Suntour ARX rear derailleur pull ratio

[fastpedaller]

Long story short.... I am using Shimano 8 speed bar end shifters with an altus rear mech on 7 speed - it works great. I have in my garage a rather nice Suntour ARX rear mech which I fitted on the bike when I first built it 4 years ago, but only used it briefly because the Shimano bar end shifters wouldn't hold on friction mode when I was going hard uphill! I'm contemplating selling the Suntour ARX rear mech, but would like to keep it (it is a rather nice bit of engineering imho) but only if it will work with the index shifter (aside from the lever won't hold in friction mode, I'm now a convert to index shifting!). Does anyone know if the pull ratio of the Suntour ARX will match the Shimano bar end shifters?

[rjb]

This mech predates indexing. It was designed for friction shifting and has no fine tuning of the cable tension. You could try an inline cable adjuster but you may have to suck it and see if it would work with an indexed system.

http://velobase.com/ViewComponent.aspx? ... 0&Enum=108

Let us know how you get on. it's a nice mech, I've got one somewhere in my spares drawer.

[fastpedaller]

This mech predates indexing. It was designed for friction shifting and has no fine tuning of the cable tension. You could try an inline cable adjuster but you may have to suck it and see if it would work with an indexed system.

http://velobase.com/ViewComponent.aspx? ... 0&Enum=108

Let us know how you get on. it's a nice mech, I've got one somewhere in my spares drawer.

If I'm correct, the fact it predates indexing doesn't necessarily create an issue (likewise the fine tuning except on initial setup) - but what is important is that it moves by the correct amount (as dictated by the lever indexing and the ratio of cable pulled c/f sideways movement). I think that's correct

[Brucey]

I have heard tell of older suntour mechs working Ok with some indexing systems, but I don't recall if ARX was amongst them.

cheers

[fastpedaller]

Update.... Measurement indicated the pull ratio for Shimano Altus is 1:2. Similarly the ratio for the Suntour ARX comes out at 1:1.5 - so no-go as far as indexing with shimano IMHO.

[Brucey]

Update.... Measurement indicated the pull ratio for Shimano Altus is 1:2..

shimano 6/7/8/9s is usually quoted as 1:1.7.

cheers

[fastpedaller]

The 7 speed cassette measures 32 mm , and a 'flag' of masking tape secured on the gear cable where it enters the cable guide on the chainstay moves 16mm when going from smallest sprocket to largest. Is there any other thing I've missed? - I can't think of any other way to measure it.

[Samuel D]

The 7 speed cassette measures 32 mm

More like 30 mm, surely, since the pitch is 5 mm?

[amediasatex]

fastpedaller wrote:
The 7 speed cassette measures 32 mm

More like 30 mm, surely, since the pitch is 5 mm?

Update.... Measurement indicated the pull ratio for Shimano Altus is 1:2..

Aye, overall width is just shy of 32mm for Shimano 7 speed, but the mech travel is less than overall width as the mech only needs to move centre-to-centre of the sprockets, 6 shifts of 5mm -> 30mm.

Either way 2:1 would be unusually high ratio for any mech, Mk1 Suntour Cyclone is close, but most mechs I've come across and bothered to measure are well below 2:1. Worth double checking your measurements maybe? Also, measure at increments too as there's no guarantee that the movement is linear!

Shimano indexed MTB mechs from 6 speed to 9 speed and road from 6 speed to 10 speed* were 1.7 ratio. I've not measured any of the pre-indexing models, which generation is your Altus, from the old friction groups or a later indexed?

I've not got an ARX to hand to measure but might have one down the workshop so if I can find one I'll measure up. I have successfully sued Suntour VX's in indexed modes with Shimano and Campag shifters though, some with more tweaking required than others.

*with the exception of Dura Ace 7400 and Tiagra 4700

[Brucey]

The 7 speed cassette measures 32 mm , and a 'flag' of masking tape secured on the gear cable where it enters the cable guide on the chainstay moves 16mm when going from smallest sprocket to largest. Is there any other thing I've missed? - I can't think of any other way to measure it.

the required lateral mech movement is ~30mm (6x5mm) but the cable pull includes the first and last shift which may (for various reasons) use a different amount of cable pull than the rest of the shifts. The nominal cable pull for six shifts is ~17.5mm if the shift ratio is 1.7.


Best to either

a) measure the cable movement within the RD itself (at the exposed last piece of cable, not possible in the case of the ARX IIRC) or
b) to crimp something firmly onto an exposed piece of cable somewhere

and then use a Vernier caliper to measure the cable pull accurately between #2 and #6 (so that the first and last shift cable pull is not going to cause an error).

cheers

[9494arnold]

Are you wedded to Index?
If not you could get a Suntour Ratchet Bar End Changer which does just what it says on the tin, nicely engineered and stays where you put it but you have to manage the gear changing.

[fastpedaller]

Thanks for the suggestions. Because I'm now a convert to indexing, I've advertised the Suntour mech for sale!

[Brucey]

the other way you can measure the shift ratio of mechs (or at least compare it between two) is to hook the mechs up to an indexed shifter and compare their lateral movement for the same shift input.

I have often mounted an RD in a bench vice (using a horrible arrangement of axle parts including a cone with the same thread as the mech uses to mount) in order to carry out such measurements. I keep telling myself that I will build a proper jig but there is always something else that needs to be done first....

cheers

[rjb]

I tried this with a Suntour ARX long cage rear mech held in a vise and hooked up a shimano 7 speed sti lever. Ignoring the first click ie 1-2 which may have some overun, the remaining 5 clicks shifted the mech 28mm ie 5.6mm per click. Its possible that with a 7 speed index shifter it could index with a 6 speed freewheel where the sprockets are spaced at 5.5mm setting the shifter up in the middle sprockets so the overun occurs at the extremeties.

I may try drilling and tapping the cable entry to enable an adjuster screw to be fitted from a brake stirrup using the information here from Highpath just for the fun of it. Any thoughts anybody.
https://highpath.co.uk/cycle-informatio ... -indexing/

[Brucey]

yes that sounds about right; when SunTour changed to indexing they didn't make big changes to their shift ratio and I've used several SunTour RDs/shifters with Dura-Ace 7400 parts; AFAICT the shift ratio is almost identical between these two systems.

It probably means that using a 9s shifter will allow the SunTour RDs to be used with 8s sprockets etc too.

cheers