Posted by News on May 19, 2011, 5:32 pm
On 5/19/2011 1:17 PM, bwilson4web wrote:
>> On 5/19/2011 8:50 AM, bwilson4web wrote:
>>
>>
>>
>>> wrote:
>>>> In article
>>
>>>>>>> Not yet since I'm trusting the ABS to moderate the braking force.
>>
>>>>>> Ohmigod, did you really SAY that? That's a TOTAL non-sequitur.
>>
>>>>> Poor baby, stepped into it again, I see. You are such my bitch.
>>
>>>> <snort> SURE, bob. SURE.
>>
>>> Yesterday, we had one of those stop sign controlled incidents where
>>> the car on the right assumed I also had a stop sign but I had a yield,
>>> the right of way. So they started to pull in front of me. I mashed the
>>> brake and felt the reassuring, ABS buzz as the car stopped with a lot
>>> of space to spare. Excellent braking!
>>
>>> Testing done and passed!<GRINS>
>>
>>> The physics remains the same. The tire foot print is the same as all
>>> Sumitomo tires are at 51 psi and kept there. They are all T4 style so
>>> the tread patterns are identical. Best of all, ABS braking keeps each
>>> tire right at edge of maximum braking based upon rpm changes which is
>>> independent of diameter and the car remains fully in control.
>>> Yesterday's test was just like all earlier, emergency braking
>>> incidents, no drama, rapid stopping.
>>
>>> So Elmo, where is your report showing that tire diameter has any
>>> effect on stopping distance?
>>
>>> You don't have any, our fool tool.
>>
>>> Bob Wilson
>>
>> REFERENCE: J.W. Daws, “Technical Considerations for Plus Sizing,”
>> submitted for presentation at the 2008 International Tire Exhibition and
>> Conference, September 16-18, 2008, Akron, OH
>>
>> "General Motors Corporation stated in a recent publication [“Plus-sized
>> Problem?”, Tire Business, July 19, 2004] that wheels used for their
>> upgrade packages have the “same mass, same offset, same width, same
>> mounting flange, same tire pressure monitoring requirements, same brake
>> clearance, [and] same dimensional tolerances” as the original equipment
>> wheels. Implicit in this tight specification are the impacts of the
>> plus-sized fitment on anti-lock brake systems, electronic stability
>> control systems, and so on. Obviously, a wheel with the same mass at a
>> larger OD has a larger rotational inertia than the OE wheel. Generally,
>> as wheel diameter increases, the mass of the tire and wheel for equal
>> load capacity generally increases, as does the inertia of the rotating
>> system. This change in unsprung weight may affect the response of the
>> suspension system. The change in rotational inertia may affect the
>> response of systems like antilock braking and electronic stability
>> control. Tire pressure monitoring based on antilock brake sensors may
>> also be affected by changes in tire size and vertical stiffness. At this
>> time, there is a significant lack of public domain data available to
>> assess these effects."
> Thanks!
> I found the paper and am reading it now. But I'm struck by this
> comment:
> ". . . conventional wisdom usually suggests that any difference should
> be within +/- 3% of the original equipment tire . . ."
> Based upon tire revs per mile, here is how the tires rate versus the
> OEM tire, 902 rev/mile, 1102 lbs:
> 175/65R14 - 919 -1.9%, 1019 lbs
> 175/70R14 - 886 +1.8%, 1102 lbs
> 195/70R14 - 849 +5.9%, 1321 lbs
> Per "conventional wisdom," the first two tires straddle the OEM tire.
> The 195/70R14 is oversized but the rest of the article discusses
> stability testing. I'll have to read it closely to see what their test
> articles were doing and compare it to the Sumitomos.
> One good thing is the 195/70R14 is the largest tire that can fit on
> the NHW11 Prius. There is one I skipped over:
> 185/70R14 - 867 +3.9%, 1201 lbs
> If someone is concerned about the 195/70R14, the next size down,
> 185/70R14 would work too.
> BTW, thanks for the reference to "The Tire Society." I wasn't aware of
> them and they look to be serious people.
> Bob Wilson
There's a lot of potential liability attached to them, hence their
seriousness.
Posted by Bob Wilson on May 19, 2011, 6:12 pm
> On 5/19/2011 1:17 PM, bwilson4web wrote:
. . .
> > BTW, thanks for the reference to "The Tire Society." I wasn't aware of
> > them and they look to be serious people.
. . .
> There's a lot of potential liability attached to them, hence their
> seriousness.
I had scanned the SAE and was not impressed. I've had a chance now to
look at some of the titles of the Tire Society earlier articles and
this looks to be a good source. Certainly better than the 'hot rod'
and 'racer' articles although they helped too. I've already done some
work using IR temperature probes to measure tire alignment and
identify problems. I'm also doing 4-wheel alignment, toe and camber.
It looks like some of these papers have the detailed tire models I've
been seeking.
Bob Wilson
Posted by bwilson4web on May 20, 2011, 5:31 am
> On 5/19/2011 8:50 AM, bwilson4web wrote:
. . .
> REFERENCE: J.W. Daws, Technical Considerations for Plus Sizing,
> submitted for presentation at the 2008 International Tire Exhibition and
> Conference, September 16-18, 2008, Akron, OH
> "General Motors Corporation stated in a recent publication [Plus-sized
> Problem?, Tire Business, July 19, 2004] that wheels used for their
> upgrade packages have the same mass, same offset, same width, same
> mounting flange, same tire pressure monitoring requirements, same brake
> clearance, [and] same dimensional tolerances as the original equipment
> wheels. Implicit in this tight specification are the impacts of the
> plus-sized fitment on anti-lock brake systems, electronic stability
> control systems, and so on. Obviously, a wheel with the same mass at a
> larger OD has a larger rotational inertia than the OE wheel. Generally,
> as wheel diameter increases, the mass of the tire and wheel for equal
> load capacity generally increases, as does the inertia of the rotating
> system. This change in unsprung weight may affect the response of the
> suspension system. The change in rotational inertia may affect the
> response of systems like antilock braking and electronic stability
> control. Tire pressure monitoring based on antilock brake sensors may
> also be affected by changes in tire size and vertical stiffness. At this
> time, there is a significant lack of public domain data available to
> assess these effects."
I've had a chance to read the article throughly and it is about the
practice of increasing the size of the wheel and installing low
profile tires. So right off the bat, the density of the wheel/tire
changes as there is more metal and less air. In contrast, I'm using
the exact same alloy wheels the car came with, no additional metal.
So let's go over the quoted elements and their impact:
"Obviously, a wheel with the same mass at a larger OD has a larger
rotational inertia than the OE wheel." Absolutely and this is an
improvement in Prius handling. The steering even with perfect, four-
wheel alignment is a best neutral stability. However, the higher
rotation inertia of the larger tire improve steering stability. I
observed this on a trip to Madison Wisconsin from Huntsville.
I drove up with the Toyota replacement, the 175/65R14, on the front
and the experimental 175/70R14 on the rear. That Sunday I swapped
front and rear and highway steering stability was improved to the
point of making the drive home easier. In contrast on the drive up, I
had to keep constantly on high alert to keep the car between the
lines. On the way back, the car tracked true.
As for the other effects, they used a lot of "may" and ". . . there is
a significant lack of public domain data available to assess these
effects." After all, they aren't 'Elmo' who acts as if asking a
question can substitute for research and experimentation. These are
serious folks to don't ask silly questions as much as proposing where
they and serious people will go to investigate.
Now this paper does discuss one risk and the experimental vehicle is a
tall, SUV body which are notorious for that risk. In contrast, the
Prius takes corners like they are glued to the road ... they have a
lot of margin. I know the larger tires have not impacted my ability to
take a sharp turn.
The one effect, a larger moment of inertia, has been found and it is
exactly what the Prius highway steering needs. As for the one risk in
the paper, the Prius was already superior and my driving has yet to
find a problem. The Prius is so good at taking a turn that it can be
uncomfortable and scary to those who are not prepared.
I'm still reading the papers and having a great time. I feel like I've
walked into a University library and that has been one of my first
loves.
Bob Wilson
Posted by News on May 20, 2011, 11:59 am
On 5/20/2011 1:31 AM, bwilson4web wrote:
>> On 5/19/2011 8:50 AM, bwilson4web wrote:
>>
> . . .
>>
>> REFERENCE: J.W. Daws, “Technical Considerations for Plus Sizing,”
>> submitted for presentation at the 2008 International Tire Exhibition and
>> Conference, September 16-18, 2008, Akron, OH
>>
>> "General Motors Corporation stated in a recent publication [“Plus-sized
>> Problem?”, Tire Business, July 19, 2004] that wheels used for their
>> upgrade packages have the “same mass, same offset, same width, same
>> mounting flange, same tire pressure monitoring requirements, same brake
>> clearance, [and] same dimensional tolerances” as the original equipment
>> wheels. Implicit in this tight specification are the impacts of the
>> plus-sized fitment on anti-lock brake systems, electronic stability
>> control systems, and so on. Obviously, a wheel with the same mass at a
>> larger OD has a larger rotational inertia than the OE wheel. Generally,
>> as wheel diameter increases, the mass of the tire and wheel for equal
>> load capacity generally increases, as does the inertia of the rotating
>> system. This change in unsprung weight may affect the response of the
>> suspension system. The change in rotational inertia may affect the
>> response of systems like antilock braking and electronic stability
>> control. Tire pressure monitoring based on antilock brake sensors may
>> also be affected by changes in tire size and vertical stiffness. At this
>> time, there is a significant lack of public domain data available to
>> assess these effects."
> I've had a chance to read the article throughly and it is about the
> practice of increasing the size of the wheel and installing low
> profile tires. So right off the bat, the density of the wheel/tire
> changes as there is more metal and less air. In contrast, I'm using
> the exact same alloy wheels the car came with, no additional metal.
> So let's go over the quoted elements and their impact:
> "Obviously, a wheel with the same mass at a larger OD has a larger
> rotational inertia than the OE wheel." Absolutely and this is an
> improvement in Prius handling. The steering even with perfect, four-
> wheel alignment is a best neutral stability. However, the higher
> rotation inertia of the larger tire improve steering stability. I
> observed this on a trip to Madison Wisconsin from Huntsville.
> I drove up with the Toyota replacement, the 175/65R14, on the front
> and the experimental 175/70R14 on the rear. That Sunday I swapped
> front and rear and highway steering stability was improved to the
> point of making the drive home easier. In contrast on the drive up, I
> had to keep constantly on high alert to keep the car between the
> lines. On the way back, the car tracked true.
> As for the other effects, they used a lot of "may" and ". . . there is
> a significant lack of public domain data available to assess these
> effects." After all, they aren't 'Elmo' who acts as if asking a
> question can substitute for research and experimentation. These are
> serious folks to don't ask silly questions as much as proposing where
> they and serious people will go to investigate.
> Now this paper does discuss one risk and the experimental vehicle is a
> tall, SUV body which are notorious for that risk. In contrast, the
> Prius takes corners like they are glued to the road ... they have a
> lot of margin. I know the larger tires have not impacted my ability to
> take a sharp turn.
> The one effect, a larger moment of inertia, has been found and it is
> exactly what the Prius highway steering needs. As for the one risk in
> the paper, the Prius was already superior and my driving has yet to
> find a problem. The Prius is so good at taking a turn that it can be
> uncomfortable and scary to those who are not prepared.
> I'm still reading the papers and having a great time. I feel like I've
> walked into a University library and that has been one of my first
> loves.
> Bob Wilson
Glad to contribute. I have seen prior mention of steering/hunting and
tracking/wandering issues, the attempted cure for which are aftermarket
strut and chassis stiffening braces. Increasing rotational inertia via
tire sizing and profile could be a more direct as well as less radical
solution.
Posted by bwilson4web on May 20, 2011, 12:42 pm
> On 5/20/2011 1:31 AM, bwilson4web wrote:
> >> On 5/19/2011 8:50 AM, bwilson4web wrote:
> > . . .
. . .
> > I'm still reading the papers and having a great time. I feel like I've
> > walked into a University library and that has been one of my first
> > loves.
> > Bob Wilson
> Glad to contribute. I have seen prior mention of steering/hunting and
> tracking/wandering issues, the attempted cure for which are aftermarket
> strut and chassis stiffening braces. Increasing rotational inertia via
> tire sizing and profile could be a more direct as well as less radical
> solution.
I've seen some references to changing the caster but these were not
single part changes. To do it right, I would need a sophisticated
suspension alignment tool along with a lift. I could do it but the
cost, labor and tools makes soon evaporates the fun.In contrast,
changing tires is relatively easy and there are a lot of articles in
the racing community about tire effects and tuning during a race.
I'm waiting for a strut to fail before tackling suspension changes. I
have looked for variable stiffness shocks but they are unGodly
expensive parts. It looks like installing shims could shift the caster
offset, a bit. However, the articles I've read indicate we would also
need to change some of the linkages.
I've read a number of reports about how adding a stiffening plate
improved NHW20 handling. But we have the earlier NHW11, a sedan-style,
shorter, stiffer body, and the ZVW30 which has been built stiffer.
I've not seen reports that 'neutral steering' was a problem with the
NHW20 and the ZVW30 handles more like our NHW11 with larger diameter
tires ... which they are. The NHW11 uses stock 14" rims and the ZVW30
15" rims.
BTW, I was looking for something else in my archives and found this
photo showing the tires I've tested:
http://hiwaay.net/~bzwilson/prius/Sumito_T4_020.jpg
Bob Wilson
>>
>>
>>
>>> wrote:
>>>> In article
>>
>>>>>>> Not yet since I'm trusting the ABS to moderate the braking force.
>>
>>>>>> Ohmigod, did you really SAY that? That's a TOTAL non-sequitur.
>>
>>>>> Poor baby, stepped into it again, I see. You are such my bitch.
>>
>>>> <snort> SURE, bob. SURE.
>>
>>> Yesterday, we had one of those stop sign controlled incidents where
>>> the car on the right assumed I also had a stop sign but I had a yield,
>>> the right of way. So they started to pull in front of me. I mashed the
>>> brake and felt the reassuring, ABS buzz as the car stopped with a lot
>>> of space to spare. Excellent braking!
>>
>>> Testing done and passed!<GRINS>
>>
>>> The physics remains the same. The tire foot print is the same as all
>>> Sumitomo tires are at 51 psi and kept there. They are all T4 style so
>>> the tread patterns are identical. Best of all, ABS braking keeps each
>>> tire right at edge of maximum braking based upon rpm changes which is
>>> independent of diameter and the car remains fully in control.
>>> Yesterday's test was just like all earlier, emergency braking
>>> incidents, no drama, rapid stopping.
>>
>>> So Elmo, where is your report showing that tire diameter has any
>>> effect on stopping distance?
>>
>>> You don't have any, our fool tool.
>>
>>> Bob Wilson
>>
>> REFERENCE: J.W. Daws, “Technical Considerations for Plus Sizing,”
>> submitted for presentation at the 2008 International Tire Exhibition and
>> Conference, September 16-18, 2008, Akron, OH
>>
>> "General Motors Corporation stated in a recent publication [“Plus-sized
>> Problem?”, Tire Business, July 19, 2004] that wheels used for their
>> upgrade packages have the “same mass, same offset, same width, same
>> mounting flange, same tire pressure monitoring requirements, same brake
>> clearance, [and] same dimensional tolerances” as the original equipment
>> wheels. Implicit in this tight specification are the impacts of the
>> plus-sized fitment on anti-lock brake systems, electronic stability
>> control systems, and so on. Obviously, a wheel with the same mass at a
>> larger OD has a larger rotational inertia than the OE wheel. Generally,
>> as wheel diameter increases, the mass of the tire and wheel for equal
>> load capacity generally increases, as does the inertia of the rotating
>> system. This change in unsprung weight may affect the response of the
>> suspension system. The change in rotational inertia may affect the
>> response of systems like antilock braking and electronic stability
>> control. Tire pressure monitoring based on antilock brake sensors may
>> also be affected by changes in tire size and vertical stiffness. At this
>> time, there is a significant lack of public domain data available to
>> assess these effects."
> Thanks!
> I found the paper and am reading it now. But I'm struck by this
> comment:
> ". . . conventional wisdom usually suggests that any difference should
> be within +/- 3% of the original equipment tire . . ."
> Based upon tire revs per mile, here is how the tires rate versus the
> OEM tire, 902 rev/mile, 1102 lbs:
> 175/65R14 - 919 -1.9%, 1019 lbs
> 175/70R14 - 886 +1.8%, 1102 lbs
> 195/70R14 - 849 +5.9%, 1321 lbs
> Per "conventional wisdom," the first two tires straddle the OEM tire.
> The 195/70R14 is oversized but the rest of the article discusses
> stability testing. I'll have to read it closely to see what their test
> articles were doing and compare it to the Sumitomos.
> One good thing is the 195/70R14 is the largest tire that can fit on
> the NHW11 Prius. There is one I skipped over:
> 185/70R14 - 867 +3.9%, 1201 lbs
> If someone is concerned about the 195/70R14, the next size down,
> 185/70R14 would work too.
> BTW, thanks for the reference to "The Tire Society." I wasn't aware of
> them and they look to be serious people.
> Bob Wilson