wider tires

[florinmano]

It's time to replace the Potenza's P215/50/R17 on my Vibe GT. They were great tires.I'm thinking to get wider tires, as maybe in P225/45/17.In the past I had mixed results using wider tires, starting from great handling improvement with mostly the same MPG (on a Chevy Metro) to much higher gas consumption and worse handling (on a Dodge Caravan).Does anyone have any experience with handling and gas milleage when using P225/45/17 on a Vibe? I'll appreciate any feedback.Thank you.

[DavidPIL]

Hiya...A few people have wider tires here. I personally have had 235/45R17 then now 245/45R17. 225/45's aren't close to the same diameter so you should consider the 235 or 245. (245's are the same size)No noticable change in mileage though when I put the 245's on, it was soon into Winter. A bit more following the ruts in the road... though I'm sure your results will depend on the brand and make of tire.I get great traction on dry and wet roads with my Toyo Proxes 4, the Continental ExtremeContacts were great wet and dry as well, though so were the OEM dunlops. I didn't notice your state but snow travel is a bit more scary, though that could be more just the tread of the tires than then wider path.I get no squeal at high speed turns, can't seem to make the tires bark to easily on spirited take-offs. They just grip well.Steering response can't really be determined as of yet. The 235 Continentals were sluggish in quick lane changes. The 245 Toyos seems to be a bit better though both seem to have fickle psi ranges. As the Conti's wore, they seemed to perform better with increased psi... up to around 38 psi at 40k miles but when new seemed to be very floaty at the same psi. The Toyos seem to have a swee spot at 36 psi now but it's colder so I don't know about warm weather yet.If you like wider tires, they should work fine on the Vibe. Just remember that 245/45/R17's will get you the same diameter as the 215/50's. Smaller will throw the speedo off a bit and might contribute to more wear (tire rotating more per-mile)Dave

[1oldbanjo]

I have done a little investigation into tire sizes and diameters. I agree that the stock tires look a little too narrow for the stock rims and will be getting wider tires when I get new 7x17 rims. I looked into revs/mile on the TireRack website and found the following:The 205/55-16 tire on the base model has 837 revs/mile. The 215/50-17 tire used on the GT has 814 revs/mile - so bumping up to the GT size rims and tires from a base Vibe decreases the number of rotation to 97.2% of the original value and will affect your speedometer and odomoter readings. If your speedometer and odomoter read correctly prior to the change at 60 mph - it will now read 58.3 mph (97.2%) when you are actually going 60 mph ground speed. If you want to calculate your change in speed just take the percentage times the MPH. If you want to calculate the change in the odometer reading to calculate mpg - divide the odometer reading by the percentage change to get actual miles driven before dividing it by the gallons used.A 215/50-17 tire has 814 revs/mile - which is 97.2% of stock Base.A 225/50-17 tire has 807 revs/mile - which is 96.4% of stock Base.A 225/45-17 tire has 837 revs/mile - which is 100.0% of stock Base.A 235/45-17 tire has 820 revs/mile - which is 98.0% of stock Base.A 245/45-17 tire has 809 revs/mile - which is 96.7% of stock Base.For those of you who have the GT - which has a different axle ratio the percentage change will be different (If your speedometer reads correctly with the stock 215/50-17 tires and the stock814 revs.mile).A 225/50-17 tire has 807 revs/mile - which is 99.1% of stock GT.A 225/45-17 tire has 837 revs/mile - which is 102.8% of stock GT.A 235/45-17 tire has 820 revs/mile - which is 100.7% of stockGT.A 245/45-17 tire has 809 revs/mile - which is 99.4% of stock GT.Remember that when you make these changes you will affect both your speedometer and odometer readings. I have often seen posts where people have said their mileage has increased or decreased by 2 or 3 mpg after the tire change - I suspect that what has really happened is that they have gone to different size tires and changed their odomoter accuracy more than they have actually changed their mpg. If you want to check your speedometer accuracy get on the interstate or a road with the milemarker posts on the side of the road. Drive at exactly 60 mph and when you pass one of the mile markers start timing yourself to the next one - it should take exactly 60 seconds for you to pass between the markers. There will be a little bit of error in just doing that over a single mile - so if you time yourself between 5, 10, etc. milemarkers your accuracy will be better and every mile should take 60 seconds. If it is not exactly 60 seconds speed up or slow down until it takes exactly 60 seconds between markers - and that will tell you what speedometer reading you actually have at a true 60 mph ground speed. To check your odometer reading do a similar thing - reset your trip odomoter when you pass the milemarker and see if it records one mile between the green signs. When I get a new car I will check it by recording a mile marker number and a corresponding reading on my odomoter when I am driving on a trip. After 50, 60 or 100 miles on that same road I will then record another milemarker and odometer reading. Subtract the difference in milemarkers (they may be going up or down depending on which side of the road you are on) and subtract the difference in odometer readings - and compare the two. Divide the odometer reading by the milemarker reading and you will get your accuracy in a percent. If your tires are rotating more than normal you will get a higher reading and your car will show more miles than you have actually traveled. You can adjust the speedometer and odometer reading the next time you buy tires by getting a slightly large or smaller tire that is the same percentage if it is important to you to have an accurate reading. It will also allow you to correct you claims for mileage or mph - if you drop a set of really low profile tires on your car your high mpg is not accurate - and neither is the 140 mph top speed you are reading on the speedometer! You can use changes in tire and rim diameters to effectively change the gearing of your car - small diameters will increase accelaration and decrease top speeds (even though the speedometer will say you are still going the same speed). One final comment (as if I should say more) - the tread width of tires can vary greatly between manufacturers. The section width 205/215/225 etc. is the distance between sidewalls on a specific rim width. The tread width is somewhat independant of the sidwall width and some manufactures have wider treads than others. If you want a wider tread tire you may be able to stay with the same size tire and choose a different brand or model that has a wider tread. TireRack lists tread widths for most of the tires in the SPECS section. You can choose the tire you are interested in and go to the SPECS section and check Revs/mile, section width, tread width, etc. so you can compare the tires.Dave

[1oldbanjo]

I just did a quick check of tread widths on the TireRack site - unfortunately they don't have all the tread widths listed. In the 215/50-17 size the stock Goodyear RSA has a section width of 8.9 inches and a tread width of 7.8 inches. The narrowest tread I found was a Yokohama Avid T4 with a section width of 8.8 inches and a tread width of 7.1 inches. The widest tire I found was a Yokohama AVS E100 with a section width of 8.8 inches and 7.9 inches of tread. This shows that section widths vary only a little and may be a result of the rim width used by the manufacturer during the measurement. The tread widths varied 0.8 inches for the same size and width of tire and in this case it was the same manufacturer but a different tire model. If the other tire Manufacturers had listed their tread widths you might be able to find an even greater difference.Dave

[joatmon]

fwiwhttp://forums.genvibe.com/zerothread?id=7087 has an explanation of the meaning of various tire size numbers and ratingshttp://forums.genvibe.com/zerothread?id=1066 has links to some online tire size calculators that will let you know the % effect on speedometer for different tire sizes. the one at http://www.miata.net/garage/tirecalc.html also has a graphic to show the size difference.

[florinmano]

Thanks everybody for the input.I decided to go for 225/45R17.It is true that 235/45R17 is the closest match to the original 215/50R17, but the difference is pretty small and I'll get a little more torque and a lower ride in the process.I'm not concerned too much about the odometer and speedometer. It looks like on my GT the speedometer was calibrated for the 205/55R16 wheels which are smaller. The GPS receiver shows larger speed than the speedometer, with a pretty noticeable difference from about 40mph up. So I guess the 225/45R17 wheels will get the reading just about right.About the tires, I'm thinking about the Bridgestone Potenza G009. They look good in reviews, and I hope they'll last longer than the OEM Potenzas which are completely worn out after 18000 miles. Anybody had any bad experience with the G009's?