fmilovanov

I all - I have a bike with 4700 Tiagra groupset, and I want to have a bit more push when I am riding uphill to my home. I have 11-28 cassette, and the obvious solution is to buy -30 or -32 cassette. But what if I instead replace "lower gear" on a crankset with a thingy with 30-32 teeth (instead of 34 now), so I have more torque when riding uphill? First of all - is it possible to do, second - is it smart/stupid idea to do, third - what would the name of this part, and forth - is it possible to replace it myself, or I'll need some special tools?

I don't what to replace the entire crankset, just the "lower gear" thingy.

CliffordK

Look at the distance between the bolts (and spider) and the teeth. It is likely bolts are quite close to the teeth...

So, assuming a 5 bolt spider, it is probably 130 BCD (oops, meant 110BCD, but see below, probably is 4 arm). You may be able to find a 33T chainring that would work, but nothing smaller.

Generally no special tools are needed, just an Allen Wrench. There is a tool to hold the back side of the chainring bolt, but it is usually not needed.

To go smaller, than 33T, you would have to change the crankset, or go with a triple (or triplizer).

DrIsotope

Tiagra FC-4700 crank is Shimano 4-bolt 110BCD asymmetric, so you are generally limited to a 34T inner ring. Some boutique companies like Wickwerks make a 33T, but their 41/33 ring set costs as much as just buying a new crankset. The FSA Omega Adventure is 46/30 and runs about $130.

Going to a 12-30 or 11-32 cassette is an option, if your rear derailleur will accommodate it. Many will, some won't. The 12-30 should be fine, my wife's bike ran a 12-30 for years on a Shimano RD spec'd at a 28T max.

kcblair

I have Tiagra 4700 , on one of my bikes, and the drive train came with 11-34 cassette, with the Tiagra 4700 RD. Much less expensive to change cassette than mess with crankset. KB.

fmilovanov

All - I see your point, but while googling for 46/30 Crankset I found this (honestly, was looking for Crankset): AbsoluteBLACK Sub-Compact Oval Road Chainring. One of those is 30T, and they claim it fits 4700.

Any thoughts? Again - the idea is only to replace my 34T one, not the 50T.

DrIsotope

From Absolute Black:

IMPORTANT:

• Due to very special offset construction and custom bolts:
• 30T can only work with 46T and special bolt set 46/30. (bolts included with small ring)
• 32T can only work with 48T and special bolt set 48/32. (bolts included with small ring)
• No other combination or mix of rings will work.

fmilovanov

Hmm..... got it

Racing Dan

30/28 is almost exactly the same as 34/32 > Get an other cassette, 11-32 or 11-34, and possibly a new rear DR.