[flash]

there is a lot of chatter lately about wheel size, harshness, and all that, - there is a tendency to apply "post hoc ergo propter hoc" to the situation - so, i thought i would start a thread to try to more effectively define the issues at hand



many things contribute to "harshness" and "noise" - they are not necessarily due to the size of the wheel



here's the deal:



tire sidewall and compound are VERY responsible for harshness - a stiff sidewall tire (like a bridgestone S0-3) will ride much more harshly than a soft sidewall tire (like a michelin pilot sport) - however, the bridgestone will outcorner the michelin at the limits, and have less rebound, but tend to be less forgiving under extreme weight shifts, resulting in a slip of traction, where the michelin would bounce back and forth instead - if you are smooth, a tire like the bridgestone will be faster for you - if you tend to get out of shape or over-correct, a tire like the michelin will be better



sidewall profile plays a part too - the lower the profile tire, the less damping available - if you want a soft ride, on a bigger wheel, choose a soft sidewall tire - there is an increased risk of wheel damage though, with a softer sidewall lower profile tire, so consider the roads on which you will be driving - the problem with 18s is the overall diameter limits how much sidewall you have available to dampen impacts



camber affects impact feel - by increasing negative camber, you reduce the contact patch area in most situations, and focus the load on one corner - that increases the amount of impact transmitted to the suspension, and resultantly the chassis



struts and shocks are the biggest culprit in creating harshness - gas struts and shocks, like the koni yellows, have fixed compression settings, and a gas preload charge that makes bumps show up much more than a hydraulic shock would - good hydraulic adjustable shocks and struts are a lot more expensive though



inflation will also play a role here - the higher the pressure, the more you will feel bumps and such



the weight of the combination is a big factor too - the oem setup is about 50lbs per corner for 17s and a few pounds less for 16s - the more weight you add, the more the suspension has to work to dampen the impacts - the heavier the tire and wheel, the more this effect shows up



there is also a lot of nonsense out there about there being a difference in how a cab will ride with larger wheels, versus a hatchback - the fact is that, under the right circumstances, a stock cab can actually ride smoother with the same wheel as a hatchback - this is because of some absorbing of impact due to oem chassis flex - however, if you have heavy wheels or tires, it can cause the suspension to have to work too hard, the chassis oscillate, and you will get a lot more movement, which can feel harsh, especially if you have gas struts and/or shocks - this can be mitigated quite a bit by reinforcing the chassis



lastly, in reference to noise, the tread pattern and compound are responsible for tire noise - a v-groove pattern will tend to be quieter than a straight groove pattern when new, but can make a lot more noise when it wears - straight groove patterns can tend to tramline though, especially if your alignment is off - toe set should be reduced some when going to a stickier and wider tire, as the oem spec tends to wear the tire more unevenly, causing noise



as you can see, there are a lot of things to consider, and unfortunately many people make a lot of simultaneous changes at once, and then blame the ride on the wheel size, when in reality it could easily have been the lowering, the alignment, the shock, the tire, or any comination of them



so, generalization like "18s ride harshly", are not particularly accurate, and there are a lot of other factors involved



i hope that clears a few things up - have fun

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