Tire sizes to improve MPG?

[ptjones]

I would hate to give up any MPG's on the Pirelli's, Michelin's got the best MPG's in testing. :)

 

Paul

[obob]

I am at 19,000 miles on my C-Max SE Hybrid and the tires still have a lot of tread left, so I am not in a hurry to replace them just yet, but I have also been thinking about this. I really liked the road feel of the new Pirelli P7 LRR EcoImpact all season. I put a set of them on my Camry and they handled very well. Did not see a mileage improvement over the BFG G-Force all season tires, but the car did have 150,000 miles on it. They have thistire in a run flat version in the right size for the C-Max.

 

The stock size Michelin 225 50 17 is 25.9" diameter. Rated 93V for load and 1433 pounds. 

 

Going to the Pirelli 205 55 17 comes in at 25.9 inches tall, close enough to be tread wear, but drops load ratings to 91V and 1366 pounds. 

 

The Max gross axle weight is the front at 2414 pounds, this is fully loaded. Assuming reasonable balance side to side, that is 1207 pounds per tire, carrying a full tank of gas, 5 passengers, and cargo load. The max cargo load does seem a bit low though, rated at just 852 pounds for people and cargo total. In any case, I certainly do not think it is unsafe to run the 205 tires. There is no 215 at the correct diameter. Going up or down 1/2 inch is not too big of a deal and seems like it would clear. 

 

As for rim fit, the 225 50 stock size tire is rated for 6 to 8 inch rims, but trust me, jamming a 225 onto a 6 inch is an serious pain. I used to run 225 50 14 on my 14 x 6 wheels when I autocross raced. The 205 is rated for rim sizes 5.5 to 7.5 inch. Putting them on a 7 inch is a very good fit. I also ran 205 60 14 on 14 x 7 inch rims, the side walls were near dead straight and the grip was excellent. The tread on the Pirelli is 7.1 inches wide with a max section width of 8.3 inches. 

 

I just may try the Pirelli in the 205 55 17 size, when I wear out the stock tires.

 

http://www.tirerack.com/tires/surveyresults/surveydisplay.jsp?type=GTAS

 

P7 got great ratings from tirerack.com  though I was concerned about the UTQG: 400 AA A  as far as tread wear.

 

The Michelin defender has UTQG: 820 A B which implies more miles.

 

How are the P7 wearing on your Camry ?

[fbov]

Be patient and the size/load issue may resolve itself. I'm seeing a far wider range of sizes available in the run-flat version of this tire, providing you with a 225/50-17 option as well as an expectation that the size will eventually be available without the run-flat feature. .

 

I would also be very careful not to confuse consumer surveys with actual tire testing. obob's link is just survey data, so it doesn't speak to rolling resistance. Their test reports do... but you need to find comparables. I'm only seeing one test that includes the P7 all-season, and one test of the OEMs, which had the lowest rolling resistance in a test of LRR tires. Not surprisingly, no tires are common across these tests. One is left to infer superior performance from the OEM because the P7 was not selected for that test. 

 

Finally, if I may be so bold as to suggest that the test results clearly point to the Conti as the superior tire, especially for wet performance (look at the spider charts). Regardless, I expect both tires would upgrade the C-Max handling over the OEMs, but at a cost in FE.  

 

HAve fun,

Frank

[GaryM]

My 2004 Camry SE 4 cyl. manual trans came originally with Michelin MXV4 215 65 16 tires. I played with tire pressure and at best, they would squeal on corners and at the stock pressure, it would wash out in understeer. Even with a 600+ treadwear rating, my front left tire had cords showing on the shoulder at just 25,000 miles. With the Pirelli P7+ tires in the same size with a tread wear rating of just 420, the car would take the same curves at a higher speed with no tire squeal and much better feel. I found myself taking exit ramps much quicker with confidence. Braking and acceleration grip were also much better. I did rotate them every 15,000 which I didn't do on the factory tires as I didn't expect to need to until 20,000 but by then the fronts were already looking bad and I didn't want them on the back. At 45,000 miles, I was showing the wear bars on the pirellis, and much more even across the tires, not the ripped up shoulders I had on the Michelins. Even running higher pressure could not keep the stock tires from rolling over and tearing up the edges. I am not as confident in the C-Max to corner as hard as I did in the Camry. The extra 600 pounds sure makes a difference. The feel on the stock Michelin tires is close to the original tires on the Camry with a little less squeal, but I do think I am going a tick slower than I did on the OEM tires but it was a long time ago. The Camry was also a much lower seating position and it cornered very flat withthe larger SE sway bars etc. The C-Max corners very flat as well, and the weight balance might even be better, but the higher driver position just feels un-natural for me to push hard into a corner. A few weeks ago, I was on a back road and I hit some sand at the apex of a turn, and it was very strange to feel the tail end drift out again. The fact it did that does lead me to believe the chassis is pretty well tuned. Most cars on the road today will always wash out the front end first, and usually by a big margin. Once I get a set of tires on it that don't squeal when pushed, I may get more confidence in the chassis to push it harder on a few bends and find the true limits. When the tires moan now, the steering gets very numb so I can't tell how much the slip angle is increasing. With the Pirellis on the Camry, I could feel the limit very easilly, and hold the car on the very edge with confidence. The lower tread wear rating is due to a much grippier compound. And when you drive at higher cornering forces, the hard compound sliding will wear faster than a soft compound that is still gripping. If you never corner (or brake or accelerate) near the grip limits, then the higher treadwear rating hard compound will last longer from just rolling wear. I don't think I will ever drive the C-Max as hard as I drove my Camry, but I will always enjoy taking highway ramps at decent speeds. It was always fun to pass Porsches and even motorcycles on the 2 lane cloverleaf ramps here. Even in the C-Max, I pulled 6 car lengths on a Mercedes SLK around the ramp, and he was weaving through traffic like a nut and ripped past me diving to the exit lane, but once in the turn, I carried speed, and drove around, passed him, and pulled away. When we got onto the straight highway, he got back on it and proceeded to weave through cars like an idiot again. I was just up the the point where I heard a low moan from the front tires, and the steering was getting numb, so I don't try to go any faster than that on the stock tires. 

[ptjones]

What tire psi are you using?  I didn't buy MADMAX to be a spots car, but it does fine for me. It looks like I will get 60Kmi. out of mine, with 51Kmi on them now. Have been using 49-50psi for last 15K. :)

 

Paul

[wab]

My 2004 Camry SE 4 cyl. manual trans came originally with Michelin MXV4 215 65 16 tires. I played with tire pressure and at best, they would squeal on corners and at the stock pressure, it would wash out in understeer. Even with a 600+ treadwear rating, my front left tire had cords showing on the shoulder at just 25,000 miles. With the Pirelli P7+ tires in the same size with a tread wear rating of just 420, the car would take the same curves at a higher speed with no tire squeal and much better feel. I found myself taking exit ramps much quicker with confidence. Braking and acceleration grip were also much better. I did rotate them every 15,000 which I didn't do on the factory tires as I didn't expect to need to until 20,000 but by then the fronts were already looking bad and I didn't want them on the back. At 45,000 miles, I was showing the wear bars on the pirellis, and much more even across the tires, not the ripped up shoulders I had on the Michelins. Even running higher pressure could not keep the stock tires from rolling over and tearing up the edges. I am not as confident in the C-Max to corner as hard as I did in the Camry. The extra 600 pounds sure makes a difference. The feel on the stock Michelin tires is close to the original tires on the Camry with a little less squeal, but I do think I am going a tick slower than I did on the OEM tires but it was a long time ago. The Camry was also a much lower seating position and it cornered very flat withthe larger SE sway bars etc. The C-Max corners very flat as well, and the weight balance might even be better, but the higher driver position just feels un-natural for me to push hard into a corner. A few weeks ago, I was on a back road and I hit some sand at the apex of a turn, and it was very strange to feel the tail end drift out again. The fact it did that does lead me to believe the chassis is pretty well tuned. Most cars on the road today will always wash out the front end first, and usually by a big margin. Once I get a set of tires on it that don't squeal when pushed, I may get more confidence in the chassis to push it harder on a few bends and find the true limits. When the tires moan now, the steering gets very numb so I can't tell how much the slip angle is increasing. With the Pirellis on the Camry, I could feel the limit very easilly, and hold the car on the very edge with confidence. The lower tread wear rating is due to a much grippier compound. And when you drive at higher cornering forces, the hard compound sliding will wear faster than a soft compound that is still gripping. If you never corner (or brake or accelerate) near the grip limits, then the higher treadwear rating hard compound will last longer from just rolling wear. I don't think I will ever drive the C-Max as hard as I drove my Camry, but I will always enjoy taking highway ramps at decent speeds. It was always fun to pass Porsches and even motorcycles on the 2 lane cloverleaf ramps here. Even in the C-Max, I pulled 6 car lengths on a Mercedes SLK around the ramp, and he was weaving through traffic like a nut and ripped past me diving to the exit lane, but once in the turn, I carried speed, and drove around, passed him, and pulled away. When we got onto the straight highway, he got back on it and proceeded to weave through cars like an idiot again. I was just up the the point where I heard a low moan from the front tires, and the steering was getting numb, so I don't try to go any faster than that on the stock tires. 

 

That's the thing about front wheel drive cars.

The front tires do most of the work.

100% of the steering

60% of the braking

50+% of the weight

 

Did you ever have a four wheel alignment?

I don't think Michelin makes a tire that will wear out that fast under normal conditions.

 

[ptjones]

That's the thing about front wheel drive cars.

The front tires do most of the work.

100% of the steering

60% of the braking

50+% of the weight

 

Did you ever have a four wheel alignment?

I don't think Michelin makes a tire that will wear out that fast under normal conditions.

Did I mention my alignment was out on my CMAX causing my tires to feather on edges and make a lot of noise. There is no adjustment for rear suspension, you have to replace part of the suspension to change the alignment. I ended up reversing the rotation of the tires to make them wear the opposite way so the noise level has gone down, but I'm looking forward to a new set of tires, but not the cost. :) 

 

Paul 

[fbov]

...when you drive at higher cornering forces, the hard compound sliding will wear faster than a soft compound that is still gripping. ...

Amen to that! It's one of many aspects of performance driving that are counter-intuitive unless you understand what's really happening.

 

At the same time, I find the OEM tires to be quite linear in their response below the limit, even if the cornering limit itsn't particularly high. Given the hybrid drivetrain, I've tried to focus on the car's strength - mileage - and so stayed in the tires' linear range more than I might have in the past. The one time I got the car balanced and cornering near its limits, the car took control and "saved me" from myself. Don't be surprised if you try to find the limits and instead find the brakes being applied in the middle of turns. Roll Stability Control.

 

Personally, a 1/2g panic stop at the apex of a turn seems like a foolproof recipe for head-on collisions... but what do I know, I only drive! Thankfully, I haven't noticed RSC all winter!

 

Have fun,

Frank