Ask Pinkbike: Whips, Carbon Rims, and Cracked Frames
Here at Pinkbike we get inundated with all kinds of questions, ranging from the basic "Can I have stickers" to more in-depth, soul searching types of queries like if you should pop the question or what to name your first child. Ask Pinkbike is an occasional column where we'll be hand picking and answering questions that have been keeping readers up at night, although we'll likely steer clear of those last two and keep it more tech oriented.
Whip it Good
Question: Pinkbike user wreckitsteve asked this question in the Freeride and Slopestyle forum: Is whipping your bike a bad thing? I meant, I do whip a lot, and land mostly on flat, with no transition because the nearest track available with big jumps doesn't have a transition landing (the builder does make some but it was way too short while I landed farther). And also I ride a lot of urban too. Today I started to feel that my bike is heavy - it can't go fast as my other bike. It seems like the rear wheel is a little bit not aligned with the frame - I've change hubs and it was no different. Is it possible that it is the chainstay that is bent? Is it because I do too much whip? Or is it because I do whip onto a flat landing?
 | You make it sound like whip is some kind of elicit drug, something sold in dark alleys by shady characters in trench coats, but I guess the feeling of getting your bike sideways is pretty addicting. It's not entirely clear whether you're talking about a tail whip, where the bike revolves 360 degrees underneath you, or a 'regular' whip, which means getting the bike as close to a 90 degree angle above the trail before straightening out for landing. It's the straightening out part that's key - landing sideways puts extra stress on your wheels and frame, and could certainly cause a bent chainstay. The same goes for flat landings - the forces generated by landing a trick to flat are much greater than if you land on a smooth transition. Just because you can overshoot a jump doesn't mean you should - aim for that transition, and your wrists and bike will thank you. As for your potentially bent frame, I'd start by examining it closely for any cracks, bulges, or sections where the paint is discolored or flaking off. Spin the wheels - do they rotate freely, without any major wobbles? How about your spokes? Do they feel evenly tensioned? Are there any creaking or popping sounds when you pedal? You may want to swing by your local bike shop to have them take a look as well, but whatever you do try to avoid telling them you were "just riding along." If everything checks out, whip away to your heart's content, but try to refrain from those hucks to flat, unless you have a wad of cash lying around to replace the parts you're sure to break. - Mike Kazimer |
This is a tailwhip.
And this is a whip.
Can Carbon Rims Be Too Stiff?
Question: Gooded asks in the All Mountain, Enduro & Cross-Country forum: I recently purchased a set of carbon rims from Light Bicycle for my 2014 Enduro 29 (carbon). The stock wheels (24mm internal) allowed the rear tire to roll a little at around 27 psi. (I'm about 160 lbs with gear). The stock wheels also felt a little flexy (mostly noticeable when traversing at low speeds, or when cornering at high speeds). My new wheels are 32mm internal-width, 32 hole, 3 cross. They felt much stiffer as soon as I started riding them. And, because they are wider, I was able to run much lower pressures without rolling my tires. I went from 25/28 psi to 18/22 psi. Because of this stiffness, and pressure, I'm able to corner faster in berms.
There does seem to be a HUGE tradeoff though. In the rough stuff, the bike seems to bounce around a lot more. I haven't adjusted my suspension based on the wheels yet, so that might help, but I don't really think that's it. The way I described the feeling to one of my buddies was, "imagine you're in some rough terrain and your front tire gets light, so it's barely touching the ground. Now you bump the edge of a rock with your front tire. It feels like my stock wheels would have deflected sideways and the impact would not have affected my trajectory much. It feels like my new carbon wheels are so stiff, that when they bump that same rock, the entire front end of the bike deflects to the side."
I had hoped that the stiffer wheels would help with the "point and shoot" method of tackling rock gardens. Each time I have purchased a stiffer bike or fork, I have been impressed with how much it helped me with technical sections of trail. I was able to put the bike where I wanted. This is the first time where added stiffness seems to be a disadvantage. My new rims are wider and stiffer. I'm glad they're wide, but I'm not sure "super" stiff rims are an advantage. I'm wondering what other riders have experienced. Do you love your carbon rims in every aspect, or do you agree, there is a definite tradeoff? Is there a way to counter this stiffness (spoke tension, spoke count, lacing pattern, etc)? Thank you.
| First, you are correct that the change in the ride quality can be noticed by many riders who switch to a stiff carbon rims after riding old wheels that have been beaten into submission, or new ones that are lighter weight or more flexible. Specialized aluminum and carbon rims tend to be very compliant (ever hear the "bawaanng" sound that comes from the change in spoke tension when you smack a Roval wheel on a rock?), so the switch to the wider Light Bicycle rims should not have been a subtle change in feel. That said, the effects of stiffer wheels are not as dramatic as pro riders and the press often insist, especially when using trail-bike-width tires at lower pressures and on a longer-travel chassis like the Enduro 29. My guess is that some of the firmness you are referring to is the added sidewall support that the wider rims give, which may require a reduction in low-speed compression on both ends of your suspension. I have experienced that as well. Also, you should expect more feedback through the handlebar because stiffer wheels and tires that don't tuck add up to much less lateral deflection. Ten millimeter wider bars may be the solution. I have also noticed that the width of the sidewalls can exceed that of the edging blocks of some tires when they are mounted to wider rims. This can cause the tire to refuse to grip off-angle rocks and often to bounce laterally through rock gardens that the bike had previously held a tight line through. You may have to choose a different front tire that has more pronounced edging blocks up front to complete your conversion to 32mm-width rims. Also, you did not mention whether your tires were tubeless - they absolutely should be when paired with wide rims. far as reducing spoke tension, I'd vote against that, because it dramatically reduces the lifespan of a wheel. Lighter gauge spokes at the correct tension would be a better solution. - RC |
Specialized moderates the stiffness of its 30mm-inner-width Roval Traverse Fattie SL carbon rims by building the wheel with light-gauge spokes.
Cracking Weekend
Question: Pinkbike user Pushnaka asked this question in the Downhill Forum: Hey there guys. Had a smashing week in Wales last week - literally. I snapped the rear chain stay on my 2010 Trek Session 8. I was wondering if anyone can get hold of one or if anyone has ever welded one back together. I've snapped it across both welds. I got in touch with my LBS and they rang Trek who said they cant get the part anymore. Sell outs. Anyone help me out I need to ride again!
| First things first, you should be thankful that the swingarm failure wasn't catastrophic! Trawling the Pinkbike BuySell might be your only hope to find a spare part, or perhaps finding another complete Session frame to cut and shut the best parts together, and then have some spares left over for the future. Unfortunately, you are out of Trek's three year warranty for the Session, so you will struggle to get any more help from them. Welding could be an option, but would need an expert alloy fabricator who can heat treat the swingarm afterwards. Something to consider is that aluminium fatigues over time and becomes more brittle and likely to fail. There are various opinions on how long an alloy frame should, could or would last, but the swingarm failure may have been the "Canary in the coal mine" - a sign that the frame's lifespan has come to an end. If a lightweight aluminum race bike like the Session has suffered a full five years of downhill abuse from new, it's likely ready for retirement. - Paul Aston |
Welding can sometimes help prolong a frame's lifespan, but more often than not it's time for a replacement.
Have some unresolved tech questions? Jump in the Pinkbike Forum and we'll look to answer it for next time.
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From their warranty page
"Chain stays and seat stays on full suspension bicycles sold after 2008 will be covered under this
limited warranty for five (5) years from the date of the original purchase."
on the helmet ..
What I should have said was, "Are you riding a Session and do you whip in the park? You do! Didn't mean nothin' by it. have a nice day!
When a good time turns around
You must whip it
You will never live it down
Unless you whip it
No one gets away
Until they whip it
Now whip it
Into shape
Shape it up
Get straight
Go forward
Move ahead
Try to detect it
It's not too late
To whip it
Whip it good
- I am running tubeless.
- When I made the switch to the 32mm internal rims, I also went from a 2.5 Minion DHF 3C EXO, to a 2.3 with all the same specs. Your comment about the tire possibly being too narrow for the rim really seems to describe the feeling that I'm getting through my front wheel. I think I'll try switching back to the 2.5 and see if it helps. (rear tire remained the same 2.3 HR2 EXO)
- I've got a PIKE RC that I've always run full open, so I can't adjust reduce compression there, but I'm running a Double Barrel out back, so I'll try to reduce the compression and see if that helps.
Aside: I demo'd the 2016 stumpy last night, with the aluminum traverse Fatties. I think I prefer the ride of those wheels to the Light Bicycle hoops I just bought. I'm fairly confident there are some carbon hoops out there that would be great, but at 150 lbs, I think buying the absolute stiffest wheels that I could find, and lacing them up 32 hole was a bit of a mistake. They'll probably make their way to the buy/sell page shortly (gotta try your suggestions first). Thanks again.
Cheers!
Aaron Gwin made me buy ex471 rim, give him a raise DT!
At 130kg/f you are at the stiffer end of the recommended range.
From Light bicycle,
"The maximum spoke&nipples tension is 180kgf .
A. Tension for "transportation riders" (Comfortability)
80-90kgf are ideal for regular transporation riders or exercise on a regular basis.
B. Tension for "enthusiast riders" (Balance)
100-110kgf are good for people with enjoyful and training purpose.
C. Tension for "professional riders" (Performance)
120-130kgf are charged for riders who are expertized in riding or competition.
the recommendation spoke tension is less than 130kgf"
According to this article, the Spoke tension is virtually irrelevant for vertical displacement of the rim, as for a rider of the same weight, the difference between lowest tension and highest tensions is measured in tenths of a millimeter. So there is a common misunderstanding that rim conforms to the terrain by flattening slightly, increasing contact patch for the tyre, thus offering more grip. In case of tenths of a millimeter, such thing cannot be true.
Rim flexes in all directions, it temporarily bends to the sides and twists across it's section. Such mechanics are virtually non-existent in case of a carbon rim.
So retension your spokes all you like, even in lightest instances, carbon rim will still be stiffer than the stiffest aluminium rim out there. Sounds splendid for racers on 29ers, not for amateurs on 26 and 650B. It's all in our heads, my head likes comfort of aluminium rims
All I need to know is right there. Future purchase decisions taken.
Thanks Specialized.
2. Shimano chief execuctive called me and wanted to sponsor me if I put #Irideshimano hashtag under every comment
3.Arnold Schwarzenegger got himself a multi-flex zone bionic penis to stimulate his prostate
Which of the above stories sound least likely to be true, to an average New Age Gravity rider?
I may experiment with running an aluminum rim out front (where I never experienced any issues with stiffness), and keep the carbon hoop out back, where the bike felt a little squirmy in berms and pumping turns.
Also one review of the nomad with the enve the riders commented on harshness of the bike until they changed the wheels (a UK review I believe).
I'm right around 195-200lb right now and have just purchased a set of 28H Torch . I originally wanted 32H but I couldn't resist the deal on these. Now I'm thinking that it might actually mitigate this overly-stiff issue. I was even considering going with the heavier, DH build (if I go LB) to make sure its durable/stiff enough, but, again, starting to think this won't be an issue and should just stick to the normal, AM layup. FWIW, they'll be going on a Stumpy Carbon Evo 29 and I ride lots of rocky, root-filled trails and like to play/jump whenever possible. I'm new to all this so any opinions or input?
The LB wheelset is noticably stiffer, and the rovals rims are wider and burlier - its all down to the spokes when it comes to equally good carbon makeups
I just bought a set of alu traverse fatty wheels versus light bicycle carbons. I wanted something with a warranty incase something went wrong. When i asked the lbs manager about the 24 spokes that were thin he said I'll be fine and if I'm not he'll take care of me.
I've only got 5 miles out of them due to a brake failing on my bike but in that 5 mi i rode a few laps of the dj track (its on my giant trance 27.5) and had some whips that landed crooked. They definately felt stiff and had more traction than my giant branded dt wheels (25mm internal) . They also roll much better.
So far so good, but if something goes wrong i know I've got the lbs and specialized warranty to back me up.
How can I get sponsored? What tire pressure does Aaron Gwin run?
What's the best way to make my own winter spikes? Screws through the tire?
Basically, if spokes are very tight, the load stopping the axle moving to the ground is held by the spokes facing upwards but are actually carrying the additional force of the spokes facing down, hence, the additional force holding the axle up from the high spoke tension is countered by the additional spoke tension pulling down. This is true of the lateral forces.
The problem is that our experience is different and high spoke tension tends to allow a little more vibration through from the trail and this implies total stiffness is higher. This would imply spoke tension is an issue with wheel stiffness.
Does anyone give enough of a shit to elaborate on this? Spring preload is not a good example although it is semi valid because the spring in a shock does not make up a set of coupled forces.
If you were to release spoke tension to the point where stiffness changes, it would be a very noisy wheel to ride.
@scary1: nope, spokes and number of spokes are the only real influence on stiffness... much more so than the rim itself.
My bike climbs like a dream but often gets pushed off line through medium rocks and small roots. Something I didn't miss from my mountain bikes in the 90's. I'm hoping the 38mm carbon rims will offset all the compromises I've made for easier climbing.
A whip REQUIRES the rear wheel to be nearly parallel to the ground. If it is not you have done a basic novice kickout.
Whip - FLAT and Sideways
Kickout (gooney) - sideways
Whips are hard.
Kickouts are easy.
Your welcome!