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  1. #1
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    questions about fork length replacing bontrager (trek proprietary system?)

    Hello, i've recently acquired a trek 1000 for a bargain on craigslist, and moved some nicer components/wheels to the bike. It was great to build it up myself and i have this forum, in part to thank for my small successes wrenching thus far.

    That being said. It has a nasty little gash in the aluminum fork, and it's pretty light @ around 20-21lbs, so I thought i might drop a bit more weight with a cheap direct-from-china carbon fork.

    For the install I went to the shop for proper sawing/whatnot, and the mechanic told me they could do it by monday night.

    He was looking at the bike and said something about Trek forks having a different measurement somewhere other than the rake and headtube angle. (i think he was referring to the crown to axel measurement.) I had never heard that so i looked it up and couldn't find anything about trek/bonty having specifically different or proprietary measurements. He said i might be better ordering from a trek dealer, and that the entire front end of the bike would come down 2mm with the install.

    he also told me that the fork rake would be increased from 43mm to 45mm (although the seller of this fork says that it's 42mm, i wouldn't mind either of those numbers).

    i know that increasing rake will make the handling "quicker more responsive, more squirley" and that sounds fine, but he was talking about the handling being altered beyond that by changing the entire angle of the bike!

    He said "it might not be rideable" and basically sort of told me it was really risky to put the fork. i had to ask if there were any other safety risks other than the change in handling, he said no, and i ended up leaving it there to have the work done.

    I'm wondering if anyone else has this experience specifically with treks, or if this guy was just talking.. he also tried to convince me that my current fork was carbon even after i told him it's a 2004 and it's aluminum for sure.

    from searching and reading on the forums. i'm seeing that fork legnth doesn't vary much with regards to road bikes.. if this guy is right about lowering the front end of my bike by 2mm, how significant an effect do you think that would have? thanks!

  2. #2
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    Can't you tell by putting a thin screwdriver throught the brake mounting hole on both forks (skewer them together on the screwdriver, or "spoon" them as we say with regard to horizontal intergender relaxation activities) and comparing the dropout and fork crown positions. Alternatively, you might be able to find a bolt that you could use to bind the two forks together for comparison. If the difference from crown to dropouts is real, don't do it. If it is just a difference in the placement of the brakes, no big deal. Messing around with top tube angle, head tube angle, rake, etc. is not for the amateur. One "death wobble" in my lifetime is more than enough; I would never intentionally do anything that might bring on another one! You could always call Trek. They may not have a replacement fork for you, but should be able to answer your questions.

    Robert

  3. #3
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    I would not be overly oncerned if the difference was really only 2mm; I think it would be difficult to even accurately measure a fork within 2mm, which is less than 1/10th inch and may be within the manufacturing tolerances.

  4. #4
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    Quote Originally Posted by rpenmanparker View Post
    Can't you tell by putting a thin screwdriver throught the brake mounting hole on both forks (skewer them together on the screwdriver, or "spoon" them as we say with regard to horizontal intergender relaxation activities) and comparing the dropout and fork crown positions. Alternatively, you might be able to find a bolt that you could use to bind the two forks together for comparison. If the difference from crown to dropouts is real, don't do it. If it is just a difference in the placement of the brakes, no big deal. Messing around with top tube angle, head tube angle, rake, etc. is not for the amateur. One "death wobble" in my lifetime is more than enough; I would never intentionally do anything that might bring on another one! You could always call Trek. They may not have a replacement fork for you, but should be able to answer your questions.

    Robert
    uh oh.. well of course i can't measure it now because it's at the shop. So you're saying i should probably stop them from doing the work? I'm sure he wasn't lying about the difference, as he was measuring the forks with a ruler. So 2mm of drop in the front would actually be a dangerous difference then?

    One troubling thing for me is that while looking up forks, i've noticed that NONE of the ones i've found have this measurement listed! hmmm.. what to do.. i feel like even with the gash the aluminum fork will probably be ok, although fork failure is nothing to joke around with.

    Thinking about having them stop the process and trying to sell the fork, as the install will be $35-$50, plus the special non-star nut since the steerer is carbon ($15), and then another $35 - $50 to reverse the whole process.

  5. #5
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    Sorry to be a wet blanket, but I can't see why you would want a less than optimum situation. I converted a 27" bike to 700c once by installing a fork that had the crown built up to make up the difference but was never happy with the appearance. Sometimes we just try too hard.

    Meanwhile I can't say you would be in danger. Handling might not be optimum is all. Why chance it?

    A compromise course would be to stop the work and just have a crown race installed on the new fork, don't cut the steerer tube. First measure the height of the old fork crown over a wheel, then remove it and the slide the new one in. Don't worry about it not being tight. Just let the weight of the bike hold everything in place. Then measure the fork crown height on the new fork. If they are not the same, I would back your way out of everything and call Trek for what models of fork will work. There are a few Bontrager forks on ebay right now for less than $100.

    Good luck.

  6. #6
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    well i don't "want" less than optimum, but i did want to replace this fork mainly because of the gash taken out of it. a little worried about that becuase i travel at very high speeds over very rough surfaces.

    this fork was pretty much 1/4 the price of one i could get at the shop, maybe less, and i'm not really a "well-off" sort of person.

    and the reason why it's taking them until monday to do the work is that they're swamped with business.. i guess i could call them and ask them to put on the crown race and see how bad it looks? hmm...

  7. #7
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    i suppose there's a chance that i'd love the way it handles, or that the 2mm won't have much of an effect, or of course, the opposite of both of these may also be true.

    anyone ever had their front end lowered about this much on a racing bike?

  8. #8
    Senior Member mechBgon's Avatar
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    According to Trek's info, the 2004 Trek 1000 has an axle-to-crown measurement of 372.5mm. Rake is either 47mm (54cm and smaller) or 43mm (56cm and larger). There's nothing too unusual about the fork's design or the height from the brake-bolt hole to the crown-race seat. And you're correct, it's an aluminum fork, as your mechanic ought to be able to see from the gash if it's down to the metal.

    Slightly-different axle-to-crown height isn't the end of the world. From what you've said here, I'd be somewhat concerned about whether the mechanic is good at cutting carbon steertubes and installing the internal reinforcement plug. If it's still not cut yet, I suggest having a 1cm spacer installed above the stem, so the stem itself isn't clamped at the end of the steertube where cracks start more easily.

  9. #9
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    Quote Originally Posted by mechBgon View Post
    According to Trek's info, the 2004 Trek 1000 has an axle-to-crown measurement of 372.5mm. Rake is either 47mm (54cm and smaller) or 43mm (56cm and larger). There's nothing too unusual about the fork's design or the height from the brake-bolt hole to the crown-race seat. And you're correct, it's an aluminum fork, as your mechanic ought to be able to see from the gash if it's down to the metal.

    Slightly-different axle-to-crown height isn't the end of the world. From what you've said here, I'd be somewhat concerned about whether the mechanic is good at cutting carbon steertubes and installing the internal reinforcement plug. If it's still not cut yet, I suggest having a 1cm spacer installed above the stem, so the stem itself isn't clamped at the end of the steertube where cracks start more easily.
    thanks! i looked all over for that info, and couldn't figure out the axel-crown measurement! the rake is definitely 43mm as the mechanic confirmed after measuring. The new fork says that it's a 42mm rake, but i think at the shop he told me it'd be changing to 45mm.. as i said i'm fine with either of those, my main concern was when he started talking about dropping down the whole front end of the bike and changing the entire frame geometry.

    as far as i can tell, he wouldn't be the one doing the work, but i'm not sure.. it's definitely a well known and reputable LBS though, so I'm not too worried about them screwing up the fork. There will certainly be a few spacers below the stem, maybe i should have them cut it a little bit longer to fit another spacer eh? i'm having it cut about 20mm higher than the current one, so that i can raise up the bars by a spacer and a half or so.

    he saw the metal, but said something like "the aluminum goes up to about here and then it's carbon".. which did loose him a little cred in my eyes especially since i told him i knew it's aluminum and he tapped on it all up and down.

    thanks for helping me research i promise i searched ha! .. thinking about going for it.

  10. #10
    Senior Member mechBgon's Avatar
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    Actually, I see they used different geometry on the 1000C and the 1000T. Which one do you have? I'll cut and paste the specsheet for you as an image file.

  11. #11
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    Quote Originally Posted by mechBgon View Post
    Actually, I see they used different geometry on the 1000C and the 1000T. Which one do you have? I'll cut and paste the specsheet for you as an image file.
    wow, i thought the frames were the same, but the stem/seatpost were different.. I found the speck sheet online in pdf format, thanks for making me aware of it.

    so i thought mine was a 1000c, because when i bought it the seatpost had a shock in it, but looking at the geometry and the different pictures on trek.com archives and bikepedia it's definitely the 1000c.. the top tube is totally flat, and it's the brushed steel with red highlights, not blue.

    good to know, and i'm so glad i have the 1000T.. the geometry is very similar to my 2008 2.3 (which i enjoy very much).. the plan for now is to let them go ahead with the work and pray that it's not another really expensive lesson.. hoping for the best. thanks!

    oh yea, and it's a 58cm. thanks!
    Last edited by hajitosan; 09-16-12 at 04:13 AM.

  12. #12
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    i'm just going to go for it.. sit back and let them do the work.. i REALLY hope it's not another very costly bike "learning experience", but i'll let you know after tomorrow when i get the bike back (fingers crossed)

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    I'm having little trouble following what you actually have and what you're actually installing, but, I cannot imagine how one could possibly even measure fork-crown length whithin 2mm, let alone feel any change in the ride or handling caused by that alone. It's about 1/16".

    The difference between a 43mm rake and a 42, again, so tiny. Even 43-45 could be noticable, maybe not. If noticable - could be positive, could be negative, but I really doubt if either is meaningful to anyone except very sensitive rider. You'll probably feel the difference in handlebar height, and that will be a huge amount greater a change than the fork geometry so as to make it (the geometry) unnoticable.
    Last edited by Camilo; 09-17-12 at 05:49 PM.

  14. #14
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    A shorter fork will increase the head tube angle and decrease steering trail. Decreasing the rake offset would increase steering trail. It seems to me that the 42 mm rake offset would be a better choic than the 45 mm rake offset if they are otherwise the same.

    In other words, shortening the fork length and increasing the rake offset will both cause quicker and less stable steering.

  15. #15
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    Well I went through with it.

    i picked up the bike tonight and that mechanic must've been just talking a lot of nonsense because it handles/rides perfectly and feels great!

    i guess he just freaked me out with all the talk of the steering being affected to the point of safety concerns.

    thanks all, very excited for my new bike!!!
    Last edited by hajitosan; 09-18-12 at 04:05 PM.

  16. #16
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    Quote Originally Posted by Camilo View Post
    I'm having little trouble following what you actually have and what you're actually installing, but, I cannot imagine how one could possibly even measure fork-crown length whithin 2mm, let alone feel any change in the ride or handling caused by that alone. It's about 1/16".
    well the mechanic was using a ruler, but you were right, the difference was unnoticeable.. maybe he was unhappy that i brought in my own fork from outside the shop..
    Last edited by hajitosan; 09-18-12 at 04:05 PM.

  17. #17
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    I've since put quite a few miles on it and i must say it rides very nice.. more comfortable than my long haul trucker as far as vibrational dampening from the road to the bars, and that's rolling 28c on the LHT vs 23c on the 1000, of course wheels are another factor, but the LHT has a 32 spoke shallow rim vs the lower spoke areo wheel on the front of the 1000..

    makes me think that fork composition, wheels, tires (width and psi) is the order of importance when it comes to comfort factor riding, but i don't have as much experience as most of you do.

    the china fork is awesome and was well worth it!

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