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How easy do aluminum forks bend?

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How easy do aluminum forks bend?

Old 04-04-21, 09:19 AM
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Lakerat
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How easy do aluminum forks bend?

I usually ride steel bikes with steel forks, and haven't bent one in 45 years of riding. A friend moved and gave me his aluminum framed and forked bike. I fixed it up and have been enjoying riding it and yesterday had a minor contact with a skateboard on a MUP. I approached the unpredictable skate boarder very slowly and waited for him to indicate where he was going to go to pass. As I got close he stopped, saw me and hopped off his board which kicked it into my immediate path. I tagged his board with what seemed like minor force without almost falling. He had ear buds in and was pretty tuned out to surroundings.

This morning I was cleaning brake tracks on rim and noticed the rim wasn't centered relative to brake pads. A light bulb went off about the possibility of bending the fork with the minor contact with the skate board. I thought it likely wasn't possible to bend a fork without also tweaking the rim, so I checked for rim distortion in truing stand, and it was true. It appears a slight adjustment in the dropout will center the wheel, where I haven't previously needed to do that when installing the wheel. I also wonder if the wheel deflected and moved the caliper.

Is it possible or likely to put enough force to bend an aluminum fork with tire contact without also bending the rim? The frame and fork are unknown make and model, it appears to built up from a bare frame with no makings to indicate maker. The rim is a Matrix mostly shallow profile rim, with a mild aero point in the center, so it isn't a massively strong rim like a deep dish rim, that might impart strong forces without bending.

Of course nobody knows how strong my fork and rim are, just wondered if you have any experience in bending aluminum forks or heard of forks being bent without bending the rim. Thanks

Last edited by Lakerat; 04-04-21 at 09:22 AM.
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Old 04-04-21, 11:32 AM
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Contemplating further, possibly the force was in line with the wheel, maybe with some twisting force from turning the handlebars. The wheel is possibly quite strong and maybe has some flexibility in the fore-aft direction. Could be able to absorb force without damage, but still has to transfer the force to the fork. Probably was going less than 3 MPH.
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Old 04-04-21, 12:45 PM
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Highly doubtful that your fork bent. I used to race an aluminum BMX bike, and I guarantee it took many worse hits, at much higher speeds than yours did. If your fork bent at such a slow speed, and low impact, you would not be able to ride it on a normal street ride involving the normal bumps and potholes. That is, unless your fork was made by joining empty beer cans together.

Center the wheel, tighten, and ride.
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Old 04-04-21, 05:19 PM
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Sounds like you want to check the fork's alignment before assuming anything.

12 years ago I posted this thread in the Bike Forum's. Front wheel turns hard right. - Bike Forums Andy
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Old 04-07-21, 06:32 PM
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Originally Posted by phughes View Post
Highly doubtful that your fork bent. I used to race an aluminum BMX bike, and I guarantee it took many worse hits, at much higher speeds than yours did. If your fork bent at such a slow speed, and low impact, you would not be able to ride it on a normal street ride involving the normal bumps and potholes. That is, unless your fork was made by joining empty beer cans together.

Center the wheel, tighten, and ride.
You took your BMX bike off of sweet jumps didn't you?
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Old 04-07-21, 06:37 PM
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Originally Posted by Lakerat View Post
You took your BMX bike off of sweet jumps didn't you?
Sick!
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Old 04-07-21, 06:41 PM
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The nice folks at Klein bicycles explained to me once that aluminum does not bend, when it does it's toast. You can heat treat aluminum to reform, but it's not malleable,.
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Old 04-07-21, 07:31 PM
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Originally Posted by Lakerat View Post
You took your BMX bike off of sweet jumps didn't you?
The bike was used on BMX tracks. It saw many jumps. What happened to your bike was slight by comparison, as you described it. There should be no issue.
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Old 04-08-21, 03:52 PM
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Aluminum forks were never very common, but of the handful I have seen leave shops I have never seen one bent or broken. Not saying it doesn't happen, but I haven't seen it.

I have seen loads of bent and broken steel forks, and a couple of broken carbon forks. I personally have broken one steel fork and badly bent at least two. Steel bike frames and forks are generally built with much less excess material than aluminum because of the weight penalty. Of the steel forks I have seen bent, some were bent back to original and the wheels were not damaged at all IIRC.

My current main bike has an aluminum fork and I use it for all terrain riding, and often more abusively than I mean to, and it has outlived two frames and several wheels. I am considering replacing it but not because I think it I structurally unsound, but because I can barely fit 38mm tires in it. Most modern steel touring forks seem to have room for up to 40mm tires.

It is much more likely that your brake caliper moved than your fork bent. Try to eyeball the centre of the tire tread relative to the hole in the crown of the fork. If it is close to appearing centred, then you are good. A very minor tweak at the end of a fork leg would throw the wheel way out of whack out by the rim and tire.

Also, don't use axle position in the dropout to align the brakes - have the axle set all the way into the dropouts and set the brakes to match. Having the axle fully seated is a repeatable position so the brakes should be properly adjusted every time you install the wheel.

One more thing to check is the little conical quick release springs - if one of these is put on the axle backwards (so the large end of the spring is over the end of the axle) it will throw your wheel out of alignment and you will have a hell of a time getting the brakes lined up.
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Old 04-08-21, 09:03 PM
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The first thing I'd check is the wheel - is it mounted and seated properly.
While at it - I'd also check what ClydeClydeson suggested above.
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Old 04-09-21, 03:24 AM
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Thanks all for your help. I really appreciate your reasoned thoughts and the time you took to consider and write them. I suspect the force from contact with the skaeboard was mostly linear, but twisted when I steered during impact. I'll know more about fork alignment when get home and use my dishing tool to verify rim being centered. I centered wheel in fork, adjusted caliper and have been riding the crap out of it.
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