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Old 10-31-12, 12:37 AM   #1
IvyCap
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Fork Rake, Head Tube Angle, Trail

I'm a little confused on the whole subject of trail in relation to headtube angles and fork rake. First question, do the leg lengths change from different rakes? For instance will the toptube level differ from rake to rake (sloped forward, or backward based on a horizontal toptube).
And as far as track racing goes, what seems to be an appropriate range for trail? From what I got on this article something +/- of 60mm of trail is ideal?

Thanks in advance!
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Old 10-31-12, 01:05 AM   #2
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Originally Posted by IvyCap View Post
I'm a little confused on the whole subject of trail in relation to headtube angles and fork rake. First question, do the leg lengths change from different rakes? For instance will the toptube level differ from rake to rake (sloped forward, or backward based on a horizontal toptube).
And as far as track racing goes, what seems to be an appropriate range for trail? From what I got on this article something +/- of 60mm of trail is ideal?

Thanks in advance!
It is my understanding that the net fork length doesn't change with the offset/rake as illustrated in the diagram as 368mm. So, swapping out forks should leave the top tube horizontal. The wheel just moves forward or backward a bit.

60mm isn't ideal for all situations...also as illustrated in the article. Sprint bikes (like the LOOK 496 and Dolan DF3) seem to have settled on 74.5 degree head tubes with 30-35mm rake forks. Pursuit bikes (like the LOOK 596 and Felt TK1) have 40mm rake forks. This makes the pursuit bikes more stable when in aerobars.

Basically, there are 3 types of bikes for track racing:

- Pursuit
- Mass Start (all-around)
- Sprint

Mass start bikes have a neutral geometry. Pursuit is more slack and wants to track a straight line. Sprint bikes are more aggressive and feel like they can turn on a dime.
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Old 10-31-12, 07:37 AM   #3
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I'm not sure what your first question - "do the leg lengths change from different rakes" - is asking. "Leg length" sounds like you're asking about a measurement called "axle-to-crown" - a fork with less clearance will have a lower axle-to-crown measurement. And yes, if you were to swap out a fork for one with a larger axle-to-crown, it'll raise the front end of a bike - just slightly. Not enough to cause a significant change in effective top tube measurement through angling.

One thing that's important to understand is that a head tube angle and rake work against each other to result in a middle-ground trail measurement. A steep head tube angle will lower a trail measurement; corresponding low-rake will bring it back into a good range.

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Mass start bikes have a neutral geometry. Pursuit is more slack and wants to track a straight line. Sprint bikes are more aggressive and feel like they can turn on a dime.
Pretty sure that the turn-on-a-dime issue is mostly due to head tube angle. A pursuit bike and a sprint bike can be made with the same trail measurement, but with different headtube angles and different rakes, they'll still have different handling.

I never really got why pursuit bikes have more rake - less rake would mean more trail and thus more stability. But I think it has more to do with weight distribution than anything: getting the front of the bike a bit more forward, and making sure that a rider's weight isn't in front of the steering, is going to lead to a more stable ride.
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Old 10-31-12, 07:44 AM   #4
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I never really got why pursuit bikes have more rake - less rake would mean more trail and thus more stability. But I think it has more to do with weight distribution than anything: getting the front of the bike a bit more forward, and making sure that a rider's weight isn't in front of the steering, is going to lead to a more stable ride.

Good point.
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Roadies can run tempo all year as that's what humans were designed for. If you want to be a cheetah, lay around and lick your paws more.
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Old 10-31-12, 08:31 AM   #5
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why do you ask?


Are you building a bike, shopping and comparing different bikes, trying to learn why bikes are built/designed a certain way?

Quote:
Originally Posted by IvyCap View Post
I'm a little confused on the whole subject of trail in relation to headtube angles and fork rake. First question, do the leg lengths change from different rakes? For instance will the toptube level differ from rake to rake (sloped forward, or backward based on a horizontal toptube).
And as far as track racing goes, what seems to be an appropriate range for trail? From what I got on this article something +/- of 60mm of trail is ideal?

Thanks in advance!
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Old 10-31-12, 11:13 AM   #6
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It is my understanding that the net fork length doesn't change with the offset/rake as illustrated in the diagram as 368mm. So, swapping out forks should leave the top tube horizontal. The wheel just moves forward or backward a bit.

60mm isn't ideal for all situations...also as illustrated in the article. Sprint bikes (like the LOOK 496 and Dolan DF3) seem to have settled on 74.5 degree head tubes with 30-35mm rake forks. Pursuit bikes (like the LOOK 596 and Felt TK1) have 40mm rake forks. This makes the pursuit bikes more stable when in aerobars.

Basically, there are 3 types of bikes for track racing:

- Pursuit
- Mass Start (all-around)
- Sprint

Mass start bikes have a neutral geometry. Pursuit is more slack and wants to track a straight line. Sprint bikes are more aggressive and feel like they can turn on a dime.
So this explains my hilarity on the weekend as I tried out my new (old) Felt TK2 with aero bars at Marymoor on the weekend.
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Old 10-31-12, 12:20 PM   #7
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why do you ask?


Are you building a bike, shopping and comparing different bikes, trying to learn why bikes are built/designed a certain way?
Both, I'm trying to figure out certain frame/fork combos and trying to understand how those combos will affect the overall ride.

Another question in relation to steering, what affect does stem length have effect on steering? I'd imagine a longer stem would seem more sluggish? but this seems unlikely since we're talking about riding on the track, unless....?
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Old 10-31-12, 01:11 PM   #8
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I associate sluggish with certain hta/rake combinations; longer stems feel stable rather than sluggish.
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Old 10-31-12, 04:04 PM   #9
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So this explains my hilarity on the weekend as I tried out my new (old) Felt TK2 with aero bars at Marymoor on the weekend.
The most common mistake people make is to use the same stem for both drop bars and aero bars.

When I use long reach bars like Easton EC90, I use a 120mm stem. For aerobars I use a 100mm stem.

If I use short reach bars like 3T Scatto or Nitto B125, I use a 130mm stem and the same 100mm stem when I use aerobars.

So, chances are that you simply need a stem that is 20-30mm shorter than your normal stem. That will fix lots of things.

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Another question in relation to steering, what affect does stem length have effect on steering? I'd imagine a longer stem would seem more sluggish? but this seems unlikely since we're talking about riding on the track, unless....?
As illustrated in my comment immediately above, stem length must be evaluated with the reach of the bars. The real question is: Where are my hands in relation to the front axle?

I've found that if my hands are directly above the front axle the steering is optimal. The further back they go, the more wonky the steering becomes.

Ever ride a beach cruiser and the steering is crazy? That's why.




Notice hand position:




Earlier this year I saw a family riding on the bike trail. Mom, dad, little girl. From a distance I noticed the little girl having trouble controlling her bike. She was weaving back and forth a lot. Not good on the narrow 2-way trail. As I was waiting for a chance to pass, she fell over. She was OK. Mom was attending to the girl and dad was checking the bike over. I mentioned to the dad that the reason she's so erratic is more because of the bike than his kid. I used my tool kit and rotated her bmx-style bars forward, putting her hands over the axle as opposed to far behind. BOOM. She rode straight as an arrow. They thought I was a wizard.
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Roadies can run tempo all year as that's what humans were designed for. If you want to be a cheetah, lay around and lick your paws more.

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Old 10-31-12, 04:32 PM   #10
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So, to clarify, in my humble opinion:

Once you get your saddle height and setback situated (your foundation) the next step is to put your hands over the front axle. Choose the right frame/bar/stem combo to do that.

If you have to stretch uncomfortably to get your hands over the front axle, that means that your top tube is too long. Many people (shorter men and women) sometimes have to run a really short stem like 80-90mm and this adversely affects the handling. It could be argued that they would be better off on a 650c bike.

If you feel cramped when your hands are over the axle and you want more reach, that means that your top tube is too short. Many really tall guys deal with this. Instead of running 140+ mm stems, they simply have to bend their elbows...A LOT.



Or get a custom frame built.
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Roadies can run tempo all year as that's what humans were designed for. If you want to be a cheetah, lay around and lick your paws more.

Last edited by carleton; 10-31-12 at 04:37 PM.
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Old 10-31-12, 05:06 PM   #11
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60mm isn't ideal for all situations...also as illustrated in the article. Sprint bikes (like the LOOK 496 and Dolan DF3) seem to have settled on 74.5 degree head tubes with 30-35mm rake forks. Pursuit bikes (like the LOOK 596 and Felt TK1) have 40mm rake forks. This makes the pursuit bikes more stable when in aerobars.
I'm pretty sure that a lower rake is more stable.
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Old 10-31-12, 05:16 PM   #12
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I'm pretty sure that a lower rake is more stable.
I've ridden the TK1 (40mm), 496 (34mm), and DF3 (30mm). All have 74.5 degree head tubes. The TK1 (40mm) was the most stable. It was great for riding in aerobars in a straight line dead-set on the black line, but sluggish for sprint maneuvering like diving into a flying 200M.
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Roadies can run tempo all year as that's what humans were designed for. If you want to be a cheetah, lay around and lick your paws more.
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Old 10-31-12, 06:16 PM   #13
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So, to summarize, steeper hta/less fork rake results in a twitcher ride, while more rake and a relaxed hta nets a stabler line?
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Old 10-31-12, 07:20 PM   #14
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So, to summarize, steeper hta/less fork rake results in a twitcher ride, while more rake and a relaxed hta nets a stabler line?
Yes.

For example. Look at this ad for a BT Stealth: http://www.fixedgearfever.com/module...wtopic&p=73228



BT makes 2 forks for that frame. A Sprint fork and a Pursuit fork.

Quote:
Top tube - 57cm
Head tube - 90mm
Seat Tube angle - 74deg
Head Tube angle - 74deg

Sprint fork rake - 37mm
Pursuit fork rake - 40mm
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Roadies can run tempo all year as that's what humans were designed for. If you want to be a cheetah, lay around and lick your paws more.

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Old 10-31-12, 07:44 PM   #15
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Interesting. How much of a difference can 3mm make?
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Old 10-31-12, 08:20 PM   #16
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Interesting. How much of a difference can 3mm make?
For most of us, not much. None of these angles or measurements will make anyone faster or slower. Now it's about feeling.

When you are doing A/B testing you'll feel the difference. In A/B testing, one is always better than the other.

All of these little angles and measurements add up. My track bike is setup as a dedicated, full-on sprint bike. I've tried to do some sprint type efforts on my road bike (Tarmac). It feels god-awful. Bad...just bad.

You'll notice that the numbers are all very similar for bikes in each different category (sprint, mass start, pursuit). These angles and measurements are the result of years of trial and error by builders and athletes.

But, as with any activity, we won't notice the differences until we've done it enough. A newbie guitarist won't have a preference of fretboard width or string gauge. But, as as time goes on, he/she will like this over that...
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Old 10-31-12, 08:27 PM   #17
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This is also why I think the Cervelo T3 fell out of favor with some people. Angles.

Most people in the market for a Cervelo T3 (also known as P3 Track) have an idea of what they want. It was a fairly popular bike for a while, then it fell out of favor. A teammate of mine (Cat1 road, World masters silver) bought one brand new and rode it for a month and didn't like it. Said that it felt weird in mass start races. He bought a Felt TK1 and has been riding it for 3 seasons already.
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Roadies can run tempo all year as that's what humans were designed for. If you want to be a cheetah, lay around and lick your paws more.
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Old 10-31-12, 08:33 PM   #18
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That makes a lot of sense. Thanks.
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Old 10-31-12, 08:44 PM   #19
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Sorry to ramble on...

But some people just don't have a preference and can still kick lots of butt. I watched a pro roadie come to our track and use the $400 steel loaner bike to absolutely slaughter the field.

To continue the guitar analogy. Here is an excerpt from an interview in Bass Player magazine:

Quote:
"I went into a guitar shop in America a few years ago," he replies, putting down the big bass, "and some guy said, 'What kind of bass strings do you use, Paul?' I said, 'Long shiny ones.'

"I don't know the model names of basses," he laughs, "I don't know about amps, I don't know about serial numbers. People say to me [adopts haughty voice]: 'I've got a *fantastic* L35.' I say, 'Oh... yeah?' It could be a motorbike for all I know. I'm just not like that, you know? With us it was always just Vox, Hofner--I never really got into the analytical end of it."
That was Paul McCartney
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Roadies can run tempo all year as that's what humans were designed for. If you want to be a cheetah, lay around and lick your paws more.
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Old 10-31-12, 10:58 PM   #20
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Leonard Zinn talking about rake and trail:
http://velonews.competitor.com/2004/...il-offset_7322

"Dear Lennard,
I’m looking upgrade to a carbon fork with 43mm rake from an aluminumfork with 40mm rake. How will the change in rake affect the bike’s handling?Will increasing the wheelbase make it more stable?
Eric


Dear Eric,
No, it will make it faster turning and less stable, albeit with a largerturning radius. The attached“block” from my book should help clarify it.
Lennard"
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Old 10-31-12, 11:02 PM   #21
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I've used a 40mm and 37.5mm rake forks on the same bike and I found the latter to be noticeably less twitchy.
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Old 11-01-12, 12:11 AM   #22
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Extremely helpful and insightful carleton, thanks. You've pretty much nailed all the questions I was about to ask. And thanks to all for the helpful input.
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Old 11-01-12, 07:08 AM   #23
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I've used a 40mm and 37.5mm rake forks on the same bike and I found the latter to be noticeably less twitchy.
Yes, that makes sense. Less rake means more trail.
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Old 11-01-12, 02:32 PM   #24
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Interesting. How much of a difference can 3mm make?
On the road, no real difference.

On the track, it was huge. Adding 4.5mm fork offset made the bike hard to ride in a straight line. It was just all over the place, which is not what you want when you are riding in very tight formation at speed on the track. It was too twitchy to work well on the track.

Kato (and Lennard) said it well (but for a street bike, anything under 5mm is going to be unnoticeable by most people.)
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Old 11-01-12, 02:36 PM   #25
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They thought I was a wizard.
But you are a wizard! (IMHO)
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