Help with Tire Selection (sizing)

[Kirill]

Need to get new tires for SLK

My stock sizes are: 225/45ZR17 and 245/40ZR17
Rims are 17x7.5 fronts and 17x8.5 rears

I want to get GoodYear Eagle F1 GS-D3
Currently Available Prices and Sizes

Problem N1: 245/40ZR17 out of stock for 4-6 weeks.
Problem N2: Tires are bald and I caught a screw in a driver side rear (it leaks slowly)

Should I try going with slightly wider rubber ? Like 255/40/17 (in stock at TireRack)
But than, I can't get 235/45-17 for front in GoodYear Eagle F1 GS-D3.
Should I go 225/45ZR17 (front) and 255/40/17 (rear) ? Per:
Tire size calculator that will give 0.2% difference in diameter front & rear

Car tends to understeer on stock rubber, so i am afraid if I'll go wide on rear and stay the same on front - it will make it even less stable.


I realy like to get GoodYear Eagle F1 GS-D3 as they supposed to have high grip and be quiet. (very important for convertible)

[Kirill]

Or may be I should just order Goodyear Eagle F1 Asymmetric

[Arnel]

how much negative camber in the rear? Most manufacturers intentionally add NC to understeer. Perhaps you can go with the 255's and dial out some NC to balance out the larger size, and even add more NC to the front. Make sure you have clearance with the rear fenders.

PS, I'm real happy with the F1 GSD3's. Sticky, quiet, and for low treadwear ratings I still have plenty of life left with 25k miles on them. Though I frequently check my alignment and set toe to zero.

[fretburnr]

Another option - 255s in the rear as you suggested, and 235/40 up front. pretty common sizes, should be in stock. A 10mm bump in section widths front and rear makes the % stagger less; therefore it should be just a hint less understeer.

(225/245 = 91.84%, vs 235/255 = 92.17%)

[Arnel]

also, how about another source besides Tire Rack? I just checked and it looks like discount tire.com has that size in.

[Kirill]

Originally Posted by Arnel

also, how about another source besides Tire Rack? I just checked and it looks like discount tire.com has that size in.

I called Home - Discount Tire Direct - they don't have them in stock either and they called Goodyear and were told the tire is out of production. I don't know if they going to make another batch, but I know people on SLK boards had problems getting replacements for few years - so If i'll need a replacement it may take a while.

discounttire.com is $1003.39 compared to $687 at tirerack

[Arnel]

Originally Posted by Kirill

discounttire.com is $1003.39 compared to $687 at tirerack

ouch. For that price, I'll step up to PS2's or whatever the best tire is currently.

I was going to suggest buying just the rears from them, but then I think you wouldn't qualify for the $50 rebate.

[Kirill]

Originally Posted by fretburnr

Another option - 255s in the rear as you suggested, and 235/40 up front. pretty common sizes, should be in stock. A 10mm bump in section widths front and rear makes the % stagger less; therefore it should be just a hint less understeer.

(225/245 = 91.84%, vs 235/255 = 92.17%)

Yeph. That's the good option
So now it's 235/40ZR17 & 255/40ZR17 Goodyear Eagle F1 GS-D3 Blackwall
or
225/45ZR17 & 245/40ZR17 Goodyear Eagle F1 Asymmetric

I like "pine tree" pattern of GS-D3, but it may be out of production and I wouldn't be able to get replacement. I get wider rears that should help reduce wheelspin when i put the power down.

I am not a fan of "off roading" pattern of F1 Asymmetric, but it's a newer tire, rated higher for dry handling and quietness of ride

Difference in price is 6$

[Kirill]

Originally Posted by Arnel

ouch. For that price, I'll step up to PS2's or whatever the best tire is currently.

I was going to suggest buying just the rears from them, but then I think you wouldn't qualify for the $50 rebate.

No more PS2s for me - Its just a freaking nail magnet. And goodyears rated better.

[Kirill]

255/40 is not available in Goodyear Eagle F1 Asymmetric - so going wider may be a problem
But 235/40 is available in Goodyear Eagle F1 Asymmetric

[Kirill]

Originally Posted by Arnel

how much negative camber in the rear? Most manufacturers intentionally add NC to understeer. Perhaps you can go with the 255's and dial out some NC to balance out the larger size, and even add more NC to the front. Make sure you have clearance with the rear fenders.

PS, I'm real happy with the F1 GSD3's. Sticky, quiet, and for low treadwear ratings I still have plenty of life left with 25k miles on them. Though I frequently check my alignment and set toe to zero.

I think it's somewhat complicated to tune camber on SLK - so i want to keep stock settings.

[Kirill]

Called the tirerack - they suggest GS-D3 over Asymmetric
So it's 225/45ZR17 & 255/40/17 in Goodyear GS-D3 and play with tire pressure to adjust handling.