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View Full Version : who says size doesn't matter?


sykikchimp
01-06-2003, 03:53 PM
What has a larger impact on traction and stability in corners, width of the tire, or height?

tnord
01-06-2003, 04:20 PM
wow.........that's actually an interesting question.

one factor would be sidewall stiffness. if the sidewall is too soft, the tire would "deflect" or "rollover" and reduce the amount of tire on the inside that is in contact with the road. i guess we should just assume Z rated tires for comparison purposes. increased tire height results in more grip for straight line purposes though, and vice versa.

i really don't know........but if i had to give an answer, i'd say reducing tire profile (to a point) is more beneficial. i say this because i get assessed 2 points for increasing rim diameter, but only 1 point for increasing rim width. but then you get into the whole argument about heavier wheels.

anybody else? mark? dave? bbp?

sykikchimp
01-06-2003, 04:50 PM
I ask b/c I was reading an article about the Z4 and they referenced that it was using 18" wheels which helped significantly in lateral stability. (believe it was C&D) anyways, got me to thinkin... Everyones all the time talking about running wider smaller diameter tires.. but if you can also increase contact patch front to back, that should put more shoulder on the pavement mid corner when the tires are using mostly shoulder and not the inside of the tire so much.

So would running 17" wheels with 50 profile tires be better as long as sidewall deflection was kept to a minimum, maybe by using a skinnier tire, and stretching them a bit?

DSC
01-06-2003, 07:10 PM
There was another topic like this a while back and we "decided" after much speculation and guessing, that as long as the gains in latteral traction from larger wheels (lower profile tires/reduced sidewall flex) aren't surpassed by the negative straightline effects of larger wheels (increased rotational mass and reduced sidwall flex) then it's worth it to move up...money and classing aside.

How you measure the latteral traction gains vs the straighline traction and power loss? I have no clue...

tnord
01-06-2003, 11:56 PM
here's another issue............once you actually get the car moving, the straight line traction benefits of taller tires really is unnecessary. you're not going to do a burnout exiting a corner for example (and if you have enough hp to do this.....i just dunno). so yeah.........i dunno...........vicatin and booze have messed up my head.

DSC
01-07-2003, 12:21 AM
Yeah, I actually said something about that but edited it out b/c I said it wrong and was too lazy to fix it. But now that I think about it, how about corner exit. Get on the gas too soon out of a turn and get the back all lose, would this still be a latteral traction issue in a low hp car or are you actually spinning the tires like you do turning too fast from a stop?

Assumeing straightline traction isn't an issue, weight still would be.

Someone buy me a few sets of rims, i'd be happy to test them out and tell you what I think is better :)

Steeles
01-07-2003, 07:36 AM
hmmm so I wonder what a 225/50/17 on a 17x8 would be like? as opposed to say a 225/45 more "traditional" setup. I've run staggered tires on same width rims on my car before and didnt really notice much of a difference between driving on all four same size. (i was running 215/45/17 and 225/45 in the back)

bbp
01-07-2003, 08:27 AM
Interesting question. I would say that with todays tire technology, width would be more important. With steel belted radial tires, they can stiffen the side wall enough that it doesn't really become a factor. Take BFG R1 for example, this tire was designed for Showroom stock racing, cars without "ideal" suspension setup. The outer sidewall is extremely stiff while the inner sidewall flexed a bit more to compensate for less than ideal camber settings. If any of you have ever mounted DOT R rated tires they can attest to the stiffness of the sidewall compare to a normal street tire.

The tire width would make a difference in grip. I would rather run a 225 than a 205, as long as the car has enough HP to warrent a larger width tire. On a NA s14, I would not go any bigger than a 225. The car does not have enough power to warrant anything wider. Also, streching a tire onto a larger rim does not really help much since the contact patch will remain the same. If you go too wide, it just creates drag and actually slows the car down. There is such a thing as too much grip.

Now in the rain, you would want to run a narrower tire, less contact patch. This will reduce the chance of hydroplaning and disapate the water more effciently.

Now to the contrary if anyone is running bias ply tire (vintage) side wall flex can be an issure.

The most important factor in grip with tires is the compound the tire is made of. This is the absolute most important factor as to how much grip the tire will have, how long it will have grip, succeptabilty to heat and so on. You can have two identically built tires in the identical size by the same manufactuer but different compounds and have completely different behaivng tires.

wherezmytofu
01-10-2003, 11:36 PM
just ask s13grl :o

240racer
01-15-2003, 11:42 PM
I have said this before, but, in general I think that whenever a setup is softer or more forgiving or whatever you want to call it, then it has more grip. Of course when it is stiffer it moves less and has better response. However, as somebody mentioned, if the tire flexes too much then the tread is no longer on the ground. I think that it depends on the tire, a tire that has better (stickier) tread compound can afford to be stiffer, because it has as much grip, but then has better response too. Like bhp said, the dot race tires are stiffer, but have better grip, that's all in the compound. Same with F1 tires, they have literaly no flex and still amazing grip (don't tell anybody, but I met the guy that built the new bridgestone tire tester and he says they have gotten Coeff. as high as 1.5 out of F1 tires, most racing tires are around 1.2-1.3) With that said, I think the size tire you run has more to do with the tire itself, whether it needs flex to grip or not. I'm planning on sticking with my 15" steelies for now, and running SO-3's on them because they are "only" $103 each. 205/55-15 I hope it is a good combination of price, ride, and traction. Does anybody have any input on this?
Also, do you guys find benefits of running 17s on the track, like do you need them to clear brakes or do you like the feel of low profile tires or whatever?

tnord
01-15-2003, 11:49 PM
240racer...........we gotta meet up at the track sometime this summer. i'm in the western suburbs of minneapolis, and i hardly know any other legimate enthusiasts in the area.

anyway, from my recent experience with steel wheels i can say this. the 15x6 w/195/60 snow tires are FAR heavier than my 16x7.5 kosei's with 225/50's. so i can say that you would have a definite performance benefit from going to a 16'' wheel, even if you keep the same width tire.

240racer
01-16-2003, 12:23 AM
Ok, I know that the 16" setups are lighter then what I have now, but I'm worried about cost in the long run. 16" tires are expensive. My friend is looking for tires for his MKIII supra and having a horrible time trying to find a "good deal" I think the SO3s are a good deal. However, if they make the brake upgrade easier, then it might be worth it in the long run. I have so many things I need to do to my car it would take me all year to do new wheels/tires along with shocks, springs, bushings, pistons, etc. :-)

tnord- check your PM

tnord
01-16-2003, 12:59 AM
well..........yeah, they can be expensive. i got my tires for $70/piece. and there are others for less. but for S03's like you have is around $150. so yeah, it adds up. pretty significant improvement in handling though.