235/40x18 fronts on narrowbody...any problems?
09-06-2002, 10:05 AM
#1
Three Wheelin'
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235/40x18 fronts on narrowbody...any problems?
I just got 18" hollow spoke twist wheels (10" rears and 8" fronts) and am going with the 285/30 rears and am considering 235/40 on the fronts. I know most people use the 225/40 fronts, but I want a bit more rubber up front if I can get it. Anybody used the 235/40 up front on '97 narrowbody coupe with stock suspension...do you think it will scrub? <img src="confused.gif" border="0">
09-06-2002, 11:44 AM
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The only problem I see is the diameter of the tire. Calculated sizes are as follows:
225/40-18: 25.1"
285/30-18: 24.7"
A 235/40-18 would have a diameter of 25.4" which is 0.7" taller than the rear tire and is a bit of a stretch. However, these dimensions vary between tire manufacturers and you might find a 235/40 that has a closer dimension to a 285/30 from the same tire type.
FWIW, the 265/35-18 has a calculated diameter of 25.3". That would be a good size to use on the rear.
225/40-18: 25.1"
285/30-18: 24.7"
A 235/40-18 would have a diameter of 25.4" which is 0.7" taller than the rear tire and is a bit of a stretch. However, these dimensions vary between tire manufacturers and you might find a 235/40 that has a closer dimension to a 285/30 from the same tire type.
FWIW, the 265/35-18 has a calculated diameter of 25.3". That would be a good size to use on the rear.
09-06-2002, 12:05 PM
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[quote]Originally posted by Viken:
<strong>
FWIW, the 265/35-18 has a calculated diameter of 25.3". That would be a good size to use on the rear.</strong><hr></blockquote>
Good point Viken. And it will help reduce understeer, where the 285's will just increase it.
<strong>
FWIW, the 265/35-18 has a calculated diameter of 25.3". That would be a good size to use on the rear.</strong><hr></blockquote>
Good point Viken. And it will help reduce understeer, where the 285's will just increase it.
09-06-2002, 12:52 PM
#5
Three Wheelin'
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Well, I'd love to go with a 245/35 up front which would give me a diameter of 24.8"...a good match for the 24.7" of the 285/30. But, I've heard that the 245/35 doesn't fit well on the 8" wheel...and worse, it seems that VERY few manufacturer's make that size.
09-06-2002, 01:11 PM
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[quote]Originally posted by Allen:
<strong>But, I've heard that the 245/35 doesn't fit well on the 8" wheel...and worse, it seems that VERY few manufacturer's make that size.</strong><hr></blockquote>
Well, it will fit but it will work better on an 8.5" or even a 9" wheel.
<strong>But, I've heard that the 245/35 doesn't fit well on the 8" wheel...and worse, it seems that VERY few manufacturer's make that size.</strong><hr></blockquote>
Well, it will fit but it will work better on an 8.5" or even a 9" wheel.
09-06-2002, 05:58 PM
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[quote]Originally posted by Allen:
<strong>Well, I'd love to go with a 245/35 up front which would give me a diameter of 24.8"...a good match for the 24.7" of the 285/30. But, I've heard that the 245/35 doesn't fit well on the 8" wheel...and worse, it seems that VERY few manufacturer's make that size.</strong><hr></blockquote>
Allen,
I run 245/35-18 P-Zero C's (old style) on 8.5 x 10" Fikses. No rubbing. Less understeer and much better traction/feel up front, albeit with a greater tendency to tramline on rough roads. Nice upgrade.
<strong>Well, I'd love to go with a 245/35 up front which would give me a diameter of 24.8"...a good match for the 24.7" of the 285/30. But, I've heard that the 245/35 doesn't fit well on the 8" wheel...and worse, it seems that VERY few manufacturer's make that size.</strong><hr></blockquote>
Allen,
I run 245/35-18 P-Zero C's (old style) on 8.5 x 10" Fikses. No rubbing. Less understeer and much better traction/feel up front, albeit with a greater tendency to tramline on rough roads. Nice upgrade.
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09-07-2002, 02:50 AM
#8
Three Wheelin'
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[quote] A 235/40-18 would have a diameter of 25.4" which is 0.7" taller than the rear tire and is a bit of a stretch. <hr></blockquote>
Maybe this is a dumb question, but what would be the impact of having this 0.7" difference?
Maybe this is a dumb question, but what would be the impact of having this 0.7" difference?
09-07-2002, 05:37 AM
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Allen
993 C4 with 235/40 Front and 275/35 Rear on S03's and Roock wheels with standard suspension. I confirm also no rubbing in the front. I do have some rubbing in the rear in hard corners and bumpy roads. The car is quite neutral and great handling, but to Anir's point, on rough roads at high speeds it feels a bit less stable in the front.
993 C4 with 235/40 Front and 275/35 Rear on S03's and Roock wheels with standard suspension. I confirm also no rubbing in the front. I do have some rubbing in the rear in hard corners and bumpy roads. The car is quite neutral and great handling, but to Anir's point, on rough roads at high speeds it feels a bit less stable in the front.
09-07-2002, 11:49 AM
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Allen,
One more point along Jean's comments. My shocks are a bit worn, and mated with Eibach lowering springs - obviously a less-than-ideal set-up.
I suspect that the planned coilover upgrade (H&R vs. PSS9) will allow the suspension to better handle/control the wider rubber up front, although there will always be a greater tendency to follow ruts, etc., than with the original 225 tires.
I love the traditional Porsche steering feedback and do not view this increased kick / tramlining as a necessarily bad thing, but you might want to take it into consideration depending on your preferences.
One more point along Jean's comments. My shocks are a bit worn, and mated with Eibach lowering springs - obviously a less-than-ideal set-up.
I suspect that the planned coilover upgrade (H&R vs. PSS9) will allow the suspension to better handle/control the wider rubber up front, although there will always be a greater tendency to follow ruts, etc., than with the original 225 tires.
I love the traditional Porsche steering feedback and do not view this increased kick / tramlining as a necessarily bad thing, but you might want to take it into consideration depending on your preferences.
09-07-2002, 02:35 PM
#11
Three Wheelin'
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Jean,
Are you on 18" wheels? What kind of tires do you have? I'm tring to figure the difference in height between your front and rear tires. Viken says that 0.7" difference may be a bit much, so I'm wondering with your set-up and good handling, what is your diffrence. Same tire sizes from different manufacturers have different height...sometimes by quite a bit. Thanks for everyones input. <img src="graemlins/beerchug.gif" border="0" alt="[cheers]" />
Are you on 18" wheels? What kind of tires do you have? I'm tring to figure the difference in height between your front and rear tires. Viken says that 0.7" difference may be a bit much, so I'm wondering with your set-up and good handling, what is your diffrence. Same tire sizes from different manufacturers have different height...sometimes by quite a bit. Thanks for everyones input. <img src="graemlins/beerchug.gif" border="0" alt="[cheers]" />
09-07-2002, 08:47 PM
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Something that I have been pondering about, related to tyre sizes, was this.
My '96 C4 has 225/40 ZR 18 at the front, which have a circumference of 2002mm according to an online calculator that I found. The rears are 265/35 ZR 18s, which apparently have a circumference of 2019mm.
What I am wondering is how this works out in practice. In a 2wd car it wouldn't make any difference, but in a 4wd car it might do. Even this small difference of 17mm is significant. If the front and rear wheels were turning at the same rotational speed, which they could be since they are physically connected, when the front is doing 70mph the back would be doing 70.6mph! Obviously it isn't, so where does this difference go exactly? Does it result in more tyre scrub and hence wear, or does the transmission somehow take care of it?
My '96 C4 has 225/40 ZR 18 at the front, which have a circumference of 2002mm according to an online calculator that I found. The rears are 265/35 ZR 18s, which apparently have a circumference of 2019mm.
What I am wondering is how this works out in practice. In a 2wd car it wouldn't make any difference, but in a 4wd car it might do. Even this small difference of 17mm is significant. If the front and rear wheels were turning at the same rotational speed, which they could be since they are physically connected, when the front is doing 70mph the back would be doing 70.6mph! Obviously it isn't, so where does this difference go exactly? Does it result in more tyre scrub and hence wear, or does the transmission somehow take care of it?
09-07-2002, 09:11 PM
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[quote]Originally posted by Allen:
<strong>Maybe this is a dumb question, but what would be the impact of having this 0.7" difference?</strong><hr></blockquote>
If you had an AWD, the negative impact would be premature damage to the viscous coupling. Or, so they say. In your case, it would affect the ABS sensors to a certain degree as the computer is programmed to read a certain range of revolutions per mile. I gather this may not be a big issue but if you don't have a good reason to have a front tire that's 0.7" bigger, I wouldn't get it.
<strong>Maybe this is a dumb question, but what would be the impact of having this 0.7" difference?</strong><hr></blockquote>
If you had an AWD, the negative impact would be premature damage to the viscous coupling. Or, so they say. In your case, it would affect the ABS sensors to a certain degree as the computer is programmed to read a certain range of revolutions per mile. I gather this may not be a big issue but if you don't have a good reason to have a front tire that's 0.7" bigger, I wouldn't get it.
09-08-2002, 06:22 AM
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[quote]Originally posted by Allen:
Jean,
Are you on 18" wheels? What kind of tires do you have? I'm tring to figure the difference in height between your front and rear tires. <hr></blockquote>
Allen, I just took a very archaic measurement of both diameters and turned out as follows:F 235/40x18:24.4" and R:275/35x18: 25.2", a difference of 0.8". Bearing in mind the inaccuracy of my measurements, the sizes could be somewhat different, however no doubt that the rear is a larger diameter, anywhere between 0.5" and 0.8" I would say. My tires are Bridgestone S03's and wheels are Roock. FWIW, Took the 993 this week end to some desert twisty roads with a friend driving an F355 GTS, in sharp fast turns the 993 was far superior, both cars with stock suspension. Handling is excellent with this tire combination for fast street use. Cheers, Jean
Jean,
Are you on 18" wheels? What kind of tires do you have? I'm tring to figure the difference in height between your front and rear tires. <hr></blockquote>
Allen, I just took a very archaic measurement of both diameters and turned out as follows:F 235/40x18:24.4" and R:275/35x18: 25.2", a difference of 0.8". Bearing in mind the inaccuracy of my measurements, the sizes could be somewhat different, however no doubt that the rear is a larger diameter, anywhere between 0.5" and 0.8" I would say. My tires are Bridgestone S03's and wheels are Roock. FWIW, Took the 993 this week end to some desert twisty roads with a friend driving an F355 GTS, in sharp fast turns the 993 was far superior, both cars with stock suspension. Handling is excellent with this tire combination for fast street use. Cheers, Jean
