Frame flex

Posted: Thu Nov 08, 2007 3:57 am

stoutblock wrote:

I've always felt the X's were quite a handfull. They are stable bikes but you have to really work to get them to respond. Of course, I've never ridden one with good tires, suspension, and wheels.

Come on down to L.A. and bring your helmet & riding gear and I will let you take my CBX that glides through the twisties like it was built for it. Wink

Posted: Thu Nov 08, 2007 4:21 am

I will attempt to describe this again,but go out pull the tank and look at the frame.

There are two parallel straight tubes right at the gas tank rear mount reaching up toward the triangle of the steering head. There are two parallel tubes at the foot spuds,one is the drop out piece,but is bolted and entered at the spigot in front. This ENTIRE section is UNSUPPORTED,this is the problem because it can deflect sideways,backwards,at a twist,whatever BECAUSE it is attached by parallel tubes that have no strength.

The 900/1100 is total this distance. The 750 frame with the solid mount engine decreases the bottom distance to the front motor mount,but really only counts if you make a receptical for the drop out piece to enter,otherwise it only has ONE bottom tube that counts. On all the bent frames I have seen the drop out piece has had no damage because there is no force on it trapped between the engine mounts. The damage is the triangluated part is twisted compared to the rest of the frame,with all the displacemt taken at the parallel tubes.

The CBX is trangulated by the cylinder head to reinforce the steering head. The early(79-80) CBX handled poorly because of the small swing arm pivot and cheap bearings,same as early 750. The next generation had the larger pivot the last had the single shock.

All of this "tuned flex" is really crap. On a road race bike that is really leaned over in a corner,the actual suspension movement is in the wrong direction and cannot absorb the movement and trys to by "flexing" the frame. For most of us that do not lean at a 60 degree angle the flexing nees to be a minimum so the front wheel and back wheel will stay "in line".

On these bikes the cornering forces provided by a sticky front tire effectively allows it to move toward the inside of a turn. This makes the angle of the tire to the road not as much lean as the rest of the bike,so steers wide in a hard corner. Effectively it handles "great" till it "pushes" in a corner,or held at this point gets a vague oscillation and lack of steering precision.

Posted: Thu Nov 08, 2007 5:28 am

I don't think Honda had any "tuned flex" in mind in 1979. Just another Honda way of overthinking something until it's F'ed up. To back up what you just said, I remember the superbike races from the Tuned Flex era (about 10 years ago Shocked

, I feel old). The Suzuki and Kawi bikes looked dead solid but the Hondas wobbled in and out of corners. I think even with all the factory frame works, the race motors overpowered it's integrity and flexed it enough to oscillate.

CB1100F Joined: Jul 02, 2003 Posts: 3189 Location: Phoenix

I know that my problem is mainly in my front suspension, not a flexing problem. It is amazing how some things may seem like the culprit, but the real problem lies somewhere else. You might want to try and stiffen your suspension. I personally have seen wonderful differences just by going up a notch.

Posted: Thu Nov 08, 2007 11:51 pm

What I am talking about is just a smooth corner load,not anything to do with the forks moving.

You can ride and lean and turn,nice swoopy turning,UNTIL you push too hard. Then it plain quits steering and runs wide on the "line". Right turn and go left of center to head on traffic,left turn and go off the road. Either a slippery tire that does not grip or the angle itself after you put on a sticky tire,but same feeling of loosing the front end.

I have said this story before. On my first ride on a 900F I went down the standard "main drag" to make a left onto our main street. Done this many times over the years on a variety of bikes and these are 35 mph limit streets. On this ride a quick lean it went about halfway through the turn and then ran wide almost going into the parking lot on the corner. The 900 was a quicker turn in but not as stable as the later 1100,but that "runs wide" is ALWAYS in the back of my mind on every corner.

Posted: Sat Nov 10, 2007 4:06 pm

anyone have a picture of drop tube receptacle mod? while cbr wheels and gs swingarm have helped tremendously, bike still has a weird flex in the corners sometimes.
thanks

Posted: Sat Nov 10, 2007 4:36 pm

Without a comlete change in the frame geometry, we are all going to feel the flex in one way or another and Honda is not going to take the time to rethink our old frames.
So, I ride my Flexi-Flyer with the knowledge that she is going to flex and wiggle as I push her in ways that she was not designed to take. Maybe the solid mounted and slightly braced "R"eplica will be a bit different in the flex department but, I do not think it will matter much.
My CBX is my handler now and my Flexi Flyer looks good as she flys bye in a red & white blur. Soon I will have the "R"eplica to flex the roads with too.

Posted: Sat Nov 10, 2007 7:52 pm

i guess the old gal will never handle like a duc but that drop connection looks like it needs a double bolted lap joint or plug or sumptin.

Posted: Sat Nov 10, 2007 9:39 pm

I will say this AGAIN.

The drop out piece of frame is NOT the problem on 900/1100 frame. It is located between the two lower motor mounts and gets no load whatsoever because of the rubber mounts. The rear section is "fit" over studs then clamped there. The front enters a reciever on the frame and is clamped there.

On 750 frame it really does nothing because it is not attached to the frame at all in front. It is only the flat plates of the front motor mount that even attaches it at all. You weld a 2" long piece of pipe to attach 1" onto the frame and leave the other end open about 1". To do this you need to cut notches into it to fit over the bolt bosses. Now it enters like a 900 frame.

On power moves the chain side gets shorter. On 900/1100 motor rotation is not prevented due to the rubber mounts in all positions. The chain load not only pulls back but also rotates that they ignored. The front links prevent it from moving rearward but is free to rotate. On a hard launch,like drag racing with a slick,the entire motor can and does rotate hard enough to dent the bottom of the gas tank.

Bottom line is on 900/1100 the frame gets no support from the motor so the ENTIRE front moves since it is a rigid section mounted by 4 skinny tubes. As I said before the triangle stays intact but gets twisted in any accident,even fairly mild hits. After you make a reciever on 750 frame the distance it can deflect is shorter since it moves in the area above the front motor mount,compared to all the way back by the foot spud/rear motor mount.

Posted: Sat Nov 10, 2007 10:01 pm

On 750 frame it really does nothing because it is not attached to the frame at all in front. It is only the flat plates of the front motor mount that even attaches it at all. You weld a 2" long piece of pipe to attach 1" onto the frame and leave the other end open about 1". To do this you need to cut notches into it to fit over the bolt bosses. Now it enters like a 900 frame. [quote]

thanks, thats the bit i needed

Posted: Mon Nov 12, 2007 2:56 pm

I’ll take the bait on this one ….
In the past year I have owned and ridden a stock solid mount 900f with 35mm forks. A rubber mounted 11F motor frame with CBR wheels and 37mm forks, and a 1123 with USD forks, big swing arm, 3.5 and 5.5 x 17 wheels with a welded up frame rail and more bracing than you can shake a stick at … here’s the results from the riding … and I mean when ‘pushing on’ on the average Aussie road, which is VERY bloody average. The riding is basically keeping up with the dudes I ride with, and the oldest bike there is a ’95 900SS Ducati, and we’re talking miles of tight switchback roads in the Hills behind Adelaide.

Stock bike – the side walls of the tyre flexes, the suspension ties itself in knots under brakes and under power. Wallowing is mandatory and “feel” from the tyres is best described as remote.
Is that a bagging?- you bet, but it should be taken in context, these bikes are old in design, they were fast in their day and are huge fun in these days. And you cloud never say the bike “gave you no warning”. Under these conditions, my rat would be talking to me all the time with movement here and there – the important thing was to listen, and know when enough was enough.

CBR wheels on Rubber mounted frame – definitely better than the stocker solid mounted frame. Could be helped by the 37mm tubes of the forks, but this bike also has an F2 (Hondaline) fairing which carries a lot of weight over the front wheel. There’s still some wallowing to be had for sure, and most of the comments from the stocker run true here, but just toned down a little. The fat rubber and smaller diameter wheels make the steering of the bike just so much better.

The highly modified bike – no comparison – make everything strong and have compliant suspension and you will have a wicked handling bike. This thing feels quite small when flicking from side to side, has felt planted the whole time and takes everything I’ve thrown at it. Think CBR 600 or FZR1000. I use these two examples as I’ve spent many thousand miles thrashing them and that’s about the company the braced frame puts you in … it’s another world altogether ..

Posted: Mon Nov 12, 2007 2:59 pm

double

Posted: Mon Nov 12, 2007 3:14 pm

triple

Posted: Mon Nov 12, 2007 3:19 pm

quadruple

Posted: Mon Nov 12, 2007 3:20 pm

quintuplets? dam double posting Rolling Eyes

Posted: Mon Nov 12, 2007 4:07 pm

Mines modded so its hard for me to say anything about flex on my F. Between the 41mm telefix braced forks and metmachex arm with works shocks, my suspension is both compliant, and more rigid. The cbr wheels with radials have now become where I notice and feel the road as precisely as I have on any bike. Granted, that is limited, but I really cant wait to try other tires as I'm sure there are better and worse combinations for my bike. And to get even more technical, tire presure variations of a pound here or there will make big differences. Race guys measure in 1/4 pounds.

In 1980, I could make the frame on my new GS1000E, which was thought to be one of the best handling bikes of its era, flex while it was sitting in my garage, not even running. You simply put your finger between the sprocket cover and the frame and step on the drive chain slightly. Your finger would get pinched. There was a brace made that would eliminate it.

If I had a bike that felt that squirley, I'd have it off the ground and checking all bearings, wheel, fork trees and swingarm. They wear quicker than we like.

To Ray I'd seriously consider new meats. New is always better, and there are tires that will squirm a whole lot less.

Posted: Mon Nov 12, 2007 4:20 pm

larryg wrote:

To Ray I'd seriously consider new meats. New is always better, and there are tires that will squirm a whole lot less.

I have been riding the F again for over a week now and have gotten used to the flexibily of the F frame in comparison to the CBX which does not flex that I can tell.
The more I ride the bike, the less flex I feel and when I took her up into Big Tujunga Canyon on Saturday, I almost eliminated my chickenstrips which I find is almost impossible on these tires I am running now on the red bike and my CBX.
3 Michelin Pilot Road tires and 1 Pilot Power front tire on those two bikes and my "R"eplica has BT56 Battlax tires that as soon as I can, I will let you all know how they compare.
When I started this thread last week, I was literally amazed at the differences of the two bikes, CBX and CB-F. Now that I have been on the CB-F again for almost a week and have all that power my CBX does not have, I am liking the CB-F because she does things the CBX cannot do without destroying internal and external parts, wheelies be it power or clutch.
My CB-F did an 11-o'clock on me the other day when I banged 2nd and I almost fell off the back, it scared the shit out of me. Shocked

My CBX never scared me, she only thrilled me with her handling ablities.

Posted: Mon Nov 12, 2007 7:00 pm

my 2 cents. some flex is good, not in the steering head. some flex is designed in to allow for shock position when laid over. I don't have to tell you guys this I'm just reminding you that suspension is more than shocks.

Posted: Thu Jan 17, 2008 8:55 pm

Hey Ray, I'm so glad your back! I've been wanting to ask you concerning your "R"eplica and the frame gussets you added. Have you pushed this bike as hard as the Flexi-Flyer yet? I'm very curious to know if this cured your flexing. I know what you mean cause when I take my F out on track days, I hold my breath every time I go into turn one at Pacific Raceways, 5th gear at redline! I plan on bracing my 750K track bike like yours.

CB1100F Joined: Mar 03, 2004 Posts: 3278 Location: Seattle

Quote:

My CB-F did an 11-o'clock on me the other day when I banged 2nd and I almost fell off the back, it scared the shit out of me.

Ive had a couple of those moments before... Shocked

Quote:

I'm very curious to know if this cured your flexing.

Yep, it is solid modification to the F frame. Tightens it up very nicely compared to stock..

Adding cross braces above the swing arm mount and the front frame engine bolts further tightens her up. If I could get my damn picture posting to work, I would post Da Beasts frame mods for reference.... but try this out..

http://img.photobucket.com/albums/v465/Baal199/framenet.jpg

Posted: Thu Jan 17, 2008 9:31 pm

Blainethemono wrote:

Ray wrote:

My CB-F did an 11-o'clock on me the other day when I banged 2nd and I almost fell off the back, it scared the shit out of me.

Ive had a couple of those moments before... Shocked

This is the frame flex thread, I forgot all about it.
My black bike that is moderately braced does not have any noticable flex like the red bike did.

Posted: Thu Jan 17, 2008 9:53 pm

Here's Andy's bracing.

http://www.cb1100f.net/modules.php?name=Forums&file=viewtopic&t=10095&highlight=frame+brace

Posted: Thu Jan 17, 2008 10:03 pm

There is something you guys are ignoring.

The late stuff is designed as a "tuned flex" in the steering head because they are leaned over so far like more than 50 degrees from vertical,that the suspension no longer moves the direction it needs to go to absorb bumps in mid corner. Also it better have some version of dampning it this flexing or you are riding a spring that rebonds later when the force is removed.

In the case of these it is not "flex" but actual displacement,more than likely not controlled.

There is no real comparison between the beam chassis of now with widely braced steering head and these with the oh shit lets put a tube inside a tube because it is a piece of spagetti.

On these they are made to ride more nearly upright. The tires are slippery. The stuff of now has tires and rims wider and stickier on the front than these have on the rear and as such puts a very large load into the frame.

One of the first observations doing the drag racing was video on the launch. No suspension on rear means chain play is not needed,so is pretty close to tight. I have seen some bikes like the FJ-1100 Yamaha flex so bad the chain goes from this tight to almost drag the ground. This is due to the swing arm pivot moving forward by the forces. A slick against a sticky track provides more traction than most people can understand,a gear drive would be close,but actually a slick is better. The slick has wheel speed over ground speed and "couples up" to maintain more than 1"G" of acceleration.

Posted: Thu Jan 17, 2008 10:31 pm

Sonic, curious what your solution is to "firm" up the bike. In your opinion, is is possible to stop the "wobbles" in a high speed turn? I'm certain that my suspension and bearings are all good.

Posted: Thu Jan 17, 2008 11:02 pm

Im sure these frames flex - I dont think I have ever felt it before. Im probably not a good enough rider to be able to get that kind of feedback from the bike....

More likely than not, I havn't put the bike through enough for it to actually flex

Posted: Thu Jan 17, 2008 11:22 pm

In my case I plain do not trust the bike to push it in a hard corner.

On one of my first rides on a 900F was down the main drag for an easy left turn onto Main St. I made this turn plain gobs of times on many bikes over the years. So mid corner the bike "pushes" and tried to run me wide into the parking lot on the corner. Some years later my 1100 F did nearly the same deal and I almost bought the front end of a pickup truck in a right hand turn this time.

End of story. Enough force load on the frame the steering head deflects to more upright than lean angle,so goes wide. There is no real way to support the steering head and I feel the entire front triangle from back by the seat around to back by the foot pegs moves as a unit. If the motor is bolted in solid at least the flex is from front motor mount to the seat,still not good.

On the drag bikes I had to support the swing arm pivot to keep that section from moving forward by launch power. I made threaded deals welded to the swing arm to bolt through the rear foot peg mounts,"K" chassis. Also metal bushings to replace the rubber deals in the swing arm where the struts bolted up. All of this is why modern Pro Stock bikes have fully triangulated deals and no "swing arm" per se,so the whole deal is bunch of triangles. In these cases the front carries no load except braking or holding the bike up in the pits.

On these bikes there are two short parallel tubes at the rear gas tank mount and basically no way is this going to support ANYTHING. Even if you weld in the drop out piece the lower tubes are also parallel. These four tubes are really close to parallel,so twist this and get junk. Every wrecked chassis I have seen this is where they moved at. The steering head triangle stays fairly good,but it twists also at the sheet metal. Just an example of 100+ HP in a 50 HP frame.

Posted: Thu Jan 17, 2008 11:49 pm

sonicrete wrote:

In my case I plain do not trust the bike to push it in a hard corner.

On one of my first rides on a 900F was down the main drag for an easy left turn onto Main St. I made this turn plain gobs of times on many bikes over the years. So mid corner the bike "pushes" and tried to run me wide into the parking lot on the corner. Some years later my 1100 F did nearly the same deal and I almost bought the front end of a pickup truck in a right hand turn this time.

End of story. Enough force load on the frame the steering head deflects to more upright than lean angle,so goes wide. There is no real way to support the steering head and I feel the entire front triangle from back by the seat around to back by the foot pegs moves as a unit. If the motor is bolted in solid at least the flex is from front motor mount to the seat,still not good.

On the drag bikes I had to support the swing arm pivot to keep that section from moving forward by launch power. I made threaded deals welded to the swing arm to bolt through the rear foot peg mounts,"K" chassis. Also metal bushings to replace the rubber deals in the swing arm where the struts bolted up. All of this is why modern Pro Stock bikes have fully triangulated deals and no "swing arm" per se,so the whole deal is bunch of triangles. In these cases the front carries no load except braking or holding the bike up in the pits.

On these bikes there are two short parallel tubes at the rear gas tank mount and basically no way is this going to support ANYTHING. Even if you weld in the drop out piece the lower tubes are also parallel. These four tubes are really close to parallel,so twist this and get junk. Every wrecked chassis I have seen this is where they moved at. The steering head triangle stays fairly good,but it twists also at the sheet metal. Just an example of 100+ HP in a 50 HP frame.

So mock up an aftermarket Alum. frame!!

....sheesh

Posted: Fri Jan 18, 2008 1:45 am

I am very very very happy with the way my CB-F racebike handles. I think there are a few things that are relatively simple to do that have all been spoken to, and that I've listed in the order I think they should be done - solid mount the motor*, ensure all the bearings in the steering head and swingarm are good, get good suspension parts, get good tires, brace the frame some around the steering head, front and rear downtubes, swingarm pivot area and rear shock mounts, and get a narrower, lower handlebar than 'stock' for the 750s and 900s.

*If it's a 750 frame, weld the removeable downtube in.

My Z1s feel 'loose' and wiggle or weave at high speed* compared to the CB-F and both Z1s have all the mods listed above for handling. The CB-F is planted and feels way more stable.

*high speed = turn 8 at Willow Springs or exiting the banking at Daytona coming onto the front straight

Posted: Fri Jan 18, 2008 2:12 am

Thanks for chiming in Dennis. I was hoping you would. Do you have any pics of the steering head bracing? Welding the front downtube...Aw man, think if I do the other parts of the frame, the downtube welding is not neccessay?

Ray, did you weld your front downtube??

Blaine, I actually downloaded all of your frame pics for bracing referance. Great stuff! Thanks. You and Stout should join me on June 13th for a track day. I have that day set aside already...

http://www.adrenalinefreaks.com/

Posted: Fri Jan 18, 2008 2:22 am

melchiro wrote:

Ray, did you weld your front downtube??

No welding was done to the front of the frame on this bike, just the back for the shock mount and the gussets I welded in.
The black bike is more stable than either of my CB1100F based Super F's were but the solid mounted engine and frame bracing made all the difference in the world on the black bike.
Neither one of my CB1100F based Super Fs were braced or had solid motor mounts.