Bicycle Mechanics - Steering is too twitchy, what can I do?

Will a longer raked fork make a big difference? :(

How long do rakes get (or "trail", or whatever it's called)?

Take a look at this site :
http://www.phred.org/~josh/bike/trail.html

Will a longer raked fork make a big difference? :(

How long do rakes get (or "trail", or whatever it's called)?

I believe that if you want to increase stability, you want to *decrease* rake, not increase it. Actually, you want to increase the trail, but if you consider head tube angle and tire size fixed, decreasing rake is the only way to do this.

Will a longer raked fork make a big difference? :(

How long do rakes get (or "trail", or whatever it's called)?

Before you do anything, check your headset adjustment. The handlebar should flop from side to side by itself if you lean your bike over. A too tight headset will handle very twitchy.

If that's not it, then you need to get a "straighter" fork to relax your steering.

What is the head angle of the bike? It is impossible to determine if a shorter or longer fork will make your bike less "twitchy" without considering the head angle and geometry of the bike.

Of course it could be a mechanical problem, and you should eliminate those variables first.

Stable equals low BB height there for you need less rake or you should work on your riding position.

What is the head angle of the bike? It is impossible to determine if a shorter or longer fork will make your bike less "twitchy" without considering the head angle and geometry of the bike.

Of course it could be a mechanical problem, and you should eliminate those variables first.

Not sure about the head tube angle. Someone's looking at it today

Is this a new bike? If so, maybe you need more time to get used to it. I found my road bike too twitchy after I first got it, but over the course of a few hundred miles I am now finding it perfect.

Is this a new bike? If so, maybe you need more time to get used to it. I found my road bike too twitchy after I first got it, but over the course of a few hundred miles I am now finding it perfect.

Yeah, it's new, but I bought a frame only -- no fork, so I'm not sure what fork is the ideal match.
I've been riding it for a week, and it still feels a bit unstable, especially if I relax my hands on the bars, or take one hand off.

What if I put on an Ouzo Pro with a 50mm rake?

What if I put on an Ouzo Pro with a 50mm rake?

Suggest you do a google search for rake and trail. Then you'll know "what" and you won't have to guess. 50 mm sounds pretty extreme and very unstable. Try 43 mm for a 72 to 73 degree head tube.

Al

What if I put on an Ouzo Pro with a 50mm rake?

To obtain what is called "neutral" steering, a 50mm fork would work well with a 72 deg head angle. Neutral steering means that the bike will respond to deliberate input you put into the front end instead of having a tendency to oversteer when you make subtle changes in your position like reach for a water bottle or take your hands off the bars. Some people consider neutral steering "slow" because the bike only does what you tell it to do.

A bike with a 73 deg head angle achieves neutral with a 45 mm fork rake, and the steeper the head angle, the shorter the rake as a rule, so a 74 likes a 40, so on and so on. Of course a few millimeters may not have a huge difference on handling, but the difference between a 40 and a 50 mm fork can be quite pronounced on a bike.

In general, the shorter you make a fork in relation to the head angle, the longer the trail. The longer the trail, the less likely a bike is to oversteer, or be twitchy. If you make the trail too long, the bike will be slow to turn at low speed, stable at high speed, but not very quick handling at high speed. If you make the trail too short, it will be quicker handling at low speed and very sensitive to rider input at high speed(twitchy). So if you put a long rake(50mm) on a steep head angle(74), you will shorten the trail and you will get a twitchy front end.

The other measurement to consider is the measurement from the fork crown race seat to the front axle center. A bike is designed to sit at it's correct head angle with a specific fork crown race/axle center dimension. If you buy a fork that is 5mm longer than what a frame is designed to accomodate, the front end will sit higher, which effectively reduces the head angle some. If you buy a fork that is 5mm shorter, the front end will sit lower, which effectively increases the head angle some.

The Reynolds Ouzo Pro with a 50mm rake has a 372mm fork crown race to axle center dimension. You can measure the fork that came with your bike and see what it is to see if it is the same.

Notice the dimension "F" on this frame specification chart. This dimension is the fork length. That is the dimension I'm referring to. As you can see, these frames were designed to take a fork 367mm long to maintain the designed head angle.

http://cbike.com/colnagospecs.htm

Just a word of caution: 9 out of 10 bike mechanics will look at you like you are speaking Inuit if you ask them these questions. Be prepared to do the measurements or research them yourself.

The other measurement to consider is the measurement from the fork crown race seat to the front axle center. A bike is designed to sit at it's correct head angle with a specific fork crown race/axle center dimension. If you buy a fork that is 5mm longer than what a frame is designed to accomodate, the front end will sit higher, which effectively reduces the head angle some. If you buy a fork that is 5mm shorter, the front end will sit lower, which effectively increases the head angle some.

The Reynolds Ouzo Pro with a 50mm rake has a 372mm fork crown race to axle center dimension. You can measure the fork that came with your bike and see what it is to see if it is the same.

Notice the dimension "F" on this frame specification chart. This dimension is the fork length. That is the dimension I'm referring to. As you can see, these frames were designed to take a fork 367mm long to maintain the designed head angle.

http://cbike.com/colnagospecs.htm

Just a word of caution: 9 out of 10 bike mechanics will look at you like you are speaking Inuit if you ask them these questions. Be prepared to do the measurements or research them yourself.


Seeing as how we're picking nits here regarding fork lengths and such...Reynolds, along with most other fork manufactuers, measure fork length parallel to the steerer tube. This is different than Colnago's "F" dimension which discribes fork length from the crown to the axle. A Colnago fork is actually 364.5 mm when measured the same way Reynolds does.

Sorry to pick, the post is very good overall. Fork length is one of my pet peeves and I've done a lot of study on the lengths of various aftermarket forks.

Ed

Seeing as how we're picking nits here regarding fork lengths and such...Reynolds, along with most other fork manufactuers, measure fork length parallel to the steerer tube. This is different than Colnago's "F" dimension which discribes fork length from the crown to the axle. A Colnago fork is actually 364.5 mm when measured the same way Reynolds does.

Sorry to pick, the post is very good overall. Fork length is one of my pet peeves and I've done a lot of study on the lengths of various aftermarket forks.

Ed

This has always been a pet peeve of mine as well. The whole fork as component concept leaves me cold. It just has to much to do with handling and ride for me to consider it something other than an integrated part of the frame.

But when you say that Reynolds measures parallel to the steerer tube, do you mean the center/axis of the steerer tube? If so, this would put the measurement to an imaginary line drawn from the ctr of the frt axle at what angle? 90 deg to the fork blade ctr? or 90 deg to the steerer axis? Just curious because I contacted Reynolds recently and asked them for the dimension from the fork crown race seat to the frt axle ctr in a straight line on their 50mm fork and they told me it was 372mm.

This has always been a pet peeve of mine as well. The whole fork as component concept leaves me cold. It just has to much to do with handling and ride for me to consider it something other than an integrated part of the frame.

But when you say that Reynolds measures parallel to the steerer tube, do you mean the center/axis of the steerer tube? If so, this would put the measurement to an imaginary line drawn from the ctr of the frt axle at what angle? 90 deg to the fork blade ctr? or 90 deg to the steerer axis? Just curious because I contacted Reynolds recently and asked them for the dimension from the fork crown race seat to the frt axle ctr in a straight line on their 50mm fork and they told me it was 372mm.


Measurement is per the diagram shown below.

For some good info regarding how fork length affects head angle, check out the following link. http://www.sheldonbrown.com/rinard/forklengths.htm

this is it!

The old Kinesis fork is the third fork in a week. I've also tried the Profile-Design BSC and the locally made alu.

Today I put in a heavier stem (12cm 3ttt) and bars (old ITM Pro 260) which I think has made more difference than anything.

Does the BSC fork have very little rake, or is it just a bad photo?

Does the BSC fork have very little rake, or is it just a bad photo?


Profile forks such as the BSC and BRC have 43 mm of rake, or offset if you prefer.

Measurement is per the diagram shown below.

For some good info regarding how fork length affects head angle, check out the following link. http://www.sheldonbrown.com/rinard/forklengths.htm

Ok. Actually this measurement is a little unwieldy for the LBS or the home mechanic. You need to mount the fork in a fixture, ideally on an alignment table to be sure it's level, then locate a vertical line off the fork crown race seat and off the front axle using machinist squares, then measure that:rolleyes: . This is good in the frame shop if you're prefitting unbrazed blades to a crown in a fixture and trimming at the top for correct length.

I think Colnago's method is much more end user friendly, although it may not be the industry standard. But then, when did the industry do anything just because it made things more end user friendly? ;)

Thanks for the link. :)

To obtain what is called "neutral" steering, ...(snip)...yourself.

Great explanation, Don D - thanks!

Profile forks such as the BSC and BRC have 43 mm of rake, or offset if you prefer.

It's disappointing that the Profile-Design web-site does have rakes (well, I couldn't find them).
In my opinion, a lot of these companies don't appreciate what total "gear geeks" we are. I cannot get enough information on something I wanna buy.

Infact, I think most companies are of the opinion that we're more impressed with 'dazzle and bull' than cold hard facts; you've just gotta check the Scapin site (http://www.scapin.com). All those jazzy pictures take ages to load....blah blah........what was I talking about? :) Oh yeah, light steering. Hmmm.

Get a larger tire with a round profile.

I just want my thread back up the top of the list :D

Will a longer raked fork make a big difference? :(

How long do rakes get (or "trail", or whatever it's called)?


It's your bars. Youve got them at a bizzare angle.

It's your bars. Youve got them at a bizzare angle.

It's not a good photo, and the wheel is slightly turned; the bottoms of the drops are 'dead' parallel with the top tube

I just want my thread back up the top of the list :D


There is only one thing you can do at this point to slow the steering; install a longer fork, hopefully with less rake. Some of the longer forks on the market are the Reynolds models and Alpha Q (longest). The longer fork with raise the front end of the bike up decreasing head angle. Less rake will increase trail; 40 mm is the least amount commonly available.

Good luck.

Ed

It's not a good photo, and the wheel is slightly turned; the bottoms of the drops are 'dead' parallel with the top tube That's the "weird" part, I think. At my fitting, they recommended (IIRC) 10-12 degrees. YMMV. You may have to reposition the brifters to compensate.

I would heartily recommend that you get an angle finder and find out the head tube angle on that bike before you make any more changes to the front end. Or find a shop that has one and have them check it. The best way to do it will be to mount the bike so the top tube is level(if it's not a compact frame) and put the angle finder on the front of the head tube. Then go from there. An angle finder is usually available at any home improvement store for ~$10-20. Or you can get one here:

www.biketoolsetc.com

Type angle finder into the search engine.

And your handlebar setting is fine if that's how you like them.

I would heartily recommend that you get an angle finder and find out the head tube angle on that bike before you make any more changes to the front end.


First off, angle finders like the type shown are not very accurate; it's easy to be off by a degree or more when using one (I know because I own one). Second, it doesn't matter what the head tube angle is since 531Aussie thinks the steering is too fast. The only answer is to slacken the head angle from where it is currently and make sure the trail is maximized by using a fork with the minimum amount of rake available.

Ed

First off, angle finders like the type shown are not very accurate; it's easy to be off by a degree or more when using one (I know because I own one). Second, it doesn't matter what the head tube angle is since 531Aussie thinks the steering is too fast. The only answer is to slacken the head angle from where it is currently and make sure the trail is maximized by using a fork with the minimum amount of rake available.

Ed


My only concern for 531 is for is time and money. Hate to see him waste any more time and money than he has to, and getting some numbers first could help avoid this. Your idea for a longer fork is a good idea though if that is in fact what he needs.

I also have an angle finder and have used it to confirm angles on all the eight bikes I currently own and have found it to be dead on with the manufacturers specs. I used one for years in the bike biz and found them to be accurate also, so possibly it's the angle finder??

Cheers. :)

The only answer is to slacken the head angle from where it is currently and make sure the trail is maximized by using a fork with the minimum amount of rake available.Ed

I don't get it (obviously :) ). Doesn't a smaller rake shorten the distance between the bottom bracket and the front axle, therefore making the steering even lighter?

Will a longer raked fork make a big difference? :(

How long do rakes get (or "trail", or whatever it's called)?

Long rake fork = smoother ride.

Shorter/tighter rake fork = tighter, more responsive turning.

Old techno - concept remains the same.

I would heartily recommend that you get an angle finder and find out the head tube angle on that bike before you make any more changes to the front end. Or find a shop that has one and have them check it. The best way to do it will be to mount the bike so the top tube is level(if it's not a compact frame) and put the angle finder on the front of the head tube. Then go from there. An angle finder is usually available at any home improvement store for ~$10-20. Or you can get one here:

www.biketoolsetc.com

Type angle finder into the search engine.

And your handlebar setting is fine if that's how you like them.

Tool? I can see it from here. Unless the natural bend of this guys wrists is 45 degrees I'm right and thats all there is to it. He could put on the forks off of Captain americas chopper or a tricycle and will still be fishing for a strait line. Honestly why do people question my advice? Did you waste your money on that tool?

I promise you, the bottom of my bars are about one degree flatter than this. The photo I posted is obviously crappy

http://www.cyclingnews.com/tech.php?id=photos/2003/tech/features/PRGW/bike_ch1825

I don't get it (obviously :) ). Doesn't a smaller rake shorten the distance between the bottom bracket and the front axle, therefore making the steering even lighter?


Shortening rake does move the wheel backward slightly, but more importantly, it increases the TRAIL. This is the important dimension that determines how fast the bike steers.

Shortening rake does move the wheel backward slightly, but more importantly, it increases the TRAIL. This is the important dimension that determines how fast the bike steers.

Does it increase trail by raising the front end, as a longer fork does?(http://www.sheldonbrown.com/rinard/forklengths.htm)

Otherwise, I can't understand how it would occur :)

Does it increase trail by raising the front end, as a longer fork does?(http://www.sheldonbrown.com/rinard/forklengths.htm)

Otherwise, I can't understand how it would occur :)


A longer fork will raise the front end and cause the head tube angle to slacken thus increasing trail (good to slow the steering).

Long rake fork = smoother ride.

Non. Rake has little effect on ride. Only materiel and tire will effect ride.


Shorter/tighter rake fork = tighter, more responsive turning.

Non. A "responsive" cycle is a less stable cycle. More stable means less responsive, but more predictable. Therefore, a shorter offset (or, as you english call "rake") will make a cycle less responsive, but more stable.

A larger dameter tire will help!

I promise you, the bottom of my bars are about one degree flatter than this. The photo I posted is obviously crappy

http://www.cyclingnews.com/tech.php?id=photos/2003/tech/features/PRGW/bike_ch1825

Its probably just me. I'm getting confused over the whole rake thing. I do know that I am very picky at the angle of my bars and at that angle your steering would seem twitchy to me both on the top and bottoms..

Update (in case anyone's interested):

I've just tried the fourth combination in a week: the heavier, longer
stem (12cm 3ttt quill) with my longest raked forks (alu), and I think
that's the best I can do without splashing out big money. It's better,
but still less than ideal.

I've gotta say, I'm still a little disappointed; being a Scapin and all. :(
I also bought the frame planning to use the 11cm stem, so now I'm a bit
stretched out, and with my aging back, it's a bit of a shame.

Thanks for all the tips :)

I guy at my shop had speed-wobble problems on a large Pinarello, and they
sold him what they desribed as the softest, longest all-carbon Mizuno fork
they could get, and he was happy with the results.

Maybe I should do the same, but the Mizuno fork was ~$310 US.

Update (in case anyone's interested):

I've just tried the fourth combination in a week: the heavier, longer
stem (12cm 3ttt quill) with my longest raked forks (alu), and I think
that's the best I can do without splashing out big money. It's better,
but still less than ideal.


At the risk of sounding like an A$$, why don't you listen to the advise listed here and read up on what TRAIL is? Several posters, including myself, suggested you try to INCREASE trail to help slow down the steering on your Scapin. By installing the "longest raked forks", you're DECREASING trail compared to a fork with a shorter rake. Don't worry if a less raked fork shortens the wheel base slightly, it will increase the trail which is FAR FAR more important.

Done now. What a crazy thread!

Ed

nessism, you are correct. to find the trail, drop a plum bob from the front hub. mark that spot on the ground. now, draw a line continuing the headtube until it hits the ground. the distance between the first mark and the second mark on the ground are the trail. the longer the trail, the slower the steering.

trust me, you want the fork with the least rake.

Long rake fork = smoother ride.

Shorter/tighter rake fork = tighter, more responsive turning.

Old techno - concept remains the same.

you are wrong.

a fork with a long rake needs a shallow head tube to handle slow.

At the risk of sounding like an A$$, why don't you listen to the advise listed here and read up on what TRAIL is? Several posters, including myself, suggested you try to INCREASE trail to help slow down the steering on your Scapin. By installing the "longest raked forks", you're DECREASING trail compared to a fork with a shorter rake. Don't worry if a less raked fork shortens the wheel base slightly, it will increase the trail which is FAR FAR more important.

Done now. What a crazy thread!

Ed

:) This must be frustrating.

I haven't been ignoring the "trail" advice -- I appreciate it, and I read the Shledon Brown stuff, etc.

My big problem is money, so I've only been able to experiment with the equipment I've got, and whatever the 2nd hand shop will lend me. The price of good carbon forks in Australia is a joke; Ouzo Pros and Columbus Muscles retail for about $550 US.

It's probably for reasons other than rake that the best handling fork just happens to be one that has my front wheel further away from my BB.

Long rake fork = smoother ride.

Shorter/tighter rake fork = tighter, more responsive turning.

Old techno - concept remains the same.


you are wrong.

a fork with a long rake needs a shallow head tube to handle slow.

Hmmmm, surely you can see the bind I'm in :)

:) This must be frustrating.

I haven't been ignoring the "trail" advice -- I appreciate it, and I read the Shledon Brown stuff, etc.

My big problem is money, so I've only been able to experiment with the equipment I've got, and whatever the 2nd hand shop will lend me. The price of good carbon forks in Australia is a joke; Ouzo Pros and Columbus Muscles retail for about $550 US.

It's probably for reasons other than rake that the best handling fork just happens to be one that has my front wheel further away from my BB.


Find a local framebuilder and have them make you a STEEL fork. They should be able to taylor the ride quality, length, rake, ect. so meet your needs.

Good luck.

Ed

If you do not understand the geometry and physics behind head angle, offset and trail, you will not be able to make an intelligent decision for your fork. Please contact a good mechanic or frame builder, or ask a vehicle engineer for advice. Many people here are giving incorrect advice, and such a place is not where you should ask for important advice like this.

Fork length is one of my pet peeves and I've done a lot of study on the lengths of various aftermarket forks.

Ed

Hi Ed,
I saw you post at Bikeforums. I'm considering a Scott CR1 but might choose a different fork than the Scott but I do not want my BB to be lower than original since I use 180mm cranks.
The Scott, as far as I know, is 375mm long? Measured parallel to the steerer from the crown race to the center of the axle?
Alternatives I am looking at are the Reynolds Ouzo Pro INTEGRATED (might differ from the normal one?), and the Time Avant Stiff.
Have you perhaps measured these? And do you know of any other forks in this length range?
Thanks in advance,
John

If the bike is merely twitchy to handle but flies straight, try a longer stem. It slows the control responses a little bit. On mine I reduce the length of the stem specificly to make them more sensitive.

Yes that was a good explanation up at the begining. :)