Tire sizes and gearing

[metromustang]

What size tires is everybody running? I am running 195/75R14.

The workshop book says the tire options are:
6.00-14-6PRLT
195SR14
ER70-14/B
P205/75R14

Only the second and fourth ones mean anything to me. (The metric sizes are recognizable.) Maybe the others are bias ply sizes? Was there a dual-rear-wheel option for this truck and maybe one of those is that tire size? Can anybody translate 195SR14? I usually see this reserved for 13" and 12" tires.

The owners manual says the pressures are as follows (front/rear):
26/45 psi 6.00-14-6PRLT
26/32 psi 195SR14
26/32 psi ER70-14/B
doesn't mention the optional size.
The sticker on my driver's door repeats this info.

When I bought my tires at Wal*Mart, their computer said my size was 195SR14. They were stumped. They didn't know what to sell me. It's kinda shameful since they are in the TIRE-SELLING BUSINESS and thus are PROFESSIONALS. Anyway, I had to do an impromptu recalculation of theoretical rolling radius to elect the size I picked. I thought I had read that the optional tire was 205/70 and thus when I did 70%×205=x%×195 I found x=74%. So I elected 75 series tires to be conservative and give me a little better gearing.

But if 205/70 isn't an optional tire, I should have chosen a 78.8 series tire (=70%×205÷195). If they didn't have that (of course they don't), I should've picked a 195/80R14.

Enough theory, let's talk empirical. I measured my rolling circumference to be 77.3 inches per revolution with the tires at 25 psi. Has anyone else measure theirs?

[metromustang]

To pick up from a WAY OFF-TOPIC discussion from north76.proboards11.com/index.cgi?board=general&action=display&thread=1081554430
...what are people's ideas about gearing?

From the workshop manual:
4.359:1 for 1st
2.519:1 for 2nd
1.507:1 for 3rd
1.000:1 for 4th
0.875:1 for 5th
times 3.90:1 final drive

Isn't it ironic that the more rev'able gas engine got a 3.307 rear end? Was there any other differences with these rear ends? Are they good to swap in?

44toy works fast!! one week after buying a truck he said he did this:

Guest-44toy said:

I put a rear axle from toyota truck with (3.58 gears?) I think it really need higher gears to run on the highway. It seems a little to high of a gear though and I am probably going to look for an axle with a little bit lower ratio.

This is evidence that a slight change to a numerically lower ratio isn't enough.


DieselDavo has experience with a better ratio:

Guest-Davotoo said:

My brother stuck his motor and trans in a gas Mazda 1984 B2000 (What a lot of work) which had 3.32 rear gears so that 4 was like 5 with the diesel. Problem was the 5th or overdrive gear didn't like it one bit.

But apparently the 5th gear isn't strong enough to push this little truck through the wind at a sustained 80mph rate. (I'm assuming the end goal was much easier cruising.) But it's all okay because even if you ignore 5th gear, you're no worse off with the bullet proof 4th gear giving you enough speed as a stock 5th gear.


Is this the solution if the 5th gear is truly this toublesome? Perhaps even lower gears would be better so that 4th can give you 75 mph. Or would around town driving be too adversely affected?

Or is 5th gear not that troublesome as long as you don't try to haul or tow much in that gear. As DieselDavo said, 350,000 miles is achievable.

What about my plan of having bigger 15" tires to put on just for long highway trips? I think I'll try it soon. I have a couple of 235/75R15 I can steal from the other truck. I hope they fit under the bed. The rolling radius of 367 mm instead of the current 312 mm. That would be like simulating changing my 3.90:1 rear end for a 3.32:1 rear end.

The bad part of the tire swap plan is that you can't feasibly swap speedo gears everytime you want to go on a trip. So mileage may reflect less than true mileage. Also bad is that I will be giving free miles to the Wal*Mart tires while two of them just sit in the bed for the ride. (I plan on cashing in the mileage warranty big time.)

[Davotoo]

205 R 70 are about 6 inches off the rim, so it about what the truck came with stock. With 205 R 70s on the rear the speedo and odometer are both off by about 7 % so that 40 MPH is really 34 MPH and 100 miles is really only 93 or so. With tires this big they will rub the frame in front on hard turns so you really can't get a combo much higher. The error on the meters is Mazda's fault for using the sane tranny gears and speedo head as the gas model. 15 inch wheels will probably work if you put smaller tires on them so the combo is as tall as the stock.

I'll bet Stumps rig moves like a herd of turtles! (see southern comfort)

[Davotoo]

26 pounds will get you a lot lower fuel milage and tax everything except the brakes. I run 205 R 70 - 40 psi front and 35 rear. The Wallworld specials should handle that ok. That crap on the side of the tire "32 psi max" is for when you put 32 psi in on a cold day and then drive to death valley on rock roads.

[metromustang]

So you got 205/70. From my theoretical rolling radius calculations, you should be in the same proverbial boat that I'm in. And yes, my speedo reads a little high. I haven't been able to determine how much but it's not negligible.

So if you went with the specified alternate tire of 205/75, you would be better off. You're current theoretical radius is 321 mm. The 205/75 would get you 331 mm. That would reduce your +7% to +3.7%.

Get this. The owner of my truck before me got some high-dollar Michelins sized 215/75. They looked good and were worn down evenly. I didn't see any evidence of trouble with interference though. Those were the tires I replaced. They didn't make it to their 80,000 mile warranty, but they were way past the allowed age.

Perhaps you get into interference when have a wider tire on a wider rim.

By the way, what is the "styled" rim that the book mentions in the lug nut torque specs?

[Davotoo]

Probably the stock stamped steel center ones. I don't think the Diesel ever came with the spoked ones.

[Dave]

is 5th gear really that bad?
for years iv always used 5th gear, once i got reved out on the major highways and upto speed.. i never noticed any speed lag in high winds, just the truck wants to wonder a bit in heavey cross winds.

and when entering on-ramps wondering if im gonna be able to gain enough speed to avoid being clobbered
by a tractor trailer..

[Davotoo]

If you have a home made fuel tank that weigh 150 kilos empty; Yea I would worry about 5th gear. It's only held on by an over-sized clip ring! Looks like the 5th gear was a after thought at the Toyo Kogyo plant in Hiroshima. Just think of Hiroshima when your going up hill at 45 mph in 5th...............

[metromustang]

Moderator Dave, what size are your tires?

My experiment with the 15" tires is not to have:

Guest-Davotoo said:

15 inch wheels will probably work if you put smaller tires on them so the combo is as tall as the stock.

This would only serve to have to buy more expensive, lower profile tires. The experiment is to have bigger wheels with bigger again tires that would change my final drive ratio the same amount as would swapping the 3.90 rear end for a 3.32 rear end. This way, only when I need to make road trips, I can have the lower gearing. A temporary alteration.

The book says that the 4-speed has the same ratios as the 5-speed, it just doesn't have the overdrive gear. So I'd agree it's a safe bet that the transmissions except for the allegedly afterthought 5th gear.

DieselDavo, when your brother swapped rear ends, did he just install a rear end from a gas B2000/Courier? The book says they are 3.307.
Has anybody heard of this swap being done?

I talked to the Wal*Mart folks. They said they don't care what I do. I can rotate them myself and I can use any air pressure I see fit and it won't affect my warranty. Because I plan on cashing in on the mileage warranty, I don't want to take any chances and give them any outs. So I'll go to 35 psi up front and 32 in the back.

My question about the "styled wheels" wasn't clear enough. The book says the nut torque is 76±4 ft·lbs for "standard wheel" and 90.5±3.5 ft·lbs for "styled wheel". I assume that my steel rims and hub caps are standard wheels and most B2200s are equipped as such. Apparently there is another type of wheel that was available as an option: perhaps only on Sundowners or perhaps on any mazDa truck. The question is does anybody know what this wheel is like? Alloy aluminum? Wider than standard steel rim? Perhaps it is shown in the dealer brochure that some of you have?

[Davotoo]

My brother got an 84 B2000 gas Mazda for free after the antifreeze ate the aluminum head into swiss cheese. He put motor, trans, dash board (spedo on diesel has speed sensor for glowplug schedule) and wiring harness in it from the 82 diesel.

Leaving the rear end, one piece drive shaft, sleezy front springs and brakes. The clip that held on 5th was first to go so he drove arround using 4th. Next was the frame which rotted from the inside. (Should have filled it with waste oil)

The motor and trans next went into a late model ford ranger which had the Pinto 4 evolvolution abortion engine. (Bad fit) had to heat and bend shifter to clear seat and relocate all oil filters where the trans ate the front berring chipping the pilot shaft gear. Trans was rebuilt for $750 plus all our spare parts and is sitting on a pallet (he got a nissan diesel and lost interest)