Di2 compatible chain set

harkmeadow

hi, does anyone know if i can replace a Di2 Double chainset with say a 105 or Ultegra compact to save a few £££'s?

thanks

harkmeadow

its a 7900 at the moment btw

jonmack

If I remember correctly I've seen someone running Di2 with SRAM Red cranks, so shouldn't be an issue.

Rodrego Hernandez

The new chainset is designed to work with the Di2 front derailleur - ie, it is built so that the chainrings won't bend under the force of the gear change - in theory any shimano chainset will work but will they last the pressure from the mech?

harkmeadow

Thanks, hmm so sounds like it would be best to keep with the 7900 series from what you say re the force. Anyone else got Di2 and changed the chainset?

LangerDan

You can run an Ultegra chainset with Di2 - Felt are doing this with one of their Di2 offerings

Spec: - Shimano Dura-Ace 7970 Di2 STI; Dura-Ace Di2 braze-on front derailleur; Dura-Ace Di2 rear derailleur; Ultegra compact 50/34T crankset; Ultegra chain; 11-25T cassette

Anonymous

Sorry if this is out of turn, but if you want to save a few ££s then don't bother with Di2 at all...

harkmeadow

Not at all. Already got the Di2 - got a very very good deal, but if i can save £150 /£200 on the a compact then thats worth doing.

From previous experience of using 105 components instead of Ultegra, I personally am not going to notice the difference. And the few extra grams will make less difference than the mince pie I just ate!

schweiz

Rodrego Hernandez wrote:

The new chainset is designed to work with the Di2 front derailleur - ie, it is built so that the chainrings won't bend under the force of the gear change - in theory any shimano chainset will work but will they last the pressure from the mech?

All the mech is doing, Di2 or otherwise, is guiding the chain.

I reckon any chainset will work.

Rodrego Hernandez

schweiz wrote:

Rodrego Hernandez wrote:

The new chainset is designed to work with the Di2 front derailleur - ie, it is built so that the chainrings won't bend under the force of the gear change - in theory any shimano chainset will work but will they last the pressure from the mech?

All the mech is doing, Di2 or otherwise, is guiding the chain.

I reckon any chainset will work.

Although that is true, the force at which it moves the chain is enough to bend an outer ring, which is one of the reasons for the chainset redesign. You are right in thinking that any chainset will work, how long it will last is different question I suppose.

schweiz

Rodrego Hernandez wrote:

schweiz wrote:

Rodrego Hernandez wrote:

The new chainset is designed to work with the Di2 front derailleur - ie, it is built so that the chainrings won't bend under the force of the gear change - in theory any shimano chainset will work but will they last the pressure from the mech?

All the mech is doing, Di2 or otherwise, is guiding the chain.

I reckon any chainset will work.

Although that is true, the force at which it moves the chain is enough to bend an outer ring, which is one of the reasons for the chainset redesign. You are right in thinking that any chainset will work, how long it will last is different question I suppose.

Having 'ridden' a Di2 equipped bike (albeit for less than 5 minutes on a turbo) the Di2 seemed like there was less force on the in the whole system or at least it was a more consistant force and I couldn't get it to do a 'bad' change (which loads up drivetrains more than anything else). Everything was definitely much smoother. Are you sure that this isn't more of Shimano's marketing to get customers to replace the whole drivetrain?

Rodrego Hernandez

It is what Shimano have told me and from setting up a Di2 bike can see that there is a fair bit of force in the front shift. Might not be an issue but personally I wouldn't risk a different chainset over a dura ace one if I had the option.

Smokin Joe

Rodrego Hernandez wrote:

It is what Shimano have told me and from setting up a Di2 bike can see that there is a fair bit of force in the front shift. Might not be an issue but personally I wouldn't risk a different chainset over a dura ace one if I had the option.

Shimano will tell you that you must use only their own componants throughout the groupset, as will Campag because they want you to buy their stuff.

It's bollox, chainsets don't care what front shifter you use with them, they are all the same size and shape. So unless Dura Ace are made from tungsten to withstand this mystical level of force you can ignore it.

rake

given that it most likely uses stepper motors with gearing i would think its highly likely that the mech can move with considerable force, especially if you were the press the button whilst not peddaling.

schweiz

Di2 is uses servos not a stepper motor. The front derailleur monitors the rear derailleur position and adjusts itself based upon the chainline to eliminate chain rub. I tried it out and it works well.

Saying that I have no idea if there is any feedback that senses loading on the servo to stop it trying to push the chain onto the large chain ring when it's not turning although a normal deraileur will be exerting a force on the chain/chain ring too if you try and shift in the same way.

rake

schweiz wrote:

Di2 is uses servos not a stepper motor. The front derailleur monitors the rear derailleur position and adjusts itself based upon the chainline to eliminate chain rub. I tried it out and it works well.

Saying that I have no idea if there is any feedback that senses loading on the servo to stop it trying to push the chain onto the large chain ring when it's not turning although a normal deraileur will be exerting a force on the chain/chain ring too if you try and shift in the same way.

i wonder if di 2 has a clutch to slip if it gets jammed. your not likely to push hard on the lever if you feel resistance.

schweiz

I've just tried changing gear with DA7900 and not turnining the cranks. If you sweep the left lever all the way inwards, the ratchet will take up the cable to change the gear and the derailleur moves over the full range but you don't feel that the front derailleur is pushing the chain up against the the large chain ring.

If Di2 does have a slipper clutch or some such to detect this situation it would be easier on the drivetrain in terms of unwanted forces on the chainrings and reduce the claimed problem from Shimano.

Especially with modern, profiled chain rings, the derailleur only needs enough force to push the chain onto the ramps. Why Shimano Engineers would make problems for themselves by have forces much greater than this seems strange. The more I think about this the more I think it's marketing!

At the end of the day, I've mixed and matched components that officially don't go together according to Shimano, as have many others. I think Di2 will be fine with other chainsets, but of course Shimano won't endorse it or recommend it.

harkmeadow

Cheers for all tulhe replies. Well, I'll go with the cheaper option....and feedback.

rake

i am sure it will work well. i think i read somewhere for optimum performance di2 actually knows where the ramped teeth are on the chainset and moves accordingly at the precise time to catch the chain. does it have a crank position sensor, thats the only way i could see this being true.

LangerDan

Fairwheel Bikes have done a lot of work around the Di2 system - including reverse engineering the controller to give them a fully sequential system across the entire gearing rang.

They have discussed the issue of using 3rd party cranks on Di2:

http://fairwheelbikes.com/forum/viewtop ... f=3&t=6458