Road Bike, Cycling Forums banner
1 - 20 of 32 Posts

·
Registered
Joined
·
75 Posts
7

weiwentg said:
I'm getting a custom (Seven), and I need a primer on what affects bike handling. I want handling suitable for a stage race, but not necessarily a criterium. what variables go in?
I'd recommend talking directly to Seven about your requirements, tell them what you plan to do with the bike and let them come up with a design, then have them explain.
 

·
Registered
Joined
·
1,108 Posts
Discussion Starter · #3 ·
bostonkiwi said:
I'd recommend talking directly to Seven about your requirements, tell them what you plan to do with the bike and let them come up with a design, then have them explain.
that's precisely why I asked the question - I'd strongly prefer to know what I'm talking about before discussing the design with them.
 

·
Registered
Joined
·
10,160 Posts
anvil site is confusing....

Anvil's comments about fork rake and trail are confusing to most folks. He makes comments about fork rake that sound backward, until you realize that he is talking about a FIXED amount of trail. He fails to note that a change in the head tube angle is required to keep a FIXED trail, while changing the fork rake.

More fork rake or (numerically) larger head tube angles both quicken the steering by reducing trail. Less fork rake or (numerically) smaller head tube angles slow the steering by increasing trail.

The formula for trail is: trail = R/ tanH - (rake/sinH), where R is the tire radius and H is the head tube angle. The anvil site offers an alternate formula that produces the same answer, but is not as straightforward. This formula breaks trail into two portions. The first half of the equation is the trail without the effect of fork rake. The second half is the reduction in trail due to the fork rake. All rake reduces trail and quickens the steering, so the more rake, the quicker the steering.

The generally accepted range for trail is 55-67mm. Colnagos will have more trail than just about anyone else. I have bikes at both extremes and like less trail, except in gusty winds, when the quick steering makes the bike with less trail difficult to handle.
 

·
Registered
Joined
·
5,558 Posts
C-40 said:
Anvil's comments about fork rake and trail are confusing to most folks. He makes comments about fork rake that sound backward, until you realize that he is talking about a FIXED amount of trail. He fails to note that a change in the head tube angle is required to keep a FIXED trail, while changing the fork rake.

More fork rake or (numerically) larger head tube angles both quicken the steering by reducing trail. Less fork rake or (numerically) smaller head tube angles slow the steering by increasing trail.

The formula for trail is: trail = R/ tanH - (rake/sinH), where R is the tire radius and H is the head tube angle. The anvil site offers an alternate formula that produces the same answer, but is not as straightforward. This formula breaks trail into two portions. The first half of the equation is the trail without the effect of fork rake. The second half is the reduction in trail due to the fork rake. All rake reduces trail and quickens the steering, so the more rake, the quicker the steering.

The generally accepted range for trail is 55-67mm. Colnagos will have more trail than just about anyone else. I have bikes at both extremes and like less trail, except in gusty winds, when the quick steering makes the bike with less trail difficult to handle.
Good info, C40. I admit this stuff kind of makes my head hurt.

For example, Tom Kellogg's statement here is a bit confusing:

http://www.spectrum-cycles.com/612.htm

"For some frame designers though, it is not always that simple. For example, look at the way Eddy Merckx designs most of his frames. He usually uses less trail than the "ideal" as he did much of his racing on the pave and likes the way a low trail frame tracks under really horrible conditions. Granted, they do not act as consistently under a variety of speeds on good roads, but they really work on northern Europe's country tracks."

What I notice about my Merckx is that it is a bit squirelly at lower speeds but really solid feeling at higher speeds. It also corners great and it feels like you can make minute adjustments to your line mid-corner. However, I would not feel comfy taking it onto fire roads like I do with my other road bike, which is more neutral.

One thing that seems to get lost in a lot of these discussions, and plays a big role to me anyway, is wheelbase. To me, a bike with neutral trail and a short wheelbase is gonna feel more squirelly than a bike with lower trail and a longer wheelbase (like the Merckx). Ultimately I feel like I want the right wheelbase for me, the right weight distribution (front-center or whatever--I've never really studied this, though), and a bike that feels stiff and solid under hard braking (I like a rock solid fork).
 

·
Banned
Joined
·
781 Posts
Sometimes, when I'm riding across campus,

I see some tail, and I twist my head angle around to ogle it, and the bike veers off ... Wait, that's not what you meant, was it?
 

·
All-purpose bike...
Joined
·
80 Posts
How much is too much, how small is too small?

I've been aggresively researching this topic, but trying to apply it to fixing an issue I have with a mountain bike. My favorite bike, a Seven cross bike, has a trail ranging from 57 mm (with 23c tires) to 60 mm (with 35c cross tires). I've descended mountain passes with both types of tires at 50 mph and it's stable as a rock -- more stable than my previous bike, a Merlin road bike with 57 mm of trail with 23c tires. I chalk that up to wheelbase -- the cross bike being several cm longer than the road bike. But for me, the 3 mm change in trail on the cross bike with different tires is not noticeable.

On the other hand, my Moots YBB mtb has at least 72 mm of trail and is a complete dog in the corners and in tight single track. I intend to decrease the trail by getting a fork with increased rake so that the trail is reduced to 60 mm of trail. I've received dire warnings from Moots and Merlin that it is a bad idea, even disregarding the loss of suspension. Of course they offered a blanket condemnation without explaining themselves. On the other hand, Seven, Zinn, and Black Sheep have indicated it would definitely be different, but not necessarily bad and even excellent depending on me and the terrain I ride. Lennard Zinn and Seven were very clear on the fact that "trail is trail" regardless of what combination of head angle and fork get you to that trail. However, the feel of the front end with a given trail will differ depending on what your rake is (less rake being often percieved as a stiffer ride). I note again that wheelbase has a significant impact on the stability of the ride -- longer be more stable.

Finally, I recently read a junior paper by a Princeton student that measured the torque forces on a bike to test some mathematical descriptions of the forces that keep a bike moving in a straight line. It supported the idea that even a bike with small trail will become more stable as the speed goes up, and at a high enough speed even a bike with a very small trail measurement will become quite stable.
 

·
Registered
Joined
·
10,160 Posts
sure you want a custom???

If I remember correctly, you're a small, light rider. I'm 5'-6.5" tall and weigh about 135. I ride frames in the 53-55cm (c-t) range. I see little benefit in ordering a custom frame myself. I'm so light that I place little demand on any frame. I have a long 83cm inseam and short torso, but even with my saddle moved far back for climbing, I can still use a respectable length 100-110mm on most stock frames.

Unless you know of a specific geometry that you've tried and feel is perfect and you're trying to duplicate it, I don't see the point. I've read several reports from folks who ordered a custom and were disappointed because they never tried the proposed geometry or anything close to it before.
 

·
Registered
Joined
·
5,558 Posts
PT said:
I've been aggresively researching this topic, but trying to apply it to fixing an issue I have with a mountain bike. My favorite bike, a Seven cross bike, has a trail ranging from 57 mm (with 23c tires) to 60 mm (with 35c cross tires). I've descended mountain passes with both types of tires at 50 mph and it's stable as a rock -- more stable than my previous bike, a Merlin road bike with 57 mm of trail with 23c tires. I chalk that up to wheelbase -- the cross bike being several cm longer than the road bike. But for me, the 3 mm change in trail on the cross bike with different tires is not noticeable.

On the other hand, my Moots YBB mtb has at least 72 mm of trail and is a complete dog in the corners and in tight single track. I intend to decrease the trail by getting a fork with increased rake so that the trail is reduced to 60 mm of trail. I've received dire warnings from Moots and Merlin that it is a bad idea, even disregarding the loss of suspension. Of course they offered a blanket condemnation without explaining themselves. On the other hand, Seven, Zinn, and Black Sheep have indicated it would definitely be different, but not necessarily bad and even excellent depending on me and the terrain I ride. Lennard Zinn and Seven were very clear on the fact that "trail is trail" regardless of what combination of head angle and fork get you to that trail. However, the feel of the front end with a given trail will differ depending on what your rake is (less rake being often percieved as a stiffer ride). I note again that wheelbase has a significant impact on the stability of the ride -- longer be more stable.

Finally, I recently read a junior paper by a Princeton student that measured the torque forces on a bike to test some mathematical descriptions of the forces that keep a bike moving in a straight line. It supported the idea that even a bike with small trail will become more stable as the speed goes up, and at a high enough speed even a bike with a very small trail measurement will become quite stable.
Is there any chance that your YBB is just too big? Maybe too much wheelbase?

My Bontrager mtb, which had a lot of trail with his special crown, was incredible in tight singletrack--so that goes against that theory. But the bike was designed to put your weight forward, so while it was great for technical climbs, it was an endo-machine on steep, technical descents. So I guess I'm saying you have to look at the whole package, not just one element. For me an Ibis Mojo fit me right and had the whole package I was looking for. There seems to be a lot more voo doo with mtbs--you can do a lot with setup, but if it's too big or too small it's probably not gonna work for you.
 

·
All-purpose bike...
Joined
·
80 Posts
Interesting idea...

Henry Chinaski said:
Is there any chance that your YBB is just too big? Maybe too much wheelbase?

There seems to be a lot more voo doo with mtbs--you can do a lot with setup, but if it's too big or too small it's probably not gonna work for you.

That is a possibility, but I do know things got worse in some ways when I went from a SID with a rake of probably 42 mm (but I'm not sure about my particular model) to a Manitou with a rake of 38.1 mm which was also too tall for my era of frame. There was a big increase in trail going to the Manitou and now the front end "drifts" when climbing and doesn't dive through corners. I have an old Bridegstone MB1 that I ride a lot (rigid) with a trail of 66 mm that is pretty quick. Both bikes were endo machines until I raised the bars to only about an inch below saddle height. The front center of the Moots and the wheel base are large in comparison to the cyclocross bike or the MB1, both of which are much better bikes on the trail when suspension isn't an issue. So maybe the Moots is too large...
 

·
Registered
Joined
·
12 Posts
C-40 said:
Anvil's comments about fork rake and trail are confusing to most folks. He makes comments about fork rake that sound backward, until you realize that he is talking about a FIXED amount of trail. He fails to note that a change in the head tube angle is required to keep a FIXED trail, while changing the fork rake.

More fork rake or (numerically) larger head tube angles both quicken the steering by reducing trail. Less fork rake or (numerically) smaller head tube angles slow the steering by increasing trail.

The formula for trail is: trail = R/ tanH - (rake/sinH), where R is the tire radius and H is the head tube angle. The anvil site offers an alternate formula that produces the same answer, but is not as straightforward. This formula breaks trail into two portions. The first half of the equation is the trail without the effect of fork rake. The second half is the reduction in trail due to the fork rake. All rake reduces trail and quickens the steering, so the more rake, the quicker the steering.
I bolded the word "given" for you so you won't get confused. The idea behind that doc is to discuss the effect those specific variables have on geometry, seperate from each other. So, if you want to talk about the effect rake/offset has on handling, you fix one aspect (in this example, trail, being the product of HTA, tire radius and offset) and isolate just the affect of rake/offset. If you want to talk about the effects of HTA or trail specifically, you need to have a fixed reference point also.

Your second paragraph is a good illustration of this, it just doesn't paint the whole picture. More rake for a given HTA does reduce trail and make for quicker steering, but if you decreased the HTA while you added rake, you may not notice any difference or if taken far enough, see the opposite result that you've stated. You don't want somebody to think that because bike A has 45mm offset and bike B has 40mm that bike A has the quicker steering. See my point here?

As for the formula, well frankly, it really seems you're just trying to pick the peanuts out of my sh!t, much as I am now by saying you're wrong that all rake reduces trail. Not all rake in the bike world is positive. Savvy the burrito? ;)
 

·
Registered
Joined
·
132 Posts
weiwentg said:
I'm getting a custom (Seven), and I need a primer on what affects bike handling. I want handling suitable for a stage race, but not necessarily a criterium. what variables go in?
Just a few questions:
what do you ride now?
what size frame?
what trail?
how long is the stem?
how long TT?
how does bike behave leaning into corners?
- is it stable/climbs out/dives in?
- at low/moderate/high speed?
how do you want steering to change?
would you prefer bike with shorter TT?
longer chainstays?
do you like to push saddle back and need post with offset?
or do you ride no-offset seatpost with saddle forward position?
which fork are you putting? Headset?
will the frame be designed to accomodate this fork/headset?

These are no simple questions b/c what can be right in general may not be right for you. There had been links posted above to Tom Kellogg's, Don Ferris' /Anvil/ and Dan Empfield articles, they all present different prospective. Unfortunately some crucial facts like weight distribution, fork height, etc are completely ignored.
 

·
Registered
Joined
·
10,160 Posts
Don't get insulted...

We've had this conversation before, probably a couple of years ago. I still say your formula should be changed. The one you present is not in it's simplest and most meaningful form. As a mechanical engineer, my math teachers taught me to present an answer in it's simplest form. The form that I present allows you to separately see the change in trail due to a change in tire radius, HTA or fork rake.

The majority of people who post on this site are NOT having custom bikes built, so changing the HTA is not an option. What most people want to know is how a fork with a different rake will affect the steering of their bike. They also most often fail to consider the fork length, which may not be the same, since there appears to be no standard for the length of carbon road forks.

As for all rake not being positive, I've never seen a stock fork that wasn't, although someone once posted a picture of a bike with a goofy looking negative rake fork.
 

·
Registered
Joined
·
1,108 Posts
Discussion Starter · #17 ·
very.

I need (OK, want) a titanium road frame with aerodynamic tubing and a steep seat angle. after all the crap I've been through in the last year, including being hit by a pickup truck, staying in the hospital for 2 weeks, and being in a wheelchair for nearly 2 months. if you think I'm wrong in the head, I'll give you my neuropsychologist's contact number. ;)
 

·
Registered
Joined
·
132 Posts
Henry Chinaski said:
Good info, C40. I admit this stuff kind of makes my head hurt.

For example, Tom Kellogg's statement here is a bit confusing:

http://www.spectrum-cycles.com/612.htm

"For some frame designers though, it is not always that simple. For example, look at the way Eddy Merckx designs most of his frames. He usually uses less trail than the "ideal" as he did much of his racing on the pave and likes the way a low trail frame tracks under really horrible conditions. Granted, they do not act as consistently under a variety of speeds on good roads, but they really work on northern Europe's country tracks."

What I notice about my Merckx is that it is a bit squirelly at lower speeds but really solid feeling at higher speeds. It also corners great and it feels like you can make minute adjustments to your line mid-corner. However, I would not feel comfy taking it onto fire roads like I do with my other road bike, which is more neutral.

One thing that seems to get lost in a lot of these discussions, and plays a big role to me anyway, is wheelbase. To me, a bike with neutral trail and a short wheelbase is gonna feel more squirelly than a bike with lower trail and a longer wheelbase (like the Merckx). Ultimately I feel like I want the right wheelbase for me, the right weight distribution (front-center or whatever--I've never really studied this, though), and a bike that feels stiff and solid under hard braking (I like a rock solid fork).
Henry,

have to agree what Tom is saying may sound a bit confusing. However, he is right 56mm gives you "neutral" handling, i.e handling which doesn't depend on speed. Keep in mind that the "neutral" handling may not be "ideal" for a particular rider and that the rest of the frame has profound effect on trail requirements.

Different riders have different preferences some prefer steeper effective STA (no-offset seatposts and seat forward positioning), others prefer shallower STA, some have longer femur some shorter, which if you use KOTS as reference will put CG at different location. To lesser degree CG is affected by higher/lower handlebar position, stem and of cause by upper body weight and pasture.

Second, different frame designers/mfg have different view on what the frame geometry is or should be, and they make them accordingly, so amount of trail right for one frame isn't for other one.

Look for example, uses shallow STA, which puts too much weight over rear wheel. To compensate for twitchiness introduced by light front they design smaller frames with more then "neutral" trail. If you ride one you'd see that it does show all the traits of long trail bike /diving into corner at lower speeds/ but you don't care, b/c at higher speeds it takes corners as on rails, granted that the frame design is the one which suits you.

Merckx are on other side of spectrum. Overall frame design (shorter TT, longer chainstays and stem, etc) puts CG forward, and makes steering slower. There're advantages of "forward" CG, better front tire grip on pave, more even weight distribution, less chances to flat rear tire, etc but it has to be compensated by shorter then "neutral" trail.

Your impression of riding Merckx confirms what Tom is saying: the handling isn't neutral /means the behaviour of bike changes with speed/ but it is ideal /high speed dynamic stability/ for your bike/rider set up.

Hope this helps
 

·
Registered
Joined
·
10,160 Posts
just trying to be helpful...

Since I own two bikes with what most folks would consider radically different geometry, I've had the opportunity to compare the extremes. My Fondriest has a 2cm shorter front-center due to a 1cm shorter TT, steeper (but unspecified) HTA and .5 degree less STA than my Colnago. It also has 2mm more fork rake.

I really don't notice any difference just riding straight down the road or turning corners at moderate speed, but at higher speeds, I kind of like the faster nature of the Fondriest. During a high speed mountain descent, it's more difficult to change your line through a high-speed corner on the Colnago. Once yout get it set, you have to lean into it pretty hard to make a correction, while the Fondriest is easy to change. Both bikes seem perfectly stable up to the highest speeds I've obtained so far (47mph).

I think the Colnago is more stable in gusty winds. The quick steering of the Fondriest makes it tricky to handle in wind gusts.

My point is that a custom should correct known problems with a previous bike. If the head tube was too short and required many steering tube spacers or a high-rise stem, get the right head tube length to produce the bar height you want. Same goes for TT length and STA. Get the angle and length that will center the saddle and use a midsized stem.
 

·
Registered
Joined
·
132 Posts
give me the number

weiwentg said:
I need (OK, want) a titanium road frame with aerodynamic tubing and a steep seat angle. after all the crap I've been through in the last year, including being hit by a pickup truck, staying in the hospital for 2 weeks, and being in a wheelchair for nearly 2 months. if you think I'm wrong in the head, I'll give you my neuropsychologist's contact number. ;)
from what I hear someone needs to make a call :p

Actually sounds you'd better off with "neutral" 56mm trail, steeper STA and lower weight should cancel each other. Just make sure frame is designed for your fork, the diff in height btw Wound Up and rebadged Ouzo Pro is 9mm will result in good .5deg change in HTA/STA and 3-4mm in trail.

And while I agree with C-40 in questioning need for custom bike, you need therapy, and what great therapy nnew cccustom 7 can be! ;)
 
1 - 20 of 32 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top