Who's running on big tires?

[Uncle-Pekka]

Means to improve high way travel qualities have been discussed frequently:

Installing over drive unit or changing rear ratio.

Unfortunately suitable OD & gears are becoming rare and prices raise high.

Some of you have adviced to use big tires instead.

I am currently running on 215/75 R15 tires.

I noticed 235/75 R16 would run almost 8% faster at the same shaft speed.

235/85 R16 would be almost 14% faster, almost the same effect as changing 4.1 rear to 3.54:1...

My idea would be install 2" lowering blocks on rear axel and hide the big rear wheels by using fender skirts. Keep 15" front tires.

Has anyone installed this big tires 235/85 16" ???

Any issues with interference to body or fenders?

[mrwrstory]

I have 235/85x16 on another car. I have 245/60x15 on my P15. With that as reference you will have enough wheel well width for the 235's,....if you are careful with the back space. Assuming you will go with different wheels, i.e. 16's, best do a mockup to assure proper placement (determined by back space) within the well.

[martybose]

I've never tried anything that big, but I looked up the sizing on Tire Rack, and those things are huge! They showed a 9.5" section width and 31.9" diameter. I did run 235/60x15 for several years, and had clearance issues side to side, so I would think these might as well.

I have no clue about whether there is room for a 32" tire on a lowered car, but ........

Marty

[greg g]

currently I am running 225 75 15 on 5 inch wide rims. They have served me well with no clearence problems except with a full trunk while turning hard right.

[Plymouthy Adams]

panhard rod time..you could be able to adapt the D24 panhard to the P15 if you should turn your hand to it..will let you know a bit later when I transfer my car to the other bay and put it on the lift..I took one from a D24 I parted long ago..

[Robert Horne]

panhard rod time..you could be able to adapt the D24 panhard to the P15 if you should turn your hand to it..will let you know a bit later when I transfer my car to the other bay and put it on the lift..I took one from a D24 I parted long ago..

The panhard bar is what I need to put on my 38 Coupe, running 235/75-15 tires on 7 inch wheels, or go with 225/75-15 tires.

I get a little tire rub on the inside, if I hit a bump while making a turn to the left or right.

[Plymouthy Adams]

I made my own panhard rod one time for a daily driver..it was one of them mom and pop cars with squishy ride..little to much squish for me..worked very well..was an easy build..pretty much copied the setup that is on my Sunbeam Tiger..

[Plymouthy Adams]

235's are quite wide tires especially if you are on wide rims..issues as rear tires change and the height you have to take the body to allow room to drop the wheel form the hub..with wheel bolts you have an advantage..with the studs should you have the Dodge or after market axle and these wide wheels you are clipping your margin of error..here is a 235/70 on a 16 inch rim that is 8 inches wide....these are positive offset wheel mind you..already setting the rubber deeper into the fender well...as these are a bit more "proud" of the opening than I care for..the use of a 6.5 width 16 rim with the exact back set keeps the rubber inside as before but no rubber protruding outside the fender opening..it is this reason I say you have to do your own searchng about and mix and match to get the look you want and total functionality at the same time..the options are out there if youy care to explore them..

the other wheel is what I am going to..but with a 225/75R16 to that will give me the less than a 1/2 MPH error at 60. I will post these another time after I go in and convert the front hubs to the 5 bolt that I have have already had machined for this application..the rear axles will be be machined as soon as I get it on the lift and start the rocker panels..

Edited August 18, 2012 by Tim Adams

[Uncle-Pekka]

As the width of the tires is the problem, I continued the search and noticed, that 215/85 R16 give almost 10% push compared to 215/75 R15.

215/85 R16 are 30" in diameter, thus will be troublesome to change as well...

For which application these 85 aspect ratio tires are made for anyway? - light trucks?

[greg g]

that size is pretty typical for mid 80'to mid 90's heavy duty pickups with dual rear wheels. if you remember like 165 15 on SAABS, Volvo's, and some VW they were considered 90 series so 85's would be slightly wider and a bit shorter in sidewall. But these were pretty typical here on chevy and ford dually trucks.

[blucarsdn]

Most people do not take into consideration the weight factor when they attempt to use large tires/wheels to increase ratio and lower RPM's.. Tire/wheel are basically flywheels that are rotating as the vehicle is in motion.

The larger the tire the more weight that is being spun, and therefore the more rotational weight that has to be overcome to stop a vehicle.

The added weight can also be a factor that can effect overall economy, especially on an underpowered engine.

I have P205/65R15's on 7" rims, 4.25" back set on my '39 Plym.. My rear ratio is 3.24 with an AOD trans.. The car cruises very nicely at 2,100 at 65/70 MPH.

To me the answer to cruising at lower RPM's on the highway is an OD trans.. I think it is more cost effective and safer. With an OD trans you have the option to shift into a lower gear range should the need arise. Trying to clabber together an odd collection of oversize tire/wheels, never made any sense to me.

I have a '36 Ford that has a Columbia overdrive. I have owned the car for just shy of 60 years. The car has always been a pleasure to drive on the highway. I have driven it over 90k during the time I have owned it....Bill

[Plymouthy Adams]

In part: Trying to clabber together an odd collection of oversize tire/wheels, never made any sense to me.

Some folks want to retain the original look of the full wheel of yesterday into the opening of the fenders..in some cases it would be very rare that these car would run 70 MPH and if so most likely not at a sustained period of time. Others build the car with the collection of parts that will allow the speedo of choice to also run without regard of new geat set or reprogramming as is the case in later swaps..

regardless of the reasons the folks are going for the look/performance they have in mind..and the very fact that they are considereing these point long before the build is complete and not as an afterthought to address a problem..more power to them..they are thinking ahead and planning...just not running around willy nilly like a chicken with its head cut off..to that I give them a thumbs up..