Carpokes Porsche Forum

So many performance cars from a variety of Manufacturers build in push ( understeer ) in their cars by using a smaller than necessary front tire. This is super common and Automakers Worldwide have a tendency to build in various safeguards to possibly keep drivers using some modicum of common sense. Corvettes, Vipers, Mustangs , etc . often come with front tires that track oriented drivers know they will likely swap out when they are worn, or the die hard ones jump right in with different wheels and tires right away. Mustangs for years have had the dinkiest tires up front and not much bigger in the back and drivers of this Blue Oval Model found out soon they need to mount wider rubber to compete with Camaros -- GM stuffed some big auto donuts on their machines. In later years Ford put some better and bigger meats on their performance models and times on road courses and autocrosses showed the difference.
Now, why am I going on this diatribe against other Manufacturers and not mentioning our little Stuttgart speedsters, well it is simply to demonstrate that Porsche is not the only one putting bicycle tyres up front. Many of you will replace your standard size tires for PCA, SCCA, NASA or other track or autocross events and whether you downsize or stay in the standard size there is one item you need to be aware of. With most of the cars I have owned and tracked , a common practice was to look for a front tire and a rear tire with the same diameter. Sure I would go wider, and maybe even a shorter diameter than stock, but matching front and rear seemed like a great set up for balance , cornering , etc. Well, no, no, no with the Cayster since the Stability Management System goes wacko if you don't have a slightly smaller diameter up front. If they are equal the sensors can get confused and think the front is not rolling right --- think back tires spinning and therefore actually going faster than the front. Those of us who have had to Dyno our cars for NASA have found out the hard way that you must find a Dynojet 4 Wheel drive Dyno and not just the conventional one. You must find their newest and most expensive unit so it can make sure the front wheels work dynamically matched to the rears. Trust me, I spent too much time and miles finding a place that could do it on my 24 GTS.
This long note is to suggest if you are looking to change or upgrade tires ( mainly for you performance folks ) go to Apex wheels and drop to the bottom of their Website ( or call and chat with Brandon ) to see how much wider you can go front and back and what tires they have tested. Obviously they can not completely keep up with all the new tires and models, but this really gives you a good idea on what should work. I found no less than 4 tires I thought would work with my car
at a equal diameter balance but I remembered in the back of my mind a past conversation I had had with Brandon. So two brands are out of the question, but with my Tarett Camber plate and GT3 A arms ( soon to be installed ) I should be able to get up to 265s up front. I hope this helps others, because with many of us running 18s and 19s, we want more tread on the ground, but at the price of competition tires now, this may help someone not make a mistake.

Great Post and thank you for sharing your experiences.

Excellent information.

I am fairly careful with newer cars to make sure I do not inadvertently void the Porsche warranty if the car is still covered. For my cars there are a number of approved alternatives as it happens and Porsche/Michelin have just released a new tire for the 992RS which is apparently superior for wet handling.

It is very unlikely a different tire choice would void your warranty RD, but I can sure appreciate you being cautious in other areas. I will admit this note is more for the folks who want to get more aggressive tires , whether DOT Competion ones or 200 TWR ones for instance, and would likely be looking at 18 or 19 inch wheel alternatives. Regardless , the key is that it is not likely optimal to use tires with the same diameter front and rear.

PS - I listed Brandon's name from Apex Wheels because someone with a discerning eye may notice a couple of choices they have listed are likely too close. This company will answer the phone and be happy to chat technical with you and the guys there practice what they preach ( virtually everyone is a track rat ).

PSPS -- they have new hub centric locking hub wheels for the GT 4 RS also!

I was a bit surprised. Apparently for the 718 GT4 with 20" wheels Apex likes the stock 245/295 fit.

In the Goodyear SC3 I've found the 295s almost impossible to find and the 305 about $100/tire cheaper. This would tend to increase understeer a bit but I'm not good enough to really notice.

OTOH, TireRack has just added the new Falkin 660+. The 295/20 is available and a lot cheaper than the GY 295. The 660 was reputedly a bit slower than the GY. The 660+ may be comparable to the SC3 but I've seen no reviews. Still, from a price standpoint it is probably close enough!

I think part of the issue is the 20 inch size and there simply are not alot of choices , regardless. I know many of my friends with GT4s have switched to 19" wheels for more choices. I chatted with a couple Engineers at the Solo Nationals in Lincoln, Nebraska , last September and have since talked to a buddy of mine who asks to remain confidential, but I would imagine the 660+ to be faster than a Goodyear SC3. One big plus for our cars is when the outside edge starts to wear is that the Falkens can be flipped as they have a symmetrical design. So overall cost may be even better.

PS - if you check TireRack and the RT660 Tests you will notice the Falken comes out near the top in their test, and then zipping over to Grassroots Motorsports the RT660 ranks higher than the SC3. I know the carcass has been changed on the 660+ ( tread design the same ) so I would sure believe it will continue to be a faster rubber donut and as you noted less money. The Falken also is stronger for those who want to also run an Autocross with their Porsche.......much faster initial heat up than a Goodyear SC3.

Sad Goodyear has not put the F1 SC 3R in sizes to fit a 20 inch rim , as that is a hot track tire.

When I put Falkens on my Cayman T, a number of folks remarked they would not put 'cheap tires' on their Porsche. Falkens merely cost much less than comparable big-name tires. I am completely satisfied with mine, and likely will buy Falkens again.

For my street tires, the total cost for four was just about half of Michelin, and the warranty is double.

Sumitomo Tires owns Falken and they are one of the largest Tire Companies Worldwide. They had a Plant in Buffalo making some Falkens so that would contribute to a lower price, but that supposed closes this year if not already. That could be part of the price, and if the future sees all the Falkens built overseas we may see the price go up. They are the tire used by the Major Drift Series as well as have been for the Optima Street Car Challenge and they are well respected in the performance genre. The new 660+ is out now and though reviews are slim it is likely better since Falken has spent plenty of time in the top area in Autocross and Track Time and many imagine they want to be a strong challenger again.

Solid comments from ReidMcT !

WillyDaP wrote: Thu Feb 27, 2025 8:23 am I would imagine the 660+ to be faster than a Goodyear SC3. One big plus for our cars is when the outside edge starts to wear is that the Falkens can be flipped as they have a symmetrical design. So overall cost may be even better.

660+ better than SC3 was my thought but I've seen no reviews yet. I have swapped the SC3 in the past. I'm going with -3° front chamber this year to see if that reduces the need to do it. Swapping is a real pain if all you have is a couple of jacks. Fortunately this is more of a front problem than rear, which reduces the labor.