3 rings or 2

[sneaky beaky]

I'm training for my first sportive, I've been building up to roughly 30 mile rides (hilly area) - sometimes twice a week using an old Raleigh light weight.

Currently the group set is all vintage shimano tri colour - works beautifuly, 8 speed - downtube shifters etc -
I love it...however

Keep doubting my ability to climb very steep hills after say 2 or 3 hours riding and might benefit from a so called 'granny cog' or triple crankset as a back up for my knees & confidence

Could anyone advise me please if there's a known compatable triple cranset to work with the 8 speed tri colour set up ?

cheers

 

[mjr]

I think the front derailleur of tri colour 8 speed is FD-7400 series which is listed as 15 tooth difference so it probably won't work, or at least you couldn't have three rings with different enough sizes to feel like triples I've used before. Sorry.

What I don't understand is Shimano made a 13-34 rear cassette group K for 8-speed but the companion rear derailleur RD-7400 is for 26-tooth maximum rear, which is a long way below 34... Hopefully someone who understand this better will be along soon!

 

[sneaky beaky]

Thanks - i'm using a hyperglide on the rear its a 11-30 and maybe not very efficient. The front mech i think is a fd-6401

 

[Elybazza61]

What size are the chainrings? You could get smaller ones if they are not compact sizes.

 

[T4tomo]

You are possibly on a 52-42 chain set there - count the teeth to check- in which case some new chain rings on the front, swap the big for 50 and the little for a 36 or 34.

Switching the 52 doesn't impact the lower gears, but you need to keep the jump between chainrings manageable over wise the front shifting will be rubbish. Given you have a 30 on the back I'd be tempted to go 36. If current is a 42 you'll notice a big difference.
SPA cycles is a good place to source replacement chainrings.

 

[mjr]

Thanks - i'm using a hyperglide on the rear its a 11-30 and maybe not very efficient. The front mech i think is a fd-6401

I can't find the 6401 but http://www.disraeligears.co.uk/Site/Shimano_Bicycle_System_Components_-_1989_scan_16.html says the 6400 is 14 tooth difference, too.

As noted above, you could lower the gears by using smaller chainrings, especially if the derailleur is the band-on rather than braze-on type and can be moved down easily. 14 tooth difference means you should use 50-36 at most, but 50-34 might work despite it exceeding the spec.

 

[sneaky beaky]

Thats great news, yes its 52-42 and a band on fd ☺

Thanks for the advice, i'll get some new rings sorted

Cheers

 

[Gravity Aided]

I can't ever remember a three ring FD for the 600 tricolor, I still have that gruppo on my Trek 600 (1985). Works great, fine indexing, but I'm pretty much running a corn cob on the rear cogs. I too would suggest compact, if necessary.

 

[Nigelnaturist]

If its a 52/42 chances are its not a compact chainset, you need to determine the Bolt Centre Diameter by measuring from the centre of one bolt to the next like this

Then convert that using the chart here
http://www.sheldonbrown.com/cribsheet-bcd.html

I suspect its likely to be about 130mm BCD which means the smallest ring that can be fitted is a 38th.

When a chainset is referred to as a compact its the BCD that is referred to and this is commonly 110mm, I have a triple compact with a 110mm and a 74mm inner.
@sneaky beaky as for referring it to a granny cog, I can actually set my inner ring up so it has quite a high low gear i.e 28x23 = 32.3" your 42x30 is 37.1" if you did fit a 34 inner with your 30 rear it gives a 34x30 or 30".

 

[Hugh Manatee]

I have fitted a 38 tooth small ring on my 130 BCD chainset. I'm not sure how much lower you can go. I refer to it as the compact.

 

[Nigelnaturist]

I have fitted a 38 tooth small ring on my 130 BCD chainset. I'm not sure how much lower you can go. I refer to it as the compact.

38th is as small as can be fitted, as I said a compact refers to the BCD size, there is no reason you can't fit a 52/42 or as I had on my 130mm bcd chainset a 40th, to a 110mm they are available, though as the rings are further from the bolts it will lead to a bit more flexing in the rings all be it very minutely. Its why i love my square bracket chainset possibilities are endless.

 

[sneaky beaky]

Darn it...just got home, checked the inner ring and it's a 39 - the BCD is 130 so according to sheldon best I can do is 38 tooth inner, probably not worth the change I guess ?

Thanks again for all the input, much appreciated

 

[sneaky beaky]

@mjray the FD-6401 is the 8 speed version it turns out

Thanks

 

[Nigelnaturist]

Darn it...just got home, checked the inner ring and it's a 39 - the BCD is 130 so according to sheldon best I can do is 38 tooth inner, probably not worth the change I guess ?

Thanks again for all the input, much appreciated

If its a square taper, Spa do a crank set for about £20 middle on a triple £15 outer £20 inner a £10 well last time I looked, nice they look too. This is a triple with a 50/38/26, but you can get doubles.

 

[sneaky beaky]

Many thanks for the input - just ordered a Stronlight 50/34 crank from Spa cycles, very pleasant to deal with.

Looking forward to this weekends hill training

All the best