You're absolutely right, David. A larger wheel/tire combo will impact acceleration because it's heavier, AND because of a larger circumferance. In other words, there's more rubber to lay down in a single revolution, which means that you've effectively raised your final-drive ratio (remember, numerically lower final drive ratios are HIGHER.) This can be backed-up by our experience with our '97 Jeep Wrangler (bear with me your honor - this is relevant!) When we lifted it enough to clear 35" tires, the stock gear ratio of 4.10 was suddenly severely lacking. When we installed the new rear axle and front and rear lockers, we went ahead and lowered the gear ratio to 4.56. Unfortunately, I should have chosen 4.88s to bring it back inline with stock gearing/tires.
Anyway, I agree completely with what you have to say. It's also quite evident that larger wheels/tires will take longer to stop (higher inertia), which is why I run drilled rotors with a good carbon/kevlar pad (probably overkill on the street), braided-stainless brake lines, and the Ford Super Blue brake fluid. Ask any grass-roots race enthusiast and they'll tell you to save your money on the expensive fluids and use the stuff from Ford! See ya, BRian ----- Original Message ----- From: "David Miller" <[EMAIL PROTECTED]> To: "Ricky Crow" <[EMAIL PROTECTED]>; "Brian-SubCultureNM" <[EMAIL PROTECTED]> Cc: "Jeremy Bass" <[EMAIL PROTECTED]>; <[EMAIL PROTECTED]> Sent: Friday, January 31, 2003 8:52 AM Subject: RE: CRX: Re: Physics lesson, and a stop to all this bickering about tires and sizes and hydroplaning. Just for fun here -- it is not the size of the wheel that matters. For performance, there are two factors involved -- first, there is the weight of the wheel/tire combination. Then, there is the location of the mass in relationship to the diameter. Let's say that you have a wheel/tire combination that weighs 25 pounds. Now, running a 175/70-13 vs. 205/30-18 (within 0.2 inch in diameter) you can see that on the 18 the entire tire portion is located beyond 9 inches from the center of the wheel. Where with the 13 it is located beyond 6.5 inches from the center of the wheel. Therefore the 18 inch wheel has a greater rotational force to overcome. This, in essence, means that everything else being equal, a car with 13" wheels will accelerate faster than one with 18" wheels. It is a simple matter of physics. IF this is what you are referring to as performance. Personal experience. My '89 DX (we must keep CRX content, right?) accelerates faster with 195/60-14's than it does with 175/70-14's because the tire/wheel combination is probably 8 pounds heavier per corner. Greater rotational mass. TTFN! David -----Original Message----- From: Ricky Crow [mailto:[EMAIL PROTECTED]] Sent: Friday, January 31, 2003 9:44 AM To: Brian-SubCultureNM Cc: Jeremy Bass; [EMAIL PROTECTED] Subject: Re: CRX: Re: Physics lesson, and a stop to all this bickering about tires and sizes and hydroplaning. You're the one that brought some pickup truck into the equation. This is a CRX List, and he was stating numbers about a stock CRX. All CRXs have the close to the same weight distribution, for the most part. Therefore his numbers apply to the vast majority of CRX's out there. Your CRX's suspension can't be much different than what my CRX is (I have one CRX on each end of the spectrum, from almost-stock to heavily-modified with various suspension braces, sway bars, roll-cage, etc). And yes, he was oversimplifying, because you didn't seem to understand. Bottom line is, no street tire will help you from hydroplaning over 50-55mph, no matter how good the tread pattern is. If you were really an engineer like you say you are, you'd realize that bigger wheels have a diminishing return on performance increase (and gets to the point where it actually is a detriment to performance). Ricky On Fri, 31 Jan 2003, Brian-SubCultureNM wrote: > Hey Ricky, > > You ever heard of a discussion? That's all this is, my man. If you can't > take it, then you have no business being in a public forum where discussions > take place. You obviously can't handle anyone disagreeing with you, my > friend (which is the statement you issue towards me, as if it's an insult.) > I don't care - I like the discussions; they're thought-provoking and get my > blood boiling sometimes. Besides, when someone's thinking is flawed, there's > no harm in pointing-out the error, especially if it's done in a constructive > way. The fact is, his thinking did not take some critical factors into > play - he assumed that all vehicles handle and drive alike. His formulas > were also over-simplified. Sometimes my Engineering education rears its ugly > head, that's all. > > Anyway, like the previous threads, you have nothing positive nor anything > constructive to add, so your point is irrelevant. Notice, I still haven't > become negative, even in the face of your insults. > > Take care, > > Brian > ----- Original Message ----- > From: "Ricky Crow" <[EMAIL PROTECTED]> > To: "Brian-SubCultureNM" <[EMAIL PROTECTED]> > Cc: "Jeremy Bass" <[EMAIL PROTECTED]>; <[EMAIL PROTECTED]> > Sent: Friday, January 31, 2003 7:53 AM > Subject: Re: CRX: Re: Physics lesson, and a stop to all this bickering about > tires and sizes and hydroplaning. > > > > Exactly why I stopped discussing this with you -- you will argue with > > anybody that doesn't agree with you, no matter what they say or how they > > prove what they're talking about (hence the reason why I didn't bother to > > give you any 'scientific' evidence, because you'd have tried to discount > > it as well). > > > > Sadly, your thought process is way too typical these days. > > > > Ricky > > > > > > > > > > > > On Fri, 31 Jan 2003, Brian-SubCultureNM wrote: > > > > > You've made some decent points, but haven't taken all the variables into > consideration. Your formulas assume a perfectly flat tire, one with no tread > pattern at all (tread pattern will, of course, take precious square-inches > away from your total contact patch.) However, a well designed tread pattern > will evacuate water from underneath its contact patch, thus nullifying a > large portion of your assumptions. > > > > > > Anyway, I'm not an advocate for driving as you would on dry pavement > when it's wet. Of course, here in NM, rarely do we have to worry about > anything more than a few rain drops on the pavement. Also, as far as the > truck is concerned, 1) it has an air-bag suspension which allows for a lot > of slop in its handling - in other words, it doesn not maintain constant > down-force on any surface; 2) it's body-dropped and has had a large portion > of its bed structure removed, so the weight over the drive wheels is > probably no heavier than a CRX; 3) as mentioned, it is front-heavy RWD, > which lends itself to more handling problems (and less predictable handling > problems with the 'bags) than a FWD CRX. Therefore, when you take all this > into consideration, it should handle even worse on wet pavement than the > CRX. It didn't, and the tire tread and compound has a lot to do with that. > > > > > > Finally, congratulations on your door handles (seriously.) I would be > curious as to how long you've had them done and whether-or-not you've > started to experience shrinking of the JB Weld. If you haven't, you will. > Believe me, having a lot of experience with custom body mods, there's rarely > a time that they are 100% trouble-free. THis isn't a critique of your work, > it's just a fact. We've had to have one door and the tailgate handle on our > truck re-done because of cracking. It happens to the best of them! > > > > > > Brian > > > ----- Original Message ----- > > > From: Jeremy Bass > > > To: [EMAIL PROTECTED] > > > Sent: Friday, January 31, 2003 3:54 AM > > > Subject: CRX: Physics lesson, and a stop to all this bickering about > tires and sizes and hydroplaning. > > > > > > > > > An end to all of this hydroplaning crapola... Welcome to Jeremy's > weird world of physics... > > > > > > Exibit A: > > > Frontal Resistance... The more surface area you present in the > direction of the movement, the more resistance you create and the more force > you need to overcome that resistance. > > > > > > The surface area is the contact patch of the tires. The direction of > the movement is the tires penetrating the water. The resistance is how hard > it is for the contact patch of the tires to penetrate that water. More > force would mean more weight pushing down on the tire or traveling at a > lower speed so that the tire has less water to penetrate. > > > > > > In other words... If you were in a 1990 Honda CRX si, and hit a > puddle with a depth of .40 in. or greater of water at 50mph with stock > 185/60/14 tires you would be less likely to hydroplane than if you were to > hit water with 205/40/16s. I use .40 inches of water because it rids me of > variables such as tire tread pattern and road surface, because your tire is > as good as slick in water that deep. If your tread is deeper than .40 inches > on your crx you need to buy tires that are not for off-road use.... > > > > > > Now, a stock 1990 Honda CRX si with 185/60/14 tires at 28psi weighs > 2174lbs, and has a weight distribution of 62% front and 38% rear. Therefore, > the front tires are putting 1396.2 lbs to the pavement which is a scant > 698.1 lbs each. So, in exactly .40 in. of water and a contact patch of 32.8 > sq. inches, it would take water pressurized to anything above 21.28 psi to > lift the car from the surface of the road. ( I think that is around 51mph??, > but that doesn't matter right now ) > > > > > > SO, if the tire variables increase the contact patch of the tire, it > lowers the water psi needed to lift the vehicle, and increases the > likelyhood of hydroplaning. > > > > > > THEREFORE THESE STATEMENTS ARE FACTS: > > > Tire outside diameter DIRECTLY affects hydroplaning. (minimaly) (18 > inch rims must use larger than stock OD) > > > The width of the tire DIRECTLY affects hydroplaning. > > > Tire pressure DIRECTLY affects hydroplaning. > > > The weight of the car DIRECTLY affects hydroplaning. > > > Speed... Duh. > > > > > > Thank you ladies and gentlemen.. > > > > > > (I'm sure my english is not perfect, nor spelling. But the numbers can > be checked with a fine tooth comb.) oh, and your canyon carving truck with > the big fat tires weighs way more than our lil rexes so your example is null > because you have more "FORCE"... nanny nanny boo boo.... > > > > > > So, may we please quit bickering??! : ) > > > > > > >
