275 vs 255 Width Rear Tires-
Burning Brakes
Joined: Apr 2002
Posts: 906
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From: SW Colorado
Here is a pic of the truck on the old 265's and 7.5 inch rims. It may be slow but, the forces involved in some of these manuvers are pretty extreme. In addition, I would think that the tall sidewall gives the tread a whole lot more leverage on the bead. Mostly I just like posting pics 
<img src="http://boards.rennlist.com/upload/moabG.jpg" alt=" - " />
<img src="http://boards.rennlist.com/upload/moabG.jpg" alt=" - " />
Burning Brakes
Joined: Apr 2002
Posts: 906
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From: SW Colorado
I don't mean to hi-jack your thread Normy. I had to post my current favorite scary off-road picture. This truck did not roll, though my heart was really pounding as I took the photo <img border="0" title="" alt="[Eek!]" src="eek.gif" />
You have to love the German autos for extreme performances while remaining extremely civil in daily use. Porsche for the racetrack, M-B for "thats a trail????" <img src="http://boards.rennlist.com/upload/erwin.jpg" alt=" - " />
You have to love the German autos for extreme performances while remaining extremely civil in daily use. Porsche for the racetrack, M-B for "thats a trail????" <img src="http://boards.rennlist.com/upload/erwin.jpg" alt=" - " />
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Joined: Feb 2002
Posts: 5,248
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From: Ft. Lauderdale FLORIDA
I don't own the place Brent! I think the pix of the G-wagen are kewl!
Last month, I spent quite a bit of time behind the wheel of Lucy's 2001 Jeep Wrangler Sahara, and was amazed by the amount of attention I got.
I was also amazed at how smooth that car was, how well it handled for a tall vehicle, and how COLD the air conditioner was! I'm not a "jeep" or "ORV" type by any means, but the rock-climbing thing looks like fun.
N!
Last month, I spent quite a bit of time behind the wheel of Lucy's 2001 Jeep Wrangler Sahara, and was amazed by the amount of attention I got.
I was also amazed at how smooth that car was, how well it handled for a tall vehicle, and how COLD the air conditioner was! I'm not a "jeep" or "ORV" type by any means, but the rock-climbing thing looks like fun.
N!
Pro
Joined: Oct 2002
Posts: 743
Likes: 1
From: Northern New Jersey
I have the 275 set up with cup rims in he rear. I can barely stick a finger nail between the tire and the fender lip. I went with the Kuhmos all around. To start off with they are very loud tires, they track or tremline all over the place and last I don't think it's the proper fit, although no rubbing has occured. I would feel safe with the 255 40. Sal
Burning Brakes
Joined: Jun 2001
Posts: 778
Likes: 1
From: Herndon, VA
The taller sidewall is part of the reason your tires don't come off the bead. Don't recommend you try it with a 285/40 on a 9" rim while cornering at 1+Gs.
Guys (and Gals) do whatever the heck you want. It's your car, your money, your life. Just don't shoot the messenger. :^( YMMV.
Guys (and Gals) do whatever the heck you want. It's your car, your money, your life. Just don't shoot the messenger. :^( YMMV.
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Ed,
I think the point is the very real difference between fact and opinion. If the messenger is delivering facts, so be it. If it is opinion it behoves him to say so. Holding opinion out as fact lack credibility, and leads to a shootin'.....
I think the point is the very real difference between fact and opinion. If the messenger is delivering facts, so be it. If it is opinion it behoves him to say so. Holding opinion out as fact lack credibility, and leads to a shootin'.....
Three Wheelin'
Joined: Mar 2003
Posts: 1,286
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From: New Berlin
</font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica">Ed,
I think the point is the very real difference between fact and opinion. If the messenger is delivering facts, so be it. If it is opinion it behoves him to say so. Holding opinion out as fact lack credibility, and leads to a shootin'.....
</font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">Well said! <img border="0" alt="[cheers]" title="" src="graemlins/beerchug.gif" />
I think the point is the very real difference between fact and opinion. If the messenger is delivering facts, so be it. If it is opinion it behoves him to say so. Holding opinion out as fact lack credibility, and leads to a shootin'.....
</font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">Well said! <img border="0" alt="[cheers]" title="" src="graemlins/beerchug.gif" />
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Burning Brakes
Joined: Apr 2002
Posts: 906
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From: SW Colorado
Ed, Did you really think about that reply? One "G" is the full wieght of the car in a sideways vector. Standing a 5500 lb truck on its side puts the full wieght of it in a sideways(relative to the tires normal position) vector. You appear to be thinking that just because the car is moving at a high rate of speed the forces are greater. I've done both.
Do you really think that the low profile tire has less grip on the rim? The sidewall is much stiffer as is the tread area in a good performance tire. They are extremely resistant to popping off the bead. You are just flat wrong about that one. The car tire will slide long before it comes off the rim. The truck tires I have seen can be wildly displaced and not come off. The forces are certainly greater than anything you can do with a car.
The whole point I am trying to make, in an admittedly long winded fashion
is that it sure would be nice if you spare us the preachers tone. The original post was about fitting a 275mm tire to a 9" rim. Nothing too strange about that. You come along and suggest that this could be dangerous. I think that is irresponsible to say.
I thought of another example. My big ol' Gran Sport Buick has 275/60-15s on 7 inch wide rims. While it wont pull 1g, I have cornered it to the point of severe tire howl. Guess what, the tire stayed on the rim! That one is down around a .65 ratio. There are lots of cars way out of the .85 range. Maybe if all this scares you too much, you should just stay home.
Do you really think that the low profile tire has less grip on the rim? The sidewall is much stiffer as is the tread area in a good performance tire. They are extremely resistant to popping off the bead. You are just flat wrong about that one. The car tire will slide long before it comes off the rim. The truck tires I have seen can be wildly displaced and not come off. The forces are certainly greater than anything you can do with a car.
The whole point I am trying to make, in an admittedly long winded fashion
is that it sure would be nice if you spare us the preachers tone. The original post was about fitting a 275mm tire to a 9" rim. Nothing too strange about that. You come along and suggest that this could be dangerous. I think that is irresponsible to say. I thought of another example. My big ol' Gran Sport Buick has 275/60-15s on 7 inch wide rims. While it wont pull 1g, I have cornered it to the point of severe tire howl. Guess what, the tire stayed on the rim! That one is down around a .65 ratio. There are lots of cars way out of the .85 range. Maybe if all this scares you too much, you should just stay home.
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From: Anaheim California
perhaps some basic information about rim width tire width and the ratios Note that tire width is the section width NOT the tread width (275 mm) and the 85% ratio was adopted as a means of simply keeping the measurements consistant from tire manufacturer to tire manufacter when measuring section widths because as you use diferent rim widths the section width changes . this link .. <a href="http://www.yokohamatire.com/utperf.asp" target="_blank">www.yokohamatire.com/utperf.asp</a> has some more detail . Running a nominal 275x40 on a 9 is with in the range of widths approved by most manufacturers as " acceptable" . HOWEVER in my opinion it will not handle nearly as well as a narrower tire or a wider rim . When you have the sidewalls pinched in at the rim it allows the rim to float from side to side and under extreme cornering may lift part of the tread off the road . Many racing sanctioning rules simply limit the allowable rim width and let you run tire as wide as you wish ...PCA does this !! but run too wide a tire and the guy running narrow ones will out corner you . So if you like the LOOK go for it just recognize that the car is probably slower.
Advanced
Joined: Aug 2002
Posts: 98
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Hi and Thanks:
I appreciate everything I've learned, and continue to on this forum.
No, they don't rub. At all. Twenty thousand miles.
I do know my way around a racetrack. Have done that (years ago). And autocross.
Also, have been doing tire/wheel stuff on foreign and domestic hobby outlets for twenty years before rolling up my sleeves into Porsches.
Fox News says: "We report, you decide."
Again, Thanks to all,
Jeff
'87 5 spd.
chips, RMB, Ott
No rear A/C
(boy, it's hot down here).
I appreciate everything I've learned, and continue to on this forum.
No, they don't rub. At all. Twenty thousand miles.
I do know my way around a racetrack. Have done that (years ago). And autocross.
Also, have been doing tire/wheel stuff on foreign and domestic hobby outlets for twenty years before rolling up my sleeves into Porsches.
Fox News says: "We report, you decide."
Again, Thanks to all,
Jeff
'87 5 spd.
chips, RMB, Ott
No rear A/C
(boy, it's hot down here).
Burning Brakes
Joined: Jun 2001
Posts: 778
Likes: 1
From: Herndon, VA
Keep the following in mind. Autocrossers tend to use the stickest tires they can afford. It is not uncommon to take a corner at well over 1G for a very short period of time while autocrossing. The shorter the tire, the less flex it has, so if the tire is gripping black-top really well, it is possible that it can nearly glue itself to
road. If the tire is excessively wider than the rim holding it - well, I think you can deduce the rest.
I'm Sorry I didn't take a photo of that tire coming off its rim. I guess what I saw was a "once in a lifetime" occurance due to extenuating conditions. Besides, if you don't believe me, that's fine. I know it to be true and that's all that really matters - to me.
As I originally said, I've had them both on a 9" rim. The 255mm tire felt more secure than the 275mm tire. I think the last thing anyone wants (especially when cornering at high speeds) is a vague or wallowy feeling from the tires. :^( YMMV.
road. If the tire is excessively wider than the rim holding it - well, I think you can deduce the rest.
I'm Sorry I didn't take a photo of that tire coming off its rim. I guess what I saw was a "once in a lifetime" occurance due to extenuating conditions. Besides, if you don't believe me, that's fine. I know it to be true and that's all that really matters - to me.
As I originally said, I've had them both on a 9" rim. The 255mm tire felt more secure than the 275mm tire. I think the last thing anyone wants (especially when cornering at high speeds) is a vague or wallowy feeling from the tires. :^( YMMV.
Racer
Joined: Jun 2002
Posts: 272
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From: Milwaukee, WI
Ed...would appreciate your opinion. actually, I run the tire sizes you recommended (225 fronts and 255 rears) on my 928 that has 7.5" front and 9" in the rear (turbo twists). However, I just got a set of cup wheels at TireRack for my 911SC which has been outfitted with widebody flares all around. 225's are going on the fronts..but they said that 265's would be fine on the rear (Bridgestone S03's)...think they will be fine on the rims or on the edge?
Advanced
Joined: Aug 2002
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Addendum:
Tire Rack reccomended the 275/40/17 on rear, and 235/45/17 on front. These were on the MM 993 rims--9" and 7.5"--(original Porsche supplier). They obviously did their homework. After I burned those up, I did my homework. I measured, and measured again (have done this for many years).
I went up one width size both front and rear. Works perfectly. I am, however, running tire spec. psi's--about 44 psi. I am not going to roll a tire off of a rim, especially at those pressures. (I have drag raced for years, and have not spun a tire off of a rim either).
Upsides:
-Speedo now reads perfectly. Previously, it was a Porsche Egometer.
-Ride quality improved, with slightly taller sidewall on performance tires.
-Higher inflation pressures can help compensate for typical poor "lifting car" alignments, by moving contact area back toward center of tire. For example, if you get a lousy alignment @32 psi, and have tires rated for 44 psi, increasing to max. rec. tire pressure can save tire life--especially with wider tires, by moving contact from inside shoulder out toward tire center.
-For autocross, I can always go back to the unattractive dish 16's with Yokos. sitting in storage. They're strong, light, and engineered to work with the system/suspension.
-They look great, and they work. That combination eats up highway miles like none other. Some of you wouldn't want to know the details.
FWIW
Thanks,
Jeff
'87 5-spd.
chips, RMB, Ott.
130K, but runs like new, goes like hell.
Tire Rack reccomended the 275/40/17 on rear, and 235/45/17 on front. These were on the MM 993 rims--9" and 7.5"--(original Porsche supplier). They obviously did their homework. After I burned those up, I did my homework. I measured, and measured again (have done this for many years).
I went up one width size both front and rear. Works perfectly. I am, however, running tire spec. psi's--about 44 psi. I am not going to roll a tire off of a rim, especially at those pressures. (I have drag raced for years, and have not spun a tire off of a rim either).
Upsides:
-Speedo now reads perfectly. Previously, it was a Porsche Egometer.
-Ride quality improved, with slightly taller sidewall on performance tires.
-Higher inflation pressures can help compensate for typical poor "lifting car" alignments, by moving contact area back toward center of tire. For example, if you get a lousy alignment @32 psi, and have tires rated for 44 psi, increasing to max. rec. tire pressure can save tire life--especially with wider tires, by moving contact from inside shoulder out toward tire center.
-For autocross, I can always go back to the unattractive dish 16's with Yokos. sitting in storage. They're strong, light, and engineered to work with the system/suspension.
-They look great, and they work. That combination eats up highway miles like none other. Some of you wouldn't want to know the details.
FWIW
Thanks,
Jeff
'87 5-spd.
chips, RMB, Ott.
130K, but runs like new, goes like hell.