Commuter Conversion, help with shopping list please

[Rubber Bullets]

My trusty '96 (ish) Specialized Stumpjumper doesn't get used for any real off roading any more, and having come off my skinny tyred road bike a couple of times last winter, I have decided to modify the Stumpy as a wet weather commuter.

What I would like to do is fit rigid forks, probably these, or something similar (I was after sone Kona Project 2's but they seem to be out of stock everywhere!), and then fit a larger chainring set, probably a 48 tooth big ring, and a set of full mudguards. My bottom bracket is also making an awful noise at the moment, and so I would change that at the same time.

What chainset and B would you suggest, how do I know what size to get?

Do I need a new front mech? If so, again, how do I know which one?

Do I need a new chain?

My old forks are Judy T2's by the way.

What further info would I need to offer in order to get the answers above?

Many thanks for any help offered.

Budget negotiable, but around £200 would be good.

RB

 

[Tim Hall]

Could you fit a 48 tooth ring to the existing chainset? That'll save a few bob. What BCD is it?

If you can, I would have thought the same length BB as the one you have now should work.

How worn is the existing chain? Measure 12 links and see how far over 12 inches it is.

 

[Rubber Bullets]

Thanks Tim,

I'm sorry but I'm not sure what BCD is though

The question over the chain was more from the point of view that the larger chain ring would need a longer chain, not wear.

RB

 

[Rubber Bullets]

Thanks Adrian,

Hadn't thought of just one front chain ring. My cassette is 11-30 so I wonder if 48-30 would be small enough for the hills round here? Maybe.

I have 5 bolt cranks that appear to have a BCD of 94mm according to my measurements (possibly not entirely accurate).

Is the BB length the only measurement I need worry about, is diameter fairly standard?

Thanks again.

RB

 

[Piemaster]

Budget for tyres too. Set of slicks will probably make the biggest difference to how the bike feels and commuting times

 

[Tim Hall]

That BCD sounds right. See the table here to check http://www.sheldonbr...gloss_bo-z.html.

What chainset (cranks and chain rings) do you have on there at the moment? How many rings? How many teeth?

BB diameter is more or less standard. A crispy fiver says yours is English threaded, most likely 68mm shell width. The shell is the bit of the frame it screws into. I'm guessing given the age of the bike it's a square taper - the "axle" that the cranks fit onto is square in section and, um, tapers. The hole in the crank is tapered too. Doing the crank bolt up Nice and Tight ensures the crank stays on. There are two tapers in use, JIS (Japanese Industrial Standard) and ISO (International Standards Organisation). You've very very likely got a JIS BB and crankset.

Good point about needing a new chain because of the bigger ring. You might get away without, but as Adrian says a new chain is always nice when fitting other drive train bits. If it is badly worn (length more than 12 1/8 inches) you could well be looking at a new cassette as well. Casette tend to wear quicker than chain rings and will wear to match the elongated, worn chain. A shiny new chain will tend to skip if the cassette wear is to much.

 

[RecordAceFromNew]

BB diameter is more or less standard. A crispy fiver says yours is English threaded, most likely 68mm shell width.

A crisp fiver? Mmmm I bet it is a 73mm bb shell with English thread. The OP should measure it.

If the chain is newish, you can use a chain length calculator to work out whether a new chainset/chainring needs a longer chain. Theoretically you need two extra links for every 4 extra teeth, but that is assuming the chain is just long enough currently.

The only reliable way to find out what replacement bb is needed is to find out what is there already, if that is not possible then one can make a reasonable guess by knowing the exact make/model/code of the existing chainset. BB comes in all sorts of spindle types, lengths etc. and must match the chainset, and to deliver the right chainline especially if there is a front mech which it must work with, and the right clearance so the chainset does not clash with the frame/chain stays.

It might be worth considering simplifying the system to a 1xN set up (i.e. a single ring chainset, no front shifter or mech or cable). You could probably drop 400g that way.

Alternatively/additionally the way to get lower gears for hills is to switch your cassette to e.g. a 11-34. New 7/8 speed cassettes are inexpensive.

My advice is don't worry about the bb or chain until you have decided what gearing and therefore chainset/cassette combination you want.

Regarding front forks, I think Judy T2 circa 1998 will have an A2C (axle to crown distance) of around 440mm +/-10mm. It is worth measuring it so that replacement forks will deliver roughly the same geometry ensuring handling is not too drastically affected. The T2 is pretty light weighing around 1.6kg so if weight reduction is the key motivation you might want to look for something lighter than the P2 (which weighs from 900g to 1200g depending on vintage and steerer length).

 

[wakou]

WOW I have saved "RecordAceFromNew" as the "go to guy" for knowing about stuff. Chapeau....

 

[Rubber Bullets]

Many thanks for all the advice guys, there was me thinking this would be simple .

I've attached a couple of images that might help, with regard to the BB I might be best going to the LBS and getting one straight from there.





I'll work out the gear inches that 48-30 would give and choose the closest ratio I already have and see if I can get up the hill to my house. Although very short it is by far the steepest bit of any ride.

I'll measure the forks, too just to check, the Surlys I linked to appear to be 413mm, I assume I measure this from the bottom of the head tube to the axle? The reason for changing is as much about a more responsive ride than weight, though any little helps.



Thanks again


RB

 

[RecordAceFromNew]

I'll measure the forks, too just to check, the Surlys I linked to appear to be 413mm, I assume I measure this from the bottom of the head tube to the axle?

Ideally you should assess the geometry with sag. See this.