Learning how to build Lotus Seven replicas...together!
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PostPosted: August 7, 2023, 2:16 pm 

Joined: August 7, 2023, 1:26 pm
Posts: 1
Hello gentlemen.

Been a long time reader of all Locost related tips and tricks but never posted.

I have a reverse trike project pretty far gone and im starting to do testdrives.I have a few steering related questions I hope you guys can help. Note this is based by just driving around the parking lot a few times.

I am using miata NA spindles & matching Miata manual rack.

The main problem is steering is way too slow. I would like to at least double the ratio.

I have narrowed down my options to 3:

1. Install a steering quickener (gearbox) inline my steering shaft.
+This is a proven method
- Limited space and some modification needed to existing parts & design

2. Have the rack professionally modified for faster steering (i have no idea if its possible for Miata rack)
+No other modifications needed
+Proven method
-I imagine If i find anyone to do this the cost might be high

3. Modify the spindles for a shorter steering arm lever (the drift guys do this and i can even purchase modified mazda spindles)
+Cost is low
+Possible to also adjust ackerman*
- I have no idea how it will effect the driving characteristics

*Another thing i have been wondering is the Ackerman geometry. I am using all mazda parts and dimensions so i´m pretty sure i´m using same ackerman as mazda did. I have the feeling that Miata doesn´t have perfect geometrical ackerman (?). Surely there is a million things contributing to the end result but now im talking purely about the geometry.

When moving and driving the trike around in slow speeds it´s obvious that the outside tire is rubbing in tight turns (it also looks like the outside tire has more angle than the inside tire but i need to measure to make sure). I would appreciate a small turning circle as i don´t have a reverse gear.

It feels like turning with a welded diff and that might be pretty close to reality with just one rear tire.

So my thinking is I´d like to modify the spindles for shorter steering arm and also added Ackerman. Basically for Ackerman I would move the tie rod attachment point closer to the brake rotor . Do you think i would get a smaller turning circle/ better slow speed turning?

The guys drifting miatas with modified spindles don´t really complain much. but would shortening the steering arm get me into more trouble with the steering feel as now the inputs from the road-> steering wheel are from a shorter lever? On the other hand is that situation any different compared to faster steering via methods 1 or 2?



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PostPosted: August 8, 2023, 9:41 pm 
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Joined: September 30, 2020, 11:44 am
Posts: 87
Location: Eastern Oregon
+1 for the modified spindle route.

Your concern with getting more feedback is gonna be a problem with any route you take. As the wheel movement is going to be emphasized in a faster rack.

You might consider moving this topic to suspension and steering as I feel like the bike engine isn't part of the cause.

Lastly, the build looks great! Did you document it anywhere?


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PostPosted: August 11, 2023, 6:07 pm 
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Joined: April 26, 2008, 6:06 pm
Posts: 3264
Location: Under the weather. (Seattle)
The NA/NB power rack has a noticeably faster ratio than the manual rack. While it still might not be 'enough' for your longer wheelbase, I would start with one of those that has been 'properly' depowered along with welding up pinion valve slop noted as optional in the link.

Are the Miata spindles steel or iron? Steel shouldn't be too much of a concern when modified, although still also curious about the precision of the modifications, but I'd have my reservations about iron.


"Orville Wright did not have a pilots license." - Gordon MacKenzie

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