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Old September 28th, 2007, 1:04 PM   #1
jh4rt
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Default Fork Discussion / Differences

I did a search or three and couldn't find the information I was looking for. I would really like to understand the differences in the forks... and what the deal is with my bikes.

Background. I purchased a M Yo new in 92. It came with a Mag-21. The fork eventually died and I decided to order a rigid fork from Wendyll / Chris.. This was probably in about 97/98. I waited and waited, got what I think is a BOI, installed it and have been riding it ever since.

Skip forward to yesterday. I just purchased a 99 YO on eBay... got it re-assembled it and took it for a test ride before I tear it down and make it SS. WOW !!!!!!! What a difference. The new one has an IF fork on it with a bit more rake, and it is about 1.25" longer than the one on my other. It is so much more stable. My old bike feels like a crit bike now... twitchy as hell. And I feel like I'm a bit dumped. I'm starting to think that Wendyll sent me the wrong length fork for my old yo.

So: Background finished, these are the questions I hope you could help me answer:

1. What is the difference between BOI and Yo fork?
2. How do I measure my 93 to decide if it is suspension corrected?

Thank you in advance
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Old September 28th, 2007, 1:42 PM   #2
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Wouldn't a simple axle-to-crown measurement tell you alot?

Curious to see the BOI vs Yo fork answer... Rody?
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Old September 28th, 2007, 1:53 PM   #3
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Quote:
Originally Posted by ameybrook View Post
Wouldn't a simple axle-to-crown measurement tell you alot?
I am not sure... That is the fork, right? The fork is a bout 1.25" longer axle to crown... but is the head-tube the right angle, etc???
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Old September 28th, 2007, 2:18 PM   #4
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Quote:
Originally Posted by ameybrook View Post
Wouldn't a simple axle-to-crown measurement tell you alot?

Curious to see the BOI vs Yo fork answer... Rody?
difference will be subtle since geometry is the same.
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Old September 28th, 2007, 2:19 PM   #5
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Quote:
Originally Posted by jh4rt View Post
I am not sure... That is the fork, right? The fork is a bout 1.25" longer axle to crown... but is the head-tube the right angle, etc???
did you measure the wheelbase on both bikes? susp corrected geometry is always something vague since some forks sag and others don't.
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Old September 28th, 2007, 3:25 PM   #6
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did you measure the wheelbase on both bikes? susp corrected geometry is always something vague since some forks sag and others don't.
I didn't measure wheelbase, but all things being equal, if the geometry is the same on both bikes then the new one will have a longer wheelbase. The IF fork is longer and appears to have a slight bit more rake. My other... well... it is so rigid. I mean.. every single bump is transmitted through my BOI/Yo. This IF fork makes a world of difference. I'm kind of in love with it...

Final question. If I was thinking about retiring my BOI for a while and runnning a suspension fork, what would be a good suggestion? I'm not looking for a huge amount of travel; and would want it to be light... and .. of course... it has to have a 1" steerer.

Thanks...
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Old September 28th, 2007, 3:33 PM   #7
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Quote:
Originally Posted by jh4rt View Post
I didn't measure wheelbase, but all things being equal, if the geometry is the same on both bikes then the new one will have a longer wheelbase. The IF fork is longer and appears to have a slight bit more rake. My other... well... it is so rigid. I mean.. every single bump is transmitted through my BOI/Yo. This IF fork makes a world of difference. I'm kind of in love with it...

Final question. If I was thinking about retiring my BOI for a while and runnning a suspension fork, what would be a good suggestion? I'm not looking for a huge amount of travel; and would want it to be light... and .. of course... it has to have a 1" steerer.

Thanks...
not necessarily a longer wheelbase. if it was susp corrected it could have a steeper headangle to compensate. susp. forks always had short rakes... but so did the BOI.
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Old September 28th, 2007, 3:38 PM   #8
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Default Pics for side by side comparison

I know ... parallax/angle/ light can play tricks... but side by side, maybe someone can tell a difference?

91 yo / BOI


99 yo / IF


Last edited by jh4rt; September 28th, 2007 at 3:41 PM. Reason: bigger pics
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Old September 28th, 2007, 3:44 PM   #9
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FYI, this article is really useful


http://www.phred.org/~josh/bike/trail.html

Also, this question would be easily answered on the frame forum (www.frameforum.net) if you dont want to sit around and wait for Rody.
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Old September 28th, 2007, 3:57 PM   #10
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the newer bike seems to have a steeper head angle which would compensate for the extended A/C and modified rake.
rake/ head angle/ front center distance all play together. hard to pinpoint what exactly goes there but if you are in love w/ the new one.. does that mean we will be seeing a black Yo eddy for sale soon?

Quote:
Originally Posted by jh4rt View Post
I know ... parallax/angle/ light can play tricks... but side by side, maybe someone can tell a difference?

91 yo / BOI


99 yo / IF

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Old September 28th, 2007, 4:12 PM   #11
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Originally Posted by colker View Post
...does that mean we will be seeing a black Yo eddy for sale soon?
NFW!!!!

But, I do think I would like to put some small suspension fork on my old yo / gearey... But this ol' yo is never leaving my stable.

;-)
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Old September 28th, 2007, 4:23 PM   #12
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Quote:
Originally Posted by jh4rt View Post
NFW!!!!

But, I do think I would like to put some small suspension fork on my old yo / gearey... But this ol' yo is never leaving my stable.

;-)
look for a 1in marz bomber on ebay. or a 11/8 in nice shape and buy just a steerer. i wouldn't use anything else on a bike as a yo, made for attacking steep technical terrain. don't go w/ flexy sids, judys etc..
70mm travel is the ticket.
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Old September 28th, 2007, 7:35 PM   #13
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Hey guy,

Here are the major differences in the forks / frames...




Big One Inch specs...

Debut around the time of the TI introduction

Dropout to race length - 15.9375" suspension corrected to 63mm


Rake offset - 1.57" or 6 degrees


BOI forks use 1.0" diameter tubing for the legs and crown

Yo specs...

Used from late eighties until BOI intro

Dropout to race length - 15.5" for standard geometry

Yo Eddy forks use 1.125" diameter tubing for the legs and crown.

Now, the frames will have a significant difference in the geometry.

Your 92 Yo will have a lower headtube height as it was designed for rigid forks, although the Mag 21 was probably put on as with your weight to sag the fork, it would not change the ride drastically.


Your 99 frame is designed to work with a 80mm fork, thus the reason that the longer axel to crown length is present on the IF fork.

The likely culprit of the handling variance of the older Yo is the resultant trail with the more modern Big One Inch. Only way to tell for sure is to take all the measurements off the rigid fork that is on it.

Hope some of this helps,

rody

Last edited by rody; September 28th, 2007 at 7:44 PM. Reason: syntax
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Old September 28th, 2007, 11:56 PM   #14
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Default Thanks Rody.

Awesome information....

Well... So... umm... I took the old nag out for a 15 mi. spin this evening. Let me just say... umm... crit bike; whatever... IT RODE LIKE A DREAM. Maybe my kung fu is just getting stronger, but it was a dream to ride tonight. And, I realized that both of these bikes are stellar, but different. The IF fork is much more flexy, and I think will be better suited for a SS. But my old Yo with the BOI was true as can be tonight. I have actually changed the stem and bars and am now running a 100mm Salsa stem with Syncros riser bars. CLASSIC and much more comfortable, cooler.

Thank you everyone for the information. I think I'm going to stick with this ol' BOI on my geary.

--j
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Old October 3rd, 2007, 11:55 AM   #15
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Fast handling was kind of the norm for east coast bikes back in the day. Your real problem is that you live in california and you are riding the bike on trails that are way too smooth and wide...
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Old October 3rd, 2007, 2:41 PM   #16
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Quote:
Originally Posted by lucifer View Post
Fast handling was kind of the norm for east coast bikes back in the day. Your real problem is that you live in california and you are riding the bike on trails that are way too smooth and wide...
HeHe. You obviously haven't done Guadalasco to the Backbone. I was scraping bush on one side and rock on the other last night. ;-)

--jim
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Old October 6th, 2007, 4:53 PM   #17
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rody - do you know what size canti studs I need for a BOI fork? I have seen different sizes of threaded studs and want to buy the right size.

Quote:
Originally Posted by rody View Post
Hey guy,

Here are the major differences in the forks / frames...




Big One Inch specs...

Debut around the time of the TI introduction

Dropout to race length - 15.9375" suspension corrected to 63mm


Rake offset - 1.57" or 6 degrees


BOI forks use 1.0" diameter tubing for the legs and crown

Yo specs...

Used from late eighties until BOI intro

Dropout to race length - 15.5" for standard geometry

Yo Eddy forks use 1.125" diameter tubing for the legs and crown.

Now, the frames will have a significant difference in the geometry.

Your 92 Yo will have a lower headtube height as it was designed for rigid forks, although the Mag 21 was probably put on as with your weight to sag the fork, it would not change the ride drastically.


Your 99 frame is designed to work with a 80mm fork, thus the reason that the longer axel to crown length is present on the IF fork.

The likely culprit of the handling variance of the older Yo is the resultant trail with the more modern Big One Inch. Only way to tell for sure is to take all the measurements off the rigid fork that is on it.

Hope some of this helps,

rody
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Old October 6th, 2007, 7:54 PM   #18
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Noah,

I'm out of the shop until Monday...I'll take a look at the post id and let you know.

rody
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Old October 8th, 2007, 7:25 AM   #19
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Quote:
Originally Posted by rody View Post
Hey guy,

Here are the major differences in the forks / frames...




Big One Inch specs...

Debut around the time of the TI introduction

Dropout to race length - 15.9375" suspension corrected to 63mm


Rake offset - 1.57" or 6 degrees


BOI forks use 1.0" diameter tubing for the legs and crown

Yo specs...

Used from late eighties until BOI intro

Dropout to race length - 15.5" for standard geometry

Yo Eddy forks use 1.125" diameter tubing for the legs and crown.

Now, the frames will have a significant difference in the geometry.

Your 92 Yo will have a lower headtube height as it was designed for rigid forks, although the Mag 21 was probably put on as with your weight to sag the fork, it would not change the ride drastically.


Your 99 frame is designed to work with a 80mm fork, thus the reason that the longer axel to crown length is present on the IF fork.

The likely culprit of the handling variance of the older Yo is the resultant trail with the more modern Big One Inch. Only way to tell for sure is to take all the measurements off the rigid fork that is on it.

Hope some of this helps,

rody
Great info; thanks.
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Old October 9th, 2007, 2:48 PM   #20
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Quote:
Originally Posted by lucifer View Post
Fast handling was kind of the norm for east coast bikes back in the day. Your real problem is that you live in california and you are riding the bike on trails that are way too smooth and wide...
You're thinking NorCal. We live in SoCal: the land of rocks and cacti. We have plenty of high pucker-factor riding out here.
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Old October 11th, 2007, 1:26 PM   #21
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Bushy-Oink,

From what I've been able to tell from the examples I've had, at least two different canti bosses have been used;

one with a threaded post insert which measures M8x1.25

and

standard one piece boss and stud...looks like a Tange product

hope this helps,

rody
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Old July 1st, 2008, 7:22 PM   #22
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Default '91 Wicked

I have a 1991 Wicked with a rigid unicrown fork. Axle to crown is approximately 400mm. What is the appropriate axle to crown measurement for this bike? The bike is a Frankenbiked and I am uncertain if the fork is original.

Thanks
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