Hey Tifosiman, Ti parts?
11-01-2002, 03:25 PM
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Hey Tifosiman, Ti parts?
So I am ready the "what do you guys do" post and I am reminded that you (Tifo) work for a Ti bicycle company. I got to thinking, wouldn't it be neat if you got them to make some Ti cross bars for Cambermeister strut tower braces? Hmm, wouldn't it? Maybe some other neat-o mosquito Ti stuff too, like A-arms.
11-01-2002, 04:55 PM
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I bought a billet titanium shift **** from him last year that his company made for the hell of it. It had a round center so I needed an adapter to make it fit my 951, which I never got. Its still sitting in my glove box...I am thinking of putting it on my rx-7 as no modifications are necessary to make it fit (not to mention it would probably get very very hot in my 951 since the stock plastic **** can get uncomfortable to touch).
11-01-2002, 05:10 PM
#4
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With the demise of the evil Russian empire, a lot of military contractors have made exotic materials available to the general public. MMC and Ti alloys are part of this. Cheaper than before, but there's still no reason we need to pay for mil-spec stuff, as a lot of the costs is in testing anyway. I remember a contractor told me about a redwood picnic table that they picked up at a local Orchard Supply Hardware store for $100. They ended up selling the table to the Army for over $10,000 because of all the testing that was involved to guarantee that it met specifications. Anyway, you can go into a hardward store in Russia and buy a titanium garden shovel if you want, the stuff practically grows on trees over there.
But it won't be good for a strut brace because the modulus (stiffness) of Ti is about 1/2 that of steel. That means if you were to duplicate the strut-brace in Ti, it would flex much more than the steel part. You have to increase the diameter and wall thickness just to get equivalent rigidity. And really, those strut braces need to have straight tubing that's triangulated back to the firewall to really do much good. Imagine looking straight onto the car from ahead. The tire's contact patches, the strut-towers and the brace from a rectangle. Even if the tops are connected, the towers can still move laterally. This is the parallelogram effect. The only way to get rid of this is to introduce a triangle into the structure.
But it won't be good for a strut brace because the modulus (stiffness) of Ti is about 1/2 that of steel. That means if you were to duplicate the strut-brace in Ti, it would flex much more than the steel part. You have to increase the diameter and wall thickness just to get equivalent rigidity. And really, those strut braces need to have straight tubing that's triangulated back to the firewall to really do much good. Imagine looking straight onto the car from ahead. The tire's contact patches, the strut-towers and the brace from a rectangle. Even if the tops are connected, the towers can still move laterally. This is the parallelogram effect. The only way to get rid of this is to introduce a triangle into the structure.
11-01-2002, 06:24 PM
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Good point Danno, I knew but never thought about what I read in suspension design, "...as seen, adding crossmembers dows little to improce torsional stiffness.....this shows adding an x-brace [4 triangles] does make considerable improvement to the ladder frames torsional stiffnes..." BTW Danno, I think I'm going to go with the idea I called you about earlier today. <img src="graemlins/burnout.gif" border="0" alt="[burnout]" />
11-01-2002, 06:54 PM
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Good point about Ti Danno, so you do exactly as you said and increase the diameter and change the shape of the tube, similar to that ***** aluminum bar that is on the market (Racing Dynamics).
Ti has a much higher strength to weight ration than Al and somewhat higher than steel. It is also far more corrosion resistant than either one and can tolerate more bending cycles than either one. The only drawback that I know is that it has funky notch strength characteristics (how it reacts to the surface being scratched).
Ask Tifo if the titanium tube sets for the bikes they build are the same diameter and wall thickness of a comparable (stiffness and weight) CrMo, Carbon or Al frame. I bet they are not.
Also a good point about triangulation. Not much I plan on doing to take care of that issue though. If I was building a race car (and rules allowed) I think I would take care of that by some other means than a simple bolt in strut tower brace. These things are great for the street and DE, but I cannot really speak to how well they work for a dedicated track car.
Ti has a much higher strength to weight ration than Al and somewhat higher than steel. It is also far more corrosion resistant than either one and can tolerate more bending cycles than either one. The only drawback that I know is that it has funky notch strength characteristics (how it reacts to the surface being scratched).
Ask Tifo if the titanium tube sets for the bikes they build are the same diameter and wall thickness of a comparable (stiffness and weight) CrMo, Carbon or Al frame. I bet they are not.
Also a good point about triangulation. Not much I plan on doing to take care of that issue though. If I was building a race car (and rules allowed) I think I would take care of that by some other means than a simple bolt in strut tower brace. These things are great for the street and DE, but I cannot really speak to how well they work for a dedicated track car.
11-01-2002, 08:24 PM
#7
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"if the titanium tube sets for the bikes they build are the same diameter and wall thickness of a comparable (stiffness and weight) CrMo, Carbon or Al frame. I bet they are not."
Yup that's right. Traditional chromoly frames are built with 1.0/1.125 tubing typically in 0.8mm thickness. You've got some of the more exotic tubing like Columbus SP/SPX/SL/SLX tubing with butted ends (thicker) to deal with the loads at the joints; a tube may have 0.8 to 0.6 to 0.7mm thicknesses. Steelman makes some frames with an oddball French tubing with 0.4/0.6mm thickness, but the frame is about as stiff as an overcooked noodle!
Next up is the titanium frames. Litespeed & Merlin are the largest Ti makers. Tubing is typically 1.125/1.25/1.375" in 0.9-1.1mm thickness. This yields roughly the same stiffness as the steel tubing with a 25% reduction in weight. Some of the track riders will have 1.6-1.8mm thick tubing to handle the power.
Finally, there's aluminum frames. Cannondale & Klein are on the extreme end with the largest tubing diameters of 1.5/1.75/2.0" tubing in 0.5-0.9mm thick tubing. Since a tube's stiffness goes up to the fourth power of diameter, even with the 1/3rd lower modulus of aluminum vs. steel, doubling the diameter can double the stiffness of a tube made from a weaker alloy. A steel tube that's been doubled in size would be about 8x stiffer, impossibly tough to ride, especially in bumpy corners.
P.S. When was the last time anyone has broken a strut-brace because it wasn't strong enough? Remember that strength (yield, fatigue & ultimate) is a different property of metals than stiffness (rigidity). In that respect, beryllium and boron would make a better strut-brace material due to their superior stiffness compared to steel. But I still thing the geometry needs to be optimized first.
Yup that's right. Traditional chromoly frames are built with 1.0/1.125 tubing typically in 0.8mm thickness. You've got some of the more exotic tubing like Columbus SP/SPX/SL/SLX tubing with butted ends (thicker) to deal with the loads at the joints; a tube may have 0.8 to 0.6 to 0.7mm thicknesses. Steelman makes some frames with an oddball French tubing with 0.4/0.6mm thickness, but the frame is about as stiff as an overcooked noodle!
Next up is the titanium frames. Litespeed & Merlin are the largest Ti makers. Tubing is typically 1.125/1.25/1.375" in 0.9-1.1mm thickness. This yields roughly the same stiffness as the steel tubing with a 25% reduction in weight. Some of the track riders will have 1.6-1.8mm thick tubing to handle the power.
Finally, there's aluminum frames. Cannondale & Klein are on the extreme end with the largest tubing diameters of 1.5/1.75/2.0" tubing in 0.5-0.9mm thick tubing. Since a tube's stiffness goes up to the fourth power of diameter, even with the 1/3rd lower modulus of aluminum vs. steel, doubling the diameter can double the stiffness of a tube made from a weaker alloy. A steel tube that's been doubled in size would be about 8x stiffer, impossibly tough to ride, especially in bumpy corners.
P.S. When was the last time anyone has broken a strut-brace because it wasn't strong enough? Remember that strength (yield, fatigue & ultimate) is a different property of metals than stiffness (rigidity). In that respect, beryllium and boron would make a better strut-brace material due to their superior stiffness compared to steel. But I still thing the geometry needs to be optimized first.
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11-02-2002, 03:53 AM
#8
Three Wheelin'
What difference does it make if the material has more flex? all its doing is keeping the strut towers from spreading. Infact most strut braces are made with either a pivot or a ball-rod end.
heck it could be a cable!
I making a Ti strut just for the hell of it, but it doesnt really matter steel or alu just the same
there are quite a few reasons for the differences in the size of the tubes.
part of the reason for using bigger ti tubes is to gain stiffness with out the added weight as opposed to the steel tubes. But the other thing is that there are a heck of alot more small guys building steel than ti(because of ability)
The ride of a steel VS ti frame with same dia/wall tubing will be quite comparable, Ti isnt as flexy as its made out to be, it is more shock absorbing for sure though.
Ofcourse those super thinwall steel tubes arent exactly the stiffest either, but hey they have to make up for the weight to compete with Ti.
PS they don't callem "CrackN'fails" for nothing
heck it could be a cable!
I making a Ti strut just for the hell of it, but it doesnt really matter steel or alu just the same
there are quite a few reasons for the differences in the size of the tubes.
part of the reason for using bigger ti tubes is to gain stiffness with out the added weight as opposed to the steel tubes. But the other thing is that there are a heck of alot more small guys building steel than ti(because of ability)
The ride of a steel VS ti frame with same dia/wall tubing will be quite comparable, Ti isnt as flexy as its made out to be, it is more shock absorbing for sure though.
Ofcourse those super thinwall steel tubes arent exactly the stiffest either, but hey they have to make up for the weight to compete with Ti.
PS they don't callem "CrackN'fails" for nothing
11-02-2002, 05:00 AM
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im interested in what type of bicycle frames...im guessing road.....hmmmm maybe if one were to disappear off the dock im sure i could find a loving home for it....mine
11-02-2002, 05:49 AM
#10
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"Good point about Ti Danno, so you do exactly as you said and increase the diameter and change the shape of the tube, similar to that ***** aluminum bar that is on the market (Racing Dynamics)."
Yup exactly! Make it dimensionally right in between a steel and aluminium bar and it should be similar in stiffness as those two.
"What difference does it make if the material has more flex? all its doing is keeping the strut towers from spreading. Infact most strut braces are made with either a pivot or a ball-rod end."
The material chosen for the strut-brace has everything to do with the amount of spreading between the strut-towers.
But first, I think we're talking about this in two completely different ways, thus we need to clarify the analysis methodology before we can even continue. I'm not looking at this in black & white, all-or-nothing, yes/not blanket qualitative statements like, "flex yes/no?". Unless you're using unobtanium, every material has a certain amount of flex and stretch. So rather, we need to look at this in a quantitative fashion with shades of grey and using numbers to determine what it does under a certain load.
Each material has some important qualities to examine in determining suitability and implementation methods:
Young's Modulus of Elasticity - A standard sized sample is tested with a standard load. The amount of stretch/deflection in the sample is measured:
Yield Strength - The load point at which a standardized sample takes a permanent set and doesn't fully recover (it stretches/bends):
Tensile Strength (ultimate) - The load point at which a sample breaks into two pieces:
Fatigue Strength - How many cycles of a given load a sample can take before bending or breaking due to work-hardening. Steel & Ti have a fatigue limit where, if loads are kept below this level, the sample will last forever. Aluminium has zero fatigue limit. That is, no matter how low the load, it will eventually fail. Yes, you can arm-wrestle your aluminium A-arms and in 210,341.3 years, you will snap it in half!
Density - How much a given standard volume sample weighs.
For this exercise, we actually want to come up with a stiffness-to-size ratio because there's only so much room to work with under the hood. As you can see from the numbers above, for a same-dimensioned piece of metal, a Ti strut-brace would be 1/2 the stiffness of a steel one for 1/2 the weight. So we need to increase the dimensions of the strut-brace bar in Ti to compensate.
It ends up being about the same weight as steel for the same stiffness at twice the size. We don't have to worry about the strength too much because the strut-brace bar is made big enough in order to be stiff enough, that its ultimate breaking point is well beyond the loads imposed on it.
"heck it could be a cable!"
Again, we can't look at this in black & white terms. What kind of cable? What diameter? Every cable will have a different amount of stretch given the same load. Can you use picture-hanging wire and just wrap it around the tops of your strut towers? Will this be just as good as the strut-braces on the market now? Or do you want a cable off the Golden Gate Bridge? There has to be a point somewhere in the middle where you have to say enough is enough.
BTW, free <a href="http://www.gururacing.net/ChipUpgrade.html" target="_blank"> GURU Chip Upgrade kit</a> to anyone who can tell me the amount of stretch in the shortest and longest hanging cables on that bridge and why that is, assuming the same load on each cable and all...
"there are quite a few reasons for the differences in the size of the tubes.
part of the reason for using bigger ti tubes is to gain stiffness with out the added weight as opposed to the steel tubes."
True that increasing diameter adds stiffness, but why do you have to do it with Ti at all? Why not keep the same size as steel tubing and save even more weight?
Also most steel frames is at the limit of tubing diameter anyway. This limit is the 'crumpling' barrier determined by a 50:1 diameter vs. wall-thickness ratio. If you keep a 1" steel tube thicker than 0.51mm, it will just bend controllably when faced with a load beyond its yield-strength (see above). However, with tubing thinner than a 50:1 ratio (less than 0.51mm thick), a steel tube will just crumple unpredictably and chaotically when stressed beyond its yield-strength like a soda can.
Since Ti and aluminium has lower density than steel, you can increase the wall-thickness 2-3x over steel for the same weight. With thicker walls, you can increase the diameter and remain on the safe side of the 50:1 crumpling limit. But with larger diameter with the same 2-3x thicker walls, you add a lot of weight for a lot more stiffness. So you can reduce wall-thickness some. As you can see, this is a juggling act with criss-crossing factors. In the end, since all three materials have similar strength-to-weight and stiffness-to-weight ratios, top-end frames of all three materials tend to have similar weights, stiffness and performance. The ultimate material IMO, is EMS carbon-fibre using Trek's OCLV method.
"The ride of a steel VS ti frame with same dia/wall tubing will be quite comparable,"
Actually the part that makes the biggest difference in the 'ride' of a bike is the fork, wheels, tires and air-pressure. Flex & displacement per given load in those components account for over 95% of the total flex in a bike. With the advent of suspension in bikes, the dampers and springs makes the most difference (who cares if a fork flexes 4mm or 5mm if the dampers has 100mm of travel?).
The best handling configuration I've ever ridden, regardless of frame-construction have always been with light supple wheels. Take minimal numbers of thin double-butted spokes in 3x lacing using 200gm heat-treated 7000-series-Al rims, finished off with some 200gm kevlar sew-up tires... wow! I could ride on that forever!
Yup exactly! Make it dimensionally right in between a steel and aluminium bar and it should be similar in stiffness as those two.
"What difference does it make if the material has more flex? all its doing is keeping the strut towers from spreading. Infact most strut braces are made with either a pivot or a ball-rod end."
The material chosen for the strut-brace has everything to do with the amount of spreading between the strut-towers.
But first, I think we're talking about this in two completely different ways, thus we need to clarify the analysis methodology before we can even continue. I'm not looking at this in black & white, all-or-nothing, yes/not blanket qualitative statements like, "flex yes/no?". Unless you're using unobtanium, every material has a certain amount of flex and stretch. So rather, we need to look at this in a quantitative fashion with shades of grey and using numbers to determine what it does under a certain load.
Each material has some important qualities to examine in determining suitability and implementation methods:
Young's Modulus of Elasticity - A standard sized sample is tested with a standard load. The amount of stretch/deflection in the sample is measured:
Yield Strength - The load point at which a standardized sample takes a permanent set and doesn't fully recover (it stretches/bends):
Tensile Strength (ultimate) - The load point at which a sample breaks into two pieces:
Fatigue Strength - How many cycles of a given load a sample can take before bending or breaking due to work-hardening. Steel & Ti have a fatigue limit where, if loads are kept below this level, the sample will last forever. Aluminium has zero fatigue limit. That is, no matter how low the load, it will eventually fail. Yes, you can arm-wrestle your aluminium A-arms and in 210,341.3 years, you will snap it in half!
Density - How much a given standard volume sample weighs.
For this exercise, we actually want to come up with a stiffness-to-size ratio because there's only so much room to work with under the hood. As you can see from the numbers above, for a same-dimensioned piece of metal, a Ti strut-brace would be 1/2 the stiffness of a steel one for 1/2 the weight. So we need to increase the dimensions of the strut-brace bar in Ti to compensate.
It ends up being about the same weight as steel for the same stiffness at twice the size. We don't have to worry about the strength too much because the strut-brace bar is made big enough in order to be stiff enough, that its ultimate breaking point is well beyond the loads imposed on it.
"heck it could be a cable!"
Again, we can't look at this in black & white terms. What kind of cable? What diameter? Every cable will have a different amount of stretch given the same load. Can you use picture-hanging wire and just wrap it around the tops of your strut towers? Will this be just as good as the strut-braces on the market now? Or do you want a cable off the Golden Gate Bridge? There has to be a point somewhere in the middle where you have to say enough is enough.
BTW, free <a href="http://www.gururacing.net/ChipUpgrade.html" target="_blank"> GURU Chip Upgrade kit</a> to anyone who can tell me the amount of stretch in the shortest and longest hanging cables on that bridge and why that is, assuming the same load on each cable and all...
"there are quite a few reasons for the differences in the size of the tubes.
part of the reason for using bigger ti tubes is to gain stiffness with out the added weight as opposed to the steel tubes."
True that increasing diameter adds stiffness, but why do you have to do it with Ti at all? Why not keep the same size as steel tubing and save even more weight?
Also most steel frames is at the limit of tubing diameter anyway. This limit is the 'crumpling' barrier determined by a 50:1 diameter vs. wall-thickness ratio. If you keep a 1" steel tube thicker than 0.51mm, it will just bend controllably when faced with a load beyond its yield-strength (see above). However, with tubing thinner than a 50:1 ratio (less than 0.51mm thick), a steel tube will just crumple unpredictably and chaotically when stressed beyond its yield-strength like a soda can.
Since Ti and aluminium has lower density than steel, you can increase the wall-thickness 2-3x over steel for the same weight. With thicker walls, you can increase the diameter and remain on the safe side of the 50:1 crumpling limit. But with larger diameter with the same 2-3x thicker walls, you add a lot of weight for a lot more stiffness. So you can reduce wall-thickness some. As you can see, this is a juggling act with criss-crossing factors. In the end, since all three materials have similar strength-to-weight and stiffness-to-weight ratios, top-end frames of all three materials tend to have similar weights, stiffness and performance. The ultimate material IMO, is EMS carbon-fibre using Trek's OCLV method.
"The ride of a steel VS ti frame with same dia/wall tubing will be quite comparable,"
Actually the part that makes the biggest difference in the 'ride' of a bike is the fork, wheels, tires and air-pressure. Flex & displacement per given load in those components account for over 95% of the total flex in a bike. With the advent of suspension in bikes, the dampers and springs makes the most difference (who cares if a fork flexes 4mm or 5mm if the dampers has 100mm of travel?).
The best handling configuration I've ever ridden, regardless of frame-construction have always been with light supple wheels. Take minimal numbers of thin double-butted spokes in 3x lacing using 200gm heat-treated 7000-series-Al rims, finished off with some 200gm kevlar sew-up tires... wow! I could ride on that forever!
11-02-2002, 06:14 AM
#11
Race Director
WOW. I stay away from the forum for a day and look what happens...
Danno is "spot on" on his comments. I couldn't have explained better myself.
In my opinion, Ti is not the perfect material for every application, like strut braces or bicycle forks. It is great for frames, bolts, etc.
Now, that doesn't mean that it can't be used in some interesting automotive applications. I've already made the shift ****. I'm working on the Ti exhaust pipes. I also have Ti brake pad backing plates that help immensly with brake cooling. Ti is very non-conductive when it comes to heat, especially when compared to steel and aluminum. So the backing plates keep the heat from transferring thru the piston and into the brake fluid, that would ultimately cause brake fade.
We've done some interesting things in Ti at work, inlcuding some coffee tables and a run of rescue gurneys that break down into a small pack for a high altitude rescue team.
We are also at the forefront R/D on Ti tubing. We have worked with Reynolds over the past year to develop the first production bike frame made from seamless 6/4titanium. All 6/4 frames in the past had had tubes made from sheet goods that are rolled and welded (and thus heat affected) into a tube. The new tubeset is actually extruded into tubed from the Ti stock. Very revolutionary, and has alowed us to create a very big "buzz" in the industry.
Tifo
Danno is "spot on" on his comments. I couldn't have explained better myself.
In my opinion, Ti is not the perfect material for every application, like strut braces or bicycle forks. It is great for frames, bolts, etc.
Now, that doesn't mean that it can't be used in some interesting automotive applications. I've already made the shift ****. I'm working on the Ti exhaust pipes. I also have Ti brake pad backing plates that help immensly with brake cooling. Ti is very non-conductive when it comes to heat, especially when compared to steel and aluminum. So the backing plates keep the heat from transferring thru the piston and into the brake fluid, that would ultimately cause brake fade.
We've done some interesting things in Ti at work, inlcuding some coffee tables and a run of rescue gurneys that break down into a small pack for a high altitude rescue team.
We are also at the forefront R/D on Ti tubing. We have worked with Reynolds over the past year to develop the first production bike frame made from seamless 6/4titanium. All 6/4 frames in the past had had tubes made from sheet goods that are rolled and welded (and thus heat affected) into a tube. The new tubeset is actually extruded into tubed from the Ti stock. Very revolutionary, and has alowed us to create a very big "buzz" in the industry.
Tifo
11-02-2002, 06:14 AM
#12
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Danno,
The Porsche factory race team would concur with your triangulation theory.
Last year there was a 924GTR at the Carlsen Porsche Swap meet. It had a tower brace that was triangulated back to the fire wall!
I went to the event thinking it was just a swap meet, so I did not bring a camera.
I was also able to drool onto a 917, If only I would have known.....
Lots of neet tricks on those cars.
The Porsche factory race team would concur with your triangulation theory.
Last year there was a 924GTR at the Carlsen Porsche Swap meet. It had a tower brace that was triangulated back to the fire wall!
I went to the event thinking it was just a swap meet, so I did not bring a camera.
I was also able to drool onto a 917, If only I would have known.....
Lots of neet tricks on those cars.
11-04-2002, 11:45 AM
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Hey Danger,
Yeah, making a Ti cross brace would mostly be for giggles and badness factor. That and the fact that the Welt cross brace weighs a ton and looks like butt after it has been under the hood for a while.
Danno,
I hadn't realized Merlin was still in business, what since most of their key welders and business manager defected to Independent Fabrication (IF). Good to see they are still around. (I got out of the bicycle business at the end of 1996 and haven't kept up on it too much)
I started selling Merlin frames back in 1989 (about a year or so after they came into existance) and over the years have sold Ti bikes from Fat City Cycles, Litespeed, Outback , etc. I am pretty well clued in to how Ti affects ride quality. As you say, it isn't as responsible for dreaded flex as critics might say. It does have a wonderful tendency to not transmit vibration. My True Temper IF and my old SLX/SPX Gianni Motta road frame were both very buzzy.
I'll tell you what though, if a fork flexes fore and aft 4-5mm, you bet your *** I am going to worry about it. That much deflection is going to radically change caster angle (yeah, like compressing the fork doesn't) and really **** your steering.
Carbon fiber would be nice, as long as you are sure it is defect free and you never put a significant blemish in the surface. Ever seen a carbon fiber seat post shatter?
Hey Tifo,
Are you all running into any issues with the dies used to draw the tubing. Any issues with the tubing work hardening to much as it is drawn? I remember Chris Chance explaining how tough Ti was on the tooling they used to cut and externally butt the tubes they used for the Ti Fat. Easy to cut, but really hard on the tools.
Yeah, making a Ti cross brace would mostly be for giggles and badness factor. That and the fact that the Welt cross brace weighs a ton and looks like butt after it has been under the hood for a while.
Danno,
I hadn't realized Merlin was still in business, what since most of their key welders and business manager defected to Independent Fabrication (IF). Good to see they are still around. (I got out of the bicycle business at the end of 1996 and haven't kept up on it too much)
I started selling Merlin frames back in 1989 (about a year or so after they came into existance) and over the years have sold Ti bikes from Fat City Cycles, Litespeed, Outback , etc. I am pretty well clued in to how Ti affects ride quality. As you say, it isn't as responsible for dreaded flex as critics might say. It does have a wonderful tendency to not transmit vibration. My True Temper IF and my old SLX/SPX Gianni Motta road frame were both very buzzy.
I'll tell you what though, if a fork flexes fore and aft 4-5mm, you bet your *** I am going to worry about it. That much deflection is going to radically change caster angle (yeah, like compressing the fork doesn't) and really **** your steering.
Carbon fiber would be nice, as long as you are sure it is defect free and you never put a significant blemish in the surface. Ever seen a carbon fiber seat post shatter?
Hey Tifo,
Are you all running into any issues with the dies used to draw the tubing. Any issues with the tubing work hardening to much as it is drawn? I remember Chris Chance explaining how tough Ti was on the tooling they used to cut and externally butt the tubes they used for the Ti Fat. Easy to cut, but really hard on the tools.
11-04-2002, 01:47 PM
#14
Race Director
"I'll tell you what though, if a fork flexes fore and aft 4-5mm, you bet your *** I am going to worry about it. That much deflection is going to radically change caster angle (yeah, like compressing the fork doesn't) and really **** your steering."
It actually flexes much more than that! The critical head-tube angle (typically 73-75 degrees) doesn't change by much when the fork hits bumps and flexes. What really changes is the rake and the resulting trail as measured on the ground (distance between pivot-axis on the ground and contact patch). That 4-5mm is actually pretty critical in absorbing bumps. On non-suspension bikes, that's why forks are built with that bend at the bottom to flex. Straight-tube forks are really harsh over bumps and doesn't lead to a better handling bike. And since that deflection is 4-5mm forwards & upwards, trail is increased for more stability, if only momentarily for milliseconds.
I've crudely measured rearward deflection of over 20mm and lateral displacements of the front hub of over 30mm. The longitudinal test was measured indirectly when I put the forks from track bike on to my crit bike for more lateral stiffness in sprints. Great for sprints in crits, but baaad for downhills and braking. I was actually rubbing my front tire on the bottom of my downtube under braking and calculated that the tips of the forks would have to move rearward 20mm for the rubbing to occur.
As for lateral deflection of the fork, this most likely is due to twisting of the headtube since the front triangle isn't really torsionally rigid (I ride a 54cm with short headtube). With one of those small uni-crown lugs on the fork, it pulls the tops of the tubes close together to form a nice triangle, so I suspect the flex is in the crown and steerer tube itself.
But stiffness in a bike-frame is over-rated anyway. Frame-flexing is actually an elastic deformation that returns an overwhelming majority of its energy (the frame pushes back on your leg when it returns, helping rotate the crank). I remember a test between extremes, a Klein (one of the stiffest bikes ever made) and a Vitus-979 (remember those?), one of the softest but vastly popular in the Tour.
They had one of the Slurpee guys, Davis Phinney or Roy Knickman do short & long time-trials on each bike to test which one would be faster. The results? Negligible difference with times that were pretty much identical!
"Carbon fiber would be nice, as long as you are sure it is defect free and you never put a significant blemish in the surface. Ever seen a carbon fiber seat post shatter?"
Yup, one of my friends had one shoved up his behind when their group got hit by a car. Ended up losing one of his legs (they found it stuck to the grill of the car, 100m down the road
). Weaving in a little kevlar would increase CF's toughness.
"Are you all running into any issues with the dies used to draw the tubing. Any issues with the tubing work hardening to much as it is drawn?"
Yeah, I want to know how these are made!!! When are you shipping me my first batch of samples!!!
<img src="graemlins/jumper.gif" border="0" alt="[jumper]" /> <img src="graemlins/jumper.gif" border="0" alt="[jumper]" />
It actually flexes much more than that! The critical head-tube angle (typically 73-75 degrees) doesn't change by much when the fork hits bumps and flexes. What really changes is the rake and the resulting trail as measured on the ground (distance between pivot-axis on the ground and contact patch). That 4-5mm is actually pretty critical in absorbing bumps. On non-suspension bikes, that's why forks are built with that bend at the bottom to flex. Straight-tube forks are really harsh over bumps and doesn't lead to a better handling bike. And since that deflection is 4-5mm forwards & upwards, trail is increased for more stability, if only momentarily for milliseconds.
I've crudely measured rearward deflection of over 20mm and lateral displacements of the front hub of over 30mm. The longitudinal test was measured indirectly when I put the forks from track bike on to my crit bike for more lateral stiffness in sprints. Great for sprints in crits, but baaad for downhills and braking. I was actually rubbing my front tire on the bottom of my downtube under braking and calculated that the tips of the forks would have to move rearward 20mm for the rubbing to occur.
As for lateral deflection of the fork, this most likely is due to twisting of the headtube since the front triangle isn't really torsionally rigid (I ride a 54cm with short headtube). With one of those small uni-crown lugs on the fork, it pulls the tops of the tubes close together to form a nice triangle, so I suspect the flex is in the crown and steerer tube itself.
But stiffness in a bike-frame is over-rated anyway. Frame-flexing is actually an elastic deformation that returns an overwhelming majority of its energy (the frame pushes back on your leg when it returns, helping rotate the crank). I remember a test between extremes, a Klein (one of the stiffest bikes ever made) and a Vitus-979 (remember those?), one of the softest but vastly popular in the Tour.
They had one of the Slurpee guys, Davis Phinney or Roy Knickman do short & long time-trials on each bike to test which one would be faster. The results? Negligible difference with times that were pretty much identical!
"Carbon fiber would be nice, as long as you are sure it is defect free and you never put a significant blemish in the surface. Ever seen a carbon fiber seat post shatter?"
Yup, one of my friends had one shoved up his behind when their group got hit by a car. Ended up losing one of his legs (they found it stuck to the grill of the car, 100m down the road
). Weaving in a little kevlar would increase CF's toughness."Are you all running into any issues with the dies used to draw the tubing. Any issues with the tubing work hardening to much as it is drawn?"
Yeah, I want to know how these are made!!! When are you shipping me my first batch of samples!!!
<img src="graemlins/jumper.gif" border="0" alt="[jumper]" /> <img src="graemlins/jumper.gif" border="0" alt="[jumper]" />
11-04-2002, 04:13 PM
#15
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Thread Starter
(Oh no, were spinning off topic. But who cares, I'm having fun rappin' with Danno)
20 to 30mm!!! Are you kidding me?! We even had a hard time getting that much deflection when we were trying to align forks on an alignment jig. That said I have watched really light Columbus tubed forks chatter over washboard. But almost and inch?
Regarding straight blade versus curved blades, well, everything I read back in the 80's and early 90's said there really wasn't a difference between the two, that most of the flex takes place near the crown. This is coming from folks like Lennard Zinn, Ben Serotta, Ernesto Colnago, etc. Think about were most forks fail (I've literally seen hundreds of failed forks over the years). I think every fork I ever saw fail, both road and mountain bike, did so at or near the crown (within 2 to 3 inches of the crown race). The only other failures I have seen have been bent dropouts or cracked steer tubes. I think a lot of the perception that straight bladed forks are stiffer is because so many where built with bigger therefore stiffer blades
I think frame stiffness is somewhat overrated as well. (Vitus, cripes, where did you dig that up from? Does it have Super Record or Huret Jubilee on it too just to make it really light?) An experienced cyclist will know how to compensate for frame flex, or rather will understand what to be concerned about and what to ignore. Flex at the bottom bracket is annoying as heck, but really doesn't pose too much of a problem (except when the low temp silver brazing cracks where the chainstay plugs into the BB shell). A chattering fork is kind of scarey at first, but as long as you don't freak you should be OK. I think a stiff frame really serves to instill confidence in newer riders. It also keeps high speed oscilation under control.
Flex in wheels on the other hand can make you fill your shorts. We had a demo set of Spinergy wheels when they first came out and I took them up to one of the trails in North Georgia (Bull Mtn Trail for those in the area). On climbs and on the straights they were great, but when you would get into a high speed downhill turn you could feel the wheel suddenly lay over under the load. Very unnerving. We even checked and double checked to make sure it wasn't the fork (Manitou EFC) or the hub. With spoked wheels (I used to build wheels) we didn't have that problem (32 hole Ringle Super Duper Bubba, DT Comp 15/16 spokes, Mavic 231).
20 to 30mm!!! Are you kidding me?! We even had a hard time getting that much deflection when we were trying to align forks on an alignment jig. That said I have watched really light Columbus tubed forks chatter over washboard. But almost and inch?
Regarding straight blade versus curved blades, well, everything I read back in the 80's and early 90's said there really wasn't a difference between the two, that most of the flex takes place near the crown. This is coming from folks like Lennard Zinn, Ben Serotta, Ernesto Colnago, etc. Think about were most forks fail (I've literally seen hundreds of failed forks over the years). I think every fork I ever saw fail, both road and mountain bike, did so at or near the crown (within 2 to 3 inches of the crown race). The only other failures I have seen have been bent dropouts or cracked steer tubes. I think a lot of the perception that straight bladed forks are stiffer is because so many where built with bigger therefore stiffer blades
I think frame stiffness is somewhat overrated as well. (Vitus, cripes, where did you dig that up from? Does it have Super Record or Huret Jubilee on it too just to make it really light?) An experienced cyclist will know how to compensate for frame flex, or rather will understand what to be concerned about and what to ignore. Flex at the bottom bracket is annoying as heck, but really doesn't pose too much of a problem (except when the low temp silver brazing cracks where the chainstay plugs into the BB shell). A chattering fork is kind of scarey at first, but as long as you don't freak you should be OK. I think a stiff frame really serves to instill confidence in newer riders. It also keeps high speed oscilation under control.
Flex in wheels on the other hand can make you fill your shorts. We had a demo set of Spinergy wheels when they first came out and I took them up to one of the trails in North Georgia (Bull Mtn Trail for those in the area). On climbs and on the straights they were great, but when you would get into a high speed downhill turn you could feel the wheel suddenly lay over under the load. Very unnerving. We even checked and double checked to make sure it wasn't the fork (Manitou EFC) or the hub. With spoked wheels (I used to build wheels) we didn't have that problem (32 hole Ringle Super Duper Bubba, DT Comp 15/16 spokes, Mavic 231).