Tires, Sidewalls, Things

[project86]

I'm eventually wanting to get into some auto-x and hpd so I'm trying to figure out a good wheel and tire set up. I have been considering 16" and 17" wheel options and I'm curious how side wall height will effect performance.

[GySgtFrank]

You will need to go with at least 17s if you want a good sticky tire for autocross. Anything smaller is very hard to find good performance street tires for anymore. There are race tires for the smaller sizes, but that could get expensive fast. The lower the profile of the sidewall, the more responsive the tire will be to changes of direction, downside being that the lower the profile of the sidewall the harsher the ride will be. Your choice on what balance you want to make.

[project86]

Originally Posted by GySgtFrank

You will need to go with at least 17s if you want a good sticky tire for autocross. Anything smaller is very hard to find good performance street tires for anymore. There are race tires for the smaller sizes, but that could get expensive fast. The lower the profile of the sidewall, the more responsive the tire will be to changes of direction, downside being that the lower the profile of the sidewall the harsher the ride will be. Your choice on what balance you want to make.

Ok that makes sense. What about the sidewall flexing enough that the lips of the rims get messed up? I feel like I’ve heard of that happening from hard cornering. Is that a thing?

[GySgtFrank]

Yes, it can happen with low profile sidewalls. Especially hitting rocks and curbs. Which is one of the reasons why most off road vehicles run a tire with generous amounts of sidewall.

[t_g_farrell]

You can get good autox rubber down to 15". Anything smaller is NLA for rdot or summer performance tires. I have Dunlop Direzza *2 on my 15" Konigs on my SA and they are an excellent tire. Had to relearn to drive my car when I put them on. Tons of grip and one of the better rated autox tires out there as of 2016. Mine are 205/50x15. Keep the pressure up on autox days and you shouldn't have any issues with the rims being damaged. On the street I run ~33psi but if I'm doing any real driving I pump em up to about 38psi or so.

[project86]

Originally Posted by t_g_farrell

You can get good autox rubber down to 15". Anything smaller is NLA for rdot or summer performance tires. I have Dunlop Direzza *2 on my 15" Konigs on my SA and they are an excellent tire. Had to relearn to drive my car when I put them on. Tons of grip and one of the better rated autox tires out there as of 2016. Mine are 205/50x15. Keep the pressure up on autox days and you shouldn't have any issues with the rims being damaged. On the street I run ~33psi but if I'm doing any real driving I pump em up to about 38psi or so.

Good advice on the pressure. I'll have to keep that in mind.

[infernosg]

Yeah, 15" wheels have good performance tire options because of the Miata guys. I can't remember if the FC's can fit 15" wheels over the front brakes though. Outside of actual race rubber, there aren't many 16" options left. I did the math once too. I compared the wheel of 16" RPF1's with 245/45R16 tires to 17" RPF1's with 255/40R17 tires. The overall weight was within a 1/2 lb or so (17" heavier) and the 16" combination puts the rotating weight slightly closer to the hub.

[project86]

Originally Posted by infernosg

the 16" combination puts the rotating weight slightly closer to the hub.

Is that more desirable?

[FC Zach]

BBS vert wheels are 15" aren't they? I could go look at my car outside but I'm too lazy at the moment.

[project86]

Originally Posted by FC Zach

BBS vert wheels are 15" aren't they? I could go look at my car outside but I'm too lazy at the moment.

I thought they were 16"....

[Nutsid]

I heart 15s on my Miata with Bridgestone RE71-R's. I had a ton of choices for tires, too. I don't know the FC size, though, but it may be worth dealing with a speedo being off.

[Nutsid]

Also the very wheels are 15x6.5

[FC Zach]

Originally Posted by Nutsid

Also the very wheels are 15x6.5

(vert?) I thought so. . I run a ~225/50/15 on mine (i think). They work well for me. There are still performance tires for the fifteen inch wheel but some are very expensive depending on the exact size. . for example, a Pirelli P Zero in my size is ~$300 per tire so with that said I currently have some much cheaper Kumho tires mounted. Considering how little I drive the car, I may try the more expensive alternatives once these wear. .

[Nutsid]

Yeah, vert. My phone autocorrected.

[infernosg]

Originally Posted by project86

Is that more desirable?

Without going into too much detail the closer the center of mass is to the point of rotation the less inertia it has. Basically, it's easier to accelerate/decelerate. It's why racers use small diameter, ultra-lightweight flywheels.

Originally Posted by FC Zach

BBS vert wheels are 15" aren't they? I could go look at my car outside but I'm too lazy at the moment.

That's a good point. I completely forgot about those. I never calculated the weight of a 15" wheel and tire combination. I was looking at RPF1's and they don't come in a 15" wheel with our 5x114.3 bolt pattern. Depending on the wheel and tire widths and tire sidewall I'm sure it could be even lighter than the 16" combination but at some point you're trading weight for contact area and sidewall flex.