Author Topic: TFA Racing Lakester "tweak" diary  (Read 98043 times)

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Offline entropy

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Re: TFA Racing Lakester "tweak" diary
« Reply #90 on: September 19, 2014, 06:38:53 AM »
I agree with Rich on rollout.   More important than pressure. Set the largest tire to the pressure you want to run, than add more to the smaller one. We try for 1/2 inch difference. Less if we can get it. Sometimes we can be right on.
And always re check air at the starting line. The right side always gains from sunshine exposure.
Frank
Frank,
We set F tires pressure to 90psi in Houston (sea level+/-) before leaving:  both L&R circum were 91.25"
At WOS 9/5 L = 91.75 @ 74psi, R = 91.5 @ 73psi (tires free standing)
               9/7 L =  ?        76psi, R =  ?         77psi  (tires on salt), didn't re-measure cirum bc psi was so close

I thought the decrease in psi & increase in circum wrt sea level was an altitude effect, but i didn't cogitate on it very much.
Interesting thought on sunshine exposure, this never occurred to me.  Do you have any measurements which demonstrate this effect?  I don't doubt it, just wondering how much it affects the tire.
Karl
« Last Edit: September 19, 2014, 08:43:55 AM by entropy »

Offline entropy

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Re: TFA Racing Lakester "tweak" diary
« Reply #91 on: September 19, 2014, 06:50:37 AM »
2. Re-determine our Cg-Cp relationship, basic vehicle info

Is your base data measured using your heaviest driver in the seat (and fluids in tanks) or empty/dry?

After stretching the car, CP is aft of CG by 42",
We did scale the car with fluids and driver, but that 42" is probably +/- 6".
Our todo list includes doing the calculation more carefully.

Offline entropy

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Re: TFA Racing Lakester "tweak" diary
« Reply #92 on: September 19, 2014, 07:10:24 AM »
I felt like I was driving the car instead of it trying to drive me
Donnie Stringfellow

My experience was like that, not severe, but I was wondering what the car would do next...
However, my total of 4 car passes ever = pure n00b, this is why all ya'lls input is so valuable
Karl

Offline entropy

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Re: TFA Racing Lakester "tweak" diary
« Reply #93 on: September 19, 2014, 07:14:37 AM »
Maybe rethink that steering reverser a little. Those gears are over kill anyway.
the steering reverser box is definitely uner scrutiny.  The gear lash is very small but it could be less.
karl

Offline entropy

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Re: TFA Racing Lakester "tweak" diary
« Reply #94 on: September 19, 2014, 07:33:55 AM »
...Hopefully you re-post all of this next summer after running with what you finally did and the results.
Sum

Sumner, SPARKY, Donnie,
110% yes, we'll re-post next summer, I love this stuff!

Trying a lil toe out was suggested to us but we just ran out of time. 
One of my WOS personal objectives was experiencing 5 miles with throttle mashed, see if it was fun, see if i wanted to continue the Project. 
It surely was, and I surely do! 
I got a lil more excitement than I expected but that slide at the 5 was totally my fault, excellent lesson, hopefully won't make that mistake again.
Karl

Offline DSR88

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Re: TFA Racing Lakester "tweak" diary
« Reply #95 on: September 19, 2014, 08:24:15 AM »
Karl,
It is always good to ask questions. This thread has a lot of good information. The way Jim Kirk and I work out issue's
we take all the info and discuss it until we agree. Sometime we have to have our phones plugged in because a cell phone battery won't last that long :-P.

Now that you have a few pass in the car you can make a change and know what it did. Don't make too many changes at one time. Remember there in no rule that say's you have to go to the 5 mile.

Sounds like you are having fun.   

Offline entropy

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Re: TFA Racing Lakester "tweak" diary
« Reply #96 on: September 19, 2014, 08:32:13 AM »
If the scrub radius is positive (a line through the steering axis falls outside the center line of the tire patch)...Rex  

…uh-oh i've been calling that condition negative scrub…  :oops:

 But in any event, we had the wheels made so that the tire center was .040"  inboard of the steering projection.  We figured that we could then shim the wheel outwards wrt the hub to get scrub to exactly zero.
However, I find it difficult to measure scrub that precisely.  Does anyone have a clever way of doing this?

Rex:  your post is great!  I simply have no experience in this kind of thing and can use all the schooling i can get.
Karl

Offline RichFox

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Re: TFA Racing Lakester "tweak" diary
« Reply #97 on: September 19, 2014, 09:08:16 AM »
Maybe rethink that steering reverser a little. Those gears are over kill anyway.
the steering reverser box is definitely uner scrutiny.  The gear lash is very small but it could be less.
karl
When I made mine, I had the gears quite snug and then lapped them together for a very nice back lash. I didn't use such killer gears as I thought anything larger than the pinion gear was over kill. And i had access to lots of CF6 sump pump gears that had been replaced.

Offline entropy

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Re: TFA Racing Lakester "tweak" diary
« Reply #98 on: September 19, 2014, 09:31:35 AM »
Been a lot of yrs since i did wheel alignments but
hunting to me has usually been a toe in/toe out issue , excessive of either ,in this case i agree with Sparky , some tow out to compensate for "pulling the car along between the wheels  "
the other influence this yr is the salt condition, it was soft and possibly getting differing traction conditions from one side to the other  as you ran , i want to say it will feel light on one side or the other but its not quite the right description and will feel less regular than hunting from toe in
but all influences interact
Karl our busa was "hunting " too about 2-4 times a second ...., that i can do without 

maj/Greg (same as OzBooster, yes?)
The possibility of differing L-R traction causing hunting didn't occur to me at WOS but afterwards the possibility was suggested.
One would think if the hunting was due to L-R accel/traction differences, hunting would stop during decel
So i just looked at my 5 mi log.
Last pass, 3rd gear / 205mph I got spooked by the hunting and briefly went to about 50% throttle, 199mph.  
In my mind i think the hunting must have stopped bc I got back on the gas hard.
But the logs show 1-2.5 degree heading changes even during that brief decel.  
I don't understand what's going on, but I LOVE this stuff.
And, i love the Racepak logging system.  I am a dumb-azero at set up and use, but with the help of my vendor (Greg Kelly), and help at WOS (Donny Cummins), i am inching up the learning curve...

I feel your pain about dealing with a twitchy Busa on the salt, you KNOW I do :-D
Karl

Offline RichFox

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Re: TFA Racing Lakester "tweak" diary
« Reply #99 on: September 19, 2014, 09:36:36 AM »
Off topic, but I was looking at this picture of a car that was fast and handled well in it's day. And looked at the kingpin/tire center relationship. As I have mentioned, I know nothing about suspension/steering. So can someone tell me why this worked once when we all know it won't work now.

Offline Sumner

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Re: TFA Racing Lakester "tweak" diary
« Reply #100 on: September 19, 2014, 09:56:24 AM »
Off topic, but I was looking at this picture of a car that was fast and handled well in it's day. And looked at the kingpin/tire center relationship. As I have mentioned, I know nothing about suspension/steering. So can someone tell me why this worked once when we all know it won't work now.



I guess I'd have to ask what you mean by "worked once"?   There are thousands of street rods running around with terrible scrub radius issues but work just fine for the owners.  The first time I gained knowledge of the 'scrub radius' deal was in the 90's talking to some guys with a roadster that ran about 160 if I remember right.  They had been driving it but said that it 'hunted some'.  They minimized the scrub radius and it drove straight.  Everyone is probably different in what they will live with or not.

In a different direction in Karl's case I'd do whatever worked to get the car handling where they are comfortable under throttle first and if I had to give up something under braking I'd do that since we use so little braking and when we do the chute should be out and that will cover up some problems right there. 

I did a little more googling and found other references to using toe-out for a front wheel drive cars.  You can go for extra toe-in or toe-out if you want but the main purpose of either is to end up with the wheels/tires close to straight when underway.  Any more, one way or the other, might help straight-line stability or turning in (not important for us).

As I mentioned before I'd put a known amount of tow-in and tow-out at home and be able to reference those points to try either on the salt,

Sum

Offline Ron Gibson

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Re: TFA Racing Lakester "tweak" diary
« Reply #101 on: September 19, 2014, 10:24:59 AM »
I'm not convinced that dead nuts on "0"  scrub is necessary but should be very close. That being said, with a straight axle what I did was with the tires on the floor and toe in at "0", to take a .plumb bob from the center of both the front and rear of the tires to the floor and mark on floor and measure height of axle. Then removed wheels and set front axle to right height from previous measurement. Then I turned the grease zerks on the spindle so the flats were parallel, used a lazer level on the zerk flats to give me a point on the floor. Then measured from that point 23/32nds (1/2" lazer offset +7/32=1/2 zerk hex) to get king pin center line. The lazer mark on the floor will be in front of the other marks because of caster. Draw a line through the tire marks to the king pin mark and you will have your scrub taking caster into account. Mine was 1.75" per side negative when I bought it.  
There are no doubt more accurate methods but I don't have or want to buy the equipment for a one time use.

YMMV
Ron
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Offline RichFox

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Re: TFA Racing Lakester "tweak" diary
« Reply #102 on: September 19, 2014, 10:28:40 AM »
What i meant was it was state of the art, built by a very respected builder of Indy and other race car chassis. A very fast car at the time. Still a lot of fun to drive today, I bet. And nobody seemed to think anything about scrub radius. I wounder about the Novi and Ferguson and Miller FWD cars. They probably had front ends applicable to what is being discussed here

Offline entropy

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Re: TFA Racing Lakester "tweak" diary
« Reply #103 on: September 19, 2014, 10:52:54 AM »
I'm not convinced that dead nuts on "0"  scrub is necessary but should be very close. That being said, with a straight axle what I did was with the tires on the floor and toe in at "0", to take a .plumb bob from the center of both the front and rear of the tires to the floor and mark on floor and measure height of axle. Then removed wheels and set front axle to right height from previous measurement. Then I turned the grease zerks on the spindle so the flats were parallel, used a lazer level on the zerk flats to give me a point on the floor. Then measured from that point 23/32nds (1/2" lazer offset +7/32=1/2 zerk hex) to get king pin center line. The lazer mark on the floor will be in front of the other marks because of caster. Draw a line through the tire marks to the king pin mark and you will have your scrub taking caster into account. Mine was 1.75" per side negative when I bought it.  
There are no doubt more accurate methods but I don't have or want to buy the equipment for a one time use.
YMMV
Ron

Ron,
thanks for taking the time to describe yr method.  We did something similar when we measured ours to derermine how much offset needed (2 7/16") to build our custom wheels. 
I was hoping you'd say:  "just go down to harbor freight, the carpentry section and get the $3.99 Crenellated Ramifier (8").
It'll take you 3 minutes, you don't have to remove any parts from the car, and results are good to .0001" :-D
Karl

Offline SPARKY

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Re: TFA Racing Lakester "tweak" diary
« Reply #104 on: September 19, 2014, 10:53:29 AM »
GUYS  go look up the definition of scrub radius:

 By definition

Positive scrub radius---the tire patch is outside the kingpin center line--
Negative  "         "   --- the tire patch is inside the center line

getting very close to ZERO scrub, caster and camber is even more important on a FWD that a rear wheel drive because steering inputs change the thrust portion of the tire patch

My experience with a race car Hunting down the track was limited to my old car---it was horrible---I learned about scrub radius from roadster guys and circle track guys.  After lots of research  I started getting rid of caster and scrub radius---as well as making my chassis stiffer---wallah a no more  hunting down the track

To understand this better I took some old spindles and tack welded them to a piece of pipe.  I then put on jack stands and move the tires back and forth with the tire barely off the ground and measured and marked how and where the closest point was..  whacked it off changed the caster and camber----with zero zero --it barely moves but not the case with much of either of caster or camber
« Last Edit: September 19, 2014, 04:54:43 PM by SPARKY »
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