Changing tires and new partners

An ongoing challenge that we've had with our car is a lack of grip with cold tires.

While we've loved our Hoosier R75 radials when they got hot, it took a bit of work to get them to the right temperature.  Not only did we have to fight the lack of grip when outside temperatures were 80+ degrees, but if the outside temperature was cooler, it was even tougher.

As the first driver in the car, Karl Coleman usually spent most of his first run getting heat in the tires.  Ron's first runs were then better, but it usually took at least a run from each driver to get the tires working well.  The same went for Alyson and Amy on the Ladies side.

Hoosier slicks have a few different compounds, with A25 being the softest, R35 being in the middle, and R45 being the hardest.  For autocross purposes, softer is usually better because they work better right out of the box.  The potential danger is that they can overheat quickly.  Unfortunately for us, there is only one compound available in the size that we ran.  The R75 compound is in between the R35 and R45.  Although we never had to worry about them overheating, we did have to worry about getting and keeping heat.

The earlier Miatas were starting to switch over to softer compound tires, making them even faster.  Jim Daniels in his '94 Miata started running Avons, while Drew Vanderploeg and Steve Hudson made the switch to 110 compound Goodyears.

Our team had been looking in to trying out Goodyears based on the very impressive results of EM driver, Jeff Keisel.  However, the cost of their Radial Slicks were extremely high, even when compared to the Hoosiers we were already running.  It's hard to spring for a $2000 set of tires not knowing if they'd be faster than what we were already running.

Jeff made the trek up for our National Tour in July, so I took them time to talk to him about the Goodyears.  He said that the compound on the radials was way too hard for our autocross purposes and that I should give the bias plies a try. 

When building the car, I wanted to keep with newer technology, starting with the car, and following through to the tires.  It seemed like a big step backwards to run old technology bias plies when radials were available.

The bottom line, however, was that we needed a softer compound, and the Goodyear 250 compound was softer than our Hoosiers.

Fortunately for us, our friend and multi-time National Champion, Andy McKee had started running these tires on his XP RX-7.  He only ran the 23.5x11.5x16 tires on the front of his car, but was willing to part with a used pair for us to test with.

After receiving them, we mounted them up and put them on the front of the car.  We didn't make any changes to the car, figuring that we needed to see first if they were at least comparable.  The intent initially was to run them in the morning at the first event on the front of the car and then switch them to the back for the afternoon.  To our joy, the first run out showed them to be better than the Hoosiers on initial turn in.  The car also rotated better overall throughout all of the runs.

Needless to say, we didn't switch them to the back of the car, as that would have been an excercise in futility with the front washing out everywhere.

We were able to continue running the tires with quick turnover allowing us to test with lots of heat in the tires, and they didn't seem to lose grip due to overheating when compared to the harder compound Hoosiers.

This made the decision easy to switch from the Hoosiers to the Goodyears.

What needed to happen next though, is that we had to change the setup of the car to match what bias plies like.  While we were able to use as much camber as we could for the Hoosier Radial Slicks, bias plies like very little camber. 

This left us with a little worry, as the rear suspension gains camber as the car is lowered.  We obviously didn't want to add ride height.  We took the car to our partners at Clarks Wheel Alignment and they aligned the car for us.  As expected, they were able to get the front to the numbers we were looking for, but the minimum amount of camber they could get out of the rear was over 2.5 degress of negative.  We were looking for 1 to 1.5 degress, so that left us in a pickle.  To add to the problem, even if we could get less camber, we would end up with the toe way outside of the specs we wanted.

The rear of the MX-5 has a multi-link set up, with five different links comprising the suspension. One link is specifically for camber, while another is for toe.  These links are non-adjustable, using cams to to change the effective lengths.

So, the obvious choice was to get different length links for the toe and camber.  Unfortunately, no one was offering different links for the MX-5.  We did find a couple of companies that offered adjustable links for the RX-8, which is very similar to the MX-5.

One of those companies was Megan Racing.  Megan Racing specializes in suspension, exhaust, and brake components for a number of performance cars.

They offer all five links with adjustable ends and spherical bearings for the RX-8.  We contacted them to see if they had tested these on the MX-5 and were told that they hadn't.  We offered to test the toe and camber links on our car, so they sent them off to us. 

Upon opening the boxes, our first reaction was that they were very high quality, with a beautiful blue powder coating.  They looked plenty strong, being more robust than the stock links.  The arms are also adjustable on the car, without disconnecting anything.  These guys at Megan Racing were great to deal with and have great products.

 Comparison of stock toe link to the Megan Racing link, part number MZ-1470

Comparison of stock rear link to the Megan Racing link, part number MZ-1410 

 

Upon Comparison to the stock arms, it appeared that both would work, although the camber link had a shorter stud on the heim joint that goes into the rear hub.  We mounted them up, and while we would prefer a longer stud, everything fit well.  Installation was simple, as it was a simple unbolting of the stock links and bolting the new links back in after adjusting the lengths to be close to the stock arm length.  Megan Racing is working on a camber link specifically for the MX-5 with a longer stud.

 

 Rear camber link

Rear toe link

 



The adjustments on these links allowed us to set them close and then fine tune with the stock cams used on the stock links.  Upon taking the car back to our friends at Omni, we were happy to see that these new links allowed us plenty of room to get our alignment specs where we wanted.

Our starting point on alignment is -2.2 degrees of camber with 0.06 degrees of toe-out in the front, and -1.5 degrees of camber with 0.06 degrees of toe-in in the rear.  We will probably look at going even less on the camber based on the current wear.