Aero Disc Covers

[Peder Torgersen]

Wheel covers can be made but also bought what about these?
http://wheelbuilder.x-shops.com/store/home.php
They also have some wheels here that cost more than a Silvio! :roll:

Peder

 

[Mark B]

I can't help but imagine that a wheel cover and a Silvio would be a bad combination in a nasty crosswind.

Mark

 

[Peder Torgersen]

Mark B wrote: I can't help but imagine that a wheel cover and a Silvio would be a bad combination in a nasty crosswind.

Mark

Would the wheel covers have some advantage in areas with little wind? Here where I live there is little wind most of the year.

Peder

 

[trapdoor2]

Yeah, I ride with a guy who has a disk on the back of his VK2. A good gust will drive him about 3m sideways before he can recover....wouldn't be pretty in traffic! However, it takes a pretty healthy gust to do that...and if gusty weather is predicted, he simply either rides another bike or switches to an open wheel.

I think one would look cool but I suspect I could gain more by reducing my personal frontal area...

 

[Mark B]

Yakmurph would certainly be more qualified to speak about wheelcovers. I think they would be scary, for me. Where I work is right in a wind tunnel. It's more of a rarity when the wind doesn't blow.

Mark

 

[Ward]

I can't speak for certain about the Silvio but I have put many miles on my Bacchetta Aero with a rear disc and found it very useful. In most cases a crosswind actually pushes you forward sort of like a sail and the ride is more stable as the bike seems to ride more as a unit.

 

[MrSteve]

Ward wrote: I can't speak for certain about the Silvio but I have put many miles on my Bacchetta Aero with a rear disc and found it very useful. In most cases a crosswind actually pushes you forward sort of like a sail and the ride is more stable as the bike seems to ride more as a unit.

I agree.
This pretty well describes my experience with my Sofrider V1.2 on windy days,
with the rear wheel faired.
I feel more secure with the rear wheel cover on than I do with it off.

-Steve

 

[Mark B]

yakmurph wrote:

Ward wrote: I can't speak for certain about the Silvio but I have put many miles on my Bacchetta Aero with a rear disc and found it very useful. In most cases a crosswind actually pushes you forward sort of like a sail and the ride is more stable as the bike seems to ride more as a unit.

I agree.
This pretty well describes my experience with my Sofrider V1.2 on windy days,
with the rear wheel faired.
I feel more secure with the rear wheel cover on than I do with it off.

-Steve

Really? Well, I guess it goes to show you, that's what I get for thinking!

Mark

 

[John Tolhurst]

Glad to hear the experience with the rear wheel covers.

The stability of a bicycle in cross winds depends on the centre of pressure being behind the steering axis, so a rear wheel cover clearly meets that test, it would move the centre of pressure further back.

I have more curiosity on the front wheel cover. For steering to be neutral in a cross wind, the fork offset should be zero, so the centre of pressure of the front wheel is right on the steering axis. One can happily build and ride such a fork, it will have a lot of trail. The Silvio fork offset is about 1". A side wind will steer the bike away from the wind, causing it to lean into the wind. Those who rode motorcycles with bikini fairings mounted to the handlebars will recall this feeling. Other 700c forks are close to 2", so side winds on those bikes will have twice the leverage to turn the wheel.

The wind generated turning force on the fork has to be resisted by the rider. On a time trial bike, the riders arms are positioned very arkwardly for providing this resistance and control, on a road bike it is not much better. On the Silvio, the whole inertia of the rider's body lends stability to the front wheel. It is interesting to note some Silvio riders confident with the front fairing in windy conditions (myself included), while the centre of pressure of the fairing is at least 12" in front of the steering axis.

This is just another case where the usual bicycle rules of thumb have to be thought through from the beginning for the FWD and for the Silvio. If the tour used Silvio's for the time trial stages, they would have dual disk wheel is my guess, and probably for all stages.

 

[Mark B]

My experience with side winds has been such that steady, predictable winds are no issue. Gusty winds are scary. It's not so much what they do to the bike, I think, but what they do to you. Your hips steer the bike and your body puts up the most area. If you're in real gusty winds, they throw your hips around and cause the bike to do some spooky things.

Mark

 

[Peder Torgersen]

johntolhurst wrote: Glad to hear the experience with the rear wheel covers.

The stability of a bicycle in cross winds depends on the centre of pressure being behind the steering axis, so a rear wheel cover clearly meets that test, it would move the centre of pressure further back.

I have more curiosity on the front wheel cover. For steering to be neutral in a cross wind, the fork offset should be zero, so the centre of pressure of the front wheel is right on the steering axis. One can happily build and ride such a fork, it will have a lot of trail. The Silvio fork offset is about 1". A side wind will steer the bike away from the wind, causing it to lean into the wind. Those who rode motorcycles with bikini fairings mounted to the handlebars will recall this feeling. Other 700c forks are close to 2", so side winds on those bikes will have twice the leverage to turn the wheel.

The wind generated turning force on the fork has to be resisted by the rider. On a time trial bike, the riders arms are positioned very arkwardly for providing this resistance and control, on a road bike it is not much better. On the Silvio, the whole inertia of the rider's body lends stability to the front wheel. It is interesting to note some Silvio riders confident with the front fairing in windy conditions (myself included), while the centre of pressure of the fairing is at least 12" in front of the steering axis.

This is just another case where the usual bicycle rules of thumb have to be thought through from the beginning for the FWD and for the Silvio. If the tour used Silvio's for the time trial stages, they would have dual disk wheel is my guess, and probably for all stages.

The Silvio would look even better with Aero disk covers on both wheels but it would also look good just on the back wheel. Some places on our planet there is much wind and many places there are not so much wind. For a well trained Silvio rider it would probably fun passing racers with Areo disk covers in front and back. They might even think you bought a Zipp Sub-9 custom hand built wheel that cost $3675 for one wheel! :roll: When you pass them they wouldn’t notice that you only bought a cheaper cover that costs $65 for one wheel! :lol:

Peder

 

[John Tolhurst]

Mark B wrote: ... Your hips steer the bike and your body puts up the most area. If you're in real gusty winds, they throw your hips around and cause the bike to do some spooky things.

HI Mark,
I don't agree here. My understanding is that balance corrections are syncronised with the cadence, which can delay steering responses to side gusts. The solution may be to create the right amount of side pressure on the steering to make the steering correction for you regardless of cadence. I think that steering corrections having a frequency equal to cadence may be behind your experiences.

I have ridden one cruzbike that I found no trouble at all in gusty side winds, while another I found unsatisfactory Ialthough I admit I had a very small width on the bars at the time. This suggests to me that the key may be to design the right amount of side pressure into the front of the bike to steer it down wind momentarily, and so create the required lean in.

 

[Mark B]

johntolhurst wrote:

Mark B wrote: ... Your hips steer the bike and your body puts up the most area. If you're in real gusty winds, they throw your hips around and cause the bike to do some spooky things.

HI Mark,
I don't agree here. My understanding is that balance corrections are syncronised with the cadence, which can delay steering responses to side gusts. The solution may be to create the right amount of side pressure on the steering to make the steering correction for you regardless of cadence. I think that steering corrections having a frequency equal to cadence may be behind your experiences.

I have ridden one cruzbike that I found no trouble at all in gusty side winds, while another I found unsatisfactory Ialthough I admit I had a very small width on the bars at the time. This suggests to me that the key may be to design the right amount of side pressure into the front of the bike to steer it down wind momentarily, and so create the required lean in.

Maybe I'm not being fair with a complete explaination. I'm talking about downhills with 17-20 mph gusts (sideways) of Santa Ana winds. Even when not pedaling, the gusts can be frightening at high speeds (downhills). The only thing I've found that helps is to keep the speed down and press my knees to the headtube, which seems to lock the steering and my hips in place. On the flats, when I'm pedaling normally and running 20 mph or less, the gusts are manageable.

There is one particular place on my commute home from work where I drop down into a river wash out of Rialto, crossing over into San Bernardino. On a good day, I can really get rolling on this section and big-ring up the other side into San Berdoo. On a windy day, I have to keep it reined in (under 30) or the gusts can blow me all over the place. A couple weeks ago, on a Saturday group ride, there was a really fun downhill, six mles long with some six and seven percent grade in there.... Great place to let it rip, but at the top where it was steepest, the side gusts were horrible and I was not comforable letting it rip. As I progressed down the canyon, the winds became less and less of a factor and I could let it go. My point is; it's not a pedaling technique thing. In fact, it's more of a problem when you're NOT pedaling and the combination of high speeds/ high winds. I would agree that more time on the bike in theses sorts of conditions will eventually render the problem a non-problem. For now, though, it's something I have to be aware and respectful of. Other than these particular conditions, the Sivio is marvelous in most wind conditions.

Mark

 

[John Tolhurst]

Thats very helpful Mark. Its a pretty extreme condition I suppose.

In theory what we need is for sudden exposure to a side wind, or a real sudden gust, to steer the bike down wind more quickly than it can shift the mass sideways, so that by the time the rider responds, the bike is already at the angle needed to lean into the wind. This is not currently happening. Currently, by the time the rider responds, the mass is already moving sideways in those very stong conditions.

On a road bike, if the rider is blown sideways, the arms steer down wind automatically, since the grips are forward of the steering axis by virtue of the stem, which faces forward as we know - not by accident I would suggest.

To gain this on a Silvio might be a simple as attaching a small wind vane to the accessory mounts above the BB, or it may be more difficult. Wind problems are notoriously complex to solve but some careful exploration might shed a little more light.

 

[Peder Torgersen]

Tom Taylor must have a reason for using wheel covers? Maybe more speed?
http://mysite.verizon.net/ts72/

Peder