The extreme AreoCRX-HF project

[Tango Charlie]

Got any photos?

[rcpmac]

Here is the best online tire size calculator that I have seen.
http://www.miata.net/garage/tirecalc.html

[ebacherville]

yeah really tire size is going to help considerably at this point .. the car really seems to be reving.. considering how little work its doing.. 2250 to do 55mph just seems like a waste of sucked in air.. if i can lower that to 1750 thats, 500 rpm. Or 500 less intake and combustions per mile.. Eiter im going to go with 155-80-15's or those low rolling resistance 185-70-14's from the insight.. the 155-80-15's would provide the largest gearing gain with the skinniest tire size .. but cant find any rolling resistance numbers for them to compair with the insight tires.. over all its all about rolling resistance.. its odd that a wider tire can have a lower rolling resistance but it can and does happen..

[1GCRXHF]

Best guess I can make on rolling resistance can be found in the treadwear rating. Its the triple digit number followed by the speed rating (620H, etc.). From what I've gleaned over the years, the higher that number, the harder the compound in the tread (hence why it lasts longer). Extreme performance tires range from 070-150ish, street performance 200-450, and the long mile touring tires are generally in the 600+ region.


Also a note on increasing the overall height of the wheel tire. You should (if you haven't) consider the following things; increase in overall height, raising the CG. But the biggest consequence I can see is the fact that your corners were not engineering to carry that much tire. I would personally prefer my transmission to do the reducing and run a smaller, lighter tire combo. Any thoughts from your experiences?

[ebacherville]

I say yes thats true however even with the 15" tires I'm proposing, the size bump is under 10% change.. lowering the suspension can reduce any added lift tires add...

Plus I already have the HF tranny thats geared well already.. Also tires are something thats fairly cheap and super easy to experiment with to get it just right .. custom gears are expensive and potentially hard to install depending on the car..

[rcpmac]

Originally Posted by ebacherville

2250 to do 55mph just seems like a waste of sucked in air.. if i can lower that to 1750 thats, 500 rpm. ... to go with 155-80-15's or those low rolling resistance 185-70-14's from the insight....

The insight tire is a 9.4% difference over stock and will give you 2057 rpm at 55mph. You of course will need to check for clearances lock to lock and under load before increasing the radius and/ or lowering

Specification Sidewall Radius Diameter Circumference Revs Mile Difference
175/70-13-----4.8in---11.3in ----22.6in -----71.1in------891--------0.0%
155/80-15---- 4.9in---12.4in-----24.8in----- 77.8in------814---------9.4%

Did I get my numbers right?
------------------------------------
In order to get close to 1750 you will need a 195/80-16 (24% difference) Bridgestone Ecopia EP-02 (Rav4-EV tire) which inflates to 44lbs is big and $125 per corner .
as best I can figure...

Specification Sidewall Radius Diameter Circumference Revs/Mile Difference
175/70-13------4.8in----11.3in---22.6in------71.1in--------891--------0.0%
195/80-16------6.1in----14.1in---28.3in------88.9in--------713--------24.9%

[Chris D.]

when it comes time for your wheels, lightweight 15" wheels @ 11 pounds a piece that are fairly inexpensive.. 15x6.5

www.18racing.com

the Slipstream are the lightweight of choice unless you want to run Civic HX 14" (if memory serves me) those are fairly light and an alloy..

I'm running the 16x7 et40 Slipstreams on my truck..
got em for just under 500 out the door for a set of 4

[1GCRXHF]

You said you have the HF tranny, but are turning 2250 at 55?? My HF turns 2250ish in third gear at 60, 55 mph isn't really moving fast enough for 5th to be a player (I think something like 1500), unless the terrain is flat. I can get more mph/rpm/gear readings for you if you want, but I suspect your transmission or final drive is not the original HF running gear.

[ebacherville]

Originally Posted by 1GCRXHF

You said you have the HF tranny, but are turning 2250 at 55?? My HF turns 2250ish in third gear at 60, 55 mph isn't really moving fast enough for 5th to be a player (I think something like 1500), unless the terrain is flat. I can get more mph/rpm/gear readings for you if you want, but I suspect your transmission or final drive is not the original HF running gear.

see thats what i was thinking also but some one said they had a first gen HF and my rpms seemed to be correct .. Maybe I got a CA or high altitude tranny?

Yeah RPM per speed would really help..

[1GCRXHF]

Ok, got a little more tuning up to do and then I'll take it for a spin.