New Cassette

[shunty]

mmm interesting, i didn't know that. why is that? is it due to the cage size?

Something to do with that. Combination of cage size/width of 3 rings and the difference in teeth numbers between smallest and largest ring. All depends on make/model/type etc as to whether you could get away with it.

 

[RecordAceFromNew]

mmm interesting, i didn't know that. why is that? is it due to the cage size?

I think Potsy has a road triple front mech (possibly a sora), they generally have official capacity of 20T, and a triple chainset of 50/39/30. So while his chainset is probably 74BCD and if so can theoretically take a granny down to 24T, he will have to keep tab on how far he can push his front mech (as well as his rear mech).

I am guessing now but since he is running a triple up front already the Tiagra rear mech would practically inevitably be the GS/mid cage model, with an official wrap capacity of 37T. If 20T of that are taken up front he has an available range of at least 17T and most likely 20T or more available at the back due to spec conservatism, meaning if his frame allows it (which can be checked per measurement I mentioned above) then e.g. a 11-30 should work just fine.

If there is any concern about chain length, it is easy to work out exactly how many links are needed before ordering one. It is highly unlikely that any will come too short.

 

[Rohloff_Brompton_Rider]

I think Potsy has a road triple front mech (possibly a sora), they generally have official capacity of 20T, and a triple chainset of 50/39/30. So while his chainset is probably 74BCD and if so can theoretically take a granny down to 24T, he will have to keep tab on how far he can push his front mech (as well as his rear mech).

I am guessing now but since he is running a triple up front already the Tiagra rear mech would practically inevitably be the GS/mid cage model, with an official wrap capacity of 37T. If 20T of that are taken up front he has an available range of at least 17T and most likely 20T or more available at the back due to spec conservatism, meaning if his frame allows it (which can be checked per measurement I mentioned above) then e.g. a 11-30 should work just fine.

If there is any concern about chain length, it is easy to work out exactly how many links are needed before ordering one. It is highly unlikely that any will come too short.

oh ok i didn't realize potsy had a triple, kinda makes my comments redundant, sorry potsy.

but the comments have helped me coz i'm on 105 5700 compact groupset, now i know what my options are once it comes to new cassette time.

cheers

 

[RecordAceFromNew]

cheers

Now the race is on to find the right 9 speed cassette. This undercuts HLaB's by more than £2!!!

 

[HLaB]

Now the race is on to find the right 9 speed cassette. This undercuts HLaB's by more than £2!!!

 

[PpPete]

Based on my experience a Medium cage Shimano road mech (like the Tiagra) can handle at least 30 T - even with a triple on the front. I've read that some people have made them work with 11-32 MTB cassettes but that might be pushing your luck.

I've butchered 2 x £15 9 speed cassettes (11-32 and 11-34) to get suitable sprockets to build up a 12-30.

N+1 might be Campag - in which case 13-29 becomes a possibility .....

 

[RecordAceFromNew]

I've butchered 2 x £15 9 speed cassettes (11-32 and 11-34) to get suitable sprockets to build up a 12-30.

Good point PpPete! Provided they are not cnc'ed from a block of metal or bolted on to adjacent sprocket

It is funny how the ratios one wants are never available. There are a few things in this business where things have gone backwards, the disappearance of take-your-pick ratios and reversible sprockets come to mind.

ps Actually Pete's suggestion reminds me that according to this Shimano and Sram 7, 8 and 9 speed sprockets are practically of the same thickness, so perhaps one can buy this Sram 11-30 for the princely sum of £9.96 currently for a Shimano and Sram, old and new, mix and match?

 

[potsy]

Thanks for all the help, it is as you thought a Sora triple 30/39/50 with a Tiagra 12-25 cassette.
I like the idea of an 11-28 Sram one like the one you have linked to, one question- How big will the gaps be between gears? Currently I have a gap of 2 teeth maximum I'm guessing it will be spaced out a bit more and not all at the low end like my Shimano Mega-range 14-34!!

Bromptonfb- How did you not realise I had a triple? You've seen the ease in which I get up those hills

Don't usually buy off Flea-bay but might have to make an exception this time

 

[Rohloff_Brompton_Rider]

Bromptonfb- How did you not realise I had a triple? You've seen the ease in which I get up those hills

sorry dude, you were using 24" for most of them......

 

[RecordAceFromNew]

I like the idea of an 11-28 Sram one like the one you have linked to, one question- How big will the gaps be between gears? Currently I have a gap of 2 teeth maximum I'm guessing it will be spaced out a bit more and not all at the low end like my Shimano Mega-range 14-34!!

Potsy in case there is any misunderstanding it is not a sram but a BBB cassette. The ratios are here and look normal to me. What you could do is to enter the ratios of front and back into this and see how the steps change (compared to existing e.g.). I have never bought from fastpartsforbikes on ebay, and there is a reputation historically in bikeradar e.g., but on the other hand the ebay feedback score since late 2008 seems excellent.

 

[potsy]

Potsy in case there is any misunderstanding it is not a sram but a BBB cassette. The ratios are here and look normal to me. What you could do is to enter the ratios of front and back into this and see how the steps change (compared to existing e.g.). I have never bought from fastpartsforbikes on ebay, and there is a reputation historically in bikeradar e.g., but on the other hand the ebay feedback score since late 2008 seems excellent.

Not very well thought of is it?

I am leaning towards the Sram 12-26 now, slightly lower gear and hopefully as my weight comes down my performance will go up.
Right, just got to check my credit card bill to see how much I have to spend

 

[Garz]

Seriously mate I wouldn't bother going from 12-25 to a 12-26 even if Colin's adept map skills are taking you over some acute terrain. Wait for a better bargain and aim for a 12-27 or 11-28. The larger gaps are not that noticeable but you will be glad of the 27/28 one day!

 

[potsy]

Seriously mate I wouldn't bother going from 12-25 to a 12-26 even if Colin's adept map skills are taking you over some acute terrain. Wait for a better bargain and aim for a 12-27 or 11-28. The larger gaps are not that noticeable but you will be glad of the 27/28 one day!

If I didn't need a new cassette anyway I wouldn't bother Garz, but I know this one is worn now so might as well get a slightly lower geared one as part of my ongoing upgrade of the bike.
Have got 105 brakes, better wheels, so next is the drive train, thinking Tiagra crankset and this new cassette.

I could always work a Saturday morning to pay for some of the parts but that thought brings me out in a cold sweat

Anyway, once our new fitness regime kicks in I might never use the lower gears

 

[Garz]

Ahh tbh mate I overlooked your last one was worn out (thought colin was making you sweat on the old route terrain). The 12-26 will do the job then just hope you get a reasonable price!

 

[potsy]

Ahh tbh mate I overlooked your last one was worn out (thought colin was making you sweat on the old route terrain). The 12-26 will do the job then just hope you get a reasonable price!

Oh he is Garz, he's got a 28t on the back so can spin merrily up the hills while I walk at the side of him