KMX Kart

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dirtwarrior

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Aug 29, 2014
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I have a KMX Kart tadpole 3 wheeler (2 wheels in front, 1 in back). I haven't put a motor on it because at speeds over 15 mph it gets twitchy in the steering. It turns sharply and becomes unstable.
Is this a natural thing with these?
 

wheelbender6

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Sep 4, 2008
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I have no experience with one, but all short wheelbase, tadpole trikes can steer twitchy. Its a very short wheelbase. Have you been riding it long? It can take a while to get the hang of it.
I have seen tadpole trikes motorized with rear rack mount kits and axle mount kits.
 

dirtwarrior

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Aug 29, 2014
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I bought it last year but stopped riding it when I rolled it when it got unstable. I still have it, but also bought a used sun usx which is steering neutral
 

wheelbender6

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You may be able to find some ideas for making the KMX Kart more stable on the forums at bentrideronline.com. There are a lot of tadpole trike riders on that site.
 

Ludwig II

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Jul 17, 2012
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Can you alter the amount of rake and trail in the steering, to make it a bit lazier? It sounds to me as if the "head angle" is too steep, and there isn't enough trail.
 

BarelyAWake

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Jul 21, 2009
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If I've got the trike correctly, the KMX Kart is unfortunately for our application & speed a "direct steering" design, making it very difficult to alter the steering ratio to suit. With "indirect steering" (linkages etc) one can often change the points of leverage to reduce steering sensitivity, but direct is pretty much inherently one to one.

You could alter caster for increased stability - but any alteration to steering geometry does have it's consequences, in this instance the force needed to turn & tire wear.

If yer interested, there's an entire chapter on the intricacies of trike steering geometry starting on page eleven here: 'Recumbent Trike Design'.

Another possible solution that could be used alone or in addition to steering modification would be a damper, which simply reduces the ease of sudden movement, be it bump steer or control input (sorry, source unknown);

 

BarelyAWake

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Jul 21, 2009
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Without being familiar with the KMX spindle assemblies, I'm afraid I couldn't say for sure - but it would very likely entail their replacement with custom fabricated components, of which you'd most likely need to make yourself as most HPV riders wouldn't be concerned with motorized speeds... but you could try to contact KMX to see if this has been addressed (speed stability).

It also wouldn't make that much a difference, it'd be a marginal improvement at best as the culprit is the one to one steering ratio, not so much tracking... if intent on using the KMX, I'd research & try a small damper for the first attempt, they're available in our scale for motorcycles & preformance gokarts - just measure the distance the arm would travel in a full left to right turn & that's the throw you'd need.

The KMX is an awesome taddy BTW, I remember clearly it was a electric KMX that first inspired me to build my hybrid ;)

(not mine);
 
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wheelbender6

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Sep 4, 2008
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Applying a little junkyard engineering, wouldn't a smaller back tire result in a more relaxed head tube angle, slowing the steering? Its not feasible if your KMX Kart has a 20" rear wheel. My other idea would be to re-attach the tie rods in a manner that would slow the steering response.
 

BarelyAWake

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Do you have a link for the steering damper?
No, the selection too vast & your application too specific (& different then mine) but if you search "motorcycle hydraulic steering damper stabilizer" there's a large selection to choose from, usually about $70 & up... & I didn't even check ebay lol ;)
 

BarelyAWake

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...My other idea would be to re-attach the tie rods in a manner that would slow the steering response.
A good thought wheelbender & while I designed mine with adjustable steering sensitivity via multiple mount points for the tie rods, the KMX Kart is a "direct steer" - the handlebars are mounted directly to the spindle assemblies with just a cross linkage that connects the two so they turn in unison (prolly a good alternate place for a damper). The only equivalent possibility for a direct steer system would be to increase the length of the handlebars... but I don't think a taddy w/apehangers would quite work as planned ;)

KMX direct-steer w/damper to spindle assembly;



Pic of the T3's steering during construction, note the "extra" hole in the mount plate on the handlebar cross-member, should I relocate the linkages to the upper, the ratio is almost exactly one-to-one & a bit too sensitive for my taste on the street but would be great for closed track course w/twisties. Dropping them to the position they're currently at reduces the sensitivity by a guesstimated 20% or so, still a bit touchy at max speed but allows me to keep the ability to make a U-turn on a two lane road w/o shoulders. I could reduce it further elsewhere, but I like being able to U-turn lol;



A unicycle is less twitchy and inherently easier to steer than any type of tricycle.

Don't need a steering damper either :D
Sorry scotto, but that's so far off can only mean you're yankin' chain - or you've no real taddy time... or unicycle for that matter rotfl

Bicycles, (yes even unicycles) being lean-steer don't have to be concerned with steering ratios. Delta trikes need be concerned but can't do anything about it, as the handlebars are connected directly to the forks/front wheel it's an inherent one-to-one & a damper is about the only option.

While some tadpole trikes have or can have adjustable sensitivity (indirect steering), almost all factory built tadpole recumbents simply don't have a steering ratio designed to be used in excess of an average 15-20mph cruise. Sure, even the HPV only ones can easily exceed that but the steering is set for average, not maximum - else it'd have a slow response & terrible turn radius for the pedal speeds they're most likely to be used at.

This is not a flaw in the design, it does what it's intended to do quite well - it's just something that needs to be accounted for with any increase in average speed is all, as would any vehicle that doesn't lean-steer.