The Stovebolt Site Forums The Parking Lot '60-'66 Trucks 20" wheels

Good evening bolters!

I am wanting to put a set of 20's on my truck, and really like the looks of the Boss 338 style wheels so I went to my local tire shop today to talk it over and get some pricing ideas and the sales person I always work with told me that with putting modern wheels like this on an old truck, you run into a spacing issue with what some call "backspace" or "offset"

I am assuming a person could use spacers to get the wheel out some. In the past I would not use spacers because I didn't think that was safe but I understand they have been improved.

Anyway, just wondering if anyone here on the forum has put wheels like the Boss 338 on their 60-66 truck and what they had to do to accommodate the wheels.

My truck is still 6 lug.

Thanks in advance for any replies!

Kevin

I get the impression from your post that perhaps you're not familiar with the terms "backspace" and "offset". Those are 2 different dimensions on a wheel, with offset being dependent on both the backspacing and wheel width.
Backspacing is the dimension from the wheel mounting surface (WMS) to the inside edge of the wheel flange on the backside of the wheel. This is a critical dimension, as it determines clearances in relation to the suspension, steering, and brake components. Offset is the dimension from the wheel centerline to the WMS, usually measured in millimeters. The backspace and wheel width both have an effect on this dimension. A wheel that has the same amount of backspace and front space would have a 0 offset. If the wheel has more backspace than front space, then it is Positive offset, and if the front space is great than backspace, that is Negative offset.
Most wheels for the vintage trucks we deal with use either Negative or 0 offset, and average 3 to 3 1/2" backspace. Modern trucks, mainly due to the suspension designs, tend to use Positive offset wheels. This is mainly in an effort to package IFS 4x4 systems while not increasing track width, but also to get better handling getting the centerline of the balljoint as close to the centerline of the wheel.
That said, ideally, you should really try to see if the wheel comes in the correct backspaceing for your truck, which as mentioned, should be around 3 1/2". The offset will vary depending on what width you're considering. If you must use a spacer, use the type that bolts to your hub and has it's own separate set of wheel studs that the wheel actually mounts to. Those are much safer that using an excessively thick spacer.
A few words of caution, using a 20" wheel is going to increase not only the rolling mass of the wheel, but also unsprung weight. Both can lead to handling and ride issues if not addressed. You'll want make sure the suspension system is in 100% working order, and preferably with upgraded shock to make up for the unsprung weight. Even more critical is going to be the brake system. The stock drums will not be adequate. At minimum, power assist should be added, and realistically, you should consider a power assisted disk brake upgrade with at least a 12" or better rotor. Another word of caution with wheel widths and backspace/offset; If you get too or too little offset, that will change the scrub radius angle. This is a critical handling angle, and while there is some leeway, going to far out can cause handling issues.

Thanks Bill,

You are certainly well versed in this subject and I appreciate that. While I didn't explain it properly and I will admit this is my first time to inquire about putting 20 inch wheels on my 65, I did get a pretty good understanding from my long time tire shop rep yesterday and understand there are clearance issues to be considered.

I do know that I have seen many trucks with these style of wheels on them, I am just wanting to know what it entails to put a set on so Thank You, for passing along the very much appreciated info.

Kevin

You're most certainly welcome. I did get the impression that your tire rep is giving you good information, I've been in the business, until about a year ago, for 23 years myself.

Well,

I have a lot of respect for folks like you! Today I told my shop manager what you said and he said "that guy knows his stuff" !

I have always been old school and never really cared for modern looks but just thought it would really make my short wide look good but I may end up leaving it alone.

Kevin

Just as a point of reference.... Changing the wheel diameter will in no way affect braking.... changing the tire diameter changes braking.

A little clarification on what I posted; I was more meaning about the additional rotational mass of the 20" wheels, rather than a change in diameter. Those 20" wheels, especially the cast aluminum ones, are much heavier than the standard steel or even a stock size aluminum counterpart. The additional weight will effect braking.

The wheel will weigh more, the tire will weigh less.

IMO Bill's braking theory is correct, but in reality it has been my experience that it is not an issue.

While I agree that there will be a weight difference I've updated numerous vehicles in my life and have yet to ever have any braking issue when updating tires and wheels.

This is especially true on a pickup truck that has over sized brakes, sized for carrying payloads.

Case in point, my '65 C10 had stock brakes, yet the rolling stock was altered. No adverse handling or braking issues. http://i645.photobucket.com/albums/...Trim%2001-24-2015/RR3-42_zps5434b9dd.jpg

FWIW: In regard to putting 20" wheels, specifically 5 spoke Boss 338's, on a stock braked, 60-66 truck: They look horrible. A 15" 5 spoke wheel looks good, but the 20's are to big, they make the stock brake drums look tiny.

The tire will not weigh less. If anything, it will weigh about the same, possibly a little more depending on size. I've mounted enough of them to know.

So the tire no longer follows the laws of physics?

For the sake of discussion.... You're saying a 35" o.d. tire for a 15" wheel weighs the same as a 35" o.d tire for a 20" wheel?

Logic dictates otherwise.

Using the tire sizes you've specified, and checking the specifications on them, the 20" rim diameter tire weighs an average of 6.5 pounds more than the comparable 15" tire of the same outside diameter. You do have to keep in mind that as the tire sidewall is shortened, the load capacity id diminished. In order to keep that load capacity the same, the tire has to be built with thicker sidewalls in order to keep the capacity the same as a smaller wheel size tire of the same outside diameter.

I stand corrected... Bill is right: the 20" version is indeed 2 lbs heavier than the 15". I also noticed the 20" tire is also twice the price!

So the wheel is heavier... and the tire is heavier... and the tire costs twice the price... explain to me again why folks are running these big wheels?

It's all about the look. Big wheels are the "in" thing. I've seen the opposite end of the spectrum, too. Back in the late '80s and early '90s when trying to fit 13" wheels on Impalas was the big thing.

You will lose your inner fenders ..
Dan

What makes you say that? A 20" wheel with properly sized tires will make no difference to the inner fenderwells. You might be surprised at just how big of tire will fit in there. Only time it would be an issue is if the suspension is slammed all the way down to ground, which would make the truck barely drivable anyway.