Wanted to find out what everyone thinks about using larger diameter wheels like 17"s or 18"s versus using 13" or 14" wheels. That is still maintaining the same outside diameter tires. Pros and Cons? Radial and Axial Performance and Handling, Traction, Heat Buildup, etcetera. thanks

[This message has been edited by Bazooka (edited 03-24-2004).]

The smaller the sidewall of the tire causes less tire roll when cornering and a stiffer ride.
The wider the tire the larger the contact patch is allowing better traction. But in winter wider tires tend to ride above the snow instead of cutting into it so you have less traction.
Tread design is also another factor. The block size and height of the tread can flex when cornering or taking off the line. Some flex is good. Too hard of a compound like Goodyear Eagle street styles are great when they get hot, But once cool like in winter or on a rainy day, they tend to stay stiff and slide more. The harder compounds tend to wear less so you can drive 60K-80K miles on a set. Where a softer compound will give you much better all-around traction, but tend to wear faster.

------------------

Happiness isn't around the corner...
Happiness IS the corner.

Depends on what you want to do.....a 18" chrome wheel would probably look great, but it would kill your performance because of weight and also rolling mass. I have some 17" wheels not chrome, but they still weigh 20lbs each and it makes a considerable difference from the 13" steel wheels. but if you have a swapped engine instead of a duke, you might not realize any real loss.

Oriefs got it right. Since Fieros handle so well anyway, i prefer smaller rims with taller tires. As he said its better in rain and snow, and the ride is twice as smooth as a set of 18s. I run 225/60 Dunlops on 16 X 8 rims. Very smooth ride, handles excellent in my opinion.

------------------

http://my.core.com/~ferrari1/MyPhotos
http://groups.msn.com/RogersCarPhotos

Good points that were brought up here. So a smaller diameter, lightweight rim would help in straight line performance, smoothness of ride and realized traction. When it comes to tire compounds, the softer ones (100-200) are trading off treadware for traction, excluding in the rain/snow. The harder compounds (350-450) would benefit in treadware and not so much in performance or traction. Evidently, drag radials are affected by surface temperatures since you have to burnout before staging to heat em up for the proper friction coefficient. A taller sidewall should then allow better traction, right?
Wbat reason is there for using the 18", 19" and 20" wheels? Are the tall rims practical compared to the stock sizes?

quote Wbat reason is there for using the 18", 19" and 20" wheels? Are the tall rims practical compared to the stock sizes?

Well the reason being is that now more of the wheel and tire combo is stiffer, thus more responsive handling, and also I think bigger rims look so much better than smaller ones IMO. Also everyone says that larger rims always weigh more, my 18's are almost the same weight as my 15 inch GT wheels, maybe lighter, and the differentce in handling is like night and day. And practicallity, anything is more practical than the stock GT rims, have you ever tried to clean all thoes little holes?!

------------------
Gold 86 Fiero GT
Future plans: Not to start on fire!

[This message has been edited by Golden86 (edited 03-25-2004).]

The best answer is to look at F-1 tires.

They have all the potential to burn out, and have to take some serious g-forces on the track. Bear in mind they run smooth surfaces only.

The tread varies from dry to wet, but not the size. They know that they need some sidewall. Look at what they run at 200 mph. The lightest, and highest traction possible.

There is a saw-off for streetability also. These currently faddy wagon wheels rely exclusively on the shocks to get any give on uneven surfaces.

Those same wagon wheels will play havock with you if you want to corner hard on an uneven surface. And how about that unavoidable brick in the road? What is a bent rim among friends?

I think on a car of our class, you need about 3.5" to 4" of sidewall to be optimum wheel weight and streetability.

Mine now has 205/55/15 on the back and 195/55/15 on the front. But if I had 16" I'd be going to 50 series but no thinner sidewall than 3.5". I just would NOT go 17" or above due to my stated point of view.

That's just my opinion on it. So I guess I am not too style conscious.

Arn

Yea, if you do go to 18 or 20 inch rims the tire sidewall is very short. Even a good pothole is going to trash your rim, theres no tire to absorb the shock. The tire / wheel store I deal with puts lots of them on pickups and SUVs. Hes got a whole room full of pothole damaged rims. Of course he likes to sell them because everyone almost who buys a set of 4 has to come back sooner or later for 1 or 2 replacements

[This message has been edited by rogergarrison (edited 03-25-2004).]

quote Originally posted by Bazooka: A taller sidewall should then allow better traction, right? What reason is there for using the 18", 19" and 20" wheels? Are the tall rims practical compared to the stock sizes?

There is straight line traction and cornering traction.
Cornering traction:
Taller sidewalls will cause the tire to flex when cornering. If you had a 205/70R14 and took a picture of the car in a hard turn, You'd see the contact patch of the tire off center of the wheel as the sidewall rolls under the wheel. This will lift the one side of the contact patch as the sidewall of the tire meet the road surface. Where if you had a 235/50R17, the side wall would be a smaller height and the tire would flex/roll less so the contact patch would remain closer to center of the wheel and equally supported. This provides equal pressure on the contact patch to allow maximum traction in the turn. (In terms of street tires)

Straight line traction:
On drag race cars, higher sidewalls aid in flexing off the line for a better launch. Just look at the huge wrinkle wall slicks used on top fuel cars. When the car launches you'll see the sidewall wrinkle. This allow the dragster to get a good bite of the track and launch. (think of it like stretching a rubber band before shooting it) Then as the dragster is approaches full accelleration, You'll notice the tires get tall and thin. With a small sidewall the tire would seperate from the bead of the wheel, lose air pressure and of course spin off the wheel. (mind you all this happens in less than a second)

Road course/racing tires like used in F1, IMSA, IRL, NASCAR, etc have very thick sidewalls to provide little flex. The tires are designed for use on the particular car. Generally these styles of racing have rules as to tire weight and size that can be used on the car.

[This message has been edited by Oreif (edited 03-25-2004).]

wow. You guys give some good explanations of the sidewall and rim size advantages. It's interesting how tire contact patch areas get distorted, especially in cornering traction. That may be why the wheel alignment (caster/camber etc) is adjusted to relieve some of that distortion on oval track racing and similar. For ideal data on wheels, the designs should be identical except for the OD variable, so that you have an "apples to apples" comparison. Also it may not be fair to compare say a stock 60 series tire with a 50 or 45 series, because the different aspect ratios will have different handling characteristics.

quote Originally posted by Bazooka: Wbat reason is there for using the 18", 19" and 20" wheels? Are the tall rims practical compared to the stock sizes?

Hmmmmm.........also bigger rims = less wheel gaps. Also the original stock diameter for the Fiero adverage is 24.0
For a engine swap like 3800, LT1, LS1, 4.9, and the Northstar you will need a higher diameter wheel due to the size of the 'original" engine swap and tires that were from the swap. Northstar front tires range from 225/60/16 to 255/55/17 which by the way is 25.0 or higher.

But if your using the stock 2.8...whats the point in getting a bigger diameter? Most will keep the same or close the same diameter..215/45/17 or 235/45/17.

------------------

Just this past weekend one of the TV car shows, I can't remember the name, added bigger brakes and larger diameter rims to a car then put it onto a dyno and immediately lost 9 Hp at the wheels. They attributed the loss to the mass of the wheels and brakes being moved out to a larger diameter. The end result is that it takes more Hp just to make the wheels rotate due to that outward movement in rotating mass. They rationalized it because they were looking at track times and the larger brakes lowered those times due to better braking in the corners but to those who just drive on the street or are interested in straight line speed we just bolted on a good looking loss in horsepower.

Dont forget if youre tire /rim combo has a diff circumfrance you are also affecting youre gear ratio. Taller tire = less gear. Smaller tire = more gear as in faster accel

------------------
85 GT 4 speed 2.8L auto X'er

I have fieros with stock 15 and 13 inch wheels. I personally prefer the 13 inch. Smoother ride. Also when buying tires there are not many choices for the stock 13 inch size, but boy are they really inexpensive.

That info on HP loss from an upgrade like brakes isn't normally emphasized. Those big 13" rotors and calipers must add a big chunk to the unsprung weight. So you can conceivably get more HP by keeping it simple with the regular sized brakes on a street car. he he strange but true.

A little more information. The TV show was Sports Car Revolution on the Speed Channel. The car was a Kia. Big brakes alone lost 5 horsepower on a 4cyl car. The wheels and tires that they used were actually each lighter weight than the stock units also. I was just that the diameter increases moved the rotating mass outward from the axial, consuming horsepower on the way out.

[This message has been edited by RickN (edited 03-26-2004).]

In determinining what is best, you need to consider several factors. For example, if you are committed to running a 12' (or 13") brake upgrade, you can eliminate the 15" wheels from your options. On the other hand, if you have a stock 4 cylinder engine, it may be impractical to run the larger sizes. Also, consider the overall diameter of the replacement tire vis-a-vis the original tire. As one member suggeted, if you are running a drive train (e.g. Cad 4.9) that used a larger diameter tire, it may be best to use a similar diameter after transplanting the drive train into the Fiero. There are some lightweight 15", 16" and 17"wheels that are still reasonably priced (eg. less than $600 per set) , but if you have the luxury of having an unrestricted budget, you caneasily spend $400+ per wheel. Also, wider tires do not necessarily equate to better performance on the track. I seem to recall reading about a Factory 5 Racer (Cobra replica) that set a track record after he reduced the tire size from 275-40-17 to 255-40-17. Of course, looks are the most important factor for many. Nothing wrong with that; its just not number 1 in my book. In the end, I would suggest that you shoot for the combination that offers the balance you think is best when all the factors are considered.

------------------
FierOmar