Looking for suggestions and advice...

I'm currently building up a bike on a used steel frame I acquired. The frame requires a 1 1/8" straight steer tube and a 45mm rake. My hope is to convert this bike to a front hydraulic disc brake. There are several forks on the market for Cross bike frames, but they have a longer axel to crown length than this road bike's original fork had. (Forks with straight steerers and disc brake mounts that Ive seen have about 395mm axel to crown length... considerably longer than the stock fork which is approx 370mm axel to crown)

How much would the geometry of a frame (and likewise the way it handled)be altered if I were to install a fork that had approx 2.5cm longer axel to crown length? I suspect it would be considerable.

Secondly, since I don't really want to install a longer fork, does anyone know of a fork on the market that fits all of these requirements but that is not as long as the cross bike forks?

Sorry for the long and possibly confusing question. Hoping to hear some good news!

Stephen

The resultant head tube angle would destroy your handling. Even a few mm change can be a problem. 25 is absurd.

Get in touch with a fork maker (Ritchey e.g. ) to learn what they may have for you that better meets your needs.

So, let's do a bit of basic trig. If you sketch a frame, and draw a line from the rear axle to the lower head cup, you'd have an angle from the horizontal with a sine = 370/1000* or .370. Solve it for the angle and you get 22°. Raise the head by 25mm and the new sine = .395and the angle = slightly less than 23°. Since the frame is unchanged, you're talking about the head tube angle changing by a bit less than 1°.

This isn't insignificant, but it's not earthshaking either, and depending on how the bike handled before, may not be problematic a all.

I suspect you're finding the disc capable forks are taller is they are more likely to be made for CX vs. road use, and are taller to allow for greater tire clearance. With disc appearing on road bikes, I suspect you'll see disc ready road bike forks with tighter dimensions showing up soon enough, and you should fine one if you search carefully.


*assumes wheelbase of 40"/1000mm for easy math

there are disc forks on the market for the road bike frames... the problem being that all of them that I can find have a tapered steer tube that my frame won't accommodate. I have found one solution that is a Chinese carbon fork, but I prefer a known manufacture/branded fork as I don't particularly want to find out the limits of the Chinese model while I'm descending at 45mph.

I suspect the solution to my problem will be to settle for rim brakes, but I will keep searching and send some inquires to a few manufactures.

I agree with what was said previously regarding contacting a custom frame maker, they should be able to whip up an appropriate fork. May not be the cheapest, but it'll work!

The problem with the custom builder approach is that so many don't build forks anymore. One that does, and does good work at not outrageous prices is Chris Igleheart. If you want to explore a built to spec fork he might be the place to start. If you do call Chris, please give him my regards.

If I'm not mistaken, a WoundUp Road X Disc fork have options for 370 and 380mm crown height

I will look into Chris Igleheart and the Woundup X options. Thanks!

Pulled the trigger on a chinese fork that fits the requirements for my build. $88 included the shipping and it will give me a first hand inspection. I will give it a go because I like the style and the cost. Should the fork not work out, I'll either go to one of the custom builders, woundup composites or I'll switch to rim brake in front (I'll be using a rim brake in back, so if my test fails, it won't be a noticeable detriment)

I suspect you will be very happy with the Chinese fork. Keep us posted on how it goes please.

any link for the chinese carbon fork? and yes please do a future review on that fork

here is the exact auction. The seller states there is only 1 left of the original 10. I have seen other auctions for the same (I assume) fork, but this seller is the only one that specified the fork offset (45mm) and the axle to crown length (370mm). If you search eBay or other known sites that sell these Chinese forks, search for "carbon disc road fork" and a handful of options will show up among the results. When I receive the fork sometime late in July or early August, I will post pictures of the unboxing, and some hi-res detailed pics of the fork I receive. Stay tuned.

New 3K Carbon Fork Rigid Straight Disc Brake 700c Road Bike Fixed Gear 1 1 8" | eBay