Tire size vs lean burn, gear ratios, etc. What tire size am I after?

[phyregod]

Ok, Big question here.. I'm building a hypermiler. So far, the build is:

1990 CRX Si
1994 Civic VX lean burn engine
1991 CRX HF transmission

I'm pondering tires size for lean burn at 75mph (my commute speed)

Stock HF tire size is 165/70-13.

Tire size I'm considering 195/55/15 (because of Konig Helium 15x6.5 wheels to save weight)

According to my calculations, the car will be at ~2200rpm at 75mph on these tires, which is well into lean burn territory if the load is low, which it should be? (Total guess here) given the .29 stock coefficient of drag.

My question is, would it be better to go with a smaller tire diameter to get the engine speed up a bit and reduce the load on the motor in order to keep lean burn active? Or would lean burn be active anyway? Would that produce better or worse mpg? From my research, I need >4 in hg manifold pressure and under 2250rpm for "high load", under 3000rpm for "low load".

I commute 200 miles a day on a pretty flat highway and I'm looking to do 75mph on the commute. Every 5mph lost is an additional 17 minutes per day, hence the "high speed" (legal speed limit) requirement.

[beneuan88]

not answeingayour q but, Your mags might be light but i bet those tyres are heavy. I geuss that shouldn't hurt at constant speeds anyway.

[phyregod]

Tire weight is something I'm clueless about. No one lists tire weight in their specs. Not that I've found, anyway..

The stock SI wheels weigh ~17lbs. The konigs are ~11lbs. That is 24 pounds of un-spuing weight saved. Which is huge. But it does me no good if I just replace that weight with rubber..

I don't have the konigs yet.. Could cancel the order as they are back ordered. Is there a better solution? Lighter/skinnier setup?

[Baltothewolf]

Go either honda civic HX rims with Bridgestone potenza Re92's or Honda insight rims with Re92's. Nothing else is more superior in the tire department. I think there are slightly lighter rims out there but they are SUPER expensive.

[phyregod]

I see the top dog here is running insight space saver 14x4 wheels. Would those be safe at 75mph for a gazillion miles?

Stock wheels appear to be 11 pounds and 14x5.5

Ref:
Insight Stock Wheel Mfg: Asahi Tec Corporation Size: 14 x 5.5 J Bolt Pattern: 4-100mm Lug Size: 12 x 1.5mm Offset: +45H Weight: 11 lbs Finish: Aluminum

[Baltothewolf]

Some insighters have 300k+ miles on theirs with no problems at all.

[phyregod]

I mean using 4 space savers. 14x4. Could get 5 and rotate in the spare. Would be handy. Assuming there is a tire skinny and tall enough to work..

[Baltothewolf]

The top dog is stock insight wheels with Re92's. I believe MetroMPG did a comparison of the tires a while back and that was the best combo.

[phyregod]

Ah, his garage states "insight space saver wheels".

Another player to enter the field is Toyota Yaris 15x5 steelies. 16 pounds with a +38 offset. Slap some aluminum moon disks on it and has an inexpensive/skinny wheel that is roughly Oem weight with the disks. Would look cool.. Would the disks actually do anything? They were all the rage in the salt flats.

[elhigh]

If you decide to go with the 14x4 Insight wheels, Tire Rack has Potenza RE92s in 165/65R14 for about $80 each.

http://www.tirerack.com/tires/tires....omCompare1=yes

22.5" tire height, 13lbs per tire. This almost exactly matches height of the stock tire, weighs a fuzz less. I don't know how the wheel weight compares to stock wheels but if they're off an Insight, I would imagine they weigh a fair amount less, too.

Your stated 195/55R15 tire will weigh more around 18lbs per tire and be about 23.5" high. That'll give a hard ride over rough surfaces and may affect drivability in stop and go traffic, and definitely throw off the odo and speedo, reading about 4 percent low unless you can change the speedo drive gears in your Frankencivic.