Results 1 to 9 of 9
  1. #1
    RoadBikeReview Member
    Reputation:
    Join Date
    Feb 2004
    Posts
    664

    Ouzo Pro v Comp Axle-Crown Difference?!

    I wanted to get the groups thought on this. I currently have a Reynolds Ouzo Pro which I am moving to a new frame. I wanted to get the bars a bit higher so I bought an Ouzo Comp with an uncut steer to use. I pull it out and am holding it up comparing it to the pro and find that the Comp has (measured) an 8mm shorter Axle to Crown (which obviously means the bars will be 8mm lower for the same number of spacers). Does anyone know why the Comp would be shorter than the Pro? I know that the measurements very slightly between manufactures, but was suprised it varied within the manufacture.

    Thanks

  2. #2
    RoadBikeReview Member
    Reputation:
    Join Date
    Feb 2002
    Posts
    19,314

    How to measure

    As has been discussed in the "complete bikes" forum, it is fairly difficult to accurately measure a fork. Are you measuring on the diagonal (string length form axle to fork crown)? If so, this would not consider the offset (aka rake). As to why two forks would have a different length, it's because that's the way the manufacturer decided to make it. They may be trying to match a given group of frames that are designed for a shorter fork.

  3. #3
    RoadBikeReview Member
    Reputation:
    Join Date
    Feb 2004
    Posts
    10,126

    bigger problem...

    As Kerry noted, making the proper measurement, parallel to the steering tube and through the center of the dropout is not easy.

    For comparison purpose, though, a diagonal measurement is fine, but be sure you're measuring to the edge of the dropout, where the axle rests, not the tip of the fork. I can't imagine such a large difference in the same brand.

    An 8mm difference will increase the head tube angle by about .5 degree and reduce the rail by about 3mm, which is about the same as using a fork with 3mm more rake. A shorter fork will make the steering quicker. This might be OK if the trail value is fairly large to start with, but if you've got something like a 56mm trail and further reduce it to 53, the bike could get twitchy.

    You're also wrong about this length difference changing the handlebar height, relative to the saddle. Only changes on top of the head tube affect this dimension.

  4. #4
    RoadBikeReview Member
    Reputation: Nessism's Avatar
    Join Date
    Feb 2004
    Posts
    1,366
    Quote Originally Posted by C-40
    As Kerry noted, making the proper measurement, parallel to the steering tube and through the center of the dropout is not easy.

    One wrench in the works is that some manufactuers, Colnago for example, measure their forks on an angle from the crown to the center of the axle. This is just another of those instances where some comanies feel the need to be different.

    Regarding carbon fork length in general, most are a fair bit longer than steel forks of old. The reason is that a fairly bulky crown is needed on the full carbon jobs to make sure they have enough meat there. On more conventional bonded carbon forks using an aluminum crown, the crown can be more normal sized thus the fork can be shorter.

    Interestingly, Colnago carbon forks are some of the shortest in the industry. Sir Ernesto recognized the need to keep the geometery of his frames consistant regardless of which fork was installed, lugged steel or carbon, thus his carbon forks are made to mimic the old steel fork dimensions. These forks are the ones to get when upgrading an old steel frame, Colnago or otherwise, since they will not raise the front end of the bike up.

    Ed

  5. #5
    RoadBikeReview Member
    Reputation:
    Join Date
    Feb 2004
    Posts
    664
    Quote Originally Posted by C-40
    You're also wrong about this length difference changing the handlebar height, relative to the saddle. Only changes on top of the head tube affect this dimension.
    If the axle to crown is 8mm longer it moves the entire front end up 8mm which raises the bars by 8mm. This will slightly raise the saddle but will also cause the seat tube angle to become slacker. This is an issue all the time with mountain bikes and going to longer travel forks (longer axle to crown difference).

    I spoke to Reynolds yesterday and they said the A-c on all their forks is 370 changing to 372 a year ago because of a dropout change. In looking at the comp, I noticed that the difference in length (remeasured to be about 4mm) comes from a shorter interface between the steerer tube and fork (they are identical up to the brake boss and then the carbon steerer pro has a slightly longer brake boss to crown). I think this may be to strenghten the carbon/carbon interface on the Pro.

    It is interesting to note that I weighed both forks. Reynolds avertises the Pro as 420 grams, and it came in at 420 grams with a 260mm steerer (40mm cut off). The interesting part is that Reynolds says the Comp with the aluminium steerer is 575 grams, but in actuality it weighed 520 grams with the full 300mm steerer. Add the extra weight of the Compression lug required by the Pro and the extra steerer lenght and the difference in weight between the Pro and Comp is more like 60-70 grams, or not very much.

  6. #6
    RoadBikeReview Member
    Reputation: Nessism's Avatar
    Join Date
    Feb 2004
    Posts
    1,366
    Quote Originally Posted by cdmc
    If the axle to crown is 8mm longer it moves the entire front end up 8mm which raises the bars by 8mm. This will slightly raise the saddle but will also cause the seat tube angle to become slacker. This is an issue all the time with mountain bikes and going to longer travel forks (longer axle to crown difference).

    I spoke to Reynolds yesterday and they said the A-c on all their forks is 370 changing to 372 a year ago because of a dropout change. In looking at the comp, I noticed that the difference in length (remeasured to be about 4mm) comes from a shorter interface between the steerer tube and fork (they are identical up to the brake boss and then the carbon steerer pro has a slightly longer brake boss to crown). I think this may be to strenghten the carbon/carbon interface on the Pro.

    It is interesting to note that I weighed both forks. Reynolds avertises the Pro as 420 grams, and it came in at 420 grams with a 260mm steerer (40mm cut off). The interesting part is that Reynolds says the Comp with the aluminium steerer is 575 grams, but in actuality it weighed 520 grams with the full 300mm steerer. Add the extra weight of the Compression lug required by the Pro and the extra steerer lenght and the difference in weight between the Pro and Comp is more like 60-70 grams, or not very much.

    Are you sure both forks have the same rake? If one has more, it's harder to compair the lengths by eyeballing.

    Regarding the longer fork raising up the bars, yes it will. But not in direct proportional relationship to the longer fork since the fork is on an angle relative to gravity. The actual formula is Length Increase x Sin (head angle). For your 8mm increase example the actual increase is 7.6mm (splitting hairs, sorry).

  7. #7
    RoadBikeReview Member
    Reputation:
    Join Date
    Feb 2004
    Posts
    664
    I did confirm that both are a 43mm rake. You are correct about the increase in the bar height, I should have factored that in.

    CDMC

    P.S. You should know not ot post trig functions here, it confuses people.

  8. #8
    RoadBikeReview Member
    Reputation:
    Join Date
    Feb 2004
    Posts
    10,126

    more on fork length measurement

    The difference between a diagonal measurement and one taken parallel to the steering tube is really not very large, if you do the trig. A fork with a 40mm rake would measure 2mm longer diagonally and one with a 50mm rake would measure 3mm longer.

    If Colnago truly measures their forks parallel to the fork blades, then the length would decrease from 368 to 365.5mm for a parallel to steering tube measurement.

    As for the handlebar height difference, the BB would rise about 1/2 as much as the headtube, so there would be a vertical difference between the saddle and the head tube, but only about 1/2 of the head tube height change.

    http://www.sheldonbrown.com/rinard/forklengths.htm

    http://www.trialtir-usa.com/2005-col...sizecharts.htm

  9. #9
    RoadBikeReview Member
    Reputation:
    Join Date
    Jun 2003
    Posts
    1,876
    [QUOTE=cdmc
    P.S. You should know not ot post trig functions here, it confuses people.[/QUOTE]

    Yeah, you can't talk about sin on a bike forum.

Similar Threads

  1. The honest difference between all of us and a pro cyclist...
    By filly in forum Racing, Training, Nutrition, Triathlons
    Replies: 97
    Last Post: 11-08-2004, 11:55 AM
  2. Replies: 5
    Last Post: 10-25-2004, 06:47 AM
  3. Roubaix Pro vs Roubaix Comp
    By zacka in forum Specialized
    Replies: 4
    Last Post: 08-24-2004, 01:33 AM
  4. Replies: 2
    Last Post: 02-29-2004, 10:20 AM
  5. Reynolds Ouzo Pro - 1" steerer ok?
    By hrv in forum General Cycling Discussion
    Replies: 4
    Last Post: 02-24-2004, 08:44 AM

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  

EUROBIKE

Hot Deals

Latest RoadBike Articles


Latest Videos

RoadbikeReview on Facebook