What frame for a light weight Full-Sus MTB conversion?

[liteCycles]

I'm sure many are pondering the same question right now.

Wish list --
1. 3 to 4 Kw (Astro most likely).
2. Light, powerful LiPo batteries.
3. Strong bottom bracket area for mounting of 2 stage reduction unit (Recumpence?).
4. Freewheel crank (2 stage unit driving a ring on the crank).
5. Room for some big chainrings. The bike would also be a used for plush high speed commuting (just change the wheel set).
6. A rugged way to mount batteries (but would like to switch out to a fresh pack quickly -- off road riding).
7. Around 40 lb would be great!

Here is candidate number 1:

 

[deecanio]

Hi Litecycles,

i would say that bike is a very reasonable choice, but you may do better?
Bearing in mind when i bought my Kona (similair geometry) i was using a hub and planned all that lovely triangle space for my cells - now i've had the issue of clamping the rc drive onto a non round downtube
that said that one looks nice and round but theres probably better to be had tbh. :lol:
you need to consider how much of the space in the frame you will need for the batteries for the range you want to achieve - imo you cant beat a triangle mounted battery container :wink: ,but you then would have to mount your dual stage right down the underside of the bike - huh may work out nice if the downtube is cylindrical all the way ??? - certainly the suspension on that bike goes the "right" way and won't encroach your pack.
Can't see too many issues with your choice tbh - anyone else see issues?
Personally i had the same dilemna, lightweight dh or xc bike? it's a tricky one for sure.


Cheers,

D

 

[grandmasterE]

From a suspension standpoint, it's not a bad design for high draive chain torque as the parallel arm suspension is meant to neutralize chain torque. In reality though you have to be very careful with chainring sizing as torque angles can tend to effectively 'lockout' this suspension design. You need the final drive ring to be big to keep the suspension neutral (like a lot of mtbs)

On the downside is the fact that the tubing on lightweight bikes is seriously paper thin, and you have to be very careful with your mounting of the drive. The other downside? That's a hellishly expensive frame, and my experience with Rocky Mountain is that you probably overpay for the name (that frame and shock probably retail for ~$2100-2300 USD).

Having said all that, it's one of the few bikes to use parallel link suspension like that (sort of a modified lawwill control arm suspension I suppose, probably only gets around the patent by having the axle under the lower control arm). Lawwill suspensions were always known as very good, the only downside was brake jack. The ets-x from Rocky has a decent suspension, but in that short of travel sometimes some of the idiosyncracies are hidden, other than chain torque lockout and brake jack. Choose a larger enough drive ring and you should be fine.

One side benefit to this particular bike-the air suspension! You can easily change the spring rate by adding or removing air. This is important if you want it to ride well and you change the weight drastically by adding and removing batteries and drive components. This can't be done with coil suspensions without changing the springs.

E

 

[liteCycles]

The ETSX was my #1 candidate because I found a screaming deal on Craigslist and didn't know if I should pounce. Thank you both for the unbiased critial reviews. I bought it last night. And to my great pleasure the cost of components alone made it worth it! I will post many details as I spec and execute this build. Deecanio, your build thread has been very helpful in guiding me in the selection process.

The Specialized FSR was high on the list a well, but the resale on these is still quite high. And they have irregualar shaped tubing. But this can be delt with. Check out the clamps on this Trek Soho --


So, my frame is a 2006, it is tight and looks fantastic. Everything else is brand NEW! (well, except the pedals :lol: and the fact that I hit the trails for an hour on my way home!). The guy had friends who worked in bike shops and he built it up over the winter and now must move to NYC. (He had an impressive quiver of bikes hanging in his garage I might add!). Full XT groupo, Chris King Headset, Hugi 240 hubs, etc... this bike was $1200. Yeah, this will make a good test bed! --

 

[deecanio]

nice 8)

the white background picture doesn't do it justice, it's very nice looking and the components are sound
I'm a fan of the fsr too (luke has a monster fsr worth checking if you haven't) but to electrify stealthily would be difficult.
with the travel the ETSX has is that an xc bike? i have a rough idea of what is what with mtb catergories but by no means an expert
Now that we are into the rc running gear and good batts this is a very good choice, i went for the heavier dh'er because my first set of batts were nearly 30lbs and my hub motor was 8-10lbs thus i would have probably snapped something if i went with a lighter frame such as yours and started to throw it off jumps, but now.........
What are you going to do for the rest of the build? mounting your electrics and batts inside, dual drive on the downtube?


Cheers,

D

 

[liteCycles]

Here is how BikeMag described it - "Epic cross country, adventure riding, call it whatever you want, the Rocky Mountain ETSX-50 is what you ride when super lightweight bikes fall apart and long-travel freeride bikes are too heavy." When I tap my fingernail along the down tube it sounds like it starts to taper thinner a couple of inches up from the last weld for the shock support. But like grandmasterE pointed out paper thin aluminum was one of my major concerns when I bought it. Feeling pretty confident. (Famous last words?!)

For non-round tubes like yours I would get some construction paper then cut out 1/2 the profile with scissors. Dry fit it, shave paper with razor blade, dry fit, shave, ... until you had an exact match. Repeat for other side of tube. Now you have a template to draw the profile onto an aluminum block. Actually machining it is a whole 'nother story.

For the rest of the build? I am laying it out in a spreadsheet. Looks like $3,300USD and 41.5 lbs. Really short on firm details at this point, but it will be driven through the crank like the Soho. Maybe a sensored Astro Flight is in the cards?

 

[MitchJi]

Hi,

when i bought my Kona (similar geometry) i was using a hub and planned all that lovely triangle space for my cells - now i've had the issue of clamping the rc drive onto a non round downtube

How big a deal did that turn out to be? How important do you think a round down-tube is for Matt's drive?

Personally i had the same dilemna, lightweight dh or xc bike? it's a tricky one for sure.

Cheers,

D

I found the following definitions on the Web:

Cross Country (XC):
Many of these bikes are designed with... steep head and seat tube angles to allow a more forward leaning body position during riding...

Typical Configuration:
Frame Geometry: Head Tube Angle 70 degree; Seat Tube Angle 73 degree;
Wheelbase 43 inches.
Average Build Weight: 20 to 30lbs depending on component selection.
Suspension Travel: 3 to 4 inches for both fork and rear shock.

All-Mountain (AM) or "Backcountry":
Mountain bikes that fall into this discipline are a cross between XC bikes and FR
bikes. They are designed for efficient pedaling but have slightly heavier frames
to handle more aggressive technical riding that may involve jumps.

Typical Configuration:
Frame Geometry: Head Tube Angle 68 degree; Seat Tube Angle 73 degree;
Wheelbase 45 inches.
Average Build Weight: 28 to 35lbs depending on component selection.
Suspension Travel: 4 to 6 inches for both fork and rear shock.

Freeride (FR):
Mountain bikes that fall into this discipline are designed to handle the stress of
large jumps and extreme technical riding. FR mountain bikes are probably the most
versatile bike for aggressive technical riding. With today’s suspension technology
and rear linkage designs, FR bikes are somewhat capable of being ridden uphill and
are moderately maneuverable at low speed regardless of a "slack" riding position.

Typical Configuration:
Frame Geometry: Head Tube Angle 66 degree; Seat Tube Angle 71 degree;
Wheelbase 45.5 inches.
Average Build Weight: 32 to 45lbs depending on component selection.
Suspension Travel: 6+ inches for both fork and rear shock.

Downhill (DH):
Mountain bikes that fall into this discipline are designed for handling extreme
technical riding at high speed. Typically with 8 inches of travel, DH bikes
can handle the biggest jumps, steepest descents and most technical rock gardens
that you have the balls for. Designed with a long wheelbase and "slack" rider
position, a DH bike is not ideal for riding general trails in the woods, but
will serve its purpose when you traverse trails on an exclusively lift
accessed terrain.

Typical Configuration:
Frame Geometry: Head Tube Angle 64 degree; Seat Tube Angle 65 degree;
Wheelbase 47 inches.
Average Build Weight: 35 to 60lbs depending on component selection.
Suspension Travel: 6 - 8+ inches for both fork and rear shock.

Based on those descriptions a "backcountry" or "All-Mountain" is probably a better choice than a pure XC. Generally similar geometry with a stronger heavier (a few pounds isn't a big deal on an Ebike) frame. Sounds like you have a "backcountry" so thats probably good.

One problem with Ebikes is that a lot of bicycles don't handle very well at higher speeds (above about 25 mph?). How will a AM, FR and DH compare in terms of handling at 25 mph to 35 mph? How well does it handle at 25mph to 35mph? Would you be better off with a FR or DH?

For a commuter Ebike is a Kona Dawg (backcountry) be a better choice or a Kona Stinky (Freeride) or a Downhill Bike? How well will a Dawg or Stinky handle at 35mph?

 

[deecanio]

Hi Mitch,

Thanks for the classifications,i was basing it on suspension travel mainly but i wasn't too far out.
The mounting on the Kona was an arseache to be honest but we have managed to mount it just not test it yet!!! Bob is away next week but there is only a days work for a test ride which will happen next Monday once he's back from leave.
It would be a LOT easier to mount to a totally round downtube for sure, looking at lite's bike it seems he will have that option which is great, he may also benefit from my fitting as he could mount in the same manner as our frames are very similair but i won't suggest it until i know it works :wink: .
Based on my experience the ETSx will be fine at 30mph+, as i said given that we don't have to have a hub and some heavy ass batts the kit could be 12-15lbs total which is nothing, tbh i don't expect lite's bike to handle much differently than standard which will be stonking!!!
Do the right thing lite, get all your batts and controls in the traingle and the drive nice and close to the bottom bracket, it will keep you with a good centre of gravity, protect your batts and look real sweet
good luck with the build!!!!


Cheers,

D