Clearance Concerns With New Wheels and Tires

[wideboots]

Truck: 1978 Chevy 1/2 ton step side.  Has been lowered via dropped spindles 2 1/2" (front only).

I currently have 10" wide 15" diameter Eagle mags that have a 3 1/2 " back space all the way around.  The wheels on the front are too wide with the 265/60 series Rementon tires which are 28" tall.  The tires will hit the fenders when taking a dip to fast.  They actually are right at the fender line which was OK before I lowered the front end.  Sooooooo, I want to go with an 8" wide wheel on the front and 10" wide on the rear using 17" Diameter Boyd Coddington five spoke "Smothie II" wheels.  I am going to order as soon as I can resolve these clearance questions.  

I want to use P255/60R17 Goodyear Eagle RSA"s all the way around (these tires are 29" in diameter as opposed to the current 28" tires on the truck now).  With this combination, I propose to use a 5 1/2" back space on the front wheels and a 4" on the rear wheels.  There will be no clearance problem at the rear.  However, I am concerned with possible interference with disk brake calipers, etc. on the front end with the 5 1/2" back space.  The front end suspension is completely stock with the exception of the 2 1/2" dropped spindles.  Do you think the 17" diameter wheels will clear the breaks, etc. with the 5 1/2" back spacing?  I have measured everything I can think of, and I think this will work.  Is there anything I am missing?  I want to use the biggest tire I can to fill up the fender wells.  I don't want to use different size tires on the front (smaller), because the truck has the perfect rake now with the dropped spindles.  Thanks for any advice.  

[wideboots]

Oh come on guys, I need some help here.  I really don't want to order these new wheels & tires until I hear from the real experts on "our" trucks.

Oh yeah, thanks for the T-shirt Chris.  I can hardly wait for a car/truck show so I can wear the really cool shirt proudly.  Thanks again.  

[roundedline]

I ran Impala SS wheels on mine for a while before I tore it down.  They are 17x8.5" rims with 5" of backspacing.  I ran 255/50/17's on it (I think, still have them on the other truck) an below is what it looked like on front/back.  The rears needed to be moved out about 1" or so to look right for me...








Does this help?  I am not quite sure exactly what you are trying to say here:

Quote:I want to use P255/60R17 Goodyear Eagle RSA"s all the way around

Because 10" wide rims are too wide for that size tire.  I planned to run 275/50/17's on mine since they were the same relative width and height as the 275/60/15's I had...

BTW, here is a good source on how to fit tires/wheels: http://www.carcraft.com/techarticles/3636/

No problem on the shirt.  Glad you got it!

Chris Lucas
www.73-87chevytrucks.com
www.captkaoscustoms.com
Project Su
Jimmy 2WD Project

Edited by: roundedline at: 3/23/06 1:16 pm

[wideboots]

Thanks Chris.  Your information is just what I needed to see and read.  The pictures really help me get an idea of what to look for.   I agree the tires should be another inch or so wider but I don't want to take any chances of tire rub when turning the front tires.  Maybe I can use a 50 series tire on the rear to fully utilize the 10" wheels there.  I was under the impression Goodyear said (I will have to check my source) those tires (255/60R17) can handle 9.5" wide wheels so I thought an extra 1/2" would not matter, maybe not!  If I can find a 50 series that has at least a 29" diameter it should work.  I'll check out the web to see if I can find that combination.  A 50's series tire would be wider too.   Hopefully, Goodyear will make a tire that will work.  If not, I will look around some more.  Thanks again for the help.  I was more worried about disk brake caliper clearance on the 17" wheels with a 5" back space than anything else.    

[roundedline]

50 series is the aspect ratio.  It has everything to do with height and nothing to do with width.

275 = width in milimeter.  divide by 25.4 to get inches
275mm = 10.8" width (not tread width)

50 = aspect ratio.  Percetange of above width that the sidewall is tall (ie how tall from the top of the tire to the top of the rim.

17 = rim diameter

If you compare 275\60\15's to 275\50\17's you get the following...

275 / 25.4 = 10.82677... x 60% = 6.496 x 2 (there are 2 side of the tire, top and bottom) = 12.9921 + 15 = 27.99" tall tires

275 / 25.4 = 10.82677... x 50% = 5.4133 x 2 (there are 2 side of the tire, top and bottom) = 10.82677... + 17 = 27.826" tall tires

If you want either of the 2 tires sizes taller, change the aspect ratio to a larger number.  example:

275 / 25.4 = 10.82677... x 60% = 6.496 x 2 (there are 2 side of the tire, top and bottom) = 12.9921.. + 17 = 29.99" tall tires

Keep in mind these number are only close and can vary some...

I wasnt' saying that my tires should be 1" wider, I was saying the backspacing in the rear should be 4" instead of 5".  You should be able to use a 275mm tire on the truck with no problem.  

Chris Lucas
www.73-87chevytrucks.com
www.captkaoscustoms.com
Project Su
Jimmy 2WD Project

Edited by: roundedline at: 3/23/06 3:36 pm

[cheyenne77]

I think that's pretty sound advice. I went to low of a profile tire and tore up the sidewalls. Then again up here our streets are full of pot holes. I do like the stance of the wideer tire though. Check out what I did at: 1977 Chevy Cheyenne The tires in the first picture are P265/50R15 and they are on 15" rims with a back space of 4.25". The other dimensions are tire width of 11" and 25" in diameter. The diameter of tire is regretful though because when my spedometer reads 80mph I'm really going 60mph. So I have to get the speedometer recalibrated at a transmission shop. But I exploring the option of different tires myself before that expense. For what it's worth, I hope that helps.

[wideboots]

Thanks for the input.  Every little bit helps me make a decision.  I want the biggest tire I can get to fill up the fender wells.  Fortunately, the speedometer thing will not be a problem.  I bought a Dakota Digital gauge set up from Chris that is easily calibrated to any tire I decide to put on the truck.  

The formula Chris just posted (thanks Chris) above works great.  He says a 275mm tire will work so that is what I am boing to go with.  Should look great.  I will post a picture somewhere on this site when it is finished.  However, that will be a while since I have lots of stuff to put on the truck when I get it back from the paint shop.  

[roundedline]

cheyenne77, look here to solve the speedo problem.  All the shop is going to do is swap out you gears...

www.73-87.com/7387garage/...speedo.htm
www.73-87.com/7387garage/...dgears.htm

Chris Lucas
www.73-87chevytrucks.com
www.captkaoscustoms.com
Project Su
Jimmy 2WD Project

[82BlazerMan]

In the pics above of your truck with impala ss wheels, are they already moved out by 1".  I'm considering buying a set and I'm wondering about spacers of more than 1".  

[roundedline]

The pics above are of my truck before I tore it down in 2000.  there are no spacers on the wheels.  That is just the wheel bolted up.

Chris Lucas
www.73-87chevytrucks.com
www.captkaoscustoms.com
Project Su
Jimmy 2WD Project