ok, here's the deal:
june, july, and august have been pretty tough on teh old(new) BFG KDWS.
three road course events in three months, and i m guessing that they have a fourth in them, perhaps.

i still have the old 18 x8.5 polished bullitt rims which were take-offs from the vert, before i shod her with the fr500 knock-offs.

so i am looking for a good road course tire to put on those, to finish out 5 more events with, this year, before santa brings some real shoes for her. i am anticipating running 275/40ish x 17 or 18

on a side note (but not the main question of this thread), i am torn between going 17x9.5ish and leaving brakes pretty much maxed out as they are, and reveling in affordable rubber, and less unsprung weight, . . . vs 18's to accommodate a big brake kit, and hope the extra stopping power offsets the extra weight.
(comments here welcome, but this is not the main question)

to tide me over for the next 4 or 5 events this year, i have looked at lots of available tires, and narrowed it down to the list below, of what will probably reasonably fit on the 18x8.5 rim.

my preference is 255>245 as it gives more rubber on teh ground, and should not come anywhere close to rubbing.
the profile is the dilemna, as i do not want to induce too much bulge, the the tier rolls over on itself, impairing handling accuracy.

to that effect, since all three options: /35 , /40, /45 are all lower profile than the stockers, it would seem to reason that that may counteract any bulge-induced rollover.

so any thoughts on section width as it relates to aspect ratio, and to the "recommended" rim width, would be most appreciated.

these will be driven to, on, and from the track, and then she will be re-shod with her usual walking shoes.
thanks,
doc


yes, i realize the typo below, the stockers are /50 series, not /55.

 

^ DUDE!!! Is that 1/2 a breast under there???? What were you Photoshopping?

 

nope
2 y.o. daughter's chin
you should be ashamed,
lol
it does kinda look it though (now that my mind is back in the gutter)

 

The quick answer regarding the Falken RT615's is that they are not R-comps. But maybe midway between typical UHP tires and R's. In street driving you'll heat-cycle the best part of the grip away long before you wear out the tread.

I knew I'd seen a discussion of RT615's and NT01's recently. That it specifically involves V8/RWD cars with PHB lateral axle location is a plus.

http://www.frrax.com/rrforum/index.php?showtopic=12072


My tendency is to either choose wheels up toward the wide end of the range for a particular size tire, or choose a tire size for which the available wheel is at least as wide as the "measuring width". The preference is for improved response and transient behavior more than the last 0.01 or 0.02g of lateral grip, which is pretty meaningless on the street when you come right down to it (actually using only 80% or so of the grip you've already got - will run away and hide from just about anybody and anything you're likely to come across on the street).


Norm

 

Norm - That link is not working for me...is there some issue with it?

I used to have the Falken 615s in 255/40/17 on 9in rims. Great tire, they are perfect for driving to/from the track and then removing. Now I'm running NT01s in 275/40/17. True R-Comps, they never see the street.

If I had to do it again, I'd get 18x9.5 rims. I went with the 17s because the tires are cheaper. But in retrospect, I rather have a little more ground clearance and the option to install 14" rotors.

Regards the width of tires: you can see the sizes I've used above. The Falkens were very quick on turn in. The bigger Nittos are a little more vague on the 9in rim. But to be honest it doesn't bother me, its just something I got use to and now I like the better grip more than the better turn in.

 

I would stay with a tire that has a diameter as close to stock so 255/45/18. This will keep your speedo accurate going to and from the track.

The other thing and more important for the track is a smaller diameter will essentially be increasing your rear gear. Depending on the remaining tracks you will go to this may be helpful or harmful. I don't know which tracks you are going to so I can't recommend going with a tire that will change your Bullitts rear gear from 3.73 to 4.10 or more. If the tracks you have left require 120mph you may want to stay with stock diameter tires otherwise you will be in fifh gear on the straights which isn't ideal.

Side note, you have a stroked, heads, and cams and you only put down 369whp???? I see you have turbos waiting so if your CR is low on your built motor due to eventual FI, then putting down 369whp makes sense.

 

Dunno. Worked for me when I first put up the post (at home), and again this morning (at work).

Maybe you need to be registered there to see all of the forums? So here's a few comments . . . boldface mine


Norm

 

is it the total mileage that heat cycles out the grip? or is it the number of trips(i.e. heat cycles)?
would one long trip to, and one long trip from the track, be particularly be bad?

for how many heat cycles doe the grip last?
(just a ballpark figure, i know, like everything: "it depends")

can you elaborate more on this?

looking specifically at the goodyear asymmetric from the table above

is that to say i should choose the 255/45 because it measured 10.0" on an 8.5" rim, (and 8.5" rims happen to be in the middle of the acceptable range?

and, i should simultaneously avoid the 255/35 because it measures 10.2 on a 9.0" rim, and 8.5" rims are on the low side of acceptability?

am i correct the the section width of the 235/35 would be even wider than 10.2, were i to mount one on the 8.5" stock bullitt rim?




i am not so inherently worried about it staying the same right now, especially as i do some track hopping, away from my usual haunt.

interesting point i hadn't thought of.
is there something particularly uncool, or disadvantageous about 5th, other than just being an additional shift?
if the car is pulling hard, and there is room to roam, does the gear really matter?
(honest question, not trying to be argumentative)

yes, CR is dropped to about 9.3:1, and teh cams are a stage II turbo grind from mmr, so i was ready to give up a little hp/tq now, in favor of being better situated to take advantage of the hair-dryers, whenever they finally go on.

 

Doc Stang - I can add input to a couple of your questions:

Regarding the RT-615s and heat cycling: I used these tires most of the summer. They had about 60 autocross runs (many of them back to back hot laps) on them and 6 track days, plus a couple thousand highway miles driving to and from events. They were still good. They still gripped fine. Did they have less grip then when new....sure but not a whole lot, not enough to bother me at all. I could have gotten at least 2 more track days out of them but I was anxious to get R-Comps on the car.

Regarding changes in tire diameter: My track tires are about 1.5" less diameter than stock (275/40/17). I have an SCTII that I use to reset the size and adjust the speedo, so its correct. But its no biggie if you don't do this, your speedo will just read way high, make you feel like your going faster - LOL. I also have 4.10 gears. This is NOT a good combo and I plan to swap them out to 3.55 soon. I spend too much time in the upper rev range. It is workable, but not ideal. I do use 5th on most long straights but its an overdrive gear and I have to get up to about 6K in fourth before the shift or the car will fall flat on its face. Depending on the corner at the end of the straight I also may be doing two downshifts, or worst case three, again not ideal but workable (more heel-toe practice).

Hope this helps. Brad.

 

Near as I can tell its some vague function of both. In auto-X terms I don't think anybody counts on getting much more than 100 runs (15 - 25 events) before the performance has dropped off enough to matter. Still better than most normal street tires, but easy pickings for new tires (or the latest ST tire). I've got about that many runs on mine (not on the Mustang), with maybe a few hundred street miles and they are decidedly less grippy than when new and harder to bring up to temperature.


To start with, even in XL construction the 255/35 size does not really have enough load capacity for extended hard driving, so I'd scratch it off the list for that reason alone.

If the 255/35 measures 10.2" on a 9" rim it would be about 10" (section) wide on 8.5". Wider than 9" will push the 10.2" measurement wider, narrower than 9" pulls it in to something less. Tread width does not change enough to matter.

The only good reason that you might run 255/35's on 8.5" wide wheels in a hard driving environment (with a car of appropriately lower weight) is if you are subject to competition class restrictions that limit you to wheels and tires of those widths (the limitations for SCCA's Street Touring classes come to mind, if not quite those numbers). Otherwise, and for what are apparently going to be tires used as a sort of interim setup you really should be on the 255/45's.

Personal choices for long term use - I look at putting 255/45's on 9.5", needing 10" for a 275 tire, and wanting still another half inch for 285's. What can I say, other than mentioning a long and very satisfactory history of using wider than measuring width rims (including one unexpected side benefit).


Norm