View Poll Results: Do 285/30 fit on an 18X10 (NB)
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Who's run 285/30, 10X18, on a NB?
12-02-2009, 07:42 AM
#17
Drifting
Join Date: Apr 2003
Location: la la land | comin' back soon nyc
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fwiw i had 285 poles on my cab (w/ bbs rs gt @ close to rs height); though they looked beefier i had a issue after a few mos. seems the inside of the passenger side tyre formed a bubble as it was rubbing on one of the oil line clamps... just be sure you're clear in that area & you'll be fine (screw side IN). also, rem that various brands & models differ in thickness & width though they may be the same size (why some 285 & even 295 will fit a nb). -bol
btw i prefer the feel of the 265 re-11 bridgestones potenza i have on there now. car never felt snappier.
bol
btw i prefer the feel of the 265 re-11 bridgestones potenza i have on there now. car never felt snappier.
bol
heh heh...
12-02-2009, 05:07 PM
#20
Rennlist Member
I run 295/30-18 on 10x18ET60 wheels with still over 5mm clearence. My car is lowered to lower than RS spec, but I have rolled the fenders using a base ball bat. 285/30-18 on 10x18ET65 should not be a problem on any NB 993.
12-02-2009, 06:42 PM
#21
Rennlist Member
Assuming that the 285 is a 30 aspect ratio and the 265 is a 35 aspect ratio, the two tires should be very similar in overall diameter, meaning that there are no increased leverage forces from a taller tire. A wider rubber on a track car means that you can get on the gas sooner in a corner before you have oversteer. For a road car, a bump from 265 to 285 has very little performance benefit, other than street "cred" and looks, the wider rear tire making a vehicle appear more aggressive.
12-02-2009, 07:23 PM
#22
Assuming that the 285 is a 30 aspect ratio and the 265 is a 35 aspect ratio, the two tires should be very similar in overall diameter, meaning that there are no increased leverage forces from a taller tire. A wider rubber on a track car means that you can get on the gas sooner in a corner before you have oversteer. For a road car, a bump from 265 to 285 has very little performance benefit, other than street "cred" and looks, the wider rear tire making a vehicle appear more aggressive.
A potential issue is the increased rear grip w/o a commensurate increase in front grip causes a change in the dynamic behavior toward more understeer, the last thing a stock suspended 993 needs. If you have PSS9/10 it's even worse as the springs that come w/ those kits also increase understeer.
In addition to stiffer rear springs wrt front I'd want 245/35 & 285/30 tires
12-02-2009, 08:07 PM
#23
Rennlist Member
285/30 is slightly shorter than 265/35 and does provide a slight acceleration edge, here's a comparison of the 2 in the same chassis w/ the same transmission, I know the lable says 285/40 but that is a typo, this is a comparison between 285/30x18 and 265/35x18
A potential issue is the increased rear grip w/o a commensurate increase in front grip causes a change in the dynamic behavior toward more understeer, the last thing a stock suspended 993 needs. If you have PSS9/10 it's even worse as the springs that come w/ those kits also increase understeer.
In addition to stiffer rear springs wrt front I'd want 245/35 & 285/30 tires
A potential issue is the increased rear grip w/o a commensurate increase in front grip causes a change in the dynamic behavior toward more understeer, the last thing a stock suspended 993 needs. If you have PSS9/10 it's even worse as the springs that come w/ those kits also increase understeer.
In addition to stiffer rear springs wrt front I'd want 245/35 & 285/30 tires
What are the tire measurements for the accel curves? Yep, a 265/35-18 is slightly shorter than a 285/3018, but I used Michelin's Pilot Sport Cup specs as a comparison and saw that the 265 is 28.1" while the 285 is 28.2". http://www.tirerack.com/tires/Spec.j...irePageLocQty= Do you think the 1/10th of an inch difference will have a significant (however significant is defined) effect on acceleration? Complicating matters is that the 295/30-18 is also 28.2" in diameter. I've run a 295/30-18 on the track and my lap times did not change a bit, although I did not do an A-B-A-B test with a 265 tire.
I agree that a wider rear tire will contribute to more understeer for a car with a stock suspension (Matt's car has Bilstein HD's and TT sways). A properly equipped race car with adjustable sways and shocks should be able to dial that out. I daresay most drivers will never feel an understeer difference between a 285 and 295 or a 285 and 265. For the slower corners, understeer would seem less desirable, but it can be a benefit for trail-braking and ultra-fast corner entry speed. For the faster corners, within reason, more understeer is exactly what I want so I can put the power down sooner and not have the back end come out. The chute at Watkins Glen is a really long and important corner where getting on the power quickly means that the car gets loose. If I had more rear stick, I could apply the throttle sooner and shave my times.
12-02-2009, 08:44 PM
#24
Bill,
What are the tire measurements for the accel curves? Yep, a 265/35-18 is slightly shorter than a 285/3018, but I used Michelin's Pilot Sport Cup specs as a comparison and saw that the 265 is 28.1" while the 285 is 28.2". http://www.tirerack.com/tires/Spec.j...irePageLocQty= Do you think the 1/10th of an inch difference will have a significant (however significant is defined) effect on acceleration? Complicating matters is that the 295/30-18 is also 28.2" in diameter. I've run a 295/30-18 on the track and my lap times did not change a bit, although I did not do an A-B-A-B test with a 265 tire.
I agree that a wider rear tire will contribute to more understeer for a car with a stock suspension (Matt's car has Bilstein HD's and TT sways). A properly equipped race car with adjustable sways and shocks should be able to dial that out. I daresay most drivers will never feel an understeer difference between a 285 and 295 or a 285 and 265. For the slower corners, understeer would seem less desirable, but it can be a benefit for trail-braking and ultra-fast corner entry speed. For the faster corners, within reason, more understeer is exactly what I want so I can put the power down sooner and not have the back end come out. The chute at Watkins Glen is a really long and important corner where getting on the power quickly means that the car gets loose. If I had more rear stick, I could apply the throttle sooner and shave my times.
What are the tire measurements for the accel curves? Yep, a 265/35-18 is slightly shorter than a 285/3018, but I used Michelin's Pilot Sport Cup specs as a comparison and saw that the 265 is 28.1" while the 285 is 28.2". http://www.tirerack.com/tires/Spec.j...irePageLocQty= Do you think the 1/10th of an inch difference will have a significant (however significant is defined) effect on acceleration? Complicating matters is that the 295/30-18 is also 28.2" in diameter. I've run a 295/30-18 on the track and my lap times did not change a bit, although I did not do an A-B-A-B test with a 265 tire.
I agree that a wider rear tire will contribute to more understeer for a car with a stock suspension (Matt's car has Bilstein HD's and TT sways). A properly equipped race car with adjustable sways and shocks should be able to dial that out. I daresay most drivers will never feel an understeer difference between a 285 and 295 or a 285 and 265. For the slower corners, understeer would seem less desirable, but it can be a benefit for trail-braking and ultra-fast corner entry speed. For the faster corners, within reason, more understeer is exactly what I want so I can put the power down sooner and not have the back end come out. The chute at Watkins Glen is a really long and important corner where getting on the power quickly means that the car gets loose. If I had more rear stick, I could apply the throttle sooner and shave my times.
MPSC
265/35x18 is 25.2" 831rpm
285/30x18 is 25.1" 834rpm
The more accurate way to do the charts is to roll out a loaded tire, barring that derive the loaded radius from the rpm
It's for sure that MPSC are closer together in rpm therefore loaded radius than some other tire choices.
I disagree about the effect on over/under steer, I went out of my way in spring choices to reduce understeer, I still have to go stiff on the rear sways. A bigger rear will make that even worse. But other things like lsd effectiveness will also come into play as an effective lsd will also increase understeer. At the Glen it can be difficult to get on the gas quickly in places because the track is pretty rough and the concrete can be slick,
12-02-2009, 09:10 PM
#25
Rennlist Member
Thread Starter
Point taken on the ratio of rear to front grip, which is why I won't bother with a 285 unless I can get at least 235 up front.
This is further rendered academic by my current soft and non-adjustable suspension. Add to that my lack of skill, and well, it really matters less and less.
Since the wheels I am looking at are evidently minted from an unobtanium derivatibe alloy, the whole premise is to buy wheels that can fit the larger sizes in the future should they be warranted, and capable of being run effectively in concert, both front and back, and with the suspension.
PS - as for size comps, my calculations yield a 265/35 OD of 25.3 inches and 285/30 OD of 24.7 inches.
That's over a half inch shorter comparing one to the other. Unless I misread that chart and measurements above, would that not yield a noticeable difference to gearing? One is worse than stock 25", and one is better, of course offset by increased weight and rolling resistance.
Thanks guys for all the input. If nothing else, this is reassuring.
Matt
This is further rendered academic by my current soft and non-adjustable suspension. Add to that my lack of skill, and well, it really matters less and less.
Since the wheels I am looking at are evidently minted from an unobtanium derivatibe alloy, the whole premise is to buy wheels that can fit the larger sizes in the future should they be warranted, and capable of being run effectively in concert, both front and back, and with the suspension.
PS - as for size comps, my calculations yield a 265/35 OD of 25.3 inches and 285/30 OD of 24.7 inches.
That's over a half inch shorter comparing one to the other. Unless I misread that chart and measurements above, would that not yield a noticeable difference to gearing? One is worse than stock 25", and one is better, of course offset by increased weight and rolling resistance.
Thanks guys for all the input. If nothing else, this is reassuring.
Matt
12-02-2009, 09:21 PM
#26
Rennlist Member
I don'r remember which specific tires I used for that comparison
MPSC
265/35x18 is 25.2" 831rpm
285/30x18 is 25.1" 834rpm
The more accurate way to do the charts is to roll out a loaded tire, barring that derive the loaded radius from the rpm
It's for sure that MPSC are closer together in rpm therefore loaded radius than some other tire choices.
I disagree about the effect on over/under steer, I went out of my way in spring choices to reduce understeer, I still have to go stiff on the rear sways. A bigger rear will make that even worse. But other things like lsd effectiveness will also come into play as an effective lsd will also increase understeer. At the Glen it can be difficult to get on the gas quickly in places because the track is pretty rough and the concrete can be slick,
MPSC
265/35x18 is 25.2" 831rpm
285/30x18 is 25.1" 834rpm
The more accurate way to do the charts is to roll out a loaded tire, barring that derive the loaded radius from the rpm
It's for sure that MPSC are closer together in rpm therefore loaded radius than some other tire choices.
I disagree about the effect on over/under steer, I went out of my way in spring choices to reduce understeer, I still have to go stiff on the rear sways. A bigger rear will make that even worse. But other things like lsd effectiveness will also come into play as an effective lsd will also increase understeer. At the Glen it can be difficult to get on the gas quickly in places because the track is pretty rough and the concrete can be slick,
12-02-2009, 09:33 PM
#27
Point taken on the ratio of rear to front grip, which is why I won't bother with a 285 unless I can get at least 235 up front.
This is further rendered academic by my current soft and non-adjustable suspension. Add to that my lack of skill, and well, it really matters less and less.
Since the wheels I am looking at are evidently minted from an unobtanium derivatibe alloy, the whole premise is to buy wheels that can fit the larger sizes in the future should they be warranted, and capable of being run effectively in concert, both front and back, and with the suspension.
PS - as for size comps, my calculations yield a 265/35 OD of 25.3 inches and 285/30 OD of 24.7 inches.
That's over a half inch shorter comparing one to the other. Unless I misread that chart and measurements above, would that not yield a noticeable difference to gearing? One is worse than stock 25", and one is better, of course offset by increased weight and rolling resistance.
Thanks guys for all the input. If nothing else, this is reassuring.
Matt
This is further rendered academic by my current soft and non-adjustable suspension. Add to that my lack of skill, and well, it really matters less and less.
Since the wheels I am looking at are evidently minted from an unobtanium derivatibe alloy, the whole premise is to buy wheels that can fit the larger sizes in the future should they be warranted, and capable of being run effectively in concert, both front and back, and with the suspension.
PS - as for size comps, my calculations yield a 265/35 OD of 25.3 inches and 285/30 OD of 24.7 inches.
That's over a half inch shorter comparing one to the other. Unless I misread that chart and measurements above, would that not yield a noticeable difference to gearing? One is worse than stock 25", and one is better, of course offset by increased weight and rolling resistance.
Thanks guys for all the input. If nothing else, this is reassuring.
Matt
We are talking subtle differences for the most part, the softer the suspension the less desirable the wider tires will be, more chassis roll will reduce grip
i like to take my hints from the Cups, back in the day the factory did a lot of testing and settled on 8.5 & 10 wheels w/ 235 & 265 tires
12-02-2009, 09:39 PM
#28
I usually race on 245/30-18 R6 Hoosiers on the front and 285/30-16 R6 Hoosiers in the rear. Two years ago, I tried BFG R1's and put on a set of 225/35(?)-18's and 285/30-18's. I agonized over putting such a narrow tire on the front (couldn't fit a 245, the next size up) and how it would increase understeer, but my lap times were nearly equal with the R6's. I know the "testing" is flawed, but the lesson that I took from the experience is that sometimes we can over think and over worry how a small change in tire width will affect handling and, ultimately, speed.
another factor is heat, the smaller tire comes up to temp quicker, it will also overheat quicker, again this can be good or bad, it depends.
12-02-2009, 09:44 PM
#29
Rennlist Member
Thread Starter
What tires?
Is your question about what I plan to run (not sure), or my calculation of the half inch delta between the 285 and 265? Not sure I understand.
PS - good advice on following what the factory did!
Best,
Matt
12-02-2009, 10:37 PM
#30
Rennlist Member
yes, that's the usual knowledgeable set up(though I usually see 245/35), as you are increasing grip at both ends, eventually you get more grip than the chassis/suspension can process and after that times won't improve w/o other chassis/suspension/driver improvements, it's a vicious/virtuous(depends on how you look at it) circle.
another factor is heat, the smaller tire comes up to temp quicker, it will also overheat quicker, again this can be good or bad, it depends.
another factor is heat, the smaller tire comes up to temp quicker, it will also overheat quicker, again this can be good or bad, it depends.