Speed at redline per gear calculator
With a 6,500 rpm redline, a 3.73 final drive and 650 mm tyres, a sixth gear of 0.7 tops out at a theoretical 305.014836 km/h. Check every gear before ordering a gear set or after changing tyre size. Free in your browser.
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Worked example
- Redline rpm
- 6,500
- Gear ratios
- 3.5, 2.1, 1.4, 1, 0.85, 0.7
- Final drive
- 3.73
- Tire diameter
- 650
- Tire diameter unit
- Mm
- Tire diameter m
- 0.65
- Circumference m
- 2.042035225
- Gear count
- 6
- Max speed gear
- 6
Builders, tuners, and powertrain engineers need a clear table of how fast a vehicle can go in every gear when the engine hits redline—not a single-point RPM check. This speed at redline per gear calculator turns an ordered list of transmission gear ratios, a final drive ratio, and overall tire diameter into theoretical road speeds at the tachometer limit. For each gear it reports overall ratio, wheel RPM, and speed in kilometres per hour, miles per hour, and metres per second, and it highlights which gear yields the highest top speed. Use it before ordering a gear set or differential, after a tire size change, or when filling OEM and track-day documentation.
How redline road speed is derived for every gear
At redline the engine spins the transmission input at a fixed maximum RPM. Each gear multiplies torque and divides shaft speed by its gear ratio: a first gear of 3.5 means the gearbox output turns once for every 3.5 engine revolutions. The differential multiplies that reduction again by the final drive (axle) ratio, so the overall ratio from crankshaft to wheels is gear ratio times final drive.
Wheel revolutions per minute at redline are therefore redline RPM divided by that overall ratio. Each wheel revolution advances the vehicle by one tire circumference, which is π times overall tire diameter when diameter is converted to metres. Linear road speed in metres per second is wheel revolutions per second times circumference; multiplying by 3.6 yields km/h and converting with the international mile factor yields mph.
The model is kinematic: it ignores tire slip, load growth, aerodynamic drag, and power limits, so the numbers are theoretical ceilings at the stated redline for comparing gear sets and speedometer calibration, not a guarantee that the car will actually reach redline in a tall overdrive.
Who uses a per-gear redline speed table
Performance shops compare candidate gear sets and final drives against a fixed redline and tire size before ordering parts, using this calculator as a deterministic oracle instead of a fragile spreadsheet. Track-day instructors and data tools fill theoretical top-speed columns for each gear so drivers know which ratios will hit redline before the straight ends. Fleet and OEM documentation generators emit per-gear redline tables for every powertrain SKU without embedding unit-conversion bugs.
Keep gear lists short, pin the rounded speeds in tests, and you get reproducible multi-gear redline checks for builders, educators, and edge workers without standing up a full vehicle-dynamics simulator of your own. Pair this capability with single-RPM road-speed checks when you need both a full redline map and a point reading at a partial throttle tachometer mark.
What you can do with it
Gear set and differential selection
Compare theoretical top speed in every gear at redline after a transmission gear-set or final-drive swap, using the fitted tire diameter.
Tire size and speedometer tables
Rebuild the full redline-per-gear speed table when overall tire diameter changes after upsizing or downsizing wheels and tires.
OEM and track documentation
Generate ordered max-speed-at-redline tables per gear for manuals, data packs, and track briefings without spreadsheet drift.
FAQ
Which tire diameter should I use?
Use the overall rolling diameter of the fitted tire (not just rim diameter).
Does this include drag, slip, or power limits?
No. Results are kinematic speeds at redline for the stated ratios and diameter. Real top speed may be lower if power, drag, or traction limit the car before redline, especially in tall gears.
How is the speed at redline worked out for each gear?
The gear ratio is multiplied by the final drive to get the overall ratio. Redline rpm divided by that gives wheel rpm, and each wheel turn moves the car one tyre circumference, which is pi times the diameter.
Will the car really reach redline in top gear?
Not necessarily. The figures are theoretical ceilings that ignore drag, tyre slip and power limits, so a tall overdrive may never reach redline. Use them to compare gear sets and check speedometer calibration.
What changes when I fit bigger tyres or a different final drive?
A larger overall tyre diameter covers more road per wheel turn, so every gear gets faster at redline. A numerically higher final drive does the opposite and lowers the speed in every gear. Re-run the table after either change.
Related tools
For developers — API access
Everything on this page is available programmatically. This section is for teams who want to wire it into their own systems; everyone else can just use the tool above.
API endpoint
Prefer to automate it? One authenticated POST creates the task; the result comes back by webhook or a signed link. The same capability also runs here on the web, by email and from Telegram — and soon from our app too.
Call it from your stack
curl -X POST https://api.kit.forhosting.com/travel/speed-at-redline \
-H "Authorization: Bearer $KIT_KEY" \
-H "Content-Type: application/json" \
-d '{"redline_rpm":6500,"gear_ratios":[3.5,2.1,1.4,1,0.85,0.7],"final_drive":3.73,"tire_diameter":650}'const res = await fetch("https://api.kit.forhosting.com/travel/speed-at-redline", {
method: "POST",
headers: {
"Authorization": `Bearer ${process.env.KIT_KEY}`,
"Content-Type": "application/json"
},
body: JSON.stringify({
"redline_rpm": 6500,
"gear_ratios": [
3.5,
2.1,
1.4,
1,
0.85,
0.7
],
"final_drive": 3.73,
"tire_diameter": 650
})
});
const { task_id } = await res.json();import os, requests
res = requests.post(
"https://api.kit.forhosting.com/travel/speed-at-redline",
headers={"Authorization": f"Bearer {os.environ['KIT_KEY']}"},
json={
"redline_rpm": 6500,
"gear_ratios": [
3.5,
2.1,
1.4,
1,
0.85,
0.7
],
"final_drive": 3.73,
"tire_diameter": 650
},
)
task_id = res.json()["task_id"]<?php
$res = file_get_contents("https://api.kit.forhosting.com/travel/speed-at-redline", false, stream_context_create([
"http" => [
"method" => "POST",
"header" => "Authorization: Bearer " . getenv("KIT_KEY") . "\r\nContent-Type: application/json",
"content" => '{"redline_rpm":6500,"gear_ratios":[3.5,2.1,1.4,1,0.85,0.7],"final_drive":3.73,"tire_diameter":650}',
],
]));
$task = json_decode($res, true);body := bytes.NewBufferString(`{"redline_rpm":6500,"gear_ratios":[3.5,2.1,1.4,1,0.85,0.7],"final_drive":3.73,"tire_diameter":650}`)
req, _ := http.NewRequest("POST", "https://api.kit.forhosting.com/travel/speed-at-redline", body)
req.Header.Set("Authorization", "Bearer "+os.Getenv("KIT_KEY"))
req.Header.Set("Content-Type", "application/json")
res, _ := http.DefaultClient.Do(req)Example request
{
"redline_rpm": 6500,
"gear_ratios": [
3.5,
2.1,
1.4,
1,
0.85,
0.7
],
"final_drive": 3.73,
"tire_diameter": 650
}Example response
{
"task_id": "tsk_a1b2c3d4e5f6a1b2c3d4e5f6",
"type": "travel.speed_at_redline",
"status": "queued",
"_links": {
"result": "/tasks/tsk_…/result"
}
}The API is asynchronous: the call returns a task_id immediately and the result arrives by webhook. Polling is capped at 1 req/s per task.
Pricing
Published price — no tokens, no invented credits. A failed task is never charged.
Errors
| HTTP | Code | Meaning |
|---|---|---|
401 | unauthorized | Missing or invalid API key. |
402 | insufficient_balance | Your balance doesn't cover the task price. |
404 | unknown_type | That task type doesn't exist. |
429 | rate_limited | Too many requests. Use the webhook instead of polling. |
Technical notes
The same pure arithmetic powers the free browser tool and the API path, so workshop notes and automation scripts always agree.
How redline road speed is derived for every gear
This capability evaluates that model for every entry in gear_ratios and returns a stable ordered table—gear one through gear N—plus the maximum theoretical top speed and which gear achieves it. Positive gear ratios, a positive final drive, a non-negative redline, and a positive tire diameter are required; empty ratio lists and non-finite values are rejected with invalid_input.
Input fields, units, and the response contract
Optional precision (integer zero through twelve, default six) controls decimal places on rounded fields for stable goldens and UI display. Send a JSON body with four required pieces: redline_rpm (engine redline in revolutions per minute, zero or greater), gear_ratios (a non-empty ordered array of strictly positive transmission ratios from first gear upward, at most twenty-four gears), final_drive (differential or axle ratio, strictly positive), and tire_diameter (overall rolling diameter, strictly positive). Optional tire_diameter_unit accepts mm (default), cm, m, or in so you can paste a measured diameter without unit mistakes. On success the response echoes redline and final drive, converts diameter to metres, gives circumference_m, and returns gear_count plus a gears array where each row has gear number, gear_ratio, overall_ratio, wheel_rpm, speed_kmh, speed_mph, and speed_ms. It also reports max_speed_gear with max_speed_kmh, max_speed_mph, and max_speed_ms for the tallest theoretical top speed at redline. Missing fields, empty or non-array gear lists, zero or negative ratios, unknown diameter units, and non-finite values fail with invalid_input and are not billed. Example: redline 6500, ratios [3.5, 2.1, 1.4, 1.0, 0.85, 0.7], final drive 3.73, and a 650 mm tire diameter produces a full six-gear redline speed table; lower gears show lower road speeds because overall_ratio is larger. Aliases such as redline, ratios, fd, and diameter help when integrating forms that use different labels.
Technical questions
How do I calculate speed at redline in each gear?
Provide redline_rpm, gear_ratios (ordered positive ratios), final_drive, and tire_diameter (with optional unit mm/cm/m/in). For each gear, road speed is (redline_rpm / (gear_ratio × final_drive) / 60) × π × diameter_in_metres, returned as km/h, mph, and m/s.
What is overall ratio and wheel RPM at redline?
Overall ratio is gear_ratio times final_drive. Wheel RPM at redline is redline_rpm divided by overall ratio—the rotational speed of the drive wheels before tire slip, evaluated at the tachometer limit.
What does the speed at redline per gear calculator cost?
The browser tool is free. API requests use prepaid KIT balance at $0.002 per successful call; invalid input is not billed.