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Would 15mm change in rake make a difference?

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Would 15mm change in rake make a difference?

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Old 12-05-16, 08:48 PM
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PrinceRein
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Would 15mm change in rake make a difference?

I currently own a Parallax with a rake of 28mm. If I were to get a fork with 43mm of rake, would that make a big difference or just a little difference in terms of toe overlap? Thank you!

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Old 12-05-16, 09:11 PM
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I suspect it would make a noticeable difference. What's the head angle? You'd need that to calculate how much the trail changed, which is what would most affect handling.
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Old 12-05-16, 09:30 PM
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Originally Posted by JohnDThompson View Post
I suspect it would make a noticeable difference. What's the head angle? You'd need that to calculate how much the trail changed, which is what would most affect handling.
The head angle ins 72.5
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Old 12-06-16, 04:37 AM
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From my limited understanding regarding frame/fork geometry.....you might wind up having a "look ma-no hands" handling bike.
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Old 12-06-16, 08:13 AM
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By incrasing the rake, you decrease the geometric trail. Trail makes the bike more stable, but for some riders it can make the bike too stable. I don't think in this case it would make a great difference, with the added rake it would still mave a moderately long trail; possibly the steering would be slightly quicker.

There are a lot of other variables such as tire width and "pneumatic trail" , weight distribution on the bike , the speed at which you generally ride, and the mysterious "flop factor".

Low trail bikes were a mark of many French builders, but the trend was toward longer trail in recent years. However during the last ten or so years low trail has been making a comeback with randonneuring bikes and the folks at Bicycle Quarterly.

There might be someone on the frame builder's forum who has studied and actually designed and built bikes with different geomtries.
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Old 12-06-16, 08:43 AM
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Assuming a 25mm tire and 72.5 head tube angle, right now the OP's trail is 78mm.
Bicycle Trail Calculator | yojimg.net
Going from a 28mm fork to a 43mm fork would bring trail down to 62mm. 60mm is generally seen as a a nice balance between stability and handling.

My experience from doing the exact same thing is that they change would definitely be noticeable. I went from a fork with 28mm rake to one with 41mm on a Bianchi Pista. It was not earth shattering but I could tell the difference in the way the bike handled right away.

The other metric the OP has to look out for is axle to crown distance or ACD. Changing ACD can raise or lower the front of the bike and change the way it handles. I chose a replacement fork which did not change ACD appreciably for this reason. ACD is not always published for replacement forks.


-Tim-

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Old 12-06-16, 09:19 AM
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Based on the numbers from @TimothyH, the OP currently has a high-trail fork (78 mm). That would provide quick but twitchy handling, like on a criterium bike.
The 43 mm rake fork would get the OP to 61 mm of trail, which is in the mid-trail realm. It should provide more neutral handling.
The OP would need to use a highly-raked fork in order to get into the low-trail realm (~<45 mm).
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Old 12-06-16, 09:21 AM
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And since the 2 lines cross above the ground plane, trail changes with tire width/radius..


Lower trail has its purpose and for front loading , porteur racks/ panniers there are people who seek this feature..





...

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Old 12-06-16, 10:24 AM
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Originally Posted by TimothyH View Post
Assuming a 25mm tire and 72.5 head tube angle, right now the OP's trail is 78mm.
Bicycle Trail Calculator | yojimg.net
Going from a 28mm fork to a 43mm fork would bring trail down to 62mm. 60mm is generally seen as a a nice balance between stability and handling.

My experience from doing the exact same thing is that they change would definitely be noticeable. I went from a fork with 28mm rake to one with 41mm on a Bianchi Pista. It was not earth shattering but I could tell the difference in the way the bike handled right away.

The other metric the OP has to look out for is axle to crown distance or ACD. Changing ACD can raise or lower the front of the bike and change the way it handles. I chose a replacement fork which did not change ACD appreciably for this reason. ACD is not always published for replacement forks.


-Tim-
this is good work and I concur.
The rake/trail change will make your bike more stable and let you put a front load on it.
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Old 12-06-16, 11:02 AM
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Originally Posted by Tim_Iowa View Post
Based on the numbers from @TimothyH, the OP currently has a high-trail fork (78 mm). That would provide quick but twitchy handling, like on a criterium bike.
Originally Posted by bulldog1935 View Post
this is good work and I concur.
The rake/trail change will make your bike more stable and let you put a front load on it.

This is backwards, no?


Trail

The product of head angle and fork rake gives you what is referred to as “trail“. Trail is a figure that will reflect how fast a bike actually steers. More trail equates to slower steering, less trail will make faster steering. Increasing fork rake for a given head tube angle will decrease trail, therefore giving faster steering at the front end. More trail is good at high speeds, but at slower speeds it can make the bike feel sluggish.
https://cyclingtips.com/2011/02/the-...bike-handling/
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Old 12-06-16, 11:35 AM
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Shorter offset on the fork (higher trail) makes for quicker turn-in and steering that tends to hunt downhill.
Low trail feels more on-center, especially with a front load.
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Old 12-06-16, 12:31 PM
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Originally Posted by bulldog1935 View Post
Shorter offset on the fork (higher trail) makes for quicker turn-in and steering that tends to hunt downhill.
Low trail feels more on-center, especially with a front load.

For the sake of this discussion, can we eliminate the loaded component? Just so we can be specific about the handling characteristics associated with low trail vs high trail numbers?

Are you saying that high trail bikes turn quicker/easier/tighter/faster than low trail bikes (all other geometry being equal)? If so, that goes against everything I've ever read that says low trail bikes will be quicker/tighter turning, more nimble, but less stable at speed (twitchy)

Sheldon Brown:
More trail increases the bicycle's tendency to steer straight ahead. A bicycle with a largish trail dimension will be very stable, and easy to ride "no hands". A bicycle with a smaller trail dimension will be more manuverable and responsive.


When you say steering that "hunts", can you explain that more? Do you mean unstable or are you describing flop?
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Old 12-06-16, 12:57 PM
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Long Trail is self steering stability. The EZ Rider Chopper in the Movie Has very long trail ..

A Stayer Bike for motor pacing has a Backwards rake , that too is quite a Long Trail
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Old 12-06-16, 01:03 PM
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with low trail, the bike pulls harder to center (same as caster on an automobile). If you steer hard with it, the steering is faster and twitchy, but it takes more force to steer, and is the bike that's better for no-hands riding - it wants to go straight on its on.
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Old 12-06-16, 01:19 PM
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Originally Posted by bulldog1935 View Post
with low trail, the bike pulls harder to center (same as caster on an automobile). If you steer hard with it, the steering is faster and twitchy, but it takes more force to steer, and is the bike that's better for no-hands riding - it wants to go straight on its on.
No. With low offset/high trail the bike wants to stay on course. Low trail bikes (forks with large offset or rake and/or steep head tube angles) can be steered into turns no-hands easily.

Caster is trail. (The definitions might be a little different, but if so they are closely related and follow the same trends.)

Ben
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Old 12-06-16, 01:27 PM
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Originally Posted by bulldog1935 View Post
with low trail, the bike pulls harder to center (same as caster on an automobile). If you steer hard with it, the steering is faster and twitchy, but it takes more force to steer, and is the bike that's better for no-hands riding - it wants to go straight on its on.
I think you have that backwards. From Sheldon Brown's pages:

More trail increases the bicycle's tendency to steer straight ahead. A bicycle with a largish trail dimension will be very stable, and easy to ride "no hands". A bicycle with a smaller trail dimension will be more manuverable and responsive.

People tend to think that low trail = greater stability, but that's because touring bikes tend to have lots of fork rake and therefore low trail, and those bikes seem stable. The major factor there is the long wheelbase, though. A touring bike can have low trail and therefore be quick-handling, but the wheelbase ensures that direction changes happen more slowly than they do on shorter-wheelbase bikes.

For more details, see "Trail" on S.B.'s Glossary page: Sheldon Brown's Bicycle Glossary Tp - Tz

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Old 12-06-16, 01:41 PM
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Originally Posted by bulldog1935 View Post
with low trail....... it wants to go straight on its on.

Weird. That's the opposite of everything I've read frame builders claim.
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Old 12-06-16, 01:51 PM
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Originally Posted by oldtryguy View Post
from my limited understanding regarding frame/fork geometry.....you might wind up having a "look ma-no hands" handling bike.

+1
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Old 12-06-16, 02:22 PM
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As I said , wheel size matters Brompton, as I read, has a 35mm trail, Though I have not measured it myself.
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Old 12-06-16, 02:34 PM
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Originally Posted by bulldog1935 View Post
this is good work and I concur.
The rake/trail change will make your bike more stable and let you put a front load on it.
To be clear, you are concurring, in part, with something I did not say.

I said that the change in handling will be noticeable but made no statement about it being more or less stable, responsive or twitchy.



Originally Posted by fietsbob View Post
A Stayer Bike for motor pacing has a Backwards rake , that too is quite a Long Trail
For the sake of clarity, a Stayer bike is used in motor paced racing.

I'm open to correction but I've never heard of changing the handling of the bike as the reason for large trail on a stayer bike. My understanding is that the primary purpose of a backwards fork is so that the rider can get as close to the motorbike as possible for maximum draft.


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Old 12-06-16, 04:44 PM
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A few years ago, I remember that a trail of ~57mm was considered 'ideal' for a road bike, less for townie bikes (maybe as low as 35mm?). If he REALLY has 78mm of trail, that bike is set up for 50+mph descents, and not much else.
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Old 12-06-16, 05:40 PM
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What about toe overlap?
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Old 12-06-16, 07:51 PM
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For reference, the OP has a Cinelli Parallax. This is a very aggressive track bike.


Originally Posted by PrinceRein View Post
What about toe overlap?
I totally missed that in your original post. Sorry about that.

The point where the tire contacts the ground is going to move forward 16mm. The tire will move forward proportionately less than 16mm relative to the pedal. I can't say exactly how much. There is going to be a trade off in handling however, and possibly an impact in terms of style. Only you can decide if it is worth the change.

Lots of guys run them on the street but that doesn't change the fact that the Parallax is a track bike. Toe overlap isn't that big of a deal on the track. Are you riding it on the street? If so then I might suggest that your use of the bike doesn't align with its design. If toe overlap is that much of an issue then you may simply have the wrong bike for how you ride. It is a sweet ride though.

Please don't take my word for it. You are going to get more traction (pun) on this issue in the Fixed Gear/Single Speed forum. I think there are a few guys there who have owned Cinelli track frames and would be able to give you first hand information.


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Old 12-07-16, 08:06 AM
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Originally Posted by TimothyH View Post

The tire will move forward proportionately less than 16mm relative to the pedal.
IF I am reading that statement correctly, I'm not in agreement. I'm thinking the toe/tire contact point will move forward exactly 16mm as well.

If the offset moves 16mm forward, the axle moves 16mm forward. If the axle moves 16mm forward, every bit of the front wheel moves 16mm along with it. I'm not an engineer or mathematician, but I' pretty sure on this one. Mostly, maybe, kinda, sorta.
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Old 12-07-16, 01:39 PM
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To answer the initial question: Yes it does matter. But -- the issue is complicated.

However:
At the speeds we bi-cyclists travel: More trail increases straight-line stability, decreases 'twichyness' and makes it easier to ride 'hands-off'. Reference link:

There are a couple of earned Doctorates out there dealing with the issues of two-wheeled stability.

Get onto Google/Youtube and look around; you'll probably learn more than you wanted to know. ;o)

Joe
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