Christie Posted February 3, 2009 Share Carbon is a fantastic material for bicycles. On paper, it is lighter, stiffer and stronger, with better fatigue life than any other frame material, and it does not have to seal, keep out electromagnitic waves of be resistant to lightning. What makes it a bit trickey is to make joints and directional changes. The joint between 2 carbon tubes is much less efficient than a weld, for example. So with carbon, great mechanical gains are made on the tubes, but some of these gains are lost at the connections/changes of direction of the fibres. An XL frame from carbon would be much lighter than the aluminium equivalent, but an XS frame in carbon may be very close in mass to an XS in alu. With that long winded explanation I am trying to say that carbon is less efficient in regions of joints and changes in direction. For this reason, it is very difficult to make a carbon stem that is significantly out performs a metal one. (cranks are similar, too) A stem has effectively 2 joints or changes in direction close together - very hard to do efficiently in carbon. But still, a lot of manufacturers make carbon stems. The reason for this is that the market is crazy for carbon, and the manufacturers are milking it for all they can. Agreed, carbon stems are more bling, but they are not significantly better. I dont think I agree on the "not enough spacers on top of stem" point. On most TT bikes, nothing is left sticking out above the stem. I also rarely see this on pics of pro bikes, Boonen, Cavendish & co make their components work very hard! Christie2009-02-03 20:26:42 Link to comment Share on other sites More sharing options...
De Renner Posted February 3, 2009 Share I wonder if that almighty stack of spacers exceeds the stack height limit for that fork in terms of the insert length? I'm assuming it is the 3T Funda and not the recalled Wolf. I always chuckle when I see inflexible people riding racing bikes with a heap of spacers. It totally alters the handling and places undue force on the fork steerer. he should have bought a Cervelo RS. Still light but has a longer headtube. On the stem, most likely as a result of over-tightening. A torque wrench is an essential tool for bike riders. A combination of an over-tightened stem, bumps, and brakes like Zero gravity (don't modulate very well) and you have an accident waiting to happen. It seems your father has also exceeded the stack height for that fork with all the spacers. Link to comment Share on other sites More sharing options...
Iwan Kemp Posted February 3, 2009 Share Thanks JB and Christie, you make for some interesting reading. Link to comment Share on other sites More sharing options...
Red Zone Posted February 3, 2009 Share Thats a dodgy belay device Johan, I dont think anyone uses a figure 8 anymore Link to comment Share on other sites More sharing options...
FanieFiets Posted February 4, 2009 Share I wonder if that almighty stack of spacers exceeds the stack height limit for that fork in terms of the insert length? I'm assuming it is the 3T Funda and not the recalled Wolf. I always chuckle when I see inflexible people riding racing bikes with a heap of spacers. It totally alters the handling and places undue force on the fork steerer. he should have bought a Cervelo RS. Still light but has a longer headtube. On the stem' date=' most likely as a result of over-tightening. A torque wrench is an essential tool for bike riders. A combination of an over-tightened stem, bumps, and brakes like Zero gravity (don't modulate very well) and you have an accident waiting to happen. It seems your father has also exceeded the stack height for that fork with all the spacers. [/quote'] thing is he takes his bike to the shop and asks them for advice. The spacers werent his idea......but he afterwards said something doenst look right. To the bike shops defence he asked them to built him the lightest possible bike. No specific reason, it just his thing. Link to comment Share on other sites More sharing options...
Johan Bornman Posted February 4, 2009 Share Thats a dodgy belay device Johan' date=' I dont think anyone uses a figure 8 anymore[/quote'] Sorry, I couldn't find a picture of the latest Figure 9 type. Link to comment Share on other sites More sharing options...
Christie Posted February 4, 2009 Share Imo aluminium is the best metal for stems. To make a steel stem that is not significantly heavier than current alu stems is hard, because the wall thickness would have to be thin, and it then becomes is difficult to machine, or weld from sections. Laser and electron beam welding a stem is also not that simple, because of the geometry of the welds. All this would make a steel stem more expensive. On to Titanium. This was the best light weight material for frames before composites. For starters, titanium is expensive. To machine a stem from a solid will create a lot of expensive shavings. Secondly, it takes a lot of skill to produce good quality welds in titanium, and a welded stem will have 2 welds close together - easy to stuff up during manufacture. It is possible to make a good ti stem, but be very very careful of "affordable" Ti stems. I would stick to stems of a very reputable manufacturer, like ITM, Easton, Zipp, FSA etc. There is a better chance that these companies spend a bit of money on engineering and R&D, as well as quality control. It is important to get the heat treatment and surface finish like shot peening/bead blasting right. I also prefer 4 bolt clamps. They may be a bit heavier because of the 2 extra bolts, but a light stem weighs 100 grams, a lightish one 130 to 140 grams. I would recommend the use the heavier stem and using 30 ml less juice in the water bottle. Also, weight weenie alu stems like Syntace have a reputation for feeling less stiff in torsion, if comments on the web are correct. This will be noticeable if you sprint/climb out of the saddle - nothing serious, but it just does not feel as nice as something more solid. I also believe in having the torque done correctly on stem bolts. For this you need a well trained expert mechanic (although Deda tested stem bolts torqued by ProTour mechanics, and found most of them incorrectly torqued) or a torque wrench. I have not seen many torque wrenches being used in the LBS that I've been to, and some stem bolts must be torqued 5Nm, some 6Nm, 8Nm etc depending on the design. I would not trust most okes behind shop counter for this. Re the amount of spacers on top of the stem - I don't like it, but I don't think it is such a critical thing. It will increase the bending stress in the steerer for forces acting in the horizontal plane, but this does not happen much - perhaps when braking down a steep hill, or riding into a wall. Because of the angle of the steerer, a higher stem puts the hbar closer to the rider than the same stem in a lower position. This will reduce the bending stress in the steerer a bit when the rider is standing. Link to comment Share on other sites More sharing options...
Johan Bornman Posted February 4, 2009 Share cut cut cut cut e the amount of spacers on top of the stem - I don't like it' date=' but I don't think it is such a critical thing. It will increase the bending stress in the steerer for forces acting in the horizontal plane, but this does not happen much - perhaps when braking down a steep hill, or riding into a wall. Because of the angle of the steerer, a higher stem puts the hbar closer to the rider than the same stem in a lower position. This will reduce the bending stress in the steerer a bit when the rider is standing.[/quote'] Christie, did you not mean underneath the stem? Spacers on top have no effect on leverage. Johan Bornman2009-02-04 01:22:50 Link to comment Share on other sites More sharing options...
ridesleeprepeat Posted February 4, 2009 Share the spacers on top of the stem are there to guard against crushing of the top of the steerer tube during use. generally only required on lightweight full carbon numbers... Link to comment Share on other sites More sharing options...
Christie Posted February 4, 2009 Share sorry about that (blush), meant to say spacers on top of headset, like in the pic Faniefiets posted. (Comes from trying to type in 2 places at once) I think a stem with a rise angle would have been the better option, it would have looked a bit better, and saved the mass of the spacer plus the extended steerer Link to comment Share on other sites More sharing options...
bustthesickness Posted February 4, 2009 Share I also believe in having the torque done correctly on stem bolts. For this you need a well trained expert mechanic (although Deda tested stem bolts torqued by ProTour mechanics' date=' and found most of them incorrectly torqued) or a torque wrench. I have not seen many torque wrenches being used in the LBS that I've been to, and some stem bolts must be torqued 5Nm, some 6Nm, 8Nm etc depending on the design. I would not trust most okes behind shop counter for this. [/quote']Agreed. I've seen a quite a few bike shops not using them. Gedore makes some very cool tools. http://www.gedore.co.za/catalogue09/section7.pdf What surprised me the most when I got one was how I'd overtightened a few of my bolts. It's very hard to tell just by hand. Not in all cases, and over the years you do get a feel for how tight something should be, but some components had much lower torque requirements than I would have thought. Link to comment Share on other sites More sharing options...
De Renner Posted February 4, 2009 Share No need for spacers on top of the stem - ever. The steerer should always be cut so that it is a few mm underneath the top of the stem. The headset cap is not designed to sit on top of spacers. Link to comment Share on other sites More sharing options...
De Renner Posted February 4, 2009 Share http://www.effettomariposa.com/ Link to comment Share on other sites More sharing options...
FanieFiets Posted February 11, 2009 Share followup on KCNC's service after the crash. https://www.bikehub.co.za/forum_posts.asp?TID=43111&PID=677419#677419 Link to comment Share on other sites More sharing options...
4ph3X Posted February 11, 2009 Share sjo! ek is bly om te hoor jou pa is ok! dissie cool nie. hoekom is daar so baie spacers onder die stem? Link to comment Share on other sites More sharing options...
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