E30 Hypermiler: What tire?

Hey GRMer's I've got a '90 318is I drive ~120 miles per day on flat highway and I'm trying to hypermile it using cheap-to-free parts, ideally cast offs from my E30 race cars and parts cars.

Step 1: installed 325e 2.93 diff [edit its a 2.79] from parts car. Result: 38MPG without trying too hard. Not freaking bad for a quarter-million mile old motor and running on 205-wide parts car tires that usually only hold pressure for a week or so.

Now I'm thinking I can really push this thing into Prius / Volt territory for very little cost. But the tires I'm driving on are pretty well shot and I really shouldn't be driving them over 100 miles/day. Soooo

What's the best (i.e. lowest rolling resistance) low rolling resistance tire I can get? For now lets say I don't give a crap about grip or road noise. I just want to get better mileage than a Prius in a $1k 26-year-old German "sports sedan". I want to use the stock 14X6 wheels, because I have a lot of them and want to use my 15's for race car spares. I realize that 14" rim limits my selection somewhat.

Currently have my eye on the Dunlop Enasave 01 A/S in a 165/65R14. Tire rack reviews are sub-stellar, but it looks like it was originally designed with rolling resistance as job one, and it fits on my rim. Better ideas?

Sounds good to me. Pump them up to like 50 PSI as well for better MPG at the cost of tire life and grip.

What are your aero plans?

In reply to Robbie:

Lowering about an inch and adding garden edging for starters. If that makes a big difference I may fab something slightly less ghetto than the garden edging, but ghetto hypermiler is kinda the theme here, so maybe not. Also planning on race-car like gutting to drop weight. The interior is not great shape and I think I would rather be looking at sheet metal anyway. If I get really inspired I may chop a few inches off the roof line and replace all the glass with polycarb, but trying to do this project in nice incremental steps, so it may be some time before I go sawzalling things.

hmm. cool. I don't think you will realistically see any difference gutting the interior in MPG, but it will be loud and buzzy.

For aero, what about taping up grill openings, mirror deletes, rear wheel well covers, underbody flat panels, or solid hubcaps? Seems like there are a lot of easy ways to go before chopping a few inches of roof.

All good ideas. Based on what I've learned on the race cars, I think I could drop 500 lbs and still have doors, windows, and most of a dash board. That won't do much on the highway, but I bet it would get the city mileage into the upper 30's.

Yes, chopping the roof is serious surgery that is not easily justified in fuel savings. But it would look cool.

Weight reduction will help city mpg. And might help a little on the highway if you've got a lot of big hills.

Under body aero, like those big clear mats your put over carpet so an office chair can roll. Going from or before the diff and connect it to the bottom of the rear bumper. Or sheet metal the entire bottom side

Robbie wrote: Sounds good to me. Pump them up to like 50 PSI as well for better MPG at the cost of tire life and grip. What are your aero plans?

Don't forget braking is a cost too. Overinflate and you add risk with little gain

A grille block could help a bit. I blocked off the Crown Vic grille, then taped up the seams around the headlights and it was good for a consistent 3 mpg improvement.

Interesting.. I just got a slightly used set of Kumho Solus KH16s for my Civic beater commuter car. No science, but compared to the winter tires, it feels like they have zero rolling resistance, even at stock pressures.

I like the ideas for gheto Aero mods too!

E30 is definitely not the best choice you could have made for this. Its got all the aerodynamic prowess of a large brick. Still, im interested to see what kind of numbers you pull!

Are you sure that you accounted for the difference on the trip odometer since you changed differential ratios? I doubt you gained that much, and would instead suspect you are counting too many miles per revolution.

Are you on ecomodder?

makes me wonder what the more aerodynamic E36 body could do. Say a 318ti with hyper-miler mods?

In reply to tuna55:

Odometer doesn't work at all (Because E30). I'm comparing to Google map distances over 3 days' commute (most of a tank). So I'm sticking by my answer.

Oh, and I'm making no argument that an e30 is the most aero-dynamic platform for a project like this. The aerodynamic similarities to a house brick are undeniable. But it's the platform I have lots of spares for, I already had this car when I got the gig with the long commute, and the hypermiler can do double duty as a rolling parts car on race day.

sporqster wrote: Oh, and I'm making no argument that an e30 is the most aero-dynamic platform for a project like this. The aerodynamic similarities to a house brick are undeniable. But it's the platform I have lots of spares for, I already had this car when I got the gig with the long commute, and the hypermiler can do double duty as a rolling parts car on race day.

I don't doubt you.. It just got my brain working :)

tuna55 wrote: Are you sure that you accounted for the difference on the trip odometer since you changed differential ratios? I doubt you gained that much, and would instead suspect you are counting too many miles per revolution.

I believe bmw uses a speed sensor in the diff anyway, and it is actually on the ring gear, so no matter the ratio, it is always counting revolutions of the axle.

In most other cars this would be a problem, but in BMWs a diff swap does not screw with the speedometer or odo.

The_Jed wrote: Are you on ecomodder?

Nope, but I am now! Thanks!

sporqster wrote: In reply to tuna55: Odometer doesn't work at all (Because E30). I'm comparing to Google map distances over 3 days' commute (most of a tank). So I'm sticking by my answer.

oof! That seems, to be understated... inaccurate.

According to Ecomodder, the answer to the original question is Bridgestone B381. http://ecomodder.com/forum/showthread.php/top-5-most-fuel-efficient-tires-lowest-rolling-2813.html

I always thought that Political signs could make nifty material for an underbody tray

My e30 rally car (with stock high-mileage M42 engine and 3.91 or 4.10 LSD depending, fully caged and with multiple extra light pods on the front bumper) pulls off 30 mpg on long trips going to rallies, loaded with gear and towing my tire trailer. I usually see mid-30s when just cruising with the car mostly empty, and I usually have the roof vents open, to boot. And my street tires are 195-width Star Specs, so definitely not LRR.

I didn't think that LRR tires are THAT significant in terms of mileage over regular all-seasons (things I have read don't give more than a 1-2% change in mileage, IIRC, but I could be wrong).

You could probably make more improvement from: 1. underbody sheeting (since mine is a rally car it has a big skidplate as well as HDPE sheeting over the entire underbody and gas tanks). In theory that should reduce a ton of underbody air drag (though my concern is obviously protection). 2. lexan panels over the headlights....that's a pretty high drag area on the e30. 3. if its a sedan, lexan the rear windows flush shoudl reduce drag

What speeds do you run? I couldn't imagine wanting to run this M42 with that low of a ratio on the rear end, unless you're really moving at high speeds or your commute is really, really flat.

irish44j wrote: ...or your commute is really, really flat.

Indiana. My commute is really, really flat. Acceleration from 70 is almost nil.

1. Awesome

2. +1 to lowering/airdam and other aero mods. This is where your focus should be. Lower weight gains you almost nothing on the highway. This is a good reference for front end work: https://hanchagroup.wordpress.com/2013/01/29/splitter-or-air-dam-which-design-is-best/

3. You still won't touch a Prius, unless mileage @ 70mph steady state is your only point of comparison :)