buffalowings

Hey guys, I bought a Diamondback RCX at a bargain price I could not refuse. It is equipped with stock Tektro CR710 brakes, 32c kenda small block 8's. One issue I have is that I can't remove the rear wheel without deflating the tire, because the seatstays prevent the brakes from opening all the way. I'm planning on racing cyclocross with the bike when the season comes around (eventually) I guess I have several questions: Was someone sleeping when welding the tubes together? Is this a defect/flaw inherent in the design? Was this influenced by the size of the frame (50cm/small)? Any brakes that could let me work around this seatstay clearance issue?

Thanks,

James

dabac

Check the orientation of the pads. Some protrude further in one direction than the other. Or switch from longer MTB style pads to shorter road style pads. Or try cartridge pads as opposed to solid blocks as they often are thinner. Or get some solid ones and cut them down. A hacksaw should do. Anything else would require mucking about with moving the brake arms rearwards, and while I could make some spacers to do that it'd be a real unusual fix.

Andrew R Stewart 

If you think that this bike was really designed with serious racing in mind... The brake/pad/stay issue wa a result of many factors, least of which was not loosing a podium because of a slow wheel change. Andy.

buffalowings

Well, I haven't actually raced cyclocross before (yes, letting the cat out of the bag) but normally, would you only change a tire/tube when it's flat, or would you swap different wheelsets depending on the condition of the race?

Right now: the situation is that I can remove the wheel if the tire is flat, if the tire is filled with air, it won't be able to clear the limited space between brake pad and tire (due to the narrow seatstays which are in the way of the brake pads). Hopefully the poor quality pictures illustrate the issue.

HillRider

From Tektro's web site these brakes have a barrel adjuster on one arm to adjust pad clearance. Set the pad clearance with the adjuster screwed almost all the way out and then screw it in to get more clearance when you need to remove or install the wheel.

rhenning

The pads on the brakes have been replaced with symetrical longer pads than they were designed for. The Kool Stops are better pads but that set is not designed to work with that brake set up. Get Kool Stops like Continentals which are shorter or some that are asymetical and your problem will be solved. Roger

Andrew R Stewart 

Well, I too don't race these days. But I do race support with our shop team as needed. So here's my take on the wheel changing during the race issue.

The serious guys have a back up bike. But they also don't tend to make tire choices that are too wrong either. Although often the back up bike has different tires on it as it usually has clinchers, and sometimes worn out ones at that.

The rest (and this is most) might have a spare set of wheels (many don't) and are racing for fitness not placing. So if they get a flat their day is done unless it's real early in the race. Either way a fast wheel change won't make the difference in their finishing order.

I'll end with the comment that the softer tire pressures (25-35lbs) that are used during actual racing usually allow enough tire compression to still push a tire past tight pads. Andy.

fietsbob

Ah picture in 4th post .. toe of pad is inside the frame tube . physical interference ..

yea as is, just let the air out, you wanted to avoid it, but a puncture will make that choice for you ,

mend the puncture , Re-install the wheel , then pump it up ..



other thoughts:
You might find a different brake caliper that sets the brake pad further aft and so clears the seat stay ..

Or, maybe instead of the lovely Koolstop Triple compound replaceable insert pad ..

get a cheaper Molded on the bolt brake shoe and saw it off shorter ..

Running without a pit bike and helper, a puncture will drop you a Lap + out
of any meaningful place anyhow ..

maybe this will be that Pit bike and your shopping education has given you insight on what your prime bike needs ..

Barrettscv 

You can create some extra tire clearance by using Kool Stop Thinline pads. The Thinline pad was designed for brake systems with tight brake clearance and for easy tire removal. This pad has a hardened rigid internal backbone that helps pack a lot of performance into a small space.

Features:

Low Profile
Hardened and Plated reinforced steel backbone
Patented Angled tip plow
Water grooves
Knurl-lock™ washer system
Self toe in
Available in Threaded and 2024 Aluminum Smooth Post

I use these on all my CX bikes, highly recommended;

https://www.koolstop.com/english/thinline.html

fietsbob

you can also make clearance with a Ball-Pein Hammer directly on the tube ..

A 2 hammer technique .. one is held over where you want the dent, 2nd one hits the first ..

JohnDThompson 

This looks like a design issue, exacerbated by the small frame size. Attaching the seat stays to the back of the seat tube narrows the space between the stays, as does a small frame size. Attaching the seat stays to the side of the seat tube is a good idea for any frame with cantilever brakes or mudguards, IMO.

buffalowings

I'll look into different pad/brake combos. Currently have a pair of Avid Shorty Ultimates coming in (amazon warehouse had a good buy) if it doesn't fit, it'll be back to the drawing board.

haha, that could be a solution, but I would prefer to maintain the posterity of the seatstays.
Definitely, I think the designer could have gotten away with the way the seatstays are formed/welded to the seat tube if it was a larger frame size. Guess it's a bit like toe overlap.

Yeah, I'm going to join a couple cyclocross races for fun and fitness, still have a lot to learn, dismount, remount, off pavement handling etc. I would just call it a day if I have a flat, or limp back and swap in the flat stock wheels, and reinflate afterwards.

It's my first cyclocross bike, so I think it'll serve it's entire life as a training steed. Not too shabby, even if it has a quirk with the seatstay clearance.
Thanks for all the input guys.

bobotech

Would running a wider rim help? I have the same issue on one of my bikes but it really isn't a big deal since I only use the bike for pleasure but I do have a set of 700x36c tires on a very narrow rim with a very pronounced light bulb profile. I have thought that if I were to use a wider rim, the light bulb profile would be much less pronounced and then I could use the thin cup washers on the brake pad post on the wheel side which would allow the pads to be further out. Then I thought that if I released the brake cable, I would have enough clearance. I haven't done this because its not really important to me but I think it might help.

buffalowings

The would help if the brakes themselves cannot open up enough to fit the tire through. On my bike, they could open infinitely wide if I wanted to (just loosen the cable tension) but my issue is the seatstays are really narrow, so the brakes end up hitting the seatstays.

At the moment, I'm thinking the shorty ultimates will face the same clearance issues, because the brake mounts are designed to be as close to the bottom of the brake bosses as possible (less shudder/more stiff etc) Another alternative could be the shimano CX50 or CX70, because the brake mounts are farther away from the bosses. We'll see, but I'm thinking of just letting the issue be.

xenologer

not a race mechanic here, more like lazy mechanic.
when this problem shows after fixing a flat, rather than uninflate and redo
i grab the spray bottle of soapy water, wet tire slips right through

Kopsis

I have the same "problem" with the Kool Stop cartridge pads on the front of my CX bike. Best solution is simply deflate/inflate when changing wheels. Even in a CX race, the time required to put in 40 psi with a B&D electric inflator is completely insignificant compared to the time required to run a half mile or more to the pit with your bike on your shoulder