Chain ring too close to frame

[penserv]

I moved from a 42T front ring to a 48T ring. I bought a SunLite crankset with front and rear chainguards. I had to discard the rear chainguard because it wouldn't fit and rubbed on the chainstay. Even now, the 48T ring has less than 2 mm clearance on the chainstay, but that's plenty for a bike. The 48T ring is great. With the 42T ring, you always feel like you're maxing out the drivetrain pedaling on the flats or slightly downhill. I also found with the 42T front that I was only using 3 or 4 of the smallest gears out of 10. With the 48T ring, I'm up to 7 or 8, but I never get to the 36T large sprocket on the back or the one next to it. Going up a steep hill is not a problem, because it's an electric bike. If you're tired and straining, just increase the PAS level for a bit or hit the throttle.

 

[Gionnirocket]

I moved from a 42T front ring to a 48T ring. I bought a SunLite crankset with front and rear chainguards. I had to discard the rear chainguard because it wouldn't fit and rubbed on the chainstay. Even now, the 48T ring has less than 2 mm clearance on the chainstay, but that's plenty for a bike. The 48T ring is great. With the 42T ring, you always feel like you're maxing out the drivetrain pedaling on the flats or slightly downhill. I also found with the 42T front that I was only using 3 or 4 of the smallest gears out of 10. With the 48T ring, I'm up to 7 or 8, but I never get to the 36T large sprocket on the back or the one next to it. Going up a steep hill is not a problem, because it's an electric bike. If you're tired and straining, just increase the PAS level for a bit or hit the throttle.

I concur... 46t is my sweet spot.

 

[JES2020]

I moved from a 42T front ring to a 48T ring. I bought a SunLite crankset with front and rear chainguards. I had to discard the rear chainguard because it wouldn't fit and rubbed on the chainstay. Even now, the 48T ring has less than 2 mm clearance on the chainstay, but that's plenty for a bike. The 48T ring is great. With the 42T ring, you always feel like you're maxing out the drivetrain pedaling on the flats or slightly downhill. I also found with the 42T front that I was only using 3 or 4 of the smallest gears out of 10. With the 48T ring, I'm up to 7 or 8, but I never get to the 36T large sprocket on the back or the one next to it. Going up a steep hill is not a problem, because it's an electric bike. If you're tired and straining, just increase the PAS level for a bit or hit the throttle.

Funny, I just came in from the garage attempting to replace my 42 with a 48t, no luck !
The taper is not thick enough so the inner chainring rubs against the frame. This is the second time a 48t did that !

Edit engineered my way out of the challenge by using metal shims to buttress the spindle. I just came back from a trial ride and it feels like a new bike ! I can easily pedal at 25 mph and can actually help the motor at 32 mph, What a boost in power.

 

[tomjasz]

A common experience, especially with fat bikes and the wide chainstays they have.
What is the bike and motor? penserv? Maybe I missed the post with that info.

 

[PedalUma]

A common experience, especially with fat bikes and the wide chainstays they have.
What is the bike and motor? penserv? Maybe I missed the post with that info.

Wheel diameter is one factor that is often overlooked or assumed as non-variable. My 29er has huge tires so running a 42-T is its sweet spot. I am building a Sweet Curry Yuba now that has a 20-inch rear tire, so it is getting a 50-T chainring. This will still allow for cargo with climbs because of the small rear wheel.

 

[penserv]

I used a SunLite dual chainguard crankset. The crankarm is permanently fixed to the crankarm but by doing that, they can get the chainline down to 45 mm. With my 104 BCD 42T ring I have to mount it on the inside of the crankarm with 2 spacers to get the chainline even close to 45 mm. With the 44T, no amount of fiddling with the chain guide could keep the chain on when downshifting. I think the key thing is to use the integrated chain ring and crankset, as you get a narrower profile. It's still tight, but 2 mm clearance between the chainstay and the front ring is more than adequate. The tradeoff is that you cannot easily change front rings as you can with a BCD ring.

 

[penserv]

The bike is a DIY built on a GT Karakorum frame. I didn't choose the GT out of any preference. In Calgary in December, that's what was available in my budget. it's a 29er with 2.3" tires and I found that with the 42T front, you can get pedaling so fast, you feel like you're out of balance. I don't get as much of that feeling with the 48T front.

 

[penserv]

Oh yeah. Without a doubt. I am 100 percent responsible. I might not even return the 42T.

This is the main reason I built my own bike. I want to be the guy responsible for something working (or not) because i can take pride from what I've done or learn from it and do it right the 2nd time. I never return parts except maybe to Amazon. It's just too much of a hassle. Since I started my build, I'm becoming a parts warehouse. Maybe that's what I could do when I retire......

 

[m@Robertson]

I have a stack of Luna, Lekkie and various 130 bcd chainrings from a variety of partial successes and total failures. The good news is at this point I have enough of them I get a good idea of where I need to be on a new build by pulling parts out of the pile. Figuring this out is part of the adventure of building... but its not for everyone as trial/error where you don't settle/compromise is pricey.

My last success was actually a retrofit of a 52T Lekkie from Cali Ebike. As noted earlier in this thread, usually 52T is a bad (bad!) choice - even for a BBSHD. For this one build, it let me kick up a couple of higher cogs and thus align the chain just right, at the level of effort and cadence I wanted, and didn't bog the motor since I was running near the middle of a 11-42T cluster. If I tried it 10 more times on 10 more builds it probably would not work on any of them.

Figuring out the drivetrain is always a dance.