My racercar is weird enough that tire selection has become an issue. Basically, I need 15" wheels (to clear the stock brakes) but I've got to keep it under 24" overall diameter. That means I'm limited to 225/45-R15 tires (23" overall).
That's not so bad, except the guys I'm running with have more power and are all running 245 or wider rubber.
Which got me thinking...
According to IMCA rules, minimum weight for a "Modified" car is 2450 lbs. My car sits at 2600 lbs, so I'm not far off. They run on asphalt, like I do. And you can get slicks that are 10" wide (about 255 mm), 23.5" overall diameter, and fit on 15" wheels. Tire prices seem to be about $100-150 less per tire than the cost of the Hoosier R7 in 245/45-R15 (about 24" overall diameter) and I suspect grip would be better with a true slick:
http://www.americanracertires.com/store.php?cid=5
Assuming you don't need to run DOT tires...why would you NOT do this? What am I missing here? Please set me straight!
I have asked similar questions for my challenge car. We are going to run Circle track slicks on it.
I don't see why it won't work.
Look up the bias ply slicks thread, as i can't seem to find it right now.
Hoosier has a 275/35R15 size for the A7/R7 that's the same 23" overall diameter as the 225s. Apparently they're also working on a 315 as well, by inserting a 2" spacer into the mold for the 275s.
They're thin and like to pop when overloaded. I'd imagine sliding on dirt relives some of that stress.
codrus wrote:
Hoosier has a 275/35R15 size for the A7/R7 that's the same 23" overall diameter as the 225s. Apparently they're also working on a 315 as well, by inserting a 2" spacer into the mold for the 275s.
A 295/35/15 A7 is coming out in May.
Not all Circle track slicks are for dirt.
Personally I think I would go for the hardest compound available to maximize life to money. You should be able to get a whole weekend out of a set.
Maybe they're only designed for left turns? 
https://grassrootsmotorsports.com/forum/grm/new-tire-found/50100/page1/
Gonna try not to be like other sites and say "Search N00b" 
I think the overall verdict is that they arent quite as fast (as hoosiers) and feel more vague, entertaining some amounts of slip angle. That said, they are a real budget option worth exploring if the last Nth doesnt matter too much.
as far as weight; this was on american racers on Polish Mountain Hillclimb a few years back. I wouldnt be concerned.
marks93cobra wrote:
Maybe they're only designed for left turns?
They are, if the tires have separate right-side and left-side variants. IIRC, the right side version is the harder compound to conserve tire life when they do that, and teams have gotten in trouble for "accidentally" running left side tires on both sides. For a road race car, of course, one runs the same version on both sides.
codrus wrote:
Hoosier has a 275/35R15 size for the A7/R7 that's the same 23" overall diameter as the 225
But they're $300 a corner. Asphalt modified tires are half that price, and shipping is cheaper: American Racer will ship up to 24 tires on a pallet for $100.
Appleseed wrote:
They're thin and like to pop when overloaded. I'd imagine sliding on dirt relives some of that stress.
We're talking about asphalt tires, not dirt track.
https://grassrootsmotorsports.com/forum/grm/learn-me-slicks/118267/page1/
https://classicmotorsports.com/forum/grm/bias-ply-slicks-question/127942/page1/
Apexcarver wrote:
Gonna try not to be like other sites and say "Search N00b"
Despite the horrible search function in this forum, I did see that thread from 2012. But there was no real conclusion. It's hardly ever discussed.
Considering the penny-pinching we do around here, I'm surprised that a low-budget race tire option hasn't been discussed ina serious way ... which made me think there was probably some obvious issue I was missing.
Apexcarver wrote:
I think the overall verdict is that they arent quite as fast (as hoosiers) and feel more vague, entertaining some amounts of slip angle.
I think any bias-ply slick has that issue; they need a different set-up and move around a lot. I was looking at Hoosier C3000 cantilever road-race slicks, which some BMW guys have been using. They have the same comments about the "floaty" feel. But they claim they're faster than R7 radials and more consistent over the life of the tire. Also about twice the price of the Asphalt Modified tires I was looking at.
Apexcarver wrote:
as far as weight; this was on american racers on Polish Mountain Hillclimb a few years back. I wouldnt be concerned.
Yeah, if a tire can hold up to a 2500 lbs. car with massive torque (compared to my 4-banger) sliding around all day on rough asphalt, I don't think I'll kill them with a handful of 20-30 min sprint races at Tremblant.
marks93cobra wrote:
Maybe they're only designed for left turns?
Actually, I think that's kind of true. I always heard that circle-track tires have some amount of stagger built in.
Most stock car series run the same tire compound left and right, but that's not saying everyone does. The manufacturer makes various compounds, but they are not specific left or right compounds. The consistent difference between them is diameter. On your average quarter or third mile paved oval, you want something like 1 1/2 to 2 inches of stagger. (Rolling diameter) If you are shopping used tires, they will all be measured and marked by whoever used them. If new, there will be a random number on the label that is supposed to be the diameter, but is generally not even close.
Its also cool how you can shrink a tire- Go out, get it hot, come in and let the air out. Zoom, it cools smaller.
Sorry, in my brain circle track and dirt track seem to register as the same thing.
Dusterbd13 wrote:
Not all Circle track slicks are for dirt.
Personally I think I would go for the hardest compound available to maximize life to money. You should be able to get a whole weekend out of a set.
Seems like the goal would be to find the right compound.
For the Merc, something of medium durability (not hard, since I would suggest that the hardest circle track tires are for pretty long races).
And for auto cross, the softest you can find, to warm up asap.
What is neat about this experiment, thanks to the cost, you can experiment. Instead of just getting the same tires as other cars and hoping.
In reply to Dusterbd13: Slicks are for pavement. Dirt tires have a tread and have a very short life.
In reply to iceracer:
Yup. Not enough coffee yet....
A pair of take off american racers from my friends stock car is what got me my first 12 second quarter mile pass. All i know is they take alot of heat to get sticky.
Whatch rollout/diameter. They tend to run stagger, so you may want a few sets to get a group of four that work well for you. Or set it up for a CW or CCW autoX course on purpose...
iceracer wrote:
In reply to Dusterbd13: Slicks are for pavement. Dirt tires have a tread and have a very short life.
What's weird is that some of the asphalt slicks are treaded and some are supposedly DOT-compliant. Not sure why you'd need treads on asphalt, since I don't think any circle track racing takes place in the rain?
As you can see, I'm new to all of this!
In reply to LanEvo:
It all has to do with local rules. Sometimes you need tread, sometimes a DOT number. These tires show up to make tire rules useless and rule makers crazy.
Remember the treaded F1 tires from a decade ago?
iceracer wrote:
In reply to Dusterbd13: Slicks are for pavement. Dirt tires have a tread and have a very short life.
One of the vintage racing tips I was told was that Hoosier dirt tires make excellent rain tires on an Alfa.
No stagger built into the tires we run. Hoosiers this year and last. And they take a huge beating. Nothing gets hotter than the front right of a banked oval car.
They are extremely thin so they shed heat very well. But they puncture easily if there are pebbles or debris on the track.
