: Don't bother putting 275s on the rears of your stock rims; it's worthless.



verbs
04-24-06, 09:53 AM
Since my tires were completely free from Goodyear I did it anyway since it cost me nothing, 245 GSD3s in front and 275s in the rear.

Here are the reasons why 275s are worthless.

1. The stock wheels aren't wide enough to make use of the extra width of the tire. By comparing the contact patch on the tread on the front and rear tire, you can see that there's at least an inch of unused tire on each side of the 275; that's right, at least 2" of unused contact patch on the 275s.

2. You now have extra rotating mass on your wheels for no reason, which will slow your car down a bit (albeit nothing SOTP). Might lose a rwhp or two on the dyno worst case scenario.

3. You can't rotate your tires so overall you'll have shorter tire life since the rears will bald quicker than the fronts.

4. Not sure if handling is compromised a teenie bit either, but it's possible.


The only cool aspects are that the extra bulge in the tires protects your wheels from curbs better, and they just look F'in cool :thumbsup:

My .02.

CIWS
04-24-06, 10:10 AM
I just wimped out and stayed with stock tire size and RSA RFs. Although the F1 was a real grippy tire and nice in summer, for a year round DD, they just didn't do the trick. Plus with the RSAs the wheel hop is basically gone.

None the less, thanks for passing on your input with the larger rear tire size. :)

Seattle CTS-V
04-24-06, 10:50 AM
I wonder if the contact patch is larger when taking a high-speed corner though??

trekster
04-24-06, 10:53 AM
I don't know if it's me but when I turn on a sharp curve with the stock tire size my car doesn't slide until I hit about a .89 on the G meter. While, with the 275's I was able to take the same curve at about 1.08 G's.

Chef
04-24-06, 11:10 AM
Thanks,

I'm in the market now and was wondering the very same Q.

Verbs, is your V lowered at all? Just wondering if the 275's rubbed? If so, then I'm thinking 265's?

Thanks,
Chef

Dreamin
04-24-06, 11:21 AM
The stock wheels aren't wide enough to make use of the extra width of the tire.

Sorry man, but this is categorically wrong.

Running the 275s on our wheels does increase contact patch width, increasing rear stick... and changing the handling of the car.

*Looking* at a tire is not the best way to judge it's handling capabilties. For info on contact patch sizes look on the Tirerack website, another good resource is the Hoosier race tire website.

Do you have any before and after handling judgements? (Same test road, same weather, etc.). Got any before and after track times?

Dreamin
04-24-06, 11:22 AM
Of course you have to push the car more than 7/10th to feel the difference... if all someone does is drive down the freeway all day long, they wont feel the difference.

50 4Ever
04-24-06, 11:51 AM
I don't know if it's me but when I turn on a sharp curve with the stock tire size my car doesn't slide until I hit about a .89 on the G meter. While, with the 275's I was able to take the same curve at about 1.08 G's.

Could be a lot of reasons why you experience the difference. How old were the stock tires? The F1 EMT's have a shelf life besides a tread life, they get hard after a time. If you just drive to church and back you will not notice the difference, but if you drive on the road course the F1 EMT's are crap after about a year. If the 275's you speak of are non-runflats then they will grab more.

AmesCTS-V
04-24-06, 01:46 PM
Real world experience with the 275's in back for me are far different than what you are saying verb.

I'll check out the actual contact area, but the 275's are providing more ground contact than the 245's for sure. This pic isn't the best but you can see the width of the tire is making pretty good contact.

http://www.blackcts-v.com/Albums/CTSV/GSD3/DSC01786.JPG

alcast082
04-24-06, 05:29 PM
I would say a world of difference.
way more grip. I even tested it when my car was stock to another stock v with 245, we raced 4 or 5 times from a stop, every time a pulled away with less hop and more grip.

ajedwardsjr
04-24-06, 08:18 PM
Dear Mr. AmesCTS-V,

You have one sweet looking ride with the Big Whopping GS-D3's in the back. I have been thinking, thinking, thinking, about going the same way.

Now, I'm doing it.

Thanks for the picture. Sweet.

wildwhl
04-24-06, 08:36 PM
If I didn't have the 275's in the rear my V would have suffered the same damage that Urby's does every 12 months or so :D

They work (yes, my rims are stock widened to 9.25").

WW

V-Max
04-24-06, 08:48 PM
Glad someone else knows there is a difference between shelf life and tread life. I notice more with ultra perf. tires as they tend to dry out after a few months of heat cycles.

I am running Fuzion 255/40, up from BFG 245/45 on all corners on my '05 GTO. With the suspension being so soft it was not until I replaced rubber with polyurethane sway bar bushings and front radius rod bushing( Ames would know) was I able to get the most out of the tires.

But running 255/40 Avon Tech 500 on the rear prior and they would rub the fender lip. It all depends on the manufacturer.

Norm - exhaust systems as music
http://www.beretta.net/board/ib3/ikonboard.cgi?act=ST;f=9;t=261;st=225

Gordy Petrovski
04-24-06, 08:52 PM
I went from 275's to 265's & found out that there is a dif. just my .02c. I am going back to 275's, now I just have to finde a way to go through this set :D . The big dif. for me was comeing out of corners,the 275's have more grip so U can exit the corner much harder.

Gordy Petrovski
04-24-06, 08:56 PM
Thanks,

I'm in the market now and was wondering the very same Q.

Verbs, is your V lowered at all? Just wondering if the 275's rubbed? If so, then I'm thinking 265's?

Thanks,
Chef

Hay Chef I have my car lowered (Eibach) & no prob. with rubbing.:thumbsup:

AmesCTS-V
04-24-06, 10:08 PM
Dear Mr. AmesCTS-V,

You have one sweet looking ride with the Big Whopping GS-D3's in the back. I have been thinking, thinking, thinking, about going the same way.

Now, I'm doing it.

Thanks for the picture. Sweet.
Thanks. There is something about they way they look on the stock sized rim that is really sweet.

I went out and measured the contact areas and the fronts look to be about 8" and rears 9". That's rough numbers. Looking at the rears the whole width of the tire was making contact, actually more so than even the pics look. I have the tires set at 30 lbs and they do have 2k miles on them. So verbs, I do wonder do you have the tires over inflated? Or maybe they need a little wear?

If I get bored this weekend I'll put a little something on the tire and drive over a piece of paper to get an exact contact patch and post it.

darvish
04-24-06, 10:51 PM
I am pretty sure the tire contact patch is a function of tire pressure and not tire width. Although the picture gets complicated with runflats as the sidewall is stiff enough to support the entire corner of the car with only ambient atmospheric pressure in it. Putting wider tires on the stock rims causing the sidewalls to curve inward to the wheel may not be a good idea. On race car classes where the wheel width is limited by regs but tire sizes are free, race tire companies such as Hoosier make what they call a cantilever sidewall design where the inward curve is molded into the tire itself and it is engineered to function in that configuration. I run this type of slicks on my Super 7.

Bill
St Louis

verbs
04-25-06, 12:08 AM
Real world experience with the 275's in back for me are far different than what you are saying verb.

I'll check out the actual contact area, but the 275's are providing more ground contact than the 245's for sure. This pic isn't the best but you can see the width of the tire is making pretty good contact.

http://www.blackcts-v.com/Albums/CTSV/GSD3/DSC01786.JPG

The width of the tire is making good contact, but if you compare your 245s to your 275s, you'll notice that the 245s are wasting a lot less tire on each side. I can also see in your pics, similar to my tires, that your tires are bulging which is a sure sign that you're not utilizing the full tire. Post a picture of your 245's tread up front and you'll see what I mean, that you're wasting a lot less tread on each side compared to the 275s.

http://members.cox.net/obesitydiscussion/contact patch.jpg

verbs
04-25-06, 12:09 AM
I wonder if the contact patch is larger when taking a high-speed corner though??


Actually as your speed increases, your tires "balloon" a bit and get taller, which I surmise would cause a decrease in contact patch at higher speeds.

verbs
04-25-06, 12:10 AM
Thanks,

I'm in the market now and was wondering the very same Q.

Verbs, is your V lowered at all? Just wondering if the 275's rubbed? If so, then I'm thinking 265's?

Thanks,
Chef

No rubbing and my car is not lowered.

verbs
04-25-06, 12:17 AM
Sorry man, but this is categorically wrong.

Running the 275s on our wheels does increase contact patch width, increasing rear stick... and changing the handling of the car.

*Looking* at a tire is not the best way to judge it's handling capabilties. For info on contact patch sizes look on the Tirerack website, another good resource is the Hoosier race tire website.

Do you have any before and after handling judgements? (Same test road, same weather, etc.). Got any before and after track times?

275s only increase the contact width minimally.....probably no more than you'd get with say a 255 tire.

Looking at a tire is a decent way to judge how much contact patch you're getting on that tire. Even easier is to run through a puddle of water and look at the water patch laid down. It gives you a very rough idea of how much tire is making contact with the ground.

As far as tire websites, you look at a tirerack, or any tire website, and they all recommend at least a minimum of a 9.0" rim on a 275 tire, and the preferred size is 9.5" wide....there's a reason they recommend that ;)

I can't compare the tire on this car because I haven't run the same brand of tire to compare, but it's similar to something I did a long time ago when I tried both 275 and 315 drag radials (same brand) on a 9.5" rim. The 315 really didn't make much of a difference in traction as judged by contact patch markings, track results and SOTP; all it really did was add unneeded rotating mass to the rear wheels.

verbs
04-25-06, 12:20 AM
I am pretty sure the tire contact patch is a function of tire pressure and not tire width.
Wouldn't it be both?

Dreamin
04-25-06, 12:26 AM
I am pretty sure the tire contact patch is a function of tire pressure and not tire width.

Absolutely correct... total contact patch area is a function solely of tire pressure and car weight... contact patch *shape* is not. By mounting wider tires, you're increase the width of the contact patch (better for handling) and decreasing length of contact patch (arguably worse for linear acceleration, i.e. drag racing, hard launches).

Dreamin
04-25-06, 12:44 AM
Looking at a tire is a decent way to judge how much contact patch you're getting on that tire. Even easier is to run through a puddle of water and look at the water patch laid down. It gives you a very rough idea of how much tire is making contact with the ground.
It would be easier to drive over sand/fine dirt and use a tape measure ;)


As far as tire websites, you look at a tirerack, or any tire website, and they all recommend at least a minimum of a 9.0" rim on a 275 tire, and the preferred size is 9.5" wide....there's a reason they recommend that ;)I meant to get actual tread width (i.e. contact patch width) data.
From the websites, for the GS-D3:
245/45 tread width is 7.8" on a 8" rim;
275/40 tread width is 9.4" on a 9.5" rim
Tire tread width changes 0.2" for every 0.5" of wheel width change.
So the 275/40 contact path is exactly 1.0" wider than the 245/45 contact patch... hard data from goodyear, no eyeballs were harmed during this test.

Totally agree on the 9" minimum recommended wheel width... but GM for some uncomprehendable reason gave us 6-lug wheels, so we can't go to a 9" or wider wheel w/o breaking the bank... and we're all just trying to improve handling with our 8.5" wheels... The 275 may not be ideal... but it works fine on a 8.5" wheel and definitely improves handling over the 245 size... as proven by many of use who track our cars.


I tried both 275 and 315 drag radials (same brand) on a 9.5" rim. The 315 really didn't make much of a difference in traction as judged by contact patch markings, track results and SOTP; all it really did was add unneeded rotating mass to the rear wheels.

See my post above...makes perfect sense. I bet the overall diameter was the same or very close on those two tires... which did not increase the linear contact patch at all... thus No difference for drag racing purposes...

PneuBird
04-25-06, 01:42 AM
Dreamin.....are you saying that 275 on the front and rear are better if we track our cars? Or just 275's on the rear? I just started checking if Hoosier has some 100 treadwear tires available for the track. :alchi:

verbs
04-25-06, 06:44 AM
I meant to get actual tread width (i.e. contact patch width) data.
From the websites, for the GS-D3:
245/45 tread width is 7.8" on a 8" rim;
275/40 tread width is 9.4" on a 9.5" rim
Tire tread width changes 0.2" for every 0.5" of wheel width change.
So the 275/40 contact path is exactly 1.0" wider than the 245/45 contact patch... hard data from goodyear, no eyeballs were harmed during this test. How did you figure that tire tread width changs .2" for every .5" of wheel width change? Going by that calculation, if you could fit 275s on a 7.5" wide rim you'd get 8.6" of tread width. I don't see how that would be possible. That calculation seems flawed. I think at some point you'd get diminishing returns. I can't imagine it's a straight linear calculation.


Totally agree on the 9" minimum recommended wheel width... but GM for some uncomprehendable reason gave us 6-lug wheels, so we can't go to a 9" or wider wheel w/o breaking the bank... and we're all just trying to improve handling with our 8.5" wheels... The 275 may not be ideal... but it works fine on a 8.5" wheel and definitely improves handling over the 245 size... as proven by many of use who track our cars.275s work fine on an 8.5" rim, but do they really give you any more contact patch than say a 255? Possibly. If so, barely. Handling? I can't imagine that having bulging sidewalls which would increase sidewall flex and sloppiness would be that much better over the stock 245s. IMO having 255/45s on all 4 corners on 8.5" rims would be better for traction as having 275s on the rear and 245s in front, give you slightly less rotating mass on the rear tires, and give you the luxury of being able to rotate your tires for maximum tire life.



See my post above...makes perfect sense. I bet the overall diameter was the same or very close on those two tires... which did not increase the linear contact patch at all... thus No difference for drag racing purposes...Diameter was about the same on those two drag radials, but the diameter is also about the same between the 245/45 and 275/40 GSD3 as well, so are you implying that people in this thread saying they noticed increased traction with 275s in back instead of 245s are wrong? A 245/45/18 is 26.68" tall, and a 275/40/18 tire is 26.66" Of course having taller tires is more important for traction in a straight line than wider tires, but wider tires should help some as well assuming you have an increase in overall contact patch.

dannystang
04-25-06, 06:51 AM
Damnit some expert on here told me to go 245 all the way around cause at the track it would be extremely sloppy if I did staggered or 255 all the way around...

Now I hear its better.

Which one is it, I dont need tires for a least 10k miles but i might as well plan ahead.

cash
04-25-06, 08:04 AM
For this size tire/wheel combo www.tirerack.com (http://www.tirerack.com) shows the narrowest rim to firt a 275 series tire on is 9".

Does not really seem safe to me? No matter what you are trying to accomplish.

If you want to fit a wider tire get some wider wheels!

AmesCTS-V
04-25-06, 01:17 PM
The width of the tire is making good contact, but if you compare your 245s to your 275s, you'll notice that the 245s are wasting a lot less tire on each side. I can also see in your pics, similar to my tires, that your tires are bulging which is a sure sign that you're not utilizing the full tire. Post a picture of your 245's tread up front and you'll see what I mean, that you're wasting a lot less tread on each side compared to the 275s.
When the pics were taken the tires were brand new and inflated to 35. Like I said I took a look last night and with the tires at 30 and with some miles on them the tires are making much better contact then the pics show. I'll take pics this weekend if you want. I measured 8" of contact up front and 9" on the rear.

Chef
04-25-06, 01:59 PM
When the pics were taken the tires were brand new and inflated to 35. Like I said I took a look last night and with the tires at 30 and with some miles on them the tires are making much better contact then the pics show. I'll take pics this weekend if you want. I measured 8" of contact up front and 9" on the rear.

Are your rims widened or stock?

AmesCTS-V
04-25-06, 02:19 PM
Are your rims widened or stock?
That's stock. I realize that widened rim would be better, like you might pick up another half inch of road contact and the sidewalls would be vertical. I had thought about doing that this summer, but I like the look of the bulging tire; plus I'm happy enough with the performance. If I do anything different it will be to get 19's with a wider rim in the back and put 285's in the rear.

AmesCTS-V
04-25-06, 02:21 PM
One of the guys on here has 285's on a 8.5" wide 20" rim. Now that's a tight fit with an even shorter sidewall and even wider tire, but it worked for him...

verbs
04-25-06, 02:51 PM
One of the guys on here has 285's on a 8.5" wide 20" rim. Now that's a tight fit with an even shorter sidewall and even wider tire, but it worked for him...I'm assuming that's not a GSD3....a 285 for one tire brand may be larger or smaller than another tire brand. That still seems nuts.

For example, Nittos Drag radials are notorious for running smaller than the listed size. My 315/35/17 Nitto drags were just as wide as my 295/35/18 BFG drags.

verbs
04-25-06, 02:53 PM
When the pics were taken the tires were brand new and inflated to 35. Like I said I took a look last night and with the tires at 30 and with some miles on them the tires are making much better contact then the pics show. I'll take pics this weekend if you want. I measured 8" of contact up front and 9" on the rear.Just curious, did you deflate front and rear to 30? You don't have to take pics if you don't want to, I can just look at my GSD3s any time too :D

I'm at 35psi FWIW.....I felt 30psi would just cause the tires to bow out even more past the rim and run even sloppier in hard turn ins....that's why I've kept it at 35.

AmesCTS-V
04-25-06, 03:43 PM
I'm at 30 all around. I started out at 35 for the same reason as you, I figured the rears would get sloppy in the corners with the sidewall not being vertical. It seemed like a lot of guys on here were running 30 with other tires so I tried it. It's working well for me so I'm going with it.

AmesCTS-V
04-25-06, 03:44 PM
I'm assuming that's not a GSD3....a 285 for one tire brand may be larger or smaller than another tire brand. That still seems nuts.

For example, Nittos Drag radials are notorious for running smaller than the listed size. My 315/35/17 Nitto drags were just as wide as my 295/35/18 BFG drags.
It does seem nuts, looked fine though. They were BFG KDW2's.

Seattle CTS-V
04-25-06, 04:48 PM
I ran my 245/275 GSD3's yesterday for over 4 hours at the track. Ran them at 42psi HOT. That was about 35-36psi cold. The performed very, very well. A little throttle on exit tucked the car in nicely w/o letting loose. I give the credit to the 275's for that.

Chef
04-25-06, 05:12 PM
Silly Q ---

Is everyone that runs the 275 rear going with a 275/40/18 and a 245/45/18 front?

or - 275/45/18 ---- 245/45/18

Need to know so I can buy:alchi:

AmesCTS-V
04-25-06, 05:25 PM
245/45 and 275/40

dannystang
04-25-06, 08:57 PM
Would 4 255/45 (which fits someone did it here) better then ^--- setup?

alcast082
04-25-06, 09:33 PM
danny you know you like the way the chunky tire looks in the rear.
just go with the 275
and damn your tires are going to last you another 10k miles, I think i have 3000 tops on my rears about 8 k on the front.

dannystang
04-25-06, 09:57 PM
danny you know you like the way the chunky tire looks in the rear.
just go with the 275
and damn your tires are going to last you another 10k miles, I think i have 3000 tops on my rears about 8 k on the front.

Hey buy a damn helmet and some pedals so we can go road racing.

Sebring is June 10th and 11th

Unless that is...your scared?

Note: By Sebring on June 10th and 11th I mean on Forza Motorsports a video game cause I do not condone road racing and I am 10 years old and don't own a cadillac yet, someone gimme money.

Dreamin
04-25-06, 11:49 PM
How did you figure that tire tread width changs .2" for every .5" of wheel width change? Going by that calculation, if you could fit 275s on a 7.5" wide rim you'd get 8.6" of tread width. I don't see how that would be possible. That calculation seems flawed. I think at some point you'd get diminishing returns. I can't imagine it's a straight linear calculation.
It's a common tire industry spec/calculation... look into those tire company websites... you'll find it. I agree it's not linear... i.e. on a 2" rim, it doesn't work... but +/- 1" it is accurate.


...Possibly. If so, barely... I can't imagine...IMO...
No flame intended, but the bench racing is getting old... do some research on tires/contact patches and go track (road-race) the car and let us know your conclusions, and we'll continue our arguement.

-Dreamin out

verbs
04-26-06, 12:46 AM
It's a common tire industry spec/calculation... look into those tire company websites... you'll find it. I agree it's not linear... i.e. on a 2" rim, it doesn't work... but +/- 1" it is accurate.


No flame intended, but the bench racing is getting old... do some research on tires/contact patches and go track (road-race) the car and let us know your conclusions, and we'll continue our arguement.

-Dreamin out

I won't have a fair comparison going from run-craps to GSD3s, so that test would be pointless. Yeah I'm giving opinions, but I'm also going by the fact that the tires do bulge a decent amount, I can visually see a decent amount of wasted contact tread on the sides of my tires, and I know from my past experience sin racing that bulging tires do lead to sloppier handling.

V-rooooom
04-26-06, 08:42 AM
That is not tread, that's the sidewall. Yes, they do bulge slightly because a 275 should technically be on at least a 9" rim.


The width of the tire is making good contact, but if you compare your 245s to your 275s, you'll notice that the 245s are wasting a lot less tire on each side. I can also see in your pics, similar to my tires, that your tires are bulging which is a sure sign that you're not utilizing the full tire. Post a picture of your 245's tread up front and you'll see what I mean, that you're wasting a lot less tread on each side compared to the 275s.

http://members.cox.net/obesitydiscussion/contact patch.jpg

cash
04-26-06, 08:52 AM
If mfg.'s do not reccommend this fitment why is there a debate on this entire subject.

The rim wide specified for a certain tire width range is there for a reason, and I bet it is safety!

For the 275 wide tire Fikse told me to go to a 9.5 wide rim for the best fitment.

I really see no point in seeing how big a tire you can fit on the smallest rim possible???

V-rooooom
04-26-06, 12:06 PM
If mfg.'s do not reccommend this fitment why is there a debate on this entire subject.

The rim wide specified for a certain tire width range is there for a reason, and I bet it is safety!

For the 275 wide tire Fikse told me to go to a 9.5 wide rim for the best fitment.

I really see no point in seeing how big a tire you can fit on the smallest rim possible???

Right. A friend of mine is a moderator in the wheel/tire section at LS1tech and has to constantly explain why they should NOT put a 315 on a stock 9.5" rim. If the manufacturer of the tire says not to do it I don't see why the argument needs to go any further... but of course, because the tire will actually mount onto the rim, the baffoons tell him it works fine and all is good because they've seen it done. You should see some of the ballooning...

The Lesson: Just because the tire will mount onto the rim, that doesn't mean the tire was designed to perform safely on that rim.

AmesCTS-V
04-26-06, 12:59 PM
If mfg.'s do not reccommend this fitment why is there a debate on this entire subject.

The rim wide specified for a certain tire width range is there for a reason, and I bet it is safety!

For the 275 wide tire Fikse told me to go to a 9.5 wide rim for the best fitment.

I really see no point in seeing how big a tire you can fit on the smallest rim possible???
GM also says not to put on a CAI, but we do that anyway. Companies make recommendations for a lot of reasons and rarely do they take into account performance as the #1 reason. Usually companies are worried first about lawsuits, like don't remove the tag on your pillow; that aint there for better sleep, it's all about the law suits.

I don't know what the safety factor is on this setup, but I know Tirerack sold me the tires and my dealership put them on and at no point did anyone say it's not safe, nor have I had problems.

Yes a 275 should perform better on a wider rim, but that doesn't mean it doesn't perform well on a 8.5" rim and that doesn't mean the car doesn't perform better with a 275 rather than a 245 on the 8.5" rim.

This isn't about getting the widest tire possible on a rim, because I'm sure you can go a lot bigger than a 275. As I pointed out earlier a guy on here is running a 285 on a 8.5" 20" rim.

What this is about is finding a tire with better performance than the stock 245 size without having to get the rims made wider.

dannystang
04-26-06, 01:02 PM
So would it be safe to say 255 x 275 in the back = the best traction setup?

verbs
04-26-06, 03:02 PM
That is not tread, that's the sidewall. Yes, they do bulge slightly because a 275 should technically be on at least a 9" rim.It becomes tread on a wider wheel :p

ssmith100
04-26-06, 04:34 PM
295 on a 10" wheel would be a better setup:) Sorry, couldn't resist.

Shane

calicadi
04-27-06, 08:12 PM
Just for comparison sake, my 265/40 BFG GForce KD's "bulge" about three-eights of an inch on 9" Jongbloeds. I'm guessing a stiffer sidewall tire would bulge less.

livingthedream
04-29-06, 04:50 PM
I also have 275's and find that they hold the road better. I keep them at 36psi cold and let em pump up when they get hot.

They stick nicely when warm and I would surely buy them again when the time comes, not going back to anything more narrow.

I am not lowered, have no rubs and enjoy both the ride and the handling.

livingthedream
turn the key and smile