Tire talk; Skinny tires, Medium tires, Fat tires

[S15DET]

There are a few schools of thought regarding tire sizes and lap times. I want to design any future suspension mods around a pre-determined ideal tire size; it will all start with the tire and go from there. In this, I'm only concerned with reducing lap times. I'll have another (probably smaller) wheel and tire set for commuting, but the overall design is going to be about lessening lap times.

It's been written that...
Small thin tires are lighter, more "feel", allow the suspension to work properly, can "dance" with the car

Medium tires (I'll say that by 2013 standards a 195 or 205 is medium) are where I am now, the largest advantage is that they are familiar and inexpensive and probably will be available for a long time in a 205/50-15 size.

Wide tires mean more rubber on the road but more weight and rolling resistance (drag). Alignments (and dynamic geometry) becomes more critical in an attempt to keep the tire square to the road surface at all times. Another thought is heat, you have to be able to get the tire up to temps, theoretically a tire could be so wide that this wouldn’t happen. Cost, wider is more expensive. As far as I know, the widest tire that will fit under a 510 (meaning that I’m targeting a 23” OD) is the Hoosier 275/35-15.

My question to the group; has anyone determined the perfect tire size for a 510? Have the Specialty guys always had to run a spec tire or had rules limitations, or have they been able to make this determination? I don’t think I want to consider slicks, only R-compounds for track days. I’m guessing that modern cantilever slicks would be the real answer, but even still is there a point where it’s too wide, or is wider always faster? Are the 275 Hoosier A6/R6 too wide? Maybe the more common and affordable 225/45-15 is the sweet spot? Heck, maybe my 205/50-15 tire is the sweet spot? I’m anxious to hear your thoughts, and again I’m focusing on speed this time around, not economy, comfort, NVH, etc.

[HudsonMC]

How much power and what type of brakes are we talking about here?

[bertvorgon]

IMHO...you want to watch sidewall construction to a great extent...this is what will give you the "FEEL" of the car. No matter the profile to some extent, you can get a flexy sidewall, which you will fight and hate.

I am going through that right now with the Toyo tires I bought, same size, yet what a difference in sidewall construction ( flexy as hell). That being said, they are going to require SIGNIFICANT tire pressure increase, so WHAT is that going to do to how I have set the car up, footprint, etc.? The jury is out on this one too, as I have a setup that I know works, with the Yoko's, and do not really want to re-set the car just to play with the Toyo's.

I have run most brands over the years, which now is old technology, but, the sidewall issue has been constant. When I had GoodYear cantilever tires on, it was hard to feel the car as they were so stiff, and the slip angle so small, I never felt comfortable at very high speed, as I had no feed back as to WHEN they were going to let go. Again though, at 20" tall and 9.5" of rubber on the road, with of course the appropriate camber set, they were hard to beat at the slaloms and some road race track days.

Specialty runs a range of sizes and compounds per corner, so that is not really an issue here. The Miata runs goodyear slicks, but, that is about to change as the quality of the goodyears has gone out the window, plus supply issues.

Mass is an issue, so you are on the right track there.

TIRES...the great unknown. I would be looking at the 205/50 x 15" size, as the best compromise for both availability and compound choice. Then, it does become a choice of how soft you want VS life.

The Toyo's have a tread wear of 100, so are a tad softer then the Yoko's, but, the life on these depending on heat cycles could be short. There is lots of discussion on the Net about the R-compound DOT tires, so you can see some of the feed back there too.

I have not touched my suspension settings from my race tire setting ( read LAZY ) yet with the Yoko's on my car, their wear and grip was spectacular when new, specially at very high speed. Could they be optimized even more...who knows..but with the camber I run, they were perfect across the tread face, with normal roll at the edge from Solo use, so I figured why mess with something that was working.

One year, I tried M + H slicks...did I ever out trick myself on that one, the sidewall again was just horrible, like rubber bands.

Personally, I think our 510's like a very firm tire, but not rocks, as most of us get rid of all the slop in the suspension pivots and bushings, and have either optimized the settings, or have the ability to tune the suspension to the tire. so the slight "feel" we get from the tire is very important.

As Hudson said above, there are other factors that the tire has to do, each may have it's strength's.

Weeding it all out is a best estimate guess...and hope it works!

[duke]

275's!!! I would think you would have a bit of a hard time fitting those under your front fenders.

Here is my .02. I am a big fan on the 205-50-15 tire size. The main reason for this is availability. I like to run UHP summer tires (basically just a step down from r-compounds) and this is typically the smallest size most manufacturers make (with a few exceptions). They also fit reasonably well under "stock" 510 fenders, while maintaining a usable contact patch (ie no crazy camber). I do not want to run flares at this time so this limits my tire sizing. Also, for my car, I don't believe that I need any more tire. Larger tires equal more weight (unsprung and rotational) and more rolling resistance. I do not have that much hp and my car is light. If I had 250+ hp I might be thinking differently.

With the above factors, and my opinion that 205-50-15's look right on a 510, this is the tire size I'm going to be sticking with.

[rnorrish]

Keith, haven't Goodyear stopped making the 15" cantilever Specialty likes using?
I though Dad mentioned that a while ago... Making nearly the whole stable of car racecars have to find an alternate.

[bertvorgon]

Yes, I did not mean to imply that they are using those still.

Collin has done some more testing on tires, so they are onto something else now.

[rnorrish]

That's good! I didn't notice what the Miata was running last weekend.
I know Malcolm will have to switch, and we've used their take offs in the past, so I'm just kinda curious...
There's a track day coming up and we're talking of more Solo1 next year in the 510.

[S15DET]

What were they using, I'm guessing a 23-9-15ish?

Duke, I'm with you, and have been in the 205 camp for all of my 51k miles in this car. Realistically I doubt I'll ever decide to go with flares, so I'm probably sticking with the 205's. But still, lets say I decide to geek out and do a re-design on the suspension and have the option to fit slightly wider rubber under the stock tin, all things being equal, would the 225's necessarily be faster than the 205's? I seem to remember that the Spec Miata guys were having this debate, that the 205's were not necessarily faster than the 195's, not sure if those were the real sizes but you get the idea.

Heck, I've got a little room so I want to mount one of my Father-in-laws old 225's on one of my wheels just to see if it clears.

And to the earlier question, I'm running a stockish SR with very capable brakes.

[okayfine]

At some point would the type of event come into play? Autocross would be different from a track day, and a track like Streets of Willow different from something more high-speed like VIR - with respect at least to aero drag of wider wheels/tires. Recip weight goes up as well.

[bertvorgon]

205 / 50 x 15" on VTO 7" zero offset rims.

Of all the tire combos I have run over the years, the car has felt the best with this package.

Nothing touches, wheels spaced out as much as possible.

If one has a ton of money, to answer OK's, it would be nice to have tires for a type of event.

I got away with slicks at both Solo and road race, medium qualifying compound, which had to last me for a season..period..as a set of competitive tires is a 1,000 up here. The balance at least kept me in the hunt at slaloms, as did ok at road stuff. I was lucky that the key hill climb event was in May, so by the time I had done two Solo's before, the tires were perfectly scrubbed for the hillclimb, as they had to be ON, with no room for error.

The last club solo I did, I got FTD on the Yoko's, which had done some serious highway SCENIC tours, so they were doing ok for a mix.

[Sleepys-14]

Personally I run a 15x7 (205/50r15) in the front, and 15x8 (225/45r15) in the rear. I really like how the car handles and I couldn't ask for much better ballance. I need to take just a bit of rear camber out of the rear to flatten the tire out (inner tire wear). I also run the UHP tire, as I do to many events in a year to use r-comp tires. I really don't like to go through more than 1 set every summer. I get about 1800 miles out of my tires, which I think is very, very good for the amount of track time.

[S15DET]

I think I'll try a set of 205 R-coupounds and see where that gets me. The last outing, my car was plenty fast on the straights, but I couldn't hang with the red-group guys in the turns. I attributed that to my 205 street tires v/s their large (modern BMW and Porshaaahs, Vettes, etc.) stickies. I was 11 seconds off the pace of my old ITS RX-7. I'm still making large set-up changes and haven't even gotten to the stage of the fine adjustments. You guys have convinced me that I need to give the 205's a real chance before considering going to something larger.

[duke]

I think that is a good path to be going down. I am just starting to get close to a set up that I like for my car, and I can't believe how much of a different car it is compared to a year ago.

[S15DET]

Awesome, that's good to hear. I know there's a lot of room for improvement, in the car set-up and especially in my driving of this car. Properly driving a turbo car is a whole new skill set to learn. But even driven as sloppy as I'm doing this car is a blast, and every time I'm blown away by the potential.

[Sleepys-14]

Im still unsure why you want to use r-comps. Z2's/rivals will do the same lap times as r888 or similar tire with much less wear. A hoosier r6 will be faster, but that gets horrible life. Considering that your car is not strictly a race car that gets trailered to the track, it would be nice to use a tire that is good at lower temps(ripping around on the country roads/auto-x). Also wet traction is something to consider...