Is a trail difference of 3mm noticable?

[CSI Man]

If you have two identical frames with 73.5 degree HT angle, 700mm rims (622mm diameter) , and 23mm tires, but with forks that have different rake offsets of 43mm and 40mm, would there be a noticably difference in handling between the two bikes.

The 43mm fork gives a trail of 54.1 mm

The 40mm fork gives a trail of 57.2 mm

54.1 mm of trail would give you quicker steering than 57.2 mm, but how much? And would an average cyclist notice the difference?


CSI Man

[Waldo]

I notice the difference in handling. Ever since Dario went from 43mm rake to 45 to me his frames don't handle right. At least not as much to my liking as when they came with 43s.

[David Kirk]

Most can feel that difference. Better or worse is in the eye of the beholder but I bet you'd feel it.

dave

[sbornia]

Most can feel that difference.
dave

Would this change also alter the bike's front-center measurement, and, if so, how might that impact handling...or the position of the rider between the two wheels?

[zap]

snipped

54.1 mm of trail would give you quicker steering than 57.2 mm, but how much? And would an average cyclist notice the difference?


CSI Man

Can't speak for the average.

If you notice it, give it several rides to readjust you're body language. Fork stiffness plays a role too.

[TimD]

I felt a difference in going from a 40mm to a 43mm (I forget what the trail values were), but I quickly got used to it.

[David Kirk]

Would this change also alter the bike's front-center measurement, and, if so, how might that impact handling...or the position of the rider between the two wheels?

I suppose one would feel all of the above......... there is no real way to tell what part of the change you are feeling.

dave

[mistermo]

The 43mm fork gives a trail of 54.1 mm

The 40mm fork gives a trail of 57.2 mm

54.1 mm of trail would give you quicker steering than 57.2 mm, but how much? And would an average cyclist notice the difference?

CSI Man

I'm glad you asked this question because I've been wondering lately too. But I'm having trouble getting my mind around this. Wouldn't a fork with a lesser rake shorten the wheelbase, tighten the handling, and make steering quicker?

Thanks.

[mister]

it will just shorten the wheelbase.
read about how trail and rake/head angle affect each other.

[WadePatton]

and don't forget that production tolerances might mean that your hta's aren't exactly the same and/or that the forks measure a smidge one way or t'other. change lower stack height, get new hta. etc.

imprecision is precision.

yo

[mistermo]

...read about how trail and rake/head angle affect each other.

I once read about trail where the author used a shopping cart wheel to illustrate the principle as it relates to handling. I forget where I read that.

Any recommendations as to a good source of reading?

[mister]

I once read about trail where the author used a shopping cart wheel to illustrate the principle as it relates to handling. I forget where I read that.

Any recommendations as to a good source of reading?

oh i just found that article you were talking about.

i think this explanation is pretty accurate though based on the bikes i've ridden.
http://www.spectrum-cycles.com/612.htm

seems to be a matter of rider preference.
i like a little bit larger trail while some prefer less trail.

[goonster]

seems to be a matter of rider preference.


Front wheel loading and tire volume also enters into it, although perhaps those factors do not vary significantly for the bikes under discussion in this thread.

[mister]

Front wheel loading and tire volume also enters into it, although perhaps those factors do not vary significantly for the bikes under discussion in this thread.

oh yeah.
i was also thinking about the randonneur guys with the big bags high up over the front axle...and their bikes with trail in the mid 40's...as i posted that link.

didn't really think it pertained to this thread.
i'd like to ride an rando bike sometime, haven't had the chance yet. if a 58cm Weigle ever comes up for sale used i'd probably give it strong consideration.

[RPS]

Would this change also alter the bike's front-center measurement, and, if so, how might that impact handling...or the position of the rider between the two wheels?If you are alluding to the change 3 millimeters in front center would have on weight distribution, it’d have less of an impact than riding without a helmet, or relieving yourself before or during a ride. :rolleyes:

Seriously, it’s a very small difference that can be easily calculated – needless to say way smaller than 1 percent change in weight distribution. I wouldn’t worry about the secondary effect due to a different front center. The primary change some riders may feel is in the trail; and I doubt many “average” cyclist would notice if tested blindly.

[Samster]

my merckx came with a 43. not enough trail given the hta. using one of those funky online calculators David Kirk pointed me to, i figured 45 would put me in the right range. another builder said "if you don't feel stable around bends at 43, you probably won't at 45." but 50 gave me theoretically too much trail... after thinking it over, i bit the bullet and got the 50. the bike now feels great.

lesson: there's no way to calculate feel. numbers only tell part of the story. forks are expensive, so if you can, try and see before you buy.

good luck.

[flydhest]

I doubt many “average” cyclist would notice if tested blindly.

Because they would crash. ;)

[mister]

my merckx came with a 43. not enough trail given the hta. using one of those funky online calculators David Kirk pointed me to, i figured 45 would put me in the right range. another builder said "if you don't feel stable around bends at 43, you probably won't at 45." but 50 gave me theoretically too much trail... after thinking it over, i bit the bullet and got the 50. the bike now feels great.

lesson: there's no way to calculate feel. numbers only tell part of the story. forks are expensive, so if you can, try and see before you buy.

good luck.

if the bike feels good after the change then that's what matters...but adding more rake actually made your trail shorter.

[Samster]

Because they would crash. ;)
i can't believe that slipped my notice. good catch.

[Samster]

if the bike feels good after the change then that's what matters...but adding more rake actually made your trail shorter.
this is why i don't build frames. you're right. i had it all straight when i did the work then promptly forgot about it and all the nuances once the problem was fixed. thanks for pointing that one out. here's the original post link from 2 years ago. LINK (http://forums.thepaceline.net/showthread.php?t=29455)

[RPS]

Because they would crash. ;)Funny. :beer:

Without blind testing, I'd expect a huge amount of "confirmation bias". People -- including cyclists -- see (or feel) what they want to see (or feel) and disregard the rest.

[Pete Serotta]

Because they would crash. ;) :D :D

Fly is a "fun" guy. need to meet him for some RED and some of his excellent cooking!!!

[djg]

Because they would crash. ;)

Another problem with double-blind testing happens even earlier -- people get hurt trying to mount their bikes so they don't even get the opportunity to crash. It's not pretty.

[Peter P.]

I would say YES; with a 3mm difference you WILL feel a change. Whether you like it or not is a personal matter.

I had a frame with a 73 degree/50mm rake setup and the handling drove me nuts. I had the fork "re-raked" to 45mm, a 5mm difference and a much more common setup, and the handling changed dramatically for the better.

Now I'm beginning to wonder if a 73/40mm setup would improve steering even more.

[PacNW2Ford]

my merckx came with a 43. not enough trail given the hta. using one of those funky online calculators David Kirk pointed me to, i figured 45 would put me in the right range. another builder said "if you don't feel stable around bends at 43, you probably won't at 45." but 50 gave me theoretically too much trail... after thinking it over, i bit the bullet and got the 50. the bike now feels great.

lesson: there's no way to calculate feel. numbers only tell part of the story. forks are expensive, so if you can, try and see before you buy.

good luck.

The more rake, the less trail...

[khjr]

[QUOTE=goonster]...tire volume also enters into it,..[QUOTE]
My experience has been exactly that. I don't consider myself a bicycle connoisseur, as I keep only one road bike. Nonetheless, exchanging the Continental 20C tires, with which I built my Tommasini, for taller 25C versions completely altered the bike’s handling at high speeds. That minute increase in trail eliminated a feeling of front wheel drift in high speed 50+ mph descents, transforming them from worrisome to confident and fun. Before the tire change, I thought I might have to replace the frame (...I still have a Rambouillet frame boxed in my garage...), but now I won’t trade the Tommasini for anything. It still surprises me as to how much a difference that small change in trail made.

[palincss]

The change in tire size might have made a minute change in geometric trail, but it made a much larger change in pneumatic trail.

[khjr]

The change in tire size might have made a minute change in geometric trail, but it made a much larger change in pneumatic trail. Hmmm - I could swear that I felt the effect when riding upright and straight ahead, vs. turning, where the effects of pneumatic trail would apply. Riding hands free became dramatically easier with the taller tires. I suppose, however, that one may be "always turning" even when riding straight, i.e. correcting direction with alternating large radius turns...

[RPS]

In this morning’s paper. Quick and easy way to test different amount of trail. Also BBKT height, STA and HTA. :rolleyes:

Just for fun, is this more or less trail compared to original wheel? Keep in mind tire OD and HTA are both different. ;)

[Tobias]

Less. As the wheel is made smaller, trail should go down. In the picture above it looks like negative trail.

BTW, cool trailer.....but needs a seat belt for safety. ;)

[Pete Serotta]

as Dave said.....He is the "expert" on this thread!!! :D


Most can feel that difference. Better or worse is in the eye of the beholder but I bet you'd feel it.

dave

[grateful]

Sorry to dredge this old thread up but...

New to me Merlin frame. Originally spec'd with a 40mm fork. I have changed the fork out to a 43mm.

I am about ready to purchase tires. Would I need a larger tire to bring in closer to the original trail or will a smaller tire bring it closer?

Thanks

[tv_vt]

Sorry to dredge this old thread up but...

New to me Merlin frame. Originally spec'd with a 40mm fork. I have changed the fork out to a 43mm.

I am about ready to purchase tires. Would I need a larger tire to bring in closer to the original trail or will a smaller tire bring it closer?

Thanks

Use this trail calculator tool and try out various tire sizes to see how it affects trail. http://yojimg.net/bike/web_tools/trailcalc.php

Bottom line: bigger tire will give higher trail number in your case, and move that number closer to what it was with 40mm fork.

[Mark McM]

The formula for trail is:

Trail = (Wheel radius) / tangent(head angle) - (fork offset) / sine(head angle)

So, trail increases as wheel radius increases, so a larger tire results in more trail.

Also note that fatter tires also increase an affect called pneumatic trail (https://en.wikipedia.org/wiki/Pneumatic_trail), which also tends to make a bike roll in a straight line.

[avalonracing]

Sorry to dredge this old thread up but...

New to me Merlin frame. Originally spec'd with a 40mm fork. I have changed the fork out to a 43mm.

I am about ready to purchase tires. Would I need a larger tire to bring in closer to the original trail or will a smaller tire bring it closer?

Thanks

I did the same thing on my Ti frame that was spec'd for a 40mm fork. But when I went to a 43 the handling was twitchy. It was fine but I didn't like it as much so I ended up getting another 40.

[redir]

When I got a new fork for my Moots, the fork that was specified for this frame, the trail decreased. I now have toe overlap but this bike now rails through corners. Made a huge difference in feel.

[redir]

double post

[grateful]

Thanks folks. That is the info I was looking for.

[saintruggler]

These sorts of discussions about minute (~3mm) differences in rake are often conflated with conversations of people swapping forks with ones that also have different lengths. Not saying that is what the OP is doing, but be cautious when someone reports feeling a significant difference in ride quality when changing forks. There may be other factors at play.