Video: Making Hope Cranks
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Designed. Tested. Manufactured. Seven years in the making, the versatile, do-it all Hope Crank has finally hit the shelves.
You may have seen various versions of the cranks over the past few years on our staff and team bikes. We spent the time testing, tweaking and redesigning them to ensure they’re as good as they can be.
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The final crank design features a unique expanding spline axle/arm interface (pat pending). Previously, cranks with splines often used a taper to ensure a snug fit. These cranks worked fine the first time they were fitted to the axle, but once they’d been taken off and on a few times, the spline became worn, so they’d suffer from the inevitable movement and annoying creak.
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To solve this problem we settled on a unique expanding spline. The cranks are pulled onto a spline, then a tapered plug is fitted inside the axle which can be tightened up each time the arm is refitted – giving a perfect fit every time.
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Added to this we CNC machine the arms from forgings which gives them immense stiffness and strength. The arms also have a splined mounting for spiders and direct mount sprockets giving excellent versatility. The spiders are available in either single (104 BCD) or double (64/104 BCD) ring configuration.
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The cranks use a 30mm axle and are compatible with the majority of bottom bracket systems via our expanded range of bottom brackets.
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Specification:
Material – Forged and CNC machined 7000 series aluminium alloy crank arms
Length – 165, 170 and 175mm
Q-Factor – 167mm
Chainline – 49mm
Axle Diameter – 30mm
Expanding spline crank arm/axle interface (pat pending)
3-piece construction
Versatile Spline mount for chainring/spider
Chainring mounting: -Spiderless Retainer chainrings 26T to 36T
-Spider Single 104BCD and Double 64/104BCD
Colours: Initially black, with red, blue, silver, gunsmoke and purple following in March
Weight: 641g (arms, axle and 34t spiderless ring)
Prices: – Arms, Axle and Spider £245/€300/$400
Arms and Axle £215/€265/$350
Spider £40/€50/$65
Spiderless Retainer Chainring £55/€68/$90
www.hopetech.com @hopetech
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There is a huge difference between 7005 and 7075 while both are of 7000 series.
The 7005 hardness is about 85-90MPa
The hardness of 7075T6 is 150MPa, 7050T6 - 147MPa
So it is just great!
And the other man tolds about 0.001mm repeating precision of their CNC machines.
That's just exceptionally great!
But the price....HOPE it will lower.
I'm pretty sure their machines already returned the costs spent on them long ago.
The 7055T6 is of 198..202MPa.
And it is what the RF Diabolus crank arms are made of (OptimAL is 7055T6 really)
So I personally will be fine for many years further on them, nevermind what some people say on the net about interface issues - mine are fine on 2 bikes under 85kg of my body pumping and jumping them badly.
Fatigue life, which is how cranks typically fail unless you are a beast, is mainly dependent on stress amplitude, mean stress, ultimate tensile strength, and fatigue limit. There is a relation between hardness and UTS, but it isn't 100% concrete. There are also plenty of processes that can be done to increase fatigue life such as peening.
And as owls said, hardness is not measured in MPa.
Shimano make:
-Their upper end cranksets like XT / Saint and Ultegra / Dura Ace in their Japanese plant
-Their mid range cranksets like SLX and Tiagra (road) are made in their Malaysian plant
-Their low end cranksets like Tourney and entry level non groupset pieces like FC-171 are made in their Chinese plant
en.wikipedia.org/wiki/Brinell_scale
Brinell hardness is sometimes quoted in megapascals, the Brinell hardness number is multiplied by the acceleration due to gravity, 9.81 m/s2, to convert it to megapascals. The BHN can be converted into the ultimate tensile strength (UTS), although the relationship is dependent on the material, and therefore determined empirically.
And here the useful links:
asm.matweb.com/search/SpecificMaterial.asp?bassnum=MA7075T6
asm.matweb.com/search/SpecificMaterial.asp?bassnum=MA7050T735
asm.matweb.com/search/SpecificMaterial.asp?bassnum=MA6061T6
Compare and see.
Also I have the datasheet for 7055T6, which is yet more better.
I didn't say any word about the relation beetween UTS and hardness, did I ?
You're right!
But it is obvious that hardness could be used as kinda indicator parameter(one of several) to compare and choose the materials.
Also the modulus of elasticity.
The metall with higher hardness also(as a rule) have higher UTS, Tensile Yield Strength, modulus, fatigue strength.
All of the mechanical params depend on inherent structure.
There are many treatment processes used to improve the params by changing an inherent structure of metal(or other material).
Correct me if I'm wrong but the cranksets with so burly arms have their bottleneck in an interfaces.
The interfaces to the axle and the pedals is how cranks are typically fail unless you are a realy BIG BEAST to broke the crank arm itself.
So, the hardness is of high important when the many small alloy splines touch the steel splines at the steel axle and you badly push the crank arm which is a lever. Imagine what a high stress that little splines cary on!
It is the same thing as with rear hub's alloy freehub to steel cogs interface.
Cromo steel piece will deform (chew-in or other way) the alloy piece FAR EARLIER BEFORE YOU GET TO THE FATIGUE LIFE END, because it is harder. It should be something to undertake against it.
I just mean that "7000 series alloy" words are have no sense: one can't get a real clue from it.
I can't accept a "bla bla" without any bit of measure.
Modulus of elasticity and hardness are just the tip of the iceberg and have far less to do with when a component will break than you might think. Modulus of elasticity (aka Young's modulus) is d(stress)/d(strain) between strain=0 and strain=yeild. You could have a young's modulus that is super low and still have a high yield strength... it just means you get a lot of elastic deformation, which isn't necessarily a bad thing.
Long story short, you can't look up spec sheets and read a wikipedia article or two and be an expert. Material is only a small portion of the design process. The cross sectional area of your crank plays a huge role in how it feels.
Also, 7000 series means Young's modulus is 72 GPa.
Actuall objects may be made different by defined treatments but not too much.
3D forging and heat treatment are usual.
Well I don't want to write same again..but:
The metall with higher hardness also(as a rule) have higher UTS, Tensile Yield Strength, modulus, fatigue strength.
All of the mechanical params depend on inherent structure, some of them can corelate to each other.
There are many treatment processes used to improve the params by changing an inherent structure of metal(or other material).
ESTIMATE - that what I did using that info.
>You could have a young's modulus that is super low and still have a high yield strength... it just means you get a lot of elastic deformation, which isn't necessarily a bad thing.
Yep, it just means you get a lot of elastic deformation, which is a GOOD THING, especially for crank arms: they must return back to it's usual state after bending.
Look at the video when they testing the crank: it is like a spring which is good.
And you are an expert, yes ?
People are not born being so experts.
If you think I'm only on wikipedia, please don't, youre wrong.
I give it for you, the simple, one of many sources, I also gave the other links.
You could give yours. Could you ?
One more time: the spec sheets is one the first stages when you compare and choose.
And the material is a important part of the designing process: they didn't take 6061 for their cranks, they choose 7075 because it's properties give much more freedom for the further designing process. Especialy the cross sectional area, which can be made, for example, smaller comparing to 6061 or other SOFT alloy because of the 7075T6 properties. Crank can be made lighter using much burlier alloy because the density is almost the same.
The 6061T6 has only 3GPa less modulus of 69GPa
The 2014T6 has Modulus of Elasticity of 73.1 GPa
So what ?
But the hardness and UTS are differ very much and HOPE choosed 7075T6 not a 6061 or 2014.
Nevertheless, many english-native people told me my english is excellent other times.
But that's not the matter.
>Large elastic deformation is not good. If your crank twists too much your foot will slip off the pedal and that's never fun.
Totally agree. But the large modulus of elasticity is very good.
You seem indeed did not understand me.
The higher number of modulus shown the more force is needed to start the elastic deformation and to make it permanent, isn't it ?
The crank should be as rigid as possible, ideally - not bending, while when the force is high enough to start the deformation the crank should return back to it's state after the force is taken off.
I totally disagree with this. I heared already such opinion from some other people and that' just wrong. I have lot experience making parts of 7075T6.
- It can be made brittle by wrong heat treatment, you can make it NON-brittle by special treatment, and the optimal is T6, T654.
- Do you know about 7075O(if I'm correct on letter ) ? Anneal 7075 which is so soft, bends like ..it in any direction many times.
- You miss one thing: The 7075T6 will start to only bend when the 6061 will be already permanently deformed ot even broken.
In other words 7075T6 has huge reserve against soft 6061 or others.
Yep, in the end 7075T6 will be broken, as any, but WHEN ?
Man, it's "end" is 3 or more times far beyond the "end" of 6061.
(HOPE you understand what I mean, because I'm already tired.)
- there are the very expensive bars made of 7075T6, 2014, 7050.
- fork stanctions' kinda standart alloy now is 7050T6
- the 6061 is cheaper and softer, but the main thing - it is very well weldable( as 7005) vs 7075 which is not at all.
- also 6061 and 7005 is very well for tubing because of it's properties which you mentioned
And the bars are tubes actually so that's why non7075 used and it is enough robust for bars.
If I'll be honest though, while I absolutely LOVE Hope products, if I buy a set of "Made in the UK" cranks...they'll be Middleburns without even hesitating.
I don't get the pinch-bolt statement though. A weak point? I haven't used MTB cranks since ISIS Drive. I just got fed up dumping scrilla to replace shit that creaks & snaps so I started running BMX stuff & for cranks, to me pinch-bolts were the answer. A properly designed spline is necessary too of course but the triangular shaped one on those hopes doesn't look like it's up to the task, and no way to pinch it? Looks like a creaky nightmare to me. The large spindle diameter would go a long way but it doesn't look nearly as tough as a pinched cro-mo BMX tube. Id love it if I was wrong though. It looks like MTB cranks have come a long way since the bad ol' days with those fat spindles. Square splines with round roots are better than triangles though. That should be obvious.
Gorgeous!!!
But, i think Guillaume (design engineer) was trying so hard to make an effort to speak like a real british gentleman. (lol)
What a guy
In the title, so I can avoid clicking on it.
Because surely the only reason anyone would buy expensive, overly complicated, heavy cranks is because they're market'ed well and bought by people who are into whatever this year's must-have is.
Junk