[cxp213]

One thing that doesn't usually get mentioned is the tire width vs the wheel width. If your tires are wider than your wheels, you'll have more "squirm" from the tires compared to the same tire that's on wheels that are slightly wider. Ideally, you want to run slightly narrower tires than your wheels so you can keep the squirm in check as it should slightly stretch the sidewalls (in addition to proper camber, pressures, etc). However, with so many other factors and considering most 2ers are running narrow/stretched tires, this is probably less of a concern for most.

[jmwilson125]

Originally Posted by capt_and

Another reason why you are getting sidewall wear is because of the body roll - the car has lots of it. I am running -3.5* front and 2.2* rear camber and am still getting wear patterns indicative of too much roll. Whenever I only had -2.5* camber front, I would be riding on the letters. We chalked 3/4 way down on the side wall and none of it was left after the session.

RS4s are very good tires. Very sticky for how durable they are. If they are wearing too low on sidewall, try increasing pressure. But, tire pressures can only do so much without some pretty aggressive camber settings on this car.

I think i misread the post above mine. Let me clarify.

I started out 35 cold, I think that ended up about 45 hot. (First half of the day was rain so I figured I'd leave it a little high untill it dried out)

Later in the day I dropped pressure. The session after that I dropped again. I think I dialed it back to about 39-40 in the paddock when they were still pretty hot. I probably finished the day running 40-42 when fully hot.

Only the last few sessions of the day I started to kiss the top of the wear triangle. It looks like I'll have to drop the pressure more for the next go around.

Also according to idrive my hottest tire was 199 F on the track. I know idrive is probably a good approximations, but not perfect. Is 199F too hot for these tires? To me the felt way better around 120-150F. Maybe that was due to overinflation??



I actually posted better time around this track with less experience on mpss. The comparison is not apples to apples though. Here were the settups

Mpss 235/40 r18 F, 265/35 R18 R. 8.5"x18 et40 F. 9"x18 et36 R
Rs-4. 235/45 r17 F, 235/45 R18R. 8"x17 et45 F+R

I do not have the wheel weights, but I suspect they are close.

Dinan springs, and me lca + ts,


The one thing I didn't really consider untill after the fact was the 265 in the rear. I think it helped me put down more power come out of the corners.

According to track addict with an external gps I did Cannan speedway in 1:11:9 last year on mpss 38 degree F. and 1:12:8 this year on rs-4 in 60 degree F.

I had higher top speed on mpss and pulled a max 1.24g. Rs-4s I pulled 1.26gs, and surprisingly 1.05 is the rain. (Not sure how accurate the accelerometers in phones or how much noise filtering the apps do for g spikes).

[cxp213]

^ Some things to consider:

• At past 40psi hot, your tires were over inflated and it's also possible you over-drove on them
• Tires will get greasy as they heat up as they begin to release chemicals from within the compound
• It's not just about tire pressures, but also about alignment specs, tire/wheel width, body roll, etc so you need to take all of that into consideration
• 200ºF is too high for most street tires (and out of operating temp range), but it also depends on other factors like track conditions, weather, compound, etc
• Lap time fluctuations really mean nothing when you're a novice as you're not going to be consistent enough to be able to objectively compare 1 lap to another, let alone those made on different days. *Side notes: MPSSs aren't sticky enough to beat any remotely-competition-worthy tire which further proves my previous statement & warmer climate means more grip at your tires but could also mean less power.
• Width definitely helps, but can't really compare the advertised width of 1 brand to another, and compound matters more

[Anthony235]

Originally Posted by jmwilson125

I actually posted better time around this track with less experience on mpss. The comparison is not apples to apples though. Here were the settups

Mpss 235/40 r18 F, 265/35 R18 R. 8.5"x18 et40 F. 9"x18 et36 R
Rs-4. 235/45 r17 F, 235/45 R18R. 8"x17 et45 F+R

You basically negated any advantage of the RS4 over the MPSS by choosing your specific RS4/Wheel sizes. I'm not surprised you got a better lap time with the MPSS setup.

I doubt the phone accelerometer is very accurate. Maybe good for comparing the delta within the app though. I've done a few track days in the rain. Most people don't realize how much grip a tire has in the wet. When you have steam coming off the tire you're doing it right

[jmwilson125]

Originally Posted by Anthony235

You basically negated any advantage of the RS4 over the MPSS by choosing your specific RS4/Wheel sizes. I'm not surprised you got a better lap time with the MPSS setup.

I doubt the phone accelerometer is very accurate. Maybe good for comparing the delta within the app though. I've done a few track days in the rain. Most people don't realize how much grip a tire has in the wet. When you have steam coming off the tire you're doing it right

I basically had to get that size, because that's what would fit my wheels. I understand its not really an apples to apples comparison. Long story short, I need some more seat time, and I need to run lower pressure before i can make a fair assessment.

I'm pretty sure the accelerators in smartphones have a refresh rate of 30 hz which is actually pretty fast. I have no idea how sensitive they are though. I tried looking up specs on specific components, but couldn't get anything. Most phone gps refresh at 1 hz with mediocre accuracy. I picked up a 10 ht gps and mount it on the roof.

Pretty sure the apps try to smooth accelerator data, so if you bump it, id doesn't register 5 gs in turn 3 haha.

yeah haha, it is weird to stop and see all of the water evaporating off of them.

[jmwilson125]

Originally Posted by cxp213

^ Some things to consider:

• At past 40psi hot, your tires were over inflated and it's also possible you over-drove on them
• Tires will get greasy as they heat up as they begin to release chemicals from within the compound
• It's not just about tire pressures, but also about alignment specs, tire/wheel width, body roll, etc so you need to take all of that into consideration
• 200ºF is too high for most street tires (and out of operating temp range), but it also depends on other factors like track conditions, weather, compound, etc
• Lap time fluctuations really mean nothing when you're a novice as you're not going to be consistent enough to be able to objectively compare 1 lap to another, let alone those made on different days. *Side notes: MPSSs aren't sticky enough to beat any remotely-competition-worthy tire which further proves my previous statement & warmer climate means more grip at your tires but could also mean less power.
• Width definitely helps, but can't really compare the advertised width of 1 brand to another, and compound matters more

Thanks for the input. I think the biggest take away is lower pressure and more seat time.

Hopefully i can get this video uploaded in the track/autox section soon.

[Anthony235]

Originally Posted by jmwilson125

Thanks for the input. I think the biggest take away is lower pressure and more seat time.

Hopefully i can get this video uploaded in the track/autox section soon.

At least you're out on the track. The hunt for laptimes is never ending

[ggggbmw]

My brother races with a ChampCar (formerly chumpcar) team, running an E30 with Hankook RS4 tires. He told me that they shoot for 32-34 psi hot on these tires. Any more and they would get loose. He really gave me crap for not talking to him first and starting at 35 cold. They start around 25-27 cold.

He did say that since we have no camber in the 2, and it's a bit heavier, that we might want to go to a bit higher psi to compensate. But no more than 36-38 hot.

[ggggbmw]

How low can we set the pressure in the tires before tripping the TPMS low pressure and putting the car into Comfort mode?

If we want these tires to be in the low 30's hot, that means starting in the mid 20's cold. If we start at 25 psi cold, will that trip the TPMS?

Are there any tricks to starting a session with below alarm pressure, and not getting a alarm? Having to pit, put it park, and then hit the TPMS Reset seems like a pain.

[cxp213]

You're not gaining anything by starting really low, like mid-20s. I posted above saying that you should start at upper 20s and let air out little by little during/after each session until they stabilize at the psi you want them at. When you're on the track, it's not a set it one time and be done type of deal; you have to keep checking.

[ChrisFulton]

Originally Posted by ggggbmw

How low can we set the pressure in the tires before tripping the TPMS low pressure and putting the car into Comfort mode?

If we want these tires to be in the low 30's hot, that means starting in the mid 20's cold. If we start at 25 psi cold, will that trip the TPMS?

Are there any tricks to starting a session with below alarm pressure, and not getting a alarm? Having to pit, put it park, and then hit the TPMS Reset seems like a pain.

Originally Posted by cxp213

You're not gaining anything by starting really low, like mid-20s. I posted above saying that you should start at upper 20s and let air out little by little during/after each session until they stabilize at the psi you want them at. When you're on the track, it's not a set it one time and be done type of deal; you have to keep checking.

Re-read my posts above made while I was at the track. You are going to adjust pressure as your track day progresses.
Once you arrive, just lower to 30psi and adjust from there throughout the day.

[dradernh]

At the bottom is an example of the sheet I use to track tire pressures throughout a day, an event, and over longer periods. This data applies to a specific tire and size (e.g., BFG R1 245/40-17).

The purpose of collecting, analyzing, and applying this data is to assist the driver in experiencing predictable performance from his tires. This enables him to drive with confidence, knowing how his tires will behave in each and every part of the track. While most drivers won't want to bother with all of this, those intent on pursuing faster lap times will benefit from this level of attention to detail. Sooner or later, those drivers will create their own processes for data collection and analysis.

One goal of capturing this data is to have the tires at the desired hot pressures during the fastest lap(s). Another is to start the first session of the day with tire pressures that are known to work; i.e., the hot pressures will be optimal or nearly optimal on the fastest lap(s) of that first session.

I reduce pressures between sessions based upon:

1) The pressures recorded at the end of the preceding session;
2) My expected fast lap time during the upcoming session (faster = more heat/psi gain);
3) The track surface temperature taken just before setting the pressures for the next session (note that this is not the paddock surface or the ambient temperature); and,
4) My prior experience with the tire compound in the size being used.

Assumptions

1) There is no "cool-down" lap at the end of a session (i.e., the driver is still running the car hard up until he must slow down to come off the track (this isn't always possible));
2) Pressures are taken immediately after the car is parked (if the driver can't do this, then someone else must do it);
3) There is a 2 psi drop between slowing for the entry to the hot pits and starting to take pressures 1-2 minutes later in the paddock; and,
4) The driver knows or has an idea as to the optimal on-track hot pressures for the tires he has on his car.

Note that this data will vary from track to track, and this is independent of the climatic conditions present on any given day. Factors leading to this are the number and types of turns, the differing surfaces on and among tracks, how fast each track is, and the types of braking zones on each track. Above all is driver consistency, where consistent driver inputs result in predictable tire pressures.