When RC makers' own specs disagree

If you’ve ever ordered a pinion using the tooth count from a product page, then opened the box and found the manual shows something else, you’re not imagining it.

Over the past few months we built RCTuneLab’s vehicle catalog: stock gearing, tires, motor and gear parts for more than 500 RC vehicles from nearly 40 makers. The rule was simple. Every figure had to trace back to the manufacturer’s own documents: product pages, manuals, exploded views, spare-parts lists and part pages, or an official distributor. No forum posts, no reseller listings, no guesses.

Following that rule meant reading the same car’s specs in three or four places, and the places often disagreed.

The headline numbers

• About four in ten vehicles had at least one discrepancy: a maker’s documents disagreeing with each other, or with a figure already recorded from another of their sources.
• Fewer than a quarter have all seven basic figures published somewhere: pinion, spur, internal ratio, final drive, tire diameter, motor KV and cell count. Kits sold without a motor are counted separately and don’t count against a maker.
• About one in five has no published internal (transmission and diff) ratio. For roughly another third, we worked it out from the published final drive and tooth counts, because the maker never prints it.
• About one in seven lists a tire without a published diameter.

None of this makes a manufacturer dishonest. Spec pages get copied between model years, manuals are shared across a whole family of trucks, and parts lists get updated when a supplier changes. But if you’re doing gearing math, the “official” number you start from may not be the one in your truck.

Six places the documents contradict themselves

Each vehicle below links to its spec sheet, which lists the sources.

• Traxxas Stampede 2WD BL-2s: the transmission exploded view marks a 21T pinion and 90T spur as fitted. With the manual’s own 2.72 internal ratio, that works out to 11.66:1. The product page says the final drive is 12.34:1. Both can’t be the stock setup.
• HPI Venture Wayfinder: the manual’s gear chart marks 17T as standard. The same kit’s parts list and exploded view name a 16T pinion. The product page’s “30.4:1 out of the box” matches neither: it works out to 15T.
• Redcat Vertex-6: the manual’s gearbox drawing and the spur’s own part page say 38T. The product page says 35T, and prints a 49.22:1 final drive that only works with 35T.
• Redcat Kaiju: the manual shows a 10T pinion fitted to the motor. The product page and a 12T pinion’s part page, tagged for the Kaiju, say 12T.
• Kyosho Ultima RB7.5: the technical data lists a 72T spur. Both spare-parts lists, scanned and online, name a 76T.
• Losi 8IGHT-XE: the manual’s parts list and the standard-parts list name a 46T spur. The spec table says 47T, and 47T is the one that produces the published 9.49:1.

Where the maker’s documents settled a question, we corrected the catalog; that happened for dozens of vehicles in one pass. Where they didn’t, we kept the figure the maker states most prominently, or left it out, and the spec sheet says which.

Pitch is the easy one to get wrong

Where we recorded a pinion pitch, the split between metric module and diametral pitch is close to even, with module slightly ahead, and often both appear within the same brand. Mod 0.8 and 32 pitch look almost the same and do not mesh properly. Neither do Mod 0.6 and 48 pitch. Some makers even describe a single gear in both systems, which is exactly how people end up buying the wrong pinion.

Our spec sheets show every pitch in one form, “Mod” for metric module and “P” for diametral pitch, whatever wording the maker used, and never convert between the two systems.

Advertised top speeds usually assume a different box

A few dozen vehicles in the catalog have both an advertised top speed and enough published figures to calculate one. We calculate the no-load speed: motor KV times pack voltage, divided by the final drive, times the tire circumference. That’s an upper bound, since real cars lose some of it to load, voltage sag and slip.

• About half advertise within 10% of that figure. The claims hold up.
• About four in ten advertise more than the stock gearing can reach on a nominal-voltage pack.
• A handful advertise more than the stock gearing can reach even on a fully charged pack. Those claims assume a different pinion, pack or setup than the one installed.

The Arrma Limitless 120 8S shows both sides. On its installed gearing, the theoretical speed is about 82 mph. The advertised 120 mph needs the speed pinion and spool that come in the box but aren’t fitted. Its spec sheet shows the speed both ways.

What this means when you’re gearing a car

1. Count the teeth. The pinion is stamped, the spur is countable. It takes two minutes and beats any spec page.
2. Check the pitch on the part itself, not the listing. If a listing mixes “32P” and “0.8M”, ask before you buy.
3. Read an advertised top speed as “with the right pinion, pack and conditions,” not as what the car does out of the box.
4. Start from sourced figures, then change one thing at a time. Each spec sheet lists where every number came from and loads straight into the top speed calculator, so you can see what a pinion change does before you buy it.

How we did it

Each figure is tied to a specific manufacturer document, which is linked on the vehicle’s page. When two documents disagreed, we recorded both and chose the reading the maker’s own numbers supported: a printed final drive that only works with one tooth count settles which count is right. When nothing settled it, we left the figure unrecorded rather than guess. Kits and rollers sold without a motor or pinion are marked “not applicable”, not “unknown”. The calculations are described in the methodology.

The catalog is a snapshot. Makers update their pages, and some of these discrepancies may be fixed by the time you read this. If you spot a figure that’s wrong, or a maker has corrected one, email hello@rctunelab.com with a link and we’ll check it against the source.