19.5's in place of 16.5's???

[The_Handier_Man1]

From: ZR91  (Original Message)
Sent: 3/12/2008 9:45 PM

I have a 1979 "C" class 24' Minnie Winnie with 16.5' wheels.

Last year, I installed 9.5x 16.5" tires that are about 3" taller than the stock tires.-they are now 29.5" tall.

Now, I have an opportunity to buy some 19.5" Alcoa aluminum wheels with 245/70 tires that measure 33"

Has anyone tried this?

I think they will fit without any issues in the rear, and will reduce the rpm's significantly, but can I install them in the front without having to cut out the fenders?

Jay



From: ClydesdaleKevin
Sent: 3/13/2008 6:25 AM

Hey Jay,

Since you have a C class, it will be a lot easier to fit your front wheels than if you had a class A, since you essentially have a van front-end.  We are putting much larger tires than stock on our Astro van, which is a little van compared to yours, but the principle is the same...lol.

You do not have to cut out the fenders.  But you are adding 3.5 inches to the height of your tires.  Measure the space above your wheel to the fender, and both the front and the back to the fender.  It isn't usually the top that will give you a problem with clearance issues, but rather it will be the front and rear of the fender opening...usually.  Now, take that 3.5 inches, and divide it in half...1.75 inches...this is how much wider your tires are from the center of the hub.  You will be 1.75 inches closer to the front and rear of the fender opening.

Here is where it gets fun.  You only need about 2.5 inches of clearance total, all the way around the wheel.  If you do, they should fit without any fender opening trimming.  For a light vehicle like our Astro, one would only need about 1.5 inches to keep the tires from rubbing on anything, even at full lock.

So here is the deal...after taking your measurements, add in your 3.5 inches to the top of the tire to the fender opening (realistically, it will be more like 1.75 inches, since the tire compresses when your rig is sitting on it, so installed its not really 33 inches tall...its shorter...plus, you don't have to worry about height from the hub to the ground, but just the height from the hub to the top of the tire...1.75 inches difference from what you have now.)  If you have 2.5 inches left over after adding in the 1.75 inch difference all the way around the opening, you are good to go!

If not, there are a couple of things you can do to achieve a little more lift in your front suspension without spending a fortune...first would be new shocks, with a heavy duty load rating...if that doesn't give you enough lift, you can install coil spring spacers or longer coils...available for Chevy and Dodge van front ends pretty cheap.  Don't space your coils or get longer springs more than 2 inches though, or else you end up with geometry problems in the front end that would require all sorts of expensive linkage and tie rod mods.

Good luck, and let us know if they fit!  They should actually give you better gas mileage by raising your gear ratio.  As you said, they will lower your RPMs at a given speed...just remember your speedometer will read lower than you are actually travelling, so you'll either have to have it recalibrated, or else drive it with someone following you who has an accurate speedometer, and using cell phones or walkie talkies, have them tell you what speed you are going, so you know approximately the difference....for instance, if you want to drive 55-60 on the highway to conserve fuel, your speedometer might be reading only 45...confirm it with your following buddy, and then you'll know where to put the needle on the highway.

Kev



From: brians69d24
Sent: 3/15/2008 4:42 PM

Here is a link to a site that can help with gearing and speedometer calculations:
http://www.dakota-truck.net/TIRECALC/tirecalc.html
brian



From: jbmhotmail
Sent: 3/25/2008 10:08 PM

Jay,

If you are now sure that your 19.5 Alcoa rims will fit, you can go to Alcoa's website and they have an email address or a phone number that you can use, just give them the Alcoa part number that is stamped on the rim and they can tell you if you are going to have a problem with installation.

If they fit and you install the rims, check with Mopar or a transmission shop for a new speedometer gear for the 19.5's.

Let us know if you get any better gas mileage.

Good luck



From: tjansen2
Sent: 4/6/2008 6:46 AM

If the wheels don't work for you I would be interested in them for my 73 D18.   that I am picking up from Sarasota on Wednesday... 
    They really do make a rig look good ,  lighter, and higher ratio. 
God Bless
Tom J
Coppell, Tx.