Down Force from over size windshield

[racer157]

Being an ex-road racer I am sensitive to the way my bikes handle. Being a mechanic I tend to try to make all of them as good as I can. I love my 2005 fjr but noticed on occasion that when I increase my speed with my windshield in the raised position the steering gets heavier. With the windshield all the way up I find the front end pushing (not wanting to turn) as I lean the bike farther and farther over at speeds above 70. I know, don't speed; but on a FJR I occasionally go a little faster than I should. If I lower the screen there is no problem. On our run last week end which was great by the way, I was offered a stock windshield to try out. I look forward to trying a stock screen, since I have never had one ( this is the burned FJR that I am driving). I mention this because I feel this might pose a problem with other riders too if they are not aware of this. The windshield is after all acting like a front spoiler on a race car. My screen is slightly wider and 4 inches taller that stock according to the seller on e-bay. Have any of you felt this on your bikes?

Well I said I would get back to you all when I was a ble to make more tests. Here are my conclusions: With my over size windsheild installed I found the bike to be hard to ride at speeds over 60 mph in turns with the windsheild raised. With the sheild up the front end wanted to push me to the outside of the turn. If I lowered the sheild to the down position the bike was ok. I now have a stock windsheild on my bike and I am very happy. No loss of control is apparent up to speeds over 90 in the same turns and the bike again feels great. Raising and lowering the sheild in a turn doesn't create the steering problem.

 

[E1Allen]

I understand what you are talking about, but I haven't come across that unless speeds go above 130. I criuse on the highway going 90 if its empty and with the shield all the way up, not much of an issue.

 

[Noddy]

I love my 2005 fjr but noticed on occasion that when I increase my speed with my windshield in the raised position the steering gets heavier. With the windshield all the way up I find the front end pushing (not wanting to turn) as I lean the bike farther and farther over at speeds above 70.

Hey racer, what you describe makes sense because you are changing the centre of pressure in relation to the centre of gravity, by raising the screen compared to it being flat.

A 4" higher screen raised up is acting as a sail in the wind. Great for protection, less so for handling. Being tallet than the std. Yam screen means it is acting as a bigger sail than std.

I find that my +2" Givi screen gives me a bit of a weave at speed if the wind is right (wrong? :huh: ) and I am gripping the bars too tight. This happens because the negative pressure on my back pushes me onto the bars. This summer I think I will revert to the standard screen, even though I am 6'1". I found that on my Aprilia RSVR, with the standard screen, my head is well clear of turbulence compared to my old RSV with a double-bubble screen. This means I am buffeted a lot less and it is much quieter.

However, I do find it easier to turn the Aprilia at 130+ than the FJR...... :lol:

 

[madmike2]

............. I love my 2005 fjr but noticed on occasion that when I increase my speed with my windshield in the raised position the steering gets heavier. With the windshield all the way up I find the front end pushing (not wanting to turn) as I lean the bike farther and farther over at speeds above 70................ I look forward to trying a stock screen, since I have never had one ( this is the burned FJR that I am driving). I mention this because I feel this might pose a problem with other riders too if they are not aware of this. The windshield is after all acting like a front spoiler on a race car. My screen is slightly wider and 4 inches taller that stock according to the seller on e-bay. Have any of you felt this on your bikes?

It will be interesting to read your take after you've swapped windshields. I also wonder if there is a way to measure actual steering input other than your "feel" and a way to compare dynamics affecting the handling.

I am not THAT sensitive to inputs, but I don't ride mine very close to the edge, either. I would also like to know how much of the dynamic is caused by the comparative size ( weight x physical size) of the FJR compared to a typical sportbike. The windshield may be "loading" the front wheel but that may be negated by the change in windshiel angle as it is raised. Of course the bike is experiencing more wind resistance but how much of that is affecting actual steering input may be more connected to the physical size of the package more than force being exerted downward on the front wheel.

Because it is such a large bike, this is one of the main causes of front tire cupping when the bike is ridden aggressively through tight corners, hence increasing the front tire pressure to maintain "profile".

 

[HaulinAshe]

On my 05, I felt more influence from the change in angle of the screen than the height. So I found steering improved when I ran a taller shield at a lower mechanical position, than a shorter shield at a higher position.

For me, all shields worked best at raised height of about 1.5" from bottom. My advice, try a +2h shield with a flip and run it about 1-1.5" above mechanical bottom. IMO that will give you a reasonable compromise between quiet airspace and good handling at low triple digits.

 

[Luke]

I have a large Rifle screen. It has the "angle optimizer" brackets that produces more tilt than stock. So you have less resistance because of the more agressive angle. As a side benefit, the down position allows ALOT more air to flow under the screen!

 

[Ignacio]

In theory it makes sense, but either with a stock windshield or a barndoor +4+3 CeeBailey's I find myself lowering them both when I get much above a buck anyway. Below that speed I don't notice any significant difference.

 

[Geezer]

I run with the stock '05 windscreen. I do notice a difference in feel with it raised but I can't say if it is caused by the change in the pressure on my back or down force on the front. I prefer the screen all the way down for sporty riding and only raise it when it's cold or wet out.

 

[Scab]

Interesting.

I have the V-Stream windscreen, which is a significant screen to say the least. I have noticed very dramatic handling changes in the bike since the installation of this screen. However, there were other changes to the bike at or about this same time so I cannot definatively say all the handling changes are due to the screen. However, my initial seat-of-the-pants analysis is that the screen tends to direct the ill effects of "dirty-air" directly into the handling of the bike. This is, of course, most noticeable at interstate speeds or above, and in foul weather that creates the need to raise the screen more than normal (which for me is prolly only an inch and a half or so). It tends to feel as though you have created a fulcrum effect that allows the wind to direct the bike side to side. The V-Stream is designed to split the air into two paths, and traverse down both shoulders of the rider. It is easy to visualize that dirty air could easily cause an oscilating effect with more air traveling one side, then alternately the other, thus pitching the bike left and right. This has been most noticeable while I was running Michelin Pilot Road tires. Holding a straight line in any kind of adverse wind conditions became a distant memory. I initially blamed the Pilot Roads exclusively but notice that the condition still exists with a different tire now on the bike, although the condition is much less. Fairness would suggest that some tires are better able to handle these forces vs. the Pilots, but it should be noted that if this is screen induced, these are forces that none of the tires were actually designed to deal with.

Also, I have ordered new roller bearings for the steering head and new bearings for the front wheel.(to eliminate that as a possible cause-22k+) After installation, if the condition still persists I guess I will have to experiment with the stock screen.

I guess I am reluctant to place all responsibility on the screen because I just plain like the silence behind it. Not very scientific, huh?

 

[unclekunkle]

Being an ex-road racer I am sensitive to the way my bikes handle. Being a mechanic I tend to try to make all of them as good as I can. I love my 2005 fjr but noticed on occasion that when I increase my speed with my windshield in the raised position the steering gets heavier. With the windshield all the way up I find the front end pushing (not wanting to turn) as I lean the bike farther and farther over at speeds above 70. I know, don't speed; but on a FJR I occasionally go a little faster than I should. If I lower the screen there is no problem. On our run last week end which was great by the way, I was offered a stock windshield to try out. I look forward to trying a stock screen, since I have never had one ( this is the burned FJR that I am driving). I mention this because I feel this might pose a problem with other riders too if they are not aware of this. The windshield is after all acting like a front spoiler on a race car. My screen is slightly wider and 4 inches taller that stock according to the seller on e-bay. Have any of you felt this on your bikes?

Absolutely... When I purchased and installed a new Cal-Sci +4" for my '05, I was inclined to post a ride report. However in that report I would not have been completely honest had I not mentioned the negetive handling effects associated with the larger "airdam". Not wanting to discourage buyers from a Cal-Sci purchase, I kept silent. This is a good thread to remind everybody that anytime you tamper with proven factory engineering of any sort, you risk the possibility of negetive results.

However, with that understood, the positive results out weighed the negetive in my case. After a long tour this past summer, I returned home with the feeling that I'd lost some level of hearing mostly as a result of wind noise. A new helmet was first, but the real fix was a Cal-Sci tall windscreen, that I only have to raise just a tad for great wind control. I'd mentioned before, how I can leave my visor open to 90 MPH...where as my visor would slam shut above 65 with the the stock shield.

Along with great wind control comes the ill handling effects you mention. I noticed right away, that this little 550 pound bike was being tossed all over the freeway, (not literally) ...but made me realize a little caution was in order. I've shot to 110, but I feel it would be inviting disaster to attempt a big triple digit speed run with an oversize, non-factory sized "windbrake".

 

[dcarver]

Along with great wind control comes the ill handling effects you mention. I noticed right away, that this little 550 pound bike was being tossed all over the freeway, (not literally) ...but made me realize a little caution was in order. I've shot to 110, but I feel it would be inviting disaster to attempt a big triple digit speed run with an oversize, non-factory sized "windbrake".

FWIW, I run a larger than stock Rifle with tuning blocks. Haven't broke the buck40 yet but up to there the screen is stable, even at 75% full up. No negative input or distress to the handling that I can tell. I've read in other posts that guys have taken their stock screens full up position at full tilt speeds. On a closed course with EMT's available of course. <_<

 

[Scab]

Angle could be everything. I am using no blocks. What I have considered is actually manufacturing an add-on track for the upper screen mounts that would allow the screen to raise and lower without changing angle period. Or, skyway could do it and save me the trouble.

 

[brazos parker]

I rode across SW Wyoming last summer w/ a CB +4+3 on my '05 at speeds of...ahem...100 - 105 mph for nearly 2 hrs. Also, had a Givi v46 on the tail. Mind you, I was only doing this to maintain my place w/ other vehicles on the interstate. But, I felt solid on the bike...no handling problems.

 

[OrangevaleFJR]

I have not read people's responses yet, so this way I will not be shy about what I write.

I noticed a HUGE handling impact when I switched from a CB +4+1 to the current Vstream. The Vstream pushes the FJR around like a punk kid when entering a turn over 50mph and especially during windy conditions.

I am swapping back to my CB as it had much less impact than the Vstream

 

[Scab]

I have not read people's responses yet, so this way I will not be shy about what I write.
I noticed a HUGE handling impact when I switched from a CB +4+1 to the current Vstream. The Vstream pushes the FJR around like a punk kid when entering a turn over 50mph and especially during windy conditions.

I am swapping back to my CB as it had much less impact than the Vstream

Crap. Outside verification. My nightmare may be true.

But...it's sooooo quiet.

 

[HaulinAshe]

I certainly don't mean to imply that I would consider lengthy runs at over a buck10 with my CB +4/+2, but up to that point it is impressingly smooth and IMO not significantly more difficult to handle than the stock screen. That's probably because of two things, one is that I expected the larger screen to have some effect, and two, because the CB has nice aircraft-grade lines and very clean edges.

Having dealt with aircraft most of my life, I can assure you that those little bitty edges have as much impact on the aerodynamics of the screen as its overall shape. Which is why I wonder what the F$*k was Yami thinking when they molded that rounded bead on the new screens? It certainly lowered the bar for aftermarket replacements.

 

[OrangevaleFJR]

I have not read people's responses yet, so this way I will not be shy about what I write.
I noticed a HUGE handling impact when I switched from a CB +4+1 to the current Vstream. The Vstream pushes the FJR around like a punk kid when entering a turn over 50mph and especially during windy conditions.

I am swapping back to my CB as it had much less impact than the Vstream

Crap. Outside verification. My nightmare may be true.

But...it's sooooo quiet.

btw... (now that I read your post) Tuning blocks had a positive effect, but didn't solve the problem completely. Now I might keep the Vstream...maybe

 

[Knifemaker]

I have not read people's responses yet, so this way I will not be shy about what I write.I

Well, I did read everyones posts and what struck me right off the bat was that all the folks with 2005 or older bikes seem to have more of a problem with the screen up than those with 06's or 07's.

I have a Cee Baily +4+4 and even at 3 digit speeds, I have not notticed any ill effects to the handling with the screen all the way up. I have noticed a strong updraft around my back when riding alone, which seems to switch to my passenger when they are abourd.

The 06-07 have diffrent venting of course and this may be reason. Does anyone with a tall screen with the "Cal Sci cutouts" on there 05 or older bike notice a diffrence?

KM

 

[Mike-H]

I have an 04 with Givi +1 screen with Cal Sci cut outs & don't notice any problem @ high speed with the shield all the way up....but then again I never go over 70 mph :derisive: ....