Toyo RA-1 Tire Pressure & setup

I recently attempted to run R-compund tires (Toyo RA-1) for the first time, and experienced a spectacular 'fail' - and I have no clue why.

The car is a Beck GTS, 800 & 1200 lb axles wet sans driver.  Previously I used 215/45R17 and 255/40R17 RE71's on 8 & 9" rims, cold pressures 20 & 24 psi, and the car was just about perfect.

The Toyos are 225/50R16 and 245/45R16 on 7 & 8" rims.  Regarding pressure, I got advice from two fairly experienced racers - one said 32+ cold, another 18 cold.   Toyo states hot pressures should be 36-42.   I started with 24 & 28 cold, figuring it's a light car...

The car became instantly psychotic, wanting to swap ends in every corner.  I lowered pressures to 20 cold all round, and it got easier to catch, but still tail happy beyond anything reasonable.  Much of the left rear tire scrubbed off in 120 track miles.  The middle had almost 1/16" more wear than the shoulders, which is traditionally a sign of overrinflation (this used to say underinflation - brain fart on my part)

Lap times were about 5s slower than with the RE71's (90 second laps), steering corrections went from 2-3 per 10 laps to 1-2 per corner.

Any suggestions on what idiotic thing I am doing wrong would be welcome. 

Right Rear Tire - not much wear, most of it on the inside shoulder (-2.4 static camber)

Left Rear Tire (-2.4 static camber)

You said "The middle had almost 1/16" more wear than the shoulders, which is traditionally a sign of underinflation."  In my experience it's a sign of over inflation, and is the reason it was tail happy.

Center wear is a sign of OVERinflation

EDIT: I just realized you also changed rim widths  stuffing too much tire on a rim will also "round out" the tire and cause the center to bulge  if that's the issue then I don't believe you can totally correct that issue with inflation 

You also might be trying to drive slicks like 200tw tires. They need heat first (you probably already knew that), but You also don't get much for traction break away alerts. Slicks give, and when they do, ouch. Whereas a 200tw is more predictable and forgiving. Just a thought here. Might be totally wrong. 

I've never run RA-1s on something that light, but 20 psi sounds way low.  On Miatas/etc you're looking for low/mid 30s at least hot.  I'm also surprised to see you running them full tread -- general recommendation for RA-1s is to shave them on dry tracks and only use full tread depth as rain tires.

Note that the RA-1 grooves are not all the same depth, so the large center rib is not necessarily a sign of more wear in the center of the tire.  They're designed so that when shaved you get fewer grooves.

Also RA-1s are not a faster tire than RE-71Rs.  Yes, they are an R compound, but they're a 25 year old design.

As for balance, I notice that you went 10 mm wider on the front and 10mm narrower on the rear.  I would expect that would tend to lead to more oversteer with any tire?

BTW the RA-1 is an awesome tire. It's not really R rubber 

ive run them on high hp machines and momentum machines with equal good success 

The under / over inflation was a brainfart - apologies. 

My confusion is that the Toyo specs suggest much higher pressures than I was running, yet the tire still showed signs of over-inflation.   Going below 20psi cold seems *really* low.  Spec Miata axles are not any heavier than my rear axle, and none of them run 20psi cold / 26 hot AFAIK. 

The Toyo specs call for 7.5 - 9" rim width for the 245/50R16 - I figured my 8" rim was reasonable, though I know a 9" would be better.

I didn't necessarily expect them to be faster than the RE71 - just didn't think they would be that much slower and more crazy to drive!

The section width changes are indeed directionally incorrect.  I have done something similar before - I used to track an '88 911 on RE11 tires, and changing from 205/55R16 & 225/50R16 on 6 & 7 rims (stock sizes) to 205/50R17 and 255/40R17 on 7.5 & 9 rims did not change the handling appreciably.  The limit was less forgiving on the 17's, and the 16's were maybe 1/2-1 sec slower, ran more slip angle, and were more fun to drive - but no fundamental change in how the car acted.

Re. heating up the tires - I did run a warmup lap.  But, the day in question was cold - the high was maybe 52 degrees.  Might that have prevented the tires from ever getting properly hot?  They felt hot after a session, but not burn-my-hands hot.  I would have figured the sliding would provide all the heat they needed, and then some.  No issues with grip on the front axle.

My first thought is, the RA-1 is ANCIENT. It's not really an R-comp, and I would not be surprised if the RE-71 is just flat out faster. Even way faster.

New street tires are faster than old not-quite R comps. I was able to run faster times on RE-01Rs than RA-1s back in 2006 when that was a hot tire. It was autocross and two different drivers and car set-ups, but both drivers were in the same car (E36 M3). Not even remotely apples to apples, but it's something I think about when I hear people running RA-1s. The RE-71R would absolutely destroy an RE-01R.

It sounds like some changes to tire pressure might gain you some time, but I still think you might be chasing the Bridgestone.

I'd actually be fine with slower - I run HPDE's and I don't have a ton of ego, so my absolute lap time is not terribly important. 

The amount of wear on only 1 tire (LR), and more importantly the complete change in character of the car, is not acceptable to me.  Other folks run RA1's, are decently quick on them, and claim they last forever.  There must be something about what I am doing that makes it not so.  Enquiring minds want to know (lord that dates me ...), but are clueless where to look.

As to lap times, I know a highly modified 1988 911 driven by a fantastic driver that ran high 1.28's at Grattan on RA1's, albeit very worn ones.  While I am not as good of a driver, I've got 30 more HP and 600lb less car to wheel around - it ought to be close.  1:32-1:34 is not even ballpark.  So again I conclude that something on my end is seriously amiss...

If I can't figure it out, I guess I'll suck it up and switch back to what works (while they are still selling the RE71's), even if I don't know why.

We use to run them as they would last for ever compared to other comparable tires. I found they don't like to be manhandled. Smooth and steady with the least amount of drama will net you fast laps. They give up quick but I think that is due to the harder compound. They were seconds slower at many of the tracks we raced at but we could run a set for 8 hours or even 12 hours on a light car with a smooth driver. This could save us several pit stops and netted us more than a couple wins. 
 

For short races (4-6 hours) we would shave them and they pick up lots of grip but still last really well.

Seems like a bunch of things are contributing.

However,  a tire pyrometer would probably point out your issue quickly.  It would help you set pressures, determine if you are in the ballpark for tire temps, and help see if you have an alignment that these tires don't like.

I run a 245 on a 10 inch wide wheel.  I agree that a 9inch wheel is a good place to be with a 245 as well.  However, I run 205 on 8 inch wheels.  Lots of squirm and worse wear when I tried to pinch a tire like that.

I seem to recall target pressures for an RA-1 being around 34-38 psi. I tried running them soft on my 1200 lb Locost and every time I added pressure, they got faster. So I just used Spec Miata suggestions. 
 

That's a wide carcass for those wheels. You might be happier with 205 and 225 on 7 and 8" wheels.

The RA-1 is ancient and not the new hotness but man are they friendly and heat cycle resistant. Great track day tire if you're not trying to win anything. 

Give Phil at Phil's Tire Service a call. I used to buy all my Toyos from him. He probably has the answer.

In Spec Miata, the target hot pressure was 38 psi. Less than that and they were a bit slippery ie not enough grip. They were fun tires. Easy to control at and beyond the limit. 

The theory that the rim is too narrow, causing a bulge in the tread that cannot be mitigated well with air pressure, seems plausible.  It would explain why the car drove better with less pressure (but still like crap), even though higher pressure was indicated by common usage of the tire.

I took a picture after my first couple of sessions, each only lasting a few laps.  Hot pressure was 30-32.  The wear (or is it overheat?) pattern covers at best 60% of the tread width.

Difficult to fix, as I don't have 9x16 rims, and I am not itching to buy another set of Porsche lug pattern wheels ($$$) - there isn't much street/track suitable rubber available for a 16x9 rim, and what there is is pricey.

burgermeister said:

Difficult to fix, as I don't have 9x16 rims, and I am not itching to buy another set of Porsche lug pattern wheels ($$$) - there isn't much street/track suitable rubber available for a 16x9 rim, and what there is is pricey.

16" is kind of a wasteland for tires these days.  You can still get a decent selection in 15s, but other than that you need to go to 17.

You said you'd previously used a set of 17" tires on this car, are those the street wheels?

Hey, I know you!  

In my RA1 experience, they sometimes get a weird ripple in them and wear the middle even though inflation and temps are even. The wear did even out with more runs though ending up with an evenly worn tire.  I can take a look this weekend if you're at the track!  

Phil

Not an expert but fwiw that wear photo makes it look like the tire is over-inflated but also wants more camber. Looks like it's doing all of the work on between like 30% and 90% of the way across the tire, as measured from the inside. Certainly the narrow wheels/wide tires aren't helping. Either narrower tires or wider wheels would help. Even just going back to the previous 17" wheels. Or if you don't care about aesthetics it shouldn't be too hard to dig up a set of wider 17" wheels. I ended up with a set of 17x9s for my 986 for a total of like $250. They weren't exactly pretty but they were straight and round. Or even just getting some modern 200TWs that probably have a stiffer carcass if you do need to stick with the narrow wheels.

Hi Phil!

I'll be running the RE71s - with the way it drives on the RA1s, I don't have enough driving skill to keep it out of the grass/armco for 3 days...

Reasonably priced 16x9 Porsche wheels are difficult to find in the air cooled offsets, which is what I need... or maybe I'm not looking in the right places.  I've got a nice and an ugly set of 17's.

Should have bought a Miata ... much easier to try things when parts don't carry the Porsche tax.

Maybe this helps.

Lacking a skidpad and pyrometer , I went back to RE71's (this time 225/45R17 in front, still 255/40R17 in back)  and the car is back to being its normal predictable and sticky self. 

So much attention on suspension tuning ... seems a set of tires & rims can have far greater implications than drastic changes in suspension setup (such as disconnecting an anti roll bar, rather than adjusting it in small increments).  An interesting lesson for me.