Turning a shallow headtube & forward-sloped top tube flat

[cribbit]

I bought a track frame that's designed to have a 24" front wheel and be very aggressively sloped forward. A pursuit frame.

I'm thinking of being dumb and sticking a 700c fork in it. I haven't even begun to mess around with this but it looks like it would put the top tube approximately flat. Still have to figure out how much it will screw up the other angles.

What I do know is that the head tube is a good few degrees slacker than a normal road frame. I'm struggling to figure out if this means I want more or less rake in the fork. Will this cause anything dangerous?

[jemdet]

You are rotating the entire bicycle backwards with the rear axle at the center of the rotation. Your HT / ST will end up slacker. Your BB drop relative to your rear axle will decrease. Your BB drop relative to your front axle will increase.

Your front end will also be higher, of course. Saddle height / setback might have to change to make yourself more comfortable.

This is a delightfully terrible experiment and one I support 100%. A 70 degree HT angle needs a rake of ~60mm to get 57mm of trail.

[spinarelli]

I would not do it. I assume it is steel and lugged?
Would rotating the angle put unnecessary stress on the head tube and the front lugs?
It would also look really clowny. Your seatpost would rotate backwards too much, maybe too much and the seat rails would not allow you to have a horizontal seat.
I think you should mock it up but I would not ride it.

I think you should mock it up but I would not ride it. Definitely post an update photo.

[FlashUNC]

Oh this is gonna need pictures. Before and after the hospital stay.

[Brian Smith]

I bought a track frame that's designed to have a 24" front wheel and be very aggressively sloped forward. A pursuit frame.

I'm thinking of being dumb and sticking a 700c fork in it. I haven't even begun to mess around with this but it looks like it would put the top tube approximately flat. Still have to figure out how much it will screw up the other angles.

What I do know is that the head tube is a good few degrees slacker than a normal road frame. I'm struggling to figure out if this means I want more or less rake in the fork. Will this cause anything dangerous?

5mm is a significant tuning parameter change in bottom bracket height. You're talking about moving it an inch or more. If you manage to finagle steering geometry and rider position you can still tolerate after the fork and wheel change, you'll still have that to suffer. That said, the danger involved herein is probably just that you'll spend money and effort to no avail.

[cribbit]

I would not do it. I assume it is steel and lugged?
Would rotating the angle put unnecessary stress on the head tube and the front lugs?
It would also look really clowny. Your seatpost would rotate backwards too much, maybe too much and the seat rails would not allow you to have a horizontal seat.
I think you should mock it up but I would not ride it.

I think you should mock it up but I would not ride it. Definitely post an update photo.

It is titanium.

https://i.imgur.com/DsDYEBq.jpg - with 650c fork

https://i.imgur.com/LVeMTDe.jpg - frame alone

[PJN]

https://bikegeo.muha.cc

Eyeball some measurements with the original fork, change the ac for the 700c fork and see what comes out...

[arimajol]

Just try it. What's the worst that can happen, it doesn't ride well?

[dave thompson]

That’s going to be a squirrelly ride!

[Mr. Squirrel]

That’s going to be a squirrelly ride!

https://media.tenor.com/images/783540b0ea6a19d41521ab7a5fbc663f/tenor.gif

that is nuts!

mr. squirrel

[dave thompson]

https://media.tenor.com/images/783540b0ea6a19d41521ab7a5fbc663f/tenor.gif

that is nuts!

mr. squirrel

Eggsactly

[jemdet]

It is titanium.

https://i.imgur.com/DsDYEBq.jpg - with 650c fork

https://i.imgur.com/LVeMTDe.jpg - frame alone

Looks can be deceiving, but your quill appears to be slightly below the horizon with the 650c fork. If that's true, you're somewhere over 73 degrees to begin with. You have a decent amount of headtube angle to give up, but remember that small variations in ATC can have pretty noticeable effects on HTA.

... that being said, you appear to be pretty much out of BB drop. I think it would ride like a pig. Might even out-awful my old Peugeot.

[Peter P.]

Your seat angle is going to slacken as well, possibly making it difficult to achieve a normal fore/aft position.

Throw a cheap eBay fork in it and see what happens. It won't be dangerous, but I think you're going to have a lot of wheel flop, and there won't be a carbon fork on the market available with sufficient rake to bring things back into the range of normal. If you choose to continue with your experiment, I think you'll need a custom steel fork at that point.

[jtakeda]

Don’t do it.

I tried this. Extremely squirrelly and I sold the frame and original fork after literally 20 minutes of riding it.

Mine was ti (not track)

[false_Aest]

If there's ever a question answer, "YES"


DO IT.


Then you'll know.


Knowledge is power.

[rustychisel]

Not worth it, even to 'try for cheap'. Those lopro frames are built to be exactly that, to mess with the geometry and steering in particular is not going to work. Been there etc

[cadence90]

.... ..
.
.

[oldpotatoe]

If there's ever a question answer, "YES"


DO IT.


Then you'll know.


Knowledge is power.

Agree..slap a 700c fork in there, a front wheel and take it for a spin..Nice project..the 'nay sayers' here may be surprised...:)

[bicycletricycle]

I am a naysayer and I say NO

:)

[nicrump]

just do it. though you'll never be as hip as this guy

http://geekologie.com/2013/04/scary-first-person-pov-of-riding-a-15-fo.php

ps, watch that vimeo full screen. i actually felt it in my gut...

[Jad]

^ Full screen was rough:eek:, especially when he was coming up to intersections. That's out of some bad dream for me, but awesome.

[cadence90]

.... ..
.
.

[cribbit]

just do it. though you'll never be as hip as this guy

http://geekologie.com/2013/04/scary-first-person-pov-of-riding-a-15-fo.php

ps, watch that vimeo full screen. i actually felt it in my gut...

I've actually ridden next to these guys! Ciclavia is a ton of fun.

Maybe bb drop isn't so important...

[guyintense]

I have a Yamaguchi funny bike with a 24 inch tubular front wheel and because I can't find a tire I was considering swapping forks but was going to use a 650.

[cribbit]

I have a Yamaguchi funny bike with a 24 inch tubular front wheel and because I can't find a tire I was considering swapping forks but was going to use a 650.

Need photos, sounds like an interesting bike. Let's do it! Do you have a fork yet?

This one originally had a 24", previous owner put a 650, I just bought a fork from another user here to try 700c.