Bolt circle/pattern of pictured crankset?

[Hankj]

Labeled "Bontrager with hollow axle, 2-piece, 42 teeth" but I can't find any technical information on the web. It's 1x.

I'd like install a smaller chainring but can only see that it's an asymmetrical 4 bolt. Anyone know the correct size? And how small I might go? I'd like 38 or 36 for some loaded hilly bike packing.

Also, the plastic bash guard - enough to keep the chain on a regular ring or narrow-wide a wise investment.

Thanks for your help!

Hank

 

[Sharky]

This might help?
https://sheldonbrown.com/cribsheet-bcd.html

How big is that rear cassette - it looks enormous!

Re N/W chainrings, have them on two of my 1x geared bikes and have never unshipped the chain.

 

[FishFright]

Labeled "Bontrager with hollow axle, 2-piece, 42 teeth" but I can't find any technical information on the web. It's 1x.

I'd like install a smaller chainring but can only see that it's an asymmetrical 4 bolt. Anyone know the correct size? And how small I might go? I'd like 38 or 36 for some loaded hilly bike packing.

Also, the plastic bash guard - enough to keep the chain on a regular ring or narrow-wide a wise investment.

Thanks for your help!

Hank




View attachment 652891

That looks similar to the Shimano's asymmetric pattern used on their MTB 1x groupsets.

 

[bikingdad90]

The markings are likely hidden beneath the chain guard. I’d measure it as per this guide from wolf tooth and then try and find a suitable chainring.

https://www.wolftoothcomponents.com/pages/how-to-measure-bolt-circle-diameter-bcd

 

[Hankj]

thanks for the tips! That Sheldon Brown chart is super helpful.

The cassette is Deore 11-51. I don't own the bike yet. I'm buying it online in Germany and having it shipped to where I'm starting a one month tour in the Alps.

Since I'm touring in the mountains (albeit credit card touring), I want a lower low than 42-51 - want to be able to sit and spin the hills so as to spare my aging knees from back to back to back high mileage days.

I want 38-51. 20.6 gear inches I think. Makes an old man happy.

I think this bolt circle is probably 110mm 4 bolt asym? The 42mm chainring seems to fits about like it would on a 110mm BCD.

And I'm guessing it's Shimano's 110mm asym pattern (not SRAM's or FSA's) - most common in 110mm, and everything else on the bike is Shimano nose to toes.

My plan is to order what I think is probably the correct chainring in 38t and hope it fits. What could go wrong?

But of course more informed opinions are very helpful, though I doubt many here own this cruddy crank. LMK if you know something!

 

[Hankj]

Gonna backtrack off my 110mm guess.

That looks similar to the Shimano's asymmetric pattern used on their MTB 1x groupsets.

I think you are probably right FishFright. Looks like there is room for a much smaller ring - the 42t chainring's "spokes" are quite long? Here is a picture of 110mm Dura-Ace w/ 42t ring. I am vacillating as to same or different BCD compared to crank in question.

I need to track down the manufacturer and call probably.

 

[Hankj]

Here's the specs from Diamant. I still have a hard time not seeing it at 96mm bcd, but if they say 110mm I'm going with that?

The crankset looks basically identical to the Shimano Metrea crankset.

Below are the Metrea's specs. Note 96mm BCD. I think I'll need to wait till I arrive to pick up the bike and then see what can be done to go smaller.

Or maybe there is a different Shimano crankset for

Specifications:​

Application: City
Compatibility: Shimano 1x11-speed
Chainring Mount: 96 mm pitch circle, 4-arm asymmetrical

Technical Information:​

Series: Metrea U5000
Crank Arm Material: Aluminium
Chainring Material: Aluminium
Axle Material: steel
Gradation: 42-tooth
Crank Arm Length: 170.0 mm, 175.0 mm
Chainline: 46.6 mm
Q-Factor: 158 mm
Axle Diameter: 24 mm
Compatible BSA Shell Width: 68 mm
Recommended Bottom Bracket: SM-BBR60 or SM-BB72-41B Press Fit Hollowtech II (not included)
Recommended Chain: HG super narrow 11-speed (e.g. CN-HG601-11)

 

[Ming the Merciless]

Might help if you posted the make / model of bike or even a link to it on the online retailer. Someone might be able to sleuth down what the crankset is that it’s supplied with.

 

[Ming the Merciless]

I should ask, have you emailed the retailer to ask for make / model of crankset?

 

[Hankj]

I did Ming, just forgot to insert the image they sent when I was writing my last. Sorry. It's there now.

The bike is the Diamant 136. The crank looks very much like the Shimano Metrea, and matches the spec, except Diamant says 110mm and Shimano reports the Metrea is 96mm BCD.