Upgrading my chainring

Question

Long story short, I have a 30t chainring and a 14-38t freewheel for a 7-speed configuration. The 7th gear is barely a workout and 6th gear is more like a 4th or 5th gear. It’s a terrible configuration. It’s a relatively cheap bike, about $400, and I want to start upgrading parts on it, beginning with the chainring to make riding more of a workout, and giving me more speed.

Can I just change my chainring to a higher tooth and larger size to accomplish this? And if so, what is the largest I can upgrade my crankset to?

Answer 1

Your frame is the limiting factor on your chainring size.

Check if the manufacturer has a suggested maximum chainring size, via their website or in your manual.

Otherwise, print out the Wolf Tooth chainring sizes PDF - make sure its at 100% scaling.

Drop your chain off the chainring to the outside, and move it back out of the way. Cut your printout so that it can slip around the spindle on the bike, and tape it together.

Check that your current chainring matches the outline in that printout, and align on that. The paper should be behind the chainring.

Then with the paper parallel to the centerline, work out which size of chainring won't touch your frame.

If its very close, aim to have at least 1mm of clearance, ideally 2~3mm. If the frame flexes, your chainring teeth could cut a gouge into your frame, which could write the frame off.

Finally, remember you'll need a longer chain, so its probably worth replacing the cassette/freewheel/block/cluster as well.
At this time you might choose to change the spread of gears, with a larger large cog to offset the larger chainring.
If the bike truely has a freewheel, then 14T is likely your lowest option, where a cassette would go down to 11T.

Longer term, keep your eyes open for a rear wheel that takes a cassette, preferably 8/9/10 speed. Or just ride the bike as it is and wear it out. There's no point replacing working components unless another need is served.

Answer 2

The largest chainring you can fit on the bike is determined by the clearance of the chainrings teeth in relation to the chainstay (that is the lower tube coming from the bottom bracket shell back to the dropout area. In your picture, the chainstay has "Schwinn" printed on it).

An educated guess would be a 36 tooth chain ring as the max large ring. The user manual for the bike should detail this spec to be sure. To increase your gear ratios, as you've stated a desire to do, the simplest and least expensive option would be to increase the tooth count of the chainring. Keep in mind that the best alternative would be 1x, "narrow-wide" chainring with the same Bolt Circle Diameter (BCD) as your current.*

*Based on the picture in your question of the Schwinn bike, it appears as though the crank-chainring is a "direct mount" configuration. The other very real possibility with an inexpensive bike is that the chainring is rivited--or permanently fixed--to the crankset. For the former situation, there is no BCD to worry about, but there are considerations about compatibility of of the direct mount. There are different types and configurations of direct mount and the direct mount chainring must be compatible with the crankset's type of mounting. If the latter situation is the case, the entire crankset must be changed in order to gain more teeth in the chainwheel.

Answer 3

A couple of years ago I asked exactly this question in Can I (easily) change this chainring?

And the answer turned out to be "yes". It was both cheap and easy. I bought a new 104 BCD crankset and chainring from eBay. This took some searching but I found a new Prowheel Zephyr 238A crankset for about £20 then bought a new Deckas 44T chainring for under £10. Both of these are at the cheap and cheerful end of the market, but then my bicycle is a 2020 Pinnacle Lithium 1 that only cost £300 (about the same as your bicycle).

And I'm very pleased with the result. The new crankset and chainring fitted perfectly and make the bicycle far more enjoyable to ride.

I note other answers have pointed out that your frame may limit the size of the chainring you can fit, but I'd be surprised if this was an issue on an entry level bicycle. Even if it is, once you have the 104 BCD crank fitted you can try different chainrings to find the best as it's quick and easy to swap chainrings.

In my case I wasn't increasing the chainring size very much. I went from 40T to 44T and I didn't need to change the chain length. You would be making quite a big change so you may find the existing chain is too short and pulls the derailleur too far forward so you need to either extend the chain or buy a new chain. In any case, if you're spending money on a shiny new chainring it wouldn't hurt to get a new chain to go with it.

For interest, this is the crankset and chainring I used:

My bicycle has the same seven speed freewheel as yours (14 - 28) and I find a 44T chainring ideal. Fifth gear is fine around town while seventh is high enough to be usable down hills.

Now you have identified your bicycle as a Schwinn Boundary 29 I managed to find a picture of the chainring:

Note that there is a depression in the frame to clear the chainring, and any new chainring you fit would have to be small enough to fit in this depression. I've marked the space available with a red arrow. A 44T chainring has a radius 50% greater than your 30T chainring so it might just about fit. You'll have to measure your current ring carefully to check.

Your bike uses square taper fittings for the crankset, which is fairly standard for cheap cranksets, so a crankset like the Prowheel I used will be suitable.

The Schwinn Boundary 29 looks a nice bike for the price, so I wouldn't worry about spending small amounts of money to upgrade it.