Amt0571

I have a mountain bike with 26“ Fulcrum Red Power XL wheels. Since I had a kid, sometimes I attach a kid seat to the bike and go on some easy paths at relatively low speed. I also use this bike to get my son back from the school twice a week. I've been doing this without problems for 1.5 years. I weight 74kg and my son weights 16kg.

Today, however on a 9km ride I did with him, I noticed rhythmic creaking on the rear wheel. Especially when climbing, but also when coasting downhill.

I supposed the spokes would be loose, but it's not the case. Is it possible that the rims can't withstand so much load? They're 24 spokes with a 2:1 lace pattern and never given me any problem. I have always been very carful when carrying my son and always go really slowly over bumps (not only for the wheels, but also to avoid him hitting the rear of the saddle).

Is it possible that the wheels can't withstand occasional use with a child seat?

Moe Zhoost

I think it's more likely that the creaking is related to the child's seat or mounting.

Amt0571

I'm sure it's the wheel. If I pedal with a 32 - 32 chairing and sprocket (same size, so cranks rpm are the same as wheel rpm) , it's totally synchronized with the cranks. If I use any other combination, it gets progressively out of sync. It also keeps sounding riding in a perfectly smooth surface even when coasting.

The wheels are designed in a way that the spokes don't touch each other when they cross. So that's out of the question too.

cyccommute 

Your problem probably is unrelated to the child seat. Inspect all of the spoke holes in the rim for cracks. If that isn’t the problem, take the tires and rim strip off and inspect inside th rim for cracks. Rims can crack between the spoke holes and creaking is caused by the edges of the crack rubbing together.

Andrew R Stewart 

Placing a small drop of thin lube on each spoke nipple/rim hole contact will eliminate that potential source, at least for a little while.

I somewhat disagree with Stuart though. The wheel described is way wrong for the use the bike is seeing and baby seats add a lot of load and leverage. Too few spokes IMO. Perhaps that 1.5 years of trouble few use was the wheel's "lifespan" in this application. Andy

AnkleWork

Sudden problem; look for something that changed suddenly.

Amt0571

Yes. I understand the wheel is not ideal for this application, but it's an old mtb and I couldn't justify buying a new bike or rim just for carrying my son. I plan on replacing the whole bike when my son grows and I have time to ride again anyway. I wouldn't have mounted the seat on a bike I loved.

I thought slowly and carefully riding with him wouldn't be worse than riding hard alone. Maybe I was wrong.

I have inspected the rim and hubs and couldn't find any crack. So I'm not sure what else to do...

Bill Kapaun

Pluck the spokes.
They should all have the same tone per side.

Miele Man

If that wheel fails when your son is on the child seat what do you think will happen?

If you don't want to spring for a new wheel with more spokes then I suggest you check out a bicycle co-op near you to see if they have one. You might also try a local bicycle shop to see if they have a slightly used wheel that someone has upgraded from.

Check your existing wheel very carefully for cracks and also check the sidewalls of the outside of the rim to make sure the rim isn't worn almost to the point of failure.

Cheers

Amt0571

Considering it has a 2:1 pattern, that's 16 spokes on one side and 8 on the other, if it fails, nothing good is going to happen. I understand this and this is why I am asking for ideas on this forum.

I've checked the rim and everything seems alright. This is what's driving me nuts. I'm thinking that maybe I'm going to fit a longer seatpost (otherwise I'm not going to fit on it) on my wife's bike and use that instead since it has 32 spokes wheels. Fitment won't be perfect even with a longer seatpost, but considering what I do when carrying my son, I don't think it will matter.

Miele Man

How much does your son weigh?

Cheers

CliffordK

Are the wheels reasonably true, and the tires without flat spots?

Amt0571

15 or 16kg. Not sure of the exact weight, but no more than 16 for sure.

Tires are new from a couple of months ago and have been ridden less than 200km. No flat spots. Wheels are perfectly true.

ThermionicScott 

Try a bit of oil at each spoke crossing to rule that out.

Amt0571

Its already ruled out. By design, spokes do not touch each other at crossings.

As soon as the kid is sleeping I'm going to disassemble the entire wheel just in case I'm missing something...

Miele Man

Take the seat off the bike and ride it to see if the noise stops. It might be that your son moving in the seat a bit that's causing the creaking. I'd go over every nut and bolt on the child seat to be positive nothings come loose or cracked at a bolt hole.

Cheers

ThermionicScott 

Ah, missed that the first time around.

Just to be sure, you've tried adding a drop of oil at every spoke hole in the rim and riding it? Disassembling the wheel won't tell you anything more than that.

CliffordK

Did you true the wheels before the noises started?

It is not uncommon for some popping to occur after truing wheels. That will go away after a few rides. It can be minimized with stress relieving or unwinding spokes (unwinding is easier for flat spokes, but it has been suggested marking them before truing. You might be able to also unwind by feel.

I'm not sure if bad bearings will also give a crunchy sound?

Novalite

What happens with the noise if you pedal with one leg (ex left, or right leg) ?

Amt0571

I loosened the bearing preload adjuster and set it again. I have ridden the bike hard and there was no noise even when I tried jumping on the pedals.

I'll have to try again with the seat mounted and my son on it, but I think that the only thing that has changed is that he's probably heavier. Maybe this is the limit for 24 spoke wheels... I rarely use this bike now, since I don't have much time and mainly ride a road bike to commute once or twice a week, so I don't think that something has worn down or broken.

djb

you should be able to find a used 32 or 36 hole 26in medium quality rear rim for not much money, and would take care of any concerns for pulling your son around, and the wheel will be much stronger than what you have.
Here in the city I live in in Canada, its not hard to find an "old" 26in wheel that would be in fine shape.

an option anyway.

re creaking--as mentioned, very carefully inspect all the child seat mounting brackets for hairline cracks etc, creaks are often a sign of metal stressing. I once had a car that made a creaking sound until one day the front wheel tie rod arm broke going maybe 40kph, wheel turned outwards and it was a sudden screeching stop....I say this given as a dad, I'd take a serious look at everything mounting wise.
good luck finding source.
could you ride past somone knowledgeable enough so that they could try to pinpoint where its coming from, or they ride beside you on a quiet street etc?

Novalite

The places to look when hunting (hairline) cracks are those where material is stressed most. Leverage effects. Mounts of longer parts that are loaded at the end farest away from the mounting point. The metal on those mount points undergoes an increased force due to the leverage.
One way to make hairline cracks manifest themselves is by pushing/pulling parts. Once I discovered a hairline crack due to a surface being wet. Hairline cracks swallow water when opening, and spill it out when closing (push, release), making them visible.
I'd say a mount place of that kid seat is the biggest suspect here. Check first the one(s) where the kids weight has the biggest leverage on. 16 kilo is quite a weight that sits on quite a distance from the rack.
As "safer" test you could fix a dead and concentrated similar weight (alike halter discs) in the seat, due to the mass concentration and low location leverage is least and no movement of the load. See if that makes a difference.