Revracer

I just finished up a project to modify a Schwinn World Voyageur and installed a new fork which has a shorter axle to crown distance. I can't recall the exact difference, bit it is maybe 5-10mm. The bike rides OK, but I noticed the top tube slants down to the head tube just slightly. Most all modern bikes have the reverse slope down to the seat tube which causes me to see the Voyageur as wrong. I have seen other vintage with the down slope to the head tube, but they have tended to be smaller size frames.

First, are most classics steel frames designed to have a level top tube? Do any intentionally slope down to the head tube?

Second, has anyone placed spacers between the fork and the crown race to level the tube and if so what did you use?

Velognome 

Level top tubes are the norm but sloping towards the seat tube has been popular from time to time; in the 1890's-20's and then again in the 70's with examples like the Jack taylor Rough Stuff


Slants to the Headtube are less common outside the realm of TT bikes



I'd find the correct fork and make a proper repair.

Photo's from vint.uk and colletvelo.

100bikes

A shorter blade fork - is it for a different size wheel?

In using a shorter blade length fork, you have altered the design
geometry and ride characteristics of your bicycle.

The geometry of the new fork can be compared the that of the old
( rake, etc) and the differences will be apparent. I would guess the
wheelbase is shorter and the bike is twitchy - er.
(Unless the new fork has a very long rake).

As to spacing the fork back up to level the top tube.

First, if you do so, the length of the steerer tube fork above the top cone
will be equally shorter by the amount of "spacing".

This would leave fewer threads (approx. 10mm from your description) ,
and you may not be able to properly space and tighten the top lock nut.

Second - Bad juju in my opinion. I agree that the fork replacement should
mimic the original geometry very closely, unless there is a planned design
reason to make a change.

T-Mar

Placing spacers under the crown race is feasible but not straight forward. The steering tube usually has a short flange that accepts the crown race and provides an inteference fit. Installing a spacer would result in a floating crown race. You'd have to create a shim to install between the steerer tube and crown race. It would be a pretty thick shim. Ideally it should be of steel. Aluminum and brass are too soft and will work properly only for a short period, untill things start to float again. At least that has been my experience with shimming headsets.

Then, there is the issue of having lost the equivalent protrusion for the locknut engagement, as already noted.

Revracer

Sorry, should have included more detail. I had measured the rake and trail and knew that the bike would change the geometry a bit, with a shorter rake (5mm) it actually increased the trail a bit. I took my chances with new carbon fork and I really like the handling in descents as it tracks well and I can turn it out of a groove if I wish at speed. So performance wise I really like the current setup.

The fork/stem is threadless so I can just remove spacers from the top and I would have no thread/nut issues.

This question is mostly an aesthetic one. The Columbus Minimal fork I put on had about .75" of interference and the Cane Creek race was very thin. I thought about dropping a 10mm 1" aluminum spacer under the race, but I was no sure if the result would be sturdy. That spacer would not rotate so it would not grind. A concern is that the force below the head tube is greater because it carries weight from my seat (transmitted through the rest of the bike frame) where a spacer above the head tube only carries the weight from your hands. Would there be a steel spacer or something slightly thicker than the usual stem spacers that is used for this purpose?

cyclotoine

I would say that if you like the way it rides now, try not to let it both you and know that that slope is why you like the ride so much. There is nothing wrong with steepening up the angles a bit and if you put it back to the original HT and ST angles you may not even like the ride as much.

There is no such spacer designed for this purpose. You would have to make something on your own. You could try the aluminum one and see how it holes up over time, but I think it would eventually start to move around as T-mar suggests.

20grit

Sounds like a 700c fork in a 27" frame to me. Maybe I'm missing something.

Revracer

Thanks all and it is a 700c fork in a 27" frame, converted to 700c all around. I have found steel and thicker aluminum tubing with the right ID so if I let it bother me I will go the home fab route.