13" rims versus taller fifth gear swap - Fuel Economy, Hypermiling, EcoModding News and Forum

cowmeat · 07-13-2014, 10:26 AM

Need some expert advice here for possible MPG upgrade to the hooptie!

Black Widow has the stock 12" Festiva rims, so I've been considering a swap up to 13" rims ever since I have owned it. I've seen a lot of Festiva owners swapping up to 13" using the Aspire hardware, but I'm not sure doing so would benefit MPG or not. The Aspire rotors & calipers would be stouter, but would also add weight. I assume the difference in tire size would leave me with lower RPMs at higher speeds, but not sure if it would benefit MPG to do the swap. Also, would I need to do anything to make the speedo & odometer show correctly?
Would it make more sense to just swap to a taller fifth gear (if it's even possible in that car), or is there a different gearbox that would work for the Festiva? It doesn't have a tach, so I'm not sure what RPM it's hitting at 55 (my max speed), but I've seen that a lot of you guys swap fifth gears with Civics & Metros with good results.

If anybody can clue me in, I'd owe you one!

mcrews · 07-13-2014, 12:45 PM

You might try searching 'taller tires'. There are many discussions on lowering rpm at cruising speeds

user removed · 07-13-2014, 03:37 PM

I would look for 14s or 15s, much better tire choices.

regards
Mech

California98Civic · 07-13-2014, 03:58 PM

I'm no expert... I'll just agree with the dudes above! So, yeah, 15" wheels if you can do it... much more to choose from in LRR tire selection. What are the bolt pattern, offset, and center bore measurements for the Festiva, anyway?

Superfuelgero · 07-13-2014, 05:47 PM

You'll need to have a BSFC map, gearing, and target mph to know what to do correctly.

As to what fits

mechman600 · 07-13-2014, 06:47 PM

You also have to consider the trade off of increased ride height and how it will negatively affect aerodynamics. Of course I am speaking of extremely tall tires with a substantial ride height increase. Extreme (ie: "let's get the most ginormous wheels that fit") changes may not net any increase in FE. However, being creative with lowering springs and bashing out wheel wells are potentially beneficial here.

user removed · 07-13-2014, 06:57 PM

I think my Fiesta's stock 15 inch wheels are right about 25 inches overall diameter and they might fit. Plenty of them with factory Kuhmo tires for sale when people buy alloys.

Take your overall diameter and divide it into 25 and you will get the difference in overall drive ratio since both roll 3.1516 times their diameter.

regards
Mech

backpacker3 · 07-13-2014, 08:24 PM

Why do you have to swap the rotors and calipers with the wheels? You're upsizing the wheel so there shouldn't be any clearance issue. I'm just curious as to why it needs the braking system changed as well.

Also you might want to look into an aftermarket tach before you swap out any gears just so you know if there's any reason to change it.

California98Civic · 07-13-2014, 08:28 PM

If you can't get larger wheels liike Old Mech recommends, then I can attest to the 13" Michelin Defenders as satisfactory LRR tires. I like 'em. And that's good because they were my only LRR choice!

cowmeat · 07-13-2014, 08:29 PM

Quote:

• Here's the 13" wheel hub bolt pattern info for the Aspire:

http://www.boltpatternguide.net/Ford..._Patterns.html

...as you can see, they're NOT compatible.

I think all the guys who swap Aspire hardware onto their Festiva use the entire hub, with caliper, etc since they're not compatible bolt patterns . . . and they're looking to get better braking action from the larger calipers and rotors. I'm just looking for either fewer tire revs per mile, or taller gears to squeeze a little more out of the Festiva the cheapest way possible.

If there's a taller 12" tire I'd go with that when I replace the tires, but then does that mean I have to adjust the speedo & odometer?