Bicycle fork straightening

June 1, 2015 5:17 PM

I would like to straighten my junker bike forks from their forward rake angle. To a straight line, to allow no hands cycling and lessen the need to pay such close attention to the path ahead. Can i pound them straight or will tbey break? Can I drive over them in a car, they are of little value.
posted by fkeese to Sports, Hobbies, & Recreation (15 answers total)

The fork rake is what makes them easier to ride no-hands. If you lessen the trail by straightening them, it'll be even more twitchy. Pounding on them may break them, and you might not get them exactly straight, which would make the bike extremely hard to ride at all. Don't do it.

I find I can only reliably ride no-hands if I have the headset well set up and properly greased. Any roughness makes no hands much harder.
posted by scruss at 5:21 PM on June 1, 2015 [5 favorites]

Not only will this make the bike less stable, but it will also weaken the forks so that they will gladly break on you at an inconvenient time, say, when you are no-handing down a hill beside traffic.

Don't do this.
posted by Sternmeyer at 5:48 PM on June 1, 2015 [3 favorites]

In addition to the above, bike forks and frames are made from very thin walled tubing - trying to bend them back is just going to kink the tubing and then it's going to be useless.
posted by backseatpilot at 6:02 PM on June 1, 2015

To bend/straighten smashed-in tubing that they use as bumpers on racecars, they use a block of wood and a large sledgehammer.
posted by Shylo at 6:41 PM on June 1, 2015

Everytime there's a dent or hairline crack on my bike frames, worried bike mechanics always take care to point it out to me and explain that the frame could fail at any time, likely while I'm riding it.

I'm seconding Sternmeyer; this sounds like a recipe for having the front end of your bicycle collapse under your weight. Used no-name bike forks are like, $20? I'm pretty sure you can pick one up for less than the dental bill on even a single chipped tooth, much less the medical bills for the grisly scenes I'm imagining.
posted by Juliet Banana at 6:45 PM on June 1, 2015 [3 favorites]

I threw out* a two month old custom bicycle frame that was make exactly for my measurements that I couldn't afford to replace once, because it had a hairline crack in the top tube from me getting t-boned by a car. It hurt, but I could picture the top tube crumpling while I was riding, and it was not something I was willing to go though.

That bike had a market price of like $1,000. It wasn't worth it. Neither are your junker forks.


*Actually, it hangs on the wall at Smart Bike Parts in Chicago, Il; it's high enough on the wall that you'd never see the fracture, and it's really a work of art.
posted by Juliet Banana at 7:24 PM on June 1, 2015 [2 favorites]

I agree that this sounds like a really horrible idea. If only because fork failure can kill you, if it happens at speed, and unless you are a metallurgist it is really hard to predict how straightening out your fork will affect strength. If you want to increase trail, look into changing out the fork.

>The fork rake is what makes them easier to ride no-hands. If you lessen the trail by straightening them, it'll be even more twitchy.

Are you sure about this? Looking at the geometry of a typical bike, it seems to me like just the opposite would be true, and this article appears to suggest the same. I admit that I am not an expert in bike geometry.
posted by Opposite George at 7:29 PM on June 1, 2015

Do not do this unless you have a death wish.
posted by fiercecupcake at 6:14 AM on June 2, 2015

Everybody here is correct about "don't do this."

Steel bike parts can be bent into new alignment - hell, bending is how they get their shapes in the first place - so if your fork is steel, it could theoretically be done. However:

• It's not the kind of thing that most shops are equipped to do, or really capable of.
• If your fork isn't steel, then forget it.
• It won't handle well.

Some other comments here miss the mark, though. "straightening" a fork will reduce the rake, or forward offset, of a fork. Doing this would actually make a bike much more stable, but not in a good way. Reducing the rake doesn't reduce the trail, as scruss states (nor would it make the bike twitchy - it would make it handle very sluggishly). It increases the trail. Rake (forward offset of the fork) and trail are opposed to each other - increase one and you decrease the other.

That is to say, Opposite George, you're right.
posted by entropone at 7:25 AM on June 2, 2015 [1 favorite]

Re-raking a fork of unknown condition is generally a Bad Idea, what you could do is ask your friendly neighbourhood bike co-op or similar (not the racing shop) to help you select a new-to-you fork with the same steerer tube size/length and headset type as your existing fork. Without knowing the geometry or any specs on your existing bike, it's hard to recommend a workable solution.
posted by a halcyon day at 1:57 PM on June 2, 2015

Response by poster: OK, I'm convinced, I won't do it. But straight forks are more stable. Prove it to yourself by looking at the forks on a no hands cyclist as he goes by.
posted by fkeese at 2:26 PM on June 2, 2015

Uhhh... That's not proof, it's an anecdote. I'm guessing the "no hands cyclists" you're seeing are riding fixies built up from track bike parts (or parts that are looking that way for the sake of fashion), and are basically show-boating by riding a twitchy bike with no hands.

Take a look at any touring or randonneuring bikes. No straight forks there. Those bikes are stable.
posted by a box and a stick and a string and a bear at 2:36 PM on June 2, 2015

Also, you can get forks with straight blades that are angled at the crown, giving the same effective geometry and handling as curved forks.
posted by scruss at 2:43 PM on June 2, 2015

straight forks are more stable

It's not just the fork, it's the interaction of the headtube angle and the fork rake, which creates the trail measurement scruss linked up top. Track bikes have steep headtubes and short offsets (rake), and don't respond to leaning as much as steering input; rando bikes tend to have slacker HTs and longer rake. Low trail in the latter case also helps stability when the fork is loaded but makes the bike more lean-sensitive, and these bikes tend to have a lower bottom bracket to drop the CG.

The 'road standard' combination of ~73deg HTA + ~42mm rake generally creates a bike that responds to leaning but isn't too twitchy.
posted by a halcyon day at 6:44 PM on June 2, 2015

Response by poster: Final answer, I straightened them by pounding with a sledge, it worked rather well, the bike, I may have failed to mention, is a junker, I am an old man who simply wants to crank his head around to see who is coming up behind him in the road, often times when I would like to cross the street to the other side, been having this problem of veering off course in the attempt, and since straightening the forks, it has been easier to do this. No worries about the bike disintegrating at high speed here. I'm done, and on to the next difficult question.
posted by fkeese at 4:55 PM on October 8, 2015