Advice on souping up a Murray Nitrox?

[TheQ]

I plan on putting a dirt bike motor(16hp with 5 speed trans) on a murray nitrox I purchased several years ago. This plan has been on the back burner for a while and I have only recently gotten around to it.

It's basically just a frame, no engine, brake, battery, seats, chain sprocket or correct tire size. Front wheels are present. I'll be purchasing new tires and rims for the rear.

I plan on cutting off the old axle and tube, then replace it with a hangar style 1" kit.

Do I need a hub style mounts for my rims or will a simple key style mount suffice? I do plan to go fast with it and I understand I am responsible for anything that happens

Anything need to be done steering wise? I noticed some people have said this lawnmower style steering system is no good. It seems in decent shape but needs some loosening up. If I have to I could get my hands on a rack and pinion system.

 

[itsid]

if you cut off the axle tube.. you remove the center rail support..
and essentially weaken the chassis by a huuuuuge amount.
then adding a more powerful engine to go fast
is frankly something you should think about more than twice.

So yeah.. keep that tube in place!

the steering is bad because it lacks proper geometry..
read about Ackermann geometry and apply that to the kart..
if done correctly, it'll turn nicely with it, I promise.rack and pinion make no sense.. it's as bad thanks to a live axle with no differnential (and the subpar geometry)
the only thing that would change is that you'd increase steering wheel angles
(depending on R/P gear ratio) if that's what you're after okay.. but it doesn't affect handling.

'sid

 

[anickode]

Rack and pinion still requires proper steering geometry to improve handling.

one advantage that it can have sometimes on a go-kart, is that because the steering wheel has a greater mechanical advantage (also dependent on r/p gear ratio), it can help reduce bump steer a little bit, which is helpful off road. Bump steer and high speed = crashing.

Go karts are particularly prone to bump steering because the centerline of the wheel is relatively far outside the steering axis, so if one wheel hits an obstacle, it applies torque against the steering mechanism. Cars avoid this by using offset rims so the pivot point of the steering is tucked inside the wheel, as close to center as possible. Big lifted trucks are prone to it as well, since they run wide tires and reduced offsets to widen the stance.

 

[TheQ]

Thanks Sid!

I'll be sure to build a new center support for the kart when I remove the tube. But it has to go! I don't have enough rooms for all my bs in the rear and have that big tube. So I'll probably cut it off and reinforce the frame with some bar stock or tubing I have lying around.

---------- Post added at 05:54 PM ---------- Previous post was at 04:56 PM ----------

Rack and pinion still requires proper steering geometry to improve handling.

one advantage that it can have sometimes on a go-kart, is that because the steering wheel has a greater mechanical advantage (also dependent on r/p gear ratio), it can help reduce bump steer a little bit, which is helpful off road. Bump steer and high speed = crashing.

Go karts are particularly prone to bump steering because the centerline of the wheel is relatively far outside the steering axis, so if one wheel hits an obstacle, it applies torque against the steering mechanism. Cars avoid this by using offset rims so the pivot point of the steering is tucked inside the wheel, as close to center as possible. Big lifted trucks are prone to it as well, since they run wide tires and reduced offsets to widen the stance.

My main goal with the rack and pinion is to improve steering 'precision'. I'd rather have more play with my steering at higher speeds so that one small mistake wouldn't send me careening into a ditch. I don't plan on any offroading. That's not really my forte. I'd also like to put less effort into steering since I'm not really a beefy person (I weigh less than 45kg even though I'm a senior in high school). Perhaps combating bump steer on old country roads would be helpful? They aren't the smoothest and even the freshly paved ones are kinda bumpy.

 

[Denny]

Rack and pinion still requires proper steering geometry to improve handling.

one advantage that it can have sometimes on a go-kart, is that because the steering wheel has a greater mechanical advantage (also dependent on r/p gear ratio), it can help reduce bump steer a little bit, which is helpful off road. Bump steer and high speed = crashing.

Go karts are particularly prone to bump steering because the centerline of the wheel is relatively far outside the steering axis, so if one wheel hits an obstacle, it applies torque against the steering mechanism. Cars avoid this by using offset rims so the pivot point of the steering is tucked inside the wheel, as close to center as possible. Big lifted trucks are prone to it as well, since they run wide tires and reduced offsets to widen the stance.

Man your idea of bump steer is way wrong. It has nothing to do with wheel offset. It is when the suspension droops or is compressed that the mechanism (tie rods ) without any input from the driver cause the wheel to turn. (short answer).


Denny

 

[jandj]

Simple explanation from "Advanced Race Car Suspension Development" by Steve Smith (with assistance from Paul Lamar (Chaparral, Titus, Shelby), Frank Deiny (Speedway Engineering),Don Edmunds (Edmunds Auto Research), and Travis Carter (NASCAR) :
"Bump steer is a common front suspension geometry problem which results from the steering tie rod moving in a path which is dissimilar to the path in which the wheel it is connected to is moving."

 

[jandj]

Also, from what I see on the intardwebs looking up Murray Nitrox, your kart doesn't have any front suspension....which means don't worry about bump steer because you don't have any and even if you did there's nothing you could do about it.

 

[bob58o]

I'm not really a beefy person (I weigh less than 45kg even though I'm a senior in high school).

Do people in SC use the kg to describe their weight?
Isn't the metric unit of weight the Newton?

Who is your physics teacher? LOL

BTW, I'm twice as massive as you. LOL I've been acquiring mass and am nearly 90kg.
I've gained like 40 lbs of weight in the last two years.

 

[ezcome-ezgo]

I blame the Germans.

 

[itsid]

Do people in SC use the kg to describe their weight?
Isn't the metric unit of weight the Newton?

Who is your physics teacher? LOL

BTW, I'm twice as massive as you. LOL I've been acquiring mass and am nearly 90kg.
I've gained like 40 lbs of weight in the last two years.

cough
just because americans usually don't care about the difference between
pounds and poundforce, doesn't mean the system itself is to blame (well it kinda is.. but yeah)
torque is lbf/ft NOT lbs/ft

Force: Newton
Weight: kilogram
1kg produces ~ 9.81 N of force in earth gravitational field.

I know you knew, unfortunately I'm also reasonably certain that some readers might get confused by your post... that's why

I blame the Germans.

Sure, when in doubt.. blame the germans..

Frankly the metric system is IMHO the best thing that france ever came up with.

'sid

 

[jandj]

Metric is taken for granted today but for a mechanic back in the 70s it meant buying a lot of new sockets and wrenches....which weren't cheap.
I cussed everytime I bought 'em.

 

[bob58o]

May the kg-force be with you.
Pound-force sounds like a team of animated super heroes.

Kg is to slug as newton is to pound.

BTW I love the metric system and scientific notation. It makes conversions and calculations easier by a factor of 10^3!

Any way... So about that bump steer?

 

[itsid]

Conversion is especially nice, isn't it?..
Take the mechanical torque for example (Nm)
it's 'coincidentally' the same as an electric Watt second (Ws)
which as per pure luck *cough* is mathematically identical to a Joule of (also chemical) energy..
And with that 100g of basmati rice essentially has around 1,450,000 Nm of torque
Try that with a predator

Anywhoo.. I thought the bump steer argument is actually two fold..
on one hand there's for sure some validity in jandj's remark.
bump steer is a suspension issue ... does (and if how much) does a wheel turn [not rotate] when it moves along it's suspension travel.

On the other hand however (and not uncommon for off road karting enthusiasts)
there is the "so called" bump steer,
how easy can a wheel get deflected by an upcoming small obstacle (sticks and stones, potholes etc.)
if hit at the wrong angle
And the better the steering ratio, the less likely such can rip the steering wheel out of your hands and the better the chance for you to keep control.
IDK, but technically that's not bump steer, but it's still a very similar train of thought.

So yeah.. IDK unless soeone know a better term to describe such
"obstacle induced unwanted deflection of the front wheel"
I guess bump steer is kind of acceptable, no?

Still, a rack and pinion setup on a lightweight kart isn't really necessary IMHO
and it surely doesn't help fixing steering geometry at all.
And while it could help reduce such 'so called' bump steering in some occasions,
it cannot prevent it entirely either
(that's why derby cars have discs on the steering wheel so you don't loose a finger on a hard impact)

'sid

 

[TheQ]

Anyways would my nitrox's stock steering hold up to ~55mph? I just would like to know this one last bit. If I need to I will adjust the toe/castor/camber. I'm not worried about bump steer really. I'm worried about it being squirrely at a high speed.

 

[jandj]

'sid makes a good point.
"Bump deflection" is probably a more accurate description of what happens with a non-suspended front wheel.
True "bump steer" requires suspension.
Think of it this way:
You're driving along in your car and hit a bump with the left front tire.
The wheel rises up, but since the spindle it's attached to mounts to upper and lower control arms that are pivot mounted to the chassis it rises in an arc towards the chassis centerline.
For a wheel that moves in bump (and rebound) while remaining pointed straight ahead (the definition of zero bump steer) the arc of the outer tie rod end and the arc of the wheel path must have the same circle center.
Probably more than you wanted to know....

 

[TheQ]

I never asked about bump steer.

'sid makes a good point.
"Bump deflection" is probably a more accurate description of what happens with a non-suspended front wheel.
True "bump steer" requires suspension.
Think of it this way:
You're driving along in your car and hit a bump with the left front tire.
The wheel rises up, but since the spindle it's attached to mounts to upper and lower control arms that are pivot mounted to the chassis it rises in an arc towards the chassis centerline.
For a wheel that moves in bump (and rebound) while remaining pointed straight ahead (the definition of zero bump steer) the arc of the outer tie rod end and the arc of the wheel path must have the same circle center.
Probably more than you wanted to know....

Could you just answer the **** question! Will the stock steering mechanism be okay for 55mph? That's all I want to know. I couldn't give a rats *** about ****ing bump steer or whatever you gender it! Will it be okay? If bump steer is an issue I'll get a bigger steering wheel for more torque!

 

[bob58o]

Nothing you build is safe at 55mph. Live, learn, or die trying.
Almost sounds like I'm quoting Poboy, LOL

 

[itsid]

my spider senses tell me somebody is getting impatient ....
most likely impatient to hurt himself badly as it seems

No Q (wait that sounds like... nevermind)
it's not safe at 55mph.. nothing is!
why isn't it?
well first: it's never meant for that speed,
and it's manufacturer claimed that it needs a crosstube to be reasonably safe at roughly half the speed, a tube you are about to remove.

How good are your math skills to calculate the exact position and size of the replacement cross bracing?
How good are your welding skills to mount said bracing?
How good are your engine skills to make the engine work reliably?
And how good of a driver are you?
Have you at least thought about adding brakes that are up for the task to stop a 55mph vehicle of such weight in case of an emergency
(not just to come to a stop at the drive through counter, but to stop in front of the kid that's coming from out of nowhere)?

We don't know any of that!
How can we make a judgement..

heck for all we know you could be a 12yo with no fricking idea at all.

Steering is the least we care about really;
how about you test the steering (or kart setup really) at 20, then 25, 30 and 35 mph first.. then decide if it's ready or not for 40, 45 and 50 ??
huh? see? it's trivial, learn to crawl before you run.
fix issues you recognize at slow speeds before they fix you to a hospital bed at high speeds.

'sid

 

[landuse]

Could you just answer the **** question! Will the stock steering mechanism be okay for 55mph? That's all I want to know. I couldn't give a rats *** about ****ing bump steer or whatever you gender it! Will it be okay? If bump steer is an issue I'll get a bigger steering wheel for more torque!

With what you have.....no, it won't be safe at 55mph.

And, watch your language. It doesn't sit well with us moderators

 

[TheQ]

Dont lecture me

my spider senses tell me somebody is getting impatient ....
most likely impatient to hurt himself badly as it seems

No Q (wait that sounds like... nevermind)
it's not safe at 55mph.. nothing is!
why isn't it?
well first: it's never meant for that speed,
and it's manufacturer claimed that it needs a crosstube to be reasonably safe at roughly half the speed, a tube you are about to remove.

How good are your math skills to calculate the exact position and size of the replacement cross bracing?
How good are your welding skills to mount said bracing?
How good are your engine skills to make the engine work reliably?
And how good of a driver are you?
Have you at least thought about adding brakes that are up for the task to stop a 55mph vehicle of such weight in case of an emergency
(not just to come to a stop at the drive through counter, but to stop in front of the kid that's coming from out of nowhere)?

We don't know any of that!
How can we make a judgement..

heck for all we know you could be a 12yo with no fricking idea at all.

Steering is the least we care about really;
how about you test the steering (or kart setup really) at 20, then 25, 30 and 35 mph first.. then decide if it's ready or not for 40, 45 and 50 ??
huh? see? it's trivial, learn to crawl before you run.
fix issues you recognize at slow speeds before they fix you to a hospital bed at high speeds.

'sid

1st off I'm a **** good welder, not the best I know that! But I ain't crap! and I'd be re-positioning the tube anyways since you've stressed its so important. I mean you make it sound like a piece of railroad track wouldn't replace it. B]Its in the way, and the old bearings are seized.[/B] Second off I ain't the ones who turned a conversation about go karts into one about bump steer and metric/imperial conversions. Which after much debate y'all decided didn't apply even though y'all the ones that posed that idea.

3rdly I'm 19yrs old, I could be out drinking, driving, doing weed, drugs, and other teen things. But nah, I chose this as a hobby instead. And yeah I know I'll need to test it at slower speeds, like as if no one ever would have had that cross their minds, I just like to plan ahead of time. I figured, you know if anyone knew anything about my go kart, it would be the experts here. Thus, I took the time to come here. Now that I see I can't get a strait yes or no you all have to beat around the bush.

And that I will probably have to just wing it with whatever steering I got. Some WD-40 and toe adjustments will just have to work. I already had upgraded brake in mind since, as I stated in my OP, they don't currently exist. I'm using hydraulic disk brakes. As for kids coming from nowhere, well that's the kids fault for playing in middle of the **** road. I'm not sure about Gerministan, but around here people know not to do that.

Peace out mon capitan.