What was the factory tire size on 87?

[bennylava]

I'm about to get new tires on my 87 2wd half ton silverado. But the tire shop seems a bit confused on what size would have been factory. I'm hoping someone here can tell me the size that would have come on the truck when it was new. It's just got the typical 15" rally wheels. Thank you

[Keith Seymore]

Base was P195/75R15.

You could order up to P235/75R15.

There also was an LR60-15B available within certain packages.

K

https://www.gm.com/content/dam/compa...olet-Truck.pdf

[bennylava]

Thank you sir

[nvrenuf]

There should be a sticker on the door with the original size and recommended psi. (not the VIN sticker)

[Keith Seymore]

Speaking of stickers: An optional tire will also appear on the SPID if you still have the label in the glovebox.

Tire RPOs are Xxx (front), Yxx (rear) and Zxx (spare).

K

[bennylava]

What are the characteristics of both these tire sizes? It would seem that the larger tire was considered to be an upgrade. Was there no advantage to the smaller tire?

[Dead Parrot]

Originally Posted by bennylava

What are the characteristics of both these tire sizes? It would seem that the larger tire was considered to be an upgrade. Was there no advantage to the smaller tire?

Ride height and engine speed. Smaller tire = lower stance and faster engine RPMs. Larger tire = higher stance and lower engine RPMs. Also will impact the speedometer accuracy.

[Keith Seymore]

Originally Posted by bennylava

What are the characteristics of both these tire sizes? It would seem that the larger tire was considered to be an upgrade. Was there no advantage to the smaller tire?

No advantage to the consumer, other than keeping the initial vehicle purchase price down.

As a manufacturer you take the cheapest tire you can offer and use that as base. Any tire savings is multiplied by 5 (or by 4 for those vehicles that do not get a spare) so it adds up.

Yes - the larger tire is an upgrade and therefore additional cost to the customer and more revenue for GM. Tire prices are shown in the info packet I linked; it cost me an additional $250 to opt up to the P235 tires on my '87.

K

[Hammered 77]

So if you opt for the larger tires what was done to correct speed and mileage?

[Keith Seymore]

Originally Posted by Hammered 77

So if you opt for the larger tires what was done to correct speed and mileage?

Different transmission part numbers were released with internal gearing to accommodate tire and (more so) rear axle ratio options.

In some cases an external adapter was also used, as in the case of my '87 (it used the "Z" shaped version).

K

[MJN]

Originally Posted by bennylava

What are the characteristics of both these tire sizes? It would seem that the larger tire was considered to be an upgrade. Was there no advantage to the smaller tire?

Different tire options also impacted the GVWR since different tires have different load ratings, this load capacity guide goes into detail on front/rear spring and different wheel/tire combos and even air pressure and how it changes GVWR.
https://67-72chevytrucks.com/vboard/...d.php?t=845046
Page 42 of this PDF shows the different tire sizes that were available
https://www.gm.com/content/dam/compa...olet-Truck.pdf

[Keith Seymore]

Originally Posted by MJN

Different tire options also impacted the GVWR since different tires have different load ratings, this load capacity guide goes into detail on front/rear spring and different wheel/tire combos and even air pressure and how it changes GVWR.
https://67-72chevytrucks.com/vboard/...d.php?t=845046

Good info.

The GVWR is established not only by how much weight the vehicle can carry, but also if you can get that weight moving and stopped. That includes rear axle ratio, too.

When I was establishing GVW (and GCW) ratings the final capping run was if you could get the load moving up the 16% grade at the Milford Proving Ground from a standing stop.

Originally Posted by MJN

Page 42 of this PDF shows the different tire sizes that were available
https://www.gm.com/content/dam/compa...olet-Truck.pdf

Yes - as linked in Post #2 of this thread.

K

[bennylava]

According to that PDF, it looks like p225 and p235 tires were available. Or at least usable.

[Axle]

What size tires have you got on it now that the tire shop is 'confused'?

[hatzie]

Originally Posted by Keith Seymore

Different transmission part numbers were released with internal gearing to accommodate tire and (more so) rear axle ratio options.

In some cases an external adapter was also used, as in the case of my '87 (it used the "Z" shaped version).

K

The parts books have tables with the drive and driven gears for the speedometer
They're based on the axle rato, transmission/transfer-case, and tire size.

[bennylava]

Originally Posted by hatzie

The parts books have tables with the drive and driven gears for the speedometer
They're based on the axle rato, transmission/transfer-case, and tire size.

IIRC you can change out that gear on the vehicle speed... thing. To adjust for tire size. Then your cable will tell the speedo the correct speed.

Also, anyone got any pics of other tire sizes on the stock 15" rally wheels? Minus all the off-roading tires. Just street tires. I wouldn't mind seeing some pics so I could choose the tires which look the best imo.

185 to 235 seems like a nice gap. Maybe 225 or 215 would look good.

[Keith Seymore]

Originally Posted by hatzie

The parts books have tables with the drive and driven gears for the speedometer
They're based on the axle rato, transmission/transfer-case, and tire size.

That is correct, for service.

They didn't swap gears in the assembly plant. The transmissions were all built up, sitting there ready to go.

K

[Keith Seymore]

Originally Posted by bennylava

iirc you can change out that gear on the vehicle speed... Thing. To adjust for tire size. Then your cable will tell the speedo the correct speed.

Also, anyone got any pics of other tire sizes on the stock 15" rally wheels? Minus all the off-roading tires. Just street tires. I wouldn't mind seeing some pics so i could choose the tires which look the best imo.

185 to 235 seems like a nice gap. Maybe 225 or 215 would look good.

p235 -

[Keith Seymore]

Lr60-15

[geezer#99]

How wide were the rims with the p235’s, Kieth?

[Keith Seymore]

15 x 8 rallys.

K

[rwjtexas]

Originally Posted by bennylava

I'm about to get new tires on my 87 2wd half ton silverado. But the tire shop seems a bit confused on what size would have been factory. I'm hoping someone here can tell me the size that would have come on the truck when it was new. It's just got the typical 15" rally wheels. Thank you

Have you purchased your tires ? I can make you a good deal on 4 or 5 Goodyear Wrangler P235/75R15 that I bought for my 1985 blazer. I bought 5 to have a new spare

I thought I wanted blackwall and after the fresh paint job I purchased a complete set of the Goodyear Wranger Duratrac to get the Outlined white letter tires.

I am not sure where you are in Texas but I am an hour out of Houston on the east side.

[bennylava]

Originally Posted by rwjtexas

Have you purchased your tires ? I can make you a good deal on 4 or 5 Goodyear Wrangler P235/75R15 that I bought for my 1985 blazer. I bought 5 to have a new spare

I thought I wanted blackwall and after the fresh paint job I purchased a complete set of the Goodyear Wranger Duratrac to get the Outlined white letter tires.

I am not sure where you are in Texas but I am an hour out of Houston on the east side.

Yeah already got em. I'm sure you can sell those tires on facebook marketplace though, especially since you're near the city.