Fir anyone wondering if you can fit a 315/35r17 on a stock 9.5 wheel, the answer is yes. It works fine. These are Toyos on Dymags which are 9.5 wide just like the stock wheels. Now the Dymag is a +44 offset and the stocks are +56 so mine stick out 1/2 more than a stock wheel, but it will work just fine. I'm running 315 rear and 275 front.

 

Um, yeah there's a difference between squishing a tire onto a wheel like that and it fitting properly. With that fitment your sidewalls are NOT going to behave correctly.

 

Yeah, not all models of tire in that size can probably be mounted at all on that rim width, but some can. But as FAUEE wrote, that doesn't mean they will work well. With your narrower tires up front, the front tires will have much more response and work at lower slip angles than the rear. This is a recipe for a car that feels like it's going to spin every time you corner near the limit of grip. The average street driver will never know the difference...until he has to avoid that deer or a car that didn't stop for a red light. If you're trying to autocross, track, or really carve up a windy road (i.e. if you want to really drive the car at the limit), then it will handle in a way that prevents you from ever having confidence in it.

 

Also doesn't quite look right on the wheel...

 

First let me say, I said they fit. I made no comments about handling. If you are installing a Toyo all season for handling, you've already chosen poorly. Now these tires are not "squished " on. Yes, other brands may fit differently. The Mickey Thompson Street Comps are almost 1/2" wider in this size. That will change the look and probably the handling. However these tires do fit and are definitely not unsafe. The handling will be negatively affected no more than going from a Street compound tire to an all season.

Will this size provide the besthandling? Probably not.
Will this size provide batter straight line performance? Possibly.
Will this size look cool? Definitely.

 

You said "It works fine." To most people, that would imply handling "fine." It also implies that they will wear fine. Neither is true, and that's what we're commenting on.

They look really "squished" on to me. The common jargon for wheel and tire fitment like this is "pinched." These are severely pinched.

Due respect here, but you're not qualified to assess the handling or safety of this setup. I promise you the handling will in fact be negatively affectively more than just going to a proper-sized all-season, for the reasons I already stated above. IOW, these severely pinched all-seasons will handle worse than the same model tire on the same wheel but of the proper size (275/40/17), especially since you appear to have correct fitment in front. Again, I already explained how/why.

If this were a tire built specifically for drag racing, it actually might provide better straight-line performance. But these tires are not that, and they will perform no better and very possibly worse than properly-fitting, narrower tires on the same wheels.

That's in the eye of the beholder. I absolutely love Dymags on a C4, though - especially the white on white look - so we agree on that!

 

I long thought that wider tires would yield better traction for acceleration. Grassroots Motorsports tested this. Turns out, it's dead wrong. They found that wheel width is what actually creates grip. They found that running a narrow limit tire on a wider wheel was actually faster (around a track and a straight line) than a wide limit tire on a narrower wheel.

 

That's true with nearly any modern radial, especially in lateral grip. However, there are cantilevered bias ply tires that are specifically made to be pinched onto narrow wheels. And like I said, there are purpose-built drag radials that are made to be used on a more pinched fitment than normal. So there are exceptions. But for regular tires, it's best for street use to stay within the manufacturer's rim width recommendations (10.5-12.5 in the OP's case), and as you noted, the more stretched end of that range typically provides better grip and handling.

 

I'm not sure if you mean qualified in a very literal sense or in a real world sense.
iIf you are being literal, then qualified would mean an automotive engineer with a complete understanding of the C4 Corvette suspension design as well as a tire engineer with full knowledge of this specific tires design and build construction. Also access to a test facility where controlled experiments could be conducted to determine handling characteristics and long term effects on tire wear and degradation would be needed.

I do not meet those requirements but I suspect neither do you or most people.

If you mean real world experience and knowledge, then how do you make that statement with no knowledge of me personally?

I have more than 40 years of automotive experience spanning many vehicles and driving disciplines. I know that there are far more factors in vehicle handling and safety than just the tires. Suspension design and geometry will have a far greater effect than tire size. For example many C4s are lowered using longer bolts for the rear leaf spring, mine included. This results in less travel and increases the chance of bottoming out and creating an infinite spring rate. That is a far greater safety concern.

As far as real world qualifications, since I actually own and drive a C4 with this tire setup, that would make me more qualified to make a statement about its handling and safety than you, unless you have this wheel and tire setup on your car.

As long as a driver understands how a vehicle will react to driver input, safety is not a factor. This isn't a case of something ridiculous like running slicks in the rain. It's a wider tire that will have more sidewall deflection and reduced contact patch. With proper tire inflation, this tire poses no safety concerns as long as you understand how the care will handle in evasive maneuvers. But in an evasive maneuver, improper tire pressure or worn tires pose the same or more risk.

As for handling, I said the difference between these tires and the same tire in a 275 will be no greater than the difference in handling degradation between a set of summer only performance tires in a 275 and a set of all season tires in the same size.

I never debated that there will be a degradation in handling.

 

I don't reccomend that

 

Just from my very first Google search:
For passenger cars, the absolute maximum safely recommended width for a 9.5-inch rim is generally 285 mm, though the ideal, flush-fitting width is 265 mm.

315 tires are definitely too wide for the rim you have them mounted to. You can easily see that in the picture. Tire looks distorted and squeezed. That's not subjective, its plain to see with anyones eyes. Now if you like it, that's all that matters... but that does not make it a correct fitment. I write service for a Ford dealership and would never advise the set up you have chosen. What's the old saying? "Just because you can, doesn't mean you should"...... Bottom line its your car, your tires.... you do what you like. That said, you have to expect input from others when posting on a public forum.... some of which you might not like or agree with. One last thing. Matthew Miller has helped countless people (myself included) with tire/wheel fitment and suspension set ups... he knows his chit.

 

You don't need to understand the C4 in any specific sense: we're talking about a tire fitment on a wheel. And luckily for us, the engineers and company that actually design and build that specific tire and test it do in fact tell us the range of rim widths on which that very tire should be used: 10.5"-12.5". Those are factory recommendations, and you are a full inch outside of them.

As for me, I'm not an engineer, but I have had the good fortune to be good friends with some automotive engineers and some of the best autocross and track drivers in the country. Some of the engineers are/were very highly placed in motorsports. They understand why you don't pinch a typical radial street tire on a rim width that's smaller than the recs, and so I. Not to mention, as someone already pointed out, that a motorsports magazine recently did a test of this very topic and already showed that pinched fitments aren't a good idea. I am friends with one of the drivers who carried out that test, BTW. I'm also an instructor in several forms of high-performance driving, including road course HPDEs, autocross, and teen Street Survival schools.

I make that statement because nobody who actually has experience driving cars at and over the limits on tire setups like these would say "It works fine." I've been autocrossing and driving cars on road courses for 40 years. I know what it feels like to pinch a tire onto a too-narrow rim (usually to attempt to work around rule sets that limit rim widths but not tire size) and drive it at/over the limit, and I know how a car handles when you do that only at one end or the other. I also know for a fact that some models of tire literally can't be mounted on a fitment that pinched, because the beads won't seat (that obviously doesn't pertain to this Toyo). For instance, a 305/30/19 Bridgestone RE71RS won't seat on a 10" rim unless you break it in on a wider wheel first.

No, it doesn't make you qualified for anything. I'm sorry to pick at this sore, but you want to discuss qualifications. Merely owning something doesn't make you an expert at it or qualified to discuss whether it's set up properly or not. As I implied before, 99/9% of drivers own cars and have no idea how to drive them or how they even feel at the limits of grip in any direction, nor in transitioning from grip in one direction to another. I see it all the time as an instructor: people can have decades of experience just guiding cars around public roads without ever intentionally approaching limits, but they can't manage anything when they actually approach those limits (especially unintentionally) because they don't have that kind of experience. Just trundling around streets doesn't make you qualified for anything except how to obey street signs.

That's an epically bad claim. I can take someone who has memorized all 900ish pages of the Milliken book Race Car Vehicle Dynamics, and if they don't have actual experience driving cars at and over their limits, that person won't be able to manage a car at the limits any better than someone who has no idea what that book even is (which I strongly suspect includes you).

Red herrings won't help your argument here: I would also strongly recommend against suspensions that easily bottom out or using improper tire pressures. If you really want to swing dicks based on your knowledge of how this pinched fitment affects vehicle dynamics and handling at the limit, then please tell us in detail how it does. "More sidewall deflection and reduced contact patch" isn't good enough. The claim about sidewall deflection may not even be true (it would depend on how you measure that). But "reduced contact patch" is the least of the problems here when the car approaches its lateral acceleration limits. I already gave you a hint about this in an earlier post, so put that bit between your teeth and run with it.

Yeah, this just isn't true. I suspect you're conflating "grip" with "handling." They aren't the same thing, and if you can answer the question above, then you would understand the difference. In general, all-seasons don't provide as much grip as "summer-only" tires (although it's very easy to find a UHP all-season that actually provides more grip and better lap times than some summer UHP tires), but that has nothing to do with handling qualities.

I really don't want to keep arguing about this, because the obvious answers are obvious, and you don't have to have my experience and knowledge to understand why this tire fitment is a bad idea. I was up until 1am last night helping build an endurance racing car that some friends and I are going to campaign in races later this year, and I have a local autocross tomorrow (for which I am Chief of Safety). So it's hard to find the time to pick apart your responses. My only reason for replying in the first place was to point out to others reading this thread that this tire fitment is a bad idea, and they shouldn't do it. All the rest is just keyboard soldiering.

 

Please tell me how one of these tires is "severely pinched" and the other is how a Mazda sold the RX7 new? Tire sizes are like women's clothing sizes. They vary a lot in actual dimensions from each manufacturer. The difference from the face of the lip to the outermost part of the sidewall, measuring with a straight edge, between my Toyo 315 and my BFG 275 on my stock wheell is only 1/8". Considering other tires like Falken run extremely wide, I'm probably narrower the a Falken 615 in 275.

 

I'm not comparing magazine pictures scanned into the internet with pics of your car. That's the kind of crap that severely unqualified people do to try to win a tech debate. The most pinched tire fitments for any 3rd-gen Mazda RX7 were 235/45 on an 8" rim, 255/40 on an 8.5" rim, and 265/35 on a 9" rim. Those aren't pinched, especially when taking sidewall height into account (sidewall height or aspect ratio also matters a lot in determining what is pinched and what isn't). They are all within the manufacturer's recs. Your 315/35/17 on a 9.5" rim is pinched, a lot. It's well outside the narrowest rim width recommended by the manufacturer, and it's a bad idea. I'm not arguing that with you any further. This is just dumb.

The section width of your Toyo 315 is 12.6". The section width of what I presume is your BFG (the only one I see in 275/40/17 size) is 10.9"...1.7" difference, or almost 7/8" per side. The Falken RT660+ (their current track tire and a pretty wide one) at 275/40/17 has a section width of 11.1", which is still 1.5" narrower or 3/4" per side. WTF are you talking about?

Please stop. This isn't going well for you. Do what you want with your own car. Don't advise others that what you've done is fine and causes no problems.

 

275- 10 inch…..315-11 inch ex

 

WTF am I talking about? Not numbers off a website but reality. And in reality, my 315 sidewall protrudes 1/4 " further than my 275 on my stock wheel. As they say, pictures don't lie.

 

Whatever, my man.

 

So that's it?

You may have some real knowledge and might be able to actually help people but this entire thread, you've been a condescending jerk who thinks they know it all. And when I showed you facts to prove that this tire isn't pinched or unsafe, that's all you've got to say?

Get bent..

 

Ahhh, well the pics didn't show up before. Don't know why. But yeah, those pics...you do understand these are different kinds of wheels, right?! You do understand that you didn't measure from the rim lip edge of your stock salad shooter wheels int he pic of the 275, right? Whereas your Dymags have the thickness of your salad-shooter's lips all the way down? If you measured off the end of your stock salad shooters instead the inset part - like anybody who understands any of this would - then you would see that your 275 Falken's sidewall only protrudes about 1/8" outside of the rim edge, whereas your 315 Toyos are protruding 3/4". Or IOW, if you had both tires mounted on the same kind of wheel, you'd see that the 315s are protruding at least 5/8" further past the rim edge than the 275s.

I mean...are you really this dense, or are you intentionally trying to mislead forum members now?

 

The Dymags lip is the same thickness as the salad shooters. I own both wheels and have measured both in detail without tires on both. Do you own Dymags? Because if not you aren't qualified to make a statement about the lip construction. If you lay both wheels on the ground without tires the salad shooters will be wider because of the width of the lip band. No I didn't measure from the lip band on the salad shooter since it isn't a representation of where the tire bead mounts. I measured from the lip on both because that's what is accurate. As for the same wheel argument, here is the 275 toyo on the front Dymags.

As far as calling me dense, insults are the last grab for those that know they're wrong.

So unless your next reply is something respectful and dignified along the lines of "I'm sorry" or "I was wrong" , I will assume your opinion is invalid and you, just like every other keyboard warrior, can't accept that they don't know everything.