Cyclist0108

We have a Kuat Sherpa 2.0. Recently it experienced a rear impact, and got a bit bent. Specifically, the spindle that the wheel hook mounts on is no longer perpendicular to the plane of the bike when in the rack, so it doesn't hook the wheel properly. I disassembled it down to the spindle, and it is bent where the weld meets the main part of the rack. I am going to try to bend it back with a pipe, but am concerned that this might further weaken the weld.

Anyone have any advice or experience making the angles 90° again?

Should I trust the rack after this, or toss it and get a new one?

jbucky1

Is it Aluminium or Steel?

Juan Foote

I also use a Kuat...love it...on to subject.

First, I would make an assumption that either this was a "your fault" situation, or that hopefully you claimed it as part of the damages in the event it wasn't...
Considering that this is a significant strong point for your bike staying snugly attached to the front/wheel mount and thus, on the rack. I would be inspecting very closely for cracks all along the structure and arm for the wheel. It would be my concern that something is broken or weakened to a degree that it could fail later, and certainly that bending it back isn't going to help .

Claim it, get a new one. Or...you might contact Kuat and see if you can buy that rear beam. As I recall it all bolts together in the middle?

Cyclist0108

Yes.

The main part of the rack is aluminum. The spindle might be steel; I can check the next time I have access. (Steel is also an alloy.)

Cyclist0108

It was my fault in that I let my wife drive the car. She backed it into a fence.

I agree.

I think that is the case. It would be great, because my wife also bent that rear beam a wee bit a few weeks ago when someone rear-ended her. Unfortunately she didn't notice at the time, and in that case the consequence of the bend was only cosmetic.

However, the spindle is welded to the tray, as indicated in that figure with the arrow.

Cyclist0108

Crappy photo, but with a pipe I got it somewhat bent back. Even for a 200lb sack of lard standing on the pipe, this isn't easy to do.

Andrew R Stewart 

I would strongly suggest frequent monitoring of the area you "repaired" for cracks. Al tends to have rapid crack growth. I might also suggest a secondary method to tether the bike to the rack so if the "repaired" spot does crack and break off at the wrong moment the driver behind you won't be looking at your bike coming through their windshield. Andy

Cyclist0108

I agree.

Also, thanks for using the correct abbreviation for aluminum.

Cyclist0108

They sell a replacement tray for $220:



A bit more than I need, but at least I wouldn't have to worry about dropping a bike.

dsbrantjr

Since almost all metals commonly used are alloys, "alloy" is not very descriptive. I find that using the base metal name (aluminum, magnesium, gold, copper, etc.) for most alloys is the most clear, with steel, brass and bronze being common exceptions.

jbucky1

In that case, I wouldn't trust it with my bike. Also Aluminium has a lower fatigue life than steel, not sure bending it back would inspire confidence in me. IMHO
I would call manufacturer and see what they say, maybe you can get a replacement assembly at a discounted price
good luck

- james
www.buckyrides.com

Cyclist0108

I shall check to see if it is ferromagnetic.

Edit: Checked, it is not comprised of Iron with carbon mixed in. (I thought it was unlikely to have steel welded to Al).

WizardOfBoz

Yeah, as Andrew mentioned, bending a welded, heat-treated aluminum alloy fabricated part (which your arm is) induces stress and weakens the part, making it susceptible to breakage.

Some aluminum alloys (as opposed to pure aluminum) can annealed (which softens it and makes it easy to bend) and heat treated (which is generally meant to mean hardening and strengthening the alloy, and relieving stresses in a welded part making it more durable). In the annealed state you can bend aluminum pretty easily. If after bending or welding you heat it up (including welding and post-weld heat treat) and let it cool it makes the alloy stronger and harder and less able to bend. Bending aluminum in this state work-hardens the aluminum and induces stresses that weaken the part around the bend. You can bend heat treated aluminum a bit better if you heat it, but this requires the kit, the experience, and some ability (including refinishing ability).

The weakening effect also depends upon alloy. The fact that your part was welded means that its probably a 6000 series (Al alloyed with Mg and Si) alloy which is much more easily welded than a 7000 (Al allowed with Zn) series. The fact that you were able to bend it a at all, and without cracking, also suggests 6000 series. Here, 6000 is better than 7000. Did rebending it weaken it enough to break spontaneously under load? Hard to say. Can it be guaranteed to hold together? Absolutely not. Your setup might last for the life of your bike. Or the bike and part of the rack may fall off in traffic tomorrow.

Cyclist0108

So, replace the Kuat part for $220, or get the coveted One-Up rack?

Andrew R Stewart 

Why is the OneUp coveted? I have to admit of not knowing it even existed. Andy

Cyclist0108

It seems to be a fad here (Santa Cruz). They are even more pricey than Kuat. It is the other main option if you don't want a hitch rack that touches anything other than your bike tires.

https://www.pinkbike.com/news/1up-us...view-2017.html

I think the company was started by two engineers as a garage enterprise somewhere in Wisconsin. (Hence the way the racks look.) A few years ago I heard they had an ugly falling out, and there were two companies and two competing websites with nearly the same name. I'm not sure how it got resolved, but only one seems to remain. They have quite a following, considering you can only purchase them on the web from the company. Made in USA, and almost no plastic parts. Very robust. First version didn't have a hitch pin, which put me off.

leob1

If it was me, and my wife backed my KUAT into a tree, I'd make her buy the new tray. Or tell her that HER bike is going on the repaired one.

Wilfred Laurier

Fatigue failure is not caused by two or three bends, it is caused by constant cycling or vibration.

When something is 'bent' - or has suffered 'plastic deformation' (past its 'elastic' limit - the point from where it can spring back to its original shape) then it has been weakened, steel or aluminum. A few bends back and forth like that will snap any metal, but this is not a 'fatigue' failure. Maybe steel would take a couple more bends than aluminum, but for most purposes, bent = failed - the part suffered a load great enough to make it no longer suitable for its original use.. Bending something back might make it work again, but it is always weaker than before it was bent.

Cyclist0108

I put it back together and it is good enough for me. (I think I will put the more expensive bike on the inside, which I do anyway, and use secondary containment just in case.)

Cyclist0108

I should have thought of this sooner:

The spindle got bent when hook-arm was down in the horizontal position, as shown in the photos. That means when it is rotated 90°, it is straight. The bike-mounted position isn't quite 90°, but it is sufficiently close as to make the consequence of the bend fairly minimal.

jadocs

Ha Ha, this made me chuckle.