You don't need to be an 'investor' to invest in Singletrack: 6 days left: 95% of target - Find out more
So I’ve got an old bmx - think it’s a Haro 124 cruiser from 2011 or 2012.
Gears have always been a bit ropey as the bike was a state - I fitted a new bb and chain and cleaned it all up.
Today whilst riding round a pump track it started a funny feeling when pedalling or back pedalling - like at one point the chain was going very tight, then very loose further round the chain rotation.
Chain all seems ok in terms of no loose links - so it must either be rear sprocket related or chainring / crank related. I suspect it’s something at the front.
Cranks are 3 piece steel jobs with a Chainring that seems to bolt on with just 1 bolt.
Any ideas what could cause the uneven tension?
Loose sprocket?
Bent hub axle?
Bent crank axle?
Something chainring related?
BMXs… they do this kind of thing 😂
Do you use chain tensioners? They can sometimes put a very subtle uneven tension on a chain that’s not perfectly straight.
I raced bmx for years & the quickest easiest fix is to slacken the chain ever so slightly (fraction mm at a time) until it doesn’t do it.
It's usually because the sprocket isn't centred in the BB axle. And yes, totally normal on a BMX because precision engineering isn't punk rock.
I do have chain tugs on the rear wheel. I could loosen it ever so slightly I suppose.
The chainring not being centred around the bb sounds like it could give the issue I have to be fair. I can’t remember exactly how it’s held on the cranks other than there is one big bolt. I guess perhaps I loosen this and try to centre it somehow….what could possibly go wrong lol?!
Surely there is a better bmx crank standard than this though….maybe I’ll have to pop to Crucial bmx for a peruse of the shiny things in cabinets
Sprockets are usually alloy and crank axles are steel so they can deform the sprocket easily. Some of them have a thick alloy spacer to protect it but in my experience they never sit perfectly central. There's always a bit of wobble and it's enough to make your chain tension go up and down.
Not sure what moden bikes have. I've got a cheap unbranded 3 piece onnl my DJ bike and I think the crankarm has a flange for the sprocket to sit on.
BMX chainring bolt holes and the bolt that goes through it to attach it to the crank arm are generally not millimetre perfect so the bolt will never be central in the hole which then causes the chainring to be off centre and gives tight and slack areas
You can improve this by fitting a spline drive chainring, this does away with the bolt as the chainring has a splined insert that pushes directly onto the splined axle of the crank giving you a much tighter and central interface
I like the sound of spline drive chainrings - although I have a 39t chainring and 16t sprocket at the back. Will do some googling
Profile do larger chainrings with spline drive inserts
https://www.profileracing.com/product-category/profile-bmx/profile-sprockets/
Good spot - I’ll have to see how many splines my crankset spindle has - will try and have a nose around it tomorrow. Thanks!
Have you got the right reducer insert fitted to the chainring?
@sillyoldman - I have no idea! I’m going to assume until I got the bike that it had never had the chainring off in its entire life. Bike was £50 or £70 (I forget which) and it was in a very sorry state.
Seized seatpost, almost seized bb, loads of rusted links in the chain, back brake essentially didn’t work, headset loose, pedals mangled, what looked like emulsion splattered all over it like someone had dropped a tin of paint near it etc.
I fitted a new chain, new bb, new back brake, new tyres, chain tugs, new seatpost. Found some old grips from mtb in the garage and then gave the whole thing a really good going over. Cutting out the old seatpost was emotional.
This sounds like a serious project. We need pictures!
I don’t think I have any before photos / although it looked very sad splattered in white paint and had original tyres on it from 2011/2012 that had seen better days. Seatpost was stuck up too high for proper bmx and it had generally been abused and left in the rain by a teenager.
It’s also got a new rear rim as I bent it 2nd ride out trying a roller on a pump track and landing wonky with all my weight on the back tyre - so I built a new rim and new spokes onto the original hub. Also regreased the cup and cone hubs both ends as they didn’t feel as smooth as they could.
I keep thinking I’d like a new one / fancier one but my riding skills aren’t that great on it and I really can’t justify it. Keep looking at those Airdrop Fades too.
[url= https://i.postimg.cc/134fjx7C/FD450153-1C4B-48A8-9A8E-A402C17F3D38.jp g" target="_blank">https://i.postimg.cc/134fjx7C/FD450153-1C4B-48A8-9A8E-A402C17F3D38.jp g"/> [/img][/url]
[url= https://i.postimg.cc/Y0Zc0K10/IMG_0145.jp g" target="_blank">https://i.postimg.cc/Y0Zc0K10/IMG_0145.jp g"/> [/img][/url]
That does look good fun. I'm really tempted by a BMX myself, preferably something with 22" wheels but it would be another toy that I don't have time for.
Maybe when junior is old enough to ride probably and he needs a chaperone.
That looks nice and tidy. A nice easy restoration. How do you like the Billy Bonkers? I’m looking for a front tyre for my ‘dad country’ build as I think a DTH on the front might not cut it on loose gravel and dirt pump tracks.
This one is a cruiser with 24” wheels - supposedly less twitchy than 20” but it’s the twitchiest thing I’ve ever ridden by miles 🤣
Tyre wise the billy bonkers has been great so far - grips well and rolls astonishingly fast. Took me a while to get used to how quick I was getting into corners.
I haven’t the foggiest idea how they’d be on gravel though - all the pump tracks I go to are all beautiful bits of tarmac. Especially the new bowl at Hillfields in Bristol and at Stockwood (also in Bristol). Both new velo solutions tracks with the red painted lines on.
I’ll mainly be riding around Bristol pump tracks (tarmac, dirt and that gravelly hard pack that seems to get used), family trails with my 4 (soon to be 5 year olds). I’ve got a Charge Blender frame and building with old parts (new tyres) to make a single speed as my big HT is too fast with gears and 29 wheels to go at their speed.
I’m to old and creaky to ride a BMX nowadays (and was fairly bad on them 20 years ago)
I’d think the billy bonkers would be ok for that sort of use. I run mine at 50psi for speed but you could drop it slightly and that would be ok.
I’m 42 and quite broken so bmx has been hard yards but it only occasionally tries to kill me now. Just when I’m feeling confident it’ll do it’s best to hurl me to the ground.
Same, 44 but not as bendy as I used to be. BMXs certainly punish mistakes, but are great for technique. Even if they are built a little more agricultural than the fancy MTBs we’re all used to.