Has anyone upgraded their stoco wheels and tires to 205's at 16 inch radius?
how did it affect gas mileage?

 

I ran 205/50/16 tires, instead of 185/55/16, on my GK and noticed that my MPG dropped by about 2-3.

 

I ran 205/50/16 on my GE for a couple tanks & swapped back to 185/55/16 on those same wheels.

The fuel economy didn't change noticeably, but the 205/50/16 were slightly more worn & therefore lighter/less rolling resistance.

Depending on total weight of the wheels/tires, the tires chosen, the offset used, etc. you could notice anything between no change and 3-5 less MPG.

Example: Using lightweight wheels, high offset (close to stock) with low rolling resistance tires, you'll see very similar MPG to now. Using lower offset 16x7 +35ish, 18# wheels and a 205/50/16 RE71R, you could see a five MPG drop pretty easily.

There are a ton of factors to be considered.

 

Agree with the ton of factors. The biggest being rolling resistance.

Even within the same size, the largest difference is likely to come from tire type. Switch from eco low rolling resistance tires to a summer only performance tire will have a bigger change than tire size alone.

My Mom went from the stock 16" tire size to 205's with the same tire and didn't see a change at all. If there was one, it wasn't measurable.

We see a solid 2mpg difference between our 195-15's and our 205-16's, but that is going up in weight, significantly up in rolling resistance (all seasons vs summer performance), and up in width.

I can't fathom how you could ever see a big mpg difference unless you put chrome spinners on the thing. I suspect that those that do are either changing diameter and not counting that in the calculations or are driving it harder when the performance tires are installed.

 

I did the same tire size change on my stock GK wheels and found the MPG change minimal, but as they say YMMV 205/50/16 Altimax RT43

 

Yeah, same with my Mom. If there was a change, it isn't measurable.

 

My current stock size is 175/65 R15.
So Id be widening by 30 mm but also increasing diameter an inch.

am I right in thinking that incrrasing diameter will improve mpg and widening will lower it?
​​​​​​​Do you think it will balance out (keeping all other factors equal)

 

Changing diameter should not have an affect on actual mileage. It will throw off your calculations due to making the odometer/speedometer not accurate, but actual fuel mileage should be unchanged.

That being said, a larger diameter wheel/tire combo is usually also heavier. Additional weight can have a negative impact on fuel economy.

If using the exact same tire, but 30mm wider, it will reduce fuel mileage due to increased wind and rolling resistance.

So, heavier equals worse fuel economy and wider equals worse fuel economy. How much worse is very hard to know for sure, but it will be worse to some amount.

 

You need to learn how to calculate tire diameter.

175/65/15 is 24" tall.
205/50/16 is 24.1" tall.

 

Glad you caught that. I wasn't paying enough attention.

Given that, if the OP picks light weight 16's, the actual change could just be width. That will have a negative impact, but shouldn't be a crazy amount.

To each their own, but I'd live with whatever fuel economy difference to not be rolling around on 175's.

 

I have '11 Sport AT that came with 185/55-16. After the first +30K miles I bought the Conti DWS in 2015/50-16 but used the OEM 16x6 wheels. Car was "squirmy" and felt like it took more time to "load" the tire while making a turn. Part way through this experiment I bought cheap FOCAL 16x7 wheels and ran the Conti's for the rest of their short lifespan (total ~30K miles) but handling did improve. I guess a wider wheel allowed the sidewalls to more immediately "transmit" my steering input into car behavior.

I still have the FOCALS although they appear to have a "skin" disease because the clear coat came off here and there and those skinny surfaces are now a blotchy two-tone. I now have General Altimax RT43 on and their sidewalls appear to be stiffer and more responsive than the Conti.

BTW, I've figured that the factory / door jam psi recommendations were too high for a larger tire, so I've keep them at +/- 29 psi (f/r). The only problem with the lower pressure is that you're closer to the TPMS "low pressure" alert at 26-27 psi for the 16" wheel system on the Sport models (I think the 15" would have a different trigger psi). Here in Pennsylvania, as well as many other places, our ambient air temperatures vary seasonally, so as it gets colder, the tire air pressure decreases and I get low psi alerts once / twice every fall / winter. Going into summer, I usually have to leave some air out of each tire or I'd be over pressure and I can feel the tires / car wandering on an irregular road surface and it feels "twitchy" (a lot less resistance when turning the steering wheel). Everything is connected, so there is a ripple-effect when making changes like this.

Yes, my gas mileage decreased by 2-3 mpg when going 205/50-16 regardless of 16x6 or 16x7 wheel size.

 

Wonder if your squirmy feeling was due to low tire pressure?

FWIW, I run our 205/45-16's at 38 psi. Any less and I don't like the feel. More handles better, but is punishing for ride quality.

 

How is tire wear at the psi?

I rotate 1/yr, drive FIT approx. 5,000 mile / yr and the Generals seem to have "even" tire wear.

The Contis were squirmy but Gen'ls feel better at same psi range +/- 29 psi. I'm sticking with the "bigger tires need less air pressure" theorem.

But I'm still interested in your experiences at 38

 

Fronts wear evenly, but rears have been getting destroyed by the factory negative camber since day one. It's within spec, but the tire wear in the rear is quite extreme.

That is one place where wider tires/wheels are not a good thing for Honda's in general. The wider the tire/wheel, the more pronounced the factory negative rear camber becomes

BTW, many say that it's toe that causes rear inner tire wear, but I firmly disagree. Our toe is fine, it's just that the rears ride on the inside edge due to the negative camber because the rear beam is not straight.

 

Your fuel economy dropped because your tire pressures are WAY too low.

And yes, cars feel better when the tires are the right size for the wheels. When my 16x7 wheels come in, I'm running a 195 on them. 205 is too wide for a 7" wheel IMO (let alone a 6" wheel).

Yep.

Agreed. I think I'm running 41 psi in my Fit, 185/55/16 Yoko Avid Ascend on OEM sport wheels. 34 PSI in my S2000.

Under 30 PSI is just throwing gas/money/pollution away and making the car slower/handle/brake worse.

 

That's an area where I just stick with the tire manufacture's recommendations.

The recommended wheel width for the 205/50-16 Bridgestone's we run is 6.5-7.5". At 7" we are dead in the middle of recommended. Honda optional sport wheels were 6.5" and they recommended 205's.

The tire we run is offered in a 195/55-16, but that is a bit taller than factory and the recommended wheel width is 5.5-7". So, you could put it on a 7" wheel, but that is at the limit.

FWIW, generally speaking cars that have 7" wide wheels from the factory have 225 width tires.

Mike, I think you just like the stretched look and feel, but that is a preference not a safety issue.

 

I generally base my stuff on what track dudes like for tire usage.

When I had my Miata, all the fast dudes ran tire sizes like this:

15x7 = 195/50/15
15x8 = 205/50/15
15x9 = 225/45/15

On the S2000 the popular sizes are:

17x9 = 245/40/17
17x9.5/17x10 = 255/40/17

(I went with 255/40 on 17x9 on the S2000 bc I'm an idiot)

I just don't like tires that 'roll over' when you turn-in.

Double lol: Why do I (a dude who has zero interest in taking a car on track) base my tire sizing on track cars?

 

Ok, just for kicks, I'll blow my 205/50-16 up to 35-38 psi. I'll file a report later this month. But the tires now have +30K miles at 29 psi, so I don't expect them to feel / have same contact patch as if they were broken in at 38 psi. May take a year / 6000 miles to wear them into the new psi. I'm no tire engineer but like to experiment but will pull the plug if my 88 yr old mom complains about the harsh ride when I take her to dr appts.

BTW, I just got a set of Gen. Altimax RT43 to put on the wife's '09 Civic. She is currently running the Bridgestone Driveguard (50K miles on tires) and I can attest that they really do well in the "run flat" mode. She was coming back from Savannah to Pennsylvania. A day after coming back I went out to the garage and saw that the one tire was real low. When asked, she said, "Wow yea, some light was on the dashboard when we got into Virginia on Rt 95 (70+ mph)". She continued through VA to Rt 81 (Winchester, VA) and then up to Harrisburg, PA.

The Driveguard is supposed to be good for 50 miles at 50 mph. Well, this tire was destroyed (massive blistering inside) but it got her home (hundreds of miles at 70 mph). Not going to allow her to be a maniac like that again (70 mph on a flat for hundreds of miles). I noted that like the gas gauge, turn signal indicator, high-beam light, any symbol that pops up on dash means something. Look in the owner's manual or call me. Tire had to be replaced but no lesson was learned.

 

A 255/40/17 on a 9" wide wheel is a popular S2000 STR setup.

Again, we always have the same discussion. I don't know where you get your 205 on a 8" wheel or 225 on a 9" wheel? I have to believe you interpreted what someone said wrong? A 245 on a 9" wheel is a popular SCCA setup. The 225 on an 8" is also popular. The 205 or 225 on the 8 & 9" wheels will leave the tires stretched for a stance look. What you suggest is popular with the drift crowd. While a motorsport, I can't believe what they do translates well to street driving? Besides I seen your 225 on a 9" wide wheel used by a 30 year autocross veteran on his Miata. He spun out at least once at every event that season. Sure the car had phenomenal turn in, but that was at an expense. Obviously you or anyone can run what they want in regard to wheel and tire combo's. What you suggest isn't anywhere recommended rim width rages from tire manufactures.

 

949 Racing used to recommend it. Whether they do or do not these days I don't know. I don't keep up with anything more anymore & I avoid autocross discussions at all costs bc those guys are weirdos.

205/225 on an 8 or 9 wheel is not really a common drift setup, but hey, now we're both just talking out our butts, right?

EDIT: I knew I'd read this somewhere

https://www.flyinmiata.com/15x8-6ul-wheel.html

"The 15x8 weighs 11.6 lbs and has a +36 offset. It's ideal for a 205/50-15 and also works with a 225/45-15."