Buggington

Hello again

I've become sick of having a bend in the chainring on my Land Rover MTB. It's constantly rubbing on the derailleur, especially when under load in largest 'ring/smallest sprite config. I this issue on the original Shimano chainring which I then swapped to the current 48 tooth Shimano 'ring, which has worsened the problem, unsurprisingly.

My question is are there reasonably strong and durable triple rings available for my bike which wouldn't break the bank? It was £40 for the current 48 tooth ring to give you an idea of the price range I'm currently in.

I know I haven't really been able to provide much information on this again, and I apologise, but I'm not quite sure what info I would need to provide.

Thanks in advance...

fietsbob

TA makes top quality chainrings of 7075t6 alloy, but they may not be cheap enough
to come within your budget,, Stronglight another..

several other makers use that 'Ergal' alloy..

Buggington

Great, thanks. Are there any features I should look out for? No idea what I'm looking for really.

mechBgon

If your crankarms are the type that bolt onto a spindle, start by confirming that the crankarm is fastened to the spindle to the proper tightness, so you know it's not the crankarm shifting on the spindle. It can't hurt to confirm that the bottom bracket (crank spindle/bearing unit) is properly fastened into the frame, since it can rock around if it's not tight.

Also: is the chainring bent, or just flexing? Sight down on it from above with the front derailleur as a reference point, turn the cranks and evaluate the straightness of the rings. If all three are wandering, and you took care of the possibilities I mentioned above, then your crank spider needs some straightening. If one ring's wobbling, you have the option of replacing it, or straightening it if you want to try that. A dead-blow mallet is good for this task, I love my Nupla StrikePro

With that said, if you want a stiff aftermarket chainring, RaceFace's 7075 rings are pretty good.

Buggington

Hi Mech

The crank arms are on a spindle. The bolt seemed to be done up quite tightly, although I've tightened it further now. All three of the chainrings seem to be both bent and flexing, which is far from encouraging. There seems to be little point in trying to straighten it if it's flexing anyway.

Do you mean this kind of thing? It's pretty damn expensive
https://www.leisurelakesbikes.com/pro...aspx?&id=16621

fietsbob

sorry if the prices of Better, are not cheap enough.. might get Sugino rings for cheaper..

you may not need the whole crankset, that same site shows replacement chainrings.

Race Face is a Canadian Import. 'Salsa' thru QBP is from TW. also a 7075t6 alloy is used.

Al1943

If you replaced a ring and it did not fix the problem replacing it again is not going to fix the problem again.

Buggington

Good point, I just assumed I'd bought two pants rings?

cny-bikeman

OK, all 3 bent would mean that when you are off the bike and turning the crankarms backward that all 3 wander back and forth in unison. If true then as mechBgon said it's not the chainring(s), its the crank arm. If there are two extremes (right/left) and they are 180 degrees from each other try removing the arms and rotating 90 degrees on the spindle. If there is only one spot that is off then the crank arm would need to be straightened at that point. If you replaced the ring and that did not fix the problem then it should be apparent that the ring was not the problem.

As for all 3 flexing, that's a little more complicated. Land Rover makes a variety of bikes, starting at a relatively modest price point. Driving hard in your high gear will cause the frame to flex on many, many bikes, and when the frame flexes the chainwheels will move back and forth inside the front derailleur cage. Again, it's unlikely the chainwheels. For the record high gear is not one in which you should be exerting extreme pedal pressure anyway - it's for using when you are already going fast, not for getting up to speed (or for getting into shape).

Buggington

Ok, so what's the crank arm? Also, when the 'rings were changed the cranks were too, not sure if that's related.

My bike's of the more modest end, and I don't often use the high gear to get shifting, more for 16mph+.

And for what it's worth, I just assumed Id bought two pants rings, what with them not being the high end stuff.

cny-bikeman

My mistake - should have specified the crankarm spider. Better yet should have just pointed you to Sheldon's site - which is why links to it are at the top of the forum. All you actually had to so was Google "bent chainwheels" (or straighten chainwheels, etc) and you would have seen Sheldon's page sheldonbrown.com/straighten-chw.html at the top of the results. No sense in reinventing the (chain)wheel - go there!

Buggington

OK, so having read through it, I sort of understand what he's getting at, but I don't think it's really going to help with them bending (particularly when under load)...

mechBgon

If you could post a photo or two of your bike's crank, that would help narrow down what you've got, without us having to play Twenty Questions

Incidentally, this is a chainring: https://aebike.com/product/raceface-4...r7109-qc30.htm One gear that you bolt onto the crankarm.

A crankset is the arms with the entire set of gears attached. In the UK these may also be called a chainset. If you wanted a high-quality crankset with a 48-tooth chainring, the Shimano Deore FC-M590 is a good baseline. I use one on my commuting mountain bike. It's heavy (two of the rings are steel) but it gets the job done and doesn't flex much, even for a gear-masher like me.

cny-bikeman

Somehow the part I added about bending did not save. ANY bike frame will deflect under heavy load, as will the crank/chainwheel, but generally to a smaller degree, and that causes the "bending." I highly doubt that a 48t Shimano ring is going to have any significant amount of flex, even under load.

Deflection at the bottom bracket, resulting in the back-and-forth chainring action at the derailleur cage is normal if you are using very high pedal pressure, which should not be the case in the higher gears. They are there primarily for when you are going fast and running out of your other gears, not for getting up to speed (or for getting into shape faster). You say you use the higher gears for 16mph+ but a very modest high gear of 48/13 at a likewise modest 80 rpm gets you almost 24 mph.

Buggington

How do you work that out? That's a neat trick

I'll have to follow Sheldon's tricks to work out what it is, but he reckons that BB's don't really flex much? Or have I got the wrong end of the stick? It's been a long day :/

And mechBgon - what parts did you particularly want photographing?

mechBgon

The crankset. For example:

Buggington

Ah ha, will do that soon. In the mean time, if it helps, these are a couple of videos I posted on here trying to fix a noisy drivetrain. This lot has been causing me a lot of issues

https://www.youtube.com/watch?v=-vJRH3vYaog

https://www.youtube.com/watch?v=WEHZMjq87fw

cny-bikeman

Well, I certainly could be wrong about what's flexing, but the point about overpushing gears still holds. If you mash the pedals you will often get rubbing in the highest gear.

As for figuring speed vs. gear and rpm: A very long time ago (pre-bike computer era) I happened on the fact that a 100 inch gear @100 rpm is about 30mph (27" tire). If one knows the gear inches speed can be figured with some effort in one's head, much easier on paper. For the above example I happened to know that a 48/13 is essentially a 100 inch gear, 80% of 30 is 24mph. An 80" gear at 100 rpm would be the same speed, 120" gear would be 30 x 1.2 = 36 mph, etc.

Sheldon's chart is derived from simple geometry and math: Chainwheel/rear cog x wheel diameter (inches) x PI x revs per minute x 60 (minutes) /12 (inches per foot) / 5280 (feet per mile).

Buggington

Handy - I think I've got 26" rims, so maybe that's slightly out, but that's quite an interesting way to gauge it. I'll remember that - thanks. I'll do some of Sheldon's stuff and I'll let you know what happens.

Cheers

Buggington

How're these?

Apologies it took so long to get the pictures - college and work have been somewhat hectic.

mechBgon

Super! Well, the chainrings on that crankset aren't replaceable, as you may have deduced already. So if you want something stiffer, you'd need to replace the whole crankset. The Shimano Deore FC-M590 crank/bottom-bracket set would be a good candidate. It's available in black or silver, 170 or 175mm arm lengths, and two chainring combinations: 22-32-44 or 26-36-48. The Deore has replaceable chainrings, too.

Buggington

I can live with that - I've just got to reconcile myself (and my bank account) to the cost of doing that, but it seems to be a good solution. But first, new derailleurs.