Good AutoX Pic

[chknhwk]

Can you find a pic of an F1 car (any era) that raced with what could be called "low-profile" tires? Or any open-wheeled series for that matter?

Great arguments, I love intelligent discussion.

The difference I would like to point out here is that you're talking about an open-wheeled series. Apples and oranges. Look at all of the Mustangs, Audis and Mazdas running around in the professional racing series. They're all running generally one or two inch larger wheels on the track than what comes out from the factory. Every vehicle is going to be different and from my experience I think that we benefit more from a stiffer sidewall than not. FWIW

IMO what it boils down to is two things: track times and personal confidence. If you're more comfortable driving on a little softer tire (i.e. taller sidewall) then by all means go for it.

 

[Jarrod]

Just as pointed out before, a lower-profile tire doesn't automatically correspond to a stiffer sidewall. There are many racing series that only use wheels big enough to clear brakes (which makes sense to me), and use tires that aren't necessarily considered to be "low profile." But, I bet that these specialty tires to have a much stiffer sidewall than what most people use in amateur racing.

So, what I said was a very general blanket statement that doesn't necessarily hold true. It really depends on the type of tire and its intended use as to how it behaves and performs.

 

[Shoaz]

The difference I would like to point out here is that you're talking about an open-wheeled series. Apples and oranges. Look at all of the Mustangs, Audis and Mazdas running around in the professional racing series.

How does the tire know whether there are fenders or not?

They're all running generally one or two inch larger wheels on the track than what comes out from the factory. Every vehicle is going to be different and from my experience I think that we benefit more from a stiffer sidewall than not. FWIW

And generally those bigger wheels are filled with bigger-than-stock brakes.

 

[chknhwk]

How does the tire know whether there are fenders or not?



And generally those bigger wheels are filled with bigger-than-stock brakes.

My point is open-wheel cars aren't generally designed the same as street cars with regards to suspension. Major automotive manufacturers have to make concessions with regards to making everything work together for the mass populace. F1 cars, et al don't have to worry about that. The suspensions are completely different, that's the point I was making. I think comparing an open-wheel racecar to a modified street car is completely unrelational due to suspension design. I can't really see comparing my Cobra to an F1 car, know what I mean?

Yes they are, it's a beautiful sight.

All things being equal, if you can get lower rotational and unsprung mass without sacrificing tire control through squishier sidewalls (which is going to be pretty difficult with 15" wheels and the inordinate amount of sidewall Ford gave us on these cars ) I guess it would be a better combination. I just can't really see that happening with the tires we have out there, especially coupled with these nose-heavy pigs.
I think in this instance, he'd be better off with less sidewall flex.

 

[Shoaz]

My point is open-wheel cars aren't generally designed the same as street cars with regards to suspension. Major automotive manufacturers have to make concessions with regards to making everything work together for the mass populace. F1 cars, et al don't have to worry about that. The suspensions are completely different, that's the point I was making. I think comparing an open-wheel racecar to a modified street car is completely unrelational due to suspension design. I can't really see comparing my Cobra to an F1 car, know what I mean?

So you're saying if you can design a better suspension with superior camber control you'd prefer a larger sidewall? I'd argue the opposite; when you've got sucky camber control you can help make up for it with a larger sidewall. To make a low-profile tire stay flat on the ground and get the best use of those stiff sidewalls and wide contact patches, you need a good camber curve on each corner. Most factory street-car suspensions, especially those with struts, don't do a great job of that.

My point of bringing up F1/open wheel is that even when you do have optimized camber curves you don't necessarily need or want a low-profile tire.

I think in this instance, he'd be better off with less sidewall flex.

Generally the reasons most folks go with 17" and larger rims for SHOs are:

1. Somebody told them that those short sidewalls handle better (which I contend is generally not true, and arguably not true for the SHO with it's McP strut suspension).

2. They like the looks better than a smaller rim.

3. They have a brake kit that precludes using anything smaller than 17".

4. The dearth of options for good, lightweight 16" rims with a 5x108 pattern and proper offset.

5. The availability of tire selections for the particular application.

The bottom line is that there are more options for 17" performance tires and wheels for the SHO than there are for 16". This drives a lot of people in that direction even for track cars, and it's a very practical consideration. Most of us ain't racin' these dudes for money, so the tradeoff of opening up options on tires and wheels is often worth it even if you take a performance hit by doing so.

Something not mentioned yet: a lower profile tire will reduce the ability to tweak handling via tire pressure changes. The amount of spring that you get from the tire goes down with the profile, and that reduces the adjustability to some degree.

I doubt that most people would notice much difference in performance on a SHO going between 16" and 17" rims, and depending on the relative tire selection I'm sure one could beat certain 16" tire/wheel combinations with other 17" tire/wheel combinations. I don't think it's correct to say generically that a lower profile tire improves handling because it just isn't so. There are other reasons to select larger rims, handling and acceleration are often not among them.

 

[shomesomesho]

FWIW, for autocross I switched to 17x8's mainly to get more contact patch with wider tire (245). Although the tire+rim is heavier by about 5 lbs/corner (!!!!!!), compared to my 16x7's with 225's, my autocross times are appreciably faster due mostly from the wider rubber.

If there were any 16x8 rims in the proper offset available for the SHO, I would gladly take those over 17x8's any day of the year.

 

[Shoaz]

If there were any 16x8 rims in the proper offset available for the SHO, I would gladly take those over 17x8's any day of the year.

The ROH Snypers are the only 16x8 option of which I'm aware, and they're hard to find.

The Borbet Type B wheels are 16x7.5 and are a decent alternative (and available from TireRack or your favorite Borbet supplier).

I have a set of each, run 245/45-16s on both sets, and can't tell any difference in lap times or handling.

 

[SHO Continental]

I have heard that before but can't make sense of it. How would heavier wheels, more stress on the hubs and raising my center of gravity make the car handle better?.

The 17" Enkei's I have while one lb heavier then a stock slicer had tires two lbs lighter then the stock sized tires. The wheels in my sig are for show use..

 

[Techpriest]

"Larger brakes help increase your rate of deceleration by applying more force to the rotor and slowing it down rather than locking up and allowing the car to skid."

Sorry, but I am not following that. Locking is when braking power overcomes traction. How will more stopping power reduce locking? That seems to be the exact opposite of what I expect to happen.

"If your ride height is lower with 15" wheels vs. 17" then you're either running the wrong sizes or not enough air pressure in your tires"

As I stated, I am already running low profile tires on my 15" rims. In order to keep my center of gravity the same on 17" rims I would need tires with no profile. I don't see that happening so I stand by my original statement that putting 17" wheels on my car will make it heavier, and raise the center of gravity. Despite this I can't count the number of times I have been told by people at events that I needed bigger wheels. Unless I have a lot of time to **** I normally just say, "Yeah." and let it go.