New rear wheel advise, please
 

I'm considering a rear wheel replacement for a Dawes Super Galaxy

The current wheel has 40 spokes has a 135mm spacing with a drum brake, 6speed freewheel and a 700c rim.

I've replaced the rim tape and inspected the inner rim, but it's still giving me persistant flats/punctures. They're all happening on the rim side of the inner-tube - nothing is penetrating the new schwalbe marathons.

It may be time to replace the wheel. Would you agree?

I don't think I'm going to get a wheel that'll give me the drum brake, but perhaps I don't need it? The max descents I'm doing is 1km with a 5%. Or maybe 500m with 12%. And I'm being conservative there - in reality they're a lot less.

So perhaps I don't need the drum?

Also, do I need 40 spokes?

Hybrid rear wheels (which I think would fit?) are 135 OLN - would a double wall wheel of this type be suitable?

No. Are you using Velox rim tape? If not, try that. Run your fingers along the untaped rim and look for burrs. I know, you already did that, do it again. Run some sandpaper along it. Blow into the spoke holes. Gotta be something.

Here's the rim and tape - Velox 13mm - I've also had the 16mm before this... same problem.

https://i.imgur.com/iAMacMC.jpg
And
And here's the puncture. It's not inline with a spoke and it's on the rim side not tyre side.

https://i.imgur.com/I93vUde.jpg


One another section of the inner-tube/rim (I've had punctures here too) you can see this line/score mark. It's not a seam. There's nothing sharp on the rim that can do this, but could the inner-tube be pushed under pressure into an extreme acute angle, enough to create a fold that splits. Like if you were to band a credit card in half - it can weaken and crack.

https://i.imgur.com/FsfbCqg.jpg

I was on a trip with a person who got a dozen flats. He scrupulously checked the inside of the tire and the rim, and could find nothing that would puncture the inner tube. Ultimately he took the wheel to a bike shop and they discovered a small shaving in the wheel that was making the punctures. I assume this was created when drilling the holes for the spokes. We scratched our heads as to how it could puncture the inner tube, but afterwards he had no flats. You might want to take the wheel to a bike shop, or try to flush or blow out the rim on the assumption there is some loose shaving in there. Obviously there is something.

https://cimg1.ibsrv.net/gimg/bikefor...a85f000bd.jpeg
OK. I've taken isopropyl and a wire brush to all. Clean as a whistle now. Electrical tape across the while width.

All I can do is test now.

I'm wondering how I might approach the seller of the tandem. This has become quite costly and if it persists, a new wheel would be in order.

You don’t need a new wheel. There’s nothing structurally wrong with the wheel. You have a problem that can be solved. Be encouraged, and keep at it. You’ll find the issue eventually, and then all will be well.

I don't know about the UK, but in the US you can't easily revisit this kind of sale with the seller. And, really, what would you want them to do? Let's see how we can best move on. I for one see a huge hump in that rim tape that is likely a spoke protruding into the tube space. There may be another. IF the tube flats again, make absolutely sure that you do not move the tube in relation to the rim as you demount the tire. FEEL the area around the puncture. Really feel it. The CarbonFiberBoy is right. Something is in there, you just have to find it. As to the rest of it ... no, you don't need 40 spokes; no, you do not need the drag brake; and, yes, a 135 OLD MTB rim 36 spoke wheel would work. But, in your own words: "this has become quite costly". So, to that end, lets see what we can do to cut your losses. Personally, my OCD would not allow me to upgrade the rear wheel and not do anything about the front :-)

OCD - hahaha. Well, they're not the same at the moment anyway.

Well, it’s just about making good on an honest sale. I spoke to the seller today 0 has suggested taking the wheel to his bike mechanic which I have agreed to do. My wife has thrown her back out so we won't be riding it for a few days at least anyway. It is our main mode of transport now - I don’t really want to get on public transport with covid still lurking - so I hope we up and running (cycling) with it soon.

I was very thorough with my last rim tape change - massive clear-out of the rims with a wire brush and alcohol cleaning - and a very close inspection. The mechanic can have an expert eye on it to see if I've missed anything and hopefully service the wheel anyway.

I've noted exactly where the punctures occurred. All in line with either side of the rim tape in 2 or 3 spots around the rim. Hopefully this will give the mechanic the info he needs to sort this out.

Thanks to you all here.

Good to know about the drag brake and MTB wheel OLN. To my knowledge, MTB are not 700c though, correct? I'm not clear whether hybrid wheels are 135.

Is the puncture occurring at the same spot relative to the stem? If so, there are only 2 spots on the rim implicated. Focus there.

MTB usually implies 26" rim diameter but, yes, a hybrid likely has the same 135 OLD as MTB and will also have 700C wheel diameter. So finding a rear wheel to fit the Galaxy should not be an issue.

Unless the wheel is old, has lots of accumulated damage, and/or spoke failure, don't replace!

It looks like the edge of the Velox rim tape is causing your problem. The line in the inner tube that bisects the hole indicates the Velox is rubbing holes in the tubes. The way the edge of the Velox is sticking up in your photo is what makes me suspicious.

You need a wider rim strip (or narrower) that goes to the edge of the rim flange, but well below the hook to ensure proper bead seating. A narrower strip that just sits in the well should resolve the problem as well. Do not use rubber rim strips, nor anything thin and/or flimsy. Some of the nylon material strips are too thin to offer enough protection, especially on a tandem. Another option would be the plastic rim strips (like Michelin) that also cover the entire rim surface from rim flange inner edge to edge. Hard to remove them without damaging them though. And I should add that with today's use of tubeless tires, there should be ample rim strip options out there that will resolve your problem.

I outfitted two touring bikes way back when that were doing an around the world trip. To increase durability, we decided to use Mr. Tuffy tire liners. BIG MISTAKE! The bikes were loaded with max weight and tires were at max pressure. These conditions were enough to cause enough wear and friction between the inner tubes and the ends of the Tuffys. The riders had holes all the way around the tubes where they contacted the edges of the Tuffys.

It looks like you're having the same issue. Velox are the go-to rim strips, especially with tandems because of the high loads & pressures on the wheels. Velox do a good job staying put and protecting the inner tubes.

Another thing you may want to try as insurance is to de-burr the spoke hole edges in the rim. These are usually punched in the manufacturing process that can leave sharp edges and burrs. But this probably has nothing to do with your problem.

PS Electrical tape alone is NOT the solution. It's too flimsy. The force and pressure of 110psi with two riders will cause problems. Now it COULD work if you put it over the existing Velox to cover the rough edges. But again, given how flimsy electrical tape is, I'd expect the tube to wear through the tape and suffer damage anyway.

Amazing advice - thanks @LV2TNDM

Your diagnosis is consistent with the issue, for sure. I had used the 16mm and 13mm. Wiggle sell a 22mm Velox. Perhaps that could be the way to go.

The good news is that the seller has agreed for me to take the tandem to his mechanic. I'm confident I can sort this out myself but it's always good to have a specialist take a proper look.

What kinda pressure should I be running a 35mm tyre? I'm guessing the max the manufacturer recommends?

I run my Continental 28's at max pressure of 120psi. Given the wider tire options many tandem teams are using these days, the old "run a narrow tire at max pressure" rule doesn't apply as it did before. Lower pressures can be safely used with higher volume tires. But there's a sweet spot that needs to be achieved. Pressures too low are dangerous to you and the wheels. I'd post what tires your using and see what others may have experienced and recommend.

But you shouldn't be worrying about tire pressure as a flat prevention measure (given your problem). Safety, traction and comfort are the priorities.

Thanks again, LV2TNDM

I'm currently running Schwalbe Marathon 35's at about 80-85psi (85 being the max). I reckon I could bring this down a tiny bit for comfort, but London roads do can induce snake bites quite frequently.

I'm confident that taking a wire brush and isopropyl to the rims has solved the issue. Probably about 35 miles without an issue anyway.