Fork Rake Question

[endosch2]

My wife has a 1993 48cm Raleigh Competition with a quill stem 1 inch steel fork. Looking at other frames in small sizes, it looks like fork rakes get longer as the frames get smaller, so I assume the Raleigh has a longer rake.

I do not know the fork rake on the frame, but I saw a nice carbon 1 inch fork with 43mm in rake for sale, and it would be a really nice upgrade to this bike.

How would this effect the handling of the bike? Is there any way to easily measure the rake on the old fork for comparison? Would this be a bad move?

[mister]

you can use three blocks of wood, all the same size and unwarped to measure rake somewhat accurately.
put on flat surface. two blocks of wood under steer tube. this should make the steer tube parallel to the flat surface you're measuring from.
a block of wood slid under fork blades jsut enough to square up the blades.
find the measurement from the surface to the center of steer tube.
find measuremnt from the surface to the center of the fork tips.
subtract the two numbers.

[dogdriver]

I'm no expert, but here's Moots' suggested fork rakes. That said, steeper (less rake) forks will give more nimble, less stable tracking, where a more relaxed angle (to a degree) will do the opposite. I recently went from a 40mm rake to a 45mm rake on my 56cm Vamoots and noticed a significant improvement in front end stability and tracking. That said, I am an old fart and like a quiet, predictable ride over a lightning quick Crit setup.

[tuscanyswe]

I'm no expert, but here's Moots' suggested fork rakes. That said, steeper (less rake) forks will give more nimble, less stable tracking, where a more relaxed angle (to a degree) will do the opposite. I recently went from a 40mm rake to a 45mm rake on my 56cm Vamoots and noticed a significant improvement in front end stability and tracking. That said, I am an old fart and like a quiet, predictable ride over a lightning quick Crit setup.

A steep headtube angle as on the moots (mine has 74) requires less rake on the fork to produce the same trail as a slacker headtube angle.

When you increased the rake (=less trail) shouldnt the opposite take place no? Meaning you would get faster steering since the lower trail despite the little increase in wheelbase?

Speculating here :)

[Mike748]

I'm no expert, but here's Moots' suggested fork rakes. That said, steeper (less rake) forks will give more nimble, less stable tracking, where a more relaxed angle (to a degree) will do the opposite. I recently went from a 40mm rake to a 45mm rake on my 56cm Vamoots and noticed a significant improvement in front end stability and tracking. That said, I am an old fart and like a quiet, predictable ride over a lightning quick Crit setup.

I'm not an expert either but you've got it backwards. Steeper fork (lower rake number) increases trail, slows steering, given a constant HTA. The Moots chart is silly. Fork rake should be matched to HTA, not frame size.

I assume Moots uses a different HTA for small vs lg frames and hence the chart only applies to that specific model.

To answer the OP's question... small frames tend to have slack head tube angles to accomodate the wheels (for 700c). A slack HTA (say 71 deg) would need a more relaxed rake (say 50mm) to get a reasonable trail (say 6.4cm). I suggest you use the bikeforest.com bikecad with a little trial and error to figure out what you have now. You can get there with wheelbase, front center, and tube lengths.

The 43mm fork will probably slow the steering too much and reduce the tire to downtube clearance too much.

[happycampyer]

Another dimension that you need to consider is the axle-to-crown height, or span. The fork on your wife's bike is probably 365mm, whereas the carbon fork likely has a span of 370mm or 372mm. If you put a taller fork on the bike, it will slacken the HT (and ST, for that matter), for which you would need more rake/offset to get to the original (or at least reasonable) trail figure.

Personally, if the current fork feels solid, I wouldn't switch it.

To Mike748, you are right that the Moots chart is specific to the model, which have different HTAs depending on the size.

[Smiley]

My wife has a 1993 48cm Raleigh Competition with a quill stem 1 inch steel fork. Looking at other frames in small sizes, it looks like fork rakes get longer as the frames get smaller, so I assume the Raleigh has a longer rake.

I do not know the fork rake on the frame, but I saw a nice carbon 1 inch fork with 43mm in rake for sale, and it would be a really nice upgrade to this bike.

How would this effect the handling of the bike? Is there any way to easily measure the rake on the old fork for comparison? Would this be a bad move?

It depends what you would call an upgrade? Your going to be limited to 1 inch steerer tube forks for one, the next issus is you probably have a longer rake to avoid TCO. A taller carbon fork span will slacken the HTA making for a longer trail which will be nice but your wifes bike may not get more comfortable in a small size with a carbon fork, steel forks ride really plush and absorb more road shock then what we assume. Smiley