KMX trike rear suspension

Jcriv

10 µW
Joined
Jul 12, 2018
Messages
6
Adam333 has given me the opritunity to test his new rear suspension upgrade. I’m starting this post to give anyone interested some info on my first hand experience.
First let me say that the quality and workmanship is outstanding. Far more impressive than the pictures present. I have had the good fortune of owning, and dealing with some very high end aftermarket products made for BMW, and Porsche racing programs. This piece is crafted, and finished every bit as well.
The install is fairly easy for someone who is handy has basic hand tools,and patience. I will say that I’m a carpenter by trade, and have been wrenching on my own toys for years. That said it took my a total of maybe 2 hours if you don’t count beer breaks, looking tools in my mess of a garage. Adam was looking for someone to beta test with a working chain and derailure. My KMX has and idler under the seat that needs to be relocated. I believe some do ,and some don’t. I think I have that issue resolved, and will post pictures as soon as I get Adam’s Ok.
 
The Toecutter said:
Is there any feedback regarding using this with a pedal drivetrain?

Also, how far reclined can the seat be set with this installed?

My web site host provider seems down atm, but here is the feedback Carroll gave me a few month ago :
Davis%20Carroll%201_800x389.jpg

Quote: HOLY SHIT! WOW! HOLY SHIT WOW!!

I didn't know that Colorado roads could feel as smooth as glass!

The rear suspension feels like riding in a stretch limo. The front was a little stiff today but I have reduced the air pressure

for tomorrow and will get that tweaked in the coming days.

I am totally impressed.


________________________________________________________________________________----

He have no motor on his trike.

The seat have roughly 45 deg right now.
If you recline it too far, you will have the wheel hit the seat at some point
Idler%20pulley%206.jpg
 
Thanks! I'm glad to see some results and that this works well! This is an upgrade I am considering making when finances permit. It will also give me something to study to help me design a chassis completely from the ground up with an integrated roll cage, and I'll get plenty of feedback riding it.

The front shocks you sold me have more than 45,000 miles on them so far. I have not replaced any of the components in the suspension other than the mounting bolts and nylock nuts that you sent me for the steering spindles, although I have repeatedly cleaned and lubed it(especially after riding it on salted roads after snow storms). It shows its wear, as there are plenty of chips and scratches, and the steel screws have a bit of surface staining, but it still functions as if it was new and holds air. I need to check the pressure of the gas shocks and add air about twice a year, or about once every 5,000 miles.

I'm aware of the seat hitting the wheel if reclined too far. I'm currently using a 26" rear wheel, with the seat mount as far forward towards the boom as possible, then reclined as much as possible without contacting the rear wheel. Will the installation of the rear suspension require the seat to be relocated? For the rear wheel, I am thinking of eventually going to a 16" motorcycle wheel equivalent in size to a 20" BMX wheel, which will allow me to recline the seat further than it is already. I just want to make sure that the suspension will allow me to do such by not posing additional clearance issues, and will allow me to retain the same seat position that I have.

From a safety standpoint, going to the 16" moto wheel in the rear is contingent upon adding this rear suspension, since most of the roads I ride on are rough and there has been a few times where even with my current 26" rear wheel a pothole has sent my rear wheel airborne at 25+ mph, temporarily causing me to lose control of the trike, so I know that a 16" moto/20" BMX sized wheel is a no-go without this suspension, especially if I'm intent on having a cruising speed anything over 35 mph to justify going to DOT rims, DOT tires, and heavier gauge spokes.

This thing can corner better than most velomobiles because of its wide 39" front track, and I'd like to not give that up, even though it is not conducive to low frontal area. With just front suspension and a 26" rear wheel with 20" front wheels, I can corner at about 0.7g without going up on two wheels, whereas it's not uncommon for typical "fast" commercial velomobiles to tip over around 0.5g lateral acceleration, mainly because they have front tracks on the order of around 25". Since the rear suspension extends the wheelbase another 2", and since a smaller rear wheel will allow a more reclined seat which will lower the center of gravity further(since the rider is heavier than the vehicle), I expect cornering to be improved significantly with the addition of the rear shock, maybe even to the point to where it is comparable to a sports car. 0.7g is already car-like, even though most cars, or trucks and SUVs, can corner faster than that.

The ability to recline the seat further back is also important for reducing frontal area and improving aerodynamics. It may be possible to get a frontal area of just under 0.5 m^2 for a full-bodied trike with recessed front wheels(my current body shell has outboard wheels which are terrible for drag!) keeping the front suspension's 39" track. I want to get a CdA comparable to some of the decent commercially-available velomobiles on the market, like the Quest or WAW, want the velo to be able to safely cruise at car-like speeds and accelerate like a car and top out like a car with the motor in use, and this rear suspension, a more reclined seat, and a smaller rear wheel with a 3T wind Leafbike motor with a high current controller would all be conducive to this goal.

adam333 said:
My web site host provider seems down atm, but here is the feedback Carroll gave me a few month ago :
Davis%20Carroll%201_800x389.jpg

Quote: HOLY SHIT! WOW! HOLY SHIT WOW!!

I didn't know that Colorado roads could feel as smooth as glass!

The rear suspension feels like riding in a stretch limo. The front was a little stiff today but I have reduced the air pressure

for tomorrow and will get that tweaked in the coming days.

I am totally impressed.


________________________________________________________________________________----

He have no motor on his trike.

The seat have roughly 45 deg right now.
If you recline it too far, you will have the wheel hit the seat at some point
Idler%20pulley%206.jpg
 
The Toecutter said:
Will the installation of the rear suspension require the seat to be relocated?

Wow, 45K miles already!

Thanks for the feedback, I am glad to hear the suspension still perform well.

With the rear suspension, the seat do not have to be relocated, the only modification you could have to do is to re drill the two seat tubes that adjust the seat angle if the current holes don't exactly fit with the desired seat angle.

One thing to know about the rear suspension though. My rear wheel is roughly 50 lbs with the cromotor and MOP wheel/tire.
This is fairly heavy and the shock rebound, when going fast, make it hard to keep the wheel all the time on the ground when hitting bumps on the road.

As much as possible, keep the un-sprung weight as low as possible to improve the suspension efficiency. This will help to keep the wheel in contact to the ground.
 
adam333 said:
Wow, 45K miles already!

Thanks for the feedback, I am glad to hear the suspension still perform well.

You designed it well. It's designed better than the actual trike itself, IMO. I'm amazed that the steering spindles have held up for that long as well, given that they are a weak link in the system, but I've also not been very harsh to it since it's been powered almost exclusively by human power thus far seeing rolling averages in the 13-22 mph range 95% of the time with roughly 24-25 mph flat ground cruising speeds, flat ground sprints to 35+ mph, and occasional downhill sprints to 40-50 mph, and one 60 mph downhill sprint. I say almost exclusively human power because there was a brief 5 mile ride under electric power a few months back using a rolling fire hazard of a battery setup and no kill switch.

With the rear suspension, the seat do not have to be relocated, the only modification you could have to do is to re drill the two seat tubes that adjust the seat angle if the current holes don't exactly fit with the desired seat angle.

Good. I probably won't need to drill any holes. This re-uses the same seat adjustment parts that came on the KMX, I presume, and simply re-orients them?

One thing to know about the rear suspension though. My rear wheel is roughly 50 lbs with the cromotor and MOP wheel/tire.
This is fairly heavy and the shock rebound, when going fast, make it hard to keep the wheel all the time on the ground when hitting bumps on the road.

As much as possible, keep the un-sprung weight as low as possible to improve the suspension efficiency. This will help to keep the wheel in contact to the ground.

I will be using a 17 lb Leafbike motor on the rear wheel, and the rear wheel itself will likely be a 16" motorcycle rim with 10-12ga spokes with a Mitas MC2 low rolling resistance scooter tire. Hopefully that's not too much. In the long term, I may end up with a 96V nominal setup that can approach 90 mph though, and there is a lot currently on the trike that will NOT be up to that task which will need replacement. I think your suspension designs are robust enough though!
 
The Toecutter said:
Good. I probably won't need to drill any holes. This re-uses the same seat adjustment parts that came on the KMX, I presume, and simply re-orients them?

Exact, same adjustment parts, the two tubes holding the top part of the seat will be oriented toward the front of the trike instead of the rear.

And yes, I over designed the suspension strength. Better be safe than sorry!

The rest of the trike is not designed for high speed though.
 
I tried this out in the street for the first time today.

Before installing this rear suspension, going over bumps at 30 mph used to send the rear of the trike airborne. I'd temporarily lose control and had to keep the steering unchanged until the rear wheel remained in contact with the ground, otherwise I could flip the trike.

I don't have to worry about that anymore. I had this installed last week, and finally got the trike ridable today, minus a functioning electric drive system. I deliberately hit a deep pothole while bombing down a hill at 30 mph, and instead of the rear wheel going airborne, the seat lifted up about an inch and it felt like the trike was going to fly, but it retained stability and lowered itself back down. My primary goal with this has been met. I no longer have to worry about deep potholes causing me to lose control because they no longer launch the rear of the trike inches into the air.

As a result, it's also a LOT more comfortable to ride. Very smooth. It's more comfortable than some cheap cars that I've ridden in. On the whole, having full suspension on this trike made it ride as comfortably as a 90s economy car, at least at the < 30 mph speeds I've ridden it like this. From the standpoint of comfort, my expectations are well exceeded.

I'm very happy I made this modification. This is a good design and it works.
 
The Toecutter said:
As a result, it's also a LOT more comfortable to ride.
I'm very happy I made this modification. This is a good design and it works.

Thanks for the feedback :)
Glad to hear you enjoy the suspension!

Just for my statistics, did you had a chance to measure separately your rear wheel weight?
 
Including tire/tube, my rear wheel weighed in at 18.8 lbs. I weigh 145 lbs and had to have the rear shock inflated to 95 psi for the bottom of the frame to be straight after performing the "bounce test".

adam333 said:
Just for my statistics, did you had a chance to measure separately your rear wheel weight?
 
I'd also like to revise my assessment of the trike with the complete full suspension. I used to run the front shocks at 60 psi, and noticed they were not as soft going over bumps as the rear shock set at 95 psi. So I reduced the front shocks from 60 psi to 45 psi.

HOLY SHIT WOW indeed. It now rides as smooth as an old Citroen, at least below 25 mph(that is all I was able to pedal it to on the limited distance of flat I had before an uphill climb ended my top speed sprint, and the batteries aren't installed at the moment). But still, this thing rides VERY smooth. With the front shocks now riding softer, it's easily a more comfortable ride than most cars I've ridden in, period. I deliberately aimed for deep 3" potholes and it felt like it floated over them, and silently at that! How much of that smoothness was the tequila I was drinking before riding and how much of that smoothness is the suspension itself is still easy to determine, as it was THAT noticeably different from before.

The removal of the body shell and battery reduced the weight sufficiently that I don't need as much air. Thus the front rode more harsh than before.

I'm anxious to see how a properly adjusted setting does at higher speeds. I hope it's not too soft for these pothole-laden roads at 35+ mph, as I don't want to damage anything or bottom out.

This was well worth the money for the kit, and well worth the time invested to make it work. Highly recommend. Looking forward to hooning about using the motor with the battery reinstalled.

:bigthumb:
 
The Toecutter said:
Including tire/tube, my rear wheel weighed in at 18.8 lbs. I weigh 145 lbs and had to have the rear shock inflated to 95 psi for the bottom of the frame to be straight after performing the "bounce test".

Thanks for sharing those numbers!
My rear wheel is 50 lbs and this does impact the rear suspension rebound!
 
Thank you for selling me this awesome suspension that you designed!

Just waiting on the braking system. I won't be in any rush to install it though, as my time to work on this project is limited due to my job demanding all of my hours. I still need to get the next body design finalized so I can start working on it. The space occupied by the brakes and the lines going to them might determine how I design my wheel wells.
 
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