Tire Fitment
12-04-2002 | 11:57 PM
#1
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From: Boca Raton, FL
Tire Fitment
Sorry for including this here and not on the wheel/tire forum, I did post but that board seems to get so little traffic I figured I'd open it up to some everyone who might have some experience...
I'm currently looking at a set of Cup I rims for my 89 951, which by my impressions should be a direct bolt up (correct me if I'm wrong)...what disturbs me is that they currently have 235's in front and 275's in the rear on what I always thought to be 17x7/17x9 rims...am I the only one who thinks this is way too wide a tire for these rims? I can go for a set of Cup IIs with appropriate 205/255 tires from the 993 setup, but I really prefer the look of the Cup I rims with the flatter spokes...I'd rather not have to push to swap off tires, but if everyone seems to be in accordance with the idea that these are just a bit too wide, I think I might have to...
any help appreciated!
I'm currently looking at a set of Cup I rims for my 89 951, which by my impressions should be a direct bolt up (correct me if I'm wrong)...what disturbs me is that they currently have 235's in front and 275's in the rear on what I always thought to be 17x7/17x9 rims...am I the only one who thinks this is way too wide a tire for these rims? I can go for a set of Cup IIs with appropriate 205/255 tires from the 993 setup, but I really prefer the look of the Cup I rims with the flatter spokes...I'd rather not have to push to swap off tires, but if everyone seems to be in accordance with the idea that these are just a bit too wide, I think I might have to...
any help appreciated!
12-05-2002 | 12:58 AM
#3
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From: Santa Barbara, CA
"am I the only one who thinks this is way too wide a tire for these rims? "
While they won't perform nearly as well as being on wider rims, they should be fine for what you're doing. If you wanted ultimate performance, you wouldn't be selecting those wheels anyway. A set of 225/45-17 and 255/40-17 would probably give you better turn-in with similar grip.
While they won't perform nearly as well as being on wider rims, they should be fine for what you're doing. If you wanted ultimate performance, you wouldn't be selecting those wheels anyway. A set of 225/45-17 and 255/40-17 would probably give you better turn-in with similar grip.
12-05-2002 | 01:52 PM
#4
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From: San Diego, CA
I'm with Danno - I also think 235 front and 275's are a tad big for the relatively low horsepower of a 944. I really like the feel of my 225/45 front 255/40 rears on Cup 2 17" wheels. Although my sprint speed is compromised.
Depending on the tire maker and the wheel offset (55?) the 235 fronts should squeeze with no rub and the 245 rears won't cause significant power loss. Net result: you'd get incredible 'stick' with optimum footprint; and if you track, you'd get minimum points off for tire size.
My next track set-up will be Azenis 225/45/17 fronts & 245/40/17 rears on 17" Turbo Twist wheels. I should stick like a fly on the wall at the next track event.
Just my thoughts :-)
Depending on the tire maker and the wheel offset (55?) the 235 fronts should squeeze with no rub and the 245 rears won't cause significant power loss. Net result: you'd get incredible 'stick' with optimum footprint; and if you track, you'd get minimum points off for tire size.
My next track set-up will be Azenis 225/45/17 fronts & 245/40/17 rears on 17" Turbo Twist wheels. I should stick like a fly on the wall at the next track event.
Just my thoughts :-)
12-05-2002 | 05:53 PM
#5
Three Wheelin'
Joined: Aug 2002
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From: Vancouver, BC
Whether or not those tires are suitable for the rims depends on the profile and manufacturer's recomendations. Check on the specifications page at <a href="http://www.tirerack.com." target="_blank">www.tirerack.com.</a> For example, a Kumho Ecsta 712 (my tire) in 225/45x17 is best suited for a 7.5" rim, but is acceptable on my 7" rim. It does look a little narrow (squeezed) on the rim. On the other hand, my 255/40x17 is ideal on my 9" rear rim.
According to <a href="http://www.tirerack.com/tires/Spec.jsp?make=Kumho&model=ECSTA+Supra+712" target="_blank">Tire Rack</a>, a Kumho 235 front would require eithr a minimum 7.5" rim (45 series) or 8" rim (40 series), but is best suited for an 8 or 8.5" rim respectively. A 275/40x17 can run on 9" to 11" rims, but are best suited for a 9.5" rim. Recommendations vary by brand. YMMV
According to <a href="http://www.tirerack.com/tires/Spec.jsp?make=Kumho&model=ECSTA+Supra+712" target="_blank">Tire Rack</a>, a Kumho 235 front would require eithr a minimum 7.5" rim (45 series) or 8" rim (40 series), but is best suited for an 8 or 8.5" rim respectively. A 275/40x17 can run on 9" to 11" rims, but are best suited for a 9.5" rim. Recommendations vary by brand. YMMV
12-05-2002 | 06:14 PM
#6
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From: Churchville, MD
I'd say those tires would be overkill for those rims. You could get them to fit, but as Danno said it wouldn't help handling/grip.
FWIW - I just mounted Toyo Proxes T1-S 245/40's and 275/40's on my turbo ----> on 8x17 and 10x17 Fikses. They fit fine on these rims, but would have a NASTY bulge on anything narrower
FWIW - I just mounted Toyo Proxes T1-S 245/40's and 275/40's on my turbo ----> on 8x17 and 10x17 Fikses. They fit fine on these rims, but would have a NASTY bulge on anything narrower
12-06-2002 | 01:08 AM
#7
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From: Santa Barbara, CA
"A 275/40x17 can run on 9" to 11" rims, but are best suited for a 9.5" rim. Recommendations vary by brand. "
Well... it's actually not quite that simple. The 'specified' rim-width in all those tables refer to the rim-width the tire was mounted on when its dimensions were measured. It's not a 'recommended' or even the 'best' width to use. From the Tire Rack: [quote]Measuring Rim Width
The measuring rim width is the industry standardized rim width upon which the tire must be mounted in order to confirm it meets its dimensional targets. Because the width of the rim will influence the width of the tire, a standard rim width for every tire size is assigned and must be used. This standardized measuring rim width allows all of the tires produced around the world to meet the same dimensional standards and therefore, be equivalent with regards to their physical size. The measuring rim width is sometimes referred to as the tire's "design rim width".
The assigned measuring rim width changes with the tire size's section width and with the tire size's aspect ratio. As tire section width increases, the measuring rim width increases proportionately in 1/2" increments. Therefore, relatively narrow wheel widths are assigned for smaller tires while wider wheel widths are assigned for larger tires.<hr></blockquote>
So a tire labeled "275/40-17" may measure with a section-width of 260mm on a 9" rim. Yet on a 11" rim it may have a section-width of 290mm, so what's the REAL width of this tire? That's where the "Measuring Rim Width" dimension comes in. An industry-wide standard for measuring a certain sized tire, in this case a 9.5" rim for a 275/40-17 tire.
It does NOT say anything about it as being recommended or even the best for performance. That's where the "Rim Width Range" comes in, because there's no black&white, all-or-nothing, yes/no answer. Within that analog range, there are shades of grey in the tire's behavior. On the narrow end of the range, you'll have a lot of sidewall flex and lateral movement of the tread. At the wide end, you'll have the least sidewall flex and the least lateral squirm of the tread, giving you the best performance, however, you may end up with clearance and rubbing issues.
The differences are because of the dynamics of cornering; it doesn't happen instantly. If you look at a car head-on as it's coming towards you, then it turns, you'll noticed that the tire appears pulled under the car while it's cornering. I'm sure you've all seen photos that look like the tires are about to be pulled off the rim. Now this is actually perfectly natural and that flex is really required in order to corner.
Here's what happens under cornering. First a tire is like an inside-out suspension-bridge. All forces are in tension in the tire's carcass. It's the air-pressure that stretches out the casing and allows it to carry a load. The fibres on the bottom have their tension by air-pressure canceled out by the weight load of the car, thus you get a bulge. This relaxation increases the air-pressure which is taken up by the entire casing that's not in contact with the ground. This is similar to how a spoked bicycle wheel works; the 4 spokes on the ground loses almost all of their tension and the remaining spokes take up the tension that was lost (the hub doesn't 'hang' from just the top spokes, but rather from all of the ones not touching the ground).
Under cornering, a similar tension effect happens. When you turn the steering-wheel, the rim points inward to the direction of travel. This causes the tire to roll at an angle to the path of the car. However, inertia continues to push the rim in a straight line, yet the tire has started to roll to the inside. Meanwhile, nothing has happened to the car's body yet.
What needs to happen is for the outside sidewall on the ground, which is normally under compression, to roll under the rim. Then as the rim continues in a straight line and the tire is rolling at an angle to it (slip-angle), the sidewall will eventually be INSIDE the rim's edge. At this point, the fibres in the sidewall starts to undergo tension. Only when the sidwall has completely stretched to the point where it's tension is equal to the mass of the car at that corner, does it then tug on the rim into the corner. The rim then pushes on the suspension, which pushes on the car and makes it turn from its straight-line path (Newton's law).
So as you can see, this straight-line to cornering transition takes some time. And that time is based upon how far the tread has to move laterally before the outside sidewall is fully under tension. With a rim that's on the wide end of the suggested range for any tire width, the sidewall will be 'pre-stretched' into the lateral-cornering position. Using the 275/40-17 tire on a 9" rim may require the tread to squirm 2" sideways (relative to the rim) before it is fully tensioned and pulls on the rim. However, with an 11" rim, the tread may only need to move 0.5" before the sidewall is in the same shape and position on the rim (anyone remember Bob Sharp's 280ZX-Turbo from the IMSA series?).
Additionally the wider rim keeps the contact patch flatter on the ground. Pinching a tire with a narrow rim causes the outside edges to not have as much pressure on the ground and they don't contribute to cornering grip.
If we look at rim-widths versus tire-width when you go up the performance ladder from ricer economy 'sporty' cars like Hondas to full-on racers disguised as 'sports' cars, you'll find that at the high-end, they will use rim-widths that are close to the same as the tire's section-width. For example:
345mm/13" rim Ferrari F40
335mm/13" rim Viper
255mm/10" rim Testarossa
255mm/10" rim 288GTO
255mm/9.5" rim C4-Corvette
245mm/9" rim 951S
etc...
Well... it's actually not quite that simple. The 'specified' rim-width in all those tables refer to the rim-width the tire was mounted on when its dimensions were measured. It's not a 'recommended' or even the 'best' width to use. From the Tire Rack: [quote]Measuring Rim Width
The measuring rim width is the industry standardized rim width upon which the tire must be mounted in order to confirm it meets its dimensional targets. Because the width of the rim will influence the width of the tire, a standard rim width for every tire size is assigned and must be used. This standardized measuring rim width allows all of the tires produced around the world to meet the same dimensional standards and therefore, be equivalent with regards to their physical size. The measuring rim width is sometimes referred to as the tire's "design rim width".
The assigned measuring rim width changes with the tire size's section width and with the tire size's aspect ratio. As tire section width increases, the measuring rim width increases proportionately in 1/2" increments. Therefore, relatively narrow wheel widths are assigned for smaller tires while wider wheel widths are assigned for larger tires.<hr></blockquote>
So a tire labeled "275/40-17" may measure with a section-width of 260mm on a 9" rim. Yet on a 11" rim it may have a section-width of 290mm, so what's the REAL width of this tire? That's where the "Measuring Rim Width" dimension comes in. An industry-wide standard for measuring a certain sized tire, in this case a 9.5" rim for a 275/40-17 tire.
It does NOT say anything about it as being recommended or even the best for performance. That's where the "Rim Width Range" comes in, because there's no black&white, all-or-nothing, yes/no answer. Within that analog range, there are shades of grey in the tire's behavior. On the narrow end of the range, you'll have a lot of sidewall flex and lateral movement of the tread. At the wide end, you'll have the least sidewall flex and the least lateral squirm of the tread, giving you the best performance, however, you may end up with clearance and rubbing issues.
The differences are because of the dynamics of cornering; it doesn't happen instantly. If you look at a car head-on as it's coming towards you, then it turns, you'll noticed that the tire appears pulled under the car while it's cornering. I'm sure you've all seen photos that look like the tires are about to be pulled off the rim. Now this is actually perfectly natural and that flex is really required in order to corner.
Here's what happens under cornering. First a tire is like an inside-out suspension-bridge. All forces are in tension in the tire's carcass. It's the air-pressure that stretches out the casing and allows it to carry a load. The fibres on the bottom have their tension by air-pressure canceled out by the weight load of the car, thus you get a bulge. This relaxation increases the air-pressure which is taken up by the entire casing that's not in contact with the ground. This is similar to how a spoked bicycle wheel works; the 4 spokes on the ground loses almost all of their tension and the remaining spokes take up the tension that was lost (the hub doesn't 'hang' from just the top spokes, but rather from all of the ones not touching the ground).
Under cornering, a similar tension effect happens. When you turn the steering-wheel, the rim points inward to the direction of travel. This causes the tire to roll at an angle to the path of the car. However, inertia continues to push the rim in a straight line, yet the tire has started to roll to the inside. Meanwhile, nothing has happened to the car's body yet.
What needs to happen is for the outside sidewall on the ground, which is normally under compression, to roll under the rim. Then as the rim continues in a straight line and the tire is rolling at an angle to it (slip-angle), the sidewall will eventually be INSIDE the rim's edge. At this point, the fibres in the sidewall starts to undergo tension. Only when the sidwall has completely stretched to the point where it's tension is equal to the mass of the car at that corner, does it then tug on the rim into the corner. The rim then pushes on the suspension, which pushes on the car and makes it turn from its straight-line path (Newton's law).
So as you can see, this straight-line to cornering transition takes some time. And that time is based upon how far the tread has to move laterally before the outside sidewall is fully under tension. With a rim that's on the wide end of the suggested range for any tire width, the sidewall will be 'pre-stretched' into the lateral-cornering position. Using the 275/40-17 tire on a 9" rim may require the tread to squirm 2" sideways (relative to the rim) before it is fully tensioned and pulls on the rim. However, with an 11" rim, the tread may only need to move 0.5" before the sidewall is in the same shape and position on the rim (anyone remember Bob Sharp's 280ZX-Turbo from the IMSA series?).
Additionally the wider rim keeps the contact patch flatter on the ground. Pinching a tire with a narrow rim causes the outside edges to not have as much pressure on the ground and they don't contribute to cornering grip.
If we look at rim-widths versus tire-width when you go up the performance ladder from ricer economy 'sporty' cars like Hondas to full-on racers disguised as 'sports' cars, you'll find that at the high-end, they will use rim-widths that are close to the same as the tire's section-width. For example:
345mm/13" rim Ferrari F40
335mm/13" rim Viper
255mm/10" rim Testarossa
255mm/10" rim 288GTO
255mm/9.5" rim C4-Corvette
245mm/9" rim 951S
etc...
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12-06-2002 | 09:47 AM
#8
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From: Churchville, MD
very good post Danno
Perhaps you can answer this question for me, with regard to your rim-width - section-width comment.
One example:
928 GT - 8x16 front wheel with 225/50R16
9x16 rear wheel with 245/45R16
951 S 7x16 front wheel with 225/50R16
9x16 rear wheel with 245/45R16
Wouldn't it have been better to put the 8" front on the 944 as well? I think it was an option, but still.
Similarly, bone stock early 90's 911s and non-S 944 Turbos had 205/225 tires, front/rear -- only the 911 did this with 6" and 8" rims, while the 944 had 7" and 8" rims?
Perhaps you can answer this question for me, with regard to your rim-width - section-width comment.
One example:
928 GT - 8x16 front wheel with 225/50R16
9x16 rear wheel with 245/45R16
951 S 7x16 front wheel with 225/50R16
9x16 rear wheel with 245/45R16
Wouldn't it have been better to put the 8" front on the 944 as well? I think it was an option, but still.
Similarly, bone stock early 90's 911s and non-S 944 Turbos had 205/225 tires, front/rear -- only the 911 did this with 6" and 8" rims, while the 944 had 7" and 8" rims?
09-19-2011 | 02:42 PM
#9
Advanced
Joined: Oct 2003
Posts: 51
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From: Bardu. Norway (Up North)
Hi,
I am considering Fikse 8,5x17 -245/40 front and 9x17 255/40 rear on standard -89 944 2,7. I believe 225/45 front will be ok for the street but I do think it will be less "turn-happy" and understeer quite a bit on some occasional track days.
Mike ! How does Your 245/40`s look on the 8" rim ? Can you please provide some pictures ?
I am considering Fikse 8,5x17 -245/40 front and 9x17 255/40 rear on standard -89 944 2,7. I believe 225/45 front will be ok for the street but I do think it will be less "turn-happy" and understeer quite a bit on some occasional track days.
Mike ! How does Your 245/40`s look on the 8" rim ? Can you please provide some pictures ?
09-19-2011 | 05:25 PM
#10
Drifting
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From: Caraquet-- New-Brunswick-- Canada
MchShnell___This is the combo I'm riding on with my 968. Cup I 17 x 8 w/225-45 ZR 17 frt /17 x 9.5 w/ 255-40 ZR 17 rear. This I presonally think will be a good choice & don't see any problems fitting them on your 951.The pics below is off the tire size mention above mounted on a 951.Btw if not done yet maybe you should consider lowering the front approx 1 1/2" & the rear 3/4".
Last edited by ernie9468; 02-04-2013 at 04:31 PM.
09-19-2011 | 05:37 PM
#11
Drifting
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Posts: 2,728
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From: Caraquet-- New-Brunswick-- Canada
MchShnell___This is the combo I'm riding on with my 968. Cup I 17 x 8 w/225-45 ZR 17 frt /17 x 9.5 w/ 255-40 ZR 17 rear. This I presonally think will be a good choice & don't see any problems fitting them on your 951.The pics below is off the tire size mention above mounted on a 951.Btw if not done yet maybe you should consider lowering the front approx 1 1/2" & the rear 3/4".
Last edited by ernie9468; 02-04-2013 at 04:31 PM.
09-19-2011 | 08:29 PM
#12
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From: Porterville, Ca.
I had a set of 996 wheels on my '90 cabriolet that fit well. 996362 128.00 (9" et 55)and 996 362 126.05 (8.5" et 50) Tire size was 275/40 rear, and 225/45 front. These fit quite well and the 3 litre was more than able to move them. This set up did not fit on my '84 however as the fronts would not clear the shock springs. While they looked good on car finish was bad and dismounted and painted. Have not remounted tires and thinking of selling rims. ( I do have 6 other sets of wheels tires) and chrome 928s4 dish wheels are on the car now.
