andy753

I am recovering from a major knee rebuild (I had a really bad ski crash!) and have decided to ride the Bike 4 Cancer London to Brighton bike ride on 6 September 2015 in memory of my dad but also as a rehabilitation ride after my surgical operation. If anyone else would like to join us, get more info at: https://www.bike4cancer.org/london-to-brighton-bike-ride

I am very worried about Ditchling Beacon though. Having ridden the route several times before, I know that my knee will be very sore if I don't have some gentle gears up my sleeve.

I am currently running a Tiagra triple up front (50/39/30) with a 9 speed cassette (12 to 27) via a Tiagra RD-4500 long cage rear mech. This is going to sound really pathetic but this is not enough at the moment while my knee recovers! Does anyone know if I can run a bigger sprocket at the back? Alternatively I could run a smaller chainring up front but I can't find any info on the Shimano website of the crank FC4503 can take smaller than 30T!

Many thanks in advance for your help.

Mr IGH

- Shimano road triples are a mixed bag. The some of the newer triples use a weird, unsupported BCD on the inner ring (92mm?), there's no way to change it to a smaller size. The older Tiagra 4503 has a 74mm BCD, the newer 4603 has the stupid 92mm BCD that forces one to have a 30T minimum inner chainring. I just bought a Shimano 105 5703 crankset and it has a 74mm BCD on the inner ring.

The 74mm BCD allows easy-to-source 28T, 26T and 24T chainrings, ideal for touring:

https://www.bikeforums.net/touring/10...ad-cranks.html

gsa103

The exploded view from Shimano's tech docs shows that the inner chain ring is removable. So you can likely replace it with any 74mm BCD chainring. I think the smallest is 24t, you might be able to find a 22t. Shifting may not be perfect, but it'll work well enough.

When you install the new ring, don't shorten the chain, since it should be sized for big-big. What this means is that your chain will go slack in the small-small combination. A minor annoyance but acceptable.

cale

Just walk that hill.

fietsbob

This, .. Just take your Time..


Touring I've done that even with a 24:32T Low.

MRT2

Don't know if you can swap your small chainring on your Shimano crankset, but I do know cranksets with smaller chainrings exist because I have one. I am using a Sugino triple 26 - 36 - 48 tooth chainrings.

davidad

Put the 24t on and enjoy the lower gear.

berner

I have a Tiagra triple, 50-39-30 also, except I've replaced the 30T with a 26 tooth. I've lowered gearing further by inserting a 30t in the cassette for very low gearing. Don't need it often but when I do, I'm very glad it is there. Best wishes for the ride and with rehab of the knee. I've brought my downhill ski career to a close before wrecking the knees. Now I play in the snow with cross-country skis and look forward to sliding through through the woods at a much slower speed.

Gnosis

The Tiagra FC-4503 crankset has a 74mm bolt pattern for its 30-tooth chainring, which means you can go as low as a 24-tooth via its 74mm bolt pattern.

This confirms the info I’ve provided:

SHIMANO Dealer's Manual / User's Manual

Just scroll down and click on FC-4503 and Open the file.

agenkin

Where do you guys buy your sub-30T 5-bolt 74mm BCD chainrings? I've looked around and it seems that anything less than 30T comes in a 4-bolt variant for MTB cranks. I have a 5703 crank and would like to replace the 30T with a 24T.

SkyDog75

This should work for you:
https://www.benscycle.com/p-13416-su...d-silver.aspx?

Niagara Cycle carries 'em, too. I don't know which vendor is more convenient when it comes to shipping across the border.

HillRider

This is correct. The OP is lucky that he has the FC-4503. The later "updated" FC-4603 Tiagra triple has the granny ring bolted to tabs on the 39T chainring with a 92 mm BCD and a 30T is the smallest that will fit.

djb

I have changed out 30 grannies to 26t on two bikes with 74bcd on FSA cranks. In both cases I chose 26 to keep the tooth diff to 13 between granny and the 39 chainring. I rode a bike for years with a 16t jump from a 24 to a 40 and personally prefer smaller than 16t diff.
Even with a 39 to 26 downshift, you generally have to shift up 2 gears at back, sometimes 3.

Note** with the profile of the FSA 30t grannies, the flat 26t rings I bought had to be shimmed out about a mm for proper operation. I used household washers that I had in a washer kit, this moved the ring slightly away from the inner part of the crank, as the original 30 rings had a slight bowed out section, and the 26 I found were flat. So I had to improvise with the washers as spacers.

I like the 50/39/26 set up, and also usually have a 9sp 12-27 on, but switch to a 11-32 and a longer chain when I tour with panniers on or in really steep stuff. My bike weighs nearly 30lbs so 25 gear inches of the low gear works well for my knees.
--both the 50/39/30+11-32 and. 50/39/26+12-27 give a low gear of about 25 gear inches, given your knee issue, I'd recommend that has a minimum, even if your bike weighs less than my bike. Low gearing is always a big advantage.

djb

Forgot to add, check out what is the maximum tooth cassette your rd can take for also possibly putting a large cassette.
Also, of you do change to a smaller granny, read up on total gear capacity etc for rear derailleur s, and re the comment on chain length, ALWAYS keep chain length safe for the large-large combo. Even if you never think you'll do it.

HillRider

I've done the same as you and changed the 30T OEM granny ring for a 26T on numerous Shimano 8, 9 and 10-speed cranks and even on a 10-speed Campy triple crank, all with no problems. This usually exceeds the published rear derailleur's wrap capacity but all that does is sacrifice the small-small gear usability assuming you do the proper chain sizing and assure it will allow big-big. Small-small is useless anyway and inadvertently shifting into it only makes a bit of noise but does no harm.

Gnosis

If I were the OP and dealing with knee surgery recovery, I’d opt for the 24-tooth chainring especially since his largest rear cog is only 27-teeth. It's better to have an easier gear than one that's potentially invoking pain.

bikemig 

If you go with a deore m591 rear derailleur, you can run as large as 34 tooth in the rear.

Camilo

I put an 11-32 cassette (or so, maybe bigger) on my wife's 9 speed Tiagra bike. I replaced the original 105 GS rear derailleur with a Deore I had on hand. I'm pretty sure the Deore is 8 or 9 speed. It works perfectly and her lowest gear is 30X32 which she loves.

If you go low grade and/or used for the parts, it will be a cheap and easy solution.

As an alternative, on my commuter I have Ultegra 6503 parts on it and simply found a cheap, used 44-XX-24 crank (can't remember what the middle ring is, but it's typical). That also works perfectly with the Shimano 9 speed triple shifters and FD. The crank is just an old unramped thing I found on ebay (intending to try it and then maybe upgrade if I liked it), but it works just fine so I haven't bothered to upgrade.

nfmisso

or if you choose the M592 RD; you can go with a 12-36 cassette.

I would change the 30T to 24T and the RD to a M592. NOTE: you need to change your chain when you replace the cassette - and it needs to be longer if you increase the maximum number of teeth.