Monster S4R Alloy Frame

[Speeddog]

aluminum alloy 7072 is aircraft grade and is pretty strong. May not be Ti strong but has very good weight to strength benefits.

Do have a link for 7072 mechanical properties?

'Cause the stuff I'm finding doesn't make it seem very good...

[MotoCreations]

aluminum alloy 7072 is aircraft grade and is pretty strong. May not be Ti strong but has very good weight to strength benefits.

A friend in the aircraft industry works with this stuff regularly (as in thousands of feet/month) -- great strength/weight benefits.  He said maybe one race season at best before he'd trashbin the frame due to fatigue and stress.  Not for the street at all.  Big concern is that if something happens to it, it will be catastrophic happening.  (steel / titanium can crack but not fatigue instantly)  Let's be honest -- how many people regularly check their frames for cracks?  (and once painted / powdercoated you really aren't able to until something big appears)

Still the very best solution for a welded trellis frame is chromoly (or derivative) and titanium. 

As for going under 300lbs?  New frame is required.  DSS swingarm is lightest (for the strength).  If using a SSS, you can pare some weight off of it with machining in certain non-stress areas.  One can also carve a few pounds out of the rear eccentric assembly. (or machine titanium parts to put within -- less suspended weight!)

[junior varsity]

I thought 7075 was the strongest of the alu's from a table I read back in the day, but its been awhile.

Again, where's ArcFab?!

[JJG1975]

Since we are talking about aluminum, I know hardcoat (Type III) anodize reduces the fatigue strength by about 50%, not positive if sulfuric anodize (Type II) has the same effect, I'll have to double check that.

[junior varsity]

Only by the amount (depth) in penetrates the surface I would think.

[DarkStaR]

Do have a link for 7072 mechanical properties?

'Cause the stuff I'm finding doesn't make it seem very good...

+1 Seems poopy to me...

http://www.substech.com/dokuwiki/doku.php?id=wrought_aluminum-zinc-magnesium_alloy_7072

[Travman]

A friend in the aircraft industry works with this stuff regularly (as in thousands of feet/month) -- great strength/weight benefits.  He said maybe one race season at best before he'd trashbin the frame due to fatigue and stress.  Not for the street at all.  Big concern is that if something happens to it, it will be catastrophic happening.  (steel / titanium can crack but not fatigue instantly)  Let's be honest -- how many people regularly check their frames for cracks?  (and once painted / powdercoated you really aren't able to until something big appears)

Still the very best solution for a welded trellis frame is chromoly (or derivative) and titanium. 

As for going under 300lbs?  New frame is required.  DSS swingarm is lightest (for the strength).  If using a SSS, you can pare some weight off of it with machining in certain non-stress areas.  One can also carve a few pounds out of the rear eccentric assembly. (or machine titanium parts to put within -- less suspended weight!)

Mark, have you ever considered making and offering a chromoly Monster frame?  There may be a market for it?  I think Kopfjager would be first in line.  I wonder what the cost would be?  The weight savings would probably be around 10-15 lbs and the frame would be stiffer than stock.     

[junior varsity]

I'd likely be interested as well. I'd be willing to work with Mitt on some 3d modeling for stress analysis. fer a discount, o' course.

[He Man]

is stiffer necessarily a good thing?

[junior varsity]

Yes, to a point. The pre-02 Monsters were based off the 851/888 frames, but actually had a cross brace removed to accommodate the air box. I want the suspension doing the work and not the frame. That's one of the reasons for the aftermarket lower triples - stiffer for less flex (as well as lighter), why they are offered in OEM offset (as well as other offsets to change the geometry).

Some things don't need to be as stiff for handling purposes. Others are important. The connections from front wheel --> Forks --> Triple Clamps --> Headstock --> Frame --> Engine --> Swingarm, we want that rigid. But the Seat? Who cares, that's just where the rider dangles from, that can be subframed if need be. And the monoposto sbk subframes are aluminum, instead of the heavier biposto sections, iirc. 

[1KDS]

Isn't chassis flex necessary when the bike is leaned over and the frame can absorb more than the suspenders?

[1KDS]

front wheel --> Forks --> Triple Clamps --> Headstock --> Flex --> Engine --> Swingarm,  

That's what I thought but could be wrong...again

[junior varsity]

Hmm, that is an interesting point, with the flex being more 'side to side' than what the suspension can absorb. Where's mitt?

[DarkStaR]

I was reading some book (forgot which one though), and (if I remember correctly) it stated that certain flex is necessary to absorb bumps while leaned over.  I think it mostly had to do with the suspension though...particularly the rear...that is if I remember correctly.

[MotoCreations]

fyi -- all is of my own opinion and experiences below.  Everyone's opinion may differ:

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Titanium -- incredible stuff.  I just welded a new bicycle frame together with 3.2 alloy for myself.  Problem with titanium is that it is time consuming to cut, fabricate and weld.  And then when welding, you need frontside/backside and backflow (until weld below 300deg) to keep the hot titanium from getting impurities.  The bicycle frame I just did, painfully slow welds and all "bright silver".  Only one small area where I got a bit of very light strawish yellow color.  Perfect -- I deserved a beer after welding! 

Bad with titanium.  Titanium dust tends to ignite easily.  Surgical clean welds required.  If you see a titanium weld with "purple", "blue" color (it looks cool) -- throw the part away if it is structural -- not good and not recommended welds.

Other problems with titanium besides the cost is a) mandrel bending -- it springs back; b) tubing choices (limited).

Chromoly -- I've built 17 frames with it so far.  Biggest problem is your HAZ weld area -- but just heat normalize when done to correct.  Easily repaired if damaged (unlike titanium).  Lots of tubing size choices.  One area with chromoly I used to my advantage is by going oversize diameter and thinner walls.  It dramatically changes the frame characteristics fast as well as trellis frame bracing location.

Building Monster frames?  Not difficult at all.  Question inevitably do you duplicate stock (diameter and some of the inherent design weak points) or do you oversize the tubing (thinner wall) and/or do you change the geometry of the headtube geometry as well?  Remember if you go oversize in tubing, then you need to adjust rubber stops on the tank to accomodate, etc. Ideal situation is a chromoly frame with a carbonfiber seat subframe.  Or use the aluminum tubing to create a visually interlocked appearance to mimic factory frames and save more weight.

Modeling of Ducati frames?  I've done it -- and learned a lot along the way.  You can do "static" basic stress analysis on the frame but it isn't truly applicable.  On my DesmoDevil's, a friend at GM took the CAD drawings and then built a true stress model for it based upon suspension input (front/rear) and how that affected things.  The difference between "static" -vs- "dynamic" modeling are quite different as we learned.  And he could never figure out how to dynamically model the bike while turning/leaning.

The problem with "too stiff" frames is basically a WSBK/MotoGP phenom due to tires / race tracks and speeds -- but somewhat applicable.  Basically what I learned with my chromoly frames is that the stiffer frame feels better as it is more "precise" -- but it requires a better suspension setup to work as well.  ie: stiff/bad suspension with a flexible frame is rideable due to frame flex.  stiff/bad suspension with a well designed frame -- not fun at all.  Best solution is quality frame and quality suspension (and the suspension doesn't fight the frame flex characteristics)

I rebuilt an 851 frame awhile back -- added better chromoly tubing and two extra braces into the frame and some gussets when repairing it.  Owner put the bike back together and called me the first time after he rode it at the racetrack.  Something felt "funny".  His suspension settings he used for years needed to be tossed out because the personality of the bike had changed.  What he later learned after having a few people ride it was he had a lot of frame flex befoe and learned to compensate for when racing.  Once he tweaked with the suspension settings and got miles on the track, he consisantly ran a few percent faster than he had for ten years -- give same engine, wheels and suspension (except suspension tuning).  His comment is that things just happen a bit faster now than before and attributed to the frame repairs and modifications.

Also I will admit -- when someone says "titanium frame" -- it's a statement nobody else can make.  It's why I did the titanium frame on the bicycle -- and it will last a lifetime.  Chromoly would have worked just as well and been a LOT cheaper and faster to weld. I still chose the titanium though because it's cool!