Quote:
Originally Posted by cycleboy
Curious about your definitive reasoning there Suberman?
I'm no expert for sure, but I'm also going to 17X8.5 w/ 245/40/17 and going to save about 3-4 lb per corner over stock.
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Wide tires just give you a wider and shorter contact patch, generally speaking. Although this site is very interesting:
http://bndtechsource.ucoz.com/index/...alculator/0-20
Wider and shorter contact patches do not give you better grip, that's a physics thing: total grip is coefficient of friction times area, assuming weight (pressure) is constant. Put another way: coefficient of friction is grip divided by weight with weight being very approximately one quarter of the vehicle weight. As weight goes up due to dynamic forces (called weight transfer) the coefficient of friction remains the same but total grip goes up. So does loading so the net result is the necessary grip remains roughly proportional to the extra load, the coefficient is a constant. For tire rubber this is not strictly speaking true as the rubber isn't just a friction device but the way the tread moves across the road surface (slip angle) also affects total grip. However, it is broadly speaking true.
So, how wide is too wide? A better question is how wide is wide enough?
Shorter contact patches are not so good for acceleration and braking. For cornering you get sharper turn in and a higher rate of rise for total grip but when a wider tire lets go it let's go more suddenly than the taller and narrower profile.
The important thing to grasp is that total tire grip is heavily dependent on tire compound and structure. The tire profile is nowhere near as important. The wider tire will not grip better than the narrower tire.
So, the stock sized 215 tire works very well, although the rubber compound fitted is hopeless. Going up to 225 certainly looks better. I prefer the slightly taller and softer feel of the 225/45 profile. This is a tiny bit over sized circumference but only by under 2%.
The size chosen by Toyota for the European TRD package is 225/40x18 which is exactly the same circumference as the 225/45x17 I chose. Interestingly,Toyota fits this tire to the ideal 18x7.5 rim, not 18x8 which you might be tempted to fit. I'm pleased I followed my instinct and bought 17x7.5 rims instead of the more common 17x8. I'll probably go back to 215/45x17 winter tires on the stock 17x7 rims in a couple of years and retain the 225/45x17 size for summer driving.
Wider rims change the handling characteristics of the same sized tire. Going too wide is generally not effective.
I'm not sure where you are getting your wheel/tire weights but the stock tire is very light, 21lbs, about 3 lbs lighter than any performance tire I've seen. The stock rims are a nice and sturdy but chunky 20lbs each. To give you an idea of how hard it is to better these weights I bought O Z Alleggeritta rims at 15lbs each (one of the lightest rims available for reasonable money) but fit Michelin Pilot Sport A/S 3 tires at a hefty 24lbs each, saving only 1 lb per corner. Low rolling resistance tires are light, but the sidewalls are like wet spaghetti. You lean on those Primacies and they hold on fine until they give up, then you end up sideways pretty suddenly and counter steering very quickly. My snow tires , 225/45x17 Pirelli Sottozeros, are nice and progressive when they finally let go and the car is transformed into a delightful machine, easy to catch and easy to corner. That shouldn't be.
This car is very sensitive to tire choice. Fit big wheels and wide tires and prepare to be disappointed.