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I recently moved cities and met someone to buy a used "vintage" bike from them. While test riding at a slow speed I gradually applied the brakes. The front brake seemed to jump from light pressure to completely locking the front wheel at once and threw me over the top promptly!

My first thought was that the front wheel was out of true - causing the brake to apply harder as the other side of the wheel came around. However, the wheel was mostly straight.

Eventually I discovered that when braking, the frame and fork were flexing enough to cause the downtube to contact the front wheel. This contact caused the downtube to completely seize the front wheel instantly.

Has anyone else encountered this before? What fix would you even go about to stop the downtube from striking the front tire? I searched online and didn't find similar stories - so perhaps this super dangerous maintenance issues is rather uncommon?

  • Shogun Selectra - old frame, probably from the 90's
  • 62cm frame
  • 700c wheels
  • Rubino 28mm tires (seller said previous owner had 32mm tires) I didn't get the exact rim measurements. Tires seamed an average height for modern road tires
  • wheels mostly true
  • plenty of clearance for the tires in the fork (next time I'll have to check the downtube too)

edit - photos from comment

From auction linked in comment

The frame paint was indeed worn away at the contact point between the front tyre and downtube - though looked like erosion over a long period of rubbing.

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    Do you have a photo of the bike? I wonder if the fork is backward, or bent/damaged. Not impossible for an old bike to have had a frontal at some point.
    – Criggie ♦
    Commented Jan 14, 2021 at 6:57
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    frankly the fork just looks too small/short?? I wonder if it was a replacement at some point. The seller wasn't the original owner, though I have no idea how he rode it without the same issue. Perhaps he only ever used the rear brake
    – Offbeat Upbeat
    Commented Jan 14, 2021 at 7:10
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    Pic 3 is revealing a lot: The tyre has almost no clearance on the top and at the downtube. It looks like it is even touching the shifter cables. IMHO the tyres are too wide (28mm) for the frame that seems to date from the 21mm days. It also has 2 different brakes. Looks like a cobbled together Franken-bike. (stolen?)
    – Carel
    Commented Jan 14, 2021 at 8:27
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    @OffbeatUpbeat you're welcome to point the seller at this page too. They may legitimately not understand the problem.
    – Criggie ♦
    Commented Jan 14, 2021 at 10:10
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    @OffbeatUpbeat no the fork is not too short - its been bent backward. This is very likely an impact with an immovable object, like a parked car, large rock, or maybe a failed attempt to jump a kerb. There's some chance a vehicle has driven into the bike while it was immobilised by a rack or similar. You can see a similar-but-opposite fork bend at bicycles.stackexchange.com/a/67961/19705 where I put effort into a write-up. Your pictured fork is bent backward, not forward, and you already know from riding what problems were created by that "spontaneous geometry rearrangement."
    – Criggie ♦
    Commented Jan 14, 2021 at 11:26

5 Answers 5

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Yes, extremely dangerous, as evidenced by your falling over the handlebars

It's evident from the photograph you linked, that the fork is pushed backwards, bringing the wheel much too close to the frame. The most likely reason for this would be crash damage, given that the fork is facing the right way.

There are two hazards then, one is locking the front wheel instantly under braking, while the other is hidden (or even visible) damage to the fork, risking structural failure. This is likely repairable with a new fork and inspection of the frame, but happily you've passed on purchasing this time. Caveat emptor I suppose

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    Third hazard: dynamic instability of the bike due to the diminished or possibly negative trail
    – Phil Frost
    Commented Jan 14, 2021 at 19:56
  • @PhilFrost no, this bike actually has increased trail. What you're thinking of is that the fork is steeper, and normally a steep fork would be a result of a steep head angle (which would indeed reduce the trail); but in this case the head angle is still as original and only the fork doesn't follow it but instead... well, trails. That said, in my experience too large trail actually also leads to instability, but it's not the dangerous dynamic one but more of an awkward low-speed wobble.
    – leftaroundabout
    Commented Jan 15, 2021 at 21:15
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Based on the photo - the fork is utterly dead and shouldn't be ridden.

The frame may have stresses/subtle bends about 2-3" / 50-75mm aft of the headtube on the top and down tubes, and should be checked closely. Being a steel frame helps, but I'd absolutely retire the fork and heatset+bearings. The front wheel (rim/spokes/hub) needs a good check as well.

Seller is either an idiot, disingenuous, or simply too unaware to know what's wrong with their bike. I recommend you find another bike from another seller.

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Sure the hub and skewer on the front wheel is not really messed up? The only other place there would be that much flex is the forks. In which case if the bike is riding like that now, I would pass on it.

Based on the pics you added the fork looks like it is the right way in, but bent in the headset. At the very least you would need a new fork and at the worst the whole frame is trashed. I would pass on buying it if you plan to ride it.

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This should not happen with a normally setup bike. Possible mis-maintenance I'd speculate could have been at play:

  • Bent or busted fork or frame
  • Replaced fork with wrong size replacement.
  • Badly adjusted headset, allowing the steerer to move around while braking
  • Fork installed backwards (I've seen it happen)
  • Too large of tires. You said seller claimed to have used a larger size, but they could have been lying.

I used to have an old 80s racing Bianchi that had about 1/4" clearance between the tire and the downtube. Never once had the two contact, even under emergency stopping conditions.

Safe to say, don't buy it.

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    Yeah I didn't buy after that - mainly because I'd never even seen that type of clearance issue (so sketchy). Haha I did check that the fork was on the correct way. I think the fork is likely busted then / missing some pieces in the headset. Useful to know that even your low clearance never resulted in contact
    – Offbeat Upbeat
    Commented Jan 14, 2021 at 6:27
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Image Commentary
Fork and headtube No question the steerer tube and blades are not in the intended alignment. Your fork ends up deflected back toward frame. I'm not sure a headset problem could create that look without some form of structural damage. I'd be checking out the bike's head tube pretty thoroughly as I prepped for a new headset install, should the frame pass muster.
Closeup on bottom of headtube Loss of detail closer in, but the fork crown-lower headtube interface looks suspect. In addition, the 28mm tires are probably the uppermost limit wide and could therefore exceed the expected overall diameter, adding to the problem and severity of the results.
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