Hi there,
I've changes the derailleur on my kid's 20 inch bike because the old one (4th photo) was broken.
I feel this one is somehow bigger than the old one and when shifting up, on gear 7 the derailleur touches the tire. I can't shift to the 8th gear.
Is there a fix for this or did I just get a derailleur that is too big for the bike?
Thanks for any tip!
by _hop_hop_hop_
9 Comments
Switch to the lowest gear and check if you can shorten the chain a bit, it might help.
This is a common problem with small wheeled bikes. I believe that (original, broken) Box components derailleur is one of the few on the market specifically designed for small wheels.
Microshift have a similar option: [https://bikerumor.com/microshift-super-short-mtb-drivetrain-20-24-inch-wheels/](https://bikerumor.com/microshift-super-short-mtb-drivetrain-20-24-inch-wheels/)
I don’t think Shimano offers a small wheel derailleur, but I could be wrong.
Increasing the B tension can pull some derailleurs back and up enough to clear a tire, or shortening the chain if you have enough slack. But those won’t work on every bike / setup.
Try looking for an short caged tourney derailleur, or maybe just the cage and try to change it. And to answer the question: yes, the derailleur is too long.
Make sure the wheel is in the dropouts squared. Check for derailleur hanger alignment. Adjust limit screws.
SHORT CAGE
Derailleur doesn’t seem angled right to me?
Dumb question – but because the derailleur is on the largest chainring, shouldn’t the derailleur be swung further forward?
On my Avanti when it’s in this gear my derailleur points vastly further forward and would easily clear the tyre. Then in a lower (higher?) gear the derailleur would move outwards and also swing down.
So my question is – is the chain slightly too long?
Looking at the damage to the old derailleur, you may want to check and see if the hanger is bent. A bike shop could check that out.
/u/SSSasky is right that this is a common problem with small wheels, but that doesn’t mean that this rear derailleur can’t work with yours.
Others have questioned your chain length / b-tension (which need to be in balance).
So let’s roll this back for a minute.
What is the largest cog on the cassette? The smallest?
What is the largest ring on the crankset? The smallest?
And that’s a TourneyTX 800 rear derailleur, right?
Lastly (I know, 6 questions) I presume this is the same chain you used with the previous derailleur? So you haven’t sized (set the length by adding or removing links) recently?