Rear wheel dusty spinouts when climbing

[Catrin]

I've had several hard falls this summer due to my rear wheel spinning out on dusty curves on the trail. If my memory serves me correctly, each time I was climbing and thus my weight would be more forward on the bike. I THINK that I was in the granny gear each time, though I am unsure of that. I was today.

MTB falls are just going to happen, that is a given. Is there something that might be going on with my body position that could make this more likely? I believe I had just down-shifted the rear to get up the hill... I've seen far more dust on the trails earlier in the summer, but there was still a good amount of dust present. I seem to be prone to this type of fall so I suspect it is something I am doing...or NOT doing.

[Hi Ho Silver]

I was taught that when climbing a loose surface, one should-
a) shift to a higher (i.e., harder) gear, and
b) assume the same position as a jockey riding a horse - your butt should be hovering slightly above and behind the saddle, your torso should be bent down.

The higher gear is required because you'll be using your full body weight on the pedals so you can power up the hill (rather than spin up the hill). The "jockey position" allows you to dynamically shift your weight enough to the rear to maintain traction if you feel the rear tire starting to spin out.

[Catrin]

hmmm, I am picturing this. So being bent forward you still have weight on the front wheel, and it doesn't sound like I would need to shift my rear much to get in the right position. I will experiment with this, almost every fall I've had this summer (outside of when I tested the laws of physics with the front brake) has been exactly this kind of fall. My poor right hip and shoulder is taking a beating from hitting the ground so I need to do something different.

Thanks - and if anyone else has other thoughts or advice please do add them. I had wondered about my gearing - but of course was also trying to climb at the same time. In this case I was on a new trail to me and wasn't sure how long the climb would go - which is why I was in the granny. It was still fun though

[laura*]

I've had several hard falls this summer due to my rear wheel spinning out on dusty curves on the trail. If my memory serves me correctly, each time I was climbing and thus my weight would be more forward on the bike.

Do you mean that you were climbing, the rear wheel lost traction, started spinning, and the loss of forward power made you crash? If so - learn to recognize the situation, be prepared to slam on the brakes and plant both feet on the ground.

Or do you mean that were going around the corner and the rear wheel slipped sideways to the outside of the turn? This probably means you were leaned over too much. When I was riding a lot on knobby tires, somehow or other I learned to keep the bike somewhat perpendicular to the (road or trail) surface. (I think this is because once the front tire skidded sideways when I was leaned over going around a fast corner.) If the speed of the turn required a lean, I'd move my body over, but keep the bike mostly upright. Sheldon et al. say not to do this - it imparts significant non-normal forces in the bike. However, some tires simply aren't able to grip off of perpendicular. Or they might deform, letting the rim roll towards the outside. In summary, be constantly aware of how your tires are contacting the ground and don't ask more of them than they are able to perform.

[Catrin]

....
Or do you mean that were going around the corner and the rear wheel slipped sideways to the outside of the turn? This probably means you were leaned over too much. When I was riding a lot on knobby tires, somehow or other I learned to keep the bike somewhat perpendicular to the (road or trail) surface. (I think this is because once the front tire skidded sideways when I was leaned over going around a fast corner.) If the speed of the turn required a lean, I'd move my body over, but keep the bike mostly upright. Sheldon et al. say not to do this - it imparts significant non-normal forces in the bike. However, some tires simply aren't able to grip off of perpendicular. Or they might deform, letting the rim roll towards the outside. In summary, be constantly aware of how your tires are contacting the ground and don't ask more of them than they are able to perform.

It is the second of your scenarios - I seem to ALWAYS be in a curve to the right when this happens, and the rear wheel skids out from under me toward the outside of the turn, exactly as you describe. I don't believe that it has ever happened on a curve to the left. This sideways slide happens FAST - perhaps the presence of the dust just adds to the effect. I also didn't think I was leaning, but that doesn't mean I wasn't. I do know I've learned unconsciously in the past (people told me later) so I wouldn't be surprised. There are never obstacles when this happens, typically just a right-hand uphill curve with lots of dust...

The first situation you describe I can easily stop with brakes - and I don't clip in so I can just brake and put my foot down. I am pretty darn good at stopping fast on the trail...

[indysteel]

Catrin, are you running the tires that came stock on your Jamis? According to Jamis' website, the bike came with Geax Mezcal. I just read some reviews of that tire on MTBR that consistently complained about bad traction in dry, loose conditions. If those are your tires, you might talk to Jonathan about getting some tires known for a bit more grip (or just replace your rear tire). Yes, you'll encounter more rolling resistance, but I think that's better than losing traction and slipping out.

[tzvia]

Unless it just rained, our trails are a mix of dust/sand over hardpack or dust over sand and roots. Sometimes, just climbing, the rear would break loose and it was always because I was not cranking smoothly, but torquing in bursts. In your case, you are in a turn, so it may be due to you leaning a bit and maybe bit of torquing? I am thinking the rear tire is spinning in jerking motions, not smoothly as you claw your way up. With a slight lean during such torque-down on the pedal in really loosely packed dust while turning, the rear tire could just kick out.

I've been trying to keep my rear end weighing down the back, while I lower myself from the waist 'tits to the tube' I think is the term. Raising and lowering my torso as needed for the incline is all I do to keep the weight centered between both wheels. Now if only I could muster a nice smooth spin, pulling up and pushing down fluidly instead of looking like a fish on a boat deck...

It also helps to have the right tire for the application. Been using a Specialized Captain Control in back (2.0), and it is ok, not great. Also have a Tioga Psycho Genius on another wheelset (front and back) and it is so much better in sand and pebbly stuff. Tires can make a big difference.

[Becky]

All good suggestions. I would also, in addition to considering tire choice, consider your tire pressure.

Are you standing or seated when you break traction on climbs?

[laura*]

I also didn't think I was leaning, but that doesn't mean I wasn't. I do know I've learned unconsciously in the past (people told me later) so I wouldn't be surprised.

To make a turn on a bicycle requires leaning - it's simple physics - one needs to balance centrifugal force with gravitational force. Of course turning very slowly needs very little lean. The conventional advice is for the rider to stay centered on the bike and to lean the whole rider and bike unit. That works in a criterium with a perfect road surface...

I seem to ALWAYS be in a curve to the right when this happens

I wonder if your attention is leading your position on the trail. In other words, while still in the turn, your mind has already moved on to the straight section - and you move your body toward it. With this always happening in the same direction, maybe it is a dominant eye related thing.


I agree with indysteel about trying a different tire.

[Catrin]

Catrin, are you running the tires that came stock on your Jamis? According to Jamis' website, the bike came with Geax Mezcal. I just read some reviews of that tire on MTBR that consistently complained about bad traction in dry, loose conditions. If those are your tires, you might talk to Jonathan about getting some tires known for a bit more grip (or just replace your rear tire). Yes, you'll encounter more rolling resistance, but I think that's better than losing traction and slipping out.

Yep, same tires that came with my bike. I don't care about more rolling resistance, I am not racing, just out there for fun anyway. I've worked hard to get strong legs so I want to use them After reading your post I went to MTBR and read the same reviews. Am already researching my options - at least for the rear. No trail riding until I replace that tire! As the Jamis XC Comp is a race bike the tires were probably meant for that - I read where someone referred to them as "semi-slicks". I've not really looked at other mtb tires before so perhaps, in comparison, they are? I guess race tires would need to be a compromise between rolling resistance, weight, and grip - though surely the latter would win out but what do I know?

Unless it just rained, our trails are a mix of dust/sand over hardpack or dust over sand and roots. Sometimes, just climbing, the rear would break loose and it was always because I was not cranking smoothly, but torquing in bursts. In your case, you are in a turn, so it may be due to you leaning a bit and maybe bit of torquing? I am thinking the rear tire is spinning in jerking motions, not smoothly as you claw your way up. With a slight lean during such torque-down on the pedal in really loosely packed dust while turning, the rear tire could just kick out.

This is a good thought and hadn't considered it. I honestly do not know if I crank smoothly or torquing in bursts. I will try to pay attention to do this next time I ride. Thanks for the tire recommendation, I am starting to research my choices but there are many to choose from. We have had a brutal drought this year, and on previous rides I've seen much deeper dust than yesterday.

All good suggestions. I would also, in addition to considering tire choice, consider your tire pressure.

Are you standing or seated when you break traction on climbs?

For the trails I ride, I run 30psi. I am a small woman and was advised by the folks at the mountain bike clinic at that same park that this was appropriate for my weight and size for those trails.

....

I wonder if your attention is leading your position on the trail. In other words, while still in the turn, your mind has already moved on to the straight section - and you move your body toward it. With this always happening in the same direction, maybe it is a dominant eye related thing.


I agree with indysteel about trying a different tire.

Laura - thanks again - of course we have to lean to corner, but it makes sense to me if the tire doesn't grip well and we might lean over too much that this would contribute to the problem. I THINK I am past this however, back when I first started last year I would lean over much too far on parts of the trail that scared me - and of course I had to stop because I was over too far.

As far as my attention, I try to keep my eyes on where I am headed. So, yesterday I had just started to climb a hill that appeared to be fairly steep with few obstacles so I geared down just 1 click (rear) and focused on what appeared to be the top (it wasn't). It was just after that I entered the curve that bit me. It is my practice when looking ahead to look around and up the trail rather than *just* looking at the top. The fall came at the bend of the curve if that makes sense.

I am unsure what you mean that this might be dominant eye related. It may be I've not had enough coffee yet, but it might be helpful if you would like to say something more about this.

I appreciate the comments and helping me think this out. I am feeling much better about this, even if I do have war wounds I am bound and determined to finish this season stronger than when I started, and more comfortable on the intermediate trails. It felt awesome yesterday to FINALLY break free of the one trail I've been riding for 2 months.

[OakLeaf]

+1 on smoothing out your pedal stroke. As you know I'm not a MTB'er, but it's pretty easy to spin the rear on a road bike too. One-legged drills, cadence intervals, riding rollers if you have them - all those will help you pedal in even circles instead of "big bang" squares.

[spokewench]

It is positioning on a mountain bike. You need to keep weight over back and front of bike; so you need to crouch down lower than you would on a road bike to keep the weight over the back wheel a bit; also off road the hill can be steeper so you still have to keep the weight over the front wheel more as well or you will start to wheelie; it is a balancing act so you can be totally static on the bike. Smooth, smooth pedal strokes when it is really loose.

[Becky]

It's been my experience that some tires have a nice transition from centerline to side knobs and can be gradually leaned in a turn, while others have fewer transition knobs and like to be "thrown" into a turn by an aggressive rider. I greatly prefer the former. Something to look for when you're reading reviews...

Also, not to beat the tire pressure horse too much, but I think it bears a second look. Breaking traction is often a symptom of overinflated tires for the bike, rider, and conditions combo.

You and I are the same weight, +/- a few pounds, and I run my tires in the 22-24 psi range. My DH, who is twice my size, runs his at 30-32 psi. Maybe lower pressures are something to experiment with? You can always pump them back up if you don't like the ride.

[laura*]

I am unsure what you mean that this might be dominant eye related. It may be I've not had enough coffee yet, but it might be helpful if you would like to say something more about this.

The thought is that (assuming your right eye is dominant) in a right hand turn, your right eye has an unobstructed view of the trail ahead. Then, like a child in a candy store, your attention "runs" forward before you're done with the turn. In a left hand turn, that same eye might stay better focused on the turn itself.

Another thought: Haven't you posted that your left ankle was surgically repaired? And as a result you are more powerful with the right leg? I think it's been written that in a turn one should put more force on the outside pedal - which would be the left pedal in the turns when you fell to the right.

[Hi Ho Silver]

To make a turn on a bicycle requires leaning - it's simple physics - one needs to balance centrifugal force with gravitational force. Of course turning very slowly needs very little lean. The conventional advice is for the rider to stay centered on the bike and to lean the whole rider and bike unit. That works in a criterium with a perfect road surface...

The problem with the above advice is the stated condition "with a perfect road surface". I recall reading an article ages ago by Alexi Grewal (I think...) that discussed cornering when the surface is wet or otherwise imperfect. His advice was to lean the bike, but keep your weight centered over the path the bike is taking (i.e., the line connecting the points where the front and rear tires contact the surface). From a physics perspective, this reduces the lateral forces on the tires and helps to prevent the tires slipping off to the sides. I've tried to follow his advice on wet roads, and it does seem to help prevent side-slip.