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  1. #1
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    Fork Rake Question - 49mm vs 45mm

    I have a quick question for you guys.

    I have a Specialized Tricross CX bike (54cm) with a stock 49mm raked fork. I would like to go to a lighter fork that has a 45mm rake.

    Will going from a 49mm to a 45mm rake truly make that big of a difference on my CX bike? We are talking about 4mm. It will shorten the wheelbase and might make the bike a little twitchier.

    Please let me know your thoughts on this.

  2. #2
    n00bsauce
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    Quote Originally Posted by mdutcher
    I have a quick question for you guys.

    I have a Specialized Tricross CX bike (54cm) with a stock 49mm raked fork. I would like to go to a lighter fork that has a 45mm rake.

    Will going from a 49mm to a 45mm rake truly make that big of a difference on my CX bike? We are talking about 4mm. It will shorten the wheelbase and might make the bike a little twitchier.

    Please let me know your thoughts on this.
    You sure it's 49mm? Specialized lists all their 54cm TriCross bikes from 2006 on with 51mm rake. 51mm to 45mm would probably affect things a bit, definitely twitchier and for a cross bike that's not a good thing. Headtube is fairly slack at 71.5 (as you'd expect on a CX bike) so that would mitigate things a bit. If you're road riding this would probably be fine but for CX I don't think I'd like the handling.
    "Those who can make you believe absurdities can make you commit atrocities." Voltaire

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  3. #3
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    The shorter rake will NOT make the bike twitchier. It will do the opposite; it will increase the trail figure and make the bike SLOWER to turn. A 4mm change in wheelbase is practically inconsequential.

    If your numbers are correct then yes; 4mm is a significant difference. I speak from experience.

  4. #4
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    Quote Originally Posted by Peter P.
    The shorter rake will NOT make the bike twitchier. It will do the opposite; it will increase the trail figure and make the bike SLOWER to turn. A 4mm change in wheelbase is practically inconsequential.

    If your numbers are correct then yes; 4mm is a significant difference. I speak from experience.
    +1. When I was figuring this out, I found a picture is worth a lot of words. The link below has a pretty good diagram and explanation.

    http://davesbikeblog.blogspot.com/20...le-bit-of.html

  5. #5
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    Ti, thanks for the link, good reference material to have bookmarked!
    Of course I'm sure...that doesn't mean I'm right......

  6. #6
    n00bsauce
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    Quote Originally Posted by Peter P.
    The shorter rake will NOT make the bike twitchier. It will do the opposite; it will increase the trail figure and make the bike SLOWER to turn. A 4mm change in wheelbase is practically inconsequential.

    If your numbers are correct then yes; 4mm is a significant difference. I speak from experience.
    Right you are. I was thinking backwards on this and I just went over this a week ago! Still, the steering will be affected and I still wonder if the 49mm figure the OP cited is correct. I checked the Specialized archive and their rake figures remained unchanged for this bike from their first listing in 2006 onward.
    "Those who can make you believe absurdities can make you commit atrocities." Voltaire

    There are your fog people & your sun people, he said. I said I wasn't sure which kind I was. He nodded. Fog'll do that to you, he said.

    "We are all ignorant about most things."
    Mel Erickson

  7. #7
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    I stand corrected, the rake on my CX bike is 51 and not 49.

    Thanks for the input and insight. So, if I can summarize your comments, reducing the rake by 6mm will increase my trail by 6mm. And this is not good?

    Can someone help me to understand why that would be? For those of you that speak from experience with this, please describe to me exactly what the bike did and how it handled. I am curious - what do you mean slower to turn? 6mm will make my bike slower to turn... is it that noticeable?

    Thanks!

  8. #8
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    fork length...

    Don't forget to compare the fork length. If the length difference is 5mm or more, it could either add to the change in trail or reduce it.
    Last edited by C-40; 10-20-2009 at 05:55 AM.

  9. #9
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    With a 71.5 head angle, you need all the rake your stock fork has to give.

    Here's an on-line tool to play with: http://www.kogswell.com/trail.php

    Measure your tire diameter and play with the numbers. Check other respected cross bike specs to see how they compare. I doubt using a shorter rake than you have would be a good move.

  10. #10
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    Slower steeting

    Quote Originally Posted by mdutcher
    I stand corrected, the rake on my CX bike is 51 and not 49.

    Thanks for the input and insight. So, if I can summarize your comments, reducing the rake by 6mm will increase my trail by 6mm. And this is not good?

    Can someone help me to understand why that would be? For those of you that speak from experience with this, please describe to me exactly what the bike did and how it handled. I am curious - what do you mean slower to turn? 6mm will make my bike slower to turn... is it that noticeable?
    A 6 mm reduction in fork offset would defintely be noticeable on a road bike (after checking for fork length as noted by C-40), but then you have to answer two questions. 1) would slower steering be a problem, and 2) if this is truly used as a CX bike, is that much of an issue in the dirt. Only you can answer these questions.

  11. #11
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    Quote Originally Posted by Kerry Irons
    A 6 mm reduction in fork offset would defintely be noticeable on a road bike (after checking for fork length as noted by C-40), but then you have to answer two questions. 1) would slower steering be a problem, and 2) if this is truly used as a CX bike, is that much of an issue in the dirt. Only you can answer these questions.
    On a related note...

    I have an older Bontrager CX bike with a 72 degree HTA, and came stock with a fork with 32mm rake. It rides differently from my newer CX bike, which has the same HTA but the fork has 43mm of rake, but the ride is not bad. Just different.

  12. #12
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    Quote Originally Posted by laffeaux
    On a related note...

    I have an older Bontrager CX bike with a 72 degree HTA, and came stock with a fork with 32mm rake. It rides differently from my newer CX bike, which has the same HTA but the fork has 43mm of rake, but the ride is not bad. Just different.
    Remember that there's more to handling characteristics than just fork rake and chainstay angle - wheelbase length, bottom bracket height, etc all play a part.
    "It's hard to tell the poison from the cure, so enjoy the disease."
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  13. #13
    rmp
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    I'm about to try the same thing. Stay tuned for details. 2009 SingleCross here, I'm going to try an EC70x on it this week. It's not much lighter, but that stock TriCross fork is just the ugliest friggen thing ever invented. I throw up in my mouth a little bit every time I look down at it.

    Specialized doesn't publish the A-C length, so I'll measure everything when I pull it off.

    rmp

  14. #14
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    Quote Originally Posted by mdutcher
    I stand corrected, the rake on my CX bike is 51 and not 49.

    Thanks for the input and insight. So, if I can summarize your comments, reducing the rake by 6mm will increase my trail by 6mm. And this is not good?

    Can someone help me to understand why that would be? For those of you that speak from experience with this, please describe to me exactly what the bike did and how it handled. I am curious - what do you mean slower to turn? 6mm will make my bike slower to turn... is it that noticeable?

    Thanks!
    I once was hit by a car and wrecked the entire front end of the frame and fork. I had the frame rebuilt and spec'd out the bike as original but added 5mm of rake, which decreased trail by roughly 5mm. I was looking to "wake up" the steering which I felt was sluggish. With the decreased trail, the bike felt like it was on caffeine. The front end felt very light but it fought me around corners because it felt like it was on ice and I was trying to keep it from slipping out from under me, which I don't think it was actually going to do, but that's the feeling it imparted. It was very lively, and almost fun to ride, but grew old and became almost unpleasant after 30 minutes or so.

    'Cross bikes use slacker head angles and higher trail figures to help keep 'cross obstacles from bumping the front end off-line such as rocks and roots. They'll make the bike feel "less slippery" on wet grass and through mud at higher speeds. You sort of have to have a knowledge of the differences between how a 'cross bike feels as a result of the geometry numbers versus a road bike, then you'll have a better understanding.

    Technically, switching from the 51 to a 45mm rake fork won't be that bad because if you look at the geometry chart from the 2010 Specialized TriCross you'll see the head tube angle and rake combinations vary enough across the range to result in trail figures from 75-58mm. that's a vast difference which makes you wonder how tall riders perceive their 'cross bikes' handling versus small riders, but if the manufacturer is okay in designing bikes like this then it must be okay, no? Changing the fork rake in your case will give your bike "roughly" the same handling as the 49cm TriCross, if you ignore the change in head angle.

    A bike with a greater trail figure will be less likely to be thrown off line from all the imperfections on the trail but the front end will not feel like it wants to turn, almost like the bars won't rotate. To turn, you'll do more leaning of the bike than turning of the bars. Some riders may find the change in steering fine, some may not.

    The high end trail figures are comparable to what you'll find on mountain bikes so I'd say to get an idea of what the handling might be like, do a side by side comparison with your cross bike and a mountain bike and see if you get the feel for the differences. Another thing you can do is browse web sites of other 'cross bike manufacturers and see if they offer a 'cross bike in your size with the 71/45 combination. They're not likely to sell a bike designed that way if it weren't marketable/rideable so if you find more than one, you can probably conclude that changing your fork rake at least won't make your bike unpleasantly unrideable.

  15. #15
    rmp
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    Started working on pulling the old parts apart tonight. Have any of you guys pulled apart a Specialized "Mindset" headset? The headset itself is fine, and the main fork crown race pops right off.

    The problem is there is a little rubber wiper/spacer that seems to fit between the crown race and the actual crown of the Specialized anchor... errr I mean fork. Not sure I'd be able to get if off without busting it up - but you'll need it (or something like it) to put another fork on the TriCross. Without that wiper/spacer the fork crown rubs the bottom of the headtube . It's not much - maybe 1-1.5mm thick - but I'll either need to get a new one from my local dealer or find a taller crown race to make up for it.

    rmp

  16. #16
    rmp
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    Quote Originally Posted by C-40
    Don't forget to compare the fork length. If the length difference is 5mm or more, it could either add to the change in trail or reduce it.
    Yeah, the TriCross fork is pretty long. I just measured axle to crown on the fork from my 54cm SingleCross frame - its about 405mm, or maybe just a tad under. The same tape shot my EC70x at 395mm - which is spec for that one.

  17. #17
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    Changing the trail may or may not be an issue, as has been covered. But what really will be an issue is if the new fork does not have enough clearance for your tires. Cross bikes usually have a lot of tire clearance, and road bikes increasingly do not. It could easily be that 34 mm knobby cross tires will no longer fit into your front end. I'm not sure a few grams saved in the front end will be worth this headache, since it can only be solved with going back to the old fork or getting yet another one.

  18. #18
    rmp
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    I think the TriCross fork is a pretty extreme example for tire clearance. I can run 1.9 29er mtb tires on that thing pretty easily - it's huge. It's kind of making sense to me why they have the large offset stock - the fork is built to take a pretty big tire (width and height). Probably hard to run a 29er tire on a 395mm a-c fork. So they make the fork longer but dial in extra offset to keep the trail in line.

    The EC70x seems to have plenty of clearance for my 700x35c Ritchey Speedmax tires (measure about 32mm) and my 700x45c Nokain W106 studded tires as well (measure about 38mm).

  19. #19
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    "Keep the trail in line?" That makes no sense. Adding more offset reduces trail, true, but adding length does not affect trail.

  20. #20
    rmp
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    Quote Originally Posted by KensBikes
    "Keep the trail in line?" That makes no sense. Adding more offset reduces trail, true, but adding length does not affect trail.
    ooops, my bad. No you're right. Should have said effective head tube angle/steering quickness. - better?

  21. #21
    cmg
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    here's a diagram that explains it.
    Attached Images Attached Images  
    Last edited by cmg; 11-05-2009 at 09:03 PM.

  22. #22
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    Quote Originally Posted by rmp
    Started working on pulling the old parts apart tonight. Have any of you guys pulled apart a Specialized "Mindset" headset? The headset itself is fine, and the main fork crown race pops right off.

    The problem is there is a little rubber wiper/spacer that seems to fit between the crown race and the actual crown of the Specialized anchor... errr I mean fork. Not sure I'd be able to get if off without busting it up - but you'll need it (or something like it) to put another fork on the TriCross. Without that wiper/spacer the fork crown rubs the bottom of the headtube . It's not much - maybe 1-1.5mm thick - but I'll either need to get a new one from my local dealer or find a taller crown race to make up for it.

    rmp
    Were you able to make the swap to your Easton fork? If so, how is the ride quality?

  23. #23
    rmp
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    Quote Originally Posted by mdutcher
    Were you able to make the swap to your Easton fork? If so, how is the ride quality?
    yup, got it figured out (the SingleCross does come with a strange two part crown race/wiper!).

    So far I think it's fine. Yes, the Easton has less offset, but it's also 10mm shorter - which steepens up the head angle half a degree or so.

    I did some rough calculations and including head tube angle change (caused by the shorter fork) there is about 2mm more trail with the Easton. I don't have a ton of miles on the bike yet after the change, but it certainly seems fine so far. And looks a ton better atmo.

    DSCF8103

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