CHECK photos added - Altrider rear rack: Cracked and Broken

[Roge]

I "had" a Pelican type case mounted on an Altrider rear rack. The case carried waterproof, jacket liner and tyre pump so not much weight.
I spotted that the bottom section that mounts to the bike was cracked between the mounting bolt holes. Removing the case, the bottom part is completely broken on one side and cracks are evident at the other two mounts and all that was holding it together was the case. Photos to follow.

 

[Roge]

Re: CHECK - Altrider rear rack: Cracked and Broken

Photos as promised

 

[Roge]

Re: CHECK - Altrider rear rack: Cracked and Broken

More

 

[Roge]

Re: CHECK - Altrider rear rack: Cracked and Broken

and more

 

[Don in Lodi]

Just the Pelican alone is a weighty item, and you make no mention of the kinds or road surfaces you've been bashing about on or how long. ::005:: Contact AltRider, they've been known to replace the broken bits on their dime.

 

[Roge]

I have sent the same info to Altrider, this was by means of a warning to other users, a option with this rack is the mounting hardware for a GIVI case which is heavier and has much more capacity. The case I use is a Pelican type case designed as a marine runaway case for flares etc and is of a much lighter construction. As to roads its mainly surfaced roads and the odd fire trail, this is the first item to break on the bike in 64,000km.

 

[Don in Lodi]

::008::

 

[Roge]

Picture of the case on the rack as you can see it is of very light construction (almost transparent)

 

[Defekticon]

I run a givi trekker 52N which is a massive case, and is at times loaded heavy, and acts as a backrest for my wife. I've only put about 10,000 miles on it so far, but no cracks yet. I don't run offroad with it, only highway. I use wolfman waterproof bags for offroad trips.

 

[JRE]

I don't run offroad with it, only highway.

This is the key...on normal road use, there shouldn't be enough stress on the components unless you put bricks in there or something.

 

[dietDrThunder]

Wow that is a surprise. I'd think that the most likely cause of that would be a metallurgy problem on that plate, since I can't imagine such a huge failure with such a light load being caused by anything else. Please let us know what you hear back.

 

[WJBertrand]

From an engineering perspective, Altrider could reduce some of the stress at the attachment points by using square stepped instead of tapered countersink holes.This would put the metal under compression instead of tension like the tapered holes do. It also looks like the whole assembly needs to be more rigid. Unlike steel, aluminum will stress harden and eventually break when flexed, even at displacements below its yield point. Some added gussets would help here.

 

[magic]

Interesting that all 4 countersunk holes are cracked out. The shiny aluminum in the countersunk areas would probably be an indication of metal fretting caused by vibration. The square head carriage bolt thing wouldn't work here because the screws go into a threaded insert. If they were through holes with a nut, it would be different. Also, the countersunk holes on the top part of the rack appear to be fine. IMHO, the rack with the top box attached set up a vibration frequency that caused the fretting, in turn causing the aluminum base to crack out at it's mounting points. Kind of like a tuning fork. (Yamaha...tuning fork. Get it?) It will be interesting to see what Altrider has to say, keep us posted...I've got the same rack.

 

[Roge]

I work in the aircraft industry on the electrical side but we do have a structurally team, I am taking the part into work this morning for them to have a look at, I will have the bike there as well. The box I had on has never had much weight in, May be a couple so kilos.
I post the outcome.

 

[Jono49]

From an engineering perspective, Altrider could reduce some of the stress at the attachment points by using square stepped instead of tapered countersink holes.This would put the metal under compression instead of tension like the tapered holed do. It also looks like the whole assembly needs to be more rigid. Unlike steel, aluminum will stress harden and eventually break when flexed, even at displacements below its yield point. Some added gussets would help here.

Spoken like a true engineer ::008:: my thoughts exactly, any stress on a design like that will make the mounting bolt holes a weak spot!

 

[Don in Lodi]

Spoken like a true engineer ::008:: my thoughts exactly, any stress on a design like that will make the mounting bolt holes a weak spot!

Normal bolt and washer down low, countersunk clean smooth surface up top. Any reason that can be thought of that a retrofit to a standard bolt and washer couldn't be done? Might be worthwhile for those running a similar setup.

 

[Roge]

Just had the guys from Aero Structures look at this.

1. The counter sinks should be no more than 70% of the thickness of the plate these are 100% to a knife edge causing the cracks to start. Non counter sunk bolts and holes would have been better.
2. The plates exhibits contact stress points at the stand offs through to the frame of the bike.
3. Looking at the folds on the structure there are bend radii that are less than 3 times the material thickness the left had side upward ben has also cracked.
4. The ali plate is not of the best quality steel or s/s would be better.

It appears that I was lucky not lose the whole lot whilst on the move and a lesson in poor structural design.

 

[WJBertrand]

Normal bolt and washer down low, countersunk clean smooth surface up top. Any reason that can be thought of that a retrofit to a standard bolt and washer couldn't be done? Might be worthwhile for those running a similar setup.

Good point, unless the bolts need to be flush for clearance reasons, and in this case it doesn't seem they need to be as the luggage attaches to an upper plate, regular bolts would have been much stronger. Using some stout washers would greatly limit the point loading the current design suffers from.

 

[trikepilot]

My AltRider rear rack is all bent to hell from 6100 TAT miles with a light to moderate load on it. Have not removed it to look for cracks, but this report from Roge has me a bit curious.

 

[dcstrom]

I had similar problems with my first-gen Altrider rack. I was carrying maybe 12 kg and over some pretty bad roads. Had it welded and beefed up in Nicaragua, it's been fine since. Sent feedback to Altrider, they said they were making modifications to the new version, and offered to replace mine. I'm presuming this IS the new version, and that cracking is way worse than mine - hmmm.