Mazdaspeeder

And for someone like myself who is trying to do his first 5 track events this year, and will use them for about 5000 miles on the street, I can probably get 2 years worth of driving out of a set. I do keep the car stored in a garage that stays around 60* and take the car out occasionally in the winter to avoid flat spots and hardening of the rubber. Not sure if either of those 2 things are really problems over a 3 month storage period or if I'm just being obsessive. I got my maxxis used with 2 events on them and paid !
$400 installed. I'd say I did ok haha

OGRacing

iTrader: (1)

talking about flat spots. the maxxis is rather flat spot resistant. I've locked them up a few times and still haven't gotten a dud-dud-dud-dud-dud feeling. if you look at the Hoosiers the wrong way they flat spot lol.

Savington

iTrader: (31)

Pic you posted is at an angle which exaggerates the sidewall stretch. The other photo from your thread is a lot better. You can see that both of the tires in this picture really need a wider wheel.

205 A6 on 15x8 vs 245 RC-1 on 15x9

OGRacing

iTrader: (1)

I don't like the feel of a stretched tire on track. it feels less forgiving. with the power i have i need all the forgiveness i can muster.

Eric Powell is very fast pte driver, and he runs the 205 Hoosier on a 9.
When i run autocross i like to run a 225 rs3 on a 9" wheel. At autocross it's much less about power, and getting it wrong doesn't have the same price.

Mazdaspeeder

My 245/40/15x9 sits really square compared to when I had the 225 RS3 on it. I hear some stretch is good for running lower pressures which with the power we really need. I have no personal experience to back any of this since I don't push my car that hard on country roads. My buddy who sold me the RC-1 found they did Best on his 2200lb car at around 20psi cold. He had them on a 15x10

OGRacing

iTrader: (1)

i'm seeing 36 hot and add an extra psi to the heaviest loaded tire. that has been giving me the best tire temps. my car is kinda heavy though 2700lbs with driver.

wannafbody

iTrader: (1)

20PSI cold seems way too low to me. It also seems to me that if pressures are to low you get more sidewall flex and tread flex. I understand why people do that as the footprint should be slightly bigger. ????

OGRacing

iTrader: (1)

it all depends on what the tire likes. you want to see even heat across the face of the tire. if your taking your own tire temps and pull into the pits, you'll want to see a 10* sweep. meaning that the inside( closest to the body) of the tire should be 10* hotter then the outside, and the middle of the tire should be right in the middle. don't use heat lasers. use a tire probe.

i bout the "deluxe" tire pyromiter and have yet to use any of the fancy functions. save your money and get the basic, it comes with a nice case. Longacre Economy Digital Pyrometer



I've seen lighter car on bigger tires take less pressure then me. but ambient temperature and driving style all play a role.

bbundy

That's weird I feel the exact opposite. I feel the biggest reason I am consistently measuring faster lap times with a wider wheel is the improvement in brake away characteristics. The build up to exceeding maximum slip angle is more gradual with a bit of stretch in the sidewall. On radial tires with the sidewalls pinched any less than square they tend to snap loose when you exceed maximum slip angle making it much harder to stay smooth at the limits of traction. I haven't gone as far as 205 on 9 but if you are talking Hoosier 205's they are basically like most 225's.

OGRacing

iTrader: (1)

Tires can be considered as springs and dampeners. They have resistance to compreshion and the dampening is built in. I know the scca f5 class uses rubber as the spring and shock (look it up, it's crazy to see for the first time.) so by stretching the tire your increasing the theoretical spring rate and dampen caricteristics. So If you can set up a car to run with or without tire strech. I can tell when the sidewall is squerming around on the rim. When i feel it i know it's time to behave. I have a harder time feeling the "squerming" when the sidewall is pulled tight.

k24madness

iTrader: (6)

I agree with Bob here. When I put the 245 on a 10" wheel the breakaway became much more progressive. I found it easier to drive at the limit that way. I also noticed they needed lower tire pressures on the wider wheels. The contact patch got better too.

emilio700

iTrader: (3)

You and Bob have it right. When properly tensioned, a radial will have more linear breakaway characteristics. With the casing moving around, it becomes non linear, a ramp then a more sudden drop off with less peak grip. Not conjecture either. I've seen slip angle vs steering angle data at some point over the years but can't remember where.

k24madness

iTrader: (6)

The 245 on a 9" rim felt like a spring being wound up and then released at breakaway. I was a non believer at one point. The 245 on a 9 looked ok. I did not realize what I was missing until I swapped to 10's. Lap times don't lie. We dropped about a second on that change alone.

Next up 275 A7's on 11's.

OGRacing

iTrader: (1)

we've had this talk before. i just like the feeling of the "spring being wound up" that k24 mentioned. i'm just saying don't shy away from the 245's because you don't have a 10" wheel.

emilio700

iTrader: (3)

Since I'm the guy who designs the wheels for them, and the primary instigator of the tire that is the subject of this thread (that I started), I'll make it clear for anyone who cares:

If all you have is 9's, don't buy 245/40's. Your car will work better with 225/45's. Buy the right tool and learn how to use it. Don't buy the wrong tool and learn bad habits to make it work.

/discussion about 245's on 9's.

Feel free to start a new thread about 245's on 9's if you are so inclined.

bbundy

Its not just the rate it's also the linearity of the spring.

Also in this case its the Kinematics that the sidewall deflection and the effect it has has on the natural contact patch of the tire. A pinched in tire will transfer normal force towards the outside shoulder as corner forces go up where as a stretched sidewall will transfer normal force to the inside shoulder of the tire. When combined these effects with the rest of the kinematics in the suspension the net effect is the the stretched tire maintains a much more consistent shape of contact patch and the center of pressure doesn't suddenly move from the outside edge further inboard as it exceeds its traction limit so everything is comparatively more stable at the limit.

The repeatedly measured improvement people Are getting with wheels being wider than tires I think is about half because the grip goes up a little with the stability gained in the contact patch center of pressure and about half because the break away characteristics improve stability and make it easier to drive at the limit.

wannafbody

iTrader: (1)

And remember, what is true of a 15 inch tire won't be true of a 16 or 17 inch tire in the same width due to a shorter sidewall.

emilio700

iTrader: (3)

245/40/15 RC-1 on 15x10. Flat rolled front and rear, not pulled.

Sorta relevant as the VR1 should be almost identical dimensions to the RC-1. being built on the same casing. Just a teaser. Anxious to see the VR-1's on street builds.

Mazdaspeeder

Makes me want my 15x10 NOW!

ot81to

Hi guys, I just want to offer some input regarding the VR-1. I work for Maxxis and I've been directly involved with the roll-out and testing of the VR-1.

Emilio is right, that the 245/40ZR15 VR-1 will be very close (dimensionally) to the same size RC-1. Both have a measured section width of 9.8 inches. However, they do not share the same casing.

Regarding the best wheel width for competition use of the 245/40ZR15...
My personal preference is a slight stretch, but I always recommend testing. The clock doesn't lie.