Fork Rake 45mm vs 50mm?

[campy man]

Currently riding a bike with a 72.75 head tube angle, thinking of changing the fork from 50mm to 45mm rake. Just wondering if there would be any significant changes in the handling of the front end.

My thinking is the 45mm fork would make the front end a little more responsive. My riding is primarily fitness/training and group rides on the road. I ride with 25mm tires.

[John H.]

The change should make it feel more stable.
With a 50mm fork, trail is about 52, a 45mm fork would bump the trail up to 58.
In my opinion the bike will ride better- it was likely under-trailed with the 50mm fork.

[Mark McM]

My thinking is the 45mm fork would make the front end a little more responsive. My riding is primarily fitness/training and group rides on the road. I ride with 25mm tires.

The other way around. Fork offset (rake) decreases trail, decreasing stability and increasing responsiveness. Assuming all else the same, the 45mm offset fork will be slower handling than the 50mm offset fork.

[John H.]

But given the 72.75 degree head angle, it should ride better with a 45mm fork.

The other way around. Fork offset (rake) decreases trail, decreasing stability and increasing responsiveness. Assuming all else the same, the 45mm offset fork will be slower handling than the 50mm offset fork.

[phcollard]

From what I understand less rake equals more trail hence more stability at high speed. I still have to learn if more trail means more stability at low speed, I think I read the opposite.

You should play with this online calculator :
http://yojimg.net/bike/web_tools/trailcalc.php

It looks like the golden number regarding trail is 56mm but as far as I am concerned I am not sure I can tell the difference between 52mm and 60mm trail. Maybe that's just me.

[tv_vt]

Boy, the 50mm rake on your bike makes for a low trail number. The 45mm rake will quiet down the steering responsiveness a little. For me, that would work very well. But maybe not for you.

Here's a question: A)can you ride your bike no-handed, sitting upright on the saddle, comfortably? Or B)does your bike go immediately out of control when you take your hands off the bars? If A, then you probably are fine with what you have. If B, then you might like the 45mm rake fork - if you want to be able to ride no-handed, or not have your bike feel too twitchy.

My bikes have around 60mm trail and I can ride no-handed for as long as I want, no problems.

(btw, I have a 45mm Reynolds Ouzo Pro fork available. Apologies if this is OT.)

[David Tollefson]

FI still have to learn if more trail means more stability at low speed, I think I read the opposite.

In my experience, it's "wheel flop" that makes slow speed handling difficult -- a shallow head angle coupled with larger rake puts more of the weight of the wheel ahead of the steering axis, so it has a tendency to want to turn off center when going slow uphill.

[bluesea]

In my experience, it's "wheel flop" that makes slow speed handling difficult -- a shallow head angle coupled with larger rake puts more of the weight of the wheel ahead of the steering axis, so it has a tendency to want to turn off center when going slow uphill.



Or going slowly period. My experience is wheel flop also makes the bike creep inward, on fast sweepers.

[Grant McLean]

The missing information from this discussion is the wheelbase of the
bike in question, which has just as much impact on handling as trail.

If it's a small bike with a short top tube, more fork rake helps lengthen
the front centre, a good thing in most cases, since very short front centre
bikes ride like crap. If the bike has a long top tube, and a long front
centre, using the combination of head angle and fork rake that produces
the trail number you want with the least off-set will shorten the front end,
and can improve the handling.

In a word, you can't isolate a single criteria of geometry and learn much
about the way a bike will ride. It all goes together, trail is part of the story
but not the whole story.

[campy man]

Top tube is 57cm(c-c), seat tube angle is 73deg and chainstay length is 42.0cm.

Hope that helps!

[David Tollefson]

The missing information from this discussion is the wheelbase of the
bike in question, which has just as much impact on handling as trail.

If it's a small bike with a short top tube, more fork rake helps lengthen
the front centre, a good thing in most cases, since very short front centre
bikes ride like crap. If the bike has a long top tube, and a long front
centre, using the combination of head angle and fork rake that produces
the trail number you want with the least off-set will shorten the front end,
and can improve the handling.

In a word, you can't isolate a single criteria of geometry and learn much
about the way a bike will ride. It all goes together, trail is part of the story
but not the whole story.

While I agree that in the initial design, all these factors come into play (along with location of CG and the balance of weight fore/aft), but it's not irrelevant to look at an existing design and see how varying a single factor will affect the handling (direction-wise -- you can't say to what degree without the other factors).

[Grant McLean]

it's not irrelevant to look at an existing design and see how varying a single factor will affect the handling.

sure, but we didn't have the existing design, only the fork and head angle,
that's the point i was making.

-g

[Grant McLean]

Top tube is 57cm(c-c), seat tube angle is 73deg and chainstay length is 42.0cm.

Hope that helps!

A 45mm fork certainly would be more conventional in this case.
The trail is quite low with the 50mm fork, and I don't really see any
benefit to having the front centre over 60cm. Most builders would
likely have put a 45mm fork in this situation, although 5mm is not
the end of the world, some may have a preference for one over the
other.

I see geometry as a series of bullseyes, you want certain targets
close to the centre as possible, the further away you get the less ideal
things tend to be. 5mm isn't a mile off the target, but it's getting near
to the edge of it. Personally, I like long wheelbase, low trail bikes for
cruising, so it can come down to the preference, and intended use of the
rider.

-g

[campy man]

Interesting, I plugged in some numbers into the calculator.

50mm fork = 53

45mm fork = 58

Considering some of my favorite riding and handling bikes, 56 seems like the magic number for me. Since 56 is not going to happen with my current bike I think the 50mm fork will provide good results considering the type of riding I'll be doing.

[John H.]

If it was my bike, I would want the 45 on it.

[campy man]

My mistake, meant to say the higher trail(58) seems to be a better fit for my intended use.

[mister]

if it was my ride, i'd want the 45mm fork on there. not that i'd worry too much about only the trail number, i'd want the front center shorter than what it is with the 50mm fork.

[Scooper]

If it was my bike, I would want the 45 on it.

Yep; I would also go with the 45mm rake fork. ~60mm of trail is the sweet spot for me.

[pbarry]

Yep; I would also go with the 45mm rake fork. ~60mm of trail is the sweet spot for me.

^^^ This.

[ultraman6970]

That size and with 72.75 head tube? what bike is it? custom made and stuff??

Top tube is 57cm(c-c), seat tube angle is 73deg and chainstay length is 42.0cm.

Hope that helps!

[soulspinner]

Interesting, I plugged in some numbers into the calculator.

50mm fork = 53

45mm fork = 58

Considering some of my favorite riding and handling bikes, 56 seems like the magic number for me. Since 56 is not going to happen with my current bike I think the 50mm fork will provide good results considering the type of riding I'll be doing.

56 trail seems best to me too on my steel bike. The carbon bike I ride has a 58 trail, longer wb and turn in is too slow for my tastes.

[tv_vt]

Actually, if 60mm trail was the sweetspot for someone, I'd recommend a fork with 43mm rake.

[JLNK]

The Richard Sachs website has an interview with the Rivendell Reader. Sachs talks about design and says "I think about all the points that connect the rider to the bike . . . . my front wheel bases are longer than most, my trail measurements are less than most, my centers of gravity are lower than most, my chainstays are longer than most . . .
IMHO a Sachs bike is the best handling and most comfortable riding bike I have owned.

[Rueda Tropical]

If I was planning on using 28mm or larger tires I'd stick with the 50mm fork. For skinnier tires I'd go for the 45mm.

[Scooper]

Actually, if 60mm trail was the sweetspot for someone, I'd recommend a fork with 43mm rake.

Yep, but the OP's fork rake choices were 50 and 45.

[Mark McM]

The Richard Sachs website has an interview with the Rivendell Reader. Sachs talks about design and says "I think about all the points that connect the rider to the bike . . . . my front wheel bases are longer than most, my trail measurements are less than most, my centers of gravity are lower than most, my chainstays are longer than most . . .
IMHO a Sachs bike is the best handling and most comfortable riding bike I have owned.

For both the front center shorter and the trail to be shorter than most, either the top tube or the fork offset (or both) have to be longer than most.

[Mike Lopez]

Yep, but the OP's fork rake choices were 50 and 45.

They were available in 40, 43, 45, 47, and 50mm. We did customs as low as 35mm and as high as 55mm. The most common was 43mm.

[C. Matthews]

For both the front center shorter and the trail to be shorter than most, either the top tube or the fork offset (or both) have to be longer than most.
But the quote you're referring to says the front center is longer.

[Mark McM]

But the quote you're referring to says the front center is longer.

Oops! I meant to say:

"For both the front center to be longer and the trail to be shorter than most, either the top tube or the fork offset (or both) have to be longer than most."

[mister]

i thought it was pretty common knowledge that atmo uses long fork offset...

[Lionel]

i thought it was pretty common knowledge that atmo uses long fork offset...

well yes it is.