Chapman’s Slimline Tonic: The Lotus 21: Anatomy of a FI Racing Car



“The 21 was introduced as a stop gap design to meet the regulations that came into force in 1961, placing a 1500 cc limit on F1 engines ”

The subject of regulation and regulation change remains relevant to the current day in FI and is a central element of Chapman’s design career as we shall demonstrate in a future article devoted to the twin chassis concept.

Within this context we take the opportunity of looking at a structural comparison between the human skeleton and that of the space frame chassis.

Both share the role of supporting a body and facilitating movement.


Figure 1.Image taken from the net. The skeleton has six major functions see text.

Subscribers might like to see also structured and integrated A&R articles on:-

  • Engines including Cosworth
  • Lotus chassis
  • Specific Lotus types
  • Aesthetics series

The Human Skeleton

It has six major functions:-

  1. Support
  2. Movement
  3. Protection
  4. Blood cell production
  5. Storage
  6. Endocrine regulation

The Lotus 21

The 21 was something of compromised design in that the preferred and potentially more competitive engine was not immediately available.

Despite this it was completed in six weeks.

It demonstrates Chapman’s flexibility and adaptability. Despite the constraints the 21 did reasonably well and raced in several categories.


Figure 2.Editors sketch of Lotus 21

From wiki: –

“The Lotus 21 was a Formula One racing car [1] designed by Colin Chapman. It was a mid-engine design using a tubular spaceframe structure skinned with fiberglass panels, of a more advanced build than seen in the Lotus 18. Powered by the 1.5-litre Coventry Climax FPF 4-cylinder engine, it used disc brakes all round.

Used by the works Lotus team and the privateer Rob Walker Racing Team in 1961, the 21 was the first works Lotus to win a Formula One Grand Prix, in the hands of Innes Ireland at the 1961 United States Grand Prix. (Previous victories were taken by Rob Walker’s team). Customer teams continued to use it up to 1965. It was soon rendered obsolete by the Lotus 24 and the monocoque Lotus 25 introduced for the 1962 Formula One season.”

Technical Specification from Taylor

Model Type 21
Year 1961-1962
Volume 11
Engine Coventry Climax FPF
C.C. 1495
Carburation Twin Weber
Power Output 155 bhp
Transmission ZF 5 speed
Chassis Multi tubular space frame
Body GRP
Front Suspension Fabricated upper rocker arm, lower wishbone, inboard cs-damper
Rear Suspension Reverse lower wishbone, top link, twin radius arms,cs-damper, anti- roll bar
Brakes F/R Girling outboard 10.5 inch /9.5 inch discs
Wheels F/R 15 X 5.5/16 X 6.5 inch magnesium “wobbly web”
Tyres F/R 5.00X15/6.00 X15
Length 141 inch
Width 60 inch
Height 28 inch
Wheelbase 89 inch
Track F/R 53/53 inch
Weight 990 lb

Lotus 21: Chassis Drawing

The chassis was tube type, clearly evident in our sketch are the hoop diaphragms constructed from tube and steel deployed in the cockpit [forming the dashboard] and at the rear to locate suspension etc.


Figure 3.Editors sketch drawing outlining the main structural elements of the space frame chassis cf with Lotus 25 monocoque.

The functions of the chassis are extremely well set out in Costin &Phipps and our subscribers are directed to this work.

We hope then our comparison with the human skeleton will be more evident.

Form and Function


“the 21 was designed with the same aerodynamic concepts and configuration as the 20, but with the intention of carrying the new Coventry Climax V8 engine to contest the incoming 1500cc formula 1…………to get the 21 mobile, Lotus redesigned it to accept the updated 4 cylinder 1497cc FPF unit….allied to ZF gearbox

The Lotus 21 of 1961 had a tubular frame but this was lower and less cigar shaped, it had a tided up body more so than predecessors .The driver’s seat was considerably more reclined .

In addition, the Coventry Climax engine was canted at 18 degrees to the vertical.


20170310122824_00001 Its perhaps worth noting the cross section of the Coventry climax engine and how this major component impacted on the overall width of the car and very much dictated cockpit width etc.

Learning Opportunities

Our learning /educational opportunities are intended to be challenging thought provoking and requiring additional research and/or analysis.

These opportunities are particularly designed for a museum/education centre location where visitors would be able to enjoy access to all the structured resources available in conjunction with any concurrent exhibition.

In this instance we suggest the following might be appropriate:-

  • What were the exact F1 regulations for 1961?
  • What controversy surrounded the announcement?
  • How did Chapman adapt ?
  • How does the Coventry Climax FPF compare with other manufacturers engines in 1961 series?

Exhibitions, Education and Economics

In the museum context the editors believe that commercial considerations are both necessary and complementary with its educational objectives.

For these reasons our suggested outline Business Plan includes provision for promoting products and services which share Chapman’s ideals of mechanical efficiency and sustainability. In addition we propose merchandising that explain and interprets the social and cultural context of Chapman’s designs in period. It’s suggested there will be catalogue for on line purchasing.

In particular we feel the following might be appropriate:-

  • The Lotus 21:Chapman gets key to the car
  • Lotus 21:The bare bones
  • Lotus 21 :structure and Framework
  • The Lotus 21: Anatomy dissected
  • Lotus 21: Constitution and Construction
  • Lotus :Cerebral Design


The Lotus 21 was possibly not chapman’s greatest success but as noted there might be explanations for this within the compromises that he was forced to adopt. Despite this the car did reasonably well; we believe it was runner up. Eleven examples were sold and this must be seen in context of times, and the very large contestant base for 1961.

The A&R attempts to analysis Lotus types and bench mark these in a continuum.Its hoped this brief study we have placed it in context whilst taking a look at constructional details and allowing designers to appreciate wider structural comparisons .

Appendix 1 :from wiki-contestants in 1961 FI World Championship

[provided to assist benchmarking the Lotus 21]

Entrant Constructor Chassis Engine Tyre Driver Rounds
West GermanyPorsche System Engineering Porsche 787
Porsche 547/6 1.5 F4 D SwedenJo Bonnier All
United StatesDan Gurney All
West GermanyHans Herrmann 1, 6
West GermanyScuderia Colonia LotusClimax 18 Climax FPF 1.5 L4 D SwitzerlandMichael May 1, 4, 6
West GermanyWolfgang Seidel 3, 5–7
BelgiumEquipe Nationale Belge EmerysonMaserati 61 Maserati Tipo 6 1.5 L4 D BelgiumOlivier Gendebien 1
BelgiumLucien Bianchi 1
LotusClimax 18 Climax FPF 1.5 L4 3
BelgiumWilly Mairesse 3
EmerysonClimax 61 BelgiumAndré Pilette 7
United StatesCamoradi International CooperClimax T53 Climax FPF 1.5 L4 D United StatesMasten Gregory 1–5
United KingdomIan Burgess 6
LotusClimax 18 2–5
United KingdomOwen Racing Organisation BRMClimax P48/57 Climax FPF 1.5 L4 D United KingdomTony Brooks All
United KingdomGraham Hill All
United KingdomR.R.C. Walker Racing Team LotusClimax 18
Climax FPF 1.5 L4 D United KingdomStirling Moss All
FergusonClimax P99 5
United KingdomJack Fairman 5
United KingdomYeoman Credit Racing Team CooperClimax T53 Climax FPF 1.5 L4 D United KingdomJohn Surtees All
United KingdomRoy Salvadori 4–8
United KingdomCooper Car Company CooperClimax T55
Climax FPF 1.5 L4
Climax FWMV 1.5 V8
D AustraliaJack Brabham All
New ZealandBruce McLaren All
United KingdomTeam Lotus LotusClimax 21
Climax FPF 1.5 L4 D United KingdomJim Clark All
United KingdomInnes Ireland 1, 3–8
United KingdomTrevor Taylor 2
BelgiumWilly Mairesse 4
United KingdomUDT Laystall Racing Team LotusClimax 18
Climax FPF 1.5 L4 D United KingdomCliff Allison 1, 3
United KingdomHenry Taylor 1, 3–5, 7
BelgiumLucien Bianchi 4–5
ArgentinaJuan Manuel Bordeu 4
United StatesMasten Gregory 7–8
BelgiumOlivier Gendebien 8
ItalyScuderia Ferrari SpA SEFAC Ferrari 156 Ferrari 178 1.5 V6
Ferrari 188 1.5 V6
D United StatesRichie Ginther 1–7
United StatesPhil Hill 1–7
West GermanyWolfgang von Trips 1–7
BelgiumOlivier Gendebien 3
BelgiumWilly Mairesse 6
MexicoRicardo Rodríguez 7
ItalyScuderia Serenissima CooperMaserati T51 Maserati Tipo 6 1.5 L4 D FranceMaurice Trintignant 1, 3–4, 6–7
De TomasoOSCA F1 OSCA 372 1.5 L4 ItalyGiorgio Scarlatti 4
De TomasoAlfa Romeo Alfa Romeo Giulietta 1.5 L4 ItalyNino Vaccarella 7
NetherlandsEcurie Maarsbergen Porsche 718 Porsche 547/3 1.5 F4 D NetherlandsCarel Godin de Beaufort 2–7
West GermanyHans Herrmann 2
United Kingdom H&L Motors CooperClimax T53 Climax FPF 1.5 L4 D United KingdomJackie Lewis 3–7
United KingdomTony Marsh LotusClimax 18 Climax FPF 1.5 L4 D United KingdomTony Marsh 3, 5–6
ItalyScuderia Centro Sud CooperMaserati T53
Maserati Tipo 6 1.5 L4 D ItalyLorenzo Bandini 3, 5–7
ItalyMassimo Natili 5, 7
FranceBernard Collomb CooperClimax T53 Climax FPF 1.5 L4 D FranceBernard Collomb 4, 6
United KingdomTim Parnell LotusClimax 18 Climax FPF 1.5 L4 D United KingdomTim Parnell 5, 7
United KingdomGerry Ashmore LotusClimax 18 Climax FPF 1.5 L4 D United KingdomGerry Ashmore 5–7
United States Louise Bryden-Brown[5] LotusClimax 18 Climax FPF 1.5 L4 D South AfricaTony Maggs 5–6
United KingdomGilby Engineering GilbyClimax 61 Climax FPF 1.5 L4 D United KingdomKeith Greene 5
Italy FISA
Italy Scuderia Sant’Ambroeus
Ferrari 156 Ferrari 178 1.5 V6 D ItalyGiancarlo Baghetti 4–5, 7
United KingdomJ.B. Naylor JBWClimax 59 Climax FPF 1.5 L4 D United KingdomBrian Naylor 7
United Kingdom Fred Tuck Cars CooperClimax T45 Climax FPF 1.5 L4 D United KingdomJack Fairman 7
Italy Scuderia Settecolli De TomasoOSCA F1 OSCA 372 1.5 L4 D ItalyRoberto Lippi 7
ItalyIsobele de Tomaso De TomasoAlfa Romeo F1 Alfa Romeo Giulietta 1.5 L4 D ItalyRoberto Bussinello 7
Italy Pescara Racing Team CooperMaserati T45 Maserati Tipo 6 1.5 L4 D ItalyRenato Pirocchi 7
ItalyGaetano Starrabba LotusMaserati 18 Maserati Tipo 6 1.5 L4 D ItalyGaetano Starrabba 7
United StatesHap Sharp CooperClimax T53 Climax FPF 1.5 L4 D United StatesHap Sharp 8
United States John M. Wyatt III CooperClimax T53 Climax FPF 1.5 L4 D United StatesRoger Penske 8
Canada J. Wheeler Autosport LotusClimax 18/21 Climax FPF 1.5 L4 D CanadaPeter Ryan 8
United StatesJim Hall LotusClimax 18 Climax FPF 1.5 L4 D United StatesJim Hall 8
United States J. Frank Harrison LotusClimax 18 Climax FPF 1.5 L4 D United StatesLloyd Ruby 8
United States Momo Corporation CooperClimax T53 Climax FPF 1.5 L4 D United StatesWalt Hansgen 8


The Lotus Book.Taylor.Coterie Press.

Theme Lotus.Nye.MRP.1986.

Stirling Moss 80_80.Russell.Flat out Productions.2009.


Please note the editors of the A&R attempt to give the broadest spectrum of references but not all are available for consultation in an article. However by noting their existence it may assist students in their research.

*Items in italics non A&R library books.