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how is 185lbs for ti spindles selected?

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how is 185lbs for ti spindles selected?

Old 12-12-06, 06:24 PM
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jrennie
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how is 185lbs for ti spindles selected?

I was looking at a set of quattro ti pedals and they say 185lb weight limit(same as speedplay x1), my question is how is this number acheived? does it factor in a 150lb guy who hammers out of the saddle or a 210lb guy who just turns the pedals?
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Old 12-12-06, 06:56 PM
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Nope, it's probably a safe guess. It probably doesn't even account for someone on a 15 lb bike vs a 25 lb tank with another 5-10 lb of gear. Personally, I will never buy ti spindle pedals because they snap without warning, and I have seen firsthand what happens when a pedal comes off the crank... ouch in more places than one!
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Old 12-12-06, 06:57 PM
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it comes from the wonders of the science of materials
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Old 12-12-06, 06:57 PM
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Originally Posted by urbanknight
It probably doesn't even account for someone on a 15 lb bike vs a 25 lb tank
It doesn't need to account. The only load on the pedals is from the rider. You could bolt them to a 20000 lb rock and they'd still be rated for 185lbs
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Old 12-12-06, 07:00 PM
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Originally Posted by urbanknight
Personally, I will never buy ti spindle pedals because they snap without warning, and I have seen firsthand what happens when a pedal comes off the crank... ouch in more places than one!
I know what you mean. I've seen and even experienced a snapped pedal spindle quite a number of times. Curiously enough, they were all steel spindles. I haven't snapped a Ti one yet. Any material can catastrophically fail.
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Old 12-12-06, 07:21 PM
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1) I'm betting it comes more from the lawyers than the engineers.

2) Ti pedal is less likely to snap than steel, ceterus peribus. Ti is very springy, so its likely to deflect a fair amount before it fails.

3) The problem is more flex than failure. If you're pushing the weight limit, you may save a few grams, but add flex, negating the $700 external bearing crankset you bought.

I don't get why people pay a lot of money to get the stiffest crankset possible and then want to put pedals on it that are going to flex given their weight.
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Old 12-12-06, 07:33 PM
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Durability really depends upon the Ti alloy used. The 6al-4v titanium is easily stronger than a lot of steels. Yeah, Ti is only 1/2 as stiff as steel, so you'd have to use more of it for the same stiffness and end up negating a lot of the weight savings.
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Old 12-12-06, 07:58 PM
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Originally Posted by merlinextraligh
I don't get why people pay a lot of money to get the stiffest crankset possible and then want to put pedals on it that are going to flex given their weight.
so they look cool
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Old 12-12-06, 08:00 PM
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The Look Keo w/titanium spindle has no rider weight limit.

Either they told the laywers to screw off (I highly doubt it), or they fatigue tested the thing with really high variables such that the pedals would never see in real life (most likely), and the lawyers were happy.
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Old 12-12-06, 08:26 PM
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Originally Posted by jrennie
my question is how is this number acheived?
It was determined by the 186 pound rider whose balls are still recovering from the broken spindle.
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Old 12-12-06, 10:50 PM
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at 150lbs I am way under the limit but the prospect of shoe surfing to stay upright is a little troubling.

merlinextralight- are external bearing bottom brackets that much stiffer(example ac BB vs. fsa BB.)
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Old 12-12-06, 11:00 PM
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Originally Posted by DrPete
It was determined by the 186 pound rider whose balls are still recovering from the broken spindle.

I don't know where it's from, but this reminds me of the response to the question, "how do they determine the weight limit on bridges?". The response was "they drive larger and larger vehicles across the bridge until it collapses, then the rebuild the bridge."
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Old 12-12-06, 11:13 PM
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Originally Posted by I_bRAD
It doesn't need to account. The only load on the pedals is from the rider. You could bolt them to a 20000 lb rock and they'd still be rated for 185lbs
Oops, I guess I didn't think that comment through, did I but yeah it still doesn't account for the strength of the rider or how hard s/he rides over bumps, etc.
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Old 12-12-06, 11:42 PM
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The loading of a pedal is very complex, since no two riders pedal the same, weigh the same, or use the pedals for the same length of time. This 185lb weight limit is therefore an arbitrary number decided on by the engineers and lawyers using probability functions that sells the most pedals while causing as few failures and drawing as few lawsuits as possible.
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Old 12-13-06, 07:20 AM
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Originally Posted by merlinextraligh
1) I'm betting it comes more from the lawyers than the engineers.
Exactly, the lawyers typically take what the engineers spec and then make that even more conservative.
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Old 12-13-06, 07:28 AM
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Originally Posted by merlinextraligh
1) I'm betting it comes more from the lawyers than the engineers.
dingdingding!!!

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Old 12-13-06, 08:50 AM
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There's no way I would push that limit, it would just suck WAY too much to deal with a pedal snapping off while you were standing. Not worth it for what, a few grams?
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Old 12-13-06, 10:52 AM
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Originally Posted by urbanknight
Nope, it's probably a safe guess. It probably doesn't even account for someone on a 15 lb bike vs a 25 lb tank with another 5-10 lb of gear. Personally, I will never buy ti spindle pedals because they snap without warning, and I have seen firsthand what happens when a pedal comes off the crank... ouch in more places than one!
but have you seen what happens when a crank arm comes off.....in a track race. I've seen that twice.
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Old 12-13-06, 12:42 PM
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Originally Posted by Dial_tone
but have you seen what happens when a crank arm comes off.....in a track race. I've seen that twice.
Yep. Once. I've also seen a pedal spindle break on the road twice, and even almost ran over my teammate's neck on a velodrome. He clipped out of his pedal while we were doing jumps for warm-up, he was leading out and I was chasing. His foot shot straight to the ground and slid on the cleat while he went down sideways and I narrowly escaped running over his falling head. It's not pretty. He did enjoy the massage the hot paramedic on duty offered him, though Oh, and he got back on his bike, borrowed my spare jersey (his was torn to shreds) and beat me in the 1st round of sprints

Oh yeah, and my crank arm cracked on me once. I was counting my lucky stars that day because I stopped riding to see what was making the annoying tick sound. I rode home with just the right pedal (2 mile left thankfully)

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Old 12-13-06, 01:47 PM
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Originally Posted by jrennie
I was looking at a set of quattro ti pedals and they say 185lb weight limit(same as speedplay x1), my question is how is this number acheived? does it factor in a 150lb guy who hammers out of the saddle or a 210lb guy who just turns the pedals?
Hi,

I guessing that everyone who answered so far is not an engineer because if any of you are some company is in for a big product liability case.

Here is a highly simplified view of the engineering process for designing a mechanical part.

The force going into a pedal is fairly predictable because it has to normal to pedal axle in the plane of the pedal rotation. The force may not be normal to the plane established by the normal force and the pedal spindle but that only decreases the primary force into the pedal by creating a "thrust" component along the axis of the pedal spindle (which is why many pedals have thrust bearings in them). So you can pretty readily come up with the range of how the forces go into a pedal.

How do you predict how much load goes into a pedal. There are all kinds of bio-mechanical and ergonomic studies that can help you decide how much force a person might put into the pedal. This is the part that is less predictable but you have to use something to and document what you used to make your analysis reasonable.

From there you can use all kinds of finite element analysis tools on your computer to assess at what force and what location the pedal will fail. After that you can run some tests on a test stand with some real hardware to see how your calculations match your analysis. Of course you are always throwing in a safety factor into your calculations. At he end the lawyers may have you throw in an additional safety factor or there may even be some requirement from the government through the CPSC.

Anyway, you better have all of this documentation available in case something goes wrong so that you don't get sued out of existence.

Oh, BTW, I am an engineer with over 25 years of experience.
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Old 12-13-06, 03:34 PM
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Yep. I thought I'd have to address this. Typically in the auto world, the SF (safety factor) is 20%. That is, take the worse case and design it so that it can take 20% more load than required. As there are government regs and then OEM regs, this usually results in a SF on a SF and the thing being built like a brick, well, you know the rest of the saying...
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Old 12-13-06, 07:10 PM
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Originally Posted by khuon
I know what you mean. I've seen and even experienced a snapped pedal spindle quite a number of times. Curiously enough, they were all steel spindles. I haven't snapped a Ti one yet. Any material can catastrophically fail.
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Old 12-13-06, 07:48 PM
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So what would the rating be for a stainless steel pedal spindle? There has to be a limit, right?
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Old 12-13-06, 10:01 PM
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Originally Posted by Cleave
Hi,

I guessing that everyone who answered so far is not an engineer because if any of you are some company is in for a big product liability case.

Here is a highly simplified view of the engineering process for designing a mechanical part.

The force going into a pedal is fairly predictable because it has to normal to pedal axle in the plane of the pedal rotation. The force may not be normal to the plane established by the normal force and the pedal spindle but that only decreases the primary force into the pedal by creating a "thrust" component along the axis of the pedal spindle (which is why many pedals have thrust bearings in them). So you can pretty readily come up with the range of how the forces go into a pedal.

How do you predict how much load goes into a pedal. There are all kinds of bio-mechanical and ergonomic studies that can help you decide how much force a person might put into the pedal. This is the part that is less predictable but you have to use something to and document what you used to make your analysis reasonable.

From there you can use all kinds of finite element analysis tools on your computer to assess at what force and what location the pedal will fail. After that you can run some tests on a test stand with some real hardware to see how your calculations match your analysis. Of course you are always throwing in a safety factor into your calculations. At he end the lawyers may have you throw in an additional safety factor or there may even be some requirement from the government through the CPSC.

Anyway, you better have all of this documentation available in case something goes wrong so that you don't get sued out of existence.

Oh, BTW, I am an engineer with over 25 years of experience.
This is exactly right, but the issue is how do you choose the safety factor for the loading, since it is extremely unpredictable? At the end of the day, it all boils down to someone saying hmmm... lets design for a maximum stress of X, which is going to be way, way higher than the average stress, and is only to withstand impact loads, in which rider weight is really not that big of a factor. Sure you can analyse exactly how much force and fatigue a pedal will take, but you can't say "a rider of mass M can only apply up to a maximum impact force F."

The engineers do a lot of work, and they design for specific loads, but the weight limit is there because they know that heavier people are more likely to break it, so they slap on a weight limit disclaimer that prevents people of above average weight from suing.
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Old 12-13-06, 10:25 PM
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Originally Posted by merlinextraligh
1) I'm betting it comes more from the lawyers than the engineers.

2) Ti pedal is less likely to snap than steel, ceterus peribus. Ti is very springy, so its likely to deflect a fair amount before it fails.

3) The problem is more flex than failure. If you're pushing the weight limit, you may save a few grams, but add flex, negating the $700 external bearing crankset you bought.

I don't get why people pay a lot of money to get the stiffest crankset possible and then want to put pedals on it that are going to flex given their weight.
1) It's more engineers than lawyers, not to say that lawyers don't have an influence.

2) The amount of flex before breaking is determined by the difference between the yield strength and the ultimate strength. The greater the difference the more deflection before breaking. However, the amount of deflection is determined mostly by the design of the part (typically the diameter) at the point of maximum bending moment.

3) The amount of actual deflection in a pedal spindle is probably so small that you would never notice it against the deflection in the frame and crank arms.

Originally Posted by DScott
So what would the rating be for a stainless steel pedal spindle? There has to be a limit, right?
All components have a weight limit -- published or not. My guess (and it's purely a guess) is that manufacturers are publishing weight limits when the probability of failure is significant for a male who weighs less than the 95th percentile male. I am fairly sure that the 95th percentile male weighs more than 185 lbs.

No rating from the manufacturer would indicate to me that with proper cleaning and maintenance that the pedal is good for someone over the 95th percentile (probably over 220lbs).
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