GURPS VEHICLES 2nd ed and real world numbers

[hal]

Hi All,
I'm guessing that many of you won't really care about this thread, but those who still use GURPS VEHICLES 2nd edition to build vehicles for use in their campaigns, I thought I'd mention the research that I went through before felt comfortable with building vehicles for my science fiction campaign world.

First, here is a handy website that you can read for formulas on how to convert Engines with "liters" or motorcycles measured in cubic centimeters engines - for use with your design systems.

In a nutshell? Divide Cubic Centimeters of engine by 15 to get the upper end of horsepower for your vehicle, and divide Cubic Centimeters of Engine by 17 to get the lower limit of the engine's horsepower. The real engine horsepower will be somewhere between those two numbers.

An alternative formula for estimating the Horsepower value of an engine is to multiply RPM x Torque and divide that by 5252 (at least, for Motorcycles).

Now - some of the "optional rules" that are GOOD for using with your campaign, are spread throughout the following books:

GURPS VEHICLES 2nd edition
GURPS WW II Core Book
GURPS VEHICLES LITE

GURPS WW II core book will give you rules for fuel consumption that is a little better balanced out when compared against real world fuel consumption.

Vehicles Lite states that if top speed exceeds 121 MPH for motorcycles, to recalculate top speed as square root of top speed x 11 (other values for cars).

As for my research, the 0 to 60 values for cars were often badly off from what real world values end up being. My "Fix" was to simply use power in Kw divided by Mass in tons. Here is another Link that may be of interest...

[hal]

So, let's look at an actual motorcycle just for giggles:

https://www.cycleworld.com/story/mot...r-review-2022/

There, we have the following information:

79.9 lb. ft. @ 9300 RPM.

79.9 x 9300/5252 = 141.48 HP

The article suggests that the HP is 155.4 HP

So, now we can try to build this motorcycle using GURPS VEHICLES 2nd edition rules. Because GURPS VEHICLES LITE suggests that a motorcycle from 1999 has a mix of TL 7 and TL 8 technology, I think it is safe to assume that this motorcycle should largely be TL 8.

Our energy in KW should be between 141.48 * .746 or 105.50 Kw and 155.4 * .746 or 115.88 Kw

[Fred Brackin]

Originally Posted by hal

As for my research, the 0 to 60 values for cars were often badly off from what real world values end up being. ...

I remember discussing this with David Pulver over several messages bt we never came up with anything that would reduce to a simple bit of text.

In a parallel matter, trying to accurately model human acceleration is frustratingly complex and the results are usually unsatisfactory.

[hal]

Originally Posted by Fred Brackin

I remember discussing this with David Pulver over several messages bt we never came up with anything that would reduce to a simple bit of text.

In a parallel matter, trying to accurately model human acceleration is frustratingly complex and the results are usually unsatisfactory.

I saw that thread, and the comments about the 0 to 60 calculation from that link in my first post in this thread. Thing is, if the same formula doesn't work equally well with human or animal power, but works reasonably well with motorcycles and cars, I'm all for the one formula that only works for cars and motorcycles.

Tomorrow, I will continue the process of fleshing out the motorcycle I linked to, just to see if it can be done. Using the torque x rpm/5252 value, along with calculating engine volume based on piston diameter and stroke length means that I can describe a fictional motorcycle in quasi-familiar terminology.

Now that I know to subtract payload weight from net weight, I no longer wince when I try to build a reasonable motorcycle that, for example, uses CHOO2 from Cyberpunk 2020 or Cyberpunk 2077.

[hal]

OK, what follows was built using a 141 Horsepower (110 Kw) engine instead of the 155.4 Horsepower engine. The reason for this is because were I to use the higher Horsepower rating, the top speed would be even higher.

TL8 2022 BMW S 1000 R Motorcycle

An attempt to use real world stats to build a GURPS VEHICLES 2nd edition motorcycle.

Crew: 1 total. 1 crew station covering vehicle control (ground).

Subassemblies: Vehicle +1, Body +1, Wheels -1.

P&P: 430-kWs lead acid battery, 110-kW HP gasoline engine (no access space), 110-kW wheeled drivetrain (no access space).

Fuel: 4.4 gal gasoline (fire 11), 4.4 gal standard fuel tank (fire modifier 1).

Occ: cycle crew station Cargo:

Statistics
Size: [LxWxH] 7’x2.5’x4’ Payload: 226 lbs. Lwt.: 621 lbs.
Volume: 16.5 cf Maint.: 194 hours (0.496 mh/day) Price: $10,663

HT: 12 HP: 30 [Body], 6 each [2xWheels].

Wheeled Ground Performance: Speed Factor 16, Top Speed 300 mph, gAccel 15 mph/s, gDecel 15 mph/s, gMR 1.5, gSR 2, Ground Pressure 3,878 lbs./sf, Off Road Speed 50 mph.


Design Notes:
TL8 light frame expensive materials [Vehicle].
Operating Duration: 1 H.
Payload Cost: $6.6
Vehicle Features: mechanical controls, no streamlining.
Wheels: quantity 2, standard, improved brakes.
Volume: 15 cf [Body], 1.5 cf [Wheels].
Area: 40 sf [Body], 8 sf [Wheels].


Addendum notes (provided by hand - not part of the GURPS VEHICLE BUILDER supplied Stats)

Revised Top Speed per GURPS VEHICLES LITE: sqrt(300) x 11 = 190 mph
Patrol Speed per GURPS WW II Core rules: .3 x 190 = 57
Revised Fuel usage: 4 x 1 hour = 4 hours
Miles Per gallon = 4 x 57 / 4.4 gallon tank or 51 miles per gallon.
gAccel = Sqrt(110/.3105) or 18.82 mph
zero to 60 value: 3.18 seconds.

Curb weight = 621-200 (weight of driver) or 421 lbs.


Conclusion: I had to google top speed for this motorcycle, and one site lists a top speed of 160 mph. This shows up as being 190 mph (not too bad, but better than the listed 300 MPH without the GURPS VEHICLE LITE formula). The extended fuel duration of a x4 multiplier due to moving at 30% top speed makes the MPG value come closer to the mark of 45 MPG instead of the 300 miles/4.4 or 68 MPG using the original GURPS rules.

Price ends up being about 1/2 that of the suggested retail value.

[Sam Baughn]

Is TL8 the right choice for a modern-day design? When GURPS vehicles was written TL7 was 'modern day' and TL8 was near-future sci-fi. 4th edition shifted the start of TL8 back to the eighties, so 5th ed. TL8 is not the same as 3rd ed. TL8. Although technology has advanced a bit since the publication of GURPS vehicles, I'd still say we're on the borderline between 3rd ed. TL7 and TL8.

[hal]

Originally Posted by Sam Baughn

Is TL8 the right choice for a modern-day design? When GURPS vehicles was written TL7 was 'modern day' and TL8 was near-future sci-fi. 4th edition shifted the start of TL8 back to the eighties, so 5th ed. TL8 is not the same as 3rd ed. TL8. Although technology has advanced a bit since the publication of GURPS vehicles, I'd still say we're on the borderline between 3rd ed. TL7 and TL8.

The fun part is, the answer lies within GURPS VEHICLES LITE. They had a category for equipment that was "Improved Gasoline Engine". When I started to look that up, I found inside of the book that it was simply the next tech level up (aka TL 8 Gasoline engines). So, 20 years later, the question is whether or not we're more into TL 8 than we were in 2002. If yes, then we should be using most of the TL 8 categories instead of a mix of TL 7 and 8.


From VEHICLES LITE pg 17:

"Unless otherwise noted, assume all components are TL7. In a few cases, early TL8 components have been made available (as “improved” systems) for increased cost."

[Fred Brackin]

Originally Posted by Sam Baughn

Is TL8 the right choice for a modern-day design? When GURPS vehicles was written TL7 was 'modern day' and TL8 was near-future sci-fi. 4th edition shifted the start of TL8 back to the eighties, so 5th ed. TL8 is not the same as 3rd ed. TL8. Although technology has advanced a bit since the publication of GURPS vehicles, I'd still say we're on the borderline between 3rd ed. TL7 and TL8.

By te 3e rules we've been in TL8 for more than 20 years. Kromm even announced it in Pyramid in 2001.

[maximara]

Originally Posted by Sam Baughn

Is TL8 the right choice for a modern-day design? When GURPS vehicles was written TL7 was 'modern day' and TL8 was near-future sci-fi. 4th edition shifted the start of TL8 back to the eighties, so 5th ed. TL8 is not the same as 3rd ed. TL8. Although technology has advanced a bit since the publication of GURPS vehicles, I'd still say we're on the borderline between 3rd ed. TL7 and TL8.

Classic (3ed) GURPS seemed to have more obsessed with when a TL started than what was actually in it: "GURPS rules lawyers please take note: we are now officially at tech level 8. Okay -- technically, we are not quite there yet. According to Basic Set, TL8 officially starts at the stroke of midnight on January 1, 2001 (see p. B185). However, those of you who are planning to submit manuscripts to SJ Games should note that it is now kosher to include TL8 technologies, characters with TL8 skills, and so on in material set in the present day. (In a few years, only outdated technologies and the skills of old fogies like me should be treated as TL7.)" — Tech level 8 Then and Now

Way back on 08-29-2005 David L Pulver gave this little quick and dirty conversion chart:

upper half 3eTL7 = TL8
3eTL8 = 4eTL9
3eTL9 = 4eTL10 and some TL9-10^
3eTL10 = 4eTL11 and some TL10-11^
3eTL11 = 4eTL11 and some TL10-11^
3eTL12 = 4eTL11 and TL10-11^
3eTL13 = 4eTL11 and TL11^
3eTL14 = 4eTL12 and some TL11-12^
3eTL15 = 4eTL12^
3eTL16 = 4eTL12^

[WingedKagouti]

Originally Posted by hal

OK, what follows was built using a 141 Horsepower (110 Kw) engine instead of the 155.4 Horsepower engine. The reason for this is because were I to use the higher Horsepower rating, the top speed would be even higher.

TL8 2022 BMW S 1000 R Motorcycle

An attempt to use real world stats to build a GURPS VEHICLES 2nd edition motorcycle.

Not to detract from your point about the formulas in V2E being silly, but the official stats for that particular bike are a bit different.

It's a 165 HP (121 kW) engine and the wet weight is either 438.7 lbs (standard version) or 427.7 lbs (carbon fittings). Wet weight includes a full fuel tank as well as lubrication and hydraulic liquids, dry weight is only a concept for non-road purposes. The average rider for performance measurements is considered to weigh somewhere between 160 and 180 lbs.

Those numbers will obviously still make the ingame version faster than anything real. Of course, if you just changed the mph label in the V2E result to km/h you'd have something closer to the actual top speed (257 km/h = 160 mph).