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View Full Version : Wheel Size/Offset for lowered 57 4door bel air


Shaggs2Dope
02-02-2008, 11:53 PM
Hows it going everyone? This is my first post here. There are a lot of nice rides on here and it seems like one of the best info resources for the tri fives. My Dad picked up a 57 Bel Air sedan last year and it spends most of the time in the garage. It is fully stock right now but for Christmas I got him started on the mods. I bought him a cross drilled slotted front brake upgrade and he has 14 inch Cragars that will not fit the new rotors. The only other mod on the car is dual flowmaster mufflers and rear air shocks. The brake kit included master cylinder and braided lines and stuff, but I need to buy him some rims now to clear the rotors.

I was thinking of doing a staggered setup of 17/18 or 18/20 to add to the 2 inch drop spindles in the front. What is the proper wheel size offset to fit that drop on stock springs to clear without rolling the fenders or tubbing the inner fenders. I work for Aston Martin/Jaguar/Land Rover so I have access to plenty of lifts and every other tool needed for proper installation of everything, and all tools needed for the brake conversion, but before I start the project I want to make sure I have the right wheel combo to make it perfect.

Also, what tire size is best used with the wheels for proper speedometer calibration to keep it close to stock. I am thinking the 18/20 would look really nice but be a little too much for his taste, as he likes factory, but you really cant complain about free wheels and brakes. He loves the brakes and the look of his cragars, so I was thinking something like the torque thrusts in 17/18.

Any input would be greatly appreciated. Thanks in Advance. And I am in NorCal Sonoma County so weather/road conditions aren't a factor in decision making. Its only driven in nice weather all year round

Tom$lick
02-03-2008, 10:05 AM
To give you an idea, I have CPP front disc conversion with 2in drop spindles and 1.5 in drop springs up front and 1in drop leafs and 2 in blocks on the rear. The rear leafs are in the stock location. I'm running 17in FOOSE Legends, 235/45 front on a 8 inch rim with 5.25 backspace, 255/45 rear on a 9 inch rim with a 5.25 backspace. I don't have any scrubbing issue with the tires. I just scrub the exhaust on the ground:D Edit for content: I am running a stock rearend and have not trimmed or rolled the fender lips. CCP claims the disc brake conversion pushes the front out about 3/8in per side if I remember right. IMHO a 9 inch rear wheel is about as big as you would want to go with a stock set up. I have just enough clearance to be comfortable, and I mean just enough.
http://i6.photobucket.com/albums/y205/NedRager/PB290057.jpg

finallyhavea57
02-03-2008, 11:32 AM
Shaggs2Dope,

Your dad has a sharp looking 4 door! Must be nice to have a son in the business to help him with the mods too! Not that I regret having two daughters mind you.

My 57 has stock brakes and actually has 18 inch rims with low profile Falcons. They don't seem to rub while driving, although I have only gone short distances to date. The front will rub if I jack up the center of the car and let the wheels hang down on their own though. I didn't buy the wheels and tires and probably would not have gone to 18's if I did.

Welcome,

Don

Chevynut
02-03-2008, 01:32 PM
ONE MORE TIME....wheel diameter doesn't affect offset or backspacing. It's the same whether it's a 14, 15, 17, 18, or 20" wheel. :eek: :D

If you're running a stock rearend, you'll want a wheel with zero offset. The axle is about 60.125" wide and the springs are 48" wide outside to outside. The rear fenderwell lips are about 72" wide. That gives you 12" between the spring and fenderwell on each side of the car, assuming everything is centered. The wheelwell centers are at (72+48)/2 or 60". So the axle mounting surface is centered in the wheelwell, which calls for zero offset to center the wheel. If it was me, I might go a little inboard, like another 1/4" with the wheel if you were trying to maximize tire size. That would give you 1/4" positive offset.

On the front try to stay at 67.5" or less overall width across the tires, if you drop the car a lot. You can get by with a little wider if the car is higher. You need to know if your spindles/discs moved the wheel mounting surface outboard before you can decide on wheel offset in front.

Shaggs2Dope
02-05-2008, 01:54 AM
I figured zero offset is pretty standard. I found 18x8 with 15 or 35 offset and 20x8.5 with 35offset. the bolt pattern isn't changing. I figure a slimmer wheel with low pros should fit. Trying to keep body mods to a minimum. My own car is down 3.5" with forged 17s and have to run 45mm, but this one doesn't get driven too much so we can do some big wheels. I know they eat brakes faster and everything, but I just want the old man to fall in love with the car all over.

http://www.performanceplustire.com/imagesProducts3/3526.jpg

This is the wheel I was checkin out for the car, as it is a smoothed out torque thrust lookin wheel. My old man loves chrome, even though I like the silver/flatblack/gunmetal sleepers. I think it should fit, hopefully without spacers too.

Only plannin on 2 inch spindle drop for now, may change springs and suspension down the road, as projects always grow. I just want to order up some rims so we can get the brakes on and make it safer in traffic.

Chevynut
02-05-2008, 11:27 AM
this one doesn't get driven too much so we can do some big wheels. I know they eat brakes faster and everything, [/IMG]



Huh? :confused: I've heard people say things like this before, and I think it's another one of those wives tales that got started by someone who doesn't like big wheels.:rolleyes: Why would brakes wear out faster with larger diameter wheels? They don't. :rolleyes:

ETriggs
02-05-2008, 11:35 AM
I think the myth got started because presumably there is more rolling mass involved with a heavier rim (more metal with larger diameter). But the vehicle weight has not changed, so it is a moot point.

Chevynut
02-05-2008, 12:08 PM
I think the myth got started because presumably there is more rolling mass involved with a heavier rim (more metal with larger diameter). But the vehicle weight has not changed, so it is a moot point.

Eldon, I'm not so sure the inertia is even higher. Rubber is pretty heavy, so it's possible that a large sidewall like on a Prostreet 30" tire might actually affect the inertia more than moving the rim outboard of the wheel center. In any case, like you said, the car's mass is MUCH more of a factor than wheel/tire inertia. And as the tire becomes larger in diameter, the brakes are less effective due to the increased leverage against the brakes. Wheel diameter has no effect on that.

Shaggs2Dope
02-07-2008, 01:12 AM
The bigger wheels do eat brakes more due to mass. Rotational inertia has more effect on suspension and brakes. Its not just overall diameter that does it, but actual wheel weight. reducing 1 lb of unsprung mass equates roughly to 10lb weight reduction on a sprung mass(vehicle chassis). Its the same idea for lightweight flywheels, vehicle wheels, lightweight pulleys. Rotational inertia has a big effect on tranny wear, brakes, everything. Larger wheels and also the overall tire diameter changes your final effective drive ratio as well. Which is why if you put big offroad tires on a truck without changing the gears you will blow the diff or the clutch/torque converter. I have two sets of the same size/offest wheels with the same brand tires. The show wheels weigh 25lbs a piece and the race wheels are 14lbs a piece. The 14lb rims shaved .4 off a 1/4 mile eta and reduced braking distances. And both were used with my cross drilled/slotted rotors w metal master pads, braided lines, etc with identical suspension settings. And the vehicles I deal with everyday have factory 19s and 20s and people often put on 24's 26's. There are many more issues with the larger wheels with brake life dropping 25-50% brake life and more tranny issues. Its physics. and a 30" prostreet tire is designed to be put on a smaller rim, so the rim can start spinning before the tire with a ripplewall so it will gain more traction at launch, so the advantage in holeshot outweighs any weight of the rubber itself. Wheel weight being located farther out from a fulcrum or lever point has much more resistance to torque, and bigger rims=more unsprung weight. a 30lb chrome wheel vs a 15lb forged wheel the 15lb wheel will get better mileage, acceleration, braking, and roadhandling. I thought this board had good information. You can't fake physics.

But like I said, this is just going to be a cruiser, and I am gonna match diameter with low pros as much as possible. But I guess not too many people sport the 18/20 staggered look on this board. Just wondering on the clearance people actually have used to clear these sized rims with otherwise factory suspension with 2 inch drop spindles.

Chevynut
02-07-2008, 03:16 AM
The bigger wheels do eat brakes more due to mass. Rotational inertia has more effect on suspension and brakes. Its not just overall diameter that does it, but actual wheel weight.

You just made my point....rotational inertia is caused by the location of the overall wheel/tire weight and not just wheel size. That's what I said in the beginning. You said larger wheels wear brakes out faster. 18, 20, or even 22" wheels don't make any difference if the tire radius is the same, and it can be. I'll wager that a fat tire like a 30"x18" prostreet tire on a 15" wheel has more rotational inertia than an 18-20" street setup, like a 275 tire 27" in diameter. I'd like to see some data on that. But I don't believe rotational inertia has that much affect on braking anyhow, compared to stopping the car's overall weight.

reducing 1 lb of unsprung mass equates roughly to 10lb weight reduction on a sprung mass(vehicle chassis).

What does that have to do with wearing brakes out? What does it have to do with anything? Are you saying that since I took ~100 pounds of unsprung mass off my car with a C4 suspension that I really took 1000 pounds off of it? :rolleyes: How does it "equate" to anything? :eek:

Rotational inertia has a big effect on tranny wear, brakes, everything.

It's a minor factor when compared to the inertia of the entire vehicle's weight transmitted through the drivetrain. I'll bet it's virtually negligible and barely noticeable in practice. Think about a 3500 pound car decelerating from 60 to 0. It takes a lot of doing to stop it, and a lot of heat is generated by the brakes. Now take that same car and put it on jackstands and get it to 60 mph....slam on the brakes and tell me what happens. The wheels stop a hell of a lot faster and with minimal heat dissipated. That shows that wheel rotational inertial is minimal compared to vehicle inertia when it comes to accelerating or decelerating a car.

Larger wheels and also the overall tire diameter changes your final effective drive ratio as well.

Larger diameter wheels don't do that....larger diameter TIRES do. We're talking about larger diameter wheels.

Which is why if you put big offroad tires on a truck without changing the gears you will blow the diff or the clutch/torque converter.

I guess I'd better not use my overdrive then, huh? Fact is, with larger diameter TIRES you'll wear the brakes out faster...because the TIRE radius is greater and therefore the leverage on the brakes is higher. The vehicle will be harder to stop. It has nothing to do with WHEEL diameter, just TIRE diameter. And you will lose acceleration due to the higher effective gearing.

I have two sets of the same size/offest wheels with the same brand tires. The show wheels weigh 25lbs a piece and the race wheels are 14lbs a piece. The 14lb rims shaved .4 off a 1/4 mile eta and reduced braking distances. And both were used with my cross drilled/slotted rotors w metal master pads, braided lines, etc with identical suspension settings.

Are the tires identical in size, tread pattern, and compound, or just the same brand? Was the only weight difference the 100 pound show wheels and the 54 pound race wheels, or was there a difference in fuel level or something else? Are you trying to say that ONLY a wheel weight change of 11 pounds apiece with no size difference gave you .4 seconds, all else identical? Sorry, I don't buy it. :rolleyes:

I'd have to see the test run the same day, with the same tires swapped on different wheels, and everything else identical to believe it. The physics doesn't support it.

And the vehicles I deal with everyday have factory 19s and 20s and people often put on 24's 26's. There are many more issues with the larger wheels with brake life dropping 25-50% brake life and more tranny issues.

I don't buy that either. You might have anecdotal observations and your own opinions, but show me the data. I have never seen any data to support such claims.

Its physics.

Yes, it is. And physics does't support your argument that larger diameter wheels cause any problems with brakes. In fact, larger diameter wheels allow you to run larger diameter brake rotors, which improves braking significantly and reduces wear.

a 30" prostreet tire is designed to be put on a smaller rim, so the rim can start spinning before the tire with a ripplewall so it will gain more traction at launch, so the advantage in holeshot outweighs any weight of the rubber itself.

The advantage of those racing wrinklewall tires is the low pressure, which makes the tire patch larger and helps keep the tire patch on the ground. The wheel doesn't "start spinning" before the tire...at least it had better not. :rolleyes:

Wheel weight being located farther out from a fulcrum or lever point has much more resistance to torque, and bigger rims=more unsprung weight. a 30lb chrome wheel vs a 15lb forged wheel the 15lb wheel will get better mileage, acceleration, braking, and roadhandling. I thought this board had good information. You can't fake physics..

Rotational inertia is not just dependent on wheel weight located further from the center of the wheel, it's overall weight located further from the center of the wheel. That can be the weight of a tire too. Bigger wheels can mean more unspung weight, but so can fat prostreet tires. SO can heavy 15" wheels. Bigger wheels can also be lighter than smaller diameter ones. Corvette wheels are magnesium...how do you think that factors into things? ;) I believe any mileage difference between 15 and 30 pound wheels is in the "noise" and has more to do with overall vehicle weight accelerating and decelerating than anything.

The problem is, you're mixing all kinds of factors in your arguments. You talk about bigger wheels, then bigger tires, then wheel weight, then wrinkled sidewalls, then mileage, then deceleration, then handling and unsprung weight. Stick to one argument at a time and make your point, and perhaps show some data or calculations to be believable.

You're absolutely correct...you can't fake physics....have you studied it? Some of us have, and we try to bring good physics and science to this board to debunk myths and wives tales. :rolleyes:

CJS57
02-07-2008, 07:28 PM
Chevynut, Well spoken! On the point of the heavy wheels: "ONLY a wheel weight change of 11 pounds apiece with no size difference gave you .4 seconds, all else identical? Sorry, I don't buy it." I would agree with .2 second increase in quarter mile time, but .4 seems excessive. I put some heavy wheels and tires on my 475hp vette, the heavy wheels and tires were say 6lbs heavier and they were .5" less in diameter. I swear I could feel the "heaviness" of them! But I have no data, only the butt-o-meter! Anyway nice post!

Tom$lick
02-07-2008, 07:51 PM
Technical but here it is... wiki-style. I read up on this due to an article I saw dealing with sportbike wheels.

http://en.wikipedia.org/wiki/Moment_of_inertia

Shaggs2Dope
02-08-2008, 01:52 AM
Thanks Tom$lick. Wikipedia owns all. I live 20 minutes from serars point raceway(infineon), and my old boss was VP of the track. I have had plenty of time to run different setups to see how they run, on cars, bikes, trucks, you name it. The tree and traps don't lie, and I have no need to make ******************** up to prove a point. My daily driver is a 4 banger accord, front drive, which made the .4 second difference. On my little brothers hatch, it saved more, knocking it down to a 13 second car all motor. You can call BS all you want but you are BS'in yourself. combine ChevyNut and Tom$licks posts and you have what I was trying to show in the first place, but without the 5 pages of typing.

I did have identical tires on different wheels, same weather conditions. i have 4 sets of wheels for my car, and have run them all. we have weekly drags here. I don't know ******************** about science, as my entire family is science teachers, and I had 3 degrees by 21, my dad was a mechanic before becoming a science teacher, I graduated high school early, started college when I was 15, and have worked on cars my whole life. You guys can be skeptics but if you really check out moment of inertia, rotation inertia and parasitic losses, specifically on unsprung weight, it will help you guys out.

And the responses like, big wheels help you because you can fit bigger brakes, has nothing to do with brake life. its a red herring to distract from what the statement is even about. if you increase the size of the wheel with the same size brakes, all else the same in a vaccuum, the bigger wheel will wear brakes faster. its a fact. It sucks when you try to hook your family up with hooking up upgrades and people want to debate validity rather than give constructive input on what size offset will actually fit the car they are supposed to know so much about, which was the question in the first place.

I really feel like even joining this site was a waste of time. I will ask a professional frame-up restoration chevy guy tommorrow, get a simple answer without the thread-jacking time wasting comments.