I'm getting a new daily this week, as soon as I decide between the Civic and Mazda3 hatches. Since my E36 is currently getting beat up on in STX, I'm thinking about making the new car the autocross car and sending the BMW to track-only.
Here's the dilemma. Both of those hatchbacks use 16x7s. I know I can move to a 17x7, but can't go wider and stay in the pax wonderland of HS. I just (2 events ago) bought RE71-Rs in 245-40-17. I know they'll fit in the wheelweels of both cars, but is cramming a 245 onto a 7-inch wheel just asking for trouble? If I were buying new tires, or if they were older, it wouldn't be a problem. But with virtually new rubber, I'm not eager to toss them aside for another (now hard to find) set.
Tl;dr 245/40 on 7-inch wide wheels. Yay or nay?
Sonic
UltraDork
6/27/18 10:40 a.m.
Nay. Even if they fit, it won’t be any faster than a 225 or maybe even 205. Weight and drag have something to do with it, along with having such a poorly supported sidewall.
Look at all of the testing that the Miata guys (and Andy Hollis) have done showing that a 225 is no faster than a 205 until it is on an 8” wheel, and that there is a notable benefit for that same 225 going to a 9” wide wheel.
True. But if they fit they'll be faster than 205/sideWALL/16 Eco tires.
I think I'm already aware that this should be a classified thread for sub 200 km (and eight run) RE71s, but need you guys to confirm the bad idea is a bad idea. :P
I have a 2012 Mazda 3 with 17x7 wheels from the factory. Stock, it came with 205/50/17's. I run a 225/45/17, and it's more than enough tire for the car and a nice upgrade. It's also cutting it close; I wouldn't want to try fitting something bigger on the stock wheels. I wouldn't recommend going wider than a 225 on the stock wheels, if they would even fit at all.
It would be about as hilarious as this:
Someone posted this on another forum, 245 Hoosier R7 (probably wider than your RE71 and a lot more grip) on an 8" wide rim.
No thanks.
Adam
Yeah. That's about what I expected. The RE71s work well on an 8, but 7 is too far. Thanks.
Now to either find a strange option package that included 8-inch wide or look at a move to STS
I suspect that a 245 on a 7, while not ideal, will be faster than the same compound 225 on a 7. For autocross, at least -- most of that "wider is slower" testing on Miatas was on big tracks where aero matters a lot more than in parking lot racing.
Carbon
SuperDork
6/27/18 11:35 a.m.
Is it the general consensus that an 8" wheel be slower with a 245 than a 225?
I don't even like my 245's on an 8" rim, can't wait for my 9" rims to get here. I would not put them on a 7" rim.
Our racecar is faster with smaller tires and they wear more even on a wider rim. Relatively light low powered RWD car.
akylekoz said:
I don't even like my 245's on an 8" rim, can't wait for my 9" rims to get here. I would not put them on a 7" rim.
+1, 245s should be on a 9" wide wheel. A 7" wide wheel should run 195 or 205 wide tires.
adam525i said:
Someone posted this on another forum, 245 Hoosier R7 (probably wider than your RE71 and a lot more grip) on an 8" wide rim.
No thanks.
Adam
In street/stock class just a few years ago the SCCAs own rules allowed R-comps and a lot of people jammed 275 Hoosiers on wheels as narrow as 6”.
Carbon said:
Is it the general consensus that an 8" wheel be slower with a 245 than a 225?
These days a lot of people seem to think so, but a decade ago the usual belief went the other way. The only way to know is to test it yourself, in an A/B/A test like GRM does and even then the answer will vary with things like compound, alignment, grip level, power level, etc.
A 245 will likely *feel* sloppier, but feel and speed are not the same thing.
FWIW, 225 on a 16x7 was a common OEM spec in the 90s.
How wide you can go tire-wise on a given wheel will really depend on the tire. Depending on how stiff the tire carcass is and where it's stiff vs flexy, some tires will do well with big mismatches, others not so much. And taller sidewalls will sometimes tolerate a bigger mismatch.
Of course, going wide on narrow wheels will give up feel, which may make some drivers slower even if the tires have more grip.
Honestly, for autocross, I might try it. I saw a bunch of guys last weekend with fat tires (RE71Rs and Rivals) stuffed on skinny wheels in ES. It's not gone as crazy as it was a few years back with the R-comps, but it's headed in that direction.
You have the tires, why not try it? It'll probably feel sloppy, but it might be fast.
There was a guy with 255s on 8.5 18s in a Mazda3 (Not sure the offset), and it fit, so I imagine a 245 on 7 wheel will clear.
Jaynen
UltraDork
6/27/18 5:51 p.m.
I mean I run 225's on a 9" wheel because the best wheel to tire ratio is almost always wheel width = section/tread width
Tire rack lists the 245/40/17s as being suitable for 8-9.5" rim with a section width of 9.8" tread width of 8.6" I am running the 225/45/17 Hankook RS4 on a 9" rim which has a 9.2" section width and 8" tread width
You are going to have to either buy the correct tires for the rims you have for the car or buy new wheels for the tires. Why don't you just use those RE71Rs on the BMW for track duty and get some appropriately sized HS tires?
The consensus on miata's was that running a 225 could be faster in autocross on a smaller than 9" rim however you gave up feel and responsiveness for ultimate grip so it was much more difficult to actually use the extra tire in a way that paid dividends as such most STS Miata's run 195 or 205
bigben
Reader
6/27/18 6:28 p.m.
GameboyRMH said:
It would be about as hilarious as this:
245/40-17 on 7" is not quite that bad.
Vigo
UltimaDork
6/27/18 9:22 p.m.
My only direct experience involving back to back A>B>A testing of wider tire on narrow rim was 205>225>205 on a 6.0" rim. The main difference i experienced was 'vagueness' in steering response. I think ultimate traction was probably similar and if i was doing my hard turning on a track and not the street I could probably have learned to drive around how bad it 'felt' and go basically as fast as 205s. But, I didn't like how it felt and was happy again when i went back to 205s.
GameboyRMH said:
It would be about as hilarious as this:
Those are cantilever slicks. They’re supposed to be like that. I’m not sure they still make them, but I had a set of those on 6.5” wheels a quarter century ago. I also ran a 235 on the same wheels but that was back when 235 was wide and a 50 series sidewall was short. I wouldn’t do that nowadays because it isn’t necessary.
adam525i said:
Someone posted this on another forum, 245 Hoosier R7 (probably wider than your RE71 and a lot more grip) on an 8" wide rim.
No thanks.
Adam
Madre de Dios. I had always suspected, but that's just nauseating.
In reply to bigben :
Wow, that's not nearly as pinched as I would have thought.
Do it! :D
bigev007 said:
I'm getting a new daily this week, as soon as I decide between the Civic and Mazda3 hatches. Both of those hatchbacks use 16x7s.
Get the Civic Sport instead so that you can have 18x8s from the factory and easily fit your tires on 17x8s?
Apis Mellifera said:
Those are cantilever slicks. They’re supposed to be like that.
Those are Hoosier A6s, not a cantilever. Some nuts were throwing 275s on their Integras for DS about a decade ago.
