I am converting my road bike (Cannondale R500 Caad2) into a tour bike for some summer touring around Lake Erie (first tour). The old tires were flimsy slicks, and had proven less than able to take on even suburban roads given how broken and potholed my neighborhood is (not to mention a few old brick roads that make for interesting rides), though they were great for paved trails.

After some research, I found the Schwalbe Marathon Plus tires pretty recommended. I bought a couple of 700x28s, and after wrestling to get them on, I found out that the additional thickness and height caused the tire to rub against my frame (note: not the brake assembly, but the frame's mount for the brake assembly, which has a little bulb for the nut that sticks out just enough to catch the tire). I had accounted for the additional width (they are fine horizontally), but the lack of vertical clearance is the problem.

Some trial and error showed that if I mounted the wheel a millimeter or two shallow in the vertical dropout, the rubbing problem was solved with a little extra clearance. (Note: I have quick-release wheels) I have yet to take it for a test-ride, and in any case figure that this situation is not as secure as I could make it. Do you agree that it is necessary to somehow put something in the dropout like some rubber or metal to buffer and give stability to the situation? Is this an immediate problem, or can I get a few test rides in first? And any suggestions on what would work well for an insert?

(And, unless this is really a dangerous option, I would prefer to do this small modification rather than getting new tires or sanding down the frame's bulb.)

Thank you for your help.

Wouldn't want to be changing the postion of the wheels in the dropouts if there is no way of fixing them in that position.

Concerns would be getting the wheel in straight with no guide after changing tubes, and the brake position.

Looking at the R500, can't see any rack mounts on the rear stays, so are you carrying much?

if light weight touring, 25mm tires will be sufficent, and fit your frame, the Marathon Plus, although good, are heavy.

Would be worth asking this in the touring forum

The old style enclosed-cam quick releases should be able to hold it in place, but if you have modern open-cam quick releases you may have problems.

With vertical dropouts, get smaller tires. I just don't see anything you do as a spacer being reliable.

If I was set on the larger tires, I would file where the tires were hitting. But you need to decide if you can get enough clearance without compromising the brake hanger.

I'm guessing your frame is ally.

Why don't you post a pic of the brake bridge? It prolly has plenty of spare meat on it.

Remember, rear brakes don't get a whole lot of load on them before the wheel locks up... I bet it'd be fine to take a file to the brake bridge.

Here's what I've done for years to improve clearance on track forks. The same method can easily be applied to a vertical rear dropout.

Fill the top of the dropout with 1-3mm of filler, carefully contoured to match the curvature of the axle, like the dropout was before modification. Note it's absolutely critical that the thickness is matched fairly precisely, so that the stays vertical and square.

I use steel filler to handle the load so the filler doesn't wear. For example to gain 2mm, you can cut and curve small pieces of 2mm spoke to match the dropout, then build around that with body filler.

My personal bike with a fork modified this way has been on the road for 40 years and there's no noticeable change in any respect.

Sounds like a pretty solid kludge ; )

It'll tighten the head angle a fraction of a degree, BTW

Fraction is right. 2mm is less than the difference created when using larger section tires in back vs front.

Thank you all for your prompt replies, here is a bit of a follow up to your questions/comments (feel free to keep them coming):

I do have a rear rack with a couple of baskets; this will be a light tour but I am hoping to build up to more intense ones (with more gear) in the future. I am not worried so much about getting the wheel straight after changing the tires, since these tires were chosen just to prevent as many flat tires as possible. (Famous last words, but then, I do not believe in jinxes either.) I can reset the brakes down a millimeter or two to make sure they work fine with the new position.

I have the enclosed-cam quick releases, so it is good to know that those ought to be able to handle the load. It seemed almost too obvious and simple to work, but I tend to trust such solutions unless told otherwise. I shall test them out without other modification before trying any more permanent fixes.

Beyond that, my first step will probably be to try filing down the infringing bridge; it definitely does seem to have plenty of "spare meat".

FBinNY, that is some great advice, and I probably will end up doing just that in the coming weeks. And great to know that it works well in the long term!

I also did ask the seller if they would exchange these for 25s with a minimum of hassle, just to round out the options. But like I said at the beginning, I am hoping this will be the first of many tours, and 28s seem to be the skinniest that most of those over at the touring forum would hazard to recommend, especially since not all of my trips are going to be as road-bound as this first one.

Thanks again for your very quick and helpful responses, and if there is anything to be added, do not hesitate. It feels great to be a part of a strong, supportive community.

If you haven't bought this bike yet, why not look for a more suitable touring bike which can take larger tires, carry a load better, and will have a better geometry for touring.

A touring bike will have more relaxed angles, and also less chance of heel strike on the rear with panniers or toe overlap on the front. no point in trying to get a bike to do something it wasn't designed to to, get one designed for the purpose in the beginning.

For the frame having plenty of "spare meat", its aluminum, most of that will be needed.

Get a bike made for them.

That's pretty much the best approach. You are trying to turn a sports car into a station wagon and it won't work well.

FBinNY's technique for obtaining more clearance will work with track dropouts since they have a lot of slot length to allow chain chain tension adjustment so giving up a little is no big deal. Most vertical dropouts are just deep enough to enclose the axle and shimming them on top can leave part of it unsupported. Not a good thing to have.

Most dropouts have enough slot depth in comparison to the locknut face diameter to allow 2mm shimming with zero overhang at the bottom. It's certainly something to check, but as long as any overhang is marginal or less, and the front of the axle at 3 o'clock is square to a vertical surface so that the chain cannot pull it forward, gravity will work with you to keep everything in place.

Yes, getting the appropriate bike for any type of riding always makes sense and is usually better than having to modify. But it isn't always practical. If starting fresh, buying right is the only smart way to go, but if one already has a bike, and doesn't wish to shell out for another, sometimes a bit of creative DIY allows expanded utility. If "go buy new" was always the advice we wouldn't need a forum, there's thousands of shops willing to give that advice, and be first in line to fulfill the need.

OK, I just wanted to be sure the OP doesn't shim the dropout depth too much in the interest of getting inappropriate tires for the frame to fit. I agree with the posters that recommended dropping back to 700x25 tires to avoid the problem.

Sure, getting a new bike isn't always practical, financially or otherwise, but it's the best way if you can do it. Maybe even "buy used" is better advice.

I was making the point that you can't always make a given bike into something it was not designed to be and it will always be a compromise. Some compromises are acceptable and others are dangerous.

If it's anything like mine, there's a fair bit of overkill going on.

I could easily lose the bulge underneath.



Mind you, given it's for a touring application, it could experience a fair bit of load... but I guess the biggest factor is the rider's weight.

Hey John - what do you weigh? How much gear do plan on loading the bike with?

Can you post a pic of your brake bridge?

There's more than one way to skin a cat.

If it were my bike and the bridge looked like that, and the area surrounding the bolt was solid, and I only needed 2 millimeters, I'd pull out my Nicholson bastards and make them earn their keep. 2 minutes later later I'd remount the brake throw in the wheel and be on my way.

Whether the OPs bridge has enough meat to spare is a judgment call, but if it has this kind of bulge in the middle it probably does.

I thought the OP implied such a case, with the option of sanding (sic - a file is called for) it mooted... it'd certainly be the most straightforward way to sort it.

...Fix the problem by removing metal ; )

I do see one potential problem with having a very close clearance between the brake bridge and tire tread and that the possibility of mud buildup locking the rear wheel.

All of my road bikes, even with short reach brakes and 700x23 tires, still have 6-8 mm of clearance between the brake bridge and the rear tire so there is some room for crud buildup without binding the wheel and it's got to be so bad you notice it well in advance before it becomes a problem.

If the OP has a very small gap, it could easily be bridged by mud or a small twig and bring proceedings to a sudden halt.

I can assure you that this won't be an issue. My track bike has zero clearance between the bottom of the front brake arch and tire. It's so small that the bottom of the arch can double as a tire saver. Mud can't build up and nothing has ever gotten caught. Every once in a while the tire will pick up a small stone which I hear get ejected with a sharp ping.

If you've ever driven a car in mud or snow and slush, the wheel wells get filled up to where you'd expect issues, but the moving tire always keeps a working gap clear. On bumps the wheel moves up carves out more clearance as needed.

BTW- I've seen some ultra-short wheelbase bikes with zero rear wheel/seat tube clearance and haven't ever heard of issues.

The only barrier to filing the bottom of the bridge for a few millimeters is the risk of weakening it's structure, and that depends on how much material it can spare and how much the OP takes away.

The thing is, you have a track bike, and the OP is trying to make a tourer out of a road bike, 2 totally different bikes, a tourer is much more likly to encounter debris, leaves and mud, especially not using roads, i.e MUP's / cycle lanes; track bikes are designed for ..... a track/velodrome, where there should be no chance of encountering debris or mud.

I should have made it clear. This was a track bike to which I added a front brake some 40+ years ago and which I rode for years as a city, weekend tourer, light utility, bopper, all conditions bike. It's set up with a 2 speed fixed bike, and goes everywhere, including where SUV's drive at less than 5mph. I only stopped riding it fairly recently when fixed gear became trendy, making it lose it's cool for me.

Mud can't build up by it's very nature, as the tire will continually maintain clearance, the type of small stone a tire may pick up will either bounce back or is small enough force through squeezing the tire down. For any type of lock up to occur he'd have to have a tire with a deep lugged tread like an aggressive mtb tire, which could trap a piece of gravel and jam it into the gap.

Seriously, wheel lockup of the type described here is of zero concern.

Well, I've had it happen once but it was under extraordinary circumstances and it didn't produce a sudden stop.

I was on a tour with three other riders and we started up a hill that had "Men Working" signs and a flag man at the bottom. We asked if the road was passable and he it was being resurfaced but we should be ok and he let us go on.

At first we were on a delightful glass-smooth brand new surface but as we climbed the hill the surface got hotter and stickier as we went. As we caught sight of the paving crew, we noticed our tires getting bigger and bigger and harder to pedal until a few feet later they wouldn't turn at all. The hot asphalt had built up until it began to rub on the fork crown and brake bridge and we were stopped dead. It took about a half hour with pocket knives, multi-tools and whatever we could find to scrape off the accumulation and be able to ride again. We road the rest of the way up the hill on the grass beside the new pavement.