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Old 11-09-2023, 02:29 PM   #21
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Join Date: Aug 2010
Location: Minnesota
Posts: 12,064

The information on handling is always interesting to me as I mess with that stuff all the time.

The steering response from sideway flexibility is a well known thing that changes with lots of things including the sidewall actual stiffness of materials. Aspect ratio is a huge determiner of steering response with the low aspect tires like 35 or 40 having very quick response and the taller ones like the 75s on most of our vans is substantially slower. The net affect of taller, softer, sidewalls is an increase in what they call "slip angle" which is the difference between the angle the wheel is pointing compared to the direction the vehicle is going.

We had the OEM V-steel S rated tires on our van when we got it and found them to not turn particularly well and ride pretty harsh. The sidewalls appeared to be very stiff to me. We replaced them with R rated MS2s and the handling and ride quality both got better, which was a surprise as I thought the softer sidewalls would degrade the handling some.

What I have found from the discussions is that many people don't seem to like very responsive steering and others like me like it quite fast. I think it all boils down to how large the steering wheel corrections need to be to get the van back on a straight ahead path if it is pushed offline by a gust of wind, road rut, bump or whatever. Many appear to be quite happy with 1-2" of steering wheel travel to correct small events and find that way too much. There does appear to be a factor involved, based on what folks say about driving style and steering wheel grip, that is typical for various likes of steering response. Those with a firm grip with both hands, at horizontal or above positions, tend to prefer softer, less responsive handling while the "lazy" drivers like me who have one or two hand light finger grip near the bottom of the wheel like it faster. It is kind of like the difference between a BMW and an older luxury car. Two hands tight is very easy to give bigger corrections and harder to make small ones, I think, and the lazy method is easier on small corrections and harder on large ones.

There is also something going on with the steering gears in the newer vehicles and the Express vans seem to show it very well. They are all old school recirculating ball units that have been around forever. But in 2007, I think, they added an assembly to the input end of the gearbox. Our 2007 has it and I have driven older ones that don't. Whatever they did seems to have added a lot of what I would call "artificial road feel" that increases the return speed a whole bunch and also increase the steering effort. What is odd about it to me is that the effort is almost the same at low and high speeds and no matter how sharp you are turning. It goes very quickly back to center to the point you have to slow it down and it not prone to go through center from momentum. Before the change you would have slower return and lower effort on most vehicles and the effort would change with speed and amount turned because of the actual tire return force feedback pushing harder to center as go faster or turn sharper. The new ones need to be aligned just right as they will sit at what they consider center even if you are going to one side or the other, while the older ones have a soft center feel that they actually put tight spot on the gear to help find that spot and keep it from going back through center. When is strong sidewind or steep crown the new systems with all the steering effort needed to get off center can be more tiring over time due to extra force needed. The older ones with the soft center are much lower effort to stay on line in continuous correction times like these. My wife's 2009 hydraulic rack and pinion CRV is even weirder. It has the same high effort off center, but with very quick response with little movement. It is also a pain to hold against the wind. What is really odd is that they seemed to build in a two stage assisted return to center in it. On a sharp right turn if you let go of the steering wheel it moves toward center very quickly to about 1/2 way and slows down in one big step and goes the slower, but still quite fast, all the way to center and then stops dead.

Maybe all the extra effort they are adding to center of the travel is to encourage more two hands tight on wheel driving, or it could be that people relate effort to responsiveness when they are nearly unrelated.

Handling preferences appear to be so personal a preference it makes it quite difficult to suggest improvements to the handling when folks ask about it. If it gets to be very responsive some with find it uncomfortably "twitch" and if it gets not as responsive others with say it is wandery an hard to control without big steering inputs. Change the tires and you may make it better, or worse, based on your preferred style.

I have tweaked my 96 Buick Roadmaster wagon to handle very well with maintaining good ride. It has the old school steering box in it that I modified to be faster ratio and slightly increased effort. The suspension has been modified to be more responsive with lots of caster and negative camber progression, plus big swaybars front and rear. It is nicely soft and very smooth progress in the center area and effort increase as speed and sharpness of turn increase. If I let go of the wheel on a sharp right turn, the steering wheel comes back to center by itself at a speed that matches the typical turn with not input. If I accelerate out of the turn the steering comes to center faster and still matches the turn well. The Buick is probably now the easiest car I have even had to keep on a straight line in wind, crowns, etc and all at low, untiring effort with my lazy driving style.
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Old 11-09-2023, 03:47 PM   #22
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Join Date: Nov 2023
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Originally Posted by peteco View Post
Is handling completely separate from speed rating, or only somewhat separate? My thinking is that a less stiff sidewall means the sidewall flexes more, and that more flexing will result in a tire temperature increase, which then reduces the speed for safe operation, and thus a lower tire speed rating. You indicate both can be designed for separately, but it seems like they are somewhat tied together. Is my logic incorrect here?
Let me put it like this:

Most of a tire's stiffness is caused by inflation pressure. For practical purposes, you can neglect the effect the sidewall itself has on the way a tire operates, except for the ride/handling thing.

As an example, if I were to test a tire with 5 psi less pressure, I could measure the difference in the speed test results and it wouldn't be very much. If the effect the sidewall itself has is taken into account, I might not be able to measure that.

So technically, you are correct, but for practical purpose, no one would go to the sidewall to improve the speed rating. And by the same token, no tire designer would go to the tread area to improve the ride/handling.
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