rpenmanparker 

All my current road bikes have 73 degree heat tube angles and 43 mm offset forks (23 mm tires). That gives a pretty standard 58 mm trail which works well for me. I am looking at a frame (only) that has a 73.5 mm head tube angle. It is out of production and information about what fork rake was originally recommended for this frame is not available. At least I am having trouble finding it. To get the same trail with this frame I would need a 40 mm offset fork. They are available but not nearly so common as 43 mm, especially at discount online sources and ebay. What would you guys recommend? Is the 40 mm offset fork the safe bet?

Just in case anyone might know the recommended fork, the frame is a Merlin Works CR in size M.

fietsbob

How much Trail do you want?

rpenmanparker 

I just know that the 58 mm I get with 73 degrees /43 mm offset/23 mm tires works well for me in general. So sure I have answered my own question. 40 mm fork it is! I dunno. I guess I was just hoping to get some discussion and maybe some info about what the factory recommended fork for this frame was. Especially since 40 mm rake forks are nearly impossible to find. (Prove me wrong...please.)

HillRider

I think a 43 mm rake fork will work fine on this frame and you will never notice any difference. Trail can vary over a fair range and the bikes still handle well. My bike was recommended to have 45 mm of rake but came with a 43 mm fork and handles just fine.

rpenmanparker 

Good to know. Thanks.

Wilfred Laurier

A half degree of head angle is a very small change. You may feel it when you first get on the bike if you have recently been riding one of your others, but the change is so small that you will forget about it within a block or two. In short, you are over thinking this. 43 or 40 will work just fine, use whichever one you have.

Andrew R Stewart 

This is why some builders will make their own forks. Andy.

rpenmanparker 

I imagine that is what I will try first. Thanks.

Al1943

I've had 43 and 40 mm offset otherwise identical forks on the same bike, 73.5 HTA, 700 X 23 tires. I could definitely feel the difference but could easily adjust to either. I elected to go with the 40 for slightly more high speed stability but I was fine with the original 43 as well.

fietsbob

And ... small radius bend towards the Tip will be more resilient , as opposed to a longer radius bend taking up more length of the blade.

Fred Smedley

Bianchi mid nineties RC frames were 73.5 & 43 MM . It works really well.

rpenmanparker 

Thanks all.

HillRider

When I first got involved with bike mechanics in the mid-'80's it seemed most road replacement forks came in both 40 and 45 mm rakes. A bit later 43 mm seemed to replace both of them. i expect that was to reduce inventory requirements and it was concluded the the small differences were inconsequential.

JohnDThompson 

These days, you need to go out of your way to find replacement forks with any curvature in the blades. Cheapness reigns supreme, and straight blade forks with offset crowns are most commonly available.

fietsbob

saves the cost of the blade bending step too . weld paint and ship.

(SJS Thorne is saying they wont sell a Disc fork that is not straight blade)

rpenmanparker 

I suspect that is right.

bradtx

Robert, I have bikes with trail in the low 50s to the upper 50s. Stability at speed is mostly the same, stability in a tight turn is better with less trail. Head tube angle effects initial turn-in more than anything else if the fork is offset to produce the same amount of trail.

Brad

HillRider

There is a bit more to it than just lower manufacturing cost. Making straight blade forks required accurate alignment from the beginning and that required modern jigs and welding/molding fixtures. Older curved blade forks could be aligned after brazing by bending the fork blades as needed. You can't do that with straight blade forks.

JohnDThompson 

With a malleable crown you can...

HillRider

Fore-and-aft, yes. Vertically, probably not.

noglider 

I just learned a lot from this thread.