normal... Then I rode some zipp 404s for a bit and realised that even with 8mm more rim depth I experienced half the crosswind forces... Then after moving to ENVE 6.7s 60mm front, 70mm back) they were better again compared to the 2012 404s I had... Clever people these engineers!

Clearly there's a price premium involved with my above choices (if I didn't buy secondhand!) but sometimes, when it comes to wheel tech, u do get what u pay for....

CKinnard · Postby **CKinnard** » Thu Mar 12, 2015 1:02 pm

IMO, all deep sections are going to be more subject to cross winds. How much it effects you will vary with bike set up, frame type, your experience, weight distribution, etc.

If you see a road race on a really windy day, count how many guys are riding deep section.

Incidentally, I know two guys who have fallen heavily when they sat up letting go of the bars, and cross winds blew their deep section wheels off line. One of them fractured his elbow. This guy had the newer toroidal shaped wheels for 3 weeks, and they handled differently to an older Easton set.

I've seen so many near misses in pack rides when the weather turns fowl and guys on deep sections struggle to hold line.

Depending on what you want to use the wheels for, I'd suggest you take on the marketing advice on Matty's link, and if seeking an all rounder, go with <=30mm (i.e. Flo30).

While you are there, check out this page.
http://www.flocycling.com/aero.php" onclick="window.open(this.href);return false;
and especially note the chart....and how the drag reduction advantage of Flow 60 and 90 wheels vs Flo30 is only significant between 8 and 18 degrees of yaw. Beyond 18 degrees, the deeper wheels have more drag.

To drive home the point, note Flo don't make a disc for the front wheel!

You want to keep in mind that deep sections are in general much stiffer, which can be very uncomfortable on long rides.

JdM · Postby **JdM** » Thu Mar 12, 2015 5:04 pm

Those Flo wheels look interesting. Well priced too. Who sells them here in Australia?

warthog1 · Postby **warthog1** » Thu Mar 12, 2015 9:21 pm

MattyK wrote:Crosswind sensitivity is caused by an unequal side force on the front and rear edge of the wheel. More force on the front edge (in front of the axle) than the trailing edge causes the wheel to steer away from the side the wind is pushing from.

Older rims did this a lot, because the round front edge (tyre) was shaped differently to the trailing edge (usually a pointed V).

The newer wheels on the market try to balance the side force at the front and rear edges. This is done by making the trailing edge round and blunt and wide, just like the leading edge (which is the tyre). You still get a side force overall, but it's not twisting the steering and making you change direction.

http://flocycling.blogspot.com.au/2014/ ... orial.html" onclick="window.open(this.href);return false;

Great post and link. Thanks

MattyK · Postby **MattyK** » Fri Mar 13, 2015 12:51 pm

JdM wrote:Those Flo wheels look interesting. Well priced too. Who sells them here in Australia?

Noone, they are exclusively direct-to-public. They charge about US$115 for shipping last time I was quoted. That plus the low AUD/USD exchange makes them pretty expensive all up.

I would also look at the Soul S3.0 or S4.0 and the 3T Acellero 40 Pro if you're up for that price range and want something wide and semi-deep. And maybe some Shimano R81 C35s, or carbon rims.