[01-Spyder]

Alright, I have been having a bit of a dilemma lately with tire pressure and tire rollover. So to start, Car has BC racing coilovers 5k front and 7k rear. -3.5 degrees camber front, -2.5 degrees camber rear. Running 15x7 wheels with 205/50/15 RE-11's. Previously I ran these tires and they were getting towards the end of their life, I ran the rear at 38psi and the front at 32psi and was getting perfect rollover. I just bought new RE-11's and I cannot seem to get them to rollover to the arrow, I'm down to 29psi rear and 25psi front. I feel like I shouldnt go any lower because they feel pretty sloppy already(which is expectable because they are at full tread). So my question is, does tread depth of the tire have a direct relation to the tire pressure that achieves proper rollover?

 

[akomsr1]

What arrow are you referring to? Are you chalking your sidewalls and adjusting from there?

 

[01-Spyder]

What arrow are you referring to? Are you chalking your sidewalls and adjusting from there?

The arrows on the sidewall that the rollover is supposed to be down to. Yes I am using the chalking method.

 

[Levi]

http://forum.miata.net/vb/showthread.php?t=461280

 

[01-Spyder]

http://forum.miata.net/vb/showthread.php?t=461280

Already read that. 46 doesn't get me anywhere close to the correct rollover. Unless I shouldn't go by rollover and experiment with what "feels best".

 

[SuperWhiteGT4]

You're fine. Ignore the rollover. It's not a great judge of anything.

 

[Ferrino]

I'm picking up some RE-11s later today, so am interested to hear about pressures. Judging by the Miata thread, people like anything between 26-50psi!

 

[silversprint]

Track or AutoX?

Tire temperatures may give you better results.

 

[01-Spyder]

Track or AutoX?

Tire temperatures may give you better results.

Sorry, autocross. As in using a tire pyrometer?

 

[sldnrck]

Yes. Tire temps will tell you if you need more or less pressure. The arrow on the edge really is not that useful. If you are wearing it off you could either not have enough pressure, not have enough camber, or not braking enough before a corner. All three of those can cause roll over and wear down to the arrow or past it. For temperatures tyou want even temperature across the surface. That would tell you you are using all of the tire surface the same. If part of the tire is hotter than another part than you are using the hot part more than the colder part.

 

[01-Spyder]

Yes. Tire temps will tell you if you need more or less pressure. The arrow on the edge really is not that useful. If you are wearing it off you could either not have enough pressure, not have enough camber, or not braking enough before a corner. All three of those can cause roll over and wear down to the arrow or past it. For temperatures tyou want even temperature across the surface. That would tell you you are using all of the tire surface the same. If part of the tire is hotter than another part than you are using the hot part more than the colder part.

Alrighty. Does anyone know of a good pyrometer to use? Found one on saferacer for 150ish.

 

[sldnrck]

Harbour freight has them on sale occasionally for $50 or less. There are a few other brands that are under $50 too. Keep searching. If you go with the probe type you'll get a little more accuracy, but I am not sure that it is worth the additional cost.

Amazon has one listed at $23.
http://www.amazon.com/s/ref=nb_sb_s...red+thermometer&sprefix=infrared+ther,aps,192

 

[silversprint]

Harbour freight has them on sale occasionally for $50 or less. There are a few other brands that are under $50 too. Keep searching. If you go with the probe type you'll get a little more accuracy, but I am not sure that it is worth the additional cost.

Amazon has one listed at $23.
http://www.amazon.com/s/ref=nb_sb_s...red+thermometer&sprefix=infrared+ther,aps,192

Those won't work properly. The surface of the tires cools too fast.

For tire temperature you should use a probe type pyrometer.

 

[01-Spyder]

Well I picked up a cheap one from RadioShack for now. I have an autocross this Sunday so I'll let you know what I find. How far over towards the sidewall should I take a reading?

 

[SuperWhiteGT4]

Well I picked up a cheap one from RadioShack for now. I have an autocross this Sunday so I'll let you know what I find. How far over towards the sidewall should I take a reading?

Take a reading at the inside tread and the outside tread and compare them.

 

[akomsr1]

Outside - middle - inside

You won't get perfectly even temperature across the tire due to camber. You want an increasing temperature from outside shoulder towards the inside without too much differences in temperature (closer they are the better).

Your rear tires will have more even temperatures across the carcass

 

[sldnrck]

Those won't work properly. The surface of the tires cools too fast.

For tire temperature you should use a probe type pyrometer.

It will be more accurate than the seeing if the triangle is worn. It will help to have another person help to measure as soon as you pull into grid. Turn the front wheels too to make it easier to get readings. 10 degree difference is pretty good. Anything more than that and you need an adjustment. Also take into account if there is a big sweeper before the finish too.

 

[cosmin]

Probe pyrometer if you really want to get it right. Or just go by lap times.

 

[01-Spyder]

Alrighty so today I got to mess around with the pyrometer a little. I found that 37 psi on all four corners was working very well. Here are the readings in degrees F. (Outside,Middle, Inside)
Front:
Drivers- 113.4-119.5-125.9
Pass.- 113.8-117.5-116.5
Rear:
Drivers- 122.3-124.3-122.4
Pass.- 125-122.2-115.4

I measured Front drivers first, then moved to rear drivers, then rear passenger, then front passenger. there was also a hard right turn just before the finish. I also measured with a laser pyrometer and I now understand why a probe type would be best, the readings changed quickly.

 

[silversprint]

Why do you say that your pressure was working well based on these numbers?

Are you trying to find the optimal pressure for the tire or check alignment?

Optimal temperature for a street tire is probably in between 170-200 depending on the brand. Your numbers are really low.

You might have ok camber setting but you didn't really get high enough numbers to determine if the pressure you have is correct pressure.

I am not sure if you can get the tire hot enough during an autox run. I have no experience with measuring temperature from single lap runs. I guess it would depend on the course.

Also you are measuring at the surface but the internal rubber is probably hotter. By how much depends on the tire.

How did the temperature change when you changed pressure? Do you have other numbers?