Ask Pinkbike - Crank Woes, Coil vs Air Shock, and Which Nukeproof?
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.
Crank Grief
Question: Pinkbike user wrovmtb asked this question in the Downhill Forum: I have a 2012 Mongoose Fireball that I use for 4X racing, but the bike's non-drive side crank comes loose every time that I ride it. The guys at the bike shop said that the cranks, Duros from Suntour, are worn out and that I should replace them, but I can't find any good Octalink cranks... should I buy a new bottom bracket as well? And if so, what type?
 | The short of it is that the bike shop is correct when they told you that your cranks are worn out, and that you'll have to replace at least the non-drive side crank at a bare minimum, although it'll be like winning the lottery if you manage to track down a shop that has a spare non-drive side crank in their parts bin. The mountain bike version of the old Octalink bottom bracket uses a steel spindle with eight splines that are each 9mm long, and the matching aluminum crankset sports the opposite shape that mates to it when the arm is pressed onto the spindle as you tighten the crank bolt. The issue boils down to this: the spindle is steel, the arms are aluminum, and you accidentally rode the bike with the crank bolt a touch loose. The non-drive side arm lost the battle because aluminum is way softer then steel, and the result is a deformed shape to the mating surface that means the arm will never stay tight for long again. The thrifty route would be to track down a new or used Octalink crankset, but I'd take this ''opportunity'' to upgrade to something else, like Zee cranks from Shimano or Gravity's Gap Mega Exo arms that go for around $200 USD. - Mike Levy |
Shimano's Zee crankset is a worthy upgrade if wrovmtb isn't lucky enough to track down some replace Octalink compatible arms.
Coil or Air Springs for Enduro?
Question: Hecop wrote: in the All-Mountain and Cross-Country Forum: I want to change my Fox Float CTD shock to a Cane Creek Double Barrel coil for my Intense Tracer 2. They have the correct coil shock for my bike's travel, but I don't know if this change will benefit my bike's response going downhill. Is a coil shock better than an air shock for an enduro bike?
| The simple answer is "yes." A coil-sprung shock with both high and low-speed damping controls will be your best option for downhill performance. The advantage that a coil spring has over an air-sprung shock is mainly in the first 30-percent of the suspension travel where a coil offers a smooth, linear rate and an air-spring is making the transition from the effects of its negative spring. The difference is small, but most good riders can feel it. There are valid arguments in both camps about the benefits of coil vs air springs in the last 25-percent of the suspension's travel, because the air spring naturally ramps up, while the coil type shocks must depend upon a rising-rate linkage or an end-stroke booster to achieve the same effect. If one checks out the Rampage bikes, the end-stroke winner appears to be the air spring, but I digress. That said, it's the first half of the suspension travel that provides traction and control, which is where coils rule and why DH racers use them. Where coil shocks disappoint is in their versatility. (negative commenter warning: you may want to read a little further here.) An air spring with high and low-speed damping controls can be firmed up for park riding, softened for loose, gravelly descents, or set up as a compromise between good pedaling for trail use while banking enough DH performance to enjoy the downs. All from the same shock. Coil springs are one-shot deals. You must select one spring rate that suits the style of riding that you like most and then live with the compromise should the terrain or trail require a different setup. Cranking up the preload won't stiffen the spring - it just makes low-speed hits harsher and reduces sag. So, to answer your second question: "No." A coil-type shock is not the best choice for enduro. An air-sprung shock like the Cane Creek DB Air is a better solution for a bike that must be ridden fast and hard in a wide variety of terrain and trail situations. If one considers that most of the top enduro racers have histories as pro DH racers, the fact that almost all of them choose air-sprung shocks should be evidence enough. - RC |
If you race DH or ride the same type of trails every day, a coil-type shock (pictured) will deliver the best performance on the downhills. Those who need a shock that can be tuned for a wider variety of situations and still want to rip the downs, should choose an air-sprung shock with a full range of damping adjustments like the Cane Creek DB Air
Nukeproof Mega AM or TR?
Question: PB user Giladgu asks the following in the All Mountain, Enduro & Cross-Country forum: Hey PB, I was looking at both the Nukeproof Mega AM and TR as a new frame but can't decide if I need the 160mm travel on the AM (I will be running a 160mm fork on both). I ride mostly trails in the Northeast (NY and NJ) and once or twice a year at Mountain Creek. I just don't know how much pedaling efficiency I lose with the AM. I am also thinking of maybe racing a bit this year and I'm kind of worried whether or not the 130mm of the TR would be able to handle some enduro events.
| The number of bikes in the 160mm category continues to grow, but that doesn't mean that everyone needs to rush out and buy the longest travel bike they can find. To a certain extent, the terrain that you're riding most often should dictate the bike you buy, and in this case I'd recommend the TR version of the Mega. It shares the same link-driven single pivot suspension design of its burlier big brother, so the actual pedaling characteristics should be similar, but its lighter weight and reduced travel will help with the steep punchy climbs that the East Coast is filled with. It'll still be able to handle a few days in the bike park without much trouble, and the same goes for the occasional enduro race, especially since you're planning on running a longer travel fork up front. There are some bikes in the 130mm travel category that are more XC oriented, but the Mega TR isn't one of them, with geometry numbers that are geared towards aggressive riding as opposed to leisurely cruising down gravel roads, making it a good choice for your intended usage. - Mike Kazimer |
Have some unresolved tech questions? Jump in the Pinkbike Forum and we'll look to answer it for next time.
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Also I set the tire pressure to 50 psi does that sound right?
1. Tighten until threads just start to strip. Tighten 1/64 turn, no more.
2. Back off exactly 3/32 turn. This is the critical step!
Torque wrenches are a scam perpetuated by the tools industry!
I own both, well i have an am 275 & the 26" TR & race enduro in the UK on both
The AM275 has 160mm Pikes & the 26" TR has 160mm 2015 fox 36's
There is a big difference in the ride between these bikes in that the 275AM seems to effortlessly barrell through and smooth out everything, where the TR feels fun and playful, but like a hard tail when things get rough.
I have raced enduro on both & all my best results have come on the 26" TR, but this is in the UK where the courses are quite pedally and not very rough. I have also ridden DH tracks on the TR and it surprised me how quick i could go to. If i could only keep one it would be the TR as it is more fun to ride.
SlowdownU, there actually are quite a few spots across the river in Westchester, NY (Sprain, Graham, Blue Mountain, etc., etc.) that have more flow than I've found most other places, particularly in the South West, where I now (regrettably) reside.
Just in case you're in the area again... you gotta check the aforementioned spots.
regarding coil vs.air: I am still trying to wrap my head around something. maybe you can clarify that for me
You state that one advantage of coil is that they don't ramp up
a little further down you state: You can change the sag with the preload on a coil spring.
So a linear Spring rate basically means you need X amount of force, or weight to keep it simple, to compress a spring for a certain distance. for example 400pound per inch is a very common rate. So if you sit on your bike, depending on the links and leverage ratio your bike sinks in because you apply a force or weight to the spring, right? lets say you are 200 pounds and your frame has a 1:2 ratio. this meas you end up with 1inch of sag. correct?
If you now preload your "linear spring" lets say with 100 pounds the spring changes its length. The spring on the shock will be a quarter inch shorter the shock length stays the same though as does frame and suspension geo.
So if you throw your 200 pounds back on your bike now, remember the 1:2 ratio this means 400 pounds on the spring.
As its a linear that means it will sink one inch further into the travel and your bike will be exactly the same as before.
even if you would but 10.000 pounds on the spring before adding 400 to a linear spring with a spring ratio of 400pounds per inch means its length will be compressed for another inch, no matter ho much weight or force you put on before.
So dear RC you can choose now from two answers: 1) a coilspring is not really linear either
2) you can not control sag with spring preload.
what do you think is the right answer?
-This all assumes you have a bike with a 1:2 ratio that is exactly fixed somehow.
-The error in the above is that adding preload is a different vector than adding weight to the bike.
-I currently believe that both statements in the OP are correct unless someone can change my mind. A linear wound coil is linear. Increasing preload will decrease sag.
www.sram.com/service/rockshox/443
Page 5 has a spring rate graph
Page 7 Shows how preload affects the shock
Page 9 Shows an air spring curve
page 11 show the difference with air pressures vs volumes
page 12-13 talks about negative spring
Hope this helps!
Wind on preload equal to your weight (let's ignore frame ratio, front suspension taking some of your weight etc) The coil is compressed but not the shock. Now get on the bike. The coil is compressed between the preload collar and your weight on the end of the piston, ie it is compressed just the same as before, and the shock doesn't compress. So, preload does control sag.
Or look at it another way. No preload. Get on bike. Shock compresses. Winding on preload uncompresses shock.
You are right it is simplified. but still hard enough to understand i guess.
Whenever RC is writing about tech stuff i get the shivers. Apparently he must taken physics classes at Pokemon university or something similar... I would like to give it some time see if RC might give us honor before coming back to your points but whatever...
-you are wrong. if you preload a number of turns equal to 1" of travel an than ad 200 pounds cause by a rider. Your resulting weight (actually its a force) compressing the spring is your 400lbs spring is 400lbs through preload+plus rider= 600lbs which will result in 1.5" of total spring deformation considering its linear or in other words in 0.5 inches of sag measured on the sock. however you twist an turn it, with linear you will always come to the same result.
-you are right it will change the properties in negative travel, a higher preload will cause the rebound to get faster as a higher force is pushing the shock back in its extended position. more force means higher acceleration means moving faster by the time you top out.
-you are right, the ratio is not fixed as long as you have a rear moving on a circular bearing. RC actually states that correctly. it does not however influence the sag as when you only preload the length of the shock does not change but stays at fully extended length. meaning your linkage will start moving from the same position hence same ratios will apply as without preload an can therefore be taken out of the equation.
-nope, the force vectors are the same. your shock is designed to accept only one direction along it longitudinal axis.
- correct both statements are well lets say not exact...but then again i just repeat what RC wrote...
400lbs of preload = the spring is already "pushing" 400Lbs when the shock is fully extend.
if you now put even more weight on it it will compress further? right? 200lbs extra will press the spring down another 0.5inch to 1.5 inch total.. its called hooks law.
You are saying it only starts moving again if you put on more than the wight you put on at first?
check out the preload graphic on page 5 of the rock-shocks document crazbiker4 shared.
no mater if you take the light blue or the dark blue line as soon as you ad 200lbs this translates in 1" of travel at their 200lbs spring ratio.
now the difference is that the spring contains more energy which while significantly change the way the spring pushes the shock back into its extended position.
Imagine your spring with the 600 lbs on top. release the spring from the weight and it will take of like a rocket. With only 200 lbs it will probably take of too but will not fly as high... its like slingshot the harder you pull the further it shoots or coming back the harder your bike will kick back and the higher your bunny-hops will be...
When you preload a sprig with 400lbs, the spring is pushing 400lbs. It can't take his initial lengh because of the schock body taking 400 lbs of the preload when in top out position. If you put 200lbs from the rider, the shock will still push 400lbs, but there will only remain 200lbs in the shock body. but the shock won't move before the rider input is over 400lbs. If the rider put 800lbs, there is no more lbs in the shock body, and the shock has move. The shock has move 1 inch from his initial position, but the spring itself has moved 2 inches: 1inch from preload and 1 inch from schock movement.
I hope someone will understand what I just wrote.
Adding preload increases the force, this way rebound damping should be increased as well. I use a 650lbs coil spring and high viscosity oil in damper, so my seals do not last too long. I preload the spring to have something around 660lbs/inch. Applying my immense weight on the spring with the right sag and some heavy landings, the oil pressure inside gets so high that I often change blown seals.
When you preload the spring it has absolutely no affect on the "piston". Your spring and preload is completely independent of the piston/dampening section of the shock and vice versa. The spring holds your weight, the piston and dampening affect the shaft speed while the shock is moving through it's travel. They work hand in hand but not even remotely like you're describing.
A spring exert a force according to that very first order and linear equation: F=k*d
F is the force (in Newtons)
d is the length the spring is compressed (in meters)
k is the spring constant in Newtons per meters (N/m). It is constant. It does not change according to the rain, the sun, the compression , the leverage or whatever else (except is it gets weaker as it gets older, just like us).
Any mass (pounds, kg), excert a force down toward the ground that is measured in Newtons also. So, your body weight exert a force in Newton down toward the ground. Invertly, a force in Newtons can be expressed in pounds. We will allow us to use Newtons and pounds alltogether to simplfy the explanation.
The force excerted by the spring basically fights against the rider's weight. When two forces are equal, there is no movement in any direction.
If you turn-in the preload collar, you compress the spring which respond by forcing the shock to uncompress. You are not on the bike yet but the shock is already trying to uncompress the shock. Eye-to-eye distance of your shock cannot stretch any longer and the shock sustain that force.
Now you sit on your bike. The force you exert on the seat-frame-linkage-shock must first counteract the force exerted by the preloaded shock. If the spring is preloaded to 100lbs, the first 100lbs applied to the spring will generate no displacement (no compression). Every other ounces will compress the spring/shock.
That is how preload allows you to set the sag.
Now, go out and ride!
www.sram.com/service/rockshox/443
Page 5 has a spring rate graph
Page 7 Shows how preload affects the shock
Page 9 Shows an air spring curve
page 11 show the difference with air pressures vs volumes
page 12-13 talks about negative spring
Hope this helps!
If you are running a coil and want to check your spring rate, here is a calc to help you:
service.foxracingshox.com/consumers/index.htm
It's the 3-400g weight benefit which I think is more significant than air offering better performance in differing conditions
Should help you out.
Personally, I'd just go for any of Race Face's CINCH cranks and CINCH BB. The cranks have removable spiders and removable 30mm spindles, so they're essentially future proof. If you change frames or drivetrains, you can just swap out spider or spindle and you don't have to change your cranks (www.raceface.com/cinch).
There is air springs and air springs. The coil VS air question depends on whitch schock are compared.
For exemple, if you compare a air sprung void and a coil sprung stoy, in the first 30 percent the air schock will be as linear and smoother than the coil one.
The ramp up in the ending stroke has benefits and drawbacks, and each bike has his own requirements.
And for enduro, now? FYI, you can change a spring on a coil-sprung shock. So you can adjust the sprin rate, too (but it take more time, and money, specially if you want Ti springs)
IMO:
benefits of coil springs:
- more grip
- more predictive feeling
- more comfort
- reliability and maintenance
benefits of air springs:
- slightly lighter
- cheaper to produce for the manufacturer (because one spring fits all) and cheaper to change spring rate.
- tunable progressivity that compensate a bad suspension layout or bad hydraulic settings.
I don't think top enduro racers se air because they like it, but because their sponsors want to sell more air shocks, and also because there is not a lot coil shocks with hydraulic and size that fits their frames and needs.
So, for Hecop: yes a Double Barrel will improve your bike's response going downhill. And the tracer won't suffer too much from the schock when climbing thanks to his suspension layout. But there are schocks like double barrel CS that will increase downhill abilities and are designed for enduro.
And you can also making someone modify your schock, like Avalanche in USA, Novypart in France ,and many others worldwide, to fits your needs, keeping the good parts of your schock.
I'd rather have a linear shoch with proper hydraulic settings (and hydraulic bump stop if needed), than a ramp up from air. Because It's way smoother. Hydraulic will give you the right amount of force ,Air will give you a given amount depending on the travel, so it will be harsh. Ramp up is needed when you don't have enough mid speed and high speed damping, or when the suspension layout of a frame isn't progressive enough.
And a too much progressive suspension (specially forks) will move too much when you change your position, or when the slope change, (because at the beginning of the travel a little amount of weight add a big amount of travel, untill the spring has raped up enough) so I don't think this will give you confidence.
And you need traction like 95% of time, so if you are constantly moving to find it you'll lose energy, and you need energy to pedal untill the finish line.
Coil