why run 15X9 wheels and only use a 225 tire?
#21
I have my car setup and run 275/35/15’s for autocross with a slight bit of rubbing on the inboard side so I can make big width fit but the big thing is diameter needs to be really close to stock to work on a properly set up Miata that retains original sheet metal inner fender. This narrows the tire selection pool a lot. Need like a 40 aspect ratio or less to go wider.
Bob
#22
2. 15x9s with 225s are faster than 15x8s with 225s, end of story
Does anyone else agree with this? seems that a 15X8 with a 225 would be a better choice and a lighter set up as well. I was also just concerned with street tires. So I guess I was just trying to find out if there was any real benefit from the 15X9. Thanks for all the input.
Does anyone else agree with this? seems that a 15X8 with a 225 would be a better choice and a lighter set up as well. I was also just concerned with street tires. So I guess I was just trying to find out if there was any real benefit from the 15X9. Thanks for all the input.
Now if your only conscerned about the street, the lightest wheels you can get makes the car feel zippy and the narrower rims give a smoother ride.
Bob
Last edited by bbundy; 07-22-2010 at 03:59 PM.
#23
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Does anyone else agree with this? seems that a 15X8 with a 225 would be a better choice and a lighter set up as well. I was also just concerned with street tires. So I guess I was just trying to find out if there was any real benefit from the 15X9. Thanks for all the input.
#24
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I've driven a 225 and a 205 on an 8 and the 205 felt much better. The slight stretch is how its supposed to be done and you can see that executed on any and every big-budget racecar. The 225 on the 9 feels incredible and makes the car feel precise.
#28
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I feel like the guy with a small ***** in a gang bang scene.
225 on my 7" wheels were much gripper than the 185 stock tires obviously, but it was noticeably squishier, if that makes sense. It lost some of it's immediate turn in crispness.
225 on my 7" wheels were much gripper than the 185 stock tires obviously, but it was noticeably squishier, if that makes sense. It lost some of it's immediate turn in crispness.
#29
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I codrove a big-boost M45 at an autocross like 3 weeks ago, and since I'm an elitist ***** we swapped his 205/55-14 NT-01s on 14x6s for a set of 9s and 225s. His comment after his first run was just "wow".
#30
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Back when i ran 99 wheels with 205 NT-01's it was pretty easy to put that tire on the dime. I had a revellation after about 4-track days on the 9's....I wasn't using the tire. The limit on 9's compared to skinnies is so far out that I couldn't really comprehend the limit. You I have to really scare the **** out of myself to "use" the 9's.
#31
The big difference that I notice between an 8” and a 9” with the 225’s is like in say a 90mph sweeping turn. Where your sphincter is puckered to begin with. Even worse on a 7”. I think 205 is as wide as should be mounted on a 7”.
With the narrower wheel you feel the tires outer edge kind of roll under and dig in with the slip angle changing less with cornering force changes as you near the traction limit then as you go over the limit it kind of pops loose and when you bring it back in it snaps back. The behavior is more non linear. With the wider wheels the slip angle to cornering force relationship near the traction is much more linear and you can drive more smoothly at and even slightly over the limit. The increase in ability to get everything out of the tire is as much to do with the lower lap times as the increase in grip levels.
Bob
With the narrower wheel you feel the tires outer edge kind of roll under and dig in with the slip angle changing less with cornering force changes as you near the traction limit then as you go over the limit it kind of pops loose and when you bring it back in it snaps back. The behavior is more non linear. With the wider wheels the slip angle to cornering force relationship near the traction is much more linear and you can drive more smoothly at and even slightly over the limit. The increase in ability to get everything out of the tire is as much to do with the lower lap times as the increase in grip levels.
Bob
#36
That's one of the nice things about setting up the Catfish; our "stock" setup is 245/35's on 17x9's. Although there's limited rubber at that size (Toyo R1R), the word that does come to mind is "wow" after you've had a chance to sample the cornering grip. Tires are at 20psi.
#37
20psi cold with a 1,550lb car. I'm pretty confident 18-19psi would be even better for track days.
The Thunderhill car weighed more than this with a full cage and started at 26psi. They quickly found out that the car was using only a fraction of its tire. I think they carefully dropped 5-6psi by the end of the race, which is a huge margin.
We ran the car with a naked frame through an autocross course with some 949 15x9's, and the tire tread did not start to roll to the edge until 21psi, with national champion auto crossers driving. The vid is on the website.
It's takes some talent and patience to be able to make suspension, spring rates, camber, sway bars and tire pressure all work together.
The Thunderhill car weighed more than this with a full cage and started at 26psi. They quickly found out that the car was using only a fraction of its tire. I think they carefully dropped 5-6psi by the end of the race, which is a huge margin.
We ran the car with a naked frame through an autocross course with some 949 15x9's, and the tire tread did not start to roll to the edge until 21psi, with national champion auto crossers driving. The vid is on the website.
It's takes some talent and patience to be able to make suspension, spring rates, camber, sway bars and tire pressure all work together.
#39
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All I've heard so far is, wider wheels are faster! Well, they are. The slight stretch increases cornering stiffness of the tire. If you look at the tire slip angle curve below (slip angle on x-axis, lateral force on y-axis), there is the region that is linear (from 0 to a some small slip angle). Being able to see the values on the graph doesn't matter, because depending on the tire size/compound/etc could range from 2 degrees to 13. Cornering stiffness measures the slope of that linear portion as it crosses the graphs origin. Increasing cornering stiffness may not increase peak force (though sometimes it does!), but more importantly it makes the tire build force faster (increasing response), and overall nets a greater area under the curve.
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