bike_galpal

i think this is my first experience like this (with more to come?)

went to a fairly well known "nice" bike shop around here recently and started chatting up a guy about installing my Look HSC4 full carbon fork on my Swobo Sanchez.

after a few minutes of chatting, i'm fairly confident he was telling me that i shouldn't install that fork on my frame because of the head tube angle?

now obviously i'm not at the level of a professional mechanic, however nor am i an idiot (yes both of those are arguable) but he seemed to be almost intentionally unclear. i asked him if he was talking about the fork rake at first, and i think he said yes? or just said rake in general? so i was like, OK, does rake refer to some part of the frame geometry as well? and he DEFINITIELY said yes. he seemed very confident albeit confusing like i said, and didn't use the word "head tube angle" yet it was 100% clear to me this is what he was trying to describe, and told me the word "rake" also applied to this.

in any case, after coming home and doing some research, the sanchez has a similar enough head tube angle to any roadbike. its 73 degrees, which is in fact tighter than some road bike frames for a "large" frame.

what's the deal here? am i totally misinterpreting something? or is this normal mansplaining amplified by LBS employment?

he also sold me the wrong chain for my friends bike, after i specifically asked him if the shimano 11 speed would work on SRAM. UGH

dabac

I've only heard rake referred to as a structural feature found in the fork, not the frame.
However, a certain frame, due to the head tube angle, might be assumed to offer a nicer built-up ride together with a fork with a certain rake. And length of course.
Sometimes simultaneous changes in length(axle-to-Crown) AND rake, and the corresponding change in head tube angle this will bring about can pretty much offset each other.
A least in theory. I haven't played with it much.

SkyDog75

You can use a Shimano 11-speed chain on a SRAM 11-speed drivetrain.

habilis

You could do your own measuring and see if the fork is compatible with the frame. Is the original fork intact? Hold the new one against it and see if they are consistent in length and rake angle (the degree to which the dropouts are forward of the main axis of the fork). If the frame currently doesn't have a fork, you could put a wheel in the new fork and hold it against the frame to check for clearance between the wheel and down tube. If there is sufficient clearance, the bike will at least be rideable, but a too-long or too-short fork would definitely affect ride quality.

Anecdote: After colliding with a car, I rode my motorcycle home with a mashed-in fork. The whole bike felt jacked up in front. Very strange sensation.

HillRider

Fork rake varies a bit with 43 mm being the most common on road bikes and variations between 40 mm and 50 mm used on some bikes. Even with in that range the effect on handling is usually not dramatic going from one to another but the bike shop guy may have exaggerated this to get a sale or because he wasn't sure.

More rake means less "trail" and gives quicker handling but less straight line stability. Less rake gives the opposite effect. For a 73° headtube angle and a mid-size frame, a rake in the 43 mm range is usually chosen. Unless your fork has a greatly different rake it should be fine.

hig4s

That doesn't seem right. Chopper front ends, highly raked, have slower handling, more trail, and more straight line stability.

spdntrxi

wheelbase is also a factor giving a plus to straight-line stability... lots of intertwined factors.

habilis

Check out the picture in the second post in this thread: https://www.bikeforums.net/framebuild...rake-fork.html
It's a good illustration of what "rake" means. It's determined by the distance between the dropout openings and the steering axis of the fork. It should be within a few millimeters of the same dimension on your old fork, or the bike will handle differently. I believe that if the distance is shorter, the bike will steer more abruptly.

Edit: More abrupt steering is a characteristic of race bikes. More relaxed steering (a wider turning radius if you're making circles in a parking lot) is a characteristic of touring bikes. It will also give a somewhat more springy ride in a steel bike. It's somewhat like a front shock, but without the complicated hardware.

JohnDThompson 

The frame's head tube angle and the fork's rake (offset) together determine a value called "trail" that defines the bike's steering characteristics. When replacing a fork, care should be taken to ensure that the resulting trail is similar to that of the original fork, unless the goal is to change the steering characteristics of the bike.

Bicycle Trail Calculator | yojimg.net

Andrew R Stewart 

Don't confuse steering angle (head angle) with rake or trail. Choppers have both very slack steering angles as well as a lot of trail. This produces what most call "wheel flop". As the wheel is turned to steer the front end will raise or drop RT the ground. It is a combo of both this flop and excessive trail that make the handling of choppers what it is.

There is a lot of less then best understood talk about bike steering issues. Anyone who is interested should read "Bicycling Science". Andy.

hueyhoolihan

it was like asking the bag-boy at Safeway whether or not the organic romaine lettuce would make a better salad than the non-organic... if pressed he or she might try to provide a justifiable answer. ...just part of the job, i would say.

BTW, i've posted this in the past so forgive me if you've heard it before, but i've REVERSED the fork, as an experiment to satisfy myself that much of the fork's rake/trail issues are way way overblown, on my '97 Gary Fisher MTB (set up with rear coaster brake and no front brake) and rode it for about 20 miles. there was not much difference that couldn't be attributed to the fact that the wheelbase was three or four inches shorter than it was. hands-free riding was not even a problem.

habilis

True, and the OP's problem is greatly simplified if she has the old, undamaged fork. She just needs to put the new one next to it and compare them carefully. If all dimensions are the same, they should be interchangeable. The only difference in that case would be characteristics of the material (e.g, carbon vs. metal.) The LBS guy should have done the same thing.

fietsbob

bugger with the fork offset just putting any fork you get a deal on can change the trail too.


run a straight line thru the head tube (without dropping or raising it with a longer or shorter blade fork)

that is one line end point of trail .. the other one is a plumb line from the wheel axis.

trail is the distance between those 2 points ..

there are many ways to alter that .. Offset/rake and crown race seat to dropout length are 2 of them. .

its 'Trail' because the HTA line is ahead of the axle plumb line .. plotted on the ground.

SJX426 

I purchased a Trek 760 that did not have the original fork. I searched for one after doing some research. I found the spec for offset was 38. The only aftermarket forks available were track forks with that offset. I solved the problem by finding an original fork that was bent and set it to the correct offset.

HillRider

You are confusing head tube angle (mislabeled as "rake"on motorcycles) with fork rake. They are different but interconnected geometric considerations.

bike_galpal

the chain simply did not fit the cogs of the SRAM rival derailleur. IDK

bike_galpal

the rake is actually 43 on both forks, which i'm pretty sure i told him at the beginning of the conversation.

the best response!!

so he WAS just being a D bag. UGH.

my issue with him was that i told him the exact frame i had, which he said they carried, he did a little web searching (i couldn't see) and then CONFIDENTLY (with a perhaps even a patronizing tone) told me that basically i could do it but it would be dangerous because the fork isn't designed for the frame geometry. maybe he was thinking about another Swobo frame i guess.

the other annoying thing is that i actually asked if they had a headset for it (a separate issue) and he didn't even attempt to give me a price on one. he knew i wasn't going to have them install it.

about your experiment, i haven't seen that, but i have seen a video in which someone reverses the fork and pushes a bike down a slight hill. it stays perfectly straight.

bike_galpal

i take that back.... it was TOTALLY a patronizing tone. ugh. i'm gonna go in there today be like "so remember what you told me, has the sanchez frame geometry changed recently? or??"

hig4s

Don't you mean fork rake is mislabeled rake on bicycles? Because both terms rake and fork rake are used on motorcycles. Technically the terms are rake angle and fork rake, just saying rake is ambiguous.

habilis

Why not take the LBS guy completely out of the equation? It sounds like you have both the old fork and the new replacement. I'd just compare them with a tape measure. If they match up, you can proceed to find out if the steering tubes match, either by checking online or pulling the old fork from the frame. I've never purchased an aftermarket fork, but I've read that they come with extra-long steering tubes that can be cut down to fit. All you need to know is the diameter.

fietsbob

I prefer 'offset' for that reason. straight blade forks still have Offset.. at the top where they join the steerer

or a tab offset added at the bottom onto the front ..

cpach

Sounds like the mechanic at that shop has an incomplete understanding--probably just knows that there's a variation of rake for forks and head tube angle for frames, but doesn't know enough to know what typical values are to actually determine compatibility. Maybe he's assuming that the frame is more track-ish with lower trail than it actually is, and thus not designed for a road fork?

If you get a chance try to explain to him or direct him to why he's wrong, and if he's too stubborn to realize he was wrong, talk to his manager. It's bad business for wrenches to be outright wrong about bikes.

habilis

Makes sense. "Rake" probably was more applicable to the older forks that had a strong forward bend to their blade tips.

fietsbob

then the radius of the curve comes into it ... the tighter radius at the tips flexed more , to act like Carbon forks are supposed to now.

bike_galpal

that was my initial plan - they definitely match up enough, the conversation was about the headset. other than the headset problem (which was pretty much already solved by a guy at a MUCH less boozhy bike shop) i pretty much knew everything i needed to, just wasn't 100% confident.

funny about the steering tubes, they're currently almost exactly the same length on my 60cm frame, and my Look fork is new and uncut. i have my stem at the bottom though, i might need to cut it so it doesn't extended more than 30mm (i think) above, etc. i have done a fair bit of research.

i'm 99% sure he was saying the opposite - that my frame was more "chopper" like, and carbon steerers don't have enough "lateral" strength or something. i did check out a few Cervelo and Look road bikes, they're VERY similar, one of them is 73.5 degrees vs my 73.


yeah, i think i'll do that. i mean at the very least i'll ask him if he had a different bike and geometry in mind when i mentioned that it's a sanchez.