Tall tire test (taller gearing advantage offset by wider, heavier wheels/tires?)

[Bill in Houston]

Originally Posted by CapriRacer

Just be aware that there are extreme differences in rolling resistance between tires - even of the same size, let alone what the differences in size make. Be careful that you don't draw conclusions without taking into account that there might be severe differences different tires make (meaning make and model of tire).

Mmm, yes, very true. The right tire makes a big difference.

[arcosine]

Darrell, how do you get over 50 mpg driving a box shaped car?

[SentraSE-R]

Originally Posted by arcosine

Darrell, how do you get over 50 mpg driving a box shaped car?

Tony,

Mostly, I drive slow. As you can tell from my original post, cruise control at <35 mph is good for about 50 mpg in my box. Anything over 55 mph is like pushing a barn door into the wind. But I only get 40 mpg at 55 mph (it's more like 30 mpg at 70 mph), and half my miles are highway miles, so there's more to averaging nearly 49 mpg for >20,000 miles than just going slow.

Avoid stops. I live in the country, relatively speaking. I drive the frontage roads paralleling the freeways, and select routes with the fewest stops. I turn off my engine and coast 3 blocks to stops.

Pulse and glide. I pulse to 55 mph and coast back down to 30, or pulse to 40 mph and coast down to 25, or P&G between 30 and 20. When I accelerate, I try to keep the engine at the peak of its brake specific fuel consumption graph. When I glide, I usually do it engine-off at lower speeds. The big benefits to P&G come at slower speeds. My engine is on 25% of the time during a 25-40 mph P&G routine. It's only on 17% of the time during a 15-30 mph P&G, and it's on just 9% of the time during a 10-20 mph P&G regimen.

P&G has its benefits even at high speeds with the engine on. My last three tanks averaged 51.7 mpg, with 90% highway driving, and the engine on all of those highway miles.

[beer]

Or you can use (used) airplane tyres and fill them up with 14 atm.
Won't be road legal I guess, but give it some groves and no cop who will notice it.

They did it in 1973 already
http://ecomodder.com/forum/showthrea...3-a-17580.html

[arcosine]

Ha! A moment of insight, Darrell, the reason for the big teeth! Its to scare the drivers that cut in front of you when you are coasting up to a red light.

[SentraSE-R]

Dropped the 195/65-15 mules off to be mounted today, but I didn't get back to pick them up before the shop closed. I won't be able to do testing until mid-June. I propose ABCA cruise control and P&G testing over the same 10 mile course. To minimize the number of mountings/dismountings, the three different-sized front pairs will all drag the same 205/50-17 rears, and I plan to run them like this:

205/50-17 cruise control 33 mph
205/50-17 P&G 25-40 mph
195/65-15 cruise control 33 mph
195/65-15 P&G 25-40 mph
185/60-15 cruise control 33 mph
185/60-15 P&G 25-40 mph
205/50-17 cruise control 33 mph
205/50-17 P&G 25-40 mph

All cruise control tests will run at actual speeds as indicated by my Garmin Nuvi GPS.
P&G tests will run 1500-2500 rpm in 4th gear at roughly 78-83 load, with EOC.
I know the stock 185/60-15 tires use a 1.033 distance calibration (10 miles on the odometer is 10.33 miles actually traveled), and the new 205/50-17s use a 1.099 distance calibration. I'll establish the distance calibration for the 195/65-15 mules before testing.
I will inflate all tires to maximum sidewall (cold) pressure.
I will record temperature, weather, wind, and road conditions. The test road has little traffic, and I will run it on a weekend to avoid interference.
I have weighed the stock wheel/tire (185/60-15) combo at 35.3 lbs, and the 205/50-17 replacement combo at 47.3 lbs. I'll weigh the 195/65-15 mules when I pick them up. I'm assuming they'll weigh about 37.5 lbs.

Now is your chance to propose any changes, and to question my methodology. Any and all comments are appreciated.

[CapriRacer]

Originally Posted by SentraSE-R

Dropped the 195/65-15 mules ............Now is your chance to propose any changes, and to question my methodology. Any and all comments are appreciated.

I would suggest you keep the same inflation pressure for all tests. Just choose one. It could be one of sidewall pressures or the placard or something in between, but the same gauge reading.

Or for a bit of additional complexity, you could test the tires at the same load carrying capacity which you would get by adjusting the inflation pressure appropriately for each size.

At any rate, don't use the sidewall pressure if they are different. That's just one more variable in the mix.

Oh and one last quibble! The size is 185/60R15. 15" not 16"!

[arcosine]

An ambitious plan, Darrell. I would suggest some highway speed tests also for data on rolling resistance plus aero drag, since front wheels contribute to 10% of a typical vehicle's drag, not including ride height changes.

[Bill in Houston]

Seems like all of the tires needs to be equally warmed up before their test runs. Not sure how much that matters, but I am guessing it is noticeable. However you do it, thanks for keeping it updated.

[SentraSE-R]

Thanks for the feedback so far. It's better to measure twice, and cut once. I fixed the 185/60-15 typos, and the 33/35 mph inconsistency.

I'll include highway testing. My test route is on a frontage road paralleling a freeway, so it's easy enough to add a freeway test.

I'll inflate all tires to the same inflation pressure, either 44 or 51 psi.

Does anybody know how long it takes to warm tires up? I was hoping since the start of the test drive is only 4 miles from home, that I could consider all the tires cold when starting the test. Then the only issue would be the final retest of the first set of tires, and they'll have had about 4 hours to cool down after their first run,

One problem is going to be ambient temperature and wind. I'll want to start the test early because vicious 30-40 mph crosswinds typically start up in the afternoon about 2-3 p.m. But if I start before 9 a.m., there'll be a 20 degree temperature change. Even starting at 9, there'll be a 10 degree change.