Technical Q&A with Lennard Zinn – Tires, stems and more big guy talk

More tire talk
Dear Lennard,
I really enjoyed your recent wet-road tire discussion with Tom Petrie and Alberto De Gioannini. Just the topic I was looking for, but I’m still a little confused. I thought the cord compound made a big difference and it wasn’t mentioned at all.

I recall racing in the rain in a crit next to a friend who was running cotton-cord sew up tires as opposed to my silks. While we’d been comparable in bike handling otherwise, I found myself nearly sideways in corners while hewent around like on a rail.

We’d pumped our tires to comparable pressures.

I’m taking a group over for some of the Spring Classics and plan toride the tourist versions of Tour of Flanders and Amstel Gold as well asrenewing my acquaintance with the cobbles of Paris-Roubaix.

Rode them in ’96 when, the night before, I had the privilege of meeting1958 winner Leon Van Daele and asked him if he had any advice for riding cobbles in the rain.

“If it rains,” he said, taking a long drag on his cigarette, “you will fall.” Fortunately, it didn’t rain. I’m building some new wheels for the trip.Since I can’t always count on good weather, I’d like to have the best possibletires.
— Phil

Answer from Vittoria:

Dear Lennard and Phil,
Actually, a tire with a more flexible casing can, at the same inflation pressure, better adapt to the surface it’s rolling on. This gives better control, which is usually a blessing when the roads becomes slippery.I don’t want to look like the ‘complicated’ guy, but casing materialis only one of the aspects:

Casing material – Keeping the same material, higher TPI is better. Comparing materials at the same TPI (nylon, cotton, polycotton), polycotton and cotton are similar, outperforming nylon. Please note, however, that a polycotton (threads with polyester core, cotton outside) casing is stronger than cotton against cuts (and to that nasty, sharp gravel that rain brings onto the road);

Inner tube – Often neglected, a tube can improve the tire+tube performance. A thin butyl tube reduces the rolling resistance/increases flexibility over a standard one (reliability aside) but a latex tube can beat any butyl as far as flexibility is concerned (that’s one of the reason why high-end sew-ups are such a joy to ride).

Tire construction – Tubulars have better cornering behavior than clincher tires, thanks to the almost constant casing radius. That’s even more noticeable on a wet surface.
— Alberto De Gioannini
Vittoria S.p.A.

Stem talk
Dear Lennard,
Your recent discussion of long-valve tubulars mentioned an option from Vittoria. It excluded an essentially identical offering from Tufo. All Tufo tires (tubular and tubular clinchers — at least all the ones I’ve ever seen advertised), offer removable valve cores. The offer valve extenders that will accept the removed valve cores. This, unlike Vittoria, also provides a solution for deep-rimmed clinchers as well.
-Rich

More on tall riders pulling wheelies on steep road climbs

Dear Lennard,
I have had my front wheel popping up while climbing for years on many bikes and that despite the fact that I am only six-feet-tall. I am relatively powerful, but I am not claiming to be fast uphill. Certainly, dropping the elbows is a good idea. My new bike, a Calfee, has long chainstays 41.5 and the front wheels stays put. Craig Calfee says this was done deliberately and doesn’t make the bike handle too slowly.After tiding this bike for a while, it seems to me that he is correct.
Mark

Dear Lennard,
I really enjoyed your explanation to the fella that had the big bike with squirrelly front-end problem when climbing.

My two favorite road bikes (for the time being) are a Merckx Majestic 59cm (2001 vintage Ti) and De Rosa Primato 61cm (1999 vintage steel).

Through use of a FitStick, I’m able to get my contact points fairly consistenton the two of them. Both frames use a 72.5 seat tube angle. The Majestic has a ‘stock’ length of chainstay used on all sizes for thi smodel. The De Rosa has chainstays proportionally longer for the largersizes of this model to go along with the slacker seat angles for the largerframes.

I have always wondered why De Rosa did this as this is no tseen all that much on stock frames from most manufacturers.Your article made sense of the issue. I’ve had the ‘squirrelly’ handling on climbs with the Merckx trying to wheelie and find that I need to concentrateon weight distribution when on the steeps.

There are also other differences(wheel base/front center, materials, etc.) that give the bikes different personalities.

They do both share a low bottom bracket height/largebb drop that I’ve come to appreciate, as I don’t have to worry about criterium racing or other foolish such activities. I really like the two bikes being in different in materials as I sweat profusely in the humid Oklahoma summers.

I ride Ti above 75 degrees and steel below 75. It makes corrosion protection issues much simpler or me. I also wanted to pass on a belated big thank you! for your tips on Campagnolo Ergopower lever reassembly.

Using a screwdriver to manipulate and retain the coil spring bushing, on reassembly, makes the job a lot easier. Have a virtual cold one on me. If you ever revise your instructions, you may want to add that using a Bondhus ball end 3mm Allen should be avoided.

NASA should use Campagnolo’s blue thread locking compound on the space shuttle tiles. It is tenacious stuff. During a Record right lever disassembly, I snapped the end off of my Park 3mm and could not extract the ball from the hex recess in the bolt. I had to use channel locks to get the bolt out. A 4mX20 Phillips pan head bolt from the local hardware store worked pretty well on reassembly.
Tony

More on carbon seatposts (and forks) for big riders.

Dear Lennard,
I recently read with interest your comments to Adam about carbon seatposts for larger guys.\

At 6 foot 1 and 220 pounds,I have similar problems. For the last year, I have been running a 27.0 diameter, 400mm long Titec carbon fiber post on one of my mountain bikes (an 18-inch steel hardtail) with significant extension, but well within the marked limits, without issue. In fact, the post acts similar to a leaf spring, softening the hardtail’s ride somewhat.

I had been using an older Control Tech aluminum post, the one with the”spine” of aluminum running down the middle of the post to stiffen it. The difference in ride quality is quite noticeable. Since carbon
fiber has a very high fatigue life (exceeding that of steel or eventitanium, when manufactured properly), the flex I’m getting doesn’t worryme in the least.

As a materials engineer (I work in plastics, primarily reinforced with fiberglass and carbon fiber), I can tell you that carbon fiber products can be made to behave almost any way you want – with certain limitations,of course. An ultra light carbon post will tend to be flexy and will have a lower tensile strength (i.e. more likely to break); a heavier, strongerpost will flex less and put up with more abuse.

Also, the fibers can be aligned such that the post may be flexible in one direction, and stiff in another. The Titec post I use is one of the heaviest models they made at that time, and has a reinforced clamping region; I bought it not for weight savings, but for the ride quality it would provide.

Also, carbon fiber products are extremely sensitive to the manufacturingprocess – slight differences in temperature and/or pressure during formingcan result in huge differences in product quality. Companies with extensive experience with carbon fiber (Easton, Titec, Race Face are examples that come to mind, but there are others) are usually the best way to go, as they have mature manufacturing processes and good quality control programs.

I can tell you though, that carbon posts are very sensitive to beingclamped incorrectly; carbon fibers lose all of their strength when fractured. Most of the carbon fiber post and bar failures that I’ve seen are the resultof exactly this problem. So long as he installs it correctly (thekey is to use a post clamp which doesn’t ovalize when tightened), stickswith a proven manufacturer, and doesn’t go for an ultra light model ofpost, I see no reason why someone Adam’s size couldn’t safely use a carbonpost on a mountain bike. But, if he’s looking strictly to save weight,then you’re probably right – a carbon post is going to be the wrong route to take. But I’ve also learned in over 10 years of mountain biking that for big guys, going light is usually the wrong answer in any material; I’ve also seen lightweight aluminum posts fracture catastrophically from excess fatigue.
—Phil

Dear Phil,
My concern was more with the scoring and tearing of the fibers from twisting and tightening the post into the frame than with the actual strength of the carbon.
Lennard

Dear Lennard,
I read today on the VeloNews site your warning about the large rider who wanted to use a carbon post.I weight 190 pounds and stand 6 foot 1 with a 36-inch inseam. I havea 410mm Alpha Q carbon post on my MTB, which gets used primarily for commutingin foul (rain & snow) weather. About 300mm of the post is out of theframe (well below the max height), and I went ahead and glued (with Elmer’swater-proof carpenter’s glue) a 7/8-inch hard wood dowel inside the post.

The 7/8-inch dowel just happens to be a perfect fit for the Alpha Q post. I don’t think the wood inside the carbon post makes it too stiff and, it adds piece of mind. For years I have used wooden plugs at the ends of aluminum MTB bars to prevent crimping from bar ends. I just switched to an Easton carbon MTB bar that is compatible with bar ends, and again used wooded plugs (a 1/2-inch dowel milled down slightly to fit). Here, too, I used waterproof carpenter’s glue, as it holds well, but can be loosened if need be.
Theodore

Hi Lennard,
It was good seeing you at VeloSwap in San Francisco. I read your article concerning the advice you gave about a carbon seat post. Does the same apply to carbon forks?

I’ve owned several aluminum frames with aluminum forks and tend to replace them after 3-4 years due to concerns about part failure without warning. I’ve always wanted to try a carbon fork with an aluminum steerer tube but know of several people that have had failures around here.

This is not friend-of-a-friend story; I know the people this happened to directly and have seen the parts after failure, not pretty.I don’t want to try the carbon-carbon forks because carbon is so notch sensitive and I don’t want to worry about the forks while I ride. I’m 6-4 and my weight fluctuates between 230 and 280 depending how much time I have to get to the gym and get on the bike.

I split riding over four bikes an aluminum cyclocross bike, an aluminum road bike, a steel road bike and a hardtail aluminum mountain bike. Lately I’ve been able to average 200 miles/week. I ride on tires no smaller than 25c on 36 hole rims.So, what do you recommend? Stay away from carbon? Stay away for aluminum forks too? Ride steel forks only?

I can actually get up all the big climbs around here so I don’t want a bike that’s too heavy, but I’ll never ride the freak-of-the-week light stuff.

Thanks for your reply. I see on your Website that you use an insert on the forks that you sell. In addition the carbon it thicker in the steerer is 25 percent thicker. Wouldn’t thissuggest that you believe that there is something that needs to be addressedin this area?
Adrian

Dear Adrian,
I certainly do think something should be addressed in this area. Justlike with steel or aluminum or titanium, you have to make the tubes thickeror bigger or both for a bigger person (or you must at least use a strongerand/or stiffer metal alloy or carbon material).

In answer to your original question, I think carbon forks are fine for big people in general. My problem with carbon seatposts is the clamping at the seat lug crushing and cutting fibers, which make it way weaker than it was designed to be. Carbon forks from major brand names are generallyvery strong, well tested, and are quite reliable.

That is not to say thatsuperlight forks will be stiff enough and perhaps even strong enough fora heavy rider. The fact that I sell forks for tall riders with thickersteering tubes (and worked with True Temper specifically to develop it)does not mean that I recommend against carbon forks for big riders, justthat, like with any material, the carbon needs to be beefed up for thebigger rider.
Lennard

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.