Wednesday, December 19, 2012

Q&A: Sizing old Treks, hoops for clydesdales, carbon frame paint chips and more

Hello fellow pedal pushers, In case you're tinkering with your 2-wheelers over the holidays maybe this selection of my recent technical questions and answers will be of interest. Most have a retro theme this time around, but that's in keeping with my Herse and Masi projects; and I always enjoy helping riders keep their classics going.
Vintage-Trek has a wealth of info and classic pics like this

Q: I'm currently riding a 2012 Trek Madone road bike, size 52cm, Jim. I've been thinking about buying a vintage Trek on ebay. My ? is, would a size 52cm from the 80's or 90's be the same as a size 52 now? 

I ask this because the top tube slopes down on my 2012 Trek and I have noticed that they seem to be straight on the older bikes. I would hate to order a 52 and have it too big for me. 


A: I’m glad you asked before you bought something Mitchell, because, yes, the sizing is different. You need to compare the overall geometry chart of the vintage bikes to the geometry chart of your modern “compact frame” (which is what modern bikes with sloping top tubes are called).

The key dimension to look at is the center-to-center length of the top tube. This should be measured on a line parallel to the ground and from the center of the seat tube to the center of the head tube. 

Geometry charts on compact frame bicycles usually have an asterisk and words to the effect “relative" top-tube length, meaning they measured along an imaginary horizontal top tube, not along the sloping top tube that would give the wrong length (longer than actual)
Click to zoom

In most cases, if you find a frame that has the same top-tube length as yours, the frame size should be pretty close to a good fit. Ideally, you would also find someone with that frame size on their vintage Trek and see if you fit it okay.

To find those classic Trek bike models and geometry charts, check the Vintage Trek Bikes website.

Have fun finding and fixing up that Trek from the past! 

DT spokes can take it
Q: Hello Jim... enjoy your website and your column at RoadBikeRider. I weigh 260 pounds and ride a Bridgestone RBT purchased in the early 90's for fitness and day rides. This year I have had to replace spokes and have the rear wheel trued on a regular basis. 

I am planning on replacing the rear wheel and I'm looking for advice on affordable and durable replacement wheels. Any advice you can provide is much appreciated. Hope to get on a trouble-free wheel soon!

A: Thanks for the email and kind words, Frank. Yours is a common question, and the answer is pretty straight forward. What I recommend is finding a good old fashioned wheelbuilder, someone who's been doing it for awhile and stands behind their work with a guarantee - and who takes pride in their wheels, too. 

This wheelsmith will talk to you and find out where and how you ride and look at the wheel that's been failing. Then they'll design a replacement wheel that will hold up. 

If I was building the wheel for you, I'd choose a quality hub made by Shimano (no need for anything more expensive or complicated), DT Swiss stainless-steel spokes 14-gauge straight (not double-butted), and a nice rim, probably from Mavic or DT Swiss, though builders usually have their favorite brand since they are the ones standing behind their wheels. 

I would go with 36 spokes, crossed 3 times or even 4 times. A wheel like this is very strong, reliable and long-lasting. DT Swiss spokes (photo) are very tough and rarely break and a quality rim will provide the strength at the road. You may have to call a few shops to find the wheelbuilder. [Update-After this email exchange Frank let me know that he was having his wheel built at Earl's Cyclery and Fitness, a Vermont bike shop I'm familiar with, so he's in good hands.]

Wheelbuilding seems a bit of a dying art with so many companies selling ready-made wheels. But, a hand-built one will serve you much better and should roll for years with little to even no maintenance on the wheel other than keeping the bearings greased. The spokes should remain in tension and the wheel should remain true side-to-side and round, too. I have actually seen hand-built wheels by Spence Wolfe and dated 1958, that were still round, true and ready for many more miles.

Since I often receive feedback on this issue, I should explain, that for heavier riders and harder use, like touring with heavily loaded bags carried over the wheels, I recommend straight-gauge spokes instead of double-butted. The argument for DB spokes is that they stretch more than straight-gauge versions and this helps the wheel remain tightly tensioned.

The argument for straight-gauge spokes is that they contain more material so they are less stressed and less likely to fail/break. In my experience, that's been true, so to build the strongest wheels for demanding riders and bikes, I go with straight-gauge (it's easy to tension them sufficiently, too).

I hope this helps you get on a quality set of wheels, Frank. Let me know if you have any questions, 
Jon's gorgeous 1989 Klein Quantum!

Q: Hello, Jim,
I found your website searching on changing bicycle tires but I have a question about freewheels - specifically about a Sachs Aris freewheel. 

I went to switch out my SunTour Winner Pro 7-speed freewheel today for a lightly used Sachs Aris LY93 freewheel that I purchased from a seller on eBay. When I reinstalled the wheel with the Sachs Aris mounted I noticed it was too wide and was binding - the chain was being pinched between the outermost cog and frame.

I took the freewheel off and compared the two: both are 7-speed with the Sachs Aris being very slightly wider (in depth) than the Winner Pro. The main difference I see is that the outermost cog on the Winner has a lip that allows for chain clearance while the Aris does not. 

For reference, my bike has 126mm rear dropout spacing. I wrote to the seller and he said that all 7-speed freewheels are designed for a 126mm dropout spacing and that often mechanics would add a 1mm or 2mm spacer to allow for the chain clearance on Sachs freewheels. 

While this may be true, it seems odd to me in part because I have an aluminum frame (1989 Klein Quantum-see pic) and I don't want to tweak it. By adding a spacer the Sachs freewheel will definitely be wider than the SunTour. 

Have you encountered this before, Jim? The Aris is nice looking and nicely made but I didn't think to ask whether some freewheels are designed for 126mm spacing and some for 130mm. Or - if there is a Japanese versus French manufacturing tolerance where the SunTour Winner Pros are slightly less in width. If of help I believe the Sachs I have was manufactured in 1994 - which may be around the time that the bike industry switched to 130mm dropout spacing. Any thoughts on this would be most appreciated!

A:  Yes, Jon, what the eBayer told you is essentially true, in that, if you switch freewheel brands, you can end up with different spacing, and then you have to fix it by adding a spacer beneath the locknut on the axle to get the clearance you need. It's usually a 1mm washer/spacer and 1mm isn't enough to harm your frame. 

It can make the rear wheel slightly harder to get in/out of the frame, but that really depends on the spacing of the rear dropouts. Often there's a little extra clearance. Frames aren't always exactly 126 or 127. Sometimes they're wider and they close when you tighten the wheel. If yours is exactly 126, it's likely that if you add the washer you'll still be able to get the wheel in and out easily. (It it's less than 126, that'll make it harder to get the wheel in/out.)

SunTour actually used compact spacing to fit 7 cogs in 6-speed spacing. Sachs just went with 7-speed spacing. That’s why the Sachs is a tad wider. At the time, the SunTour spacing was considered “advanced” technology. It let you go to a 7-speed cassette on a 6-speed wheel.

On your frame, having the extra 1mm in there won't cause any serious stress. If it bothers you or you don't want to change the spacing of the wheel, you should probably sell that Sachs freewheel on eBay and look for one like you had before so you can use the same spacing. 

A bigger issue than the spacing is the rear wheel dishing. When you install the axle spacer, it pushes the rim to the left (the rear rim is centered over the axle, not over the hub due to the space on the hub that the freewheel takes up). So the wheel won't be centered perfectly until you redish it. This requires loosening the left side spokes and tightening the right side spokes. 

So, this is a truing/tensioning exercise that requires a little skill and also the wheel, spoke and nipples have to be in good shape or else you won't be able to redish the wheel. Overall, the easiest thing would probably be finding that Winner freewheel.


It takes skill to touch-up chips nicely
Q: Check out this photo of my carbon frame, Jim. I'm wondering how to repair the chips on the paint? Would using nail polish help? Do I need to sand it down? I read that some people use epoxy. How should I go about doing this repair?


A:  Carbon is super tough stuff, Daniel, so you don’t even need to do anything if you don’t want to. It’s just paint chipping off. It has nothing to do with the frame’s strength or ride. If all the paint chipped off, it wouldn’t matter. That’s another way to think of it. 

If you had a steel frame you would have to worry about rust and you would want to paint it and get any rust off first. But, with carbon, paint is just a decoration. It adds no strength/structure, just fashion, really. Well it does add another layer on top of the carbon but not a very tough one as you can tell from the chipping. 

But, if the chips bother you in terms of how they look (and they would me, too), then you will want to find some paint in the same color and touch them up. Touching up paint is an art and it’s not easy to do it and have it come out invisible and looking perfect. Most of the time it looks like you touched up the paint, but if you get a good color match it will at least be the same color and that usually makes the bike look a little nicer. 

Typically, to touch up paint chips on any frame – even carbon – you would sand and clean the chipped area. The sanding knocks down the edges to help prevent further chipping along those edges and to help transition the new paint into the old. Use a very fine sandpaper or cloth, like 600 grit you can work with wet.

With carbon you don’t want to harm the carbon so you would sand lightly and carefully, trying to smooth the paint, not the carbon. Once the edges around the chip are smooth, clean the area with isopropyl ("rubbing") alcohol, which will remove any dirt, oil, grease, dust and dry quickly.

Nail polish is actually a good thing to use for touch-up paint since it comes in so many colors. You can usually find a good match and the containers often have the brush in the top and seal nicely so there’s no cleaning to worry about. You’ll want to test the paint in a hidden area on the frame to see how it looks and to ensure it’s compatible with the paint you have now.

Clear nail polish works to fix chips on carbon frames that are painted with a clear coat, but that's not your frame. But, if your frame has a clear coat over the frame, you may want to add clear over your yellow touch-ups. That will help seal it and add the high gloss finish the clear coat put on the rest of your frame.

If you were okay with the expense, another approach would be to have the frame repainted so that it was 100% perfect-looking. But even that paint would have a chance of chipping so it might not look perfect for a long enough time to make the cost worth it to you. I would give touching it up a try first and see how you like it,


PS: My friend Robert Studdiford at TwoFish painted an entire frame with nail polish, one little dot at a time, hour after hour, day after day - it became an obsession, until he ended up with his Revlon Dream:

Robert's remarkable Revlon Dream paint job

Until next time, 


Nerd From Space said...

Your bias against double butted spokes for heavier riders is misinformed. Butting of stressed members (spokes, frame tubes, etc.) while contributing to a nominal weight reduction, greatly increases the life span and durability of the wheel system in particular. The increased resiliancy (as opposed to mere flexibilty) of the double butted spoke translates into a much more compliant and strong structure.
You are correct in suggesting that more material equals more strength, overall, yet the more favourable recommendation might have been for something along the lines of DT Swiss' Alpine III model triple-butted spoke: they pack an extra 0.3 mm of material at the head end ( where the vast majority of spoke breakage occur), swaging down to 2.0 mm, then 1.8, and finally 2.0 mm at the thread. I have built wheels using these spokes, delivering performance far beyond any straight gauge option (and they still weigh less than a corresponding straight gauge version!).

Jim Langley said...

Thanks for commenting so that I can address a reply to someone named "Nerd from Space." Ha, ha. I appreciate you writing but my recommending straight gauge spokes is not "misinformed" - it's based on longtime hands-on wheelbuilding and wheel repair experience, which tells me (and other wheelbuilders) that there are times straight spokes are better than double butted ones. And, as a longtime wheelbuilder who has studied it, of course I know the interesting details you wrote about double butted spokes. But, none of that helps when they break out in the middle of nowhere and the guy on the straight ones is still riding happily over the horizon. If you build enough wheels with both types of spokes, you'll see, as I have that the straights are less likely to break than the butted ones. And, as a wheelbuilder your reputation rests on riders not breaking spokes. I do appreciate you writing and sharing your opinion, though. Thank you, Jim