Alignment and tires for Birkin

[pethier]

I have a 4:00 appointment tomorrow with thealignmentguy.com to swap tires and set the front alignment on my Birkin. Lucky me that there was a cancelation. He was all booked up in the week before our first double-autocross weekend. 

 

I assume that a live-axle Birkin has no rear-alignment adjustability. 

 

The front camber is adjustable via a system I have not come across before.  I intend to shoot for the same area as my non-adjustable Caterham has.

 

The tires I am going to put on are takeoff Yoko A052 205-15 from a friend who is a national champion.  I was a bit disappointed that the bolt circles on the Caterham and Birklin are different.  The wheels on this Birkin are 7x15.

 

Well, I'm off to measure the camber on the Caterham.

[pethier]

In my shop, getting a perfect reading on each camber is iffy.  Since the front camber on the Caterham is not adjustable anyway, I figured i could just check the total negative camber for both sides and divide by two.  I zeroed the electronic gizmo that measures angles on the RF wheel.  Then I brought the gizmo to the other side and read the difference.  Bang on 5 degrees.  Therefore, I surmised that Caterham were probably shooting for 2.5 degrees of negative camber.

 

Got the front of the Birkin set to 2.5 degrees negative camber and zero toe.  The caster is not adjustable, and measures 8 degrees.  Dogtracking does not appear to be a problem:  The thrust angle is -0.02 degrees.

 

I'm not ready to buy new tires for these 7" wheels.  I have 8" wheels for the Caterham, which will be a faster car when it's finished.  I got the secondhand Yoko A052 205-15 tires mounted.  These don't seem to have any flange-side voids, unlike the Prisoner wheels and the 8" wheels I have for the Caterham.

 

If the weather cooperates, I'll take it around the cones this weekend.  It appears that I can adjust the front swaybar without crawling on my belly like a reptile.  

Edited Thursday at 07:53 PM by pethier

[pethier]

Well, it's autocross eve.

 

It will be a bit chilly tomorrow.  A little warmer on Sunday.  

 

For reasons I don't understand, there were 1/4-inch spacers under the back wheels.  I took them out.

 

There were no spacers at the front. The hub on these wheels just clears the front caliper.  The studs in front would not be long enough for spacers.

 

So it goes.  You buy a Birkin that has who knows how many owners, you find stuff.

[11Budlite]

8 hours ago, pethier said:

For reasons I don't understand, there were 1/4-inch spacers under the back wheels.  I took them out.

 

There were no spacers at the front. The hub on these wheels just clears the front caliper.  The studs in front would not be long enough for spacers.

 

IIRC the Birkin recommended offset was different than the typical Miata-based wheels that most people used when they upgraded from the stock wheels. The stock wheels on my old Birkin were quite a bit heavier than the RPF1's that I replaced them with. I remember several Birkins that used the same Kosei wheels that you have on your car. If you have the 38mm version of the Kosei it could be that they added the 1/4" spacers to get the offset closer to the Birkin stock recommendation. I think stock was around 30mm but it's been a long time since I played with Birkin wheels so I could be mistaken.

[pethier]

14 hours ago, 11Budlite said:

 

IIRC the Birkin recommended offset was different than the typical Miata-based wheels that most people used when they upgraded from the stock wheels. The stock wheels on my old Birkin were quite a bit heavier than the RPF1's that I replaced them with. I remember several Birkins that used the same Kosei wheels that you have on your car. If you have the 38mm version of the Kosei it could be that they added the 1/4" spacers to get the offset closer to the Birkin stock recommendation. I think stock was around 30mm but it's been a long time since I played with Birkin wheels so I could be mistaken.

The weird part here is that 1/4-inch for roll radius on the front would have a heck of a lot more significance than on a solid back axle.

Edited 21 hours ago by pethier

[pethier]

It rained Saturday morning.  I took the Cayman, still on its all-weather tires.

 

Hope runs high for a drier Sunday.  

[pethier]

Did get a drier Sunday.  Raining when we arrived at the site.  Managed to wait out the rain and get annual tech inspection on the Birkin.  Then I put the car in the trailer in cse it rained while I walked the course.

 

Not raining  when it was time for my first 3-run heat.  I was not getting traction on the dodgy surface of Canterbury Park's overflow lot.  Ever since they sealcoated this lot, it releases aggregate we call "Canterberries".  These tires may wake up with a better surface and warmer temps.  When I went to start the engine for the third run, I needed a push start.  Cranking slow.  After the run, I found a place on the paddock lot higher than my rig.  Turned off the engine to see if it would restart.  Nope.  Pushed it down the hill to my rig.  Removed the air filters.  Removed the hood.  Fired up the F-150 and hooked up the jumper cables. After a while, I was able to start the Birkin.  Let the big Ford charge the little Ford for a while.  Turned off the Birkin, disconnected the cables and tried to start it again.  No go.

 

Hooked up and let the big Ford charge the little Ford again.

 

As time approached for my three runs in the afternoon,  I started the Birkin, refitted the hood, reinstalled the air filters, and drove the Birkin to its spot in grid.  

DIdn't turn off the car until I had completed my runs and driven the car behind my trailer.  Winched it in and tied it down.

 

I carried passengers all day.  My best was 39.859.

FTD was 33.405.

Not exactly great.  Still was fun.

Now I will have to figure out whether the battery is toast or the alternator circuit is not working.  My money is on the battery.  

Edited 1 hour ago by pethier