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PostPosted: June 12, 2012, 9:03 am 
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Location: Southern NH
rx7locost wrote:
Use the search tool and look for "bump steer". All will be revealed. I used the section cut out of the rack to make the tie rod extenders.


Hah yea, I know what bump steer is, but it didn't answer my question about track width. But, I'm just realizing that the only reason we are shortening, is for mounting purposes, but need to use extenders (Thanks, MYTF!) to create the proper width. And using the section of the rack to make the extenders is obviously an excellent idea (perfect length!).

Welded more last night. Oy. Needing long sleeves/pants is a murderer in hot weather. Oh well, want to try to get most of this done ASAP to avoid the REAL hot weather coming up! I'm definitely getting there, but keep finding welds that I've missed... seems a common occurance haha. Oh well. Then on to engine/diff fitting, tranny tunnel, and suspension. I want to get this pig rolling by the end of the summer. Running? No way. But rolling on it's own yes for sure.

I've been looking for books on suspension.. did some searching here, but it seems to me that everything is either out of print, or upwards of 200-400$!! Does anyone know off hand any great suspension design books that are more in the .. under 50 range? I'd still love to read Keith Tanners book, but it's like 300 on amazon/ANYWHERE. Ridiculous! Maybe someone would be willing to rent it out to me for a monthish?

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PostPosted: June 12, 2012, 9:41 am 
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You said earlier:
Quote:
the front track width should match the rear track width (this isn't a drag frame), so, if the rear is staying stock, the front should be staying stock width.. which means, the stock steering rack would stay.. well, stock length. Yet, people are shortening them some 6". ... Why?


You just said:
Quote:
I'm just realizing that the only reason we are shortening, is for mounting purposes


Based on your previous statements, I'm still not sure you understand the bump steer aspect correctly. We shorten the rack only to control bump steer. Not for "mounting reasons" and not based on track width, but the rack length (actually the tie rod inner pivot location) is based on the 4 front control arms' inner pivot locations. There is so much well written info in this forum about bump steer design, I don't feel the need to go into detail here. Yes, once the rack is shortened, the tie rods must be extended (or replaced with longer ones) to reach the tie rod end attached at the upright.

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PostPosted: June 12, 2012, 10:32 am 
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Location: Southern NH
rx7locost wrote:
You said earlier:
Quote:
the front track width should match the rear track width (this isn't a drag frame), so, if the rear is staying stock, the front should be staying stock width.. which means, the stock steering rack would stay.. well, stock length. Yet, people are shortening them some 6". ... Why?


You just said:
Quote:
I'm just realizing that the only reason we are shortening, is for mounting purposes


Based on your previous statements, I'm still not sure you understand the bump steer aspect correctly. We shorten the rack only to control bump steer. Not for "mounting reasons" and not based on track width, but the rack length (actually the tie rod inner pivot location) is based on the 4 front control arms' inner pivot locations. There is so much well written info in this forum about bump steer design, I don't feel the need to go into detail here. Yes, once the rack is shortened, the tie rods must be extended (or replaced with longer ones) to reach the tie rod end attached at the upright.


You're right, I was thinking about it wrong. Since the inner pivots are so much further in than the stock miata, the pivot locations of the inner tie rods would be well outside of them at stock length, resulting in a CRAZY amount of bump steer due to the extreme angle of the tie rod ends comparatively. At least, I think that's what would be happening. -- When I learned about it, it was stock cars, stock everything, not designing it into a system. So, we learned what it was, not so much how it would change should you move pivot points (no need, you wouldn't change it on a stock car, ever). Clearly I need to read up further on this. Anyway, thanks for pointing that out, it definitely cleared it up a bit.

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PostPosted: June 12, 2012, 1:14 pm 
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Location: meadview arizona
draw a line between the top and bottom pivots of the "a" arms at the chassis from the front,
draw a line from the top and bottom ball joints from the front, all at ride hight.

you now should have two lines which converge at the top, draw a line parallel to the ball joint line going through the track rod ball joint, measure the distance between the lines, thats the ball joint line and the new track rod line, the two parallel lines.

now draw a line parallel to the chassis "A" arm pivot line, the same distance and the same side as the track rod line, your rack ball joint will fall on this line and must be the same hight as the track rod ball joint.

now mount the rack at this hight and you are in the ball park for "0" bump steer, if you change the chassis hight you will get bump steer.

if you can't mount the rack at that hight, then you must change the hight of the trackrod ends at the ball joint to bring them level with the rack.

see rough sketch, and it is one rough sketch

Attachment:
susp.jpg


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Last edited by john hennessy on June 22, 2012, 2:09 pm, edited 4 times in total.

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PostPosted: June 15, 2012, 10:35 am 
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Location: Southern NH
Haha, concise and confusing. Perfect!

Last night I located my rear diff and installed the rear most tranny tunnel tubes. Oh man, seeing actual car parts on/near this thing is getting me excited!! I need to locate the engine/tranny so I can get vertical location of the diff so I can mount it up proper. Didn't realize that the input on the diff is offset 2" to the passenger side... good news for me, bad news for the passenger hahaha. Oh well. I didn't notice if the tranny output was also offset, but I guess it wouldn't be terrible to have the entire engine offset a little to the pass side... would give me more foot room, as well as a LITTLE bit better weight balance, since i'll be driving alone most of the time.

-- Side note: I ordered a 'like new' used copy of Tanner's book yesterday for around 49$. Robbery, but at least didn't have to bend over for the staggering new price of 273$. Can't wait to get it. For those of you who have read both Tanners and Champions books... is it worth picking up Champions (can be had for 60$ used), if I'm building an oversized miata powered locost (aka not really any part of that book)? My build seems to replicate Tanners moreso, but didn't know if Champions really delved any deeper and was worth the read/ownership if I was already getting Tanners. If it is, I'll pick it up.. if not, maybe I'll pick it up later on just to read for fun. --

Image

Image

Image

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PostPosted: June 15, 2012, 10:53 am 
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The Champion book is better for building the frame and inspiration. The Tanner book goes into the finishing details much better.


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PostPosted: June 16, 2012, 10:45 am 
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Dave wrote:
The Champion book is better for building the frame and inspiration. The Tanner book goes into the finishing details much better.


Nice, thanks Dave! I think I'll stick with the Tanner book for now, and see about the Champion book later. Considering I've already finished the frame, the Tanner book sounds like a better fit for right now.

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PostPosted: June 16, 2012, 11:39 am 
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BrokeAssSeven wrote:
Dave wrote:
The Champion book is better for building the frame and inspiration. The Tanner book goes into the finishing details much better.

Nice, thanks Dave! I think I'll stick with the Tanner book for now, and see about the Champion book later. Considering I've already finished the frame, the Tanner book sounds like a better fit for right now.


The Tanner Website is pretty good too.

http://www.cheapsportscar.net/index.php

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PostPosted: June 20, 2012, 11:00 am 
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wemtd wrote:
Brad
I'm usually in Manchester on thursdays... if this rain ever stops i'll drive up in my seven to motivate you. our friend Mr. Rogers enjoyed his blatt in my car last year!

cheers.


Paul, looks like its gonna be pretty nice tomorrow... HINT HINT :D :D hahahaha.

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PostPosted: June 21, 2012, 5:42 pm 
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Received Tanner's book the other day... perfectly brand new condition. Awesome. Love when things are described as being worse than they are.. that almost NEVER happens these days! So far it's a pretty good read. -- Also, ordered a pair of Mazda Competition Motor Mounts from Flyin' Miata today.. I wanted to go with the beefier than stock option because this car will be turboed not long after it begins it's driving journey through life. Apparently the stock Miata mounts are junkkk (I should have known this, with them falling completely apart when I took the motor out), and even new stockers go by the wayside shortly after turboing (like.. 6k miles). It made sense to just spend the money the first time rather than buying stock first, and then upgraded ones within months. First part that wasn't steel that I've bought for this thing... exciting!! That, along with the Grant steering wheel i got as a gift... the parts pile is growing! -- I just need to find the proper Grant adapter to attach this wheel to the Miata column.... It has every single car listed on the back of the box with the correct adapter... besides the Miata. Figure that out! Time to just call them.

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PostPosted: June 22, 2012, 2:38 pm 
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Brad,

i modified my post with err, a rough sketch, to try to make it simpler, it took a lot of reading to bring bump steer to a point where even i could understand how it is resolved,

where the rack is located infront of the axle for front steer or behind the axle for rear steer.

the part that confused me was the difference between front and rear steer spindles to provide ackerman, the track rod being outside the ball joint line in front steer and inside on rear steer and what to do with this measurement, add this to the rack, take it away or just plain ignor it.

what i do know is if you do ignor it you will have bump steer and probably need to modify the rack mounting and length to reduce it, hence i built my rack to be adjustable for length and my track rod location adjustable for hight, this allows me to change the chassis ride hight without incurring bump steer.

if i lower the chassis i can lengthen the rack and lower the track rod ball joints or the opposite if i raise the chassis for more ground clearance.

the track rod length is just adjusted to suit the toe at any hight.

just a note on caster, if you increase the caster, you will incurre bump unless you raise the rack or lower the ball joints in a front steer system, the same applies in reverse if you decrease the caster.

rack hight is directly related to the distance the track rod ball joint is from the ground, they should be the same.

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PostPosted: June 22, 2012, 10:29 pm 
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Brad..
how about next thursday (weather permitting) ?


Paul.


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PostPosted: June 23, 2012, 2:47 pm 
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wemtd wrote:
Brad..
how about next thursday (weather permitting) ?


Paul.


Paul, that sounds fine. Ill let you know tues or wed if ill be in the office,unless you're planning for after five?

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PostPosted: June 23, 2012, 10:24 pm 
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PM sent

p.


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PostPosted: June 27, 2012, 8:56 am 
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The weather report looks good for tomorow

paul


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