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aka bOb
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Discussion Starter · #1 ·
Ok I'm an idiot when it comes to trail (and many other things) but what effect does it have on bike handling and steering?

So let's say we have 2 bikes with the same head angle but one is made for a 450 a-c and the other is made to run a 468 a-c. My question is even though said bikes have the same head angle when running the proper forks will the steering respond different between the two due to having different trail?
 

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Ok I'm an idiot when it comes to trail (and many other things) but what effect does it have on bike handling and steering?

So let's say we have 2 bikes with the same head angle but one is made for a 450 a-c and the other is made to run a 468 a-c. My question is even though said bikes have the same head angle when running the proper forks will the steering respond different between the two due to having different trail?
With the same HTA the fork length makes no difference at all. For the trail to be different the forks need to have different amounts of offset.
 

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https://encrypted-tbn3.gstatic.com/...JfSMXuvq_Ss9jzX8SRJjMUzYsc8K-55LZUoSjRB7CEb3x

Rake, trail, and rake, or head angle explained in the image

My understanding on the effects of various things is a bit incomplete, but here goes:

As head angle Decreases (fork tips farther out at the bottom) the geometry is said to get "more slack". Cruiser bikes and downhill bikes use slack geometry to increase stability. Chopper bikes take it to an extreme for the sake of "cool".

As offset or rake increases on a bike, stability increases as well; the weight of the bike tends to want to keep the fork aligned in the direction of movement. Turning the fork takes some energy input. But as rake or offset increases past a certain point, the fork becomes "floppy' and the bike difficult to manage especially when moving slowly when there is little centrifugal effect to aid returning the wheel to normal.

Stem length can have a profound effect; a very long stem used to compensate for a tall rider's long arms on a small bike will usually make the bike steer very clumsily; a lot of effort must be expended to get the desired result because the handlbars are no longer rotating near the head's center point and too much rider weight is on the front wheel...increasing the 'flop" effect of the rake and rake angle.
 

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https://encrypted-tbn3.gstatic.com/...JfSMXuvq_Ss9jzX8SRJjMUzYsc8K-55LZUoSjRB7CEb3x

Rake, trail, and rake, or head angle explained in the image

My understanding on the effects of various things is a bit incomplete, but here goes:

As head angle Decreases (fork tips farther out at the bottom) the geometry is said to get "more slack". Cruiser bikes and downhill bikes use slack geometry to increase stability. Chopper bikes take it to an extreme for the sake of "cool".
Sort of. More to it than that.


As offset or rake increases on a bike, stability increases as well; the weight of the bike tends to want to keep the fork aligned in the direction of movement. Turning the fork takes some energy input. But as rake or offset increases past a certain point, the fork becomes "floppy' and the bike difficult to manage especially when moving slowly when there is little centrifugal effect to aid returning the wheel to normal.
No, increasing the offset reduces the amount of trail. Less trail can make the steering more responsive, but more easily knocked off line at speed--less stable.


Stem length can have a profound effect; a very long stem used to compensate for a tall rider's long arms on a small bike will usually make the bike steer very clumsily; a lot of effort must be expended to get the desired result because the handlbars are no longer rotating near the head's center point and too much rider weight is on the front wheel...increasing the 'flop" effect of the rake and rake angle.
Mostly because of changes in the weight distribution. Points out why the wrong size frame will handle poorly. Not about the basic steering geometry.

As always, you can not isolate one aspect of the bike's geometry and tell how it will handle. The whole of the bike needs to work together.
 

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I put an X-Fusion Trace fork at 100mm (51mm offset) on my SC Highball, size XXL (70.5mm HA. Seemingly designed for Fox 46mm offset). I notice and don't like the sensitivity to being knocked offline. I also notice the tire scrubbing entering turns - a bit sketchy in slick conditions.

Question - can I remedy this with a CaneCreek adjustable angle headset?
 

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I put an X-Fusion Trace fork at 100mm (51mm offset) on my SC Highball, size XXL (70.5mm HA. Seemingly designed for Fox 46mm offset). I notice and don't like the sensitivity to being knocked offline. I also notice the tire scrubbing entering turns - a bit sketchy in slick conditions.

Question - can I remedy this with a CaneCreek adjustable angle headset?
Likely, if your frame will accept the headset. I'd slack the head angle a bit and try it.
 

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Likely, if your frame will accept the headset. I'd slack the head angle a bit and try it.
What is the best headset angle adjustment? I had an Angleset, but returned before installation because it didn't come with 0deg cups.

With above equation - I calculate trail of 76.3mm with bike as is - assuming 70.5deg HA. Increases to 79.7mm with 70deg (edit - not 71deg!) HA. Increase of 3.4mm, seems like not much, but I can imagine these things are sensitive.
 

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What is the best headset angle adjustment? I had an Angleset, but returned before installation because it didn't come with 0deg cups.

With above equation - I calculate trail of 76.3mm with bike as is - assuming 70.5deg HA. Increases to 79.7mm with 71deg HA. Increase of 3.4mm, seems like not much, but I can imagine these things are sensitive.
Something is wrong with your calculation...all else being equal, trail should DECREASE with a steeper head angle change. So if you want your trail to INCREASE (feel more stable) you should slack your head angle.

Bicycle Trail Calculator | yojimg.net
 

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Why people want a head angle that guarantees the bike's steering being floppy at low speed in tricky conditions beats me.
 

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Discussion Starter · #14 ·
Why people want a head angle that guarantees the bike's steering being floppy at low speed in tricky conditions beats me.
I know you have always like fast steering but what has been the lowest angle that you have tried that you felt comfortable with?
 

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I know you have always like fast steering but what has been the lowest angle that you have tried that you felt comfortable with?
Not that I was asked but the lowest I've ridden and been comfortable with was 69°. Comfortable but not ideal. 71° feels good to me on 100mm 26er.
 

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aka bOb
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Discussion Starter · #16 ·
See where I am going is I am thinking about getting a custom frame and there is an up charge for changing the HA. The normal for this company is a 70.5 and I have had 2 pugs and I thought they where a little fast so trying to decide if I want to pay extra to drop it to 69.8 that I really like on my Yampa.
 

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Discussion Starter · #18 ·
What kind of custom bike has an upcharge for changing the head angle?!?

For what it's worth, .5 degrees is not going to be super noticeable to most riders. That's right at the threshold of detectability.

-Walt
How about .7 deg.?

I am making changes to an existing design so in the end it is custom.

Edit: I could always just run an anglset but I have not heard great things about em.
 

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Most people will notice about 1 degree/something around 7mm of trail difference if you don't tell them in advance what's going on. Below that threshold some people will notice down to about .5 degrees, some won't. Below .5 deg I don't think anyone on earth could tell by riding the bike.

Setting that aside for a moment, there is an awful lot that goes into how a bike steers beyond head angle/offset/trail. I would suggest finding someone who really knows their stuff and picking their brain in person, or alternately trying some more different bikes to see what you like and what you don't. This ask-online thing is a terrible way to design a bike.

-Walt
 

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I know you have always like fast steering but what has been the lowest angle that you have tried that you felt comfortable with?
HA 73.5º with 36mm offset has been the most extreme I have felt ok on. (Couldn't get it any steeper than that)

...there is an awful lot that goes into how a bike steers beyond head angle/offset/trail....
It's well worth reading what Walt has to say on this subject. Waltworks Bicycles: The Fat Geometry Post

Position on the bike makes a huge difference because unlike a motorbike, the majority of the mass is the rider, so where that mass is placed affects the handling.

To me the big attraction of a fatbike is the ability to get into difficult places. That usually means dead slow, lots of stoppie type obstacles, so a geometry that has you sawing the forks back and fore at low speed is not ideal, especially on climbs. Ruts are another problem and I'm convinced a steep HA makes these more rideable. This is particularly important in the snow because a frozen rut can be hidden under a layer of fresh soft snow.

If you don't venture off the beaten track, then none of that is a problem. I think we're going to see a divergence in fatbikes. XC style for most and expedition style for the others.

BTW it's worth remembering that on a bike like a fatbike with such large diameter tyres that simply raising or lowering the tyre pressure can vary your effective HA, so it's not worth getting too concerned about 0.5º or so.
 
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