Hi all, I've been wheel to wheel racing my S2000 for 4 years now and continuing to develop the car.

Ive recently been thinking about increasing the grip and therefore widening the track on the car. I currently use Enkei PF01 8" front et 50 and 9" rear et 60, with 235 and 255 tyres respectively. These are near perfect offsets without modifying the wheel arches although some rubbing with -3 deg on the front.

Im guessing there are 2 options, to go for a much lower et and something like 9" all round, and modify the arches or keep a sensible offset and go something like 10". I'm not sure on the impact to the geometry setup of the car with either option (going to be more load so possibly more camber needed for a same wheel size) and if the latter option would interfere with any suspension components as you're effectively going further in towards the centre of the car.

I also have Stoptech calipers on the car so need to clear them with any revised wheels.

I'm sure this has been looked at before so any threads would be appreciated.

 

Do you plan on changing tire size to be able to run a non staggered setup?

Also are you looking for suggestions where you won't have to roll the fenders?

 

If you want a wider track your going to have to either run spacers or get another set of wheels with a lower offset and then roll fenders. If your just looking for more contact patch, neither is a requirement compared to what your running now. With the right offset and width wheel, you can run up to a 9"/245 F - 10.5"/285 R without fender modification/rolling, assuming your running a reasonable lowered ride height. If you want to get more creative with the stock fenders such as rolling and pulling with a little inner "manipulation", you can run up to a 10"/275 F 11.5"/315 R, putting your contact patch at the most inner and outer limit of what the stock s2k body can accommodate, increasing the total effective track width per side at right about 40mm in the rear and 30mm up front over factory wheel position/offset. It goes without saying that the inner contact patch will be increased as well, but your question was focused on increasing track width.

 

Is your intent to increase grip or widen the track? While not mutually exclusive, it is certainly possible to increase grip while minimally increasing track.

Grip is easy: add wheel/tire and you add grip. Many people can say "add 10mm tire and drop 1s per min on track". I can talk the pros/cons of a widened track when autocrossing or on track, but I can only speak to the real world impacts when autocrossing. The theory is to raise the roll centers, decrease the moment arm, and decrease roll, thereby increasing grip when loaded. To understand the impact of a wider track, read up on scrub radius and roll centers; the math isn't terribly difficult. It isn't as easy to determine the benefits of a wider track- you can't say "add 10mm track and drop 1s per min on track".

Increase grip:
You can start by going to 255/40-R17 on 17x9+63 all around. Some wheels will clear the StopTech ST-40 (TSW Nurburgring) while 949 6ULR and Volk CE28N need +55 (8-10mm spacer). Fitment of a 255/17x9+63 requires little to no fender modification. Your next step up would be a 9.5" or 10" wheel, followed by a 275. Fitment much beyond the 255/9 will require some rolling or pulling.

Widen track:
You can lower the offset or add spacers, either of which will necessitate fender pulling or widened fenders. The proper way to widen track is to widen the arms themselves, not push the wheel centerline beyond the hub.

Back to increase grip:
With modifications for widening track you can step into 10"+ wheels and 275mm+ tires. At this point you likely switch to an 18" package. Unfortunately I don't have the offsets for a 10.5" or 11" but a few people here run them.

 

The easy button is the 17x10 +55 Forgestar setup that I am running. I run it square with either a 275/35/17 Maxxis RC1 or a 245/40/17 Hoosier A7. They clear the Stoptechs easily and you can customize your offset if you want a wider track. My fenders are all OEM with a roll and a slight pull. Other options would be the 17x10 +50 Advan RZII or the 17x9.5 +50 Volk CE28Ns.

 

Although I agree with just about everything you say, and its a good explanation, I do have to disagree with the mechanics of how wider track width improves performance. Although the wider track width will have a small effect on roll centers it will be very small. According to our 3D suspension model adding 10 inches of track width (~17%) only raises the roll center enough to decrease the roll moment by about ~1.5%. Additionally the roll moment doesn't have a much of an effect on the performance of the tires.

The reason that the wider track improves performance is that you are reducing the load transfer by increasing the track width to CG ratio decreasing the load transfer during cornering. In the above example the load transfer is decreased by 17%. This improves lateral load transfer because of the load sensitivity of the tires. Load sensitivity is the fact that as a tire's load increases, it's coefficient of friction decreases. Effectively two tires with 500 lbs vertical load each can produce more than a single tire with 1000 lbs load. By decreasing the load transfer you move closer to having two equally loaded tires and as a result increase the potential cornering performance.


Also worth mentioning that increasing track width increases frontal area and therefor drag. Everything is a trade off and here you are trading cornering performance (and therefor corner exit speed) for straight line performance. Usually corner exit speed trumps end of straight speed but it depends on the specific track. Tracks with longer straights will put more emphasis on low drag, track with more corners will put more emphasis on corner apex and exit speed.

 

Thank you for the data and explanation. I didn't articulate the load transfer well; you and Ross Bentley (Speed Secrets) articulated it far better. I did some calculations on widened tracks some years ago on some M3s but unfortunately I can only offer track width theory for the S2000.

 

One thing to note when playing with track widths is that while any increase in track width on a single axle will increase steady-state grip at both axles, it will increase it more on the opposite axle than on the axle you widened. So increasing rear track width will actually edge the grip balance more towards oversteer than understeer, which is counter to most people's "common sense" expectation. That's why you'll notice that when manufacturers make that "hardcore" track version of a car with extra power, they almost always increase front track width, and why many supercars have wider front tracks than rears. Unfortunately the S2000 has a wider rear track from the factory and not a ton of room to increase front track without messing with the fenders (plus you push the tires out into the airstream). There are also small differences in wheel rate when you change the track due to changed leverage (pretty small though).

Despite the compromises, I use spacers to get maximized front and almost maximized rear tracks for my given fender rolls. I rub slightly on my bumper and fender up front. Although my end-of-straight speeds haven't changed much from my stock-wheel days, my lap times are faster. Might be interesting to take off the spacers again to compare again.

 

Very good point thomsbrain. By increasing the average track width you are decreasing the total load transfer and therefore increase the total grip. By increasing a single axle's track width you are effectively adding more antirollbar bar to that axle. Roll stiffness is a function of single wheel vertical stiffness and track width so increasing the track width is roughly equivalent to adding antirollbar bar to that axle.

 

I disagree. An anti-roll bar increases weight transfer at its axle while a wider track width decreases weight transfer at its axle. They have the opposite effect.