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Thread: Psychotic bike

  1. #1
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    Psychotic bike

    Our bike has gone nuts...

    I think this is a wheel-building (dish) issue, so I'll probably go over to the wheel board, but thought I'd run it by here first.

    Just got back from our first ride on a new wheel-set. I felt like I was on a track-bike, and not in a good way. The bike wanted to turn! Anything but straight ahead. A little left and it would pull left, a little right and it would pull right (but not as much). It was downright scary on the downhills. Climbing was better, but any maneuvering was still very strange. Like I was on ice.

    Here are the particulars:

    Rims - Replaced DT Swiss FR 6.1D with Mavic EX823. UST, slightly heavier, but only a few grams.

    Tires - Replaced tubed WTB Mutano 2.4 (very light and flexible, flat profile) with UST Continental Trail King 2.4 (heavy [but no tube] and stiff, round profile and significantly bigger despite the specs to the contrary)

    Don't have a dish tool. Checked rear dish by clearance between the stays after I mounted the tires (not much, so seems to be within 1/16"). On the front I used a calipers against a machinists square on the fork stanchions. Not terribly precise, maybe 1/8" error.... but no more than that.

    Not a fun ride ... Anyone have any idea what's going on?

  2. #2
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    How are the spoke tensions?
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  3. #3
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    I have very little experience, though this is not my first build. I am of the opinion (perhaps wrongly) that the tighter the better. I work largely by pitch. Initial truing was done only tightening, which I did until I twisted a nipple off. I used that pitch as my maximum tension limit.

    I can deflect a spoke at mid-point about a 1/4" with some effort.

  4. #4
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    Tires

    Tire shape can be a real blessing or curse depending upon the dirt.

    Could be spokes but that just seems like the wheel would need to be super slack.

    Before going to crazy, verify the tire pressures make sense for those tires and the dirt.

    PK
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  5. #5
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    All rock, loose on loose and gnarl. The gravely stuff was the worst. I ran them at 30psi. The previous tires where much less stiff and much less round and that seems a possible explanation but the difference was crazy. It's like it's a different bike, and I don't like it at all! I cut the ride short because I was so unnerved. Do you really think it could just be the tires?

  6. #6
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    You said the new rims are UST. Are you using UST tires?
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    Well try the old tires if is not to much of a pain in the butt, at least you isolate one variable..

    Ps: 30psi is way to low I run my tandem tires at least 50psi to prevent "snake bite" flats..

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    NY, Yes. The whole point was to have a "real" UST wheel-set and tires. Have had great luck on the singles in this terrain when we switched over. My wife, at 130 lbs, runs 18 psi with no issues and great traction. I'm 215 and run at about 28 psi.

    Pat, I was thinking that, but the old tires are not UST. I guess I could put them back on with tubes and see what it was like. I'm thinking of mounting some Nevegals, a similar tire to what we had been riding and the tire we run on our singles.

    Went to tubeless to avoid snake-bites. I'm guessing higher pressure would make this worse. Already sliding around too much.

  9. #9
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    Is this a new wheel set, or a new wheel set on a different bike? new fork or any other changes? just looking at other variables outside of the new wheels, haven't really heard of anything like you describe.

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    Quote Originally Posted by ki5ka View Post
    NY, Yes. The whole point was to have a "real" UST wheel-set and tires. Have had great luck on the singles in this terrain when we switched over. My wife, at 130 lbs, runs 18 psi with no issues and great traction. I'm 215 and run at about 28 psi.

    Pat, I was thinking that, but the old tires are not UST. I guess I could put them back on with tubes and see what it was like. I'm thinking of mounting some Nevegals, a similar tire to what we had been riding and the tire we run on our singles.

    Went to tubeless to avoid snake-bites. I'm guessing higher pressure would make this worse. Already sliding around too much.
    We run Nevegals tubeless on our Fandango, me 180, wife 100. The handling when we're down in the 30lb range is very sketchy. MUCH oversteer, just as you're describing. The example where this is most notable is when I let the front wheel on my Yamaha Riva moped get too low...it does exactly the same thing, only more pronounced, likely because of the small diameter wheel.

    Put the pressure at 40 and try it. Better yet, try 45 just for giggles.

    We had a slow leak in that front last week on a ride...couldn't get it to seal and I used 2 CO2's, inflating periodically to get through the ride. When it got too low, it was oversteering like crazy. I knew exactly when it was time to throw some more CO2 in there.

    MR

  11. #11
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    Mark, it seems everyone agrees I've been running too little pressure. I'll give it a bump and see what happens. Jeff, new wheel-set that I built (so anything possible could be wrong with it ) and new tires.

    As for how it feels... If you ever redesigned bikes as a kid, it's like when you put took the raked fork from your banana bike and put it on upside down, bolted on a little wheel so it'll fit in the frame, held on with some vice-grips for a head-set, you know, like that feeling

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    Most previous air pressure threads have shown results to generally be in the high-30s to low 40s range. I run 40 front and 35 rear, tubes, and get terrible wander when the front drops much below 35.

    As an alternative test, can you mount your newly-built tandem wheels to a single bike and see how it goes? I also like the old-tires test, just to see what happens. Easier tests than dealing with redishing the wheel or somesuch.

  13. #13
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    Quote Originally Posted by Okayfine View Post
    snip... can you mount your newly-built tandem wheels to a single bike and see how it goes? I also like the old-tires test, just to see what happens. Easier tests than dealing with redishing the wheel or somesuch.
    Blow'n like stink, too windy to ride today, which got me to thinking.... the wind has been blowing like bat-**** lately, and two days earlier, both my wife and I crashed (on our singles) because of the high winds. Maybe this is all just wind related?? I don't remember it being particularly windy, but maybe I just didn't notice...

    Eyeballing the dish, it looks good. Tires are as close to exactly centered as my eyes can discern. I'm not sure why I latched onto that idea, probably just my insecurity in my ability to build a wheel well.

    This tire (Continental Trail King) is REALLY stiff. At 30 lbs, it feels far less compliant than what we've been running, but I'm thinking of putting the Conti-King on the back of my single and putting the Kenda on the front of the tandem and giving that a go. Okayfine, I like the idea of putting the new wheel on the single, that's smart, but changing rubber sounds easier than changing brake discs so I think I'll go that route. I'll report back after we've had a chance to ride with the Nevegal mounted on the new rim up front.

    Thanks for all the input! Love this site

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    Put 10 more lbs in the tire and ride it first, before giving up on the tire??

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    Also, what are the respective widths of the old rim vs. the new rim? A narrower rim for a given tire size will have handling implications. Moreso if the new tire is even wider than the old.

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    No riding yet.... event at school keeping me busy. Will report back after the weekend...

  17. #17
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    Added pressure and had a terrible ride. Came "that close" to a crash when I turned into the upside of the trail and washed the front end out. Stoker is still nursing bruised ribs from that crash on her solo last week and a slide down the downhill side would not have be fun. My confidence is pretty much in tatters at this point which is of course, making me a danger to my wife. Sure hope I get this worked out soon.

    Was reviewing all the obvious considerations when I noticed that I mounted the tire in the wrong direction! Hopefully it's that simple.

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    Hopefully, but I doubt it. I've mounted directional tires backwards on the front and didn't experience this sort of change.

    When you say you added pressure, what did you go from and what did you go to? Any other experiments (change back to old tires, swap rims to a single)? Rim width comparo?

  19. #19
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    Tread orientation - Yeah, I'm thinking that probably isn't it either.

    The old tires are not tubeless. If I run out of ideas, I will put them on with the tube, but I think that will be my last option.

    Pressure - I was running a bit over 30, went to a bit over 40. Very counter-intuitive to me because the front already felt "hard" to me, with far less traction than I am accustomed to, but enough people suggested it when I asked for advice, I figured I'd take it

    So, I had established the dish by measuring from the fork to the rim, but there is no consistent reference spot to do that. Today, I made some wood feeler gauges and used the tire and the narrowest spot between tire and fork as my reference point. This worked quite well; it was very clear that the rim was not centered. I added what turned out to be more than a full turn to the disc side to pull it over. That seems like a lot... Figured that if I was that far off on the front, I better check the back too; sure enough, that was just as far off.

    So, I've corrected (I hope) the dish, remounted the tire in the correct orientation, and our next ride will be with the pressure back down where we usually ride. Should have a report to offer tomorrow.

  20. #20
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    Stupid question...How accurate is your gage. We can tell you a pressure, but if your gage is wacked it could be grossly wrong.

    PK
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  21. #21
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    I'm still sayin' the spokes are loose.
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  22. #22
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    Well I'm running out of threads, so if it's spoke tension my spoke length is wrong. Certainly could be, I didn't do the calculations myself, and the Mavic inserts might throw the calculator off... When I re-dished, I only added tension so overall tension is higher than it was.

    Not at all a stupid question Paul. I used to do a lot of rock-crawling and my truck buddies and I would routinely find enormous differences from one gauge to the next. My digital reads about 2 psi higher than the floor pump that I usually use to measure pressure.

    Heading out for a ride now...

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    Quote Originally Posted by Okayfine View Post
    Rim width comparo?
    According to my quick search on the Goog, you went from a rim width of 32mm to a rim width of 24mm. That, when combined with a large-volume tire, will give you a lot more squirm on its own, but especially in changing from the wider rim itself. Can you verify your actual rim widths to compare?

  24. #24
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    Good ride, problem fixed! It seems it was the dish (and perhaps spoke tension). Guess I know what my next shop purchase is going to be

    Park Tool WAG-5 Portable Wheel Dishing Tool - Normal Shipping Ground

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    Okayfine, You're right, the old rims are wider. Measured on the outside I get 29 mm vs bit less than 32 mm; not as big a difference as the specs suggest but maybe I'm measuring wrong. This was the only tandem suitable UST rim I could find, so width wasn't a consideration when I chose these.

    There is certainly less squirm with the higher pressure, but during the 2 short rides I took with higher pressure, washouts seem to happen faster, more frequently, and with no sense that there might be a chance to ride out of it. I dropped the pressure back down to 32 today and had a much better ride (along with re-dishing). Twice I washed out "big" and recovered, something that has become routine on our rides in this loose gravely terrain. Psychotic bike-2013-09-07-08.34.38.jpg

    It's clear I'm in the minority here, but I am much more secure with softer tires. I'll trade a bit of squirm for the added traction. I would probably feel differently on more stable surfaces.

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    Glad you found a fix! And terrain definitely has an impact on suitable air pressures.

    Any data on how much your dish was out? Just for future reference.

  27. #27
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    The medium feeler gauge I made is 2 mm and the thick is 4 mm I would put the difference somewhere between there. That amount was similar on front and back, both on the same side (flat side).

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