How To Add More Tire Clearance To Your Road Bike — DYI

For the past many years I have been using the Continental 4000S II tire in 25mm width on all my road bikes. After a tough 1000K this past summer, I wanted to try out some 28s and see if the ride was better. During the winter of 2017–18 I started experimenting with 28mm 4000S tires on my Trek Domane. Although they fit, the tolerances were very tight. I also wanted to use the set of full-length Bontrager fenders with these tires. For the rear tire, I have plenty of space behind my bottom bracket, near the chain stays, but oddly enough, the room below the brake bridge was tight. It left little room to spare (yet my stock Ultegra brake had plenty of adjustability). I inquired into having a custom frame builder move the bridge up a few millimeters, but the cost was $800 — way too much.

I came up the idea of taking either a small piece of wood or plastic and epoxying it inside the drop-outs. In my business I have lots of 1.5mm (.062″) HDPE scraps, so I took a piece of plastic, about 5 x10mm and bent it gently and glued it in place, making a shim of sorts. I also filed it down so the edges so they were smoother. I have done this on two of my road bikes, my Trek Domane to accommodate 28mm tires and also my Cervelo P3C TT bike (on the front fork only) so I can get 25mm tires on that frame. Because the skewers are pushed down a little more, I am most careful about tightening a lot now. (On the Domane I have to crank them down a ton anyway, otherwise it creaks!) On the Cervelo fork, I filed down the lawyer-tabs so they were smoother, as the fit was too funky without doing that.

With the 700c x 28mm 4000S tires I am getting width measurements of between 29 and 30.5mm on an 18mm I.D. alloy rim.

I have only had these in place for a few months now, but so far, it is working. Time will tell, but, it is better than investing $5,500 on a new carbon-fiber Domane with disc brakes!

Brake bridge with 28mm tire before adding shim. Conti 4000S’s measure 29 to 30mm wide on this 18mm I.D. rim (the pressure causes small variations).
Shim added to rear drop-out.
Brake bridge clearance after shim.
Shims added to front fork.

Author: Rando Richard

I’m an old guy (age 69 in 2023) who enjoys aerobic, endurance sports. I call myself a cardio-junkie. Perhaps the more appropriate term would be “ultra” endurance sports. Since I was a teenager I have always enjoyed “slow twitch” outdoor sports like backpacking, ice climbing, running, mountaineering, hiking, alpine skiing and randonnée skiing (alpine touring, backcountry skiing or skimo). In 2005 I starting running with more regularity — except this time it was not for the intent of getting ready for a mountaineering trip, but as an end to itself. From 2005 to 2007 I managed to eek out two seasons of ultramarathons — that is competitive trail runs up to 50 or 100 miles. Due to a nagging ankle injury from the 80s (an accident while ice climbing in the 1980s where my lower tib and fib were badly broken), I had to cease that grueling, but rewarding activity. I then migrated into ultra distance road cycling or randonneuring. The rides are called brevets (pronounced bruh-VAY, it’s French) and are minimally supported — they are similar to ultrarunning and backpacking where one must be self reliant. Although brevets are non-competitive, they do have have cut off times to qualify as a finisher. They are usually are done in groups, which can have a competitive slant to them. Today, I continue to participate in long distance cycling including some ultra-racing, randonnée skiing (a blend of cross country and downhill disciplines) and still get out on an occasional mountaineering trip. Since 1996 I have been designing, manufacturing and selling camera bags. That is Kinesis Photo Gear (kgear.com). In 2005 I started selling cycling bags under the Kinesis label and eventually expanded it to including other sports like SUP (stand-up paddle boarding and some skimo). Consequently, it become eoGEAR — the “eo” stands for endurance outdoor. My wife and I are empty-nesters now and we live and work out in the boondocks of central Utah, half way between Salt Lake City (great powder) and Moab (great red rocks). Well, I guess that is all for now. Safe travels mate! Perhaps I’ll see you on the road or trail. — Richard Stum

2 thoughts on “How To Add More Tire Clearance To Your Road Bike — DYI”

    1. Interesting suggestion. Thanks. This device adds about 10mm which is way more than I need. I believe it is designed for horizontal drop out, not conventional vertical ones.

      One of the problems I had with this technique was that the clearance between the derailleur pulley and the cassette became tighter and rubbing (only because I am using a medium long cages road derailleur and a 36-tooth cassette).

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