suntour cyclone front derailleur capacity

[sveno]

Hello there,

I am currently considering the upgrade of an old ten speed to a machine that would allow me to dash up the slopes of Mount Ventoux this summer. It is equipped with Suntour Cyclone Mk I derailleurs, and even though I was a bit sceptical at first, I am quite surprised to find that they are actually quite good, better than the Shimano 600EX on my opinion.

Now, I recently found a nice Stronglight 106 triple crankset (52 - 44 - 34) from back in the day, and as the Cyclone front derailler has a capacity of 18, I thought that I was a lucky man, as 52 minus 34 is 18. However, before I started to demount the double crankset, I took a look at a manual for bike mechanics from 1980, and it has all kinds of information on the components that were around back then. It states that the Cyclone Mk I front derailleur has a capacity of 18 all right, but that this count starts at 53. Which would come down to 35 for the lowest. Which means that it is not fit for the purpose I'd like to use it for.

I believe that they are talking about the max diameter for a chainring. The rest depends on where I fix the derailler on the downtube. Would you agree with that?

Cheers,

Sven

 

[RecordAceFromNew]

IMHO the max ring size spec for front mech is only of limited relevance, especially when you are deviating by only 1 tooth.

If your existing large chainring is very close to 52, you might not even have to move your front mech up/down. Each tooth difference represents a change in radius of 2mm.

Depending on your rear mech and existing chainset range you might find that your existing rear mech does not have enough wrap capacity though.

 

[sveno]

IMHO the max ring size spec for front mech is only of limited relevance, especially when you are deviating by only 1 tooth.

If your existing large chainring is very close to 52, you might not even have to move your front mech up/down. Each tooth difference represents a change in radius of 2mm.

Depending on your rear mech and existing chainset range you might find that your existing rear mech does not have enough wrap capacity though.

I completely forgot about the wrap. That is going to be tricky, as the rear derailleur can cope with 24 while the setup would require 28. No good.

 

[RecordAceFromNew]

I completely forgot about the wrap. That is going to be tricky, as the rear derailleur can cope with 24 while the setup would require 28. No good.

Depending on how you got the 24 limit figure of course, but if it is just a published figure, this might give you some hope.

You can also kind of figure out, assuming neither large are going to be changed, first step is to examine on large/large if the chain can be shortened, second step with the chain split on top see with B-screw adjustment when on small/small whether a suitably longer imaginary chain (by range increased number of links minus number of links chain can be shortened) can still remain under tension. This is a hopeless description! But maybe you got the idea.

 

[heretic]

I still have a Cyclone front mech on an old Claud Butler tandem hung up in the shed. It was originally equipped with an SR 50/36 double chainset (Compacts, New??) but later upgraded to a TA 52/40/30 triple. This was with downtube friction levers (and an Ultra6 13-32 screw-on rear block). The front mech coped fine with both chainsets.

 

[sveno]

Thanks recordacefromnew, that is very interesting. I am not sure if there is something like that B screw on a Cyclone, but I guess I will try to spin the derailleur a little backwards. Even if it should not work for the 34-14 this would be a big progress.