Help my EMTB go faster - tech says it can't :(

The duke

Active Member
Hi guys. I've got a BH EasyMotion Atom X. It's got a 38T chainring in front and the smallest (fastest) chainring in the back has 11T (teeth). The tech at my local bike shop says 11 teeth is the smallest there is at the back wheel, and anything bigger than 38 teeth up front would hit the frame or gear cable.

I love passing fit, muscular roadies on uphill with my fat tired ebike, but they always catch up to me on the downhills, as my top speed is about 25mph with my legs spinning like crazy. I'd like to be able to go a little faster on those downhills. Thanks in advance!
 
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Timpo

Well-Known Member
Is your 38T chainring an aftermarket?

I saw some pictures of Atom X, and looks like you do have space to go slightly bigger, but the chainring said 32T.
 

The duke

Active Member
Is your 38T chainring an aftermarket?

I saw some pictures of Atom X, and looks like you do have space to go slightly bigger, but the chainring said 32T.
Where did you see it was 32T? Maybe the tech was wrong! I dropped it off to the shop requesting a tune up and to increase the chainring size. It's currently stock. I hope you're right.
 

Timpo

Well-Known Member
ok I just noticed that chainguide has an adjustment that goes up to 38T, but I don't know what you have though.
 

Timpo

Well-Known Member
I'm not familiar with Brose mid drive crankset is attached, but here are some possible ideas.

As you know, there's only 1 chainring on the Brose mid drive, but where is that chainring exactly located if you compare to the 3 speed crankset?

Because let's look at the typical RaceFace crank, as you can see there are 3 chainrings.
Obviously each ring has different location.

But where's the Brose chainring located in comparison to RaceFace 3 speed crank?
My guess is that RaceFace's middle gear probably is equivalent to the Brose's chainring location.

So here's are 2 possible solutions:

1. Get the RaceFace crank, and just keep the highest gear. And get the chainguide custom made? This kind of fabrications happen all the time at motorcycle shops.

2. See if you can attach the stock chainring outwards. As you can see, the stock chainring is attached inwards, but is it possible to attach it from outside? I am talking about those 4 bolt attachments. As of now, you know how chainring is sort of hiding behind the crankarm? What if you attach the chainring on top (outside) like RacaFace is doing for the top gear? (sorry I don't know if I explained it clearly)

 

Timpo

Well-Known Member
you're gonna mess up the motor.
That's what a lot of ebike shop owners and mechanic say, but I never understood.

The classic example is when people install speedbox or something to unlock the 20mph limit, their argument is something like "Yamaha designed this motor to go up to 20mph, not 28mph or 30mph"

But why does it matter? Since it's a mid drive, as long as the cadence (110rpm or whatever) doesn't change, wouldn't that be a same thing?
What if you get a larger chainring? How is that any different from a light person going on flat surface with larger chainring, than a heavy person climbing up hill with smaller chainring?

Also there's a motorcycle called Suzuki TU250x, what a lot of TU250x owners do is to change the front sprocket (equivalent of ebike chainring) to get a better highway cruising capability and wider gear range, to keep the rpm low at top gear, etc.
 

The duke

Active Member
you're gonna mess up the motor.
Hi Mike. I consider you an expert! Can you expound? Will I really mess it up, or just tax it a little more. As an almost 50, easy riding person, I'm far below the max parameters of the engine on a day to day basis. Think I could really kill a brose with 2 extra teeth?
 

The duke

Active Member
I'm not familiar with Brose mid drive crankset is attached, but here are some possible ideas.

As you know, there's only 1 chainring on the Brose mid drive, but where is that chainring exactly located if you compare to the 3 speed crankset?

Because let's look at the typical RaceFace crank, as you can see there are 3 chainrings.
Obviously each ring has different location.

But where's the Brose chainring located in comparison to RaceFace 3 speed crank?
My guess is that RaceFace's middle gear probably is equivalent to the Brose's chainring location.

So here's are 2 possible solutions:

1. Get the RaceFace crank, and just keep the highest gear. And get the chainguide custom made? This kind of fabrications happen all the time at motorcycle shops.

2. See if you can attach the stock chainring outwards. As you can see, the stock chainring is attached inwards, but is it possible to attach it from outside? I am talking about those 4 bolt attachments. As of now, you know how chainring is sort of hiding behind the crankarm? What if you attach the chainring on top (outside) like RacaFace is doing for the top gear? (sorry I don't know if I explained it clearly)

I got the info from here: https://bikerumor.com/2017/08/23/bh-overhauls-emtbs-asymmetric-integrated-atom-x/

Look, it says "32T" on the chainring.

You're awesome Timpo. I forwarded this to my bikeshop owner. He said my chainring has no such marking he recounted and there are 36T. I'm weirded out. He thought 38T, online shows 32T and hes now counting 36T. How do you know it fits up to 38? What would the noticable benefit be in going up 2 teeth at the crank? Much?
 

Timpo

Well-Known Member
You're awesome Timpo. I forwarded this to my bikeshop owner. He said my chainring has no such marking he recounted and there are 36T. I'm weirded out. He thought 38T, online shows 32T and hes now counting 36T. How do you know it fits up to 38? What would the noticable benefit be in going up 2 teeth at the crank? Much?
I know it fits up to 38T because if you look at the picture, you can see the chainguard is adjustable.
Look at the bolt that's holding on to the chainguard, it says "32T, 34T, 36T, 38T".

My guess is that BH gave you an option to choose from 32T to 38T.

Now, the question is, will you be able to go above 38T?
You will definitely not be able to use the stock chain guard (if you need it or important to you).
However, the chain guard can easily be relocated or refabricated.
Just to go a motorcycle shop, or any other metalwork shop, metal fabricator, etc.

I am not sure how big you can fit up to without hitting the frame, 40T? 42T? I don't know... so that's why I suggested getting a RaceFace (or any other brand that offsets the chain ring) so that you would not hit the frame. In the perfect scenario, you "might" be able to go as high as 52T (such as one that you can see on AliExpress). However, please note that I have no way of confirming with 100% certainty that RaceFace offsets far enough that chainring will not hit your frame.

There are numbers of bicycle gear calculator, but I used this one.
The stock Atom X comes with 27.5 x 2.80 tires.
http://www.berkshiresports.org/index.php?ID=bikegearcalculator

If you use 36T front & 11T rear, the speed at 90rpm cadence will be 25mph.
If you switch to 38T, at 90rpm cadence, it will be 26mph.

So only 1mph difference if you go up to 38T.

I will make a few list here,
Speed @90rpm cadence with 11T rear cog:
32T - 22 mph
34T - 24 mph
36T - 25 mph
38T - 26 mph
40T - 28 mph
42T - 29 mph
44T - 31 mph
46T - 32 mph
48T - 33 mph
50T - 35 mph
52T - 36 mph

Also if you get a larger chain ring, as you know you will lose the lower gear ratio.
You might want to consider getting a different cassette as well.

Here's a 11T-50T casse for 10 speed MTB.
https://www.aliexpress.com/item/32866565957.html?spm=2114.search0204.3.57.7674a081OVc3nH&s=p&ws_ab_test=searchweb0_0,searchweb201602_2_10065_10068_10130_10547_319_10059_10884_317_10548_10887_10696_321_322_10084_453_10083_454_10103_10618_10307_537_536,searchweb201603_51,ppcSwitch_0&algo_expid=96b6a665-0f91-4313-9ed1-9c2d921539bc-7&algo_pvid=96b6a665-0f91-4313-9ed1-9c2d921539bc&transAbTest=ae803_5
 
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Ebiker01

Active Member
Prob. The mid drive won’t support the much higher torque needed for a bigger chainring. Bigger then 42 maybe is a problem and definitely a big priblem if it’s 46t and higher.
That motor is designed for spinning not high torque or instant high torque. Or high torque on a big load (48t).

I went on mine from 48t to 52t (rear motor) and from 29mph top speed 90-95rpm, i go 31-32mph @85-92rpm.
 

The duke

Active Member
Prob. The mid drive won’t support the much higher torque needed for a bigger chainring. Bigger then 42 maybe is a problem and definitely a big priblem if it’s 46t and higher.
That motor is designed for spinning not high torque or instant high torque. Or high torque on a big load (48t).

I went on mine from 48t to 52t (rear motor) and from 29mph top speed 90-95rpm, i go 31-32mph @85-92rpm.
Wow, 4 tooth increase only equaled a 3mph gain. That's a little disappointing. I find wind resistance really starts kicking in above 25mph and hurts my ears, so I actually would just like to keep it there with a lower cadence. How does the 5 lower rpm translate as user experience? Is it noticeably more comfortable to ride? If I go up from 36T to 38T, I'll only gain about 1.5mph, but I'm hoping that at my old top speed, I'll lower the hamster wheel effect.
 

Bamboo44

New Member
I’ve got an Atom X with a 32T chainring - and just bought a 38T chainring.

Where can I find instructions or videos on changing the chainring. The chainring looks like it can be changed without removing the crank - but I need to know how to get at the chain guard at the top of the chainring that appears to be screwed in from inside the motor side cover.
 

The duke

Active Member
I’ve got an Atom X with a 32T chainring - and just bought a 38T chainring.

Where can I find instructions or videos on changing the chainring. The chainring looks like it can be changed without removing the crank - but I need to know how to get at the chain guard at the top of the chainring that appears to be screwed in from inside the motor side cover.
In reviewing my BH warranty info, I saw that they have regular tune up intervals that they require to keep coverage. Theres a sign off section in the warranty manual for the dealer to stamp and date his service. I took my bike in to an authorized dealer for the tune up, which was $60 and they installed the chainring for an additional $10. They also adjusted everything so it would still shift well with the new and unworn chainring and my stretched chain. I think $10 well spent and hopefully a little backup in case I ever need to make a claim.