I've got a steel TT bike from back when funny bike configuration with 700c rear and smaller fronts were common. Given the front wheel is 650c, I'm thinking of converting it to a standard 700c fork. Anyone tried this or know if the slight elevation in the front end will be as minimal as I suspect it would be? I haven't quite decided if I would use it as a road bike or a legal TT bike. (kinda hard before riding it...) I'd appreciate some wisdom before going ahead with the HS/fork replacement.
I've got a steel TT bike from back when funny bike configuration with 700c rear and smaller fronts were common. Given the front wheel is 650c, I'm thinking of converting it to a standard 700c fork. Anyone tried this or know if the slight elevation in the front end will be as minimal as I suspect it would be? I haven't quite decided if I would use it as a road bike or a legal TT bike. (kinda hard before riding it...) I'd appreciate some wisdom before going ahead with the HS/fork replacement.
Ideally, you could do a drawing. But if a suitable fork is handy, just try it. You'll most likely find your new lower head angle ( with a taller fork) wants an excessively long rake to keep trial constant (~~50mm). The long rakes are generally found on touring forks with even taller clearance so it may be hard to keep up with the head angle change looking for more trail. The result may handle poorly with skimpy trail. Or not.
If you can experiment with stuff you already own this may be interesting. I would not pay for any standard fork for such a project.
-- Andrew Muzi www.yellowjersey.org Open every day since 1 April, 1971
I've got a steel TT bike from back when funny bike configuration with 700c rear and smaller fronts were common. Given the front wheel is 650c, I'm thinking of converting it to a standard 700c fork. Anyone tried this or know if the slight elevation in the front end will be as minimal as I suspect it would be? I haven't quite decided if I would use it as a road bike or a legal TT bike. (kinda hard before riding it...) I'd appreciate some wisdom before going ahead with the HS/fork replacement.
Josh
I've gone the other way (700C to 650C fork and tire). IIRC, I calculated the head angle change as 4 degrees. It sure felt about that -- in my case it went from slightly slow to very quick handling, though you're going the other way so it "might" be tolerable. Andy's right tough: look for lots of rake and don't pay anything unless you've tried it first.
On the other hand, I've used a bumper jack to bend steel frames to change head angle too...
I've got a steel TT bike from back when funny bike configuration with 700c rear and smaller fronts were common. Given the front wheel is 650c, I'm thinking of converting it to a standard 700c fork. Anyone tried this or know if the slight elevation in the front end will be as minimal as I suspect it would be? I haven't quite decided if I would use it as a road bike or a legal TT bike. (kinda hard before riding it...) I'd appreciate some wisdom before going ahead with the HS/fork replacement.
Quoted message said:
I've gone the other way (700C to 650C fork and tire). IIRC, I calculated the head angle change as 4 degrees. It sure felt about that -- in my case it went from slightly slow to very quick handling, though you're going the other way so it "might" be tolerable. Andy's right tough: look for lots of rake and don't pay anything unless you've tried it first.
On the other hand, I've used a bumper jack to bend steel frames to change head angle too...
I assume you were _restoring_ the original head angle after a crash and not 'upgrading' an otherwise sound frame ???
-- Andrew Muzi www.yellowjersey.org Open every day since 1 April, 1971
I've got a steel TT bike from back when funny bike configuration with 700c rear and smaller fronts were common. Given the front wheel is 650c, I'm thinking of converting it to a standard 700c fork. Anyone tried this or know if the slight elevation in the front end will be as minimal as I suspect it would be? I haven't quite decided if I would use it as a road bike or a legal TT bike. (kinda hard before riding it...) I'd appreciate some wisdom before going ahead with the HS/fork replacement.
Ideally, you could do a drawing. But if a suitable fork is handy, just try it. You'll most likely find your new lower head angle ( with a taller fork) wants an excessively long rake to keep trial constant (~~50mm). The long rakes are generally found on touring forks with even taller clearance so it may be hard to keep up with the head angle change looking for more trail. The result may handle poorly with skimpy trail. Or not.
If you can experiment with stuff you already own this may be interesting. I would not pay for any standard fork for such a project.
-- Andrew Muziwww.yellowjersey.org Open every day since 1 April, 1971
Yes, I can experiment with parts I already have. My plan was to put a Kinesis aero (aluminum) fork on it but the rake does not look very long, at least by sight. The handling was indeed my main concern as the only thing scarier than riding a TT setup with insufficient trail would be riding no hands on a TT bike (which I foolishly did on my first TT bike thinking it would be similar to a road bike)
Thus in order to increase or maintain trail, a fork of the same or lower rake/offset would be required. No?
Theoretically, I can modify the rake of a steel fork with the Park fork-bending tool that I have, but don't want to be bending forks if I don't have to.
I've got a steel TT bike from back when funny bike configuration with 700c rear and smaller fronts were common. Given the front wheel is 650c, I'm thinking of converting it to a standard 700c fork. Anyone tried this or know if the slight elevation in the front end will be as minimal as I suspect it would be? I haven't quite decided if I would use it as a road bike or a legal TT bike. (kinda hard before riding it...) I'd appreciate some wisdom before going ahead with the HS/fork replacement.
Quoted message said:
A Muzi said:
Ideally, you could do a drawing. But if a suitable fork is handy, just try it. You'll most likely find your new lower head angle ( with a taller fork) wants an excessively long rake to keep trial constant (~~50mm). The long rakes are generally found on touring forks with even taller clearance so it may be hard to keep up with the head angle change looking for more trail. The result may handle poorly with skimpy trail. Or not. If you can experiment with stuff you already own this may be interesting. I would not pay for any standard fork for such a project.
Quoted message said:
Yes, I can experiment with parts I already have. My plan was to put a Kinesis aero (aluminum) fork on it but the rake does not look very long, at least by sight. The handling was indeed my main concern as the only thing scarier than riding a TT setup with insufficient trail would be riding no hands on a TT bike (which I foolishly did on my first TT bike thinking it would be similar to a road bike) I am confused by Andy's response as I thought that elevating the front would increase the trail by pushing forward point B in the diagram : http://www.prodigalchild.net/Bicycle6.htm#Shimmy Thus in order to increase or maintain trail, a fork of the same or lower rake/offset would be required. No? Theoretically, I can modify the rake of a steel fork with the Park fork-bending tool that I have, but don't want to be bending forks if I don't have to.
That drawing is a great link for this project of yours. When you raise the front (650C=>700C), the head angle goes lower (e.g., 74 deg=>70deg). Point B in your drawing moves forward. Adding rake brings it back, hopefully to about 50mm.
Generally steeper angles need less rake, lower angles , more rake. In your specific case, since a typical road fork rake of 40~45mm will be about the same rake as your typical 650C tri fork, your new head angle will add way too much trail. A more ample rake will reduce that hopefully back to the same 50mm value with which you began. Sketch it and see! [p.s. don't bend that aluminum fork!] Before making a mandrel to shape steel blades, see what free long-rake forks are available to you. Curving the blades shortens the axle-to-brake bolt length. -- Andrew Muzi www.yellowjersey.org Open every day since 1 April, 1971
