GPX Crank on Road Bike

[Jim77]

Has anyone had experience putting a GRX crankset on a road bike?

I have an Ultegra 11 speed crankset and want to lower the gearing by putting a GRX crankset on instead.

Thanks in advance.

[Cyclothesist]

I did it on a 2017 Kona Jake CX swapping the original FSA adventure 2x crankset. Now 2x GRX 600. Both 10sp.
It'll work no problem provided you also fit a GRX front derailleur. The GRX crankset chainline is about 3mm further out than the usual road chainline. The original Tiagra 4700 FD wasn't able to accommodate the chainline and I suspect the Ultegra won't either.

[Jim77]

Thank you - that is very helpful.

[gxaustin]

I fitted an 11 speed GRX 600 in place of a 105 crank set. After carefully measuring I found that the left hand crank is interchangeable with road cranks - and replaced the GRX LH crank with a tatty Dura Ace crank to save a bit of weight (and confuse people). It works very well. Initially I got it to work with the 105 front mech but later it jammed and I had to fit a GRX item.

[Brucey]

I have always thought that it should be possible to fully (or at least partially) compensate for the GRX chainline by respacing the BB. This might allow a 'road' FD to be used.

By hook or by crook I think it will prove possible to slightly shorten the BB spindle too, thus making everything symmetric again.

[Reece]

I fitted a 10 speed GRX Crankset and my existing 9 speed Sora front mech worked perfectly after some minor adjustment.

[Nearholmer]

I have always thought that it should be possible to fully (or at least partially) compensate for the GRX chainline by respacing the BB

Likewise. And ditto in the other direction to use a not-GRX crankset with a GRX FD.

[pigman]

I did it on a 2017 Kona Jake CX swapping the original FSA adventure 2x crankset. Now 2x GRX 600. Both 10sp.
It'll work no problem provided you also fit a GRX front derailleur. The GRX crankset chainline is about 3mm further out than the usual road chainline. The original Tiagra 4700 FD wasn't able to accommodate the chainline and I suspect the Ultegra won't either.

Exactly my experience fitting one on a mate's bike

[pigman]

I have always thought that it should be possible to fully (or at least partially) compensate for the GRX chainline by respacing the BB. This might allow a 'road' FD to be used.

By hook or by crook I think it will prove possible to slightly shorten the BB spindle too, thus making everything symmetric again.

Not sure how you'd shorten it? It's a one piece affair. The only way I could see the chainset being moved closer (more inboard) is to shave something off the BB shell. But then you'd have to pack the left side with washers

[rareposter]

Not sure how you'd shorten it? It's a one piece affair. The only way I could see the chainset being moved closer (more inboard) is to shave something off the BB shell. But then you'd have to pack the left side with washers

When have you ever known Brucey to take the simple solution of "if you have a GRX chainset, use a GRX front mech" when options exist to void the entire warranty by drilling, dremeling, angle grinding, welding and bodging?!

The idea of cutting down an integrated one-piece axle to adjust chainline sounds like something that follows on from Baldrick saying "I have a cunning plan..."

To answer the OP - yes, GRX crank works fine on a road bike, just use a GRX front mech and all will be well.

[Cyclothesist]

I have always thought that it should be possible to fully (or at least partially) compensate for the GRX chainline by respacing the BB. This might allow a 'road' FD to be used.

By hook or by crook I think it will prove possible to slightly shorten the BB spindle too, thus making everything symmetric again.

To move the RH driveside inwards you'd need to machine material off the RH external bearing (I don't think there's scope for that) or off the RH BB shell or use a lathe to reprofile the crank spindle shoulder so that it's closer to the spider. Or some combination of those. Then you'd need to either add spacers to the LH at the BB bearing and/or crank spindle or shorten the LH spindle while preserving and possibly recreating the splines.
As inferred by rareposter none of that is remotely a trivial job and risking the frame and/or crankset to save the cost of a £40 GRX FD (I've seen it discounted to £10 online for 'black Friday') is foolhardy.
A much better option if you really want to preserve chainline and extant™ FD is to fit a Spa Cycles ultra compact double. It's cheaper than GRX too.
https://www.spacycles.co.uk/m8b0s109p33 ... cral-Rings
Or just fit a GRX FD with a GRX crankset.

[Jim77]

Thank you all for the valuable comments.

[pigman]

Has anyone had experience putting a GRX crankset on a road bike?

I have an Ultegra 11 speed crankset and want to lower the gearing by putting a GRX crankset on instead.

Thanks in advance.

How low a gear do you want to go to? I ask because I fitted 33 and 46 rings to a standard compact crank set. 34T cassettes are commonplace so you can achieve less than 1:1 gearing without resorting to a new crank set and mech

[NickJP]

I have always thought that it should be possible to fully (or at least partially) compensate for the GRX chainline by respacing the BB. This might allow a 'road' FD to be used.

By hook or by crook I think it will prove possible to slightly shorten the BB spindle too, thus making everything symmetric again.

I did this (or something similar) when using some 10-speed Deore XT cranks on a road frame. In order to reduce the chainline for the road frame, I didn't use the 2.5mm spacers each side that are supposed to be used when fitting the cranks to a 68mm BB, and to be able to reduce the spacing between the LH and RH cranks I used a small grinding wheel on a dremel to remove about half the length of the splines on the LH crank where it slides onto the axle, so that the crank could slide further on to the axle.

This modification has now been in use for about 15 years and has proved perfectly reliable.

[Jim77]

How low a gear do you want to go to? I ask because I fitted 33 and 46 rings to a standard compact crank set. 34T cassettes are commonplace so you can achieve less than 1:1 gearing without resorting to a new crank set and mech

That is an interesting suggestion, but I am very heavy and already have a 34 cassette and 34 on the front. So I need something less than a 33 on the front. I need it for when I am going to be doing a lot of hill climbing with 20% plus climbs.