enough down force at top speed

[GoFast85]

A light bulb came on. Having enough weight up front with the fuel cell and battery up front, I would like to lower the car but at less expense and trouble than suspension changes.
How about 13" tires up front and 15" on the rear? That should drop the front end down 1" and create more angle for wind to deflect down on the front end.
Comments?

[dguy]

I vaguely (and I mean vaguely) remember some no-no about different diameter tires front-to-rear, but couldn't find any mention of it in the link to that document you posted the other day.

Pure speculation on my part, this be.  

...but why not go the drop springs and/or spindles route if you want to lower the front end?  13" rims are for Festivas and wheel barrows.  

[aaron88]

There is a restriction on having two different tire diameters front to back.  However; a Lotus has 17” rims on the back, 15” rims on the front and 50 series tires on both.  I’m not sure how they got around it but I can only assume (since I don’t want to read the whole traffic act) that the restriction is on changing things from the factory setup.

But here is something else to look at.  If you reduce the front tire diameter you will get more braking force to the ground.  Torque = force x distance.  Because the braking torque is produced by the callipers it remains constant, so if you reduce the distance you must be increasing the resulting force.

Moreover; you are also reducing the car’s footprint and therefore reducing the force that can be applied before skidding.

Therefore the result is, less brake fade but a slight reduction in handling.

As a footnote; I’m planning on keeping the font tire diameter the same, but increasing the rear tire diameter.  This will give me a slightly better ratio on my transmission gears, since I have way more power now.

Downforce is much better and easier achieved with a proper front spoiler.

Aaron

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[GSXRBOBBY]

first of all good luck finding a nice looking wheel that has the same bolt pattern. And why would you want to go with a rim that small? I don't think you looked into that idea enough, if anything I would just replace the front spring with a 1" or so drop spring and if your really worried about cost take it out and have 1 full loop of the spring cut off. My .02  

[GoFast85]

Lots of good ideas Prase be to the internet GOD.
1. I can get the same looking wheel in the same bolt pattern from anumber of manufacturers. 2. Some say the economical way of cutting springs is not recomended. If I don't like how low it is I have to go buy another set of springs/labour (increased cost) 3. The fiero came with 13" 14" and 15" wheels stock. 4. Legaly no problem with different rim sizes as long as you don't interchange 50 and 60 series tires. (note previous link on Highway trafffic Act) 5. By using a wide 205 x 13 instead of the 205 - 15 stock, the footprint would be the same. Tire qould rotate more so tire wear would be increased and increased bearing wear. 6. I am also increasing my rear tire width to 225 Arron, due to the increased engine/tranny weight. 7. Am I corect that I would get substancial down force at hight speeds. Look at the muscle cars of years ago jacked up in the rear and lowered in the front.

[FieroBUZZ]

I think this will end up as mostly a 'looks' thing.  To me a 13" wheel will be lost in that wheel opening.  I'd rather see a 15/16 or even a 14/15 combo.  There are lots of rods running around with 'bigs & littles' that seem to escape the wrath of the powers that be.

Mine will have 225/50/16's all round to start (since that the tires I have), but I do have a couple of 235's that I can go to.

Back in the day (I feel old) the rears were up mostly for looks and done with shackles.  Came from drag racing where the object is to keep the front down.  We tooled around in these in HS and university and I can't brag about the excellent handling of a 68 Roadrunner jacked up with a screaming 383.

The Fiero is a bottom breather, both rad and engine compartment.  If you have the proper air dam on the front to direct cool air to the rad, and perhaps vent the hood area, there should be no issues.  Assuming the suspension is up to snuff.

[aaron88]

The footprint will be reduced if the wheel diameter is reduced (It’s hard to explain without a model).  Try this: large wheel dia \___/ small wheel dia \__/.  The deflection of the tire will be the same because you will likely be using the same tire pressure, so therefore a smaller footprint.  You can compensate by going to a slightly wider tire, say 215.

The downforce generated by the hood and windshield shape far surpasses any lift created by the under bumper shape.  It’s just unfortunate that the lift is enough to raise the light covers.

Aaron

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[GoFast85]

So a 205 tire has the same "footprint" wheither it is on a 13 or a 17" tire. The contact with the road is the same. Only the RPM of the wheel changes. If anyone in "Fiero land" has a good set of Fiero 13" rims, I would like to give it a try.  

[dguy]

Lots of good ideas Prase be to the internet GOD.
2. Some say the economical way of cutting springs is not recomended. If I don't like how low it is I have to go buy another set of springs/labour (increased cost)

Hey I said "drop springs," not "chop springs."  

If I was interested in lowering the car, I'd be most likely looking in to adjustable coil-overs.  But I'm not.  I already find it far too easy to make the formula nose's air dam kiss the dirt.    Assuming that you're talking about your yellow beast, I suspect that you'll find the same.

If you're really concerned about nose lift at high speeds, I would as Aaron said look in to setting up a proper front spoiler.  Alternatively, consider installing a vent in the hood or hidden under the headlights which releases some of the speed-induced pressure in that area.

But that's just me.

[GoFast85]

I was refering to the suggestion by GSXRBOBBY on cut springs that I am/are considering. I will be venting the hood but am looking for some cost effiient meens of "keeping rr on the ground at lift-off speed. A rim change is fairly easy and hate to buy a front dam and knock it off on the speed bumps around town. I have seen somewhere a set of 3 front wings for each side but they look cheap and maybe not efficient.  
Decisions, Decisions, Decisions