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Old 03-29-2010, 02:28 AM   #1
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Default Alignment testing for upcoming track day

I have an upcoming track day at Talladega Grand Prix this coming weekend. Before then I need brake pads, tires, and .... who knows. Heatshielding most likely. I also aligned the car today mostly to lower the caster and to verify what the car was actually set at so I understood it's current handling characteristics.
The previoius alignment was done to my specs by a local Firestone shop. They obviously did not come even close to my specs. This was over a year ago.

Original Alignment Negative toe is toe out
Front Left Right
Camber -1.26 -1.76
Caster 6.32 6.08
Toe -0.1mm -0.3mm

Rear
Camber -1.38 -1.69
Toe -0.1mm -0.2mm



Current Alignment
Front Left Right
Camber -2.13 -2.08
Caster 4.32 4.24 (Dropped due to depowered steering rack)
Toe -0.4mm -0.4mm (Close to 1/32nd toe out)

Rear
Camber -2.36 -2.22
Toe 0.3mm 0.3mm (Like 1/43" toe in)


Koni sports with GC 525/350 springs and Racing Beat 1.125 hollow front with no rear bar. Considering installing the stock rear again.

I need to adjust my ride heights from last time I did it. Where is everyone measuring from and to for the heights given? Center of hub to fender?
I need to drop the car more to achieve more front camber. It currently couldn't achieve anymore than -2.3* on the front left and the right side wouldn't go past -2.13*. The rear had endless camber ability like up to -5* if I remember correctly, I had no idea it could go that far with the stock bushings and cam bolts.

The car is much much easier to drive with my depowered power steering rack. It was nearly impossible at 6* caster at any type of race speed. It's a completely different car now with the lowered caster setting. It turns in much better and does is much more predictable now that it no longer has the toe out in the rear and the irregular camber settings. The car understeers mid turn now, crisp turn in with a good initial bite but then it understeers some though it is very controllable and allows me to apply throttle without worrying the car is going to do something completely unexpected.

So the plan is to lower the car to achieve more front camber, set the rake to 1/4 higher in the rear.
Install new brake pads and flush the system with Motul 600 and replace a stuck slider bolt in the front left caliper.

My RT615s are pretty much done right now for any sort of track day. I don't think I have enough tread left to do anything more than an autocross. I have no idea what my tire options are for my 15x8 6ULs so I need to start researching now. I know I can run 225 RA1s and NT01s but I don't want to drop the coin for R comps right now. The car needs many other things before it needs super expensive rubber.
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Old 03-29-2010, 02:58 AM   #2
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225's are a great size for that rim. I am planning on getting 225/45 RA1's when my 205's are done.

When I had my spec I measured to the pinch welds. As long as they are not all ben up then it's a good place to measure. If your fenders rolled are rolled it can be hard to get an accurate measurement.

From what I have seen here most ride heights have had 1/2in difference from front to rear. Just what I noticed. Also try to get all measurements as equal as posible.

Thats all I got at this time. Enjoy the track.

Have a great day,
Jared
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Old 03-29-2010, 11:45 AM   #3
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Most of the miata crowd measures ride heights from center of hub to fender lip, but as Jared said, that can be problematic. I'm going to start taking mine from the ground to the pinch welds or frame rails.

I'd say your new alignment looks reasonable. The main thing is you have gotten rid of the rear toe out. There wasn't a ton there before, but too much tends to make a car twitchy under heavy braking. A little rear toe in is good, mine is 1/32" per side. In addition to tweaking the alignment, once you get the ride height approximately where you want it I'd recommend having the car corner balanced. My cross weights went from ~53/47 to 50.2/49.8 and it made a big improvement in handling. IMO it's worth the extra money to have a race shop do your alignment & corner balancing versus just having it aligned at the local tire shop. I had a Spec Miata guy do mine.

Your mid-corner understeer can be addressed by reinstalling the stock rear bar. No rear bar is fine for putting power down out of sharp corners at an autox, but on track it will be suboptimal unless you have springs stiff enough to not need the bar. Stock rear bar is good; if you go bigger it will probably suck, BTDT. I'm on 450/300 with FM front bar and stock rear bar and it's great.

Street tire options in 225 include RS2, RS3, R1R. If you shop around, NT01s really aren't that expensive. I probably wouldn't drive them on the street but if you have an extra set of wheels then NT01s would be the way to go. OTOH if I was buying one set of tires for street & track it would probably be the RS3. Lots of positive feedback on those.
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Old 03-29-2010, 12:38 PM   #4
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Do what Emilio tells you, I have seen the light.
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Old 03-29-2010, 02:44 PM   #5
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do you have a rear sway bar installed? mid-turn understeer is a good thing on a high hp car with a short wheelbase - you can always correct it with a bit of throttle (or blipping the brakes if you feel adventurous.)
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Old 03-29-2010, 04:10 PM   #6
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Quote:
Originally Posted by ScottFW View Post

Your mid-corner understeer can be addressed by reinstalling the stock rear bar. No rear bar is fine for putting power down out of sharp corners at an autox, but on track it will be suboptimal unless you have springs stiff enough to not need the bar. Stock rear bar is good; if you go bigger it will probably suck, BTDT. I'm on 450/300 with FM front bar and stock rear bar and it's great.
How do you like the 450/300 setup? Do you feel you wish it was a bit stiffer? I'm putting my setup together right now and have been told 550/350 is a good setup but I've also seen a lot of people with 450/300 so I wonder if this is a bit better for me. I am running non-valved bilstiens ATM (will be valved in the summer) and apparently 550/350 is too much spring for them?
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Old 03-29-2010, 05:09 PM   #7
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I'm happy with 450/300 for now. The spring rates feel adequate on track (on RS2s) and are fine for street driving around here. Actually, after installing them I was pleasantly surprised with how well it rode around town (once I adjusted the konis) despite ~tripling the stock spring rates. I could probably live with a stiffer setup on the street, and I will need to go stiffer for track when I get r-comps on the car, but 450 is already towards the upper end of what my Koni sports will handle long-term so that will require at least revalving the fronts. If I was going to use street tires on the track forever, I'd just keep what I have and be happy.

IDK what stock Bilstein valving will handle but if 550/530 can be sufficiently damped by your shocks then it should ride okay if your roads don't suck. You have to be willing to tolerate a few extra bumps but that is not terribly stiff IMO. Try to get a ride in a similarly sprung miata and see how you like it.
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Old 03-29-2010, 10:06 PM   #8
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Quote:
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IDK what stock Bilstein valving will handle but if 550/530 can be sufficiently damped by your shocks then it should ride okay if your roads don't suck. You have to be willing to tolerate a few extra bumps but that is not terribly stiff IMO. Try to get a ride in a similarly sprung miata and see how you like it.
Well I'll be running r-comps so I guess I should go with the 550/350. I'm not too concerned with the ride on the street. Our roads are good if you stay out of downtown and since it will be mainly a track car I can deal with the harsher ride on the street.
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Old 03-30-2010, 11:26 AM   #9
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In that case you may want to go even stiffer. There are several track miatas on r-comps that run 700# front springs (not just spec miatas) and I'm told that when paired with properly valved shocks the street ride isn't too bad. If you're getting a custom revalve anyway that might be the way to go.
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Old 03-31-2010, 01:06 AM   #10
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I'll do all of my measurements to more consistent points on the car instead of the fender to hub. Easy enough to do while it's on the rack. I think the car currently has positive rake some how.
I'm doing all of my alignments on a John Bean Arago V3D alignment rack. It's very precise and I can corner weight the car easily, I have scales available to me.

I think everyone has affirmed that I need to re-install the stock rear bar again for the type of driving I'll be doing. I have it in storage so it should be an easy install.

It looks like I won't be able to make the track day this weekend. I'll be working all weekend so buying pads, tires, and redoing my alignment this week won't be taking place. I will hopefully get to make the alignment adjustments in two weeks after the team goes to Barber.

On a positive note. I hooked up EBC and turned up the boost. I'm out of injector at 14-15 psi with my 550s and stock fuel pressure. Looks like I'll be in the market for some 750s here soon. Strictly so I have the head room to turn the volume up to 11 when I feel like it. That'll have to wait a while though. Torsen and many other things have priority on the to be installed list.
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Old 03-31-2010, 04:10 PM   #11
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Quote:
Originally Posted by ScottFW View Post
In that case you may want to go even stiffer. There are several track miatas on r-comps that run 700# front springs (not just spec miatas) and I'm told that when paired with properly valved shocks the street ride isn't too bad. If you're getting a custom revalve anyway that might be the way to go.
+1 on this. The ride is definitely a lot stiffer. But I have driven my LS1 track NA on the street a few times now with 700#F/450#R springs and Koni races (stock valving) and it is really not unbearably stiff. This is with 225 NT01s. It is no Cadillac, but it is no go-kart either.
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