I am changing to 15" wheels to accommodate a Wildwood front disc brake conversion. I bought one Allied smoothie wheel, size 15x6 with 3.75 backspacing.
No problem on fronts but rear, of course, has little clearance on the outside wheel well lip. The old tires on the old stock 14" rims were Coker 205/75R15 and there is about 1 inch of clearance with these. Figuring that I need to stay close in size, I am considering a 215/65r15 or a 205/70r15. Wheel diameters are very close as well as width.
The original 14' wheels were 5.5" and these new ones are 6". Am I going to have any clearance issues with this set up? and which tire size would work best?
Many thanks!
Scott
Redding, Ca.
Welcome to the forum.
The problem is the 3.75 backspace, it won't let you run a very wide tire. Most of us are able to fit 7" wide rims on the back, but with a 4.25 backspace. I'm actually running a 235/70-15 tire on the back. Neither my fender lip or wheelwell are modified. I do have my rear narrowed 3/4 inch per side, but the mentioned tires did fit on before it was narrowed. Since you've only purchased one wheel (which is a good size for the front), if it were me,I'd check to see if they are available in wider wheel with a deeper backspace. Not sure what you meant by "figuring I need to stay close in size", but most of us run narrower wheels and tires on the front and as big as posible on the back. Just looks better.
btw, I am running 215/70-15's on the front with a 6" wheel/3.50 backspace.
Lots of recent posts on this topic.
Rich,
Appreciate the help! I guess I am not all that concerned about running larger tires on the rear. I just want them to clear and have enough of a load rating to work properly. I just found a 215/65r15 that measures up very well with the Coker. Its only about a quarter of an inch wider than the Coker. I might just order one to see if it works in the rear. If not, I could use it on the front. Ideas?
Thanks again,
Scott
Just my suggestion about checking to see if you can get a deeper backspace wheel for the back. You really need at least a 1/2" or so clearance on the back at the fender lip to prevent rubbing when the car is leaning into a curve.
Sorry to keep bugging you! I can get a 15x7 wheel for the rear and they have a 4.25 inch backspace. But won't I be adding to the problem by using a 7 inch instead of a 6 inch rim, or not? If it won't matter, I'll use a 7 inch rim on the rear with the deeper backspace.
Thanks!
15 x 7 with 4.25" backspace wheels should work fine with tires up to 235/70 section width. I am running that wheel with 225/60 tires on my stock rear (and front) setup.
What lynn said. In rereading your first post, I think maybe you need to take a second look at how much space you have in the back with the 6" wheel. You said it was close, but it really shouldn't be, even with the shallower backspace. I guess that's subjective depending on what "close" is. You are correct in that a 7" wheel with a 4.25 backspace will actually be 1/2" closer to the fender than a 6" wheel with a 3.75 backspace.
One of the "fun facts" to know... the rim width does not move the tire out the same amount. For any given section width there is a "measuring rim width" that will give you that dimension. A wheel wider than that will increase the measured tire width but not by the same amount. Even though your rim is 1/2" closer to the fender, the tire will not move that 1/2" where the interference actually is. This is because a 6" wheel with 3.75" B.S. and a 7" wheel with 4.25" B.S. have the same offset and that keeps the centerline of the tire in the same place for both wheels.
Thanks to you all who have replied-it has helped a great deal.
I have decided to order one tire to go onto the 15x6 smoothie with 3.75 backspace for testing purposes. Its a 215/65R15 Cooper Cobra Gt . According to the data, the diameter of the Coker tire I am taking off (205/75R14), even with the 15 inch rim, the tire diameters are almost identical and the width of the Cooper is only .24 inch wider than the Coker. With the current Coker tire on the car, there is 1 inch of clearance on the lip of the fender.
My plan is to mount the tire on the smoothie and test fit it into the rear rear well. If it is a go, I am good. If not, I'll use it on the front and come up with another plan for the rear.
Ideally, a 15x6 smoothie with a 4.25 inch backspace would cure all problems but I was unable to find one anywhere. If I need to, I can try a 15x7 with the deeper backspace.
Again, many thanks to all who have responded thus far and I will update this with results.
You may have to jack the car on the frame and unbolt the shock so the rear end drops enough to squeeze the tire in.
I'm running 235/70/15 on a 6 inch steel rim and that's what I have to do.
When you're ready for new shocks, switch to 56(55?) Ford Monroe shocks and you won't have to unbolt them any more. I'd have to look up the number, but there's threads from a few months back on them.
Ok, here is my report on rear wheel clearance on my Fairlane. I ordered one Allied 15x6 smoothie wheel with 3.75 backspace and mounted a 215/65R15 Cooper Cobra tire on it. I mounted it on the car and as the advice stated, I had to loosen the shock to get the tire on. After it was mounted and the car lowered to the ground, I have 1/2 inch clearance on that fender lip that comes closest to the tire.
The magic question is: Will that be enough clearance in everybody's mind to make this set up work?
Many thanks for all of your help in this. I want to make a good decision and order the rest of the wheels and tires if this is a go.
Thanks!!
Scott
I would think you're ok, but just barely. Actually alot depends on your suspension. If it's old and worn out, your more likely to have some rubbing in curves, but as I said, I think you'll be ok.
New springs and new shocks will help alot, and you may be planning on that anyway. JMHO
BTW, that's about how much clearance I had before I narrowed the rear end, had old 4 leaf springs and NO shocks, and I did not have an issue with rubbing, albeit I was not driving it hard because I also had NO rear brakes, lol.
Rich,
Thanks for the help and advice-I think I will go ahead with the changeover. I am not a hard driver and baby the thing most of the time. I appreciate the suspension issues. My springs are original but will put in new shocks. Can you look up the Monroe number I should be looking for? Would appreciate it. I could go with a smaller tire yet but then I get out of the white raised letter sizes that I want.
Ideally, a 15 x 6 smoothie wheel with a 4 inch or 4 1/4 inch backspace would be ideal but I have not been able to find one.
Thanks again, you have been a big help.
Scott
You clearance is CLOSE but OK to me. You can buy steel wheel with any backspace... Wheel Vintiques, Wheelsmith.. more expensive, an extra $50 to $75 per.
Lyn,
Wow I love this board. Thanks for the suggestion. Got hold of Wheelsmith in Corona Ca. They are making me two each 15 x 6 smoothies with 4 1/4 inch backspace. Price was reasonable and they should ship by the end of the week. Those should give me just the little extra I need. Plus Rich M. has suggested new shocks which should help as well.
This will allow me to use the Cooper Cobra tires which I like and all should be well. My grandson is named Cooper so I had to get those!
Thanks again, Lyn.
Scott
We are all glad to help out!!!! :003:
Rear shocks (55 Ford) Monroe 31125, Just for added info, I used KYB KG4515 on the front. I'm real happy with both choices.Best pricing I found was at Rockauto.com
The added backspace your getting and the Monroe shocks will let you get that tire changed without having to unbolt the shocks. You are jacking the car up by the frame, not the rear end, correct?
Shocks are on my to do list to. I'm looking at Rancho rs 9000's adjustable, so there a little tune able for drag strip use. Need to find the right compressed and extended length with the right ends.
I have shock extensions on now which help with tire removal.
Thanks, Rich-ordered those Monroematics for the 56 from RockAuto today!
Scott
Well, a result note on the conversion of my front disc brake and wheel situation. The wheels were just right-put a 4 1/4 backset in the rear and it was perfect. But now another problem: the Wildwood kit went in smoothly with no hitches but the mechanic tells me there is a hard pedal-no boost going on at all. He is going to measure the vacuum level today to make sure the engine is putting out enough vacuum. I added a vacuum canister last year into the system and the booster itself was rebuilt two years ago.
Question for you is: How much vacuum should I need to run the booster with a disc/drum setup? The posts on the other forums indicate about 18-20. Is that accurate?
Second: If I need to add a vacuum pump into the system, what kind should I use with my 57 Fairlane? Mechanic says he has checked pedal play and that it is set up properly.
Any help greatly appreciated!!!
What are you using for a booster? Master cylinder? Engine? Factory engines typically run around 18 psi vacuum at idle, if you have a high performance camshaft, 10 is probably closer to an average. Vacuum reservoirs can help but the amount of assist depends on a lot of things. Drum brakes are self actuating in that with contact the friction will pull the leading shoe into the drum. The result is that less pedal pressure is required for braking compared to disc.
Thanks for the reply!
I have a stock 312 engine. I added an ABS booster and dual master cylinder unit about 2 years ago when the car was drum/drum brakes.
It worked sporadically with that set up. The Wildwood kit has just been added to add front disc brakes but, only a hard pedal indicating that either the booster is bad or there is not enough vacuum or I don't know what else. I took it to my brake mechanic last year when I was having problems and they had the booster rebuilt at that time indicating there was something wrong with it. He is checking vacuum pressure as we speak. thanks!
One of our local guys with a 57 Fairlane had his changed from vacuum to an electric master. I haven't seen him to see how that worked out. I did look at them but they are out of my budget at around $1200..
Just a wrap up note on this thread that I started regarding wheel and tire clearance on the rear of my Fairlane. The Wheelsmith wheels with a deeper backspace was the ticket. The 215 tires fit just right with no problems at all and I love the look (photo attached)! The brake conversion is wonderful. Even tho my vacuum is only 15 it works well. I have a canister installed which might help but my brake guy suggested I get a larger booster-I have a 7 inch on in now. The wheels all lock up in a power stop which was my main concern and the hard pedal was just the new pads working themselves in. Thanks for all who helped! Now off to the road!
Tire change in the rear ok with the new Monroe's??
Thanks for the update.
Rich-yes the new Monroes are just right. Makes it much easier to get that tire out of that well. as they are just a bit longer than the stock ones. For the first time in many years I can now drive without having that fear that every time I push the brake pedal that there would be nothing there! I have located a great "hot rod" brake guy that is giving good advice and knows his stuff . Plus I have you guys! Thanks so much for the encouragement and good ideas-it means a lot!
Scott
Same here, the help I've gotten here has been remarkable...including the tip on those shocks from Jim Nolan who did all the research and testing.