Need a bigger chain ring need advice..

Hello All,

I have my ebike running and I am overly satisfied with it. Its a 700C commuter with a Q128CST 36V 201 RPM on 52 volts. I am 230lbs and i can go in excess of 30 mph with pedaling. I only have it as a PAS setup. Anyhow the bike has a SRAM 1x11 setup and my front Chainring is 40T and at PAS level 4 I have hardly any resistance left in the cranks. At PAS Level 5 the cranks have almost no resistance. I would like to have some resistance at PAS 5 which will give me more bike feel in PAS 4. At PAS 3 I can average a bit over 25mph with only 150 watts helping and me pedaling pretty good. PAS 4 jumps to about 350 watts help and 29 MPH or so with same pedal force until I run out of resistance. So my question is I have a few option in the chain ring sizes available. 42T, 44T, 46T, 48T & 50T. If I switch to the road group I can go above 50T but I think the ring may hit my chain stays if it gets too large. My smallest cog on the rear is 11T. If I jump to say 46T or 50T what is the feel in resistance between a 6 tooth jump as opposed to 10 teeth. I will likely need a longer chain. Also being a 1X no front derailer to limit me, more so what looks like tight clearance in my chainstays. The bike works so well I am also riding at times on the flats with the system off PAS 0 and it feels like a regular bike with not much loss in the bike feel as opposed to a BBS setup where it feels weird pedaling power off.


I still need to shorten the waterproof wiring harness



Open to any advice.

Marc

Put an Mtb crank on it. 48t front ring should do the trick for all but the very fastest riding. It won't rub your frame like a road crank might. And 48t will not be hard to find in an MTB crank.

It will have three rings, of course. If you buy a good one, you can take the unused rings off. If you go with a cheaper riveted one, no worry. And in a breakdown, you can still drop to a lower gear by hand, for an uphill limp home.

Better still a two ring road crank, if it does not rub, for 52t on the big ring.

The way you ride, I would get the biggest possible chainring that will fit with no issues. You still have the rear gearset, and apparently there is some advantages to not being on the 11-tooth for chain wear issues.

Nice bike! I love it! Its similar to some of my builds.

So, you need to tell us your real speed and a cadence you like. A 201rpm cute is not going to do much more than 25mph. I typically ride at 100 rmp – its not a lot of resistance, by my legs are putting out a lot of power (average about 250 watts). Remember, power is torque x speed. Its less tiring on the legs to pedal faster anyway.


Just for grins, lets say you like 70 rpm and 25mph.

53t chainring and 12t cog gets you at that speed.

For reference 40t x 11t is 101rpm at 30mph.
Generally speaking changing 3 teeth in the chain ring is like changing 1 tooth in the rear cog.

Hopefully that helps.

Thanks everyone for the advice.

Since I worked really hard to get the PAS ring to work on my current ISIS spline cranks I'd prefer to see if I can just upgrade my ring. However if i do have clearance issues its nice to know its an option.

I emailed the bike MFG to see if they had data on the max size chainring that will fit. Unfortunately the chain rings just show tooth count and dont give a max diameter so I am unable ot just figure it out on my own unless I buy it. I suppose I could cal SRAM and ask if the MFG takes too long to get back to me.

I would like to get off the dependence of the 11 tooth cog for chain reliability as well.

The outer diameter of a round chainring in inches is very close to the number of teeth divided by 2π, plus a variable amount that's close to 0.3" and is a function of tooth shape. Use 0.4" as this value and your chainring will be no bigger than that.

How big a chainring will fit is not just a matter of its diameter, but also of where it's located laterally, and this amount can vary with different cranks and bottom brackets.

I converted my 21 speed using a BBS02 so I now have a 7 speed with a 52 tooth chainring in the front. I went as large as I could go. I can't hardly move it all at in the top gear without the battery. However, with the power on I reach 33 MPH and I also have at least a little pedal resistance.

In low, without the battery, I can still pedal it but I couldn't go up a hill.

Chalo said:

The outer diameter of a round chainring in inches is very close to the number of teeth divided by 2π, plus a variable amount that's close to 0.3" and is a function of tooth shape. Use 0.4" as this value and your chainring will be no bigger than that.

How big a chainring will fit is not just a matter of its diameter, but also of where it's located laterally, and this amount can vary with different cranks and bottom brackets.

Click to expand...

Chalo this is exactly what I needed to know. so with your math can you check this on a 50T... I am a bit unsure on if you meant i just add .4 to the results. I will run your formula through my 40T to see how it correlates.

50 / 6.28 = 7.96" + .4 = 8.36" Diameter

With this info I can see if 8.36" will clear my chainstay. The bike has a depression in the chain stay on that side for clearance but unsure if its 4.25" away from the crank center.

Marc

I put one of these ony radwagon that also has a q128c as well as a q100h on the front

http://m.ebay.com/itm/BCD130-chainring-narrow-wide-NW-teeth-Circle-single-speed-chain-ring-50-52T-58T-/282274548138?var=&hash=item41b8dfc9aa%3Am%3AmN6cDUJQMuZ3f_K7e4JA_Dw&_trkparms=pageci%253Ac82c85ca-41b0-11e7-a11d-74dbd18050fa%257Cparentrq%253A425272d515c0a9921b270bb8ffff9582%257Ciid%253A3

Just had to also swap in a 130bcd crankset. It's awesome, I most never use the 11t cog. I went with the 54t. The chain is very stable on there as well.

Also there is the Patterson drive, you have to swap out you BB and it's a little pricey but the 36t chainring ends up being the equivalent of 55 or so in the high gear.

https://www.pattersonbike.com/product/chain-ring-patterson-transmission/

Nice bike! I'm quite fond of the light and nimble and I've been running a Q128CST in a 700c wheel 28km/day most days for the past year.

I have a different problem, in that I find my motor maxed out most of the time on level ground to descents. I'm currently running the 201RPM@36V version with 48V (= ~260RPM), and I estimate I'm getting around 38-40kph maxed out, with a cadence of 90-100 in an 11/42T. I'm strongly considering installing a 328RPM version, as I can keep it above 25kph on the steepest hills on my commute; thus, burning out the motor shouldn't be a problem and I'd appreciate the extra speed.

I'd be interested to know where people are sourcing these larger MTB chainrings? I looked before but came up with few options from the obvious online parts dealers.

addicted2climbing said:

[so with your math can you check this on a 50T... I am a bit unsure on if you meant i just add .4 to the results. I will run your formula through my 40T to see how it correlates.

50 / 6.28 = 7.96" + .4 = 8.36" Diameter

Click to expand...

That's right. With most chainrings, the measured size of a 50t is probably closer to 8.25", but better to be on the safe side.

With a reasonably large ring, a polygon made of all the chain pin axes approximates a circle closely enough that tooth count/2π gives you the diameter at the pins. Plus 0.4" is to account for the diametral extent of the sprocket teeth outside of that, which is a variable amount.

molybdenum said:

Nice bike! I'm quite fond of the light and nimble and I've been running a Q128CST in a 700c wheel 28km/day most days for the past year.

I have a different problem, in that I find my motor maxed out most of the time on level ground to descents. I'm currently running the 201RPM@36V version with 48V (= ~260RPM), and I estimate I'm getting around 38-40kph maxed out, with a cadence of 90-100 in an 11/42T. I'm strongly considering installing a 328RPM version, as I can keep it above 25kph on the steepest hills on my commute; thus, burning out the motor shouldn't be a problem and I'd appreciate the extra speed.

I'd be interested to know where people are sourcing these larger MTB chainrings? I looked before but came up with few options from the obvious online parts dealers.

Click to expand...

I think the version you would want, would be the 500W 328 @ 48Volts, which if rated @36 Volts would be 260 RPM.

https://bmsbattery.com/ebike-kit/769-q128c-135mm-500w-rear-driving-ebike-hub-motor-wheel-ebike-kit.html

I think the 328 @ 36 Volts, unless you are a super-human cyclist, would be too much in a 700 cc wheel.

Concerning the chain ring, I think the biggest that will fit would be the way to go.
I have a pretty good relationship w/ a local bicycle accessories store and bought my 50T from them so I could take it back if it didn't fit. It cleared the chain stay by a milimeter. Even so, w/ my 11 X 50 gearing w/ a 24" X 2.4 tire, the best I can pedal is up to about 23 MPH.

My other bike w/ 11 X 48 and a 26 X 1.75 tire is good to 20 mph.

You only have to look at the gap between the chain-stay and the chain-ring to see how big you can go. It looks tight already in the photo. You can gain a bit more clearance on some bikes by adding a spacer behind the BB on that side, but you can't gofar without getting problems of alignment.

molybdenum said:

Nice bike! I'm quite fond of the light and nimble and I've been running a Q128CST in a 700c wheel 28km/day most days for the past year.

I have a different problem, in that I find my motor maxed out most of the time on level ground to descents. I'm currently running the 201RPM@36V version with 48V (= ~260RPM), and I estimate I'm getting around 38-40kph maxed out, with a cadence of 90-100 in an 11/42T. I'm strongly considering installing a 328RPM version, as I can keep it above 25kph on the steepest hills on my commute; thus, burning out the motor shouldn't be a problem and I'd appreciate the extra speed.

I'd be interested to know where people are sourcing these larger MTB chainrings? I looked before but came up with few options from the obvious online parts dealers.

Click to expand...

With the chainring, I just bought a road double crankset, that had a 53t large chain ring. That should cost about $50 (if it fits without hitting your chainstay).

I have a 48t “touring” mountain bike crank set, but unless you have some high end stuff, you can just put a road bike crankset on your bike.

I’ve been using the 36v 328rpm motor in my light and nimble build for years. It works great with 700c wheels because there is so much less rolling resistance than mountain bike sized tires – and even better if you ride it in a somewhat aero position. I’m amazed how fast a light bike with good 700c tires is compared to my mountain bike builds. With a 53t chainring and 17t rear cog, I’m doing about 100rpm at 25mph. It does need some effort by the rider. 25mph needs 450 to 600 watts, depending on how efficient your bike is (mostly, how aero you want to make yourself).

I appreciate the advise regarding the faster wind hub motomech and chas58; I'll repost on my original build thread to avoid usurping the OP. In regards to

addicted2climbing said:

Its a 700C commuter with a Q128CST 36V 201 RPM on 52 volts. I am 230lbs and i can go in excess of 30 mph with pedaling.

Click to expand...

you may be running the 328 version, as I certainly don't get close to 30mph on my 36V 201 Q128c. Although BMSB service has improved by leaps and bounds, mistakes still happen. I've noticed something else about my system. When I'm under full throttle, the LCD3 indicated speed is about 30% higher (50kph vs 42kph) than when I release the throttle. I think the accurate speed is the one without throttle in my case.

chas58 said:

With the chainring, I just bought a road double crankset, that had a 53t large chain ring. That should cost about $50 (if it fits without hitting your chainstay).

I have a 48t “touring” mountain bike crank set, but unless you have some high end stuff, you can just put a road bike crankset on your bike.

Click to expand...

I didn't realize a road crankset would fit a mtb; certainly this is the easiest option and I'll be applying my measurements to Chalo's equation in preparation for a faster wind Q128CST.

molybdenum said:

I didn't realize a road crankset would fit a mtb; certainly this is the easiest option and I'll be applying my measurements to Chalo's equation in preparation for a faster wind Q128CST.

Click to expand...

If it is a square taper bottom bracket, any crank set will do (given the appropriate clearance). Some of the new high end stuff has diverged, it might not work in some cases. Alternatively, you can just get a chain ring. Traditionally, Road bike double chain rings have a BCD (Bolt Circle Diameter) of 130, while mountain bikes triples were often 110. Chain rings cost about as much as a basic crank set, so a new crank set is often the way to go.

And of course, with the newer high end stuff, there are all kinds of new standards.

I roll with a 52t 11t and peddle at 34mph windmill at 36mph. It's a two ring road bike rim that I bought at a bike swap meet. Then changed b.b. from a 115mm to a 121mm( just guessing) on a colmoly mtb and had to massage the frame with my 5 pound Hammer . Just use 52t and rear derailleur 2-7 and 7,000 watts to 47mph.

Is worth noting that above 30 mph, you're making more drag than power by pedaling. At those speeds, it's most efficient to crouch down, level the pedals, and pull your knees in tight. Not very stealthy, though.

Edit:
I went to the Kreuzotter.de power and speed calculator, which indicates that I personally would reach 35.0 mph coasting an 8 percent downhill on a roadster type bike. Ghost pedaling at 90 rpm would bring that down to 33.1 mph, and I'd have to develop 250W at the pedals to get back up to 35 mph. Why bother, right?

Anyway, I don't think there's a compelling reason to build in pedal gearing that works at over 30 mph. The best reason to use great big rings is to get a good top speed without having to depend on an 11t or 12t sprocket to get it. Since most freewheels have a 14t small end, and most rear hub motors are made for freewheels, it's valuable to us as a group to know how to make such gearing work for us. In that situation, 53-39 or 52-42-30 road cranks are a good starting point. (53/14 on a 26 x 2.3" tire yields about 27mph at 90 pedal rpm.) But aftermarket rings up to 60t are readily available and relatively affordable.

Somtimes you got to fake it for the man. Remember Dorothy in The Wizard of Oz riding her bike thru the wind. They just have to belive. As calif law is 20mph assist. Yea 52t - 50t for your 11t. Where do you live I a have 48t-11t too. You can try them.

So, can Kreuzotter give you your terminal velocity?

I like to pedal at speed because I am still getting some physical activity rather than just being a passenger. I don't really care that I am 'losing power' to the wind. If I did care about the ~200W, I would just slow down a couple mph and save it that way.

That said, my favorite addition is my FSA Metropolis Patterson Crank. Gives me 1X and 1.6X gearing on my front ring. I can only fit a 39T due to frame limitations, but I can pedal at 40+ mph with the Patterson (11T top gear).

chas58 said:

So, can Kreuzotter give you your terminal velocity?

Click to expand...

I think if you set the slope to -10000 or something like that, you'd get an approximation.

All very interesting, this is why I like to read what Chalo has to type.

The used bike store in the retail strip mall here has road cranks available, I snatched up a Campagnolo 53T just because it was $5. How I will attach it to my crank I have no clue, maybe I gotta convert to road crank or do up some sort of fabrication.

A 60T is $70(cad) which I guess is "affordable" but here is a 60T BMX for $30 another for $50-$60 which seems about average.

Perhaps me being a penny pincher for no apparent reason, not like I dont have the money (especially in this hobby), I think I need to try a fab on my 53T and keep an eye open for a bigger crank ring. Lots of Shimano 52T in the basket at the store.

But yeah I definately need more then whatever I got currently, perhaps its a 46 or 44.

for my mtb, the current 42T is 7.1" diameter, whereas the 52T works out to 8.7"; measuring to the chainstay, I have at least another 1.2" before it impacts; thus a diameter increase of 2.4" will likely work, and I could probably fit a 60T.

Aliexpress has 4 hole mtb chainrings for 8-12spd up to 52T in a 104BCD which should fit my crankset here.