Dropout Length Question / Fixed Gear TT frame?

[BudhaSlug]

I’m wondering if anyone can tell me approximately how much dropout adjustability they have on their TT/Tri frame, as I’m contemplating getting a Tri/TT frame and setting it up as a fixed gear, using the dropout adjustability to achieve proper chain tension.

I’ve been having the hankering for a new aero fixed gear bike for long solo rides and was thinking of building up something like one of these:

as a fixed gear. The plan would be to get some carbon clinchers (probably 50-60mm front, 80-90mm rear) built up around a track hub with a longer axle and some spacers, a 165mm crank and at least a front brake. My riding is in mostly flat-rolling hills, and I’m an experienced fixed rider (see below). The other alternative is to get a nicer aero track frame (Cervelo T4 ideally) with a drilled road fork and set it up with a similar build.

I’m wondering what people’s thoughts are on this, especially if anyone has experience with something similar (TT/Tri bike set up fixed). I know I won’t have nearly the range of adjustability on the gearing with the short dropouts of the TT/Tri frame, but I’m hoping it will be enough to make the gearing work without an eccentric Bottom Bracket.

Any tips, thoughts, advice would be greatly appreciated.

Now for a bit of background on me and the project. I’ve been riding fixed for about 15 years now. Currently my main fixed bike is an Independent Fabrications steel Planet Cross that was designed to be Single Speed only. A few years back, after I had settled on cow horn bars as I was always riding it on the road, I added a set of clip on aerobars to it and have used it primarily for long solo rides as an alternative to my geared road bike. The bike is anything but aerodynamic, and the dimensions are all wrong for me for an effective aero position. I also converted my old 1993-ish Trek 2200 (aluminum lugs/stays/fork, carbon main tubes) to a fixed gear for commuting purposes about 10 years ago. I think the commuter has reached the end of it’s life, thus the reason for the plans above. The IF will be “retired” to my commuting bike, which means it will actually get more use than it has now, and I might even take it out for a bit of actual cross riding as well.

[jackmott]

When you do that with typical TT bike dropouts, like the one pictured in your images, it is quite a hassle. Like only certain gear combinations will work, because otherwise you can’t get proper tension.

so, if you do this find a TT frame with the longest dropouts you can. Or even better, why not buy a proper fixed gear bike to begin with?

[Former_User]

The “Fix Me Up” calculator is valuable for determining if you will have enough adjustment range:

http://eehouse.org/fixin/fixmeup.php

I used that to set up an old MTB frameset with semi-vertical dropouts as a single-speed commuter
.

[damon_rinard]

Hi BudhaSlug,

It also depends on the state of wear of the chain you’re using. I tried a single speed Kestrel 200EMS using 52 x 16 in vertical dropouts. Didn’t quite work with a new chain, but worked perfectly with a worn (but still good) one.

Cheers,

[Deej]

I used this on my 2001 P2K, machined slightly to fit because of the short dropouts (I think 1"). Works fine.
http://www.lfgss.com/thread53594.html

[BudhaSlug]

Yeah, I’ve had that same problem with the Trek 2200. I filed the dropouts a bit to fit the original setup, which involved a used chain, and when the chain finally wore enough to need replacing, I found that I had to file the dropouts a second time to achieve enough slack to make it fit. I’m guessing that as long as I pick a close to perfect gear, the horizontal dropouts should provide enough space to make everything fit no matter how much chain wear there is.

Anyone with any measurements of how much space/adjustability I’m likely to actually have in the dropouts? That will make the calculations a lot easier.

[Czechyourself]

Would an eccentric hub work in this case? If I understand the concept correctly, you would be able to convert a frame with vertical dropouts to a fixed gear without the slack issues etc…

[BudhaSlug]

An eccentric hub would be a possibility, as would one of the new eccentric bottom brackets that you can fit in a BB30 or similar shell and use with a BSA BB. The disadvantage of the former is that there are not many of these (I only know of the White Industries ENO), and so I would have a tricky time getting the hub and rim to match in drillings and I was actually hoping to buy a complete wheel rather than build this one up myself as I’ve never worked with such a deep wheel much less carbon rims. The eccentric BB also seems a bit bulky and prone to loosening/creaking if my tandems are any indication… and those are frames that are built for an eccentric rather than adding one after the fact.

But these do give me some backup option if I find I need more adjustability beyond the range I can get in the horizontal dropout/track end of the Tri/TT frame.

[BosMudPhud]

I’m wondering what people’s thoughts are on this, especially if anyone has experience with something similar (TT/Tri bike set up fixed). I know I won’t have nearly the range of adjustability on the gearing with the short dropouts of the TT/Tri frame, but I’m hoping it will be enough to make the gearing work without an eccentric Bottom Bracket.

I did this with a Lynskey titanium tri- frame. It turned out great; it’s a super fun bike to ride. But it did take some doing; TT dropouts tend to be a good bit smaller than real track fork ends. I was able to use the FixMeUp calculator, but keep in mind there are few things that can mess you up. I have about 1 mm of rear wheel clearance, so it wound up being close.

(1) Tires. Many dropouts are cut deep enough to allow you to slam some tires all the way into the seat tube. So check the actual usable depth of your dropouts with the wheel and tire you’ll use. (If you’re heavy, you may also want to actually sit on the bike to make sure rear-triangle flex won’t be a problem.)

(2) Chainline. Depending on what you do with the bottom bracket, you may wind up without a perfectly straight chainline, which will make things tighter than you expect.

(3) I haven’t found chain-wear / stretch to be a significant factor (over 2 years of daily riding), but your mileage may vary.

(4) I put a Shimano free-hub on the opposite side of the hub thinking I’d use it if I was on a long ride and got tired, and no matter what I do to try to protect it it accumulates rust. I’d ditch it unless you’re sure you’d use it. Most freehubs are 16T, but your fixed cog will likely be smaller, so it’s a pain to arrange things so that the freehub is actually easier to pedal, but the chain still fits, and you don’t have slack in the fixed gear.

(5) Keep in mind that with super-small rear wheel clearances (sub-mm) then grit you pick up off the road can sand down your seat tube. (All tire clearance problems get fixed eventually!)

(6) If I were doing it again, in practice I’d get a few chainrings, a few cogs, and a half-link and just try a few things.

Good luck!

-Mud

[Sweeney]

Don’t forget about half links to make you single speed chain just right:

http://www.pricepoint.com/Brand/KMC/KMC-Single-Speed-Half-Link.axd

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[BudhaSlug]

Thanks for the tips and feedback. I’m starting to think more seriously about getting a White Industries ENO eccentric, which apparently does come in 130mm/28h and would give me both better chainline and more adjustability and just lacing it up myself (I’ve built a number of wheels before, but all with alloy rims, nothing deeper than 30mm). Other than being a bit nervous about working with a deep carbon rim, and the added couple hundred bucks of the parts over a fully built chinese wheel, I think it might turn out better in the end.

I’ll be setting it up fixed/fixed most likely. I’ve never once used my backup freewheel either, but have on rare occasion (windy out-and-back days) benefited from flipping to an easier/harder gear halfway through a ride. Tires will be 23C, and I’m only about 140lbs, so my weight on the bike doesn’t impact wheel fitting much at all.