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I really like the 35 side wall tires as it lowered by car by 3/4 of an inch which means the CG is lower and weight transfer is less across the car and also front to rear. The downside is some will argue that they have trouble with their driveways and speed bumps. The 35 side wall does have a higher spring rate than 40's so think about your shocks. Back country roads are bumpier and add more vibration. However, turn in and steering control are much better with the 35's. One guy really tried to make a statement about the 40's he used due to his home hydraulic lift would not allow his car to be run over the lift's crossmembers without ramps. Well, I say that's his problem, for the rest of us who want this added car control without the negatives of shorter stiffer springs rates, that's our choice.

So, the question is where are you using your car? I am happy with my lower ride, especially the lower CG. I slow for speed bumps, swerve around manhole covers and pot holes. One unfortunate item is Bridgestone does not make a RE71R in 285/35/18. You have to order the 285/30/18, which is slightly lower still than the 275/35. My next set of RE71R's will be 265/35/18 f and 285/30/18 R as the contact patches are proportional to my 2 year old 255/35/`18'f and 275/35/18 r's. They fit my wheel wells/rims, but will put a few more marks on my LN deep sump skid plate as I daily drive my car.
 

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I really like the 35 side wall tires as it lowered by car by 3/4 of an inch which means the CG is lower and weight transfer is less across the car and also front to rear. The downside is some will argue that they have trouble with their driveways and speed bumps. The 35 side wall does have a higher spring rate than 40's so think about your shocks. Back country roads are bumpier and add more vibration. However, turn in and steering control are much better with the 35's. One guy really tried to make a statement about the 40's he used due to his home hydraulic lift would not allow his car to be run over the lift's crossmembers without ramps. Well, I say that's his problem, for the rest of us who want this added car control without the negatives of shorter stiffer springs rates, that's our choice.

So, the question is where are you using your car? I am happy with my lower ride, especially the lower CG. I slow for speed bumps and swerve around manhole covers. One unfortunate item is Bridgestone does not make a RE71R in 285/35/18. You have to order the 285/30/18, which is slightly lower still than the 275/35. My next set of RE71R's will have 265/35/18 f and 285/30/18 R as the contact patch are proportional to my 2 year old 255/35/`18'f and 275/35/18 r's and they fit my wheel wells/rims.
I'm using the car for maybe 2 track days a year and a lot of spirited driving in the canyons.

If I understand this right you want the rpm ratios on the tires rake to be similar to stock to not trip PSM. It seems 255/35 and 285/35 RS-4 are almost identical to stock and should not be a factor. That's also 30mm disparity between factory tire sizes so the balance should be similar at the limit.

I guess now I need to account for this also lowering my car? The 255/35 seems pretty close to the 245/40 in 18" sizing. I would prefer to leave my car at the same height it is on now (I am on 19" Cayman R rims with 245/275 PS4S tires on the wheels)

I know the smaller sidewall is better in terms of feel, but the car is essentially sitting at factory height as is. If its much lower than currently I'll probably start to hit some of my driveways I regularly use. Is the fix here to run 255/40 and 285/40 tires? That seems like a worse option.
 

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987 Cayman S:
18x8 w/235-40-18 +50et w/4mm spacer now +46 offset (flush)
18x10 w/265-40-18 +41et w/7mm spacer (flush) now +34 offset(flush)

actually +33 offset would be flush on the rear, but I chose 1.5 neg camber and wanted to make sure a 275 would fit next time...
 

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Porsche08, I would choose the 255/35/18 f and 275/35/18 r. I have a set of Michelin PS4's on my OEM wheels for wet weather racing. I use 18 mm spacers in f and 23 mm in the rear for these OEM offset wheels 57f 8 in and 43r 9 in. This is the result.
269333
 
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Porsche08, I would choose the 255/35/18 f and 275/35/18 r. I have a set of Michelin PS4's on my OEM wheels for wet weather racing. I use 10 mm spacers in f and 23 mm in the rear for these OEM offset wheels 57f 8 in and 43r 9 in. This is the result.
View attachment 269333
I think a 255 is way to wide for an 8” wheel?? .. your car looks great tho..
Thanks for the guidance tho.. I’m not sure on tyres yet, but I’m thinking S04’s... 235/275... I do plan on a second set of wheels, probably 19x8.5 and 19x10.5.. I’m a flush guy but not a stance guy.. it’s gotta be track worthy or it’s not going on my car... My 18’s are the ever common SR’s... but there a good wheel for the Ching

also getting an NR GT3 wing, other than that... it’s pretty good for now
 

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The wheel spacers actually do work to change the roll balance slightly. That is the reason I try to push out the fronts as far as possible, which does give a little more traction. In the front's case, a little less understeer, with full power just before the apex. The wider stance also reduces weight transfer across the car slightly. I have three sets of wheel/tires in the same size, except for the OEM wheels are 8 in f and 9 in r, while the others are 9 in f and 10 in rear. The OEM's tires do have more crown from being over sized. I use slightly less pressure in the front to get a good foot print. 245/35/18 would be the best combo with the 275 if you wanted to match the tires to the OEM wheels. The OEM rears seem to work ok with the PS4S's in 275/35/18 on 9 inch wheels.

I actually thought about buying a 9 in rear OEM wheel and mounting it in front. 43 off set would work with the amount of camber I use to tuck the outside shoulder inside the wheelwell lip on brake/turnin or bump/turnin. With the 5 mm spacers, I am at 42 on one set and 43 on another so I know they would work. It would be great to see someone using the square 9 inch combo with a lowered car and race tires. The 255/35/18 Michelin's would then fit perfectly. Maybe I will look on e bay to find a set of OEM rear wheels to match mine and have the 255/35/18's.
 

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The wheel spacers actually do work to change the roll balance slightly. That is the reason I try to push out the fronts as far as possible, which does give a little more traction. In the front's case, a little less understeer, with full power just before the apex. The wider stance also reduces weight transfer across the car slightly. I have three sets of wheel/tires in the same size, except for the OEM wheels are 8 in f and 9 in r, while the others are 9 in f and 10 in rear. The OEM's tires do have more crown from being over sized. I use slightly less pressure in the front to get a good foot print. 245/35/18 would be the best combo with the 275 if you wanted to match the tires to the OEM wheels. The OEM rears seem to work ok with the PS4S's in 275/35/18 on 9 inch wheels.

I actually thought about buying a 9 in rear OEM wheel and mounting it in front. 43 off set would work with the amount of camber I use to tuck the outside shoulder inside the wheelwell lip on brake/turnin or bump/turnin. With the 5 mm spacers, I am at 42 on one set and 43 on another so I know they would work. It would be great to see someone using the square 9 inch combo with a lowered car and race tires. The 255/35/18 Michelin's would then fit perfectly. Maybe I will look on e bay to find a set of OEM rear wheels to match mine and have the 255/35/18's.
Ya, square setup would have to be the case if you 1 Lap it forsure... I’m looking at CCW’s for a precise perfect offset... First I’m going to fix the camber a little a then re-measure. I’m still on struts/spring setup and it’s going to stay that way.. I’m finished with coilovers... which reminds me, I was going to call Swift to see if they will make springs for the 987.... they are the best springs I’ve ever owned..

question for you tho... I’ve had 275-40-18’s on another car and I think the side wall starts to get chunky... would a 275-35-18 work better in this case ?? 35 vs 40
 
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