Rear end setup

#1

I’m about to take my new (to me) SE30 out to VIR for it’s maiden (to me) voyage. The rear subframe is still stock with no sort of toe correction, and I don’t have time to install anything before this weekend. What has me worried is that it’s toed out quite a bit and I anticipate that it’s going to be a handful.

I’m looking for things that I can do to offset the oversteer I’m fully expecting to have thanks to the rear toe-out. Here’s what I’m thinking, would really love to hear your opinion and any additional ideas:

  • Rear spring pads are still installed, I should remove them.
  • Friday is looking to be wet, so will disconnect rear sway bar
  • Possibly keep it disconnected for the dry as well?
  • Adjust rear tire pressures – not sure in what direction?

Any other ideas or suggestions?

Cheers,

Julian

#2

Instead of installing toe adjusters, consider a frame shop bending out your rear toe. A couple guys have done this and said it was cheap and worked very well. With a bit of luck you could find a shop with an empty frame jig and you could get this done this afternoon.

I’ve had a couple types of adjustable toe kits and they all have warts. Next time I’ll install adjustable camber and I’ll do as described above for toe.

#3

Thanks, Ranger. Unfortunately my work schedule doesn’t afford me an opportunity to get this done this week. I had some adjusters on the last car and agree with you about the warts.

The frame shop method has been mentioned before and I’m seriously considering it. Can any frame shop do this or do I need to find one with a particular type of equipment? What is it that they ultimately end up bending, the trailing arms?

#4

I’ve not done this myself so I don’t know the details. Talk to Jim Levie and Al Kritter. You can email them via the Members page.

I figure that any frame shop ought to be able to do this. I have E30 frame specs if you need them, but I don’t think you will.

#5

Thanks, man. Since that’s not going to get done by this weekend, any thoughts on the other ways to mitigate the oversteer?

#6

How bad is the toe? You have both absolute and relative #'s?

#7

I just did a quick measurement with toe plates since I knew I wouldn’t be able to adjust it anyway, so I just have the absolute number. 1/4" out total. (!) I just pulled the spring pads and unhooked the sway bar. If I can figure out which way to adjust tire pressures I’ll try that. Might also try running spacers in the rear. I have a set of 10mm Raceland spacers. I’m not a big fan of them, but will run them if I have to.

Definitely getting it addressed before the next event.

#8

Those are relative #'s. Hard to say what the impact to handling will be w/o absolute #'s and you can’t do that with toe plates. Use a laser level and shoot a beam from each rear wheel forward past your front wheels.

That said, I would just blow the whole issue off and not worry about it. Drive hard drink beer, tell lies, flirt with the girls, and be done with it.

It doesn’t sound like you’re going to get absolute toe #'s. So you won’t get the info to really know how it might handle. So screw it, have a beer.

#9

[quote=“Ranger” post=80459]Those are relative #'s. Hard to say what the impact to handling will be w/o absolute #'s and you can’t do that with toe plates. Use a laser level and shoot a beam from each rear wheel forward past your front wheels.

That said, I would just blow the whole issue off and not worry about it. Drive hard drink beer, tell lies, flirt with the girls, and be done with it.

It doesn’t sound like you’re going to get absolute toe #'s. So you won’t get the info to really know how it might handle. So screw it, have a beer.[/quote]

I just want to avoid snap oversteer in the uphill esses in the rain. It tends to put a damper on all the rest of the stuff that goes with a race weekend. I could set up a string box, but I don’t see the point since it’s completely non-adjustable right now. I know that I’ve got 1/4" total toe out. Whether that’s 1/8" on each side or zero on one side and and 1/4" on the other doesn’t help me all that much. I know it’s going to tend towards oversteer. (I found myself in this exact position with the last SE30, before welding in adjusters.) Anything I can do to bring it closer to neutral will give me peace of mind if nothing else.

#10

You’re going to defeat yourself worrying about this. All you know is that the wheels aren’t parallel. Maybe your handling will be fine. Maybe it will be a teensy bit tail happy on one side or the other. Maybe it will be a lot. Maybe it will drive like a crab. There’s no way to know with only relative #'s. Don’t go in with assumptions. Just drive hard and feel it out.

If it’s wet, disconnect the rear sway. That doesn’t have anything to do with toe tho.

#11

1/4" will be manageable and not something you should be overly worried about. Most importantly, expect the car to be predictable; just take it a bit easy until you feel out corner exit behavior.

#12

You should be fine, but it will keep you on your toes. See what I did there?

I had the exact same issue at my first race last July. I measured rear toe during the build and thought it was fine, but all I can figure is I got my measurements backwards. It wasn’t until the day before I left for the track that I checked again and realized I had toe out on both sides. I ran the rear bar loose and no rear spring pads. I really don’t know if that helped, but I made it through the weekend. Fortunately it stayed dry because I wouldn’t have attempted laps in the rain. I think the pucker factor would have been super high.

By the next race in October I corrected the toe and the car was soooo much easier to drive. I wasn’t any faster, but I was much more consistent. I’m still looking for the fix that helps me find 3 seconds!

#13

Well, this is interesting. When I started this thread, I was measuring using a borrowed set of toe plates. I was in a crunch for time and didn’t feel like getting a string box set up. Afterwards, once I no longer had the toe plates I removed the spring pads (all four were still there) to lower the rear in an attempt to reduce toe out. I never got a chance to re-measure using the toe plates.

Today, I busted out my own alignment crap and set up the string box. I have standoffs and plates from Iron Canyon (from my Miata days) that help you measure exactly from the center of the wheel when setting up the box, and I’m certain it was set up accurately. It’s hard to see in the pic due to crappy focus, but the alignment is dead straight. Zero toe on both sides. I’m thrilled.

#14

I like your alignment hardware. I have a decent way to do the stringing, but that measuring appliance looks pretty trick.

#15

Thanks, Chuck. That’s another Iron Canyon part. I don’t remember paying what they say it costs, but I’ve had it for years and got it along with a bunch of other alignment stuff from them, so who knows. It was designed with SM in mind, but works for any 15" wheel. Measuring both sides of the wheel at the same time does simplify things.

http://www.ironcanyonmotorsports.com/icm-spec-miata-toestick/

#16

Re. removing spring pads to change toe. A couple years ago I did some testing to see if toe changed with different rear suspension angles.

I measure toe by shooting a laser forward past the front hubs. The geometry of this makes for super precise measurements because toe changes become multiplied by 6 or 7.

I could not detect a change in toe with reasonable changes in rear suspension angles.

#17

[quote=“Ranger” post=80618]Re. removing spring pads to change toe. A couple years ago I did some testing to see if toe changed with different rear suspension angles.

I measure toe by shooting a laser forward past the front hubs. The geometry of this makes for super precise measurements because toe changes become multiplied by 6 or 7.

I could not detect a change in toe with reasonable changes in rear suspension angles.[/quote]

I remember reading about that at some point. It’s possible I initially measured wrong with the toe plates, but I don’t think it’s likely, as it’s not exactly rocket science. I measured and re-measured today with the strings, making absolutely certain it was correct. It was. The only thing different between then and now is the lowered rear. At some point, I’ll borrow the toe plates again and take another measurement.

#18

More importantly, how did it feel on track? You’re in for Gateway, I presume?
Cliff

#19

[quote=“cpp” post=80621]More importantly, how did it feel on track? You’re in for Gateway, I presume?
Cliff[/quote]

On track it was great. First day was wet so went out without the rear bar connected. As it progressively dried, I could tell I was pushing a bit and having to work to rotate the car. Hooked the bar back up and it was perfect. I was still slower than I would have liked.

Definitely in for Gateway. We’re heading out on Wednesday and I’ll be doing the track day on Friday. Looking forward to meeting you in person!

J.