SeanMc
NoMoSHO
245s on my 8" rim. Fit is perfect, and tire wear is very even.
Drawbacks to 245's on 7.5" rim
- Thread starter jayro
- Start date
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245s on my 8" rim. Fit is perfect, and tire wear is very even.
lowc
aka vapah lock
245s on my 8" rim. Fit is perfect, and tire wear is very even.
man you just love showing off those sweet ass caliper covers dont you!
will also add that I run 245/40 18 on my rims and get just about 9 inches of tire contact to pavment and have had very evan wear on all four.Now granted I havent tracked it yet so not sure if this post will help at all. They also sit just about the same as Sam's 17's pictured above
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SeanMc
NoMoSHO
Hells yeah! It's the best tire pic I have, guess I could have gone out and taken another pic.....
hawkeye18
Sorta cares
Armed Forces have bad optometrists??
Actually, all kidding aside, they are pretty bad. Right before I went to Iraq I had one tell me I had 20/20 uncorrected vision, which is simply amazing, since from the day I joined the Navy I've had 20/35 in my right eye and 20/30 in my left. Apparently my eyes healed!
That's not related to the fact that I've somehow grown 2 inches taller since I've joined the Navy, but that's another story...
Free medical: You get what you pay for.
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SHOspazz92
Banned
Regardless, now that I've got my monthly "Argument with Ron Porter" out of my system, all I can say at this point is it is personal preference. Ron brings up many Valid Points. I just go off my Auto-X/SHO experience.
The choice is yours young grasshopper, choose wisely, or die a fiery explosive death because your tires were to wide for the rim. (Just Kidding Ron ).
-Sam
The choice is yours young grasshopper, choose wisely, or die a fiery explosive death because your tires were to wide for the rim. (Just Kidding Ron
).-Sam
thebigjimsho
LSA = YUM
A tire and wheel of matched width WILL work better than a tire a little too wide for the wheel. Physics don't magically disappear when we shop for tires. A 245 tire WILL work better on a 8.5" wheel than a 7.5". Will a 225 tire work better than a 245? Not sure.
But a 245 R compound on a 7.5" wheel will work better than any street tire, so...
But a 245 R compound on a 7.5" wheel will work better than any street tire, so...
jayro
SHO Member
Yeah. The two size choices I have are 225/50 and 245/45. I was just curious what were the benefits and drawbacks of the 2 different size tires on my 7.5" rim.
A 7.5 rim is within the recommended range of each of those tires. So IMO, which ever one is less expensive. The 225 is closer to stock diameter though.
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DrivinhardLLC
New Member
First thing with tires sizes, ignore the size printed/molded into the sidewall. It's a useless measurement. Measure the actual tire. Sizes vary all over the map.
We had tire rules changes in NASA PT/TT for '11 and thus we've had to play with a LOT of various rim/tire sizes (have to run skinnier tires this year). I will say from experience:
1. Rim width is extremely important, especially for transient stuff and overall feel of the car.
2. general rule of thumb, tread width should be very close to rim width.
3. wider doesn't equal faster, especially if the rim width stays the same. It may not be much slower, but generally the car gets more numb when the tire width goes up and the rim width stays the same.
I had a chance to test Hoosier A6's 315's on 10" front, and 11" rear wheels back to back with 10.5" width wheels and 275 A6's on the same track, same day, same car (C5 Z06), same driver. There was some temp increase in the track, which based on notes, is similar to what the track will fall off with any tire, but in reality, I went 1.5 sec slower on the 315's vs the 275s, and the car felt way more numb and less light on it's feet on the 315s. Even if the net time stayed the same with temp increase, the car still felt way worse, enough to be distracting and less confidence as a driver, which is the last thing you want.
There is a point based on the car weight, and the rim width, where you have "enough" tire, and anything beyond that you are adding unsprung and driveline rotational weight and degrading steering crispness. This "point" is going to vary from car to car, so the only way to find it, is test.
On the SHO, I ran faster at Road Atlanta with 225 V700's on 8" wheels than I did with 225's V700s on 7.5" rims.
If you are doing long endurance racing, there may be something to extra tire = more thermal capacity = more consistent over a long run, but again, you gotta test.
We had tire rules changes in NASA PT/TT for '11 and thus we've had to play with a LOT of various rim/tire sizes (have to run skinnier tires this year). I will say from experience:
1. Rim width is extremely important, especially for transient stuff and overall feel of the car.
2. general rule of thumb, tread width should be very close to rim width.
3. wider doesn't equal faster, especially if the rim width stays the same. It may not be much slower, but generally the car gets more numb when the tire width goes up and the rim width stays the same.
I had a chance to test Hoosier A6's 315's on 10" front, and 11" rear wheels back to back with 10.5" width wheels and 275 A6's on the same track, same day, same car (C5 Z06), same driver. There was some temp increase in the track, which based on notes, is similar to what the track will fall off with any tire, but in reality, I went 1.5 sec slower on the 315's vs the 275s, and the car felt way more numb and less light on it's feet on the 315s. Even if the net time stayed the same with temp increase, the car still felt way worse, enough to be distracting and less confidence as a driver, which is the last thing you want.
There is a point based on the car weight, and the rim width, where you have "enough" tire, and anything beyond that you are adding unsprung and driveline rotational weight and degrading steering crispness. This "point" is going to vary from car to car, so the only way to find it, is test.
On the SHO, I ran faster at Road Atlanta with 225 V700's on 8" wheels than I did with 225's V700s on 7.5" rims.
If you are doing long endurance racing, there may be something to extra tire = more thermal capacity = more consistent over a long run, but again, you gotta test.
RonPorter
SHO Club of America
In all the clutter, these are basically my points. Well put, Mark.
Without having track rubber experience, just my own experience jumping back & forth between rim sizes with the same tire size showed a noticeable different in steering sharpness.
Shoaz
Studly dood
This. Tire carcas construction varies widely across brands and makes of tires, and not all need the same wheel width with respect to the tread width, especially the width printed on the side of the tire. Find the recommended wheel widths for the specific tire and specific size used from the manufacturer and make a decision from there.
And this can be used to one's advantage if your ruleset assesses points based on indicated tread width.
While I agree completely with Mark's points I wanted to point out that his example compares a 4 cm difference in indicated tread width across rim sizes that cross the recommended wheel size width from the manufacturer, i.e., Hoosier recommends up to 11" rim width for 275s and over 11" rim width for 315s. 7.5" rims are within Hoosier's recommended wheel width for both 225s and 245s. Check with your manufacturer for the recommended width for the model and size of tire being used.
I ran a mix of 245s and 225s from various manufacturers across my two wheel sets, 16x7.5 Borbets and 16x8 Snypers. I could never correlated lap time, feel, or rate of wear to the wheel width. They seemed to behave the same for me regardless. I set rack records with both. Pressure and condition (i.e., rotation management) seemed to make far more difference to me than the half-inch rim width within recommended spec for the tires.
I should also point out that the 225s that I ran were essentially 245s, as you could stack the 225s up next to a stack of 245s and the difference in the cumulative *stack* height was less than 1cm. This was a cheater size that Hoosier made for some Porsche series, which helps make the point that the size stamped on the side should be taken for what it's worth.
And narrower can definitely be faster, especially if you're not getting the wider tire up to adequate temperature. Loading a narrower tire can bring the temps higher and may result in better grip. The weight difference is important as well.
Profile probably matters as well. A lower profile tire may be more sensitive to wheel width than the high profile stuff I was running.
All valid points gentlemen, but the only thing that really matters is this:
All your wheels are belong to me!!
All your wheels are belong to me!!
thebigjimsho
LSA = YUM
Bottom line: go out and test and find out...
-DVP-
NaNaaNaNAAAA!!!
From my experience a 225 is not wide enough for a 8" wheel. Then again it all depends on the tire brand/model. I prefer a 235 on an 8", both sets of 225s on my MM2 where stretched herra frush looking.
jayro
SHO Member
Yeah, that's what I'm gonna do. Part of the fun is the doing.
shomesomesho
G-force addict
Look at these pics:
These are 215/50/17 Hankook V12 tires on 17x7.5" rims.
They are PERFECT. Note that the rim width equals the tread width (look carefully to see the dirt patch on the tread). And the sidewalls are perfectly vertical.
You cannot get a better combo than this. For a 225 tire, an 8" rim does the same thing.....BTDT.
Get the 225. The 245 is WAY too wide for that rim. You gain nothing by doing that, except sloppy handling, and you won't get any benefit from the 245 width.
The 225 on that rim will handle better, and have better steering response.
Oh man, those rims look b@d@ss!!
jayro
SHO Member
You autox'ed a sho a lot....what is your opinion on this subject?
I've run R-comps in 205 (might have been 215 its been many years) and 225 series on the stock 6 inch wide rims, and 225 and 245 series on 16x7.5 inch rims. BFG R1, BFG R1 Rain, BFG R1a, lots of Toyo RA1 to name a few, mostly autocross some open track/time trials.
You can get away with a 245 tire on a 7.5 inch rim on the front and have it perform well because of the higher loading pushing the tread flat when under high cornering loads. I notice less inside wheel slip with an 8 inch wide rim at corner exit, mine is Quaife'd car. Would recommend 225s on the rear, they are much more lightly loaded and a 225 will heat up much more quickly in autocross.
Biggest complaint is tire pressure tuning. The pressure range for good traction is much wider for an 8 inch wide rim with a 245 tire than on the 7.5 inch rim, also noticed this with 205 vs 225 on a 6 inch rim.
Hope this helps, there are 16x8 inch rims out there if you are willing to workto get them.
zak
You can get away with a 245 tire on a 7.5 inch rim on the front and have it perform well because of the higher loading pushing the tread flat when under high cornering loads. I notice less inside wheel slip with an 8 inch wide rim at corner exit, mine is Quaife'd car. Would recommend 225s on the rear, they are much more lightly loaded and a 225 will heat up much more quickly in autocross.
Biggest complaint is tire pressure tuning. The pressure range for good traction is much wider for an 8 inch wide rim with a 245 tire than on the 7.5 inch rim, also noticed this with 205 vs 225 on a 6 inch rim.
Hope this helps, there are 16x8 inch rims out there if you are willing to workto get them.
zak
shomesomesho
G-force addict
I'd go with 245's in a heartbeat. Hankook sidewalls are stiff enough to hold a 7.5" rim just fine. IIRC I was running 245's on 8" rims when I autocrossed the SHO. That 0.5" difference isn't a big deal. There's plenty of people in autocross using tires wider than recommended for their rim and they are still fast as ****.
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thebigjimsho
LSA = YUM
I love how people keep thinking a .5" difference in rim makes little difference but then they'll go on and on about a .5" difference in tread. Is it because you can't see wide rims like you can see wide tire tread?
I bet those fast as **** guys on 245s would still be fast as **** on 225s. At all the old NESHOC autocrosses I went to in my SHO in the mid 90s, I was getting best times for ANY car there not driven by an instructor. That was with Vipers, M3s, GTIs, etc. And my poor '92 had to make do on 16X8" rims and 225/50 16 BFG R1s...
I'm not saying X tire in 245 size on a 7.5" rim will be worse than said tire in 225. My problem is there are a number of you guys proclaiming it WILL when you have nothing to back it up. I just know, in my experience, the widest tire on the widest wheel WILL get you better handling than the widest tire on a narrower rim...
I bet those fast as **** guys on 245s would still be fast as **** on 225s. At all the old NESHOC autocrosses I went to in my SHO in the mid 90s, I was getting best times for ANY car there not driven by an instructor. That was with Vipers, M3s, GTIs, etc. And my poor '92 had to make do on 16X8" rims and 225/50 16 BFG R1s...
I'm not saying X tire in 245 size on a 7.5" rim will be worse than said tire in 225. My problem is there are a number of you guys proclaiming it WILL when you have nothing to back it up. I just know, in my experience, the widest tire on the widest wheel WILL get you better handling than the widest tire on a narrower rim...
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