I thought I read someplace where someone was claiming that by increasing the track via wider wheels and tires a few inches(or even spacers) it was equivialant to a 100hp increase in power on large track

I know that is just way too much of a general statement, but could it be based on facts??

wider track will only help you getting around corners faster.
which could help you getting times closer to the car with 100HP more than yours. if that's what he meant.

bigger tires is more surface-friction and might also lower your CW (what's CW in english? you know, air-friction/resistance constant) ...

Andy

Coefficient of drag?

aha, looked it up in the dictionary, it was actually in there:

der cw Wert = air drag coefficient

voila!
Andy

I added 3/4 inch of spacer to each side, front AND rear and the turns at Willow Springs seem to be a little easier to take. I can't give a real idea yet as I have only done one race with the new six installed and the gearing is a little off. Makde sure you use the long Porsche racing wheel studs and steel nuts.

John,

Any way of quantifying the increase in steering effort?

i'm not john, but i will answer anyways

having driven both quite a lot, narrow body and wide body cars,
i can say that there is a very noticeable increase in steering effort.
my car has 225/50 on the front on 7" wheels with 1 1/4" spacers,
the wheel comes out all the way to the lip of the GT flare.

yes, you have to work the steering more, especially when going slow (like getting into a parking spot) BUT:

the steering (while driving) actually feels MUCH more precise and stable.
the feedback from the suspension through the steering wheel is perfect.
you can feel exactly where your car is in terms of grip or understeer.
also, the steering is much more responsive (which is a guuud thing!)
the car actually goes where you want it to go without hesitation.

if you get a chance, get in a wide-body car (that has a wide track too, i hate it when people slapp on flares and don't widen/match the track )
and throw it into some hard corners. you'll know what i'm talking about

Andy

As noted, high speed seems better. I don't do much low speed driving with it, especially with the Goodyear slicks but it seems a little harder to turn such as getting into pre-grid or something like that. It would be expected since one side of the steering lever just got a lot longer when the spacers are added.

I was curious, because I have already installed a 320mm Momo, and steering effort, as expected, increased.

I do know from racing the Sentra (with a 13.5" Grant) that once the pack hits the straight towards the green that things like higher steering effort and tight harness belts don't really get noticed unless they are extremely painful. My focus is elsewhere, until the cool off lap.

Widening the track can be benefitial to lap times, but there is more than one way to do it. One way is to increase the offset of the wheels, which is by far the most common approach. This is what you are doing when slapping wide rims under a body kit. It can also be done with spacers and stock rims. In either case, you are messing around with the suspension geometry and will usually be making some sort of tradeoff. Bearings will wear faster. The scrub radius is increased, making steering harder, tires wear more, and it will cause more "feedback" from surface irregularities (not always good, btw). I believe it would also change the wheel rate. Basically, it is a hack. Race cars often do it because they are typically restricted by regulations from doing it right and they are more than willing to live with the tradeoffs. The "proper" way is to literally move the suspension outward and/or change the geometries (like kingpin inclination). This is how it would be done by the factory or by well-funded race teams in advanced series. Not exactly grassroots DIY stuff.

I see no problem widening the track of a car moderately, as long as the benefits outweigh the tradeoffs. Like lowering the car, less is often more. Be conservative as you can afford to be.

BTW, the reason a wider track is "better" (in some respects) is because it reduces weight transfer. Weight transfer is "bad" (in some respects) because while the grip of the loaded tire increases, it does not increase at a greater rate than that lost by the unloaded tire (presuming good camber control, etc). Other ways to reduce weight transfer include lowering the Center of Gravity (CG) or reducing the weight of the vehicle. Increasing the wheel rates and/or roll stiffness can also help in a practical sense. So, there are alternatives that are equally effective and often less costly in terms of tradeoffs. This is all oversimplified, but true in general presuming I didn't mistype or have a brain fart.

Do you have any experience when the tradeoff occurs concerning scrub radius and increased front track?

Mike T

Well, any change in scrub radius creates a tradoff by definition. No way around that. It might be a net gain or a net loss, depending on your perspective. If you draw a line through the upper and lower ball joints, you get the kingpin inclination. That line intersects the ground and the difference between that location (center of rotation) and the center of the tire is the scrub radius. If they were the same (zero scrub radius) the effort to turn the wheel would be minimized (best leverage). Also, feedback from imperfections in the road surface will tend to be minimized (again, best leverage). And, so on. The suspension is designed with a certain scrub radius in mind and changing it (like changing anything in the suspension) is pitting your knowledge against that of a highly trained engineer. Now, that doesn't mean you can't accept certain tradeoffs the engineer didn't have the luxury of making and use some common sense in keeping things reasonable. If the car has very light and numb steering, increasing the scrub radius a little s not a bad 'hack' (buying a tigher ratio steering box might be the proper solution). But, if a quarter inch is nice, that does not mean 7/8th is better. And, I would tend to do this after more obvious ways of reducing weight transfer, like lowering the car an inch or so (again, in moderation) or removing excess weight. Anyway, the proof -- and consequences -- are in the pudding; experience is the best judge. I'm not telling anyone not to put on a wide body kit and run super wide wheels/tires on a stock suspension, but you should at least be aware there are potentially real tradeoffs. Just a heads-up.