sgraber
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| posted on 8/2/07 at 09:24 PM |
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1.5 turn lock to lock steering - too quick?
I've been looking for an inexpensive quick rack and have found something I think will work. But the unit moves approx. 5 inches over 1.5 turns
lock to lock (ie; 2.5" over 3/4 turn). I am not worried about it feeling too heavy, or bumpsteer or self-centering.
I am a little worried that a simple sneeze (or a bumpy road) will find me in the weeds wondering what just happened...
Thoughts?
Steve Graber
http://www.grabercars.com/
"Quickness through lightness"
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JoelP
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| posted on 8/2/07 at 09:33 PM |
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well, for what its worth, this is what i want on my new car. It is fast, but with these cars the driver should be paying close attention to the road,
so combined with sufficient self centering, i think it would be fine. How cheap is cheap though?! 
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mark chandler
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| posted on 8/2/07 at 09:34 PM |
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Go-carts are 1/2 turn lock to lock, I would be more worried about clipping a curb and the wheel being yanked out of my hands......
As long as it centres well I expect you would quite quickly get used to it but it may need a PAS conversion as well !
Regards Mark
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ecosse
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| posted on 8/2/07 at 09:36 PM |
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That'll be like driving a kart  not sure what it would be like in a car, scary possibly!
No harm in giving it a try though
Cheers
Alex
[Edited on 8/2/07 by ecosse]
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snapper
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| posted on 8/2/07 at 09:42 PM |
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Can't be any worse than a Kart can it?
I would think that the extra effort would be tiresome at low speed and you would have to teach youself as quick reactions to a problem could get you
all twisted up. ala Kart racing over and understeer moments.
Bigger steering wheel would counteract a quick rack, so you could fine tune it with a wheel from 280mm to 350mm.
I eat to survive
I drink to forget
I breath to pi55 my ex wife off (and now my ex partner)
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sgraber
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| posted on 8/2/07 at 09:55 PM |
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What I haven't included in this conversation is the length of the steering arm - which is 4.75" from axle centerline. This is a critical
dimension.
Steve Graber
http://www.grabercars.com/
"Quickness through lightness"
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sgraber
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| posted on 8/2/07 at 10:14 PM |
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So 12:1 - You can see where that puts me on the chart below.... I may benefit from a longer steering arm. I'm at work right now, so I
can't sit down to work out the maths. Tonight.
Rack and Pinion Ratio Chart
1.57 inches per turn:
Very slow steering, mainly for superspeedways (Daytona Dash cars) or road courses (GT classes) where top speeds exceed 160 mph. Ordinarily applied as
manual steering. Also used to compensate for the short steering arms on small cars. With long steering arms, the overall ratio can range down to 24:1.
For power steering with this rack on short tracks, use a #850 or #855 servo valve with a KRC standard 7.2cc pump and #8 and smaller output fitting;
The same servo valve with a KRC 5.9cc pump and a #4 or #5 fitting will handle a ratio like this on superspeedways.
1.83 inches per turn:
Slow steering for paved tracks 5/8 mile and over; usually run as manual steering. Formerly popular in GT classes, as this ratio closely approximates
that of OEM sports car steering when used in conjunction with short steering arms. Use #850 or #855 servo valve with KRC 7.2cc or 5.9cc pump and #8
and smaller output fitting.
2.09 inches per turn:
Formerly the most popular ratio for manual steering pavement applications in both stock car and road racing. Known as the 16:1 rack, it feels about
like a Corvette. Used with power assist about half the time. Use #855 servo valve, KRC 7.2cc pump, #6 and larger output fitting
2.36 inches per turn:
Quicker steering for paved tracks, especially those 1/2 mile and under. Useable as either manual or power steering, although run as power steering in
80% of cases. Its overall ratio usually works out to around 14:1. For power steering, use a #855 servo valve with a KRC 7.2cc pump #7 and larger
output fitting
2.62 inches per turn:
Ten years ago this ratio was commonly used as manual steering on dirt late models. At 12:1, it still gives relatively easy steering on dirt, and is
the best entry-level choice for manual steering limited late models. It's most common application today is on pavement with power assist. Use a
#855 servo valve with KRC 7.2cc pump and #8 and larger output fitting.
2.88 inches per turn:
Quicker than average manual steering for dirt tracks. At about 10:1, this will require setting the car’s caster and camber for minimum effort, unless
power assist is used. Much faster steering than any road vehicle. For power assist on pavement, use a #855 servo valve, on dirt use a #850, with a KRC
7.2 pump and #8 and larger output fitting.
3.14 inches per turn:
For powersliding around bull rings. This is about the fastest ratio usable as manual steering (and was considered radical in the early 1980’s). If
used without power assist, most front ends will need the positive caster backed way off to street-vehicle levels (under two degrees), and the caster
split reduced. With power assist, use a #855 servo valve on pavement, #850 on dirt, with a KRC 7.2cc or 8.5cc pump and #8 and larger output fitting.
If a spline drive pump setup with a slow drive ratio is used (as is now common on dirt cars) a 9.6cc pump is required for this and quicker ratios.
Steve Graber
http://www.grabercars.com/
"Quickness through lightness"
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JoelP
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| posted on 8/2/07 at 10:18 PM |
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i really feel for you steve, working nights  lol
but as chris says, it depends on the length of the arm on the hub, which that chart above seems to neglect.
My car use to turn to about 50 degrees, and the arm was about 4" long. So your 2.5" wouldn't have got me to full lock, probably
something around 35 degrees? This would be equvilent to my old car having around a 2.5 turns lock to lock but lacking the extreme angles.
You could always drill the hubs to shorten the arms.
[Edited on 8/2/07 by JoelP]
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sgraber
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| posted on 8/2/07 at 10:33 PM |
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I can see now that this rack will not provide enough travel to induce full lock. And is a ratio that is way too quick for an average driver (myself)
on a road course.
The ratio is 3.3:1!
I'll keep looking.
Thanks guys!
Steve Graber
http://www.grabercars.com/
"Quickness through lightness"
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andyps
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| posted on 8/2/07 at 10:45 PM |
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I have a Fiat Coupe with only just over 2 turns lock to lock - it is nice and direct, but not overly so - mainly because the car could never be
described as having a turning circle - a circle is way smaller than I can ever achieve, supertankers have been known to turn around in less space In
other words, as already figured, it isn't just how many turns, but how far does it move the wheels during those turns.
Andy
An expert is someone who knows more and more about less and less
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NS Dev
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| posted on 9/2/07 at 10:17 AM |
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Berrisford does a 1.5 turn rack (5" ish travel iirc) for £150
Retro RWD is the way forward...........automotive fabrication, car restoration, sheetmetal work, engine conversion
retro car restoration and tuning
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sgraber
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| posted on 9/2/07 at 01:36 PM |
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I can get mine for $93... 3.5Lbs.
But price is not everything - as Andy clearly points out - if I adjust the length of the steering arms to compensate for an overly quick rack with
short travel, I am left with a car that rivals a supertanker in turning radius.
Steve Graber
http://www.grabercars.com/
"Quickness through lightness"
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JoelP
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| posted on 9/2/07 at 06:49 PM |
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quote:
Originally posted by chris mason
wouldn't shortening the arm length increase the steering angle, hence a larger effect should the steering wheel twitch. that how i understand
it, but i could have got it the wrong way round
Chris
Quite right chris, i meant to shorten the arms to regain full amount of required lock - this would serve to quicken the rack by comparison, however,
its not as quick as it sounds due to the lack of travel. Drilling the arms shorter to regain the full 50 degs or so of lock, would've
transformed it back to a sierra equvilent 1.5 turns, which would be as fast as we were assuming at the beginning of the thread, not the roughly 2.5
turns lock to lock that it actually would be if you had the full range of motion
Now where are the cold peas for my headache?!
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timg
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| posted on 9/3/07 at 06:48 PM |
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Steve,
May I ask why you want a quicker rack?
I'm assuming (found it hard to follow all the early design details on your website regarding the steering design, etc) that you are using the
MR2 manual rack and the MR2 front hubs with the OEM steering arm?
The reason I'm asking is I'm considering a barebones mid-engined car using AS much of the OEM MR2 parts as possible (as you have).
Thanks
Tim
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sgraber
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| posted on 9/3/07 at 06:56 PM |
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The car is driveable with the setup. But it just feels like I am working the wheel more that a car of this design should have to rotate. With only 600
or so lbs over the front wheels the whole thing feels very light through the steering wheel, so having to perform these large inputs to make the turns
just feels counterintuitive to how I expect it to feel. hmm, maybe a smaller steering wheel would help?
The difference I believe is that the MKI MR2 has a 92" wheelbase and I have a 98" wheelbase (and of course a lot less weight on mine).
Steve Graber
http://www.grabercars.com/
"Quickness through lightness"
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Gaz 1977
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| posted on 9/3/07 at 07:17 PM |
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if you want a cheap quick rack, Try alfa 145 cloverleaf. Silly fast rack for a road car might be good for something sportier
GAZ
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sgraber
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| posted on 9/3/07 at 07:23 PM |
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quote:
Originally posted by Gaz 1977
if you want a cheap quick rack, Try alfa 145 cloverleaf. Silly fast rack for a road car might be good for something sportier
GAZ
LHD? USA? Tell me more please...
Steve Graber
http://www.grabercars.com/
"Quickness through lightness"
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andyps
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| posted on 10/3/07 at 11:59 AM |
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Very similar rack to the one in my Fiat I would think. Must be readily available in LHD as that is how the majority were sold. Pretty sure it is
behind the axle and has to my knowledge only been produced with power assistance.
Andy
An expert is someone who knows more and more about less and less
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