V Tire Pressure and Ride Comfort

[Blind Guy]

I wanted to post my impressions of the V's sensitivity to tire pressure variations.

When we picked up our V on 8/4/2009, one of the things I had to do on my delivery checklist, was to see what the tire pressures were at time of delivery. Since I have a talking Tire Pressure Guage, I was easily able to check them before we left on our 195 mile trip home. The pressures were 37.5lbs Front and 36lbs Rear at time of delivery. Since the recommended pressures are 33lbs Front and 32lbs. Rear for the 17"s, I had been contemplating raising them anyway to see if slightly higher pressures would inmprove mileage somewhat. So I decided to let those pressures stand.

On our trip home the ride was on the firm side, actually almost sporty, my wife and I were VERY pleased with BOTH it's ride and handling. My wife is an excellent judge of a cars handling characteristics, since she attended the Bob Bondurant High Performance Driving School back in 1990, she was in the class just after the one which was attended by Rick Mears (Indy 500 winner). At the end of each class, each student is given a grade, 5.0 is perfect (which NO perfect scores are given, stated by Bob Bondurant himself, who actually graded and handed out the certificates to each student) and 1.0 which is...well let's say, pretty bad, Rick Mears received a 4.7, my wife received a 4.2, she also received Most Improved student! Some of the cars she has driven have been a, BMW 3 Series, BMW 6 Series, BMW 850, Jack Roush prepared Thunderbird, Acura NSX, 400 Hp Nissan 300ZX Twin Turbo, Mid-Engine Lotus Esprit and A fERRARI 206gts, so her understanding and appreciation of High Performance autos is extensive.

I must state here, before we decided to acquire the Prius, we had some, well, let's say impassioned debates. She feared we were getting, as she called it, a refrigerator on wheels, and was only succoming because of the FANTASTIC fuel mileage!

However, I digress. Her opinion of the new car as we progressed home, steadily and rapidly improved! She was initially struck by the ride, and how compliant it was, along with the better than expected road feel. She also stated the steering was reasonably sharp and precise and it displayed minimal body roll.

Now, back to the tires. Since the pressures set at the dealers PDI were left alone, and quite acceptable on the ride home, I asked her once we arrived home if she would like the ride to be firmer or softer, she said she'd like to try harder, just to see if it would effect handling. So I changed the pressures to 39lbs. Front and 38lbs. Rear. HUGE difference!!! The handling remained unchanged, however, the ride suffered GREATLY. We had taken some friends for a ride when we first arrived home, and a few days later we took them again to go for lunch, and they commented "what happened?". The ride became harsh and every expansion join in the road could be felt, and it's impact seemed to be magnified.

So, next we decided to try a lower pressure to mitigate the harsh ride, the pressures were lowered to 35lbs. Front and 34lbs. Rear. Now the ride was SOFT, and my wife began to notice a little deminishment in it's handling characteristics, a little more body roll etc. So, once again we tried a different pressure setting, this time we tried 37lbs. Front and 36lbs. Rear, and just like the 3 Bears...it was just right! The ride seemed to her to be firm yet compliant and the handling was still very good.

The thing I most wanted to comment on, was when filling and evacuating air from the tires for the various saettings, I noticed that removing a VERY small amount of air from the tires DRAMATICALLY effected the tire pressure! For example, I would fill the tire to 43lbs. and then with the tire pressue gauge bleed the air down to 39lbs., on previous tires I was accustomed to bleeding the air down for a few seconds, when I did this on the V's low profile tires, those pressures would go from 43lbs. to 32lbs. in about a second! I found I had to be VERY diligent to get the pressures precisely where desired. The time or two I tried adjusting the pressures on all four tires it took me about an hour to get the hang of it.

The second thing noted, was the relatively miniscule pressure changes it took to radically effect the ride and compliance of the car. It is my supposition that the extremely low profile of the 215x45 tires is responsible for and small changes making an enormous effect. Since the 45 on the sidewall indicates that the height of the sidewall is 45% of the width of the tire, or 45% of 215 = 96.75mm tall for the sidewall, not much air volume for the tire, that's why minute air pressure changes make a large difference.

Those of you with V's with 17" tires, may want to play around with your tire pressures to find a setting best suited to your driving likes. Remember, small air pressure changes make HUGE differences in ride and comfort levels, and bleed down those pressures VERY MINUTELY!

I had posted earlier that once we received our car, I would post my impressions from a blind man's perspective, it's tactile and audible feedbacks, and our general impressions and feelings for the vehicle...COMING SOON!

David (aka Blind Guy)

[wvgasguy]

I found the 40 psig setting to be uncomfortably harsh.

[DeanFL]

David

Thanks so much for your experimentation and feedback on your V tires. I too had modified the air pressure - similar to your methodology - over the last 7 weeks. I finally settled on 40/39. And actually had not noticed that huge of a difference in "tush feel". Mine isn't padded THAT much.... But I do notice a bit more noise from expansion joints - the "ping....ping". Yes, the handling far exceeds my expectation before buying the car. I'm out of town right now but will moderate my pressure to the levels you feel are "just right". I have a feeling that together - both your wife's driving experience and your elevated senses provide the best of the best.

I so appreciate all your valuable input on the Forum. And anticipate an informative review by you soon. What brand tires did you receive? I have Toyos.

Dean

[ggood]

I agree, setting the tires above 40 makes for a harsh ride on potholed city streets, and like I'm feeling every pebble on the highways. I've settled in at 38/37 for now, which seems soft enough for comfort but firm enough for good handling. I've considered bumping it up 1 or 2 psi, because at the current levels I can feel just a bit of give in the tires around curves (someone else referred to this as rollover). I suppose if I got rid of all the give though, I'd be back at the too hard place again. Some people seem not to not mind that though.

[jsharpe]

Originally Posted by ggood

I agree, setting the tires above 40 makes for a harsh ride on potholed city streets, and like I'm feeling every pebble on the highways. I've settled in at 38/37 for now, which seems soft enough for comfort but firm enough for good handling. I've considered bumping it up 1 or 2 psi, because at the current levels I can feel just a bit of give in the tires around curves (someone else referred to this as rollover). I suppose if I got rid of all the give though, I'd be back at the too hard place again. Some people seem not to not mind that though.

Hmmm. Maybe my wife and I are just a bit numb or perhaps the tire brand/model make a bigger than expected difference. But after bumping the delivered 36/35psi to 44/42 neither of us noticed any additional harshness. This was even on a trip that included a couple high speed passes over a 30 mile stretch of windy mountain gravel road that the mag chloride was breaking down so there were potholes and washboards.

p.s. We happen to have the Bridgestones and even though the trip mentioned was at relatively high elevations (most above 8000 and peaking at 11,000) and we made no attempt at driving nicely we still averaged 52mpg for the trip. - I knew I picked this car for a reason!

[ggood]

Originally Posted by jsharpe

Hmmm. Maybe my wife and I are just a bit numb or perhaps the tire brand/model make a bigger than expected difference. But after bumping the delivered 36/35psi to 44/42 neither of us noticed any additional harshness. This was even on a trip that included a couple high speed passes over a 30 mile stretch of windy mountain gravel road that the mag chloride was breaking down so there were potholes and washboards.

p.s. We happen to have the Bridgestones and even though the trip mentioned was at relatively high elevations (most above 8000 and peaking at 11,000) and we made no attempt at driving nicely we still averaged 52mpg for the trip. - I knew I picked this car for a reason!

Good point. I'm sure the specific tires make a big difference. I have the Toyo Proxes A20. All the more reason to follow David's suggestion to experiment for ourselves.

[Blind Guy]

Originally Posted by DeanFL

...What brand tires did you receive? I have Toyos.

Dean

We received the Michelin Pilot's, and I do susppect that the tire brand plays a substantial role in the ride characteristics demonstrated by that manufacturer's tires. The 37lb./36lb. settings for a Michelin, may be all wrong for a Bridgestone or Toyo.

And Dean, THANK YOU for the kind words.

David (aka Blind Guy)

[wvgasguy]

Originally Posted by jsharpe

Hmmm. Maybe my wife and I are just a bit numb or perhaps the tire brand/model make a bigger than expected difference. But after bumping the delivered 36/35psi to 44/42 neither of us noticed any additional harshness. This was even on a trip that included a couple high speed passes over a 30 mile stretch of windy mountain gravel road that the mag chloride was breaking down so there were potholes and washboards.

p.s. We happen to have the Bridgestones and even though the trip mentioned was at relatively high elevations (most above 8000 and peaking at 11,000) and we made no attempt at driving nicely we still averaged 52mpg for the trip. - I knew I picked this car for a reason!

I have the Bridgestones. I can imagine you not minding the difference going from 36 to 44 but I can't imagine you not noticing the difference.

On a gravel road, it would be so noisy and rough that I don't know that it mattered what the air pressure would be. But on an interstate (concrete road) with expansion strips the difference in 36 to 40 was quite noticible.

[eglmainz]

Originally Posted by Blind Guy

...

The second thing noted, was the relatively miniscule pressure changes it took to radically effect the ride and compliance of the car. It is my supposition that the extremely low profile of the 215x45 tires is responsible for and small changes making an enormous effect. Since the 45 on the sidewall indicates that the height of the sidewall is 45% of the width of the tire, or 45% of 215 = 96.75cm tall for the sidewall, not much air volume for the tire, that's why minute air pressure changes make a large difference.

David (aka Blind Guy)

David, I think that a sidewall height of 96.75cm would be a very different, and almost monstrous (as in monster truck) ride. I think that you mean 96.75mm (or 3.8 Inches) sidewall height.

[jsharpe]

Originally Posted by wvgasguy

I have the Bridgestones. I can imagine you not minding the difference going from 36 to 44 but I can't imagine you not noticing the difference.

Just to add a bit more detail. Could we tell the difference in a blind test? Sure, but it's not substantial enough to be bothersome. To me the difference between the standard and lower profile tires (at the recommended pressures) is far greater than the difference between 36 and 44 psi on these 45 series Bridgestones. So perhaps the characterization of "harshness" lies in our expectations. It's quite possible that what I expect from a low profile tire on less than perfect pavement would be considered harsh by different standards.

On a gravel road, it would be so noisy and rough that I don't know that it mattered what the air pressure would be. But on an interstate (concrete road) with expansion strips the difference in 36 to 40 was quite noticible.

Actually the noise and roughness on the gravel road was really not that bad. I was more concerned with the rocks we were flinging up at the speeds we were traveling. Sure wish those mud guards would show up soon.

Where I do notice noise is probably not as strongly correlated with tire pressure as it is with tread pattern and that is on grooved or worn concrete at higher speeds.