Change from standard to compact chainset

[thefensman]

Hi all, been riding a while and am begining to do more climbing now but i,m struggling a little with my current set up which has standard chainset (double 9 speed). To try to improve situation i am thinking of changing to a compact double. Existing groupset is currently full Tiagra 9 speed with square taper bb. I have been looking at fitting hollow tech compact crank but just want to know if I will need to change anything other than the bb and fit new double Tiagra compact cranks

 

[Sharky]

What's you current ring sizes and largest sprocket on the rear?

Keith

 

[smokeysmoo]

A cassette with larger sprockets, (upto 32T), may help and would be a lot cheaper.

Just check your rear mech will handle it.

 

[thefensman]

Hi sharky/smokeysmoo, thanks for reply. Not at home right now so can,t be 100% but I think front is 52/42 and large on rear is 25. Will check later and post any changes. Cheers .

 

[jay clock]

If newish you are probably on 53/39. Need not be hugely pricey, probably under £100. I am one who did exactly that. One thing to look for is if the from mech mounts to a brazed on mounting, can it cope with the smaller chainrings?

 

[Sharky]

As Smokey says, changing the cassette for one with a larger bottom cog would help. Also changing the inner to something a bit smaller. I think you can fit a 39 tooth inner.
http://www.sjscycles.co.uk/shimano-105-fc-5700-130mm-bcd-5-arm-inner-chainring-silver-39t-prod27663/

This two together will give you a couple of lower gears and would not upset the front changer too much. If changing the cassette, you will probably need a new chain as old & new stuff often causes the chain to jump sprockets.

Good idea to get a quote from your LBS as it might not cost as much as you think for the labour and it will come out running smoothly.

Good luck

Keith

 

[thefensman]

hi again, just got home and checked a few things and chain rings are 52/42 and large cog on rear is 25. I do all work on my bikes myself but gearing still baffles me , i understand the basics of large wheel at front and small at back = better flat gearing and vice versa better climbing, however working ratios etc just makes me run up a white flag so all your suggestions will be useful. Just had a rummage thru my parts box,s an have found a shimano fit 11/34 cassette in pretty good nick and was wondering if i could utilise this along with a smaller inner ring. Forgot to add front mech is band on so dont know if this will help. Cheers

 

[jay clock]

what bike is it and how old? That is an unusual set up for a modern bike, so it may be older, in which case you may not want to spend a lot

Someone else can advise but a quick look showed some reasonable Sora level kit for about £40-50

 

[Sharky]

If you have a spare cassette, you have nothing to lose if you try it. 52.11 will be a bit big though.

If both cassette body's are the same, you might be able to inter mix them and make up a more even range. You shouldn't need any smaller than a 14 for normal riding.

Good luck,
Keith

 

[thefensman]

hi again, i ride a carrera valour but theres basicly just the frame thats original as i,ve changed every thing ( i do like to get my tools out). as for age its a hard one as i,ve bought a lot of stuff new and some used, drive train is Tiagra, sti gears and Tiagra hubs. Carbon forks and seat tube and Bontrager racelite bars and stem.Etc,can,t fault it and its served me well but like i say i am starting to do a little more climbing and it just falls abit short. I also have a carrera mtb with compact 8 speed which i use on the dirty stuff but which climbs easier than the road bike hence my asking about a compact conversion. Hope this helps.

 

[KneesUp]

Band on is good because you can adjust the height of the whole thing if you need to - e.g. if both chain wheels are smaller.

You need to take into account the total capacity of your rear mech.

Total capacity = (No teeth on big cog in cassette - No teeth on small cog in cassette) + (No. teeth on big chain ring - No. teeth on small chain ring)

At the moment your set up needs a capacity of (25-12(?)) +(52-42) = 13+10 = 23

If you put the other cassette on you will need a capacity of (34-11)+(52-42) = 23+10 = 33

If you use the other cassette and get a compact you will need a capacity of (34-11) + (50-34) = 23+16 = 39

The total capacity of your rear dérailleur should be marked on it somewhere - 33 might be too much if it's a short cage one.

 

[thefensman]

If you have a spare cassette, you have nothing to lose if you try it. 52.11 will be a bit big though.

If both cassette body's are the same, you might be able to inter mix them and make up a more even range. You shouldn't need any smaller than a 14 for normal riding.

Good luck,
Keith

hi, with regard to the 52 front thats partly why i was gonna do the compact change over. I dont mind spending a few quid and i reckon i could do it for around £70 with new parts. All i need to know is, is it workable with the remaining gear i have ie mechs and cassette. Cheers again.

 

[thefensman]

Band on is good because you can adjust the height of the whole thing if you need to - e.g. if both chain wheels are smaller.

You need to take into account the total capacity of your rear mech.

Total capacity = (No teeth on big cog in cassette - No teeth on small cog in cassette) + (No. teeth on big chain ring - No. teeth on small chain ring)

At the moment your set up needs a capacity of (25-12(?)) +(52-42) = 13+10 = 23

If you put the other cassette on you will need a capacity of (34-11)+(52-42) = 23+10 = 33

If you use the other cassette and get a compact you will need a capacity of (34-11) + (50-34) = 23+16 = 39

The total capacity of your rear dérailleur should be marked on it somewhere - 33 might be too much if it's a short cage one.

hi there, almost had the white flag out there but have read your post a couple of times and think i get your drift, NO meaning number of teeth yes, if so i,m with you, but will need to take a look at my deraillear.

 

[thefensman]

As i,ve said i dont mind doing work myself so thats not a problem, and although i aint loaded i dont mind spending on my bikes ( wife hasn,t a clue) so really i just need best option to get me climbing better, apart from more hills of course but i don,t want to be hitting them and not giving myself the best tools i can to nail them. Hope that makes sense. Cheers.

 

[KneesUp]

hi there, almost had the white flag out there but have read your post a couple of times and think i get your drift, NO meaning number of teeth yes, if so i,m with you, but will need to take a look at my deraillear.

Yeah, sorry No = number

I had a quick search for Tiagra, and found that there are versions with a capacity of 31 or 37 - • Total Capacity 31T (SS)/37T(GS) but obviously it might be different for the model year of your groupset. Shimano are normally quite good at putting the info on the cage somewhere.

http://www.chainreactioncycles.com/shimano-tiagra-rear-mech-9sp-4500/rp-prod19461