Kreb said:What about the idea that such a wide tire won't get warm enough to really hook up at an autocross event?
It can definitely happen, Dusterbd13 had that problem with the AMC Spirit with its huge cartoon steamrollers, so there is a point where more width can actually hurt grip, but it's deep into silly-wide territory. Around a track, you'll more likely hit the point where aerodynamic drag losses exceed grip gains first.
Knurled. said:In reply to LanEvo :
Yeah, that doesn't make sense to me either, then. When people find that tires much wider than 285mm hurt lap times, with 600+hp engines, one starts to wonder...
Terry Fair when building his red Mustang GT, showed that with less 450whp and tons of aero, he continued to lower his lap times the bigger he went on Hoosiers. All the way out to his 335/345 A7 setup.
So I'm not sure where you're getting this idea that people aren't getting faster with wider tires than 285s.
mazdeuce - Seth said:LanEvoComing from the BMW world, I’m used to seeing cars that are much heavier and significantly more powerful that run 225 and 245 tires.
The big question is, can you shove bigger tires under the BMW's and stay legal for the class, and if you do, do they get faster? Miatas do this because they're faster with more tire, as Keith says, until they're not. I personally love Miatas with low grip, but I do acknowledge that they're slow that way.
The strut geometry on most BMWs tends to limit tire width a bit more than the Miata. There isn't as much room to go inwards with the tire because the strut tends to be closer to the factory sidewall than the Miata's shock is.
Adding grip improves speed through the corners, but adding drag decreases speed down the straight. There's a tradeoff there and the sweet spot is going to vary a lot depending on things like how much power the cars makes, the amount of grip it has, the altitude of the track, the proportion of the course that's turning vs straight, and on the top speeds down those straights. The top speed is critical (and probably the dominant factor) because drag is a function of speed squared, meaning that doubling the speed gives you four times the drag.
This matches up fairly nicely with what we see in the real world, where naturally aspirated Miatas will see top speeds at autocross that are roughly half what they see on big tracks (say 50-60 mph vs 100-110). 275s appear to be a net win for those Miatas at autocross, whereas I've seen reports from people who've done back-to-back testing on bigger tracks that (in some cases) 205s have been faster than the same tire in 225s.
mazdeuce - Seth said:The big question is, can you shove bigger tires under the BMW's and stay legal for the class, and if you do, do they get faster? Miatas do this because they're faster with more tire...
That's really the whole point of this thread: do BMWs (and many others) run relatively narrow tires just because of class rules? Is there a disadvantage to gigantic tire footprint in real-world use?
At least in theory, I'd expect pretty much any car to be faster on steamrollers even on track (not just autocross). So, why doesn't everyone run them?
TurnerX19 said:Now with your TR6, if it still has stock suspension your geometry is not good enough to take advantage of that much tire, and the chassis will fail at the suspension mounts if you could produce that much grip.
That's definitely a consideration. The TR6 is a project car and beefing up the suspension, diff mounts, half-shafts, etc. is already on the to-do list. It's not built to class, just a fun toy to screw around with and run some open lapping days here and there. I have a properly built racecar I run with the BMW CCA and various vintage series.
The "why" is just because I think flared fenders and fat tires look cool. When I see a Miata on 275s it makes me happy. Totally immature. I know it's stupid.
I can't help it..
People usually don't run them for either rules or cost.
In reply to LanEvo :
Ooooof..... Yes Please!
Keith Tanner said:LanEvo said:^^^ does that hold true on an open track as well?
It’s like downforce. It keeps making you faster until it doesn’t anymore.
There's also the cajones factor. As grip continues to increase, so does cornering speed, to the point where where the whole "thrill of speed/fear of death" can become overwhelming and you realize two things. 1. I shouldn't be going this fast. and 2. If this thing lets go, I'll end up 3 counties over, upside down.
Or so I'm told by persons braver than I. I'm a giant chicken, so I've never needed to go beyond a reasonable width autox tire to "see the elephant" on track.
z31maniac said:Knurled. said:In reply to LanEvo :
Yeah, that doesn't make sense to me either, then. When people find that tires much wider than 285mm hurt lap times, with 600+hp engines, one starts to wonder...
Terry Fair when building his red Mustang GT, showed that with less 450whp and tons of aero, he continued to lower his lap times the bigger he went on Hoosiers. All the way out to his 335/345 A7 setup.
So I'm not sure where you're getting this idea that people aren't getting faster with wider tires than 285s.
It was one of the Corvette special models. The chassis engineers found that wider tires actually made lap times slower, despite higher cornering speeds.
I can't speak to autocross cars because I have no experience with them but with track cars the only times I've seen wider tires hurt lap times was when weird offsets that messed up geometry were needed to fit them or needed alignment changes weren't made to accommodate them.
In reply to Knurled. :
Obviously they were doing it wrong
I have heard that there is a maximum size for BMW 2002s with stock suspension mounting locations. In FSP, they can go as wide as they want but I think people downsized to avoid turning the car into a bicycle.
Knurled. said:z31maniac said:Knurled. said:In reply to LanEvo :
Yeah, that doesn't make sense to me either, then. When people find that tires much wider than 285mm hurt lap times, with 600+hp engines, one starts to wonder...
Terry Fair when building his red Mustang GT, showed that with less 450whp and tons of aero, he continued to lower his lap times the bigger he went on Hoosiers. All the way out to his 335/345 A7 setup.
So I'm not sure where you're getting this idea that people aren't getting faster with wider tires than 285s.
It was one of the Corvette special models. The chassis engineers found that wider tires actually made lap times slower, despite higher cornering speeds.
OEMs likely have different targets than someone looking for the absolute fastest times in AutoX and Time Trials on Hoosiers with tons of add-on aero.
That's just a guess though.
I’ve only driven two miatae so no first hand experience but years ago when I regularly participated with CVO there was a guy with a Cabby who had cut out the fenders and had some HUGE Hoosiers and absolutely blew everyone away at auto-x. It’s a 90-125 hp car so it shouldn’t have “needed” that much tire but it cornered flat and didn’t seem to transfer weight as suddenly. I think 84fsp knows the guy if he sees this. We were both watching him.
Simple answer: because it works.
At solo nats 2017 (ignoring 2018 because of the great flood), CSP was faster than ASP, BSP (with Tom O’Gorman running), SM, FP, and many other “fast” classes. They also took top PAX.
Back in the day I ran an old MG in a showroom stock sort of class and used to love when the competing cars stuck huge boots on their cars. Over-tiring an under powered car could result in the loss of a couple of hundred rpm at the end of the main straight simply from increased cross-sectional area, and they didn't pick up much, if anything, in the corners over the more sanely tired cars.
wspohn said:Back in the day I ran an old MG in a showroom stock sort of class and used to love when the competing cars stuck huge boots on their cars. Over-tiring an under powered car could result in the loss of a couple of hundred rpm at the end of the main straight simply from increased cross-sectional area, and they didn't pick up much, if anything, in the corners over the more sanely tired cars.
Rallycross is even more fun.... the tuning goes backwards, you want more transfer to get grip, and you want narrower tires for cornering traction, up to the kneepoint where you lose forward grip. (You need to drive hard enough to get enough traction to drive hard...) So there comes a point where more power is detrimental to cutting good times because you need a wider tire than will give best cornering traction.
That was a hard lesson to learn.
wspohn said:Back in the day I ran an old MG in a showroom stock sort of class and used to love when the competing cars stuck huge boots on their cars. Over-tiring an under powered car could result in the loss of a couple of hundred rpm at the end of the main straight simply from increased cross-sectional area, and they didn't pick up much, if anything, in the corners over the more sanely tired cars.
Right, that was likely not with radials, but with bias ply tires. They are quite different beasts. Also modern tires are so incredibly different and better in many ways than the older tires that it is quite amazing.
Coupled with the Miata’s better suspension geometry (something an MG could only dream of) they can make good use of those tires with a competent driver.
In reply to Stefan :
Miatas are better?
I've seen the massive bump steer issues that Miatas have in the rear suspension, and it makes me understand why the solution for Miata handling seems to be to make it so stiff that the suspension can't do anything bad. MGs, in contrast, have lever shocks and no good way to deal with that. And leaf spring rear suspension and no good way to deal with that. And... etc.
The Miata geometry is perfect for plastic 185/60-14s and 100hp, but much beyond that, it really kinda sucks without a lot of shoring up. (So leave it alone so it stays fun! Or not)
What? I've never seen such complaints about Miata geometry.
Where does the rear get bump-steer? Its DWB. Without a toe link or anything nothing should change toe during travel, no? (NA/NB)
Also, I don't know that "so stiff the suspension can't do anything" is the Miata solution. Most Miata setups have plenty of compliance, esp. compared with strut cars.
If a Miata has bad geometry, what has good geometry?
In reply to ProDarwin :
Funny, when I saw DWB, since it's not called that a lot, I read DBW, and I was wondering how bump steer was effected by electronic throttle.....
Running 275/35/17 square RC1's on a BMW e36. From my research, e36/e46 bmws do NOT have an issue decreasing track times as rubber width increases.
Terry Fair (Vorshlag) is very vocal about this on Bimmerforums, that the more tire the merrier. I know its anecdotal, but I sure as hell have more fun with a 2750 lb BMW on steamrollers!
Tires last FOREVER......
ProDarwin said:What? I've never seen such complaints about Miata geometry.
Where does the rear get bump-steer? Its DWB. Without a toe link or anything nothing should change toe during travel, no? (NA/NB)
Also, I don't know that "so stiff the suspension can't do anything" is the Miata solution. Most Miata setups have plenty of compliance, esp. compared with strut cars.
If a Miata has bad geometry, what has good geometry?
I've decided he is trolling. The issue with Miata suspension is lack of travel in the rear when lowered, but this has been handled with aftermarket solutions for more than a decade. Never heard of "bump steer" on wheels not controlled by the steering wheel.
Not to mention the "cars go slower with wider than 285 tires" uses a Corvette as an example. A 2015 Z06 has 285/335 staggered setup stock.
You can have bump steer on the rear. It’s toe change with suspension travel. Not much you can do to change it without moving pickup points. I can’t say I realized it was so fatally flawed, though. All this time we’ve been dealing with junk :)
But the NA/NB Miata does have bushings that are designed to provide toe change under cornering load for stability. If you chuck in a bunch of poly without realizing, you will change the way the suspension works.
"But the NA/NB Miata does have bushings that are designed to provide toe change under cornering load for stability. If you chuck in a bunch of poly without realizing, you will change the way the suspension works. "
Keith, Please elaborate.
Keith Tanner said:You can have bump steer on the rear. It’s toe change with suspension travel. Not much you can do to change it without moving pickup points. I can’t say I realized it was so fatally flawed, though. All this time we’ve been dealing with junk :)
But the NA/NB Miata does have bushings that are designed to provide toe change under cornering load for stability. If you chuck in a bunch of poly without realizing, you will change the way the suspension works.
Yep. I've just never heard the term "bump steer" used in relation to the rear wheels.
http://www.longacreracing.com/technical-articles.aspx?item=8162
You'll need to log in to post.
