Replacing Tyres and Speedometer Recalibration

[Heuer]

Many people consider changing the tyres on their cars to a lower profile than the standard 185's. Reasons vary from "it looks better" to "they cost less" the later being particularly true. The cost of a Michelin 185VR15 is about ?200 and Vredestein ?95, whereas a modern Pirelli P6000 205/65 VR15 is about ?55 fitted (avoid the P4000!). Given the tyres need to be changed every 5 years, regardless of mileage and wear, there is plenty of incentive to move to the newer and more available product.

If you go down this route you really should have the speedometer re-calibrated and you will need to do the following.

1. Disconnect the flexible drive from the speedometer
2. Make a cardboard 'arrow' and press on the end of the inner cable
3. Jack up one side of the car, put blocks on the other wheels, gears in neutral
4. Mark jacked rear tyre with chalk line or masking tape
5. Mark body with masking tape corresponding to the mark on the tyre
6. Turn driving wheel exactly 20 times while an assistant counts the number of complete turns the cardboard arrow makes, to the nearest 1/8 of a turn
7. Note make and size of tyre.

Speedograph Richfield http://www.speedograph-richfield.com/ will do the re-calibration for you (they operate a mail order service) and they will need:

a) The number of turns of inner cable for 20 turns of the drive wheel e.g. 13.75
b) Make and size of drive wheel tyre e.g. Yokohama TWI 205/65/15; dia. 647mm
c) Make and part number of speedometer e.g. Jaguar E-Type, SN .6322/09A; C25190
d) Is car fitted with a limited slip differential e.g. Yes

A tyre size calculator is available here: http://www.tyresave.co.uk/tyresize.html

The chronological age of any tyre can be found on the tyre sidewall by examining the characters following the symbol "DOT".

For tyres manufactured after the year 1999, the last four numbers identify the date of manufacture of the tyre to the nearest week. The first two of these four numbers identify the week of manufacture (which range from "01" to "52"). The last two numbers identify the year of manufacture (e.g., a tyre with the information "DOT XXXXXX2703? was manufactured in the 27th week of 2003). For tyres manufactured prior to the year 2000, three numbers instead of four indicate the date of manufacture. Also, during the early 1990?s, Continental added a triangle (◄) to the end of the character string to distinguish a tyre built in the 1990?s from previous decades. (e.g., a tyre with the information "DOT XXXXXX274◄? was manufactured in the 27th week of 1994).

Any tyres (including the spare) with a DOT number earlier than XXXXXX1603 should now be changed regardless of mileage - 5 years is the maximum age. You should also be aware in the event of an accident any tyres beyond their recommended expiration date, or of the incorrect speed rating, could be grounds for voiding your insurance claim - regardless of the speed you were traveling at the time. All E-Types must be fitted with V rated tyres (149mph). I have seen many cars fitted with H rated tyres (130 mph) but as Jaguar made great claim as to the E-Types maximum 150mph speed these are deemed 'incorrect'. Worth checking if you are buying a car - good grounds for reducing the price!

There is a pressure rating on the sidewall e.g. 44psi - this relates to the maximum pressure the tyre should be inflated to - not the running pressure (typically 32-34psi for an E-Type).

In the UK you can be fined and your licence endorsed for each tyre that fails to comply with tread, pressure, speed rating and age recommendations. It is no excuse to say "I only ever drive at a maximum of XX mph". Always pays to be nice to the Policeman if you are stopped for any reason!

David

[andyp]

Good post David. Many owners seem to be unaware of the difference even between a modern 185 70 and the original fitment 185 (which were about 675mm dia IIRC).

It varies from tyre to tyre but is generally over an inch. That makes for an over optomistic speedo which is better than getting fined for speeding but it is nice to know what speed you are really doing.

Andy

[andyp]

I see you have just covered most of the above in another post.

Better late than never.

Andy

[christopher storey]

I shall be very interested to see the statutory provisions ( either Act of Parliament or Statutory Instrument) which decrees that there is an age limit of 5 years on tyres . Perhaps someone can enlighten me

[Heuer]

"Road Vehicles (Construction & Use) Regulations 1986", specifically Reg.. 24 to 27. My layman's interpretation at least!

[christopher storey]

Thanks for that david. I shall look at them

[Heuer]

I found the table below in the Jag-Lovers archive detailing speedometer serial number, turns per mile, axle ratio and tyres. You will see Jaguar produced a wide range of speedos for various applications. The list is missing some TPM figures so if you have one of the listed speedometers and can provide the TPM figure (will be on the right hand side of the needle boss) I will include them.

Series 1 3.8 - All fitted with 6.40x15 RS5 tyres

Number; TPM; Diff; Calibration

SN 6322/00 ; 1216; 3.31; mph
SN 6322/01 ; 760; 3.31; kph
SN 6322/02 ; 760; 3.31; kph (Germany/Italy)
SN 6322/03 ;1312; 3.54; mph
SN 6322/04 ; 820; 3.54; kph
SN 6322/05 ; 820; 3.54; kph (Germany/Italy)
SN 6322/06 ;1086; 2.93 ; mph
SN 6322/07 ; 678; 2.93 ; kph
SN 6322/08 ; 678; 2.93 ; kph (Germany/Italy)
SN 6322/09 ;1120; 3.07; mph
SN 6322/10 ; 700; 3.07; kph
SN 6322/11 ; 700; 3.07; kph (Germany/Italy)

Series 1 4.2 - various tyres as specified

Number; TPM; Diff; Calibration;Tyre

SN 6322/00A; 1216; 3.31; mph; 6.40x15 RS5
SN 6322/02A; 760; 3.31; kph; 6.40x15 RS5
SN 6322/03A; xxxx; 3.31; mph; 6.40x15 SP41
SN 6322/05A; xxxx;3.54; kph; 6.40x15 SP41HR
SN 6322/09A; 1120; 3.07; mph; 6.40x15 RS5
SN 6322/11A; 700; 3.07; kph; 6.40x15 RS5
SN 6322/13; xxxx; 3.31; kph; 6.40x15 SP41
SN 6322/14; xxxx; 3.54; mph; 6.40x15 SP41HR
SN 6322/27; xxxx; 3.31; mph; 6.40x15 SP41HR
SN 6322/28; xxxx; 3.31; kph; 6.40x15 SP41HR
SN 6322/29; xxxx; 3.54; mph; 6.40x15
SN 6322/30; xxxx; 3.54; kph; 6.40x15
SN 6322/31; 1020; 2.88; mph; 6.40x15
SN 6322/32; 638; 2.88; kph; 6.40x15
SN 6322/33; xxxx; 3.07; mph; 6.40x15 SP41
SN 6322/34; xxxx; 3.07; kph; 6.40x15 SP41
SN 6322/35; xxxx; 3.31; mph; 185x15 SP41
SN 6322/36; xxxx; 3.31; kph; 185x15 SP41
SN 6322/37; xxxx; 3.54; mph; 185x15 SP41
SN 6322/38; xxxx; 3.54; kph; 185x15 SP41
SN 6322/39; xxxx; 2.88; mph; 185x15 SP41HR
SN 6322/40; xxxx; 2.88; kph; 185x15 SP41HR
SN 6322/41; xxxx; 3.07; mph; 185x15 SP41
SN 6322/42; xxxx; 3.07; kph; 185x15 SP41

If you want to work out the expected speed from different axle ratios, gearboxes and tyre sizes, 5Speeds.com has a neat downloadable calculator: http://www.5speeds.com/rpm.htm which is fun to play with! Another online calculator is available here: http://wahiduddin.net/calc/calc_speed_rpm.htm

If anyone fancies a DIY approach to speedometer calibration Mike Frank has an excellent write up on his site: http://www.westnet.com/~mfrank/Speedometer/Smiths.html

The SBM Society also has a good write up on speedo repair and calibration.
http://www.sterlingbritishmotoringsocie ... Repair.pdf


David

[iani]

Apologies for the lazarus post here:

SN 6322/08 ; 678; 2.93 ; kph (Germany/Italy)
SN 6322/09 ;1120; 3.07; mph

The speedo on my car says:
SN 6322/08 ;1120 and it's a UK car with mph

Are the records shown above in the post above incomplete? My speedo bounces around erratically, I intend changing the cable but am waiting until I swap the gearbox out. I have noticed that it is fairly consistently 10mph low at the highest point of its inflection though so I'm not convinced something isn't amiss twixt speedo & diff.

Ian

[Heuer]

Ian

There were 12 different speedometers listed in the Jaguar SPC:

Number; Diff; Calibration
SN 6322/00; 3.31; mph
SN 6322/01; 3.31; kph (not for Germany/Italy)
SN 6322/02; 3.31; kph (Germany/Italy)
SN 6322/03; 3.54; mph
SN 6322/04; 3.54; kph (not for Germany/Italy)
SN 6322/05; 3.54; kph (Germany/Italy)
SN 6322/06; 2.93; mph
SN 6322/07; 2.93; kph (not for Germany/Italy)
SN 6322/08; 2.93; kph (Germany/Italy)
SN 6322/09; 3.07; mph
SN 6322/10; 3.07; kph (not for Germany/Italy)
SN 6322/11; 3.07; kph (Germany/Italy)

Sounds as though your speedo has been recalibrated/restencilled to mph whilst retaining the original part number.

[iani]

Thanks David, I'll see how it behaves after I fit the S Type 'box & OD I'm having refurbed and then decide how to proceed, I'm running a HUD speedo on my phone for now due to number of ave speed restrictions around here now anyway.

Ian

[stevemanc]

We are changing our diff from 3.54 to 3.07 so the speedo will read 15% low. Can anyone suggest where I can get the speedo recalibrated or a new gear to achieve this. At present I have a SN 6322/03 ;1312 tpm; (3.54 diff) in mph speedo

What I will need is this speedo type SN 6322/09 ;1120 tpm; (3.07 diff) in mph

thanks Steve

[The Ultimate 3.8]

Try John Ostick

www.jdo1.com

Geoff

[Heuer]

From our Forum Knowledge Base:

Speedograph Richfield (instrument restoration/calibration): http://www.speedograph-richfield.com/
Speedy Cables (instrument repair, restoration, calibration): http://www.speedycables.com/index.html
Speedometer calibration: http://www.westnet.com/~mfrank/Speedometer/Smiths.html
John D Ostick (instrument repairs, re-calibration): http://www.jdo1.com/