Knobbies safe for twisty paved road descents?
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  1. #1

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    Knobbies safe for twisty paved road descents?

    Here's the short version of my question: Can I safely go as fast on a CX bike with knobby tires on a fast 40+ paved twisty downhills, as I can on my road race bike?

    Here's my plan:

    I plan to do this steep 9-mile, 4000-foot elevation gain climb on a dirt fireroad (Mt. Wilson Toll Road for you L.A. locals) and come down on a paved twisty road descent. My tires are knobbies up front (28?) and semi-slicks (30?) in back.

    I've used my CX only for commuting and a few fireroad rides. On my roadbike I've gone down the mountain road at 45 mph, slowing down a bit on the twisties. I've gone above 30 mph on the CX, but never on curves.

    I would think that even with the knobs, the CX would have better grip on the curves b/c of what seems to be a larger contact patch area. Am I wrong?

  2. #2
    kam
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    good question, i was thinking of doing the same kind of thing. i am working on a ss/fixed cx. i am going to run 35 kenda kwiks. i was hoping i can do a road climb, single track decent, and maybe mix it up the other way around.

    i am also a so cal'er, i ride the turnbull canyon area alot.

    sorry i can't help, but hopefully, we get some answers/opinion.

  3. #3
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    NO. Road tires are for pavement, the contact patch of the smooth tire will be bigger than the tips of your knobbies. Do the ride but DON'T push it in corners at 40+ mph on your knobbies. Even at lower speeds you can become familiar with the sensation of "knob squirm". Learn it, know it, and avoid it because it means you are about to crash.

  4. #4
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    Quote Originally Posted by wunlap togo
    NO. Road tires are for pavement, the contact patch of the smooth tire will be bigger than the tips of your knobbies. Do the ride but DON'T push it in corners at 40+ mph on your knobbies. Even at lower speeds you can become familiar with the sensation of "knob squirm". Learn it, know it, and avoid it because it means you are about to crash.
    Yep. Get some different tires.

  5. #5
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    I've done about 35 MPH down a paved road on my IF w/ Ritchey Speedmax 30's. Bike was stable, but I wouldn't recommend it if you have to do ANY turns, no matter how slight.

    It ain't worth the risk.

  6. #6

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    Danger WIll Robinson.

    If you really like the feeling of a two wheel drift at high speed then go for it. Otherwise it's a really bad idea.

  7. #7

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    'safe' is in the eye of the beholder. i've ridden decents that exceeded 40mph on mtb knobbies on a windy paved access road. it may not have been the most 'safe' thing that i've ever done, but i stayed upright. road tires are obviously going to be better in this situation, but don't avoid the ride or the speed because of it. but please do excercise caution.

    the_dude

  8. #8
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    Quote Originally Posted by the_dude
    'safe' is in the eye of the beholder. i've ridden decents that exceeded 40mph on mtb knobbies on a windy paved access road. it may not have been the most 'safe' thing that i've ever done, but i stayed upright. road tires are obviously going to be better in this situation, but don't avoid the ride or the speed because of it. but please do excercise caution.

    the_dude
    I concur. Don't push it in the corners, going straight is no different than with slicks.

  9. #9

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    Quote Originally Posted by the_dude
    'safe' is in the eye of the beholder. i've ridden decents that exceeded 40mph on mtb knobbies on a windy paved access road.
    Except the original question was:
    "Can I safely go as fast on a CX bike with knobby tires on a fast 40+ paved twisty downhills, as I can on my road race bike?"

    But then again, we don't know how fast he's going on the road race bike to begin with. Suffice to say that if the slicks are barely hanging on, then the knobbies would have slid out several mph earlier.

  10. #10

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    Thanks all. I'll take it easy on the turns.

    From the above responses, it looks like I shouldn't go stupid fast on the downhill turns.

    I think I can still make this a fun ride.

  11. #11
    pi makes wheels go round
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    Quote Originally Posted by NoMSG
    From the above responses, it looks like I shouldn't go stupid fast on the downhill turns.

    I think I can still make this a fun ride.
    Out of curiosity, why do you need knobs at all? Wouldn't slicks be fine for a dirt road climb? Assuming reasonably dry soil and not horrendously steep (although that isn't even a problem). I used to make a 45-ish mile commute that was 90% road (twisty back country roads) and 10% fire road with some rough washboard sections and pretty darn steep climbs. My little 23c vredesteins did pretty darn well for that 10%! Admittedly, i didn't go very fast around the dirt corners, and i only took this route when dry, but it was a lot of fun to do it that way...

    I guess my point is it sounds like slicks would suit your ride plan better than knobbies.

    -Damon

  12. #12
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    Knobbies are overrated

    Quote Originally Posted by damon
    I guess my point is it sounds like slicks would suit your ride plan better than knobbies.
    I agree 100%. Get some cushy 32mm slicks and have a blast.

  13. #13

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    Don't think I could do it on slicks.

    Quote Originally Posted by damon
    Out of curiosity, why do you need knobs at all? Wouldn't slicks be fine for a dirt road climb? Assuming reasonably dry soil and not horrendously steep (although that isn't even a problem). I used to make a 45-ish mile commute that was 90% road (twisty back country roads) and 10% fire road with some rough washboard sections and pretty darn steep climbs. My little 23c vredesteins did pretty darn well for that 10%! Admittedly, i didn't go very fast around the dirt corners, and i only took this route when dry, but it was a lot of fun to do it that way...

    I guess my point is it sounds like slicks would suit your ride plan better than knobbies.

    -Damon
    I've done this particular fire road about a dozen times on a mountain bike with standard knobbies and there are some sections that were difficult with that setup. Super steep sections with fist-sized rocks, sandy sections on the uphill, etc. And were talking a 2+ hour uphill climb with practically no breaks. I think the elevation gain may be closer to 4500 feet during these 9 miles.

  14. #14

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    Lightbulb all tires are not created equal

    Quote Originally Posted by NoMSG
    I've done this particular fire road about a dozen times on a mountain bike with standard knobbies and there are some sections that were difficult with that setup. Super steep sections with fist-sized rocks, sandy sections on the uphill, etc. And were talking a 2+ hour uphill climb with practically no breaks. I think the elevation gain may be closer to 4500 feet during these 9 miles.
    There are knobbies that squirm a lot on pavement (i.e. conti twister pro) because the knobs are tall and they have a squarish profile. Then there are ok tires for pavement cornering (bontrager & other shorter knobs) then there are tires that bomb pavement and are a bit of a compromise for dirt.

    The tires that will allow you to careen downhill while successfully summitting the dirt are Continental Contact tires. They're listed as touring/city/safety but they're quite light and nimble for what they are. They could market them as more of a performance tire versus utilitarian.

    http://www.conti-online.com/generato...ontact_en.html

    I may not have ever pushed my road tires to their max so don't just trust them blindly. In short, don't take my word for it and experiment for yourself.

    When I ride, I tend to corner aggressively on tighter corners at lower speeds. Once I hit 30+ I get a bit more cautious.

    The bigger question is whether they'll be enough for the dirt section. In SoCal sand I'm thinking if these tires can't do it, you'll be carrying anyway. oh.. get the 32's

    good luck
    Chaz

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