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Discussion Starter #1
When I first bought my Sky it was equipped with the Goodyear GSA's. They were 245/45/18. First problem I had was the they rubbed in the rear. Second wet traction was horrible and finally they were too soft in the turns. I decided to swap the tires out for Toyo Proxy 4's. I went with 245/40/18. Not only did the rubbing go away wet traction improved probably 300%. Dry cornering improved so much my Sky now puts my heavily modded WRX to shame in the twisties. Last by going to a 40 series from a 45 series it increased acceleration. I highly recomend this swap to all Sky and Sol owners.



 

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I've been looking for someone to swap rubber for me. All the tire dealers I've talked to so far want to hose me really bad on a swap.
 

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Discussion Starter #3
i went to this place called Big D tire in buffalo ny they did the swap for free
 

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For those not in the know though you gotta remember that swapping to a lower profile tire will throw of your speedometer, also increasing the gap between the fender wall and tire by 0.5" which can be very noticeable, and also lowering top speed in a gear.

The speedo will be 3.6% off equating to when it reads 60mph you're actually going 57.8 mph. This is a great tool for figuring these things out;
http://www.miata.net/garage/tirecalcold.html

This also correlates to top speed in a gear too. Instead of maxing out at 60mph in 2nd gear you're now going to max out at 57.8mph. Not much of an issue unless you're doing auto-x and top speed in 2nd gear can be pretty important. So far dropping down to 245/35x18 hasn't stopped Dasto from winning in his Solstice though. :thumbs:

I have 245/40x18 tires on my race wheels and once they're on the car the 0.5" extra space in the gap is amazingly pretty noticeable. It might actually be 1" of increased gap, because I know 245/40x18 drops the cars ride hight 0.5" so that probably adds up on both sides to a 1" gap increase.
 

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Bentril, I saw one of the SS/B Sol at the national Solstice convention here in KC. It had 245/35x18 Hoosiers.
IMG_0121.JPG
If you click on the picture you'll see how empty the wheel well looks. It is also interesting how "square" they look on the rim. This may be why Tire Rack is talking up 285-295 width Hoosiers for autocross. That is only 1.5 to 2 inches wider than the 245's and should be okay.

That said, for street use it is best to stay with the original spec tires for street use. Many reasons. First, 18" are a pain to mount even in a standard size. Oversized lower profile tires could be nearly impossible!. Second, the Hoosiers will work because they are a softer competition tire (marginally DOT approved!). Third, shorter profile tires will throw things off just as you say. Fourth, lower profile tires are even MORE prone to carcass and rim damage than the 45's. Last, a mile or two and hour difference in an autocross won't matter. The Redline and NA Skys have different final drive ratios. So, it won't really make much difference as most autocross courses are designed NOT to be that fast as it starts bumping up against safety issues and Solo 1 restrictions.

Bottom line, it is my most humble opinion :lol: that one should stick with the standard size tire that comes on the Sky.:thumbs:
 

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Discussion Starter #6
i understand that the speedometer might be a lil off, i am more prone to rim damage and there will be more wheel gap. my point is that i like to push it everywhere i drive and the stock goodyears where holding me back quite a bit. going from a 45 to a 40 series wasn't that big of a difference where it is going to out weigh all of the bonuses of have a higher performance all weather tire for weekend cruising.
 

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Homer said:
i understand that the speedometer might be a lil off, i am more prone to rim damage and there will be more wheel gap. my point is that i like to push it everywhere i drive and the stock goodyears where holding me back quite a bit. going from a 45 to a 40 series wasn't that big of a difference where it is going to out weigh all of the bonuses of have a higher performance all weather tire for weekend cruising.
The profile is not where you will get a handling improvement. It's mainly a compound issue in these types of low profile tires. Call Tire Rack and see what dry weather performance tires they have. There are a lot of companies that produce what you are looking for and probably have the correct sizes.
 

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snaponbob said:
The profile is not where you will get a handling improvement. It's mainly a compound issue in these types of low profile tires. Call Tire Rack and see what dry weather performance tires they have. There are a lot of companies that produce what you are looking for and probably have the correct sizes.
snaponbob - you're right that compound plays into the tire handling, but profile (actually sidewall height) is also a very important part of the overall performance.

The profile affects the "shape factor" of the carcass of the tire, along with the carrying load and load effects on cornering stiffness and the contact patch. The compound determines what you can do with the contact patch as the tire goes from linear region to the limits of adhesion. It's not THAT simple, but it does work like this to a large extent.

If you have two tires of very similar compounds and constructions, a 40 series will generally be stiffer and carry less load than a 45 of the same section width. IN GENERAL... :thumbs:
 

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You are correct. BUT ................. as cars become more slaved to on board computers it is more and more important to keep things "in spec" so that there are no operational issues.

A lower profile tire should "handle" better, but a crappy compound on a 30, 35, or 40 series tire makes for a crappy tire!! What might look good may not work well. Ask anybody that had a Firestone 721 come apart!!!

Specifically in reference to Kappas, they come with Goodyear 245/45x18s as we all know. The non-turbo has its own compound and the GXP/Redline will have F1's. I have owned GM vehicles for years, and for the love of god, GM specs weird tire sizes. I have owned 3 Silhouttes and the tires are goofy sized!! An important issue is keeping everything within the allowable parameters that are in the on board computers software. Why? If a big enough variance is imposed upon the computers due to tire size then codes COULD be set because wheel/vehicle speed vs. engine speed could screw up the stability and abs controls. Granted, a change from 45 to 40 series shouldn't cause computer issues, but the trip/mpg cals will be off.

If I were to be looking into lower profile tires then I would do a bit of study work on Tire Rack's site. The key numbers are going to be Revs per mile and overall diameter. You may be able to "cheat" up to a 255/40x18 and have it fit well. Then you will have a lower profile tire with more availabe tread on the ground. Best bet, though, is simply buying a better compound in the correct size.
 

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Discussion Starter #10
this could be argued all day but my point was simple. drivability increased, its more fun in turns and better in the rain.
 

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snaponbob said:
You are correct. BUT ................. as cars become more slaved to on board computers it is more and more important to keep things "in spec" so that there are no operational issues.

A lower profile tire should "handle" better, but a crappy compound on a 30, 35, or 40 series tire makes for a crappy tire!! What might look good may not work well. Ask anybody that had a Firestone 721 come apart!!!

Specifically in reference to Kappas, they come with Goodyear 245/45x18s as we all know. The non-turbo has its own compound and the GXP/Redline will have F1's. I have owned GM vehicles for years, and for the love of god, GM specs weird tire sizes. I have owned 3 Silhouttes and the tires are goofy sized!! An important issue is keeping everything within the allowable parameters that are in the on board computers software. Why? If a big enough variance is imposed upon the computers due to tire size then codes COULD be set because wheel/vehicle speed vs. engine speed could screw up the stability and abs controls. Granted, a change from 45 to 40 series shouldn't cause computer issues, but the trip/mpg cals will be off.

If I were to be looking into lower profile tires then I would do a bit of study work on Tire Rack's site. The key numbers are going to be Revs per mile and overall diameter. You may be able to "cheat" up to a 255/40x18 and have it fit well. Then you will have a lower profile tire with more availabe tread on the ground. Best bet, though, is simply buying a better compound in the correct size.
:agree: :agree:
 

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When I first bought my Sky it was equipped with the Goodyear GSA's. They were 245/45/18. First problem I had was the they rubbed in the rear. Second wet traction was horrible and finally they were too soft in the turns. I decided to swap the tires out for Toyo Proxy 4's. I went with 245/40/18. Not only did the rubbing go away wet traction improved probably 300%. Dry cornering improved so much my Sky now puts my heavily modded WRX to shame in the twisties. Last by going to a 40 series from a 45 series it increased acceleration. I highly recomend this swap to all Sky and Sol owners.



I totally agree, the 245/40/18's makes a HUGE difference(for the better) in overall handeling of my redline....and if having a "slightly smaller" tire is the price I have to pay, it's worth it.....and with all the "rubbing issues" folks are having with the stock 45's, that's one less thing I have to worry about...
 

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This is all interesting reading folks. However, I have not heard of ANY issues or rubbing problems with either the Sky or the R/L regarding "rubbing" with the OEM tires. Those OEM tires were selected for a reason we will all agree. The only people that have found problems were those that modified their cars, IE; different shocks/springs, and or lowering their cars, or have done other modifications to the body or other wheel well area changes.

I was also under the impression that a smaller tire makes for a "harder" ride because of using a lower profile tires gives less of cushion between the road and the rim. I would think that if you buy the same exact tire as the ones we are taking about here, at the correct size, the ride would be "just as good" as far as handling. I would have to see proof to convince me otherwise. Now I am not a racer mind ya, I love and want performance, but I also want a somewhat comfy ride, and not get hammered when hitting a little bump.. Also throwing off the speedo, and all the dics mileage calculations bothers me also, since it'll throw everything off IMO. Also, donno if changing the size of the tire will effect warranty, with lets say shocks or brakes should something fail and they can point to the smaller tires..

I will agree with snaponbob and will replace the OEM tire with one of the same size, but with a better quality one for the way we drive down here & for the weather we have. Lotta rain, hot sunny days, no snow ice or sleet, but I don't want F1's either. Haven't decide yet on a brand, but I have partial to Michelons all my life, but I have purchased other brands when I thought it was a better tire and a better price. We'll see what is out when the time comes, tire manufacturers are always coming out with new "improved" rubbers..

BTW, nothing wrong with what ya'll have done, it again just come down to personal preferences, which is what makes us all so unique and special as individuals..:thumbs:

Finally, my RSA's have done pretty well. I rotated them every time I went in for oil change (about every ~6k miles) they have over 25,052 as of 1/7/09, and can still go another 5-10,000 miles looks like. So they are not bad for what they are as far as wear. Now also keep in mind, we drive normal with the Sky, no racing, no peeling out, no tire squealing and no donut driving..:D Other than that, not a bad tire at all really... :thumbs:
 

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My car's suspension is stock, with the exception of the Kappasphere reBar on the back. When it comes time to replace the tires, I'm going to go the other way, and replace the stock 245/45's with 225/50s. The overall diameter will increase slightly, from 26.68 to 26.85, so I'll have a little more sidewall to absorb the bumps and potholes. No way I'm going to a lower profile tire, the car rides hard enough as it is, and I don't want to increase the wheel well gap.
 

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I too would not stray from a stock overall diameter tire. If you really want to go to a lower profile, I would say go get larger rims........put some 19's on that bad boy and you will keep your speedo and get the harder ride/tighter handling! And it will look way more bada$$

Just :jm2c:
 

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This is all interesting reading folks. However, I have not heard of ANY issues or rubbing problems with either the Sky or the R/L regarding "rubbing" with the OEM tires.
Agree. If anyone is having a rub issue on stock, the suspension is out of spec, not the tires. In fact, changing tires to "fix" the rub might be bad. Cures that hide the disease are often worse than no cure at all because they give a false sense of cure while the disease continues to thrive.
 

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Agree. If anyone is having a rub issue on stock, the suspension is out of spec, not the tires. In fact, changing tires to "fix" the rub might be bad. Cures that hide the disease are often worse than no cure at all because they give a false sense of cure while the disease continues to thrive.
Homer installed Kappasphere Lowering springs AND had a Major accident with his SKY , the rubbing is probably due to one of those issues. Just a guess. :dunno:

http://www.skyroadster.com/forums/f2/installed-kappashere-springs-8596/

http://www.skyroadster.com/forums/f2/wrecked-my-sky-18338/
 
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