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sfair74 12-10-2018 05:06 PM

Wheel swap? 175/65-r15 Steel to 185/65-r14 Insight Wheels

I recently purchased a 2017 Toyota Yaris L hatchback. I have added factory cruise control but am otherwise stock. I have run some fuel system cleaner through the first tank of gas. It's still using the factory 5w-30 oil from the dealer and has yet to reach the next OCI. I plan to switch to Mobile 1 0w-20 EP when the time comes.

I drive around 25,000 miles per year. My drive is mostly 50 to 55 MPH with some 25 to 40 MPG stretches and may contain some 70 MPH expressway.

When I first got the car I was getting around 37 to 38 MPG on the lie-o-meter. As colder temps and winter blend gas has set in I'm getting 35 to 36. I typically get significantly above the listed highway mileage as my average but i'm quite disappointed in the MPG so far.

I think it would greatly benefit from a upper grill block and maybe a partial lower block. I don't have a scan gauge installed yet and will probably hold off till the dealer replaces a wiring harness next month on my car as part of a recall.

The thing I'm interested in is it worth it to swap wheels for lower weight and aerodynamics? I previously owned a 2001 Honda Insight and those wheels were light weight and have the same 4x100mm holes spacing and a very close offset to the Toyota Yaris. I have tracked down a set of salvage insight wheels and lug covers for under $200. Going to a 14" aluminum wheel with great aerodynamics should help compared to the stock 15" steel with hubcaps.

I am also a huge fan of Nokian's all weather tires. I have my sights set on their new WR-G4 tires. Unfortunately the only 14" size for that particular tire is 185/65-r14. The stock tire size is 175/65-r15. The purposed 14" tire has a higher weight rating so there shouldn't be any safety concerns. It's obviously 10mm wider than stock and about 2% smaller diameter. The total diameter of the tire is around 1/2" less so it should lower the ground clearance by 1/4".

Unfortunately the car is already geared pretty short with a traditional 4 speed slush box automatic. I fear the changing the tire size to be 2% smaller may negate the expected fuel savings from a lighter wheel and tire package and aerodynamics.

The other hangup is I would either need to buy a new set of TPMS sensors at $60 or pay probably $16 each to have them removed from the old wheels and have them moved to the new.

Is it worth the trouble and $250+ to swap to wider shorter tires in the name of aerodynamics and lower wheel weight? Another option is to get a set of clip on racing disks for around $100. I plan to drive the car for 3 to 8 years as of now.

Thanks for your suggestions.

mpg_numbers_guy 12-10-2018 07:20 PM

Welcome to Ecomodder! :)

If you block off part of your grille, be sure to monitor your engine temperature using more than just the indicator on your dash.

Regarding wheels, switching from 18lb OEM alloy wheels and 17 lb tires to 11 lb HX rims and 16 lb tires on my Civic gained me 2-3 MPG. Lighter wheels find their biggest benefit in hilly driving and city driving.

My rims were 15" and downsizing to 14" required using a 1/4" spacer. May or may not be a problem for you.

Since you also live in Michigan, I would recommend getting winter tires. From what I've heard and seen Bridgestones are the best summer tires and Nokians are the best winter tires. Michelins are right up behind them.

So to avoid having to remount tires every time the season changes, I would pick up a set of lightweight wheels for summertime, put summer LRR tires on them, and then put winter tires on your steelies.

Going with a smaller diameter tire will essentially shorten your gearing and reduce fuel economy in most situations except hard city driving due to the smaller rolling diameter. Increasing your diameter will improve highway fuel economy, but slightly reduce city fuel economy due to the heavier weight. Going narrower is a good alternative.

Both Insight rims (10.5 lbs) and HX rims (11 lbs) are excellent choices. If your stock tire size is 175/65R15, you would need 175/70R14s to keep the same size. Going narrower would be 165/75R14s, both of which aren't that common to find.

Best bet would be Insight wheels + Bridgestone Potenza RE92s and a taller transmission swap to offset the shorter gearing from the wheels, but the return on investment for that would be in the hundreds of thousands of miles. :rolleyes:

Don't spend a lot of money on rims if your goal is to save money. The return on investment will never be there. I spent only $100 on my HX rims and they haven't paid for themselves...yet. I will be using them as wheels for my Insight's winter tires, and that will count as a break even point for me. Insight rims are generally harder to find and more expensive than HX rims.

Smooth coroplast discs are a very inexpensive way to do smooth wheel covers, but your opinion may vary depending on how important aesthetics are to you.

oil pan 4 12-11-2018 12:23 AM

Don't waster money on light weight wheels.
A little bit of leg work saved me a lot of coin.
The light weight wheels I was looking at were only about 2lb lighter than steel wheels.

If you drive mostly highway lighter wheels will give the least benefit.

For me I am going to replace my alloy nissan leaf wheels with steel wheels and aero covers.

Concentrate on those aero mods.

iikhod 12-11-2018 03:39 AM

Also, remember to check if the smaller diameter wheels fit over your brakes.

oil pan 4 12-11-2018 01:21 PM

Go bigger not smaller on the overall diameter.
With smaller tires you will see a MPG hit once the miles traveled are corrected.

Can you get 185/65r15 tires?

sfair74 12-12-2018 08:05 AM

Thanks for the replies. I'm a long time lurker and huge geek.

I forgot to mention I also upped the tire PSI to 40 after the first couple weeks to get a baseline.

As far as grill block and engine temperature I don't have a scan gauge yet. I guess I could use one of my ELM23 sensors and Torque pro android app. The Yaris doesn't even have a temperature gauge. It has a blue engine temp idiot light that is on when it's cold and a red light if it's too hot. On my 2001 Insight I just shoved a coroplast yard sign between the grill and the radiator during the winter.

I live in Michigan and winter tires are a must in my book. I have recently been a big fan of Nokian's all-weather tires. They are different and not to be confused with all season tires. They are a softer winter compound but they were designed to hold up to heat and can be run year round. The are heavily siped and feature aggressive winter tire patterns. They aren't the best for noise vibration and harshness but if I was too concerned with that I wouldn't be driving a Yaris. I prefer the all weathers vs having to switch a dedicated set of winters and all season tires. If my car didn't have TPMS or had indirect TPMS I would probably just buy a separate set.

I would really prefer to stick with the Nokian WR-G4 tires so my size selections are a bit limited.

185/65-R14 (Stock -2.04%) *Honda Insight Rims $250+ w/ moving TPMS
175/65-R15 (Stock tire size) *Stock 15" steel with OEM Hubcaps
185/65-R15 (Stock +2.14%) *Stock 15" steel with OEM Hubcaps
195/65-R15 (Stock +4.27%) *Stock 15" steel with OEM Hubcaps
205/65-R15 (Stock +6.41%) *Stock 15" steel with OEM Hubcaps

14" rims will fit fine. I have found a few posts detailing that 13" rims should fit the Yaris. Unfortunately there's not much good information out there on what size taller tiers fit in the Yaris without rubbing. There's a good deal of information about going to wider tires with a lower sidewall ratio but the diameter is usually pretty close.

I have run the Yaris specs through a spreadsheet that I use to analyze any vehicle I'm interested in regarding gearing and piston speed. The gearing is quite pathetic and I think should either have a couple more gears or a taller final drive. The engine stroke is 84.7mm. The forward gears are 2.847, 1.552, 1, and .7. With a final drive of 4.237. The stock tires are 175/65-R15. In top gear the speed the piston reaches 5 m/s is 43.01 MPH and the speed it reaches 6 m/s is 51.91 MPH.

I think my mostly steady highway driving could benefit from taller tires but it inevitably will come with wider tires and more ground clearance.

How tall of a tire is too tall provided that it will fit? Has anyone gone to drastically larger tires with good results?

I'm not concerned about the speedometer. I use a GPS as a heads up speedometer. On top of that the Yaris speedometer is trash. It has numbers every 20 MPH and a line every 10 MPH. But don't worry they decided to use the space for some weird dot pattern on the outside that doesn't associate with MPH vs the standard line pattern used on most every other car.

arcosine 12-12-2018 08:27 AM

Every time I put larger diameter tires I see mpg improvement, fatter tires though, are harder to push through snow and slush, hydroplane easier.

I have 195/65R15 from the stock 175/70R14. Ive had 205/70R15 at one time, but used spacers. Car was not as stable at interstate speeds, but the spacers helped some. I liked how it cruised,lower rpm. Around town it would roll farther,no penalty.

Ecky 12-12-2018 08:37 AM

I wouldn't go over a 70 aspect ratio. I also wouldn't go any wider than stock, either. The Insight wheels will improve acceleration, handling, and aero by a bit. I can't see any downsides other than price.

sfair74 12-12-2018 09:58 AM


Originally Posted by arcosine (Post 585743)
Every time I put larger diameter tires I see mpg improvement, fatter tires though, are harder to push through snow and slush, hydroplane easier.

I have 195/65R15 from the stock 175/70R14. Ive had 205/70R15 at one time, but used spacers. Car was not as stable at interstate speeds, but the spacers helped some. I liked how it cruised,lower rpm. Around town it would roll farther,no penalty.

Thanks for the real world experience arcosine.

If I crunch those numbers a bit I get the following info.

Stock tire size:
175/70-R14 = 23.65"

Stable Upsize:
195/65-R15 = 24.98" +5.64% +20mm width

Unstable upsize:
205/70-R15 = 26.30" +11.22% +30mm width

I would love to switch to a taller narrower tire with the same or higher weight rating. Unfortunately the selection of tires in that size let alone a tire I prefer are limited / non existent.

I will do more digging and see how much extra room there is in the wheel wells without adding a spacer.

I get my tires through discount tire. I will have to see if they will install larger tires than the listed stock.

roosterk0031 12-12-2018 05:33 PM

195-65-15 G3/G4's on my cobalts & elantra, all weigh 3-500 lbs more than your Yaris, 100-150 lbs each tire less weight doesn't sound that much different. Actually have G3/G4 on all my cars. Tires are cheap vs tows or deductibles.

Recently I've been buying mine on Ebay (tireseasy), they often have lower prices on ebay than their own website, past have been from simpletire. Simpletire looks cheapest today.

They also make 195-60-15 if you wanted to stay a little bit closer to stock diameter.

Checked Nokian site, the
195-65-15 is listed at 25" OD, 832 revs/mile
195-60-15 is listed at 24.2 OD. 859 revs/mile
175-65-15 is 24.0 - 866 rev/mile

I don't know if you calculated or used their numbers. Page 19

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