NormanPCN
02-21-2005, 09:37 PM
Here is a modification you can do to make backpressure a non issue at any shield positon. Yes even all the way up. I basically did 2 2/3 cuts so you get to learn from my attempts ...err... mistakes. This will be a little wordy since I am go to explain what I did and why and how I tested.
The whole point of this modificatoin to to get air flowing "through" the shield. Wind blows from high to low pressure. The windshield punches a "hole" in the air. This is low air pressure. Air will rush into that hole. With the ST1300 shield up high the backpressure is huge at superslab speeds. Makes you feel like you are doing push-ups. Don't anybody go saying that this modification will let air past the shield and on you. Duh... that is the whole point and the only way to get rid of the backpressure. The air is going to hit you on the front, side or back. Take your pick. This modification attempts to balance the airflow.
I cannot speak for the Honda designers were thinking but the stock design seems to try and let air past the bottom of the shield but the opening is small and very restrictive. The air will take the path of least resistance and it is easier to go over the top and not through the "hole". This is becasue there is a high pressure point at the body and the shield opening needs to get far enough away from that to let any air through. Move your electric shield from bottom to top and watch the bottom of the shield and the space between the body. You can ride around and stick your hand behind the shield to feel the air passing through. Hardly anything. Hence backpressure. This modification opens up that gap.
My first test cut and arc are in the flat spot between the "points" at the bottom of the shield. I tested this and it worked quite well. No more push-ups but still some backpressure. So what kind of a backpressure "meter" was I using. My head. I have an RF-1000 and this helmet is designed to flow air over/around your head and exhaust it out the top vents and the nape of your neck. With backpressure air gets pushed up gap at the nape of my neck and I feel cold air around my head. This "meter" would not work in warm temps. As I raised the shield I could feel none/little/more cold air pushed up the back of the helmet. Cool. :D I was surprised that more air was not making its way through the "port". I felt I wanted a little more since my "meter" was still measuring some pressure even though the body was happy. With the shield all the way up airflow was good. Done deal, but I was not interested in the shield that high and I needed more airflow at a lower position. I slowly tapped the shield button, raising in tiny increments, and measured the point where the restriction released. I figured that cutting 1/4 to 1/3 of an inch more should do the trick.
Cut number two. This cut started just outside the "points" and had a mild arc with the center probably 1/3 inch higher than the first cut. Did a test and Bingo! Good airflow at the shield height I was interested in. The speed of this airflow is something like 30-50 when the bike is going 75-80. The airflow is not going up but is hugging the top of the dash. This makes sense because the lowest air pressure is behind the instrument cluster. Can you feel the air? Nope, it is not enough to feel. If you stick your hand up to the dash you can feel it.
I used a rotary tool with a multipurpose bit to cut the shield. I have never done anything like this ever and my first cut was a little crappy.
To draw an arc all you need is a piece of string. Tie one end to something and your marker to the other an you are now drawing an arc. The shorter the string the more the curve to the arc and the longer string the flatter the arc. I took the shield off the bike and fixed up a "clamp" with the peice of 1/4 inch plywood. I used 5/16 inch bolts an neoprene washers to protect the shield from the steel washers. Nothing special about neoprene. That is all Home Depot had. No plastic washers. I then bolted a 2x4 to the plywood. Somewhere on this was going to be my endpoint to tie the string to. I just slapped this together, no need to be precise. To get an even arc your stringbase point should be centered. To figure this hold the string down with your finger and measure to one of the shield mounting holes. Hold the string and swing over to the opposite hole. If you do not hit the same spot on the hole your base point is off. Remember that the length of the string determines the arc so you do this step in combo with determining what arc you like. Once you have your base point put a screw or nail in the spot to tie the string to. You can play with arcs using a hilight marker. Don't like it. Wipe and try something different. When you get something you like use a permanent marker. When you draw the arc reverse direction and go back the other way. This is a double check that nothing slipped (or the angle you held the pen). If you do not trace the same arc. Wipe and redo. GooGone will take off the permanent marker. I did not try other cleaners.
Now you cut. Put some masking tape around your arc. This will keep the rotary tool cutting guide from scratching the shield. I did try attaching the string to the rotary tool but I suggest you skip this. Freehand with the multi-purpose cutting bit. Cut close to but not right on the line. This bit, at least in my hands, does not make the cleanest cut and increases the sanding necessary. My first cut was done freehand cutting "on the line". From the pics you can see it is not too good. After cutting the majority of material away the use a high speed cutter bit that has a cylindrical shape. With this you can slowly and cleanly cut right onto your line. Now take the cutting guide off and freehand using the bit on the edges to clean up any burs and/or shavings. Apply pressure if you want your cut to have a bevel to it. I also felt the cut with my fingers looking for bumpy spots and tried to even those out by shaving them with the high speed cutter. This just saves sanding time.
Now you sand. Use a flap wheel sander attachmet for your drill. Ignore the sanding drums the rotary tool has. Use a mediam grit (80) flap wheel. The 80 works better than the fine (120). Keep the tape on the shield when you sand. You will on occasion slip and the tape will keep you from scratching the shield surface.
If you want to cut the minimum necessary and test to get exactly what *you* like, remember that with the multi-purpose bit you will want to cut about and 1/8 inch of material and the bit cuts a 1/8 inch path so your increments will be 1/4 to 1/3. Trying to cut extra with the high speed cutter bit will be quite slow. You migh want to buy some plastic at the home store and practice cutting on that to get the feel for cutting. Remember that plastic will melt some while cutting it. The melting is not an issue but you should know that it will happen. If you apply too much pressure with the sander, or stay in one place to long, that is what will happen as opposed to "sanding". You can draw test/final arcs with the shield on the bike. Tie a knot in the string and press it into the top gap in the "N" in Honda. Tape that down. Draw away. It is not a perfectly centered endpoint, but then neither is the one in the jig I assembled. If you want a different endpoint, tape the string to some other point.
The pictures.
1) FirstCut. After my test run. Just got home before the downpour! You can gauge how much I cut by looking at the plastic trim pieces using your uncut shield as a reference. I left one of my "wings" on for the pic. They do add to backpressure so understand that I was testing with those on my bike. Mark Lawrence made those wings and they attach with pasting removable rivets. They go on/off in a handfull of minutes.
2) This is a picture of my attempt at using the string to force the cutter on the arc. I quicky abandoned this and cut freehand.
3) This is a picture of my hilite maker and arc for the second cut after my test run of the first cut. The arc is not too visible but you can see that it starts just outside of the bottom "point".
4) FinalCut. Ain't she pretty!
The whole point of this modificatoin to to get air flowing "through" the shield. Wind blows from high to low pressure. The windshield punches a "hole" in the air. This is low air pressure. Air will rush into that hole. With the ST1300 shield up high the backpressure is huge at superslab speeds. Makes you feel like you are doing push-ups. Don't anybody go saying that this modification will let air past the shield and on you. Duh... that is the whole point and the only way to get rid of the backpressure. The air is going to hit you on the front, side or back. Take your pick. This modification attempts to balance the airflow.
I cannot speak for the Honda designers were thinking but the stock design seems to try and let air past the bottom of the shield but the opening is small and very restrictive. The air will take the path of least resistance and it is easier to go over the top and not through the "hole". This is becasue there is a high pressure point at the body and the shield opening needs to get far enough away from that to let any air through. Move your electric shield from bottom to top and watch the bottom of the shield and the space between the body. You can ride around and stick your hand behind the shield to feel the air passing through. Hardly anything. Hence backpressure. This modification opens up that gap.
My first test cut and arc are in the flat spot between the "points" at the bottom of the shield. I tested this and it worked quite well. No more push-ups but still some backpressure. So what kind of a backpressure "meter" was I using. My head. I have an RF-1000 and this helmet is designed to flow air over/around your head and exhaust it out the top vents and the nape of your neck. With backpressure air gets pushed up gap at the nape of my neck and I feel cold air around my head. This "meter" would not work in warm temps. As I raised the shield I could feel none/little/more cold air pushed up the back of the helmet. Cool. :D I was surprised that more air was not making its way through the "port". I felt I wanted a little more since my "meter" was still measuring some pressure even though the body was happy. With the shield all the way up airflow was good. Done deal, but I was not interested in the shield that high and I needed more airflow at a lower position. I slowly tapped the shield button, raising in tiny increments, and measured the point where the restriction released. I figured that cutting 1/4 to 1/3 of an inch more should do the trick.
Cut number two. This cut started just outside the "points" and had a mild arc with the center probably 1/3 inch higher than the first cut. Did a test and Bingo! Good airflow at the shield height I was interested in. The speed of this airflow is something like 30-50 when the bike is going 75-80. The airflow is not going up but is hugging the top of the dash. This makes sense because the lowest air pressure is behind the instrument cluster. Can you feel the air? Nope, it is not enough to feel. If you stick your hand up to the dash you can feel it.
I used a rotary tool with a multipurpose bit to cut the shield. I have never done anything like this ever and my first cut was a little crappy.
To draw an arc all you need is a piece of string. Tie one end to something and your marker to the other an you are now drawing an arc. The shorter the string the more the curve to the arc and the longer string the flatter the arc. I took the shield off the bike and fixed up a "clamp" with the peice of 1/4 inch plywood. I used 5/16 inch bolts an neoprene washers to protect the shield from the steel washers. Nothing special about neoprene. That is all Home Depot had. No plastic washers. I then bolted a 2x4 to the plywood. Somewhere on this was going to be my endpoint to tie the string to. I just slapped this together, no need to be precise. To get an even arc your stringbase point should be centered. To figure this hold the string down with your finger and measure to one of the shield mounting holes. Hold the string and swing over to the opposite hole. If you do not hit the same spot on the hole your base point is off. Remember that the length of the string determines the arc so you do this step in combo with determining what arc you like. Once you have your base point put a screw or nail in the spot to tie the string to. You can play with arcs using a hilight marker. Don't like it. Wipe and try something different. When you get something you like use a permanent marker. When you draw the arc reverse direction and go back the other way. This is a double check that nothing slipped (or the angle you held the pen). If you do not trace the same arc. Wipe and redo. GooGone will take off the permanent marker. I did not try other cleaners.
Now you cut. Put some masking tape around your arc. This will keep the rotary tool cutting guide from scratching the shield. I did try attaching the string to the rotary tool but I suggest you skip this. Freehand with the multi-purpose cutting bit. Cut close to but not right on the line. This bit, at least in my hands, does not make the cleanest cut and increases the sanding necessary. My first cut was done freehand cutting "on the line". From the pics you can see it is not too good. After cutting the majority of material away the use a high speed cutter bit that has a cylindrical shape. With this you can slowly and cleanly cut right onto your line. Now take the cutting guide off and freehand using the bit on the edges to clean up any burs and/or shavings. Apply pressure if you want your cut to have a bevel to it. I also felt the cut with my fingers looking for bumpy spots and tried to even those out by shaving them with the high speed cutter. This just saves sanding time.
Now you sand. Use a flap wheel sander attachmet for your drill. Ignore the sanding drums the rotary tool has. Use a mediam grit (80) flap wheel. The 80 works better than the fine (120). Keep the tape on the shield when you sand. You will on occasion slip and the tape will keep you from scratching the shield surface.
If you want to cut the minimum necessary and test to get exactly what *you* like, remember that with the multi-purpose bit you will want to cut about and 1/8 inch of material and the bit cuts a 1/8 inch path so your increments will be 1/4 to 1/3. Trying to cut extra with the high speed cutter bit will be quite slow. You migh want to buy some plastic at the home store and practice cutting on that to get the feel for cutting. Remember that plastic will melt some while cutting it. The melting is not an issue but you should know that it will happen. If you apply too much pressure with the sander, or stay in one place to long, that is what will happen as opposed to "sanding". You can draw test/final arcs with the shield on the bike. Tie a knot in the string and press it into the top gap in the "N" in Honda. Tape that down. Draw away. It is not a perfectly centered endpoint, but then neither is the one in the jig I assembled. If you want a different endpoint, tape the string to some other point.
The pictures.
1) FirstCut. After my test run. Just got home before the downpour! You can gauge how much I cut by looking at the plastic trim pieces using your uncut shield as a reference. I left one of my "wings" on for the pic. They do add to backpressure so understand that I was testing with those on my bike. Mark Lawrence made those wings and they attach with pasting removable rivets. They go on/off in a handfull of minutes.
2) This is a picture of my attempt at using the string to force the cutter on the arc. I quicky abandoned this and cut freehand.
3) This is a picture of my hilite maker and arc for the second cut after my test run of the first cut. The arc is not too visible but you can see that it starts just outside of the bottom "point".
4) FinalCut. Ain't she pretty!