Chain Rattling

[Rexi29]

Hello
I just got my 2021 GIANT Fastroad and I love it. I also just had it assembled at a bike shop. I have rode it twice since this past Saturday and I notice
that when I go through the gears on the Shimano Claris shifters, I hear rattling on most of the gears and none on some. Any advice as to why?
Thank you for any answers

 

[Ajax Bay]

If you're sure that it's the chain rattling on something, then my best guess (on low information) is that you're hearing the noise of the chain rubbing against the front derailleur cage when the chain is on the largest or smallest sprockets. Google cross-chaining. It could be other stuff, but that's my first suggestion. https://www.giant-bicycles.com/gb/fastroad-sl-2-2021

[ https://wickwerks.com/support/crosschaining/ ]
Then put the chain on small/small (front ring / rear sprocket). How many mm are there between the return section of the chain (the lowest section) and the chain going round the rear derailleur guide jockey wheel?

[ https://www.parktool.com/blog/repair-help/chain-length-sizing-campagnolo ]

 

[iluvmybike]

Also be aware of the trim facility on the froint derailleur - if in big ring at front a short press on the down lever as you move to bigger sprockets on back will 'trim' the derailleur. If in small ring and getting towards smaller sprockets a small press on the up lever will 'trim' it the other way. The advice on cross-chaining above is helpful

 

[weareHKR]

also just had it assembled at a bike shop.

In addition to the above ...
The best thing to do at this time is to take it back your LBS, they will have set up the gears probably on the work stand, which is fine.
Generally in a riding situation is when you'll need to use the barrel adjuster to fine-tune its position, I doubt they will have done that!
If you're confident in making adjustments then crack on, if not you should have the LBS check it over!

 

[Lovacott]

Hello
I just got my 2021 GIANT Fastroad and I love it. I also just had it assembled at a bike shop. I have rode it twice since this past Saturday and I notice
that when I go through the gears on the Shimano Claris shifters, I hear rattling on most of the gears and none on some. Any advice as to why?
Thank you for any answers

Cables stretch and contract with air temperature so what is perfect one minute might not perform the same half an hour later.

Teach yourself how to index your gears.

It's not as hard as you think and there is so much good info on YouTube and bike forums.

Set your gears up so that you can "index on the fly" using just the barrel adjusters on the shifters.

Set them up so that every gear combination (including the crossovers) is noiseless once the chain has settled.

If you can get your gears running sweetly, you will make your rides so much easier.

 

[C R]

Cables stretch and contract with air temperature so what is perfect one minute might not perform the same half an hour later.

Teach yourself how to index your gears.

It's not as hard as you think and there is so much good info on YouTube and bike forums.

Set your gears up so that you can "index on the fly" using just the barrel adjusters on the shifters.

Set them up so that every gear combination (including the crossovers) is noiseless once the chain has settled.

If you can get your gears running sweetly, you will make your rides so much easier.

Is thermal expansion really enough to affect indexing?

ETA, steel expands anywhere between 9 and 20 microns per metre per degree C, depending on type. Assuming a rear gear cable, 2m long, take 15 as typical expansion coefficient, and a reduction in temperature of 10 C the cable would shorten by 0.3 mm, not sure that would be enough to alter shifting.

 

[Paulus]

The problem is probably either the indexing is slightly out, so what you are hearing is the chain rubbing on the cogs of the cassette thinking , about changing up or down.
Or,
as suggested by a couple of others, the chain is rubbing on the front derailleur.
There are a couple of things that could be wrong there, derailleur not lined up with chainrings correctly,
the cable is too tight so not letting the mech go right over,
The limit screw needs to be slightly loosened to allow the mech to travel a little further, but not too far or the chain will come off the rings.
All slight adjustments, but you need to find out were the adjustment needs to be made first.
If you are not confident enough to DIY, then your local bike shop will do it for you.

 

[Lovacott]

Is thermal expansion really enough to affect indexing?

ETA, steel expands anywhere between 9 and 20 microns per metre per degree C, depending on type. Assuming a rear gear cable, 2m long, take 15 as typical expansion coefficient, and a reduction in temperature of 10 C the cable would shorten by 0.3 mm, not sure that would be enough to alter shifting.

From limited experience, I'd say it does.

More so with the "crossover gears".

 

[Ajax Bay]

Cables stretch and contract with [air] temperature

I thought it'd be interesting to quantify this, with specific attention to rear mech gear cables.
Cables do indeed stretch with temperature, but (and @C R has got in with the key 'so what' while I started the morning's maths )
Cable Pull
The OP has an 8sp drivetrain (Claris) and the (rear gear) cable pull (ie per click) is 2.8mm. (Note that 9sp = 2.5 and 10sp = 2.3 (Shimano))
Thermal Expansion and Contraction
( https://www.certex.lv/en/technical-...t/properties-of-extension-of-steel-wire-ropes )
The coefficient of linear expansion (∝) of steel wire rope is 0.0000125 = (12.5 x10^-6) per oC
Change in length Δ(mm) = ∝ x L(mm) x 'T'(oC)
where:
∝ = coefficient of linear expansion
1800 = original length of cable (mm)
So ~20 microns (mm^-3) per degree of temperature change (o C)
So an extreme variation, say 20 degrees C, will result in a change of cable length of about 0.4mm
I guess the indexing error tolerance is sufficient to cope with such expansion/contraction due to temperature.
Elastic Stretch
Bicycles cables do not remotely approach their elastic limit so all stretch due to tension is elastic.
Elastic Stretch = (W x L) / (E x A)
· W = Applied Load ( kN )
· L = Cable length ( mm )
· E = Strand Modulus ( kN/mm²)
· A = Area of Cable = (D2 x pi) / 4 (where D= Dia of cable mm)
So for me: Elongation of cable at the RD is 3mm - seems quite a bit, doesn't it? But this aligns with the distance (about 30mm) one has to push the STI lever sideways (1:10 lever ratio) before the force applied (through another 20+mm) pulls the cable shifting the RD and then engaging the next ratchet in the STI mechanism.
BUT. Each shift up the cassette (assumes the same force required on the lever) stretches the gear cable the same amount so the actual (additional) cable pull is still 2.8mm each time, and thus the indexing works.

Assumptions/estimates:
W = 200N so 0.2kN (NB 1:10 ratio of STI lever, assumes a finger pressure of 2kg wt (20N) changing up the cassette)
L = 1800mm (RD cable)
A = 1.13mm^2 (1.2mm dia gear cable)
Typical value for E is (from https://www.s3i.co.uk/wire-rope-technical.php )
· 1x19 = 107.5 kN/mm² (wire rope with 19 strands)

Finally an 'aside':
"Newly installed cables can seem to elongate, requiring readjustment. While it is generally agreed that inner wires actually stretch very little - if at all - housings and linings may compress slightly, and all parts may generally "settle in". Lightweight assemblies such as those used on bicycles are more susceptible to this phenomenon." ( https://en.wikipedia.org/wiki/Bowden_cable )

From limited experience, I'd say it does.
More so with the "crossover gears".

What experience are you drawing on? Slight indexing misalignment in very hot temperatures?
Why would this make a difference particularly when cross-chaining? (if that's what you mean by "crossover gears")

 

[Lovacott]

What experience are you drawing on? Slight indexing misalignment in very hot temperatures?
Why would this make a difference particularly when cross-chaining? (if that's what you mean by "crossover gears")

When I say crossover gears, I mean cross chaining.

On my 3 x 7, running from the smallest ring to the smallest cog, unless the indexing is perfect, the chain will either rub the front derailleur or refuse to engage correctly (skip). I use the crossovers as a benchmark when setting up the gears (if big to big and small to small both work, the rest will work).

When I set up my indexing, I leave the barrel adjuster a full turn in either direction for on the fly adjustment.

When cycling, I will make very minor adjustments to the cable tension using the barrel adjuster.