Rear tire sizing with disc brake conversion - Chevelle Tech
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post #1 of 5 (permalink) Old Jun 24th, 19, 9:53 PM Thread Starter
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Tom
 
Join Date: Sep 2018
Location: Southern Maryland, U.S.A
Posts: 36
Rear tire sizing with disc brake conversion

I'm getting ready to purchase all new wheels and tires for my '66 Chevelle after having added The Right Stuff big brake kit rear disc conversion. They said it brings the wheels out an extra 1/8" from stock.

I'm trying to size my tires and have read all I can on this forum about it. I want to go with an 18" rim. It looks like a lot of you run 275/40R18 on the rear. But I'm worried about the fit and if that will fit within my wheel well opening?

I am going to go with American Racing VN507 Rodder chrome wheels, 18x9.5 with 0mm offset, 5.25 backspace.

My current wheels are an 8" Cragar with what I measured to be a 4.25" backspace, with 245/60R15 tires. I had zero more clearance to the outside and about 2.5" of clearance to the inside.

Wheel offset calculators say that a 275/40R18 will push the wheel outward by about .33". That's not going to work, unless I roll the lip. And if the disc brakes push it out another 1/8", well...

So I am considering going down to a 255/45R18. This still has the height, but loses some of the width but doesn't push out further than I already have.

I'd like to hear if there is anyone running close to this wheel/tire combination, especially if using the TRS big brake kit. How does yours fit? Will I be OK with the 275's?

Thanks,

Tom

1966 Chevelle SS, 355 V-8, TH-350.
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post #2 of 5 (permalink) Old Jun 25th, 19, 7:08 PM
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Greg.
 
Join Date: Apr 2011
Location: Ottawa, On, Canada
Posts: 4,579
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Re: Rear tire sizing with disc brake conversion

Time to get out your Measuring Tape and a Pad of Paper/plus Pencil

Every car is different from Dr side to Passsenger side and taking measurements of your car's Fenderwells etc is the key to what Wheel / Tire Combo size will fit without rubbing or hitting anything ;
BACK SPACING & WHEEL WELL / Shock Mount Room https://www.rsracing.com/tech-wheel.html
First measure with the current sized Wheels/Tires =
1.Wheel’s Rim room inside curved lip of Wheel Rim to bottom part of Shock Nut =
This is because as you increase the BackSpace on a Wheel and or increase the Width of the Wheel it may interfere with the Lower Shock Mount/Bolt
2.SPACE from Front of Fender Well to front of current tire when mounted to rear end this is for to measure the MAX height/diameter a tire can be as it is Important that you allow Bias tires a growth margin .
Second with the Wheels/Tires removed from Both DR & Pass sides, one side at a time or all same time measure the following;
1. Rear End Width – Face of Brake Drum/Disc Driverside to Face of Drum/Disc Passengerside = “
2.OUT SPACE from inside Lip of outside Fender to Face of Rear Drum/Disc Brake Hub/Wheel Mounting Pad
DR Side = “
PASS Side = ”
3.IN SPACE from Face of Rear Drum Brake Hub/Wheel Mounting Pad to Frame/Inner Fender
DR Side = “
PASS Side = ”
4.Total Wheel Well Space = # 2 + # 3 measurements #s
DR Side = “
PASS Side = ”
if one side is less then use it as the applicable number or make sure the Rearend is centered properly
Important things to NOTE;
1. the Rear Lower Shock Mount Bolt may interfere with the Wheel’s Rim
2. and yes your car's exhaust may interfer with the Tire on a 10" Wide Wheel
3. Type of Brake system on rearend, Drum or Disc ! as the Disc setup is usually wider than a Drum setup
4. Is Rearend centred ?
5. Has the car been Lowered ?
6. Side Wall/Section Width of the Tire = ?
7. Diameter Height of Tire = ?
8. Size of Wheel you wish run ?

Measure twice and you will only need to buy once the Wheels/Tires
you need to fit within your car’s Fenderwells .

Supply the above info and then I can calculate for you !

67 Chevelle Malibu SS Cdn
Born 283 / PG / A51
468/TH400 2,500 stall/ S60 3.70 Gs
Prev Best on M/T ET S/S #3454 street Tires/Dress 2018/05/20
60' = 1.664
1/8 = 7.532 et / 91 mph
1/4 = 11.814 et / 115 mph
NEW Best with 3,500+ Stall TC 2019/06/23
60' = 1.561
1/8 = 7.411 et / 90.18 mph
1/4 = ??.??? et / ??? mph


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post #3 of 5 (permalink) Old Jun 25th, 19, 9:30 PM Thread Starter
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Tom
 
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Location: Southern Maryland, U.S.A
Posts: 36
Thanks for the instructions, I'll get going on it.
I am limited in the back space of the wheel...all of the single piece cast wheels seem to have the same backspace and 0 offset. So I'll have yo work with that. Can't afford a custom set of wheels!
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post #4 of 5 (permalink) Old Jun 26th, 19, 12:33 PM
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Greg.
 
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Re: Rear tire sizing with disc brake conversion

Quote:
Originally Posted by Gunn317 View Post
Thanks for the instructions, I'll get going on it.
I am limited in the back space of the wheel...all of the single piece cast wheels seem to have the same backspace and 0 offset. So I'll have yo work with that. Can't afford a custom set of wheels!
If you click on My Garage to the Left and Click on the First Album go to the Bottom of the Page
you will see the Wheels / Tires I have on my 67 = Pics # 21 / 22

Street Fronts
Wheels - JEGs Sport Stars#66062 Alum 15”x7” BS= 4” Billet Specialties ET Lug Nuts #999980
Tires - Cooper Star Fire SF 340 P205/70R/15”

Street Rears
Wheels were - Cragar 3915834 15” X 8” BS= 4.25” M/T sportsman S/R Radial
Tires# 6641 Gorilla LNuts # 71974
Tires - M/T sportsman S/R Radial Tires# 6641
28” Dia. / 10.4” Tread Width / 12.1” Sidewall Width

Strip Rears
Wheels - JEGs Sport Stars # 555-66086 15" x 10" BS= 5.5"
Tires - M/T ET Street S/S # 3454 295/55/15 =
27.7” Dia. / 10.6” Tread Width / 12.2” Sidewall Width / RO 87

67 Chevelle Malibu SS Cdn
Born 283 / PG / A51
468/TH400 2,500 stall/ S60 3.70 Gs
Prev Best on M/T ET S/S #3454 street Tires/Dress 2018/05/20
60' = 1.664
1/8 = 7.532 et / 91 mph
1/4 = 11.814 et / 115 mph
NEW Best with 3,500+ Stall TC 2019/06/23
60' = 1.561
1/8 = 7.411 et / 90.18 mph
1/4 = ??.??? et / ??? mph


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post #5 of 5 (permalink) Old Jun 30th, 19, 7:22 PM
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Clint
 
Join Date: Sep 1998
Location: Wichita Falls,Tx
Posts: 5,702
Re: Rear tire sizing with disc brake conversion

Quote:
Originally Posted by Gunn317 View Post
Thanks for the instructions, I'll get going on it.
I am limited in the back space of the wheel...all of the single piece cast wheels seem to have the same backspace and 0 offset. So I'll have yo work with that. Can't afford a custom set of wheels!
Not all one-piece cast wheels are limited to a 0 offset. My American Racing VN215's 20x10 rears had 5.75" backspace (+6 offset). Other one-piece AR wheels have different offsets.

My personal rule of thumb, on these cars, is to avoid negative offsets on wheels wider than 7". On a 66-67, I would be leery of an 18x9.5 with only 5.25"bs (0 offset) because there's very little margin for error. It might work fine but it may not. I would want at least 5.5"bs (+6 offset) or 5.75"bs (+12 offset). To be safe, use Kurt's method of measurement.

15" wheels are a different ballgame, altogether.
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