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vega

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Posts posted by vega

    Tire vs power and weight?

    in Brakes, Wheels, Suspension and Chassis

    Posted

    There is no tire, other then a purpose built drag racing slick, that will give you "no spin" levels of traction with the horsepower you're talking about. My 325hp, 2,100 lb. 240Z could spin its 275/45-16 Hoosier R4s at will in 1st and most of 2nd gear if I tried. Build your engine with good throttle response, make sure your throttle linkage has plenty of travel and is smooth, run a good LSD, and learn how to drive the car.

     

    Good point, although to add to what you said... Where are you making that hp on the curve(rpm)? What amount of tq are you making and where is that coming in at? v8? l6? what transmission gearing do you have? Rear differential gearing? What kind of suspension?

     

    Also out of curiosity with have you run in the 1/4 mi with that car to date? (just to compare power to weight to your setup etc)

     

    Great info you guys, its much appreciated, it is quite obvious why you guys are admins.

    Who the heck's datsun is this?!

    in Non Tech Board

    Posted

    It not an "atypical" name- no racial/political/religious intent behind it. Just thought it was interesting. I enjoy names, I have been writing books for a myriad of years- I have a certain affinity toward names such as these. Also for future reference, all that politically correct "stuff", may as well through it out the window. There is too much emotion for me to even remotely care. People will be offended by a couch if they want to. If someone wants to be offended by something they will choose to be offended. THAT sounds like a personal problem that they need to seek out psychiatric help for which is beyond more than I personally care. Just for future reference.

    Tire vs power and weight?

    in Brakes, Wheels, Suspension and Chassis

    Posted

    Never really thought about i, but if I were to hazard a guess I would suppose that they use a set of criterion that does not include "dry road course handling with slicks with several hundred lbs less and several hundred hp more than originally designed" (which is what is important to me) and that style, cost, safety, ride comfort, and tire wear are very high on the list for most car manufacturers.

     

    I would agree, if one were to stay the same weight same suspension setup, same (comparable) compound as factory. would the 130 (whp for a z) and the 195mm be a way to try to factor that in? 130/195=0.666666667.

     

    So every 1hp needs 0.666666667mmm of width for the tire. so a 450whp z would need a 300mm tire- etc.

    Tire vs power and weight?

    in Brakes, Wheels, Suspension and Chassis

    Posted

    Look at a given class for a particular type of racing, the class regulations for the max wheel and tire size and the size tire that was run by the champion in that series, and then show me the car that won a championship by running narrower tires than are allowed. There are VERY few examples where a tire less than the max allowed size will be faster, but they are out there. A couple of examples come to mind: 1. Land speed racing or circuits where the top speed is very high and there aren't many turns; places where aerodynamic efficiency trumps traction. 2. Power and/or weight limited cars like your FSAE example. If they were allowed unlimited power or set a minimum weight it's a pretty safe bet that they would run bigger tires. But they're maximizing to a particular rule set and they have optimized designs for weight and limited power, both of which dictate against large wheels. 3. Using bigger wheels at one end to balance a car that is not able to be balanced within the ruleset or by adjusting suspension settings. I used to autox with a guy who ran 8's on the front of his EP Ford Fiesta and 6's in the rear and this was faster because it balanced the handling. Likewise you might see a 911 running bigger tires in the back. I know Coffey has mentioned 350Z cars in stock classes running their slightly wider rears in the front. 4. As you mentioned, ice racing. Skinny tires with studs means more pressure per stud, so they're really trying to get the best balance of weight per stud to maximize traction. 5. Some classes of mud racing where you want a tall tractor tire that gets to the ground under the mud rather than trying to drive over it. I'm sure there are more, but for the vast majority of racing classes, more tire is better.

     

    If you're going to play monkey-see monkey-do with tire sizing though, I think the best place to start is the car that is most directly related to your own. For most of us that means looking at someone like John Thomas who runs a 16x10 which is the largest allowable tire and wheel combo in FP. He could choose a 16x7 or a 16x8, but he doesn't. Or Greg Ira, who runs a cantilevered slick on his EP car. If skinnier was better, one assumes he would run a regular sidewall. Those are the two most successful Z racers at present, but it's important to keep in mind that they are very limited in power compared to a lot of the cars on this site. Even at the power levels they run, they have opted for the max wheel and tire size.

     

    For those of us who are road racing and autoxing in a world of far from perfect suspension designs and not so limited horsepower, I think the best way to play is to get the widest tire you can fit to the car. We're shooting for the Glenn Bunch model, not the FSAE model. If you haven't seen it, Glenn has a 2500 lb Challenger running 15x14's on front and 15x17's on the back.

     

    http://www.youtube.c...ennbunch/videos

     

    How does one calculate how much tire is needed for a given amount of power (from a dig) then? If you have a 80hp fwd crx and you have 305s (modded to fit of course ;) )on it i am betting this isn't going to help. So how much is needed based on power?

    Tire vs power and weight?

    in Brakes, Wheels, Suspension and Chassis

    Posted

    Your contact patch will remain the same if you run a 175mm wide tire or a 235mm wide tire IF, and this is a big if, you use the same make and model tire and same tire pressure in this comparison.

     

    Now if you would run a wider tire with lower tire pressure, your contact patch would increase also increasing your static traction.

     

    Now before all of you either start arguing with me or go out and buy super wide rubbers and stuff them under your cars, hear me out further.

     

    Narrow tires will not roll as well as wider tires. Wider tires will distribute your vehicles weight across the wider contact patch, deforming the tire less. The more tire deformation will result in more rolling resistance of the tire. But, wider tires are less aerodynamically efficient at high speeds and add extra drag to the overall vehicle.

     

    Taller tires have more affect on tire traction than wider tires in pure lateral movement (i.e. drag racing). But as a result of running taller tires, you increase the torque on your entire suspension and drive train systems, causing potential for component failure.

     

    In the case of tires, although traction increases with load, it increases less than linearly, and coefficient of friction decreases with load. A larger contact area reduces the load per unit area, resulting in more grip. There is a point of diminishing returns, such as weight and aerodynamic drag. It's also true that a larger tire dissipates heat and with a lighter load involved, it wears less. Another reason for a larger contact area is to compensate for debris or track imperfections interfering with the tire and pavement contact.

     

    Note that load sensitivity is commonly used to adjust the understeer or oversteer of car. When a car turns, the down-force on the outside tires is increased and the down-force on the inside tires is decreased. The body of a car also rolls a bit, and the suspension can be used to unequally distribute the load between the front and rear tires. If the front end is relatively stiffer, then more of the down-force is exerted on the outside front tire, and the relative grip is reduced because of tire load sensitive. A stiffer front end causes the front end to lose some grip in turns, resulting in understeer. A relatively stiffer rear ends results in oversteer. Street cars are generally setup with understeer, while race cars are setup with a small amount of oversteer.

     

    For a variety of reasons, such as deformations, molecular bonding type reactions as well as surface roughness, real world friction isn't the simple thing described in physics books.

    Now to sum up everything rather than starting an endless rant…

    Going wider will not always give better traction.

     

    If you want an all sweeping statement that is roughly true. Wider contact patch sacrifices linear traction for lateral, narrow tires sacrifices lateral for longitudinal traction. And the most important thing about tires is not contact patch area but that they are at correct working temperature.

    Wider tires are not always better. They don't always give better traction. It depends on the car, the situation, the conditions.

     

    Eg. Rally cars use wider tires when on tarmac rallys, and use (surprisingly) very thin tires on ice rallys.

    F1 cars used to use narrow tires until aero began to be used in the 60's.

    Drag racers actually want tall tires, width is there to stop the tire being destroyed.

    An example I can think of is formula student cars, they used to use 8 inch tires but couldn't get them up to temperature. They switched to 6.5 inch and got more grip because they can get them up to temp.

    So before you go out and buy some super wide meats and cut the crap out of your fenders to stuff them in there…. Sit back and consider some factors.

     

    What temperatures are you going to be driving in? Are you only accelerating in straight lines like drag racing or are you autocross racing and need more lateral stability? How long do you want your tires to last? Obviously sticky tires don’t last as long as hard compound tires, but have a much higher coefficient of friction. And running tires with lower tire pressure can put too much heat into the tire.

     

    Lastly, if you are using your car as a DD, running 235mm wide tires when the stock size is 195mm, probably isn't helping you at all. Instead of modifying your car to fit these tires and paying higher prices for these wide tires, really isn't worth anything to you unless you plan on whipping it through your local neighbor hoods like a rally driver on a daily basis (which I will never encourage or think is “cool†to drive like an idiot on public roads)the point is though the mentality that wider always = better is wrong. There is an optimum limit even on drag racers.

     

    Basically though, there are just so many factors to consider when choosing a tire that one post cannot cover all of them. Gearing, suspension setup, driver preference, car classing rules, car style/power-train layout, car weight, wheelbase, wheel width/diameter, compound, heat generated, tire aspect size, power of car, overall width of setup, ...the list goes on.

     

    The theory all summed up sometimes a narrower tire will be faster than a wider tire for a variety of reasons.

    does anyone know gregg allred shop is "oldschool horsepower"

    in Non Tech Board

    Posted · Edited by vega

    There is a guy in anoka mn that claims he had a shop in the oc in cali his name is gregg allred. The shop in mn is called "oldschool horsepower". Has anyone heard of this guy? Dealt with him, or know anyone who has done work with him? he had a video he showed with a z doing a high 9 he claimed it was a l28 with 50mm webbers (claiming to be an old car of his he did up). I am trying to find if he is a reputable person. I have a 327 i need some work done to.

     

    Everyone I know around town has never used him nor do they know anyone who has. He has beeen in mn for "3 years" according to him.

     

    Please help!

    Any last thoughts before the build ?

    in Gen I & II Chevy V8 Tech Board

    Posted

    Crane cam 110931 (duration 228/238)

    http://www.cranecams.com/72-77.pdf

     

    Or

     

    Comp cam 12-677-4 (duration 236/242)

    http://www.compcams.com/Company/CC/cam-specs/Details.aspx?csid=226&sb=0

     

    With a lower duration and a bit more tq producing at lower rpms these are the two I am stuck between, with lunati, comp, crane, and isky in mind. I just went through all of their catalogs again and compared them all.- again (fml) I can advance the the cam on either of these to bring the rpm down a bit too if needed.

     

    Thoughts?

    Any last thoughts before the build ?

    in Gen I & II Chevy V8 Tech Board

    Posted · Edited by vega

    For my road race car (78' 280z) the engine that is being put together goes as follows.

     

    small journal 327 bored 40 over KEEPING the 3.25 crankshaft making it a 333ci motor. I am also having the mains splayed. Full arp studs for heads and mains.

     

    5.7 rods (i already have them)

     

    800 holly double pumper carb

     

    The heads (i was told the springs would be perfect for the cam?)

    http://www.jegs.com/i/JEGS-Performance-Products/555/514032/10002/-1?parentProductId=1593012#moreDetails

     

    The intake (i will be having it gasket matched to the heads which should up the operating range also)

    http://www.jegs.com/i/Weiand/925/7547-1/10002/-1

     

    The rockers (i have yet to determine if i should go the extra mile and get a girdle as well)

    http://www.jegs.com/i/Harland+Sharp/851/1001/10002/-1

     

    The Forged pistons (should be around 10.4-10.5:1 compression)

    http://www.jegs.com/i/Sealed+Power/844/L2166NF40/10002/-1

     

    The cam (i think i am going to degree the cam to 110 instead of 108)

    http://www.compcams.com/Company/CC/cam-specs/Details.aspx?csid=232&sb=0

     

    head gasket(.41 i didn't want too big because of the quench squish affect)

    http://www.jegs.com/i/Fel-Pro/375/1142/10002/-1?parentProductId=758649

     

    Headers(180 degree header part#180-1)

    http://www.schoenfeldheaders.com/180_crossover.htm

     

    I am also considering this unit

    http://www.jandssafeguard.com/MarineRacing.html

     

    Just wanted a quick update to those of you that know me for 1 and 2 to see if there are any rebuttals to what is going together here.

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