Reducing Tire Width - Fuel Economy, Hypermiling, EcoModding News and Forum

Meph · 09-14-2010, 12:57 AM

What could one expect to gain reducing two tires on a car from 285/40 to 225/50, the larger tire being a soft 180 tread wear compound and the new tire being a 400+ LLR.

The car seems to do 35MPG on a good day so lets use that as a starting point. The newer tire would be 1-2% smaller that the original so hopefully the gain would outweigh the loss in diameter.

For kicks what would be your guess at a final MPG if I did the following

- New tires
- Alignment (currently pull a bit to the right and totally ate the inside tread of the front right tire in a couple thousand km's, Toe is off, and at least 3/16ths toe in
- Switching from dino to synthetic oil in the trans and diff, lightest weight possible.

Wanna see if I can hit 40mpg one day

mcrews · 09-14-2010, 01:23 AM

Meph,

not sure where to begin......
How about you giver us enough info to make a decission????

For starters, how about the last number on the tire size???
it's kinda important.......

The car came stock with 205/60/14. they wiegh 19lbs and have a diameter of 23.8 inches.

THere is no 285 in a 14, 15, or 16 (at tirerack.com so I can only assume they are 17 inch??????
I 285/40/17 wieghs 30lbs. that is just the tire!!!!! so you have 11lbs X 4 spinning on each corner 44extra lbs.
the diameter is 26inches.
Again, I assume you are staying with 17 inch rims to runn the 225/50/17. they wiegh 31lbs.....1lb more or 48 extra lbs from stock spinning. They are 25.9ijnches in diameter.....why bother????? the only upside is the high sidewall "COULD" give a little softer ride.

Bottom line .....you will not get better mileage.
225/50/17 wieghs more and the profile is 9.5inches down from 11inches.

more info needed....

good luck

Meph · 09-14-2010, 01:40 AM

sorry its been a long day, new baby in the extended family (not mine). They are 15's and you'll never find them for sale, long outdated.

The 285/40/15 is on there now, balding like a middle aged man. My only option is to stretch a 225/50/15. We already discussed the stretching issue in another thread so if we put that to the side and focus on the reduction in tread width, weight and switching to a much stiffer compound. what gains could be expected?

sorry for the confusion

Olympiadis · 09-14-2010, 02:04 AM

You know those things can't be predicted with much accuracy. It always depends. The first thing that comes to mind for me is your driving style.
If you are hypermiling and already doing a lot of coasting, then your tire upgrade and improved alignment are going to help proportionally more.

The individual gains are going to depend on how bad your situation is presently, - how much your current specs are hurting you while using your current driving style.

I think I've seen several people post individual gains between 3% and 6% by just increasing tire pressure from 32 PSI to 45 - 50 PSI. I'm sure that was for all four tires.

The LRR tires have claimed as much as 7% if I am remembering correctly.

I would just expect the worst and hope for the best.

The toe alignment can actually make a very large difference on some vehicles. Of course you'll have to check for play at all of your mounting points. Odd wear on just one tire usually means slop on one side. I know little to nothing about your particular car model.

CapriRacer · 09-14-2010, 04:58 AM

Quote:

Originally Posted by Meph

What could one expect to gain reducing two tires on a car from 285/40 to 225/50, the larger tire being a soft 180 tread wear compound and the new tire being a 400+ LLR.........

First, no one is going to be able to answer your question with any degree of accuracy. To understand why, you need to read this:

Barry's Tire Tech

and this:

Barry's Tire Tech

So your proposed going from a 285/40R15 to a 225/50R15 is going the wrong direction for load carrying capacity. You are going smaller in load carrying capacity and that's the wrong direction for RR. Try a 255/50R15 or something like that.

Patrick · 09-14-2010, 10:20 AM

Here's my SWAG (Scientific Wild Ass Guess) at it: +5 mpg.

euromodder · 09-15-2010, 02:09 PM

Quote:

Originally Posted by CapriRacer

So your proposed going from a 285/40R15 to a 225/50R15 is going the wrong direction for load carrying capacity. You are going smaller in load carrying capacity and that's the wrong direction for RR. Try a 255/50R15 or something like that.

Or pick the higher load index versions (XL) of a given tyre size.

That'd help too, wouldn't it ?

Meph · 09-15-2010, 07:02 PM

So does this all mean there are no gains to be had going from a wider to narrow tire? All this points to everything being a big catch 22.

At the very least I know my current performance tires are not anywhere close to a LLR tire, and the potential gains of switching to a LLR are probably at their greatest.

Would we not all be rolling around on the widest tires available if they key to minimizing resistance was a wider tire?

Im very much in limbo as to what I should do.

Also did my alignment today, my measurements showed almost 1" of toe out. Im not surprised after all the new parts on it. I used some DIY skills on it and now im about 1/32" toe in. Drives about the same but I notice when its int he garage, it wants to roll a lot easier. I use to push it out if I didn't want to start it, now i just give it a nudge and it rolls out all by itself. The results from my 15 miles test drive showed about a 1mpg increase from before, but my speeds were a lot higher at times 60-70km/h before and up to 90 or so today with a couple boost incidents as well.

I think the lower temps here are starting to have a noticeable effect, Ive dropped a few mpg from when it was 80 outside, its about 55 now so maybe that accounts for lower numbers.

Saberj2x · 09-15-2010, 07:16 PM

ah, The classic Z...

skinny tires reduce the tire friction with the road, but I guess you'd need to change all 4 to make it worthwhile, including the aerodynamic improvements.

I'd suppose the difference would be minimal regardless and not worth the loss of traction to keep you safe

and what Capri said...