frame bracing question "C" brace specific

[gsryder]

so for the last three or so years i had the standard "C" brace on my 81 gsx 7/11 turbo bike. And i believe it worked fairly well, however i always had minor fitment issues with the tank and clearance issues with the plenum. For those of you in the know, has anyone given any thought to a "X" style brace under and inside connecting at the opposing corners of where the typical "C" braces would reside respectively. I have no math or computer program to base this off of.....but looking at the stress path and moments that we all try to stiffen..it looks like it would work. I apologize i have no way to make drawings or sketches....so i hope i was descript enough....cheers.

[gsryder]

Something like this, but a little stronger than painters tape....lol

[arnout]

Hmm.. Well, I've never liked the "C" bracing (had to look that one up..) as it cuts into the space for air filters, or like you've found out in your case, a plenum..  Also I think the "C" bracing doesn't ad much to the stiffness of the frame anyway..
From the picture I see the X you're planning to put in still eats into the space you were looking to free up, so I can't see much of an improvement there.. In spite of that I think it should work apart from a cross tube that is missing to complete the bottom triangle of the X..

[gsryder]

Yeah, there is some more bracing going in, I am taking to my welder tomorrow to have the swingarm pivot plates tigged. I really wanted to sort this portion out tonight so he can do both..but it will be back a couple times as I progress through the mock up......what about something like this only with much better contact points

[gsryder]

[gsryder]

[gsryder]

Any thoughts comments?

[gsryder]

Going to take this in to get proper weld, seems strong, although flat plate obviously can flex easiest of any other options....I may add some small stiffners on the open sides...this will double as my electrics plate as well

[arnout]

Mar 25, 2015 2:16:53 GMT gsryder said:

Going to take this in to get proper weld, seems strong, although flat plate obviously can flex easiest of any other options....I may add some small stiffners on the open sides...this will double as my electrics plate as well

Hmmm yeah, although I don't think it looks very pretty using a plate instead of tubes in X-configuration should work too, but (like you wrote) the plate is weak without something substantial between the downward bends of the main frame tubes.. (perhaps bending a lip on the edge of the plate would suffice, or else ad a cross tube)
But still this plate too protrudes below the main frame tubes, taking away space you were looking to free up.. Rolling a curve/bend into the end of the plate so it follows the shape of the main frame tubes would solve that issue..
IMHO I really don't think the frame needs that much bracing in that horizontal plane (apart from 1 or 2 cross tubes).. Especially as there's no further bracing to continue the "reinforcements" towards the swingarm pivots.. (that need cross tubes too btw!)

Oh.. played around with your frame picture a bit and added some tubes where I might put them..

[slim]

I see your problem with space but IMHO the area the C brace addresses is the weakest point on the stock frame in the vertical plane, it also ties in with Brace D (shown below) if done properly substantially strengthening the whole area .... Again IMHO one is of little use without the other.

Brace c can be cut back a fair bit in depth or shaped to provide a little clearance the X shown in the above pic could be bent upwards to follow the frame & give a little more clearance & would no doubt help but not be as effective as the normal C brace

[gsryder]

Thanks for the replies. There will be a lot more bracing coming up. Just had to get the swing arm pivot plates and the "C" situation first so I can locate the turbo.
A pic of how it was before



And where I am heading....sans the tubular C brace obviously

[slim]

Could the tubular brace could work if you bent it to follow the stock frame & welded it underneath or even on top ?

[gs1168]

your surrounded by shovelheads , yours?

what about some smaller gussets in the c-brace area in the bends of the frame and tubular bracing in the top area like u are thinking about

[gsryder]

Yes, both the shovels are mine. 1978 fxe and a 1983 flht with a 1975 fxs engine, i also have a 73 bmw r60/5...but thats in the house. The shovels just need some minor stuff and their good to go but the GS takes precedence in my garage.

[arnout]

Mar 25, 2015 23:56:19 GMT slim said:

I see your problem with space but IMHO the area the C brace addresses is the weakest point on the stock frame in the vertical plane, it also ties in with Brace D (shown below) if done properly substantially strengthening the whole area .... Again IMHO one is of little use without the other.

Brace c can be cut back a fair bit in depth or shaped to provide a little clearance the X shown in the above pic could be bent upwards to follow the frame & give a little more clearance & would no doubt help but not be as effective as the normal C brace

I don't dismiss the logic and benefit of the C brace, but as it often makes fitting large (pref. straight dual) air filter pods difficult, I prefer to leave these out myself.
Instead I think if you make brace the front of the frame (esp. B brace) really well, this will still be able to make the overal more rigid.. Compare it to a rectangular shaped construction where you only brace 1 out of 4 corners (instead of 2 out of 4).. It is a compromise, but it should work..

Designing a brace in the C position that follows the main frame tubes and does not cut into the space below for carbs/filters is still possible though -like you say-.. Either put it on top (the long way round) or perhaps just rely on stiffnes form tube cross sections alone, and simply ad more of them.. (or perhaps extend the big tube from the steering head further back and down..)

Lots of possibilities, and about any brace will have some use, but they all also ad weight.. It would be interesting to experiment with all the options in a steel construction design program.. And see what brace does what exactly, and gain some hard data instead of only relying on assumptions and guesswork..