Wheel and tire change, any FE improvement here?
 

Okay guys, I'm on a quest for 50MPG while trying to maintain 70MPH on the freeway. I know this is going to be very hard to do considering the 70MPH speed. I know that dropping speed by like 15MPH would probably get me my goal, but in Houston, everyone hauls ass. I'm getting better at not caring about this, but it's tough...

Okay for my next mod, do you guys think switching from a 195/50/15 to a 185/70/14 would be a wise choice? I plan on running them at a very high PSI to maximize rolling resistance. My current wheels are RPF1's and I'd be going to 14" steelies. I'm not getting rid of the RPF1's, I sort of want a spare set of Honda wheels anyhow....

Thanks in advance guys!! Oh BTW, I would plan on putting Mooneyes on these wheels for better aero...

Doing a little comparison I found the following information:

195/50 15 vs. 185/70 14: 185 tire will run 6.71% slower than the 195 tire at the same speed. That means that the 185 tire will show only 56.2 mph when the car is moving at 60 mph. So if you want to be travelling at 70 mph, your speedo should only read 65.6 mph.

Checked tire weight on Tire Rack and the selection is pretty meager for those sizes. Seems like tire weights are fairly comparable - so unsprung weight should stay close to the original size.

I did however notice that you can get a Bridgestone B381 in the 185 size. If I remember correctly this is one of the tires that did very well in a tire comparison in terms of rolling resistance.

So with all that in mind, you should be well on your way. I would experiment with some "drafting" to get you past the 50 mpg. By drafting I mean, following a larger vehicle at a distance you feel safe and comfortable with.

Sometimes I like to leave a larger gap, speed up just before a downgrade and then release the accelerator in gear and let the engine brake the car while catching the vehicle in front gradually. That way I can squeeze maybe a few miles of "fuel-injection-off coasting" while still having all ancillaries (A/C, power steering and brakes) operational in case of an emergency.

I'm curious to see other comments on this matter, as I may be going in a similar, but less drastic, direction. (205/55 16 current, 205/60 16 proposed.)

You said it!

Did you check the circumference difference?

This tool shows you'd raise your effective gearing slightly, since the diameter of the 175 is larger.

And the narrower the tire, the better, in terms of aero drag. See here: http://ecomodder.com/forum/showthrea...g-cd-7475.html

You'd raise the ride height slightly, which is probably bad for drag.

But the smooth wheel cover would be a plus.

And even at the same pressure, two tires could have vastly different rolling resistance.

So... it's not easy to say for sure, but I'd do it.

(Actually, I'd do what Ben did on his CRX: put smooth alloys with the even narrower Insight tires on: http://ecomodder.com/forum/showthrea...ghts-9517.html )

Thanks for the replies guys!!

Yes, I've considered the ride height will be about 1/2 - 3/4" taller (tire differences are about 1.5" diameter), however to conteract this I will be installing a full under body tray very soon. I like that my effective gear ratio will go down, also it's a narrower tire which is better for aero and the wheel covers will help too. I'm only worried about them being a lot heavier. Currently my wheels with tire weigh less than 25lbs each...

Oh and is there any way to correct the speedo? Or will I have to make my own corrections when doing MPG calculations?

One more thought: Sealing panel gaps could smooth out the air flow. I would also check the underside of the rear of your car for any parachute-like objects. Mounting mud-flaps in front of the front tires may help offset the increased ride height? Good luck :thumbup: - I'm all for real world mpg improvements!

I'm a long time lurker on this site, and I have since removed, tightened up, etc. most everything I could on the outside of the car. I am going to make a belly pan, and I want to do some sort of small bump across the rear hatch of the car to detatch the air properly and quickly from the car's behind. Anyone with a CRX make such a wing/spoiler yet??

Guys, I'm worried about the steel Honda wheels being way heavier than what I'm currently running and potentially making my MPG worse.

Current wheels are 15x7 RPF1 Enkei mounted on 195/50/15 Toyo Proxes4. My tires are getting to the point to where the need to be replaced.

How heavy is the steel wheel tire combo going to weigh? One of my wheel/tires right now wheel less than 25 lbs.?? Wouldn't the extra rotational mass hurt things more than help MPG?

Stock CRX HF wheels are 13" steel wheels that are 4.5" wide and weigh around 12-13 pounds, stock civic vx wheels are also 13" by 4.5" wide alloy wheels but weigh around 11 pounds, same with the civic HX rims only they are 14" around, not sure how wide but in the 11 pound range, I think Honda Insight rims are a bit lighter, are also 14" by I think 4.5" with a smooth face to them so you could skip the wheel cover cost and wheel cover weight.
You might also check in to 1985 and maybe 1986 crx hf rear brake drums, along with the first gen honda insight rear brake drums as they were both aluminum drums instead of cast iron.

90crxHF -

I am 90% sure that my Saturn has the 100 mm 4-lug bolt pattern that you have (let others chime in to correct me). If I'm right, and (BIG) *IF* you have the wheel-well space, you could use Saturn steelies and go up to 195/65/15 :

http://ecomodder.com/forum/showthrea...ires-2642.html

But, maybe that's just too insane.

CarloSW2

I'd suggest going to some 155x80x13 tires on American Racing Estrella rims. I went from that size 13 to the 195x50x15 tire/rim package on my Geo Metro 3 banger and the tire/rim pacage is 8 lbs heavier per corner. The old tires had a max tire pressure of 35 while the new ones would take 51. In the end the gas mileage on flat ground/highway speeds remained the same due to much less rolling resistance, BUT the 1/4 mile times went from 19.9s normally to 20.6s. When the weather gets warmer I will return to the 13 set up. The Power Star 13" tires are 14 lbs while my Estrellas in 15" are 18 lbs. My 15 inch rims are 16 lbs while the Am Racing 13s are 12.8...BUT, the newer 13s can take more tire pressure than my old ones. Going back to my 1/4 mile ets, I did take an extra 32 lbs out of the car to make the wt the same as it was earlier with the 13s. When I go back to the 13s I will loose anoth 32 lbs so that my new wt will be 1598 compared to the present 1630. I have taken 132 lbs out of it, but added 32.

Another idea I was thinking about was to keep my 15s, but go to the 175x55x15 size that are 4 lbs lighter and less costly than a new tire AND rim set up!

Not going to be an issue in highway driving.

That's what you're setting this car up for, right?

Also the issue is more complicated that simple weight. Mass distribution of the 15's - more mass toward the outside - could potentially be less favourable than 13's or 14's. (Someone feel free to correct me on that - just something I read elsewhere that makes sense.)

fudge factor for FE to account for OD difference
 

did you calculate in a fudge factor to allow for the difference in OD when making the FE comparison between the
155x80x13 versus 195x50x15 tire wheel combination ?

are you thinking the change in 1/4 mile times are a direct result of
increased mass of the wheel tire assembly
or
increased aero drag of the wider tires / wheels
or
change in final drive ratio due to larger OD of the 15" wheel / tire ?

i have the same car and of yet un installed 15" alloy acura legend wheels with 195 60 15 tires

The 155x80x13s were 22.8" in dia while the 195x50x15s are 22.7, a difference of only .2%....and even though tiny I correct the miles per tank to reflect the shorter tires...for example every 100 miles traveled is really 99.8.

The 1/4 ets are slower due to the extra wt of the tire/rim combo...not aero drag because the car aero was cleaned up better with a grill block and headlight covers. The new aero mods made the top speed on the hiway rise from 81 to 87 mph! The slower ets were not caused by the difference in tire diameer because the 15s are a bit smaller and should have helped a quicker et.

As for putting 195x60x15s on your car you might run into clearance troubles. That size is 24.2" in diameter, and if your speedo says 60 you will be really doing 63.8 or a error of 6.3%. If I am on a undulating country road I can hear my LR tire barely scrape the fenderwell...your problem will be MUCH worse due to the much larger dia of those 60 series tires. If you think you'll get better mpg because of the larger dia you will also need to figure in that the 195x50x15 tires are about 5 lbs heavier each than the stock 13s.

Here's a link to what my stuff looks like, and the cars I race against:

Even the 3 cylinder Geo gets action
UMTR Nationals at Edgewater - 9/26/09 - Hyper-Performance Motorsports Inc. Photography
The White Gnat strikes again
UMTR Nationals at Edgewater - 9/26/09 - Hyper-Performance Motorsports Inc. Photography

Yes, I do like 90% highway with this car.

Oh and BTW, I got the 14x5.5" and I've already mounted them on the car. They fit great, now onto some Moon Eye covers...

I've found them online for like $85 for the stainless steel ones, anyone know of anything cheaper?

And BTW, Firestones on these wheels can take 44psi. What MPG difference would it make from 36PSI to the 44PSI? I guess only real world testing will tell, considering all the other variables... I try to drive as consistently as possible so my numbers are the least amount skewed....

Also, what size tire should I put back on these?? And if there is a 14" tire recommendation, please let me know. I've been looking at 175/70/14...

EDIT: There seems to be no difference in accelaration, and considering I don't drive fast anymore, it really doesn't matter....

If you get the 165/60 R14 tires that the insight has they will be Low Rolling Resistance tires, also you should be able to get the lighter aluminum moon disc hub caps for around $100 used.

look at some of the pizza pan mods you would be surprised how good they can look.

Dang, that will put me at 3600rpms at 70mph... With the 195/50-15 I was at 3400rpm at 70mph, and now with these 185/70-14 I'm at around 3200rpm at 70mph. I guess it really won't make much difference since I'm driving more around 60-65mph on the freeway now. I occasionally hit 70mph, but really only going downhill now.

Thanks so much for the replies guys. I will look into the pizza pan moon disc mod. I've already been thinking of doing that anyways, probably much cheaper, but I don't want it to look cheap. Know what I mean?

Okay guys, I'd like to report that I have now hit solidly in the 40's MPG wise... With this tire change I have now hit 41.35 MPG. This is running the tires mostly around 34 PSI. How much of a MPG improvement does pumping them up to say 40 or 44 PSI do? Would I see another 1 to 2 MPG? If so, I might try it and run my Illumina's on setting 1.

Oh BTW, I'm using the stock 2003 hub caps on the steel wheels. They seem pretty decent for aero, besides I waxed the crap out of them. I might eventually get the moon discs.

I've been researching wheels lately, as I plan to replace my stock 18" boat anchors when the tires wear out (wheels are 24 lbs each, stock!) I've got my eye on the Enkei RPF1 also, since they are so light. Are you still running the steel wheels? Did you really see a mileage increase when you swapped out the 15" Enkeis? I see that the 15x7s are specced at a staggering mere 9.5 lbs each! That's amazing. The 18 x 7.5 RPF1s for my car run 17.6 lbs, and the 17 x 7.5 are only 15.2 lbs (big for you, but a huge unsprung weight diet for me). I also see you have one car for high mileage, and one for high speed :thumbup: Unfortunately, living in the high-cost socialist city of Chicago makes it difficult for me to support too many cars (2 is enough for now), so my DD has to suffice as my track toy also - all the more reason for the RPF1s.

I am not really sure about putting steelies on mine. The 14 inch ones are way heavier than my 15s.

All I can say is, getting good MPG is cool, but I have since put my RPF1's back on with brand new 205/50 Nitto NeoGen's, and I have been having fun again on my commutes. The 14" wheels I was running was mainly to just get me by until I could by tires again. I bought the 14" wheels and tires for $80, and I used them for a couple of months. My Toyo's were getting scarey in the rain.

I have yet to check my MPG again really with these new NeoGen's. I have checked once, and even with a lot of playing around (not trying to get MPG at all) the car still get's 38-39 MPG. This is at like 32 - 34 psi. So, with trying to get MPG and pumping the tires up, I'm sure I can get the same as I did with the 14's.

Oh and BTW, if you get the RPF1's, you'll love them. They are one of the strongest wheels for the weight you can buy.