The 1979 GMC Rally sits in the full-size van era when passenger vans, camper conversions, and heavy-duty people movers covered a wide range of jobs on one platform. That matters for tire selection, because this exact model spans several load classes, wheel diameters, and both bias-ply and radial-era fitments. Depending on the sub-model, a 1979 GMC Rally may use 15-inch alphanumeric sizes such as FR78-15, GR78-15, HR78-15, J78-15, and JR78-15, or 16.5-inch truck sizes such as 800-16.5, 875-16.5, and 8.75R16.5. Some owners will be choosing among period-style bias-ply options, while others will be confirming a radial setup or considering a radial equivalent for J78-15 with close attention to wheel and clearance details.
Which Tire Size Is Right for The 1979 GMC Rally
The 1979 GMC Rally uses eight distinct tire sizes, and the right one depends first on the exact sub-model and wheel diameter. Some versions use 15-inch alphanumeric passenger-vehicle sizes, while heavier configurations move to 16.5-inch truck sizes and may use either bias-ply or radial construction. Before choosing a tire, confirm the Rally's specific GVWR grouping, whether it is a DRW model, and whether it is riding on 15-inch or 16.5-inch wheels.
FR78-15 is a vintage alphanumeric radial size in which the letter-based code indicates the tire's size class, the 78 identifies the profile family, and the 15 denotes a 15-inch rim. On the 1979 GMC Rally, this is a primary radial fitment used on certain G1500 configurations. Selection in this size centers less on sidewall styling and more on making sure the van's exact sub-model and wheel setup match the intended application. It is a useful size for owners keeping a proper 15-inch radial-type fitment on lighter-duty Rally models.
GR78-15 is another vintage alphanumeric radial size, with the letter code marking its size class, the 78 indicating the profile family, and the 15 calling for a 15-inch rim. This size appears on multiple 1979 GMC Rally G1500 configurations, so it can overlap across more than one GVWR grouping. Practical selection starts with confirming which G1500 version you have, since FR78-15, GR78-15, and HR78-15 are all used within the same broader model line. For a van still on its original-style 15-inch wheel diameter, GR78-15 is one of the key radial fitments to verify.
HR78-15 uses the vintage alphanumeric radial system, where the initial letter represents the tire's size class, the 78 marks the profile family, and the 15 identifies a 15-inch rim. For the 1979 GMC Rally, this radial size appears across several G1500 sub-models, including heavier GVWR versions that narrow the fitment choices. Because it is shared by more than one G1500 configuration, the main task is confirming that your van belongs in the HR78-15 group rather than a lighter FR78-15 or GR78-15 setup. It suits owners preserving a correct-style radial presentation on 15-inch wheels.
J78-15 is a vintage alphanumeric bias-ply size, with the letter identifying the size class, the 78 designating the profile family, and the 15 calling for a 15-inch rim. On the 1979 GMC Rally, it is one of the primary fitments for certain G2500 applications and represents a traditional bias-ply construction choice. Available tires in this size include BFGoodrich options from the Silvertown Classic Bias Ply series with Dual-White-Stripe and Narrow Whitewall sidewall treatments. It is the size to study closely if the goal is a restoration-oriented 15-inch bias-ply look, while still checking whether a radial alternative is under consideration.
JR78-15 is an alphanumeric radial size that uses a letter-based size class, a 78-series profile designation, and a 15-inch rim diameter. For the 1979 GMC Rally, this size appears as a radial fitment in certain G2500 configurations alongside J78-15 bias-ply applications. That makes the distinction between the exact sub-model and existing wheel setup especially important, since the broader model line includes both constructions. JR78-15 is the relevant choice for owners confirming a 15-inch radial fitment on a heavier Rally variant rather than a bias-ply presentation.
800-16.5 is a numeric bias-ply truck size in which 800 refers to an approximate 8.00-inch nominal section width and 16.5 identifies the wheel diameter. On the 1979 GMC Rally, it is used on certain G3500 configurations, including some dual rear wheel and higher-capacity van applications. Available choices in this size come from STA, including Super Transport and Traxion series tires, both with blackwall sidewalls and truck-oriented construction details. It is a fitment to evaluate when a heavy-duty Rally remains on a 16.5-inch bias-ply setup and the priority is preserving the proper load-class character.
875-16.5 is a numeric bias-ply truck size, with 875 indicating an approximate 8.75-inch nominal section width and 16.5 denoting the wheel diameter. This is one of the most widely used heavy-duty sizes within the 1979 GMC Rally range, appearing on several G3500 and G3500 DRW applications. Product choices include STA Traxion and STA Transport Highway tires, both blackwall designs intended for truck service. For owners working with a heavier Rally or dual rear wheel van, this size is central to confirming the correct 16.5-inch bias-ply fitment before comparing tread style and service-focused tire series.
8.75R16.5 is a radial truck size that combines an 8.75-inch nominal section width with radial construction and a 16.5-inch rim diameter. On the 1979 GMC Rally, it appears on certain G3500 and G3500 DRW sub-models where radial construction enters the heavier-duty 16.5-inch fitment range. Its practical role is different from the 15-inch passenger-style alphanumeric radial sizes, because here the key issue is confirming a heavy-duty 16.5-inch wheel setup rather than a light-duty van application. It is the size to verify when a heavier Rally uses a radial-style truck fitment instead of a 16.5-inch bias-ply configuration.
Fitment for the 1979 GMC Rally varies substantially by sub-model, especially once GVWR class, G1500 versus G2500 versus G3500 designation, and DRW configuration enter the picture. Checking the exact sub-model matters because both tire size and wheel diameter change across the range, and some versions also span bias-ply and radial-era choices.
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1979 GMC Rally G1500 (GVWR 4900)
The 1979 GMC Rally G1500 (GVWR 4900) uses 15-inch radial fitments and has the widest spread of G1500 tire-size choices within this model range. Tire selection starts with confirming which of the radial sizes belongs on the van now, then matching that choice to the wheel setup and the kind of period-style road use the vehicle will see.
The 1979 GMC Rally G1500 (GVWR 5600) stays within the 15-inch radial family but narrows the size range compared with the lighter G1500 version. That makes the decision more focused: confirm whether the van is in the GR78-15 or HR78-15 group and keep the tire choice aligned with the existing wheel diameter and overall setup.
The 1979 GMC Rally G1500 (GVWR 6000) carries a straightforward 15-inch radial fitment within this page's covered sizes. For this sub-model, the main consideration is less about sorting through multiple primary sizes and more about confirming the existing wheel arrangement and choosing a tire that suits the van's intended road use.
The 1979 GMC Rally G2500 (GVWR 6400 & 6600) is one of the clearest places where construction choice matters, because it can fall into either a 15-inch bias-ply or a 15-inch radial fitment. That means owners should verify not only the exact size in use, but also whether the goal is to retain a traditional bias-ply presentation or continue with a radial setup.
The 1979 GMC Rally G3500 (DRW) (GVWR 6400 & 6600) moves into 16.5-inch heavy-duty bias-ply truck sizes. Tire selection here revolves around confirming which of the covered 16.5-inch sizes belongs on the van and choosing an appropriate truck-oriented blackwall tire series for dual rear wheel service.
The 1979 GMC Rally G3500 (DRW) (GVWR 6900 & 7100) spans both a 16.5-inch radial truck fitment and a 16.5-inch bias-ply truck fitment. Choosing correctly means confirming the present wheel and tire configuration first, then deciding whether to maintain the current construction type or return the van to a more traditional heavy-duty setup.
The 1979 GMC Rally G3500 (DRW) (GVWR 7100 & 7900) also crosses between 16.5-inch radial and bias-ply truck sizes, so fitment is not a one-size-fits-all matter. Owners should verify the current wheel and tire combination carefully, especially on a dual rear wheel van where heavy-duty use and clearance considerations are part of the decision.
The 1979 GMC Rally G3500 (GVWR 6400 & 6600) uses 16.5-inch heavy-duty bias-ply truck sizing. That points the buyer toward confirming whether the van is on the narrower or wider covered fitment and then comparing truck-oriented blackwall tire series that match the wheel diameter and service character.
The 1979 GMC Rally G3500 (GVWR 6900 & 7100) can be found with either a 16.5-inch radial truck tire or a 16.5-inch bias-ply truck tire. The practical task is to confirm the van's actual wheel and tire arrangement before selecting a replacement, since construction and size both affect the proper heavy-duty fitment path.
The 1979 GMC Rally G3500 (GVWR 7100 & 7900) continues the 16.5-inch heavy-duty pattern and includes both radial and bias-ply possibilities within the covered fitments. That makes careful verification especially important before replacement, particularly for vans that may have seen wheel changes or long service in commercial or conversion use.
The 1979 GMC Rally G3500 V8 uses a straightforward 16.5-inch heavy-duty bias-ply fitment within the covered sizes. Selection is mainly about staying with the proper truck-style size and then choosing between the available blackwall tire series that suit the van's working character and road-use expectations.
The 1979 GMC Rally G3500 V8 (DRW) uses a single heavy-duty 16.5-inch bias-ply fitment among the sizes covered here. For this dual rear wheel configuration, the focus shifts from sorting through multiple primary sizes to confirming wheel compatibility and choosing a truck-service tire series appropriate for the van's load-carrying role.
Bias-Ply to Radial Tire Conversion for the 1979 GMC Rally
J78-15 has four radial-equivalent choices for a 1979 GMC Rally. Those options are 225R15 as an 80-series metric radial, P235/75R15 as a P-metric 75-series radial, P235/70R15 as a P-metric 70-series radial, and 800R15 as a bias-look radial equivalent. Together they offer a mix of metric, P-metric, and traditional-looking radial formats around the original J78-15 sizing. A recommended rim-width range of 6 to 8 inches applies to these equivalents, and any conversion should be checked against wheel dimensions, overall setup, and clearance.
Modern Radial Equivalents
225R15
Equivalent 80-series Metric Radial (J78-15)
P235/75R15
Equivalent P-metric 75-series Radial (J78-15)
P235/70R15
Equivalent P-metric 70-series Radial (J78-15)
800R15
Bias-look Radial Equivalent (J78-15)
Important Considerations When Replacing Bias Ply With Radial
Compare overall diameter and section width carefully to ensure proper fit.
Verify recommended rim range (6-8 in) and load needs match your vehicle specifications.
Check fender clearance, steering clearance, and stance before installation.
Consider suspension condition and intended road use when choosing equivalents.
Important Fitment Notes
The tire sizes listed on this page assume factory-standard vehicle configuration. The following modifications may affect tire fitment and are not reflected in this guide:
Suspension changes (lowering, lift kits, spring replacements)
Body alterations (fender modifications, custom bodywork)
If your vehicle has been modified from factory specifications, verify tire clearance before purchase.
Best 1979 GMC Rally Tires for Sale
Available 1979 GMC Rally tire choices center on J78-15, 800-16.5, and 875-16.5, with BFGoodrich and STA offerings across Silvertown Classic Bias Ply, Super Transport, Traxion, and Transport Highway series. Sidewall treatments include Dual-White-Stripe, Narrow Whitewall, and Blackwall depending on size and intended use.
Common 1979 GMC Rally tire questions usually come down to identifying the exact sub-model, confirming whether the van uses 15-inch or 16.5-inch wheels, and deciding between period-style bias-ply fitment, radial fitment, or a radial equivalent where one exists.
Tire Size & Fitment
What tire size fits a 1979 GMC Rally?
A 1979 GMC Rally can use FR78-15, GR78-15, HR78-15, J78-15, JR78-15, 800-16.5, 875-16.5, or 8.75R16.5, depending on the exact sub-model. The G1500 range uses 15-inch radial sizes, the G2500 can use either J78-15 bias-ply or JR78-15 radial, and the heavier G3500 models move into 16.5-inch truck sizes in both bias-ply and radial form.
The important next step is identifying the van's exact GVWR grouping and whether it is a dual rear wheel configuration, because those details change the size and sometimes the construction type. A quick wheel check is just as important, since the Rally spans both 15-inch and 16.5-inch rims and not every covered size belongs on every version.
What size rim does a 1979 GMC Rally use?
The 1979 GMC Rally uses either a 15-inch rim or a 16.5-inch rim, depending on sub-model. FR78-15, GR78-15, HR78-15, J78-15, and JR78-15 are 15-inch fitments, while 800-16.5, 875-16.5, and 8.75R16.5 are 16.5-inch fitments for heavier-duty applications.
Rim diameter should be confirmed before anything else, because a 15-inch tire and a 16.5-inch tire are not interchangeable even if the van looks broadly similar across trim lines. On an older full-size van, it is also wise to verify that the wheels currently installed are the ones the vehicle is actually using now, especially if it has seen conversion work or fleet-style service.
Why does the 1979 GMC Rally have more than one tire size?
The 1979 GMC Rally covers several sub-models with different GVWR classes, and those differences lead to different tire sizes, wheel diameters, and in some cases different constructions. Lighter G1500 vans stay in 15-inch radial sizes, the G2500 bridges bias-ply and radial 15-inch fitments, and the G3500 range uses heavier 16.5-inch truck sizes.
That spread means the correct tire choice is tied to the van's exact configuration rather than the Rally name alone. Checking the sub-model badge, the wheel diameter, and whether the van is single rear wheel or dual rear wheel will narrow the field quickly and help avoid choosing a tire that matches the era but not the actual setup.
Bias-Ply & Radial Options
Is J78-15 a bias-ply or radial tire for the 1979 GMC Rally?
J78-15 is a bias-ply tire size on the 1979 GMC Rally. It appears on the 1979 GMC Rally G2500 (GVWR 6400 & 6600), where it stands alongside JR78-15 as a separate radial fitment rather than as another way of writing the same tire.
That distinction matters because a bias-ply J78-15 and a radial JR78-15 do not represent the same construction choice, even though both fit 15-inch rims. Owners preserving a traditional look may stay with J78-15 bias-ply, while those considering a radial path should confirm wheel suitability, vehicle clearance, and the current setup before moving away from the original construction type.
What radial tire sizes are equivalent to J78-15?
Radial equivalents for J78-15 include 225R15, P235/75R15, P235/70R15, and 800R15. In that group, 225R15 is an 80-series metric radial, P235/75R15 is a 75-series P-metric radial, P235/70R15 is a 70-series P-metric radial, and 800R15 is a bias-look radial equivalent.
These choices give a 1979 GMC Rally owner several ways to approach a radial conversion while staying close to the original J78-15 fitment intent. The recommended rim-width range for those equivalents is 6 to 8 inches, and each option should still be checked against the van's wheels, overall tire dimensions, and available clearance before treating it as a workable alternative.
What should I check before converting my 1979 GMC Rally from bias-ply to radial tires?
Start by confirming the Rally's exact sub-model, wheel diameter, and the specific bias-ply size currently in use. On a J78-15 application, radial equivalents include 225R15, P235/75R15, P235/70R15, and 800R15, but the van must also have wheels that suit the intended radial size and the rest of the setup.
A careful conversion check includes wheel width, fender and steering clearance, and the condition of suspension and steering components on an older van. It also helps to compare the tire's intended look with the vehicle's restoration goals, because a standard radial and a bias-look radial can give the 1979 GMC Rally a noticeably different presentation.
Choosing the Right Tire
What should I consider when choosing a tire for a 1979 GMC Rally?
Begin with the exact sub-model, because the 1979 GMC Rally spans light-duty G1500, mid-range G2500, and heavier G3500 applications with different sizes and even different wheel diameters. Construction also matters: some versions are radial, some are bias-ply, and the G2500 and certain G3500 applications can place those choices side by side within the same broader model family.
Once the correct size is confirmed, the decision shifts to how the van will be used and presented. A restoration-oriented owner may focus on traditional construction and sidewall appearance, while a work-focused heavy-duty van may lean more on truck tire series, blackwall styling, and matching the tire to the wheel and service role already on the vehicle.
What sidewall styles are available for 1979 GMC Rally tires?
Available sidewall styles for 1979 GMC Rally tires include Dual-White-Stripe, Narrow Whitewall, and Blackwall. The whitewall choices appear in J78-15 through BFGoodrich Silvertown Classic Bias Ply offerings, while the 16.5-inch truck sizes 800-16.5 and 875-16.5 are available in blackwall form through STA truck-oriented lines.
That means sidewall choice is tied closely to the size and type of Rally you own. A G2500 running J78-15 can lean toward a more passenger-van or restoration-style presentation, while G3500 applications in 16.5-inch truck sizes stay focused on utility-oriented blackwall tires that suit the heavier-duty character of those vans.
What brands offer tires for the 1979 GMC Rally?
BFGoodrich and STA offer tires for covered 1979 GMC Rally fitments. BFGoodrich appears in J78-15 with Silvertown Classic Bias Ply options, while STA covers the 16.5-inch truck sizes with Super Transport, Traxion, and Transport Highway series aimed at heavier-duty service.
Brand choice here is really a size-and-application choice rather than a simple preference question. A 15-inch G2500 owner considering J78-15 will be looking at passenger-style bias-ply presentation, while a G3500 owner on 800-16.5 or 875-16.5 is comparing truck-series options designed around the heavier working role of the larger van.
Restoration & Appearance
Which tire should I choose for a period-style 1979 GMC Rally?
A period-style 1979 GMC Rally tire choice starts with using the exact size and construction that belong to the van's sub-model. For a G2500 using J78-15, a bias-ply tire keeps a traditional late-1970s look, while heavier G3500 applications in 800-16.5 or 875-16.5 naturally point toward blackwall truck tires with an appropriately work-oriented appearance.
Appearance should follow fitment, not the other way around. Owners concerned with exact originality should compare the van against marque references, restoration photos, or build documentation, since a tire can look convincingly period-style without necessarily matching the precise sidewall treatment or construction the vehicle carried when new.
How does tire construction affect the appearance of a restored 1979 GMC Rally?
Tire construction can change the visual character of a restored 1979 GMC Rally even when the wheel diameter stays the same. A bias-ply fitment such as J78-15 gives a more traditional period presentation, while a radial fitment like JR78-15 or the 15-inch G1500 radial sizes tends to create a later, more contemporary look within the same era.
That difference matters most on vans being restored with a strong period feel in mind. A radial equivalent can still be a sensible choice for road use, but owners who care about the van's stance and visual impression should compare construction, sidewall style, and overall presentation together rather than selecting only by the nearest size code.
Fitment, Maintenance & Road Use
Can modifications affect tire fitment on a 1979 GMC Rally?
Yes, modifications can affect tire fitment on a 1979 GMC Rally, especially because the model already spans two wheel diameters and several load-class tire sizes. If the van has aftermarket wheels, altered ride height, conversion-van body additions, or changes to the rear-wheel setup, the correct original-style size may still need a closer clearance and wheel-compatibility check.
The safest approach is to verify actual wheel diameter and width on the van before choosing a replacement tire. On heavier G3500 and DRW versions, small setup changes can matter more because truck tires, rear-wheel spacing, and fender clearance all work together, so replacement should follow the vehicle's current hardware rather than assumptions based on model name alone.
What should I inspect before driving a 1979 GMC Rally on new tires?
Before driving a 1979 GMC Rally on new tires, inspect the wheels for the correct diameter and general condition, then check that lug hardware, valve stems, and inflation are in order. It also makes sense to look over steering, suspension, and brake components on an older full-size van, especially if it has been parked for long stretches or recently returned to service.
A short clearance check is worthwhile before regular road use. Turn the steering lock to lock on 15-inch applications, and on heavier 16.5-inch or DRW setups, confirm that nothing rubs under load or at the rear duals. After the first few drives, recheck air pressure and look for any signs of uneven wear or contact.
How should tires on a collector 1979 GMC Rally be maintained?
Tires on a collector 1979 GMC Rally should be maintained with regular pressure checks, visual inspections, and attention to age-related condition even when tread looks good. Sidewall cracking, flat spotting from long storage, bulges, cuts, and slow air loss are all worth watching on a vehicle that may spend more time parked than driven.
Storage habits matter just as much as mileage. Keeping the van away from prolonged sunlight, excess heat, moisture, and ozone sources can help preserve tire condition, and moving the vehicle occasionally helps reduce long-term standing stress. Before any longer trip, inspect the tires closely and make sure the actual wheel-and-tire combination still matches the Rally's intended setup.
