Nyah

I'd like to have a custom frame built, which will be optimized for large-chainring road cranksets. The problem is, every time I've upgraded cranksets on bicycles (or pieced together a bicycle from the frame-up), I've ended up with unsatisfying drivetrain performance. All of these have been bicycles designed for 20" wheels. Always the cranksets have been Shimano Hollowtech2 integrated spindle for road bikes, 1x chainring with approx 135mm rear hub.

One example is a folding bicycle with rear dropout spacing of 130mm. I built a rear wheel that has a 135mm OLD hub, figuring that there wouldn't be much issue with compatibility, based on what I've read about spreading the dropout spacing. Well, no matter what I try, I can't get all 10 of the rear cogs to engage properly. Shimano FC-7800 crankset w/53t chainring mounted to the outer location. Ten speed setup.

Question: Would a frame designed for 20" wheels, have less of a chance of success in spreading the dropouts, because of the shorter distance between the rear hub and structures that span the chain/seat stays (such as the brake-bridge)?

Another example is a bicycle that I pieced together from a new frameset (again, for 20" wheels). This frame has 135mm rear dropout spacing but the rear hub is about 136.5mm width. This example too was impossible for me to get all rear cogs to properly engage. I took it to the LBS and they got it tuned, but, told me that they had to open up the B-screw all the way to get it done. Shimano FC-6603. It's a road-triple crankset and I'm using just a 52t chainring, mounted on the center-ring location. Nine speed setup.

Question: If I want to have a custom frame built, and I want to use these Shimano Hollowtech2 cranksets that are intended for road bicycles and 52t (or greater) chainrings, will I need to have 130mm spacing on the rear hub? My intent is for these cranksets to be usable with two types of drivetrains - an IGH w/cassette (they exist!) and as the standard multi-chainring w/F.derailleur.

Question: What about Hollowtech2-compatible, integrated-spindle (yet non-Shimano) cranksets such as those by Litepro? Would they have the same constraints (if any) as the Shimano road cranks? What are the important details that I need to know?

Kontact

Your problems seem to come from the very short chainstays, which increase chain angle, and possibly having a cassette with sprockets too large for your rear derailleur's design capacity.

There is nothing particularly different about the cranks you are using. The problem likely lies with the frame, component selection and (possibly) the derailleur hanger/dropout relationship.

alcjphil

I agree. 20" wheels allow for very short chain stays. Unless the bike is designed with exceptionally long chain stays for the wheel size, chain rub is always going to be a problem

Nyah

So the crank width and the rear hub width are always compatible with each other? I mainly want to be sure that I don't make any mistakes in what I specify for the custom frame rear dropout spacing.

I'd prefer to specify 135mm rear spacing, but, can do 130mm spacing if necessary. Is one more optimal than the other? I need to be able to have large chainrings. 32t is the largest cog I will ever need on a 20" wheel. Maybe I could even limit this to just 28t cog, though.

Chainstay length of the custom frame will be no shorter than that of a standard road bicycle, but, I want to be able to do 1x setups.


Details I should've included:

The 10spd setup derailleur is Sram X5 medium cage. Not sure of its capacity.
Shifter is Microshift BS-10.
Chainring is 53t and cassette is 32t cassette, which are both the same number of teeth that this bicycle came with.
Chainstays are 15.75"/40mm long.

The 9spd setup derailleur is Microshift RD-R43M medium cage w/capacity of 30t-34t.
Shifter is Microshift BS-09.
Chainring is 52t and cassette is 32t.
Chainstays are 18.5"/47mm long, which is longer than on most road bikes. Maybe even longer than Surly LHT.

Nyah

Would you mind elaborating on that? On one bicycle I get chain rubbing on the seatstay when I'm in 11-52. Chainstays are very long 18.5", but, the seatstays don't seem to be shaped properly for the 11-52 combination. The other bicycle has 15.75" chainstays but doesn't rub with 11-53 combo because the seatstay is shaped to accommodate it.

alcjphil

You have to sit down with the custom frame builder to discuss what you want. This bike is going to be very far out of the norm. You want to be able to use very large chainrings on a bike with small wheels. This will necessitate very long chain stays so that the chainrings will not rub on them. Really, this going to be a very unique bike, possibly costly

Kontact

I missed the part about it being 1x. That is going to make it harder because the low gears are a big cross over, but it should still work. 18.5" chainstays are long.

Some 20" bikes have weird hangers that angle the derailleur up and toward the crank. Does yours? I'm wondering if the way the hangers are prevents the B screw from getting the clearance it normally would. If that's the case, try putting something under the B screw.

Nyah

Any guess on the minimum chainstay length needed to accommodate a 32-52 cross over in a 1x setup? I was considering getting a frame made with chainstays shorter than 18.5". Something closer to what a standard 622 road racing frame has, if it'll work.

Not sure if it angles upward, but, it's definitely forward of where I have the axle in the horizontal dropout slot. Thanks for pointing that out. The custom frame will not have horizontal dropout slots and will have the hanger in the correct location, those are already for sure. I have no use for the horizontal slots.

shelbyfv

You are going about this wrong. You need to decide on the features, let the builder figure how to do it. If you show up with a list of numbers you don't understand you'll just muddy the water. If you can find someone willing to build the type of bike you think you want, the you can have a dialogue. You put forward what you think you want, he tells you if and how it can be done. Finding someone who wants to build a strange bike will be your biggest challenge.

veganbikes

Tell your builder what you want to do and they can help build your bike. If you are getting a custom frame built you don't need to worry about respacing the rear dropouts or odd stuff like that. If you are respacing a custom frame that isn't built yet then you might not understand what a custom frame is because with a custom frame they can build you basically whatever you want within the limits of possibility so getting an incorrectly spaced frame is silly.

Kontact

The industry standard is about 405mm, or thereabouts.

I agree with the others - the more you dictate how the custom is built, the more likely it is to go wrong.

But I'm interested in why your bikes don't shift. There is no obvious reason they don't work right. Consider posting some pictures.

squirtdad

maybe more information on the bike would help

is is to be a folder? need to find a builder that does that

is goal mini-velo and that is the focus on 20" tires, if not why 20 in tires? this seems to be the biggest issue

instead of custom you could buy a frame designed for mini-velo like https://velo-orange.com/products/neutrino-minivelo

https://biria.com/bike/20-road-bike

I have seen some bilenky min-velo https://www.bilenky.com/

shelbyfv

I'd start with his goofy crankset kludges. Plenty of room to screw up there.

Kontact

How do you screw up removing one ring?

shelbyfv

I don't.