Is a full-on Downhill DIY ebike a mistake for XC Singletrack?

General Discussion about electric bicycles.
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slm9s   100 mW

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Is a full-on Downhill DIY ebike a mistake for XC Singletrack?

Post by slm9s » Jul 25 2021 12:00pm

My build will be ridden for exercise on XC trails, 30min to an hour usually. This bike will be getting a BBSHD. I'm a big guy, exFB player 6'5 270lbs. Its hard to find suitable used/older FS bikes in XL or XXL that don't break the bank. Last week I bought an '08 20" Kona Dawg Supreme, which is Kona's "Backcountry XC" full suspension bike with 5" travel front and rear. My other bike is a Specialized SX Trail 6" bike that I put a 1500w hub on because the BBSHD wouldn't fit due to the Burley BB. Riding the Kona (non-electric) sure seems "flimsy" compared to the Freeride/Light DH SX trail. (maybe its the 5" fork that only has a QR) Now a full-on DH Transition TR450 with 8" F/R popped up for sale. Its twice the money, but my concern is that my 270lbs with another 30+lbs of DIY conversion would snap the Kona and I'd be better off with the burlier DH bike. However, I've never ridden a DH bike on trails, just a couple test rides down the street/etc. Would a DH bike and its angles/geometry not be fun on level/normal XC singletrack, or would the BBSHD take away the negative aspect of it being heavy/tough to pedal and all that travel would be an absolute blast?
Anyone with experience care to chime in?
Thanks in advance!

HrKlev   1 kW

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Re: Is a full-on Downhill DIY ebike a mistake for XC Singletrack?

Post by HrKlev » Jul 25 2021 12:14pm

If you are planning to pedal, I would look for an enduro or all mountain frame which still has decent travel and is meant to be pedaled, rather than full on DH frame. That being said, I have never built a DH frame, so Im in for being proven wrong 😀
Hubdrive as middrive, with torque sensing EMTB build: viewtopic.php?f=6&t=107622

6x6 conversion: viewtopic.php?f=34&t=109567

TNC   100 W

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Re: Is a full-on Downhill DIY ebike a mistake for XC Singletrack?

Post by TNC » Jul 25 2021 1:55pm

slm9s, doesn't that Transition have an ISCG BB like your Specialized has? If it was a problem for the mount in the Specialized, what would be different for the Transition TR450? It's not impossible to mount a mid-drive on an ISCG BB, but it presents its own challenges.

I think your concern about your weight and the off road use is probably warranted. You'll need beefy wheels to go along with that too. I went the all-mountain/enduro type setup with a Santa Cruz Nomad, and there are probably a fair amount of used and not totally abused bikes like this in this category. I weigh 200 pounds. I use a backpack battery setup and ride this bike on fairly aggressive trails...some downright gnarly. However, like most places one rides there are more mellow sections with tight corners, trees, and other obstacles where you still need some sharp cornering.

Your observation on bike weight is correct. My Nomad weighs nearly 50 pounds without battery, but it melts away when you're riding. In fact I will contend the bike is more stable and instills more confidence. The motor erases the burliness of the bike.
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slm9s   100 mW

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Re: Is a full-on Downhill DIY ebike a mistake for XC Singletrack?

Post by slm9s » Jul 25 2021 2:36pm

The SX trail did have the tabs, but instead it was the fact that the downtube was reinforced toward the front wheel at the bottom bracket (thicker) that made the BBSHD not fit.

I will of course inspect the bottom bracket area to make sure it will fit. And I would love to find the perfect AM/Freeride bike like yours for a good price locally, but I've been scouring the internet and XL/XXL bikes are tough to find. Instead I'm seeing if people have been happy converting a full-on downhill bike for use on XC trails.

Thanks.

Grantmac   10 kW

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Re: Is a full-on Downhill DIY ebike a mistake for XC Singletrack?

Post by Grantmac » Jul 25 2021 3:16pm

If it's fitness you're after leave the motor at home, especially a DIY setup which includes a throttle.
If however you must add a motor then do something like this:
viewtopic.php?f=6&t=107622
Which offers minimal weight and just enough assist to help without taking over. Also it'll fit on nearly any frame.

TNC   100 W

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Re: Is a full-on Downhill DIY ebike a mistake for XC Singletrack?

Post by TNC » Jul 25 2021 3:30pm

One of the problems with many DH bikes is that the downtube has that curved feature as it approaches the BB. It's done for a strength and geometry effect, but it puts the motor at a pretty low ground clearance. I have seen the older Santa Cruz V10 and VP Free models that have the straight downtube fit BBSHD with good results. There are some links and YT vids of them. Just be aware that most of these DH frames and geometry design are hard to turn if your trail has a lot of between-the-trees, tight turns, or switchbacks. This is even apparent in my Nomad pictured, and I don't even have the slacker geometry and length of many of the DH bikes. Since I'm used to riding dirt motors, trying to turn a long, slack MTB around corners isn't as weird an effort for me. Most MTB-only people who have jumped on my bike think its unwieldy, while their bikes often feel twitchy to me. Depending on where you ride, a DH bike may be difficult to corner and such. Just something to consider.

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Re: Is a full-on Downhill DIY ebike a mistake for XC Singletrack?

Post by TNC » Jul 25 2021 3:43pm

Grant, I'm sure you're not suggesting that a rider doesn't get a decent workout on an emtb. If you've dirt motored, you know that even the power of a gas motor and 12-14" of travel will wear out a rider after a bit. It is the beauty of PAS where if you care about the fitness and fun of pedaling, that you're still working to scoot down the trail. The throttle only has to be used when a critical point in the trail causes the rider to have to resort to it to save a nasty ascent or obstacle.

I rode for two hours yesterday morning and ended just before temps hit the high 90's after noon. Pedaling and doing all the normal body english to get a bike over and around challenging obstacles still takes it out of you even with assist. But it's still fun as heck. I could not have ridden that long or aggressively on so warm a day without PAS anymore. I know BC generally has much nicer temps this time of year...LOL!

Grant, I'm sure you've mentioned it before, but what do you ride and prefer for your own personal riding conditions?

Grantmac   10 kW

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Re: Is a full-on Downhill DIY ebike a mistake for XC Singletrack?

Post by Grantmac » Jul 25 2021 5:35pm

Sure +2 two hours of EMTB does have certain fitness challenges so long as you are riding difficult terrain. But 30-60 minutes around home isn't going to do much when you're using a motor that simples adds way more power than you need.

I ride a lot of classic West Coast single track and the iconic "Dump" Aka Hartland is my local (not me riding but a similar level):
https://youtu.be/xnvG84k-FWc

Currently all pedal powered because my Cyclone DH build is just too much motor to enjoy in that environment and I'm not totally sold on what's currently available in the DIY realm. Specifically I want to build an Enduro 650b under 45lbs. Lightest and X1 Stealth are getting really close though, I just need them to rack up some miles first.

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Chalo   100 GW

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Re: Is a full-on Downhill DIY ebike a mistake for XC Singletrack?

Post by Chalo » Jul 25 2021 6:10pm

Grantmac wrote:
Jul 25 2021 5:35pm
Specifically I want to build an Enduro 650b under 45lbs.
If by "Enduro" you mean a bike that has a suitcase full of battery instead of a frame, then your weight goal is not feasible. It's barely feasible if you start with a proper bike.

If you have what I would consider to be a very modest weight budget of 20 pounds for motor, battery, controller, and cable harness, then that would leave a margin of 25 pounds for a full suspension bike including battery mounting furniture. It's not strictly out of the question, but it seems like it would be both expensive and fragile.
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Grantmac   10 kW

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Re: Is a full-on Downhill DIY ebike a mistake for XC Singletrack?

Post by Grantmac » Jul 25 2021 8:36pm

Chalo wrote:
Jul 25 2021 6:10pm
Grantmac wrote:
Jul 25 2021 5:35pm
Specifically I want to build an Enduro 650b under 45lbs.
If by "Enduro" you mean a bike that has a suitcase full of battery instead of a frame, then your weight goal is not feasible. It's barely feasible if you start with a proper bike.

If you have what I would consider to be a very modest weight budget of 20 pounds for motor, battery, controller, and cable harness, then that would leave a margin of 25 pounds for a full suspension bike including battery mounting furniture. It's not strictly out of the question, but it seems like it would be both expensive and fragile.
I'm mean a 27.5er (possibly 29er mullet) with ~160mm of travel. Power systems I'd consider are around 10-15# including battery. I intend to use power simply to build momentum to clear sections rather than hike them, not flow uphill.

I have no interest in the "enduro" style of light electric motorcycle which has no place where I ride. If I wanted that I'd ride my Cyclone build.

COAR   100 W

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Re: Is a full-on Downhill DIY ebike a mistake for XC Singletrack?

Post by COAR » Jul 25 2021 10:57pm

I wouldn't want to take a DH bike on relatively tame XC trails. I.e if I can ride my cyclo cross bike on it, taking a DH bike there would be a slow and frustrating endeavor. You'd get some good exercise without a motor but IDK how enjoyable it'd be. I've rented DH bikes at winter park a couple times and needless to say, I'm glad they had a lift - pedaling a DH bike is tolerable on flat for shorter distances, doing it uphill just sucks.

However if you add a BBSHD and enough battery to a DH bike and take it on those same XC trails at 30+ MPH, that'd be a lot of fun, but you probably won't be pedaling very much.

In short, no. Maybe look into an enduro style bike?

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ferret   1 kW

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Re: Is a full-on Downhill DIY ebike a mistake for XC Singletrack?

Post by ferret » Jul 26 2021 1:48am

Chalo wrote:
Jul 25 2021 6:10pm
Grantmac wrote:
Jul 25 2021 5:35pm
Specifically I want to build an Enduro 650b under 45lbs.
If by "Enduro" you mean a bike that has a suitcase full of battery instead of a frame, then your weight goal is not feasible. It's barely feasible if you start with a proper bike.
What mountain bikers mean when they refer to Enduro bikes is mountain bikes designed for Enduro Racing or enduro riding (what used to be called All Mountain riding ) like these:

https://www.redbull.com/gb-en/the-best- ... ikes-guide

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