Fork rake 43mm, 45mm, 50mm
 

I realize that a larger fork rake does several things:

For the same HTA decreases trail make steering faster.

Increases wheel base making toe overlap less likely.

I ride a smaller size 52cm frame but never noticed any toe overlap problems.
One bike has a 45mm carbon, the other has 50mm steel fork.

I am looking at ordering a new steel frame and will be using a carbon fork.
The question is does a 50mm fork have more compliance and comfort than a 45mm fork. I could not find this info anywhere.

Depends on the fork, and the rider.

The better answer is "no"; assuming everything else is equal a 5mm offset change in a carbon fork will not affect either comfort or compliance.

Of course everything else is never equal so I am sure there are some 45mm forks that are more or less comfortable than 50mm forks. Flip a coin to determine which one is which when you are looking to buy.

Ive seen builders use the same forks across frame sizes, however use oneswith different rakes depending on size. So I imagine the HT angle might change too for those smaller bikes to allow for better handling to compensate for shorter tubes

Also I dont imagine 5mm of rake would give you much more or less compliance. But def would change the way the bike rides given it is the same size with the same HT angle

This is a custom frame so I can adjust the HTA so the trail is the same with either fork. Is there any other reason to chose 45mm or 50mm other than toe overlap?

Do your pedal through a turn?

A modern bike should get it's comfort from wider tires run at lower pressure. At my 135 lb weight, I use 28mm front and 30mm back with the same 52-55 psi in both tires. I could also run 30mm in both and drop the front pressure by 3-4 psi. I use the Zipp pressure calculator for a starting point.

Your builder should have some opinion on the combination of HTA and fork offset that would give the desired trail and front-center dimension. My frames are next to smallest size and have 67-68mm of trail. Some models use the same 58mm across the board.

These days, I use stack and reach to determine what size I need, since the numbers and letters used today mean nothing.

I do all the time :cool:

I am 140lbs and use 28mm tires 68psi rear and 65 psi front. The roads here are not bad and I find this works well for me. I do like some road feedback not total isolation.

you can enter your head tube angle and fork info on the site link below and get trail results:
http://yojimg.net/bike/web_tools/trailcalc.php

around 57mm is considered optimal between being too twitchy (less trail) or stable/sluggish (more trail).

I ride the same size frame (around 52cm), and notice there's lot's of variation on how manufactures deal with toe overlap as frame sizes get smaller. I'd personally rather live with toe overlap and have great riding geometry than visa-versa. Between 45mm and 50mm, if the trail is dialed in for your preference, each fork would incur a different head tube angle that may create differences in wheel flop vs directness in the steering feeling.

Do any current carbon fork makers make the same road fork in 45 and 50?

Yes

https://www.columbus1919.com/en/port...caliper-sl-en/

You don't try to build in comfort by changing fork rake.

If you want compliance in a carbon fork, seek a fork that offers such qualities in the carbon layup.

How do you define "great riding geometry" with respect to fork rake?
My current steel bike has 50mm rake and I would say it rides great.
But how would I know if 45mm would ride even greater?
My Cannondale EVO has 45mm rake fork and I feel like there is more vertical shock coming to the bars but that could be for reasons other than the fork rake.

Is there such a thing? Suggestions?

Wheel flop IS a thing, that can occur with large offset forks. It's an annoyance, more than a problem, since it only occurs at parking lot speeds. I know because I built a frame/fork, which had this quirk. Also, with a 50mm offset fork, using soft fork blades, you can get chatter. I think this is slightly less a concern with lesser offset.