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  1. #1
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    650b floppy steering issue ?

    I have an 08' Turner RFX running a Pike fork . The axle to crown height @ 520mm is 15mm less than the spec'd 535mm fork. I purchased a Blunt / Neo-moto combo which is roughly 1/2" taller in diameter- thought it would make for a perfect geometry. Took it for a driveway spin and the front end feels slack / floppy. I checked the HA using an angle protractor and there wasn't much of a change from the original 68*. I read on the 29er forum about a forks "trail angle" . Any thoughts on this ? Thanx

  2. #2
    TNC
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    Yeah, that's an issue with a 29'er in many cases, but the 650B usually doesn't introduce that radical a change. I'll mention something on my Nomad that kind of goes the other way. When I had my 66SL (170mm) on my Nomad with a 2.5 26'er setup installed, it felt floppy at rest. It felt absolutely great as soon as it was moving to any degree, but it had that flop at rest or pushing it across the shop. When I installed the Nixon 160 with the 650B, that flop was barely noticeable. The ride height of the bike was really quite close between these two setups. I don't know...just food for thought.

    My '03 Bullit when it had that '02 Monster T on it had a flop to it at rest, but again, it felt great under way. I'm thinking you'll like the feel of the setup under real riding conditions.

  3. #3
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    Feels like I went from a 5" to a 6" fork. May need some time on the trail but I thought I wouldn't notice much even in the driveway.

  4. #4
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    A little change in head angle and trail can cause a significant change in handling feel, especially for a bike like a Turner that is pretty carefully designed for a specific handling feel. I'm not surprised that this change is noticeable. Can you reduce the travel a couple of cm? Try a test ride with more sag just to reduce the fork length and see how it feels...

  5. #5
    Mr.650b - Mr.27-5
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    The increase in trail is likely the culprit for the floppy feel at slow speed. Rest assured that at the right speed this bike will literally "come to life" on trail.

    I have had similar experiences with one of my conversion projects. The Ibex flopped at slow speed and wandered on climbs, but once I hit anything over 15mph, the bike came into its own. It almost as if someone threw a switch and "turned the bike on"; it had a whole new personality.

    Keep us posted!

    KP
    Last edited by Kirk Pacenti; 12-19-2008 at 09:30 AM.
    “Those that say it can’t be done should get out of the way of those doing it.”

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  6. #6
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    {QUOTE}The other important change is that the trail value has gone up quite a bit. This is due in part both to the larger wheel, but also the X-Fusion fork. The fork has a very scant 33mm of offset built in. This means it automatically increases trail by about 6mm over the industry standard 39mm off set forks . Combined with the larger wheel the trail value goes from roughly 87.9mm way up to 99.5mm, [based on some quick calculations]. This does a couple things. Slow speed handling is a bit vague and the front end will wonder a bit on climbs.

    I think this is the problem. The one thing I really liked about the RFX / Pike combo was it's precise steering and now it seems a bit vague. I'll have to hit the trails and see if it is easy to adjust too. Thanx

  7. #7
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    The biggest change in handling going to 650b front only, or less so going to 650b both front and rear on the same bike, comes from the changed rider weight center, IMO.

    Some riders find that the slacker steering and more rearward weight balance going to 650b front only improves their bike’s handling feel, especially when the trails are loose and rough.

    Here's what worked best for me to maintain familiar steering feel going to 650b front only:

    Lower the handlebars 1/2 inch by swapping spacers under the stem to over the stem or a using a lower rise bar. This will put your weight balance back to be neutral as before with same sized wheels. Also, but not as important, if you have an adjustable travel fork lower it slightly, up to 10mm to steepen the head tube and steering angle which reduces steering trail to be closer to what it was with the smaller front wheel, and this also further shifts weight forward slightly. Adjusting rear sag to be slightly less in the rear is another way to shift rider weight forward closer to the familiar prior balance over the wheels and pedals.

    Later I fit 650b on the rear of my bike and found that, unlike 650b front only, going to 650b both front and rear on the same bike has almost no noticeable handling effect change compared to smaller wheels, other than increased traction, easier rolling, and smoother feel. The steering trail difference is just not enough to be noticeable. Only the 1/2 inch higher rider weight center makes it a bit more difficult to keep the front wheel on the ground while steep seated climbing, and I left the handlebars 1/2 inch lower to maintain easy climbing, and have a remote dropper seat post I often drop 1 inch on technical trails.

  8. #8
    TNC
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    keen, why did you change from the Pike? I thought the Pike fit a 650B with no issues.

  9. #9
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    I went to a flat bar and found no real difference in handling. Moving my CG forward and down seems to do the trick.? FWIW, my Reign has a 67 degree HA anyway. It isn't going to clinbe like an XC bike, no matter what. On long sustained climbs I will dial the TALAS down a few mm, just to make it hook up better. I just hate when I forget to dial it back up before I descend, so I usully leave it alone and ride.

  10. #10
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    Quote Originally Posted by TNC
    keen, why did you change from the Pike? I thought the Pike fit a 650B with no issues.
    I still have a Pike - The quote / Velvet was another poster. In anticipation of the 1/2" taller 650b I removed a 10mmm & 2.5mm spacer from under the stem. The 08' RFX has 6.4" of travel, to better match my 140mm Pike I have a rear shock w/ less stroke (same eye to eye) that gives 5.6" of travel. I also run 17mm of sag vs. the stock 20mm. Even w/ my current suspension and 26" wheels the bike seems really rearwardly biased - lifts the front very easily on any inclines.

    Would a 650b rear help this trail steering issue enogh ?

  11. #11
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    Quote Originally Posted by keen
    I still have a Pike - The quote / Velvet was another poster. In anticipation of the 1/2" taller 650b I removed a 10mmm & 2.5mm spacer from under the stem. The 08' RFX has 6.4" of travel, to better match my 140mm Pike I have a rear shock w/ less stroke (same eye to eye) that gives 5.6" of travel. I also run 17mm of sag vs. the stock 20mm. Even w/ my current suspension and 26" wheels the bike seems really rearwardly biased - lifts the front very easily on any inclines.

    Would a 650b rear help this trail steering issue enogh ?
    granted, there's no "right" way to do it, i would suggest trying a stem that is 10 or even 20mm longer, maybe bumping your seat a little more forward in the clamp, running the full-length stroke rear shock w/ maybe a little less sag, or run rear at 20mm and front at 25-30mm

    there's a lots of ways to shift/change your front/rear weight bias to suit your preferences

  12. #12
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    Quote Originally Posted by onespeedpaul
    .... bumping your seat a little more forward in the clamp, ...
    Keen, compared to more smooth trail climbing oriented XC full suspension bikes with low BB's which are nearly 1 inch lower than your '08 RFX, your relatively high BB places the rider weight higher than a climbing oriented bike. On most full suspension designs, the higher rider position on a bike with a high BB exaggerates the rear squat and lighter front wheel when climbing.

    As onespeedpaul mentioned above bumping your seat forward will help climbing. Your weight would be more forward while climbing and the front wheel won't be as light.

    Changing to a longer stem as much longer as you move the seat forward would retain your reach, but it would also slow steering. An alternative to maintain familiar steering response is to lower your bars by moving stem spacers above the stem or using a flatter bar or stem with less rise or reversing the same stem to be negative rise, and bend your elbows a little more when steep climbing. Even without changing handlebar position, just bumping the seat forward will make climbing easier.

    Additionally, here's some geometry to confirm your earlier post about the 650b front-only being near spec in steering trail. The '08 RFX has a pretty high BB at 14.1 with speced shock and fork (a good design for rough trail and the deeper sag of longer travel). Your short stroke shock with same i2i didn't lower the rear (and your reduction in sag actually raises ride time height in the rear), but the Pike is nearly 1 inch lower at full height than the speced fork so the BB is lowered to about 13.8 with 26" wheels, and steering trail much quicker than design spec. Adding the 650b raises the BB up to about 13.9 and the larger wheel geometry returns steering trail (and flop at low speed) to be very close to design speced responce.

    Adding a rear 650b would bring the BB back up to 14.1 using the Pike fork and make the frame angles steeper which will reduce steering trail to be quicker steering than designed spec with your RFX with non-spec shock and fork. This should feel nearly the same as you were accustomed to with the 26" wheels.

    No matter how you go with wheels, bumping the seat forward even just 1/4 in will have a noticeable effect on keeping the front wheel down while climbing. 1/2 inch or more forward would be a major help for climbing, but maybe affect overall handling more than you want.

    The attached pic is clipped from the '08 Turner RFX web page.
    Attached Images Attached Images

  13. #13
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    Quote Originally Posted by derby
    Keen, compared to more smooth trail climbing oriented XC full suspension bikes with low BB's which are nearly 1 inch lower than your '08 RFX, your relatively high BB places the rider weight higher than a climbing oriented bike. On most full suspension designs, the higher rider position on a bike with a high BB exaggerates the rear squat and lighter front wheel when climbing.

    As onespeedpaul mentioned above bumping your seat forward will help climbing. Your weight would be more forward while climbing and the front wheel won't be as light.

    Changing to a longer stem as much longer as you move the seat forward would retain your reach, but it would also slow steering. An alternative to maintain familiar steering response is to lower your bars by moving stem spacers above the stem or using a flatter bar or stem with less rise or reversing the same stem to be negative rise, and bend your elbows a little more when steep climbing. Even without changing handlebar position, just bumping the seat forward will make climbing easier.

    Additionally, here's some geometry to confirm your earlier post about the 650b front-only being near spec in steering trail. The '08 RFX has a pretty high BB at 14.1 with speced shock and fork (a good design for rough trail and the deeper sag of longer travel). Your short stroke shock with same i2i didn't lower the rear (and your reduction in sag actually raises ride time height in the rear), but the Pike is nearly 1 inch lower at full height than the speced fork so the BB is lowered to about 13.8 with 26" wheels, and steering trail much quicker than design spec. Adding the 650b raises the BB up to about 13.9 and the larger wheel geometry returns steering trail (and flop at low speed) to be very close to design speced responce.

    Adding a rear 650b would bring the BB back up to 14.1 using the Pike fork and make the frame angles steeper which will reduce steering trail to be quicker steering than designed spec with your RFX with non-spec shock and fork. This should feel nearly the same as you were accustomed to with the 26" wheels.

    No matter how you go with wheels, bumping the seat forward even just 1/4 in will have a noticeable effect on keeping the front wheel down while climbing. 1/2 inch or more forward would be a major help for climbing, but maybe affect overall handling more than you want.

    The attached pic is clipped from the '08 Turner RFX web page.
    Thanx for the well thought out analysis. Currently running a Thomson straight post about mid position - i'll bump it forward. My stem bar combo works just right for descending so no changes / sacrifices will be made in that area. As I mentioned the RFX feels really rearwardly biased & I have owned quite a few AM/ FR / DH frames. Gonna hit the trail w/ the front only & if there is a positive overall gain I might try the rear as well.

  14. #14
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    just wanted to throw this out there:

    could it be a possibility that the stem is (while not the sole cause for sure) attributing to the floppy feel at low speeds? seems to make sense to me...

    either way, at trail speeds, probably your concern will vanish

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