I'm about to install my e-bike kit onto a mountain bike with rear suspension. I understand if you tighten the spring, this will make the bike more rigid to make the bike go faster when pedaling.

Q1: I don't really use suspension because I mostly travel in the city on flat streets. Would tightening the suspension all the way also improve the speed I get with a hub motor?

Q2: Also, some rear rack (for mounting batteries) instructions tell you not to mount the rack to the rear axle and the seat post with rear suspension because if you mount an immovable object to a movable object then there is a chance you could break your rack. I assume that I should be fine if I tighten my rear suspension all the way making the bike as rigid as possible. Does anyone have any experience along these lines?

The reason you might gain speed with tighter suspension is the bike is sagging as you pump on the peddles causing you to lose thrust and torque. To most people this is not a major lose factor and the gain in having suspension out weighs the loses. One of the major gain of couse is personal comfort and reduced slamming on the spokes and rim when you hit bumps (both small and large). This all being said I see no reason a suspension system could effect the speed of a hub motor. It's in the wheel and uneffected by the suspension. This would be the same situation if you are looking at a non-hub motor. If torque is uneffected by the suspension if properly installed.

You are correct you can not attach a solid rack on a suspension bike unless the rack is connected to parts of the bike that are not involved in the suspension. Thinking of a suspension as a 2 peice bike you need t ofind a rack that only connects to the drop out bars and the axle. This type of rack is only connecting to the rear section of the 2 peice bike.

Honestly I think trying to lock the suspension is a mistake especially now when you are going to be adding weight to the bike.

Bob

I got you, thanks for the info. I just need now to devise a modification to the bike rack. My e-bike kit comes with a rack and I cannot afford another so I have to figure out a way to make this work. It's finally getting shipped here tomorrow! I cannot wait to get this thing together. I may have to bolt on some extra extension bar/parts or some kinda of clamps to make this work.

It can connect to the seat post. I am thinking perhaps still connect it there but where it can pivot up and down instead of being locked down tight. This way the rack will still move with the rear suspension.

BE VERY CAREFUL

your batteries are the most expensive part of the conversion kit.....

I have seen racks that are designed to be bolted onto the 2 suspension bike, and just by looking, i would go with that........ it bolts onto the seat, so the batteries would be suspended as well.....

considering the cost you have already gone to for the kit and batteries, i would hang off and wait until you could afford the proper rack for your bike....

riding ebikes is fun but
are bad

hope this helps, let us know what you do and how it goes

You say you don't use the rear suspension does this mean it has lockout? because if it doesn't have lockout your still using it and just don't know what it's doing for you.
You can't mount a rack to the swingarm and frame, that connects to moveable objects(once again unless you have lockout)

your speed will improve very little from tightening the suspension but only when pedaling, realistically i'm not really sure how much energy gets absorbed by the suspension.

Nope, I don't think you can do that. The seat does noy just go up/down when the suspension moves. While up/down maybe the prime movement it is actually moving in a radius. Therefore, the true distance from the seat to the rack changes constantly depending on the degree of suspension movement.

As others have already stayed those batteries no matter how good or bad they are are the most expensive part of your purchase. You need to think this through so you don't have them bouncing down the roadway.

Bob

I have built 7 ebikes - both rear hubmotor suspended mountain ebikes and front hub motor non-suspended.

I have found the rear conversions to be less than satisfactory...

a.) More complexity with drive train/spacing/disk brake issues.
b.) Rear rack must be fortified or braced down to seat tube, as it is not connected to near the dropout.
c.) Forces batteries to be mounted in frame as too much weight on back on questionable rack support otherwise - all of the weight would be on the back - motor and batteries. Very unbalanced.
d.) Can't use internal hubs such as Nexus or Nuvinci.
e.) Not really good for normal panniers with side-to-side shifting of loads possible even with fortified seat racks.
f.) Too much bobbing around with all that weight on the suspension.
g.) Easier to have a removable battery solution for use on multiple bikes in a frame which has no battery "well" ie. a non-dedicated ebike frame.

The front hub motors are easy to install and are nicely balanced against a battery on a rear unsuspended rack. The battery can be put in a wire office tray on the rack to give it some side impact protection. Or the battery can be put in a pannier.

I also have a recumbent and a 20" folder with front hubs, they are both much better and easier to build than the mountain bike with the rear motor, and the battery placement makes much more sense (under the seat low down on the recumbent, or on the rear rack of the folder). Good balance.

If you are pedalling oriented rather than just building an e-motorcycle, the batteries in the frame or in the diamond are a painful struggle to realize and rather get in the way of pedalling.

Much prefer the front hubs - need two very good torque arms, no alloy forks, decent dropouts...

I use 48V 15Ahr Ping batteries in a Plano 1412 waterproof marine box (fits perfectly with 1/2 inch closed cell foam inside the box around the battery except not to smother the BMS), placed and bungied into a wire office tray zip-tied to the top of my rear rack on the folder - easy to remove the battery and very well protected if the bike falls over. I open the box for charging, due to BMS heating during charging.