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What the Fork?!?! I can't even fit a 23 tire

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What the Fork?!?! I can't even fit a 23 tire

Old 01-21-23, 11:36 AM
  #26  
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Anyone can restore a vintage bike. It takes a real man to cut one up.
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Old 01-21-23, 11:44 AM
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Here it is as I've got it set up. I will post pics of the finished fork job - after cleaning up the edge, priming and painting. It's been a rewarding challenge and now I have bonded with this bike! Off for a ride...


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Old 01-21-23, 11:52 AM
  #28  
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Thanks again for all your comments, insights and advice. Oh and Ozzy says to say hello!
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Old 01-21-23, 11:58 AM
  #29  
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It seems you may have finished but if you wanted to have a nice uniform appearance, a half round file will give you that.

Now that you have the shape laid out, the file will no longer slip and scratch. It will give a smootth, clean, uniform contour.

Filed or not, a bit of sandpaper (wet/dry type) will remove any burrs from the newly formed edges before priming and painting.
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Old 01-21-23, 12:37 PM
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Thank you Bad Lag! I am definitely not finished. I will do the final work this weekend.
I was planning to use the dremel to smooth the edge (using a different attachment )
Thanks to you, I will do exactly as you suggest and instead use a half round file.
Slipping was a big issue for me and I was trying to be careful! After I put a nice scratch in the head tube, I put down the file, wiped my tears and went for the dremel.
I've learned so much from you guys - even more than I could have asked for.
For sure, you guys would have told me to remove the fork, brace it properly, use a file and keep filing...
But somehow I had to walk that leg of the journey on my own

Last edited by Biketiger; 01-21-23 at 12:41 PM.
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Old 01-21-23, 01:13 PM
  #31  
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Nice work, I am still curious as to why the wheel did not fit originally was it meant to have a 700c wheel or something different, what do you think it came with from the factory?
Best, Ben
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Old 01-21-23, 03:01 PM
  #32  
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Originally Posted by Trakhak View Post
In the mid-'60s, I rode Pirelli Gran Premios (26 mm) and some other tire brand I can't remember. Clement had wide (maybe around 30 mm) Paris-Roubaix and Campione Del Mundo tires, too.
I didn't get into tubulars until about '73-74, my first were skinny D'Alessandro, but as soon as I saw some fat Clements I went for them. I raced in the late '70s early '80s on Del Mondos, which I couldn't afford so I got cast-offs from older or more well-heeled riders (team mates and bike shop customers) who couldn't be bothered to fix their own flats. I got good at sewing tires.

Some other racers thought it was dumb to use such fat tires in say a criterium on smooth pavement, but I also dropped some guys in corners. Plus if there was some rough pavement I'd aim for it, kind of a nasty way to get someone off my wheel but I regret nothing, I didn't put those pot holes there! What do you all think, is that "unsportsmanlike"?

Now that everyone is using fatter tires, even the pros, I feel vindicated. And the pros aren't done in their migration to fatter tires, I predict the first guy to use 38 to 42 mm tires will win P-R in a romp. Of course then the morons who run UCI will make them illegal...

But back to Del Mondos, I don't think they were quite 30 mm, I think more like 28 mm. Don't have one aired up at the moment, anyone know? Paris Roubaix was even a little narrower like 26-27 mm, strangely since the name implies a tire for pavé. I always thought P-R and CdM tires should have swapped names.

Del Mondos look so skinny to me now! I can't believe anyone ever used 21 mm tires, what were they thinking? And making a track bike that can't use anything larger? That's just idiocy, you can't even use the best 6-day tires from the C&V era like Conti Sonderklasse. (They still make a tire under that name, but the old ones were nicer, and about 24 mm IIRC). Any track crown with such unreasonable clearance deserves to have a half-round bastard applied to it. Maybe not if it's chrome plated? That could be a tough decision.

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Old 01-22-23, 12:57 PM
  #33  
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Bike looks better with the tubulars and will perform better but putting 25s on track bikes would already suggest you’re not worried about performance

But as I have a habit of saying, it’s your bike and your rules. If it gives you a better perceived experience, Then your experiment is a success

I used to like riding my track bikes On the road sometimes too. I even drilled the Fork crown on my Waterford to fit a front brake years ago . That is an even more blasphemous sin
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Old 01-22-23, 03:55 PM
  #34  
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Originally Posted by Steel Charlie View Post
Anyone can restore a vintage bike. It takes a real man to cut one up.
I feel like I read that on a car forum once.
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Old 01-22-23, 03:57 PM
  #35  
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Originally Posted by Bad Lag View Post
Filed or not, a bit of sandpaper (wet/dry type) will remove any burrs from the newly formed edges before priming and painting.
Signal boost on this. @Biketiger, you'll want to use sandpaper (perhaps backed by a rubber eraser block or something) to round all of the edges so that the paint has a good continuous surface to adhere to.
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Old 01-22-23, 08:19 PM
  #36  
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There are a lot of purists on this forum, I'm not one of them. I would have done the same thing. Looks good to me.
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Old 01-22-23, 11:48 PM
  #37  
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Originally Posted by krakhaus View Post
There are a lot of purists on this forum, I'm not one of them. I would have done the same thing. Looks good to me.
No doubt about it, he did a darned good job with that Dremel tool.
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Old 01-23-23, 07:24 AM
  #38  
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Originally Posted by Steel Charlie View Post
Anyone can restore a vintage bike. It takes a real man to cut one up.
Somewhere, an individual named Drew might be reading this and smiling.

Not my style - I'd have probably tried to find another fork for routine riding and kept the original in case I sold the frame later. But it's not my bike, either.

If it worked and didn't compromise the fork, I'm OK with it.

Last edited by Hondo6; 01-23-23 at 07:31 AM.
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Old 01-23-23, 10:56 AM
  #39  
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With that "big" tire it looks to me that you are near to making contact with the downtube. Hit a bump and lock up the front wheel? Doesn't sound appetizing to me.
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Old 01-23-23, 01:03 PM
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Originally Posted by daka View Post
With that "big" tire it looks to me that you are near to making contact with the downtube. Hit a bump and lock up the front wheel? Doesn't sound appetizing to me.
Luckily, bumps make the tire move away from the DT, not towards it. That's for bumps that hit the bottom of the wheel, more or less straight down from the hub, which is most bumps, but the bigger an obstacle is, the further forward it hits on the wheel. An obstacle over a certain size reverses the direction of the bending force on the fork, flexing it back instead of foward. But if you hit something that big, you already got bigger problems.

If he were to add a rim brake to that fork, then that's a different story. Braking forces do push the tire closer to the DT.

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Old 01-23-23, 02:16 PM
  #41  
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I've used stiff beltsander paper running along the top of the rotating (back and forth) tire to machine some tire clearance, benefit being that the clearance ends up being very uniform.

It's kind of like when I use the same sort of "sandpaper" to machine brake pads in-situ, leveling the surfaces to meet the rim's brake track with the brake lightly applied:

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Old 01-23-23, 03:21 PM
  #42  
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Originally Posted by krakhaus View Post
There are a lot of purists on this forum, I'm not one of them. I would have done the same thing. Looks good to me.
I have found that it is easier to a purist with another person's bike rather than my own.
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Old 01-23-23, 04:35 PM
  #43  
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Another thought: when you're sending metal dust all over the place from your fork crown, make sure you mask off the lower headset bearing, or plan to take out the fork and service both bearings well before riding.
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Old 01-23-23, 05:29 PM
  #44  
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Originally Posted by bulgie View Post

.....................But back to Del Mondos, I don't think they were quite 30 mm, I think more like 28 mm. Don't have one aired up at the moment, anyone know? .........................
These are 28mm

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Old 01-23-23, 08:31 PM
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Originally Posted by bulgie View Post
Luckily, bumps make the tire move away from the DT, not towards it. That's for bumps that hit the bottom of the wheel, more or less straight down from the hub, which is most bumps, but the bigger an obstacle is, the further forward it hits on the wheel. An obstacle over a certain size reverses the direction of the bending force on the fork, flexing it back instead of foward. But if you hit something that big, you already got bigger problems.

If he were to add a rim brake to that fork, then that's a different story. Braking forces do push the tire closer to the DT.

Mark B
If there was no momentum, that would be true. But, if we are moving forward and the obstacle slows the bike at all, inertia will push the bike and rider ahead relative to the contact point, thereby deflecting the fork back.
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Old 01-24-23, 02:34 AM
  #46  
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Originally Posted by daka View Post
If there was no momentum, that would be true. But, if we are moving forward and the obstacle slows the bike at all, inertia will push the bike and rider ahead relative to the contact point, thereby deflecting the fork back.
Only true for large bumps.

For evidence, I offer the track bikes I've seen with minuscule space between the tire and the downtube. They didn't develop paint scratches on the underside of the DT from the tire hitting, so if any rearward flexing ever happened, it was negligible. Also, when I've seen forks bent from landing big jumps (landing both wheels at the same time), they bent forward, not back. Doesn't matter how fast the rider was going, only the angle of the force vector.

Note this sad case, where the front end of the guy's bike tore off,

...it was clearly torn off in the forward direction not back, or else the wheel wouldn't have been out in front of him for him to face-plant into.

If you have evidence that suggests a rearward bending (flexing) of forks is possible or commonplace, outside of hitting large obstacles, please share it. My experience is the opposite.

Mark B
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Old 01-24-23, 08:19 AM
  #47  
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Originally Posted by daka View Post
With that "big" tire it looks to me that you are near to making contact with the downtube. Hit a bump and lock up the front wheel? Doesn't sound appetizing to me.
Might be the angle. One of the pictures makes the clearance look a lot tighter than another of them.
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Old 01-24-23, 08:54 AM
  #48  
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Man I can relate. I bought a Ferrari and I can’t even fit the groceries in the back.
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Old 01-24-23, 11:58 AM
  #49  
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Originally Posted by bulgie View Post
Only true for large bumps.

For evidence, I offer the track bikes I've seen with minuscule space between the tire and the downtube. They didn't develop paint scratches on the underside of the DT from the tire hitting, so if any rearward flexing ever happened, it was negligible. Also, when I've seen forks bent from landing big jumps (landing both wheels at the same time), they bent forward, not back. Doesn't matter how fast the rider was going, only the angle of the force vector.

Note this sad case, where the front end of the guy's bike tore off,

...it was clearly torn off in the forward direction not back, or else the wheel wouldn't have been out in front of him for him to face-plant into.

If you have evidence that suggests a rearward bending (flexing) of forks is possible or commonplace, outside of hitting large obstacles, please share it. My experience is the opposite.

Mark B
Your photo shows a logical extreme and I don't disagree with it. And, similarly, don't disagree with your example of landing from a jump bending the fork forward. Like you say, it's the force vector relative to the head tube angle. But consider the opposite logical extreme - guy bounces up over a curb at speed, which way is the fork going to bend? Guy hits a wall (a bump the bike can't roll over), which way is the fork going to bend? In the smaller scale of everyday riding over bumps both forces act simultaneously - The resistance to forward progress pushes the fork back, the elevation change vs. gravity pushes it forward thanks to the head tube angle. And the effect is somewhat self-cancelling. But don't ever think that speed doesn't matter, while I used the term "inertia" since it is easier to visualize, that is actually not the correct term - forward motion is kinetic energy which is 1/2 MV squared. So the energy to be absorbed is more about the velocity than anything else. A 100 lb rider at 40 mph will have far more kinetic energy to dissipate than a 200 lb rider at 20 mph if they were to hit a curb, a car or a pothole. The effects you have described for forward bending are bike vs. gravity and don't change with speed. The forward velocity component (resistance when encountering a bump) increases exponentially with speed. Expressing the reaction force to hitting a bump as a vector will point straight up (bending the fork forward as you've described) at 0 mph and it will rotate towards the bottom bracket as speed increases. At the point where the vector angle relative to horizontal is less than the head tube angle, the fork will start to bend back rather than forward. Ain't physics fun?!

Last edited by daka; 01-24-23 at 12:02 PM.
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Old 01-24-23, 03:02 PM
  #50  
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Originally Posted by daka View Post
Your photo shows a logical extreme and I don't disagree with it. And, similarly, don't disagree with your example of landing from a jump bending the fork forward. Like you say, it's the force vector relative to the head tube angle. But consider the opposite logical extreme - guy bounces up over a curb at speed, which way is the fork going to bend? Guy hits a wall (a bump the bike can't roll over), which way is the fork going to bend? In the smaller scale of everyday riding over bumps both forces act simultaneously - The resistance to forward progress pushes the fork back, the elevation change vs. gravity pushes it forward thanks to the head tube angle. And the effect is somewhat self-cancelling. But don't ever think that speed doesn't matter, while I used the term "inertia" since it is easier to visualize, that is actually not the correct term - forward motion is kinetic energy which is 1/2 MV squared. So the energy to be absorbed is more about the velocity than anything else. A 100 lb rider at 40 mph will have far more kinetic energy to dissipate than a 200 lb rider at 20 mph if they were to hit a curb, a car or a pothole. The effects you have described for forward bending are bike vs. gravity and don't change with speed. The forward velocity component (resistance when encountering a bump) increases exponentially with speed. Expressing the reaction force to hitting a bump as a vector will point straight up (bending the fork forward as you've described) at 0 mph and it will rotate towards the bottom bracket as speed increases. At the point where the vector angle relative to horizontal is less than the head tube angle, the fork will start to bend back rather than forward. Ain't physics fun?!
I don't think KE is useful in this scenario, and it doesn't change the direction of the force vector.

Remember when you're going say 100 mph, the tire where it touches the road is going very close to zero, would be zero in fact if the tire were a perfect circle hitting a perfect plane, but it's very close to zero within the contact patch area unless you're skidding.

Now introduce a bump, of a size that you could ride over at speed without denting your rim or doing an endo. That's the range we're interested in here, right? To answer the original question, which was "is a track bike with minimal tire/DT clearance safe to ride on the road". If we're going to talk about hitting curbs at speed, or a wall, then what bike is safe? Outside of some monster long-travel DH machine, if you hit a curb without unweighting or bunny-hopping ('blindfolded'), you're probably not riding anymore, you're flying off the bike.


So, with this smallish bump, a size you can ride over on a road bike, the tire is hitting it pretty low, in front of the normal contact patch, but the tire is still moving fairly slowly there, and mostly in a downward path as it nears the ground (where it will hit zero speed).

The obstacle (rock, pot-hole, etc) at first is just moving tire tread and casing, but the casing forces soon start pushing on the rim, radially toward the hub via the spokes. Considering only forces in the plane of the bike (ignoring sideways forces seems safe here), wheels can't really transmit much force in any other direction than radially, because hub bearings are plenty slippery. (Remember, no brakes, just the tire contact patch and the dropouts as places where force is applied to the wheel.) So the force on the fork, appled at the dropouts, has a vector that points from the point of contact with the obstacle, aimed exactly at the hub axle. This vector will never exceed the threshold where the bending moment on the fork flips from forward to rearward, for any "survivable" bump size. Even a 2x4 (piece of lumber that is) will dent the rims on a skinny-tire road-race bike, ask me how I know! So if we restrict the track bike's bump-hitting question to only the bumps a road bike could survive unscathed, then even a 2x4 (really about 1-1/2" tall) is too big. And that's still too small to bend the fork backward.

We don't need to theorize though, we can do the experiment. Ride a track bike with very tight clearance there, for some reasonable amount of testing (a year? A thousand miles of typical pavement?) Oh wait, that experiment has already been done, multiple times. Did any of those people ever get any paint rubbed off their downtube? Not that I've heard of.

Anyone else here ever heard of a track bike ridden on the road, where the tire hits the DT in normal riding (not crashing)? Remember, this is for track bikes with no brakes. Any front brake can easily flex the fork back enough to hit the DT on one of these tight-clearance track bikes, unless the frame and fork are very stiff. Note that round blades are less stiff fore-and-aft than oval blades of the same guage and pre-ovalization diameter, they're optimized for side-to-side stiffness since they aren't made for brakes. So be careful adding a brake to a track bike, plan on more rearward flex under braking.

Here's a frame where applying the front brake caused a cascading failure that made the tire slam into the DT so hard it bent the DT where the tire hit!


The rider reports that he may have hit a small bump while braking, but definitely not a pot hole. The wheel is fine, rim not dented. He heard a loud pop, which was probably the brake lever being snapped shut, because the cable path to the brake got longer as the steerer bent back, tugging on the cable. So more bending caused more braking, which caused more bending which caused more braking, all within milliseconds. The root cause was use of a single-bike 1" steerer on a tandem, and they apparently didn't have the right length steerer so they shortened it from the bottom, cutting the butt off. A steerer not even adequate for a decently-loaded single bike, let alone a tandem. I believe there were lawyers involved but I didn't get all the later details.

Though the decal says Hetchins, this was made by Bob Jackson. Apologies to BJ fans, but this is just another in a long line of reasons I would never buy one. A couple other framebuilders have shared the same opinion with me in private. It might have been unseemly to say this in public while they were still in business (trash-talking the competition), but now that they're dead and gone the cat's out of the bag. Yes they also made some perfectly fine frames, you just have to watch out for the ones with hidden flaws, and I don't know what percentage that is. Uncomfortably high, to my taste. An exception would be any frame made by Kevin Sayles back when he worked for JRJ, his work is beyond reproach. That was long ago though, a few years in the '70s I think? But I don't think there's any way to know which BJs he made. You could ask him. He recently retired from a long posting at Woodrup and last I heard he was building a frame shop at his home, to make Sayles frames. His work is stellar so seek him out.

But there I go again getting all off on a tangent, sorry!

Mark B
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