Technical Q&A with Lennard Zinn: Using different wheels; more on carbon and damping; and torque-wrench warning
Dear Lennard,I have two sets of wheels I use for my bike with two different sets of clinchers, each with a different maximum-pressure rating. My race wheels have tires with a max pressure rating of 116 psi (Michelin Pro Race). However, my training wheels have tires with a max pressure of 145 psi (Vredestein Fortezza Tri Comp). I use my training wheels as my pit wheels while racing. If I have to change a wheel during a race, will the different pressures between the front and rear cause me handling problems or other dangers? Secondly, I am 175 pounds and use paired-spoke wheels (Shimano
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By Lennard Zinn
I have two sets of wheels I use for my bike with two different sets of clinchers, each with a different maximum-pressure rating. My race wheels have tires with a max pressure rating of 116 psi (Michelin Pro Race). However, my training wheels have tires with a max pressure of 145 psi (Vredestein Fortezza Tri Comp). I use my training wheels as my pit wheels while racing. If I have to change a wheel during a race, will the different pressures between the front and rear cause me handling problems or other dangers? Secondly, I am 175 pounds and use paired-spoke wheels (Shimano WH-7701) to race. I have problems keeping the wheels true. Other riders have informed me that the wheels go out of true because I am over 165 lbs. Is this true?
No, the pressure difference will probably not throw you off, especially if you follow my recommendations from last week, since I can’t imagine any road race or crit where you would want to run those Vredesteins at higher than 120psi or so anyway. You may, of course, notice the higher rolling resistance and reduced cornering performance of the stiffer, lower-thread-count Michelin.
As for the wheels, the heavier you are, the more you can cause the nipples to lose contact at the hub as the wheel rolls, deforms, and de-tensions each spoke as it comes past the bottom, making it possible for the nipples to loosen up. That said, I find that riding style has at least as much to do with it as weight. Some riders who are quite a bit heavier yet who have smoother pedaling styles and are more graceful over road imperfections can ride the same races and events problem-free on the same wheels that constantly fall apart under lighter riders. Some Loctite or Spoke Prep on your nipples might help.
Revisiting carbon and damping
I purchased a 54cm 2004 Roubaix Comp after test-riding numerous bikes, including the Trek 5200. The difference between the Trek and the Roubaix is like night and day as far as harshness is concerned. As far as I’m concerned, all of Specialized’s claims about the Roubaix’s shock absorption are true.
I have arthritis in my hands and they always hurt to some degree, but most of the bikes I tested on my favorite neighborhood rough roads make me want to do ibubrofen-loading immediately. On the Roubaix, I feel the low-frequency component of the bumps but it’s not at all painful.
I was shopping to replace a 20-year-old Viner track bike with an added derailleur hanger and brake bridge. Surprisingly, most of the current road bikes that I tested including the Trek were harsher than the Viner.
The sensation of riding the Roubaix is quite peculiar in that there’s a real absence of sensation; it comes close to disappearing under you. I’ve had bikes like the early vintage Cannondales that felt very dead and it’s nothing like that; it’s a desirable sensation closer to floating. I still have the Cannondale; I’ve tried to give it away and it always comes back. The Roubaix also handles out-of-the-saddle climbing as well as the old Viner and about the same as a friend’s Dean with a carbon fork, which is the best bike I’ve ever tried for climbing.
Specialized chimes in:
Thanks for the opportunity to respond to your reader’s question regarding the damping and compliance advantages of our Roubaix versus a standard aluminum frame.
The reader will certainly find the Roubaix vastly superior for road comfort compared to his older alloy frame. The advantages of the Roubaix from a compliance and vibration perspective stem from several major factors, including Specialized’s unique FACT carbon-fiber layup, our patented Zertz vibration damping technology, and the Roubaix’s geometry, which is designed to increase road comfort and improve fit.
Considering that Specialized has designed the Roubaix FACT carbon-fiber lay-up to have high torsional and pedaling frame stiffness with very low frame weights (56cm S-Works Roubaix with hardware and paint is 1025g, 56cm Roubaix Pro is 1135g) demonstrates that Roubaix offers more performance with less rider sacrifice.
The same reader asked for advice on carbon fiber bars and stems. Our findings are that Specialized’s FACT carbon-fiber S-Works bar is super comfortable due to the ergonomic shape in the top and drop parts of the bar. Our bar is designed to fit the rider’s hand shape better. Our bar’s vibration damping has been noticed and appreciated by nearly all of our team riders and testers.
Replacing/upgrading a frame will provide a quantum leap in performance over just swapping bars.
Director of engineering
But what about shimmy?
I am a big fan of your column and books, but was a bit tardy getting around to your column on softening the ride. You mentioned shimmy when discussing the Specialized Roubaix and I was unclear why.
I am considering the S-Works Roubaix, not for Zertz or carbon, but because I found a slightly longer wheelbase to be most important (after frame fit, tires, and saddle) to determining comfort over long distances. I am 55, haven’t raced in 18 years, but enjoy brevets at a slightly brisk pace.
Can you clarify the shimmy comment?
That was an unfortunate choice of words on my part. I hope people did not interpret it as my saying that the Roubaix shimmies. What I was merely trying to say was that, as more weight is loaded on any bike, the resonant frequency of vibration of the bike is reduced. This is something I have learned from studying shimmy problems. However, shimmy is not the issue here. Rather, I was discussing the shock-damping characteristics Specialized has designed into the frame.
Regarding torque wrenches
Thank you for an excellent article on torque wrenches. Unfortunately, I have some bad news – I have come across several beam-type torque wrenches that were significantly out of spec. In one case, a freshly overhauled engine had a big end failure due to the rod bolts being torqued under spec (thankfully, not my work).
Why these beam-type torque wrenches were reading low even though properly zeroed, I do not know. Possibly they had been stressed by trying to use them beyond their intended range – though that is pure speculation on my part.
I do not mean to imply that beam-type torque wrenches are inferior to other types, just that they also need to have their accuracy regularly checked by a proper torque-wrench tester. It also follows that you should never attempt to use one torque wrench to calibrate another.
Regarding parts-cleaning solvents
Just an FYI…www.biodiesel.org.
Technical writer Lennard Zinn is a frame builder (www.zinncycles.com), a former U.S. national team rider and author of several books on bikes and bike maintenance including the pair of successful maintenance guides “ Zinn & the Art of Mountain Bike Maintenance” and “Zinn & the Art of Road Bike Maintenance.”Zinn’s regular column is devoted to addressing readers’ technical questions about bikes, their care and feeding and how we as riders can use them as comfortably and efficiently as possible. Readers can send brief technical questions directly to Zinn. Zinn’s column appears here each Tuesday.