Speedo readings at 70 mph?

[Alun Ivor]

I know this has been discussed before but on a run today my Chimi 4.6 suggested 70mph revs 2100/2150! Does that seem right because I feel like I'm going slower than speedo suggests. More like 2400 revs and that's more like 70mph??? It feels high geared does anyone know if you could have a high ratio dif specified! She's an awesome 2000 crossbolted model, pretty late! Thanks chaps. Cameras everywhere I got to be sure. Happy tivvin.

[SILICONEKID340HP]

Alun Ivor said:

I know this has been discussed before but on a run today my Chimi 4.6 suggested 70mph revs 2100/2150! Does that seem right because I feel like I'm going slower than speedo suggests. More like 2400 revs and that's more like 70mph??? It feels high geared does anyone know if you could have a high ratio dif specified! She's an awesome 2000 crossbolted model, pretty late! Thanks chaps. Cameras everywhere I got to be sure. Happy tivvin.

Do you have a sat nav ?

[Quietlybonkers]

My thought exactly, get the sat nav out. You could have different ratios, but most are doing around 2600 revs at 70 in 5th.

[Alun Ivor]

As the sat nav says. Im miles out then, jeez thought it was quick to 60! Thanks for that, best get a mate to give me various speed readings, thanks.

[Quietlybonkers]

If you ever lose the speedo on a journey (I have lost mine three times due to 100 amp fuse, faulty sender and mice), it is useful to know and easy to remember that 80mph in 5th is almost precisely 3000 rpm.

Of course you will never be doing this speed on the public road - seeing 3000 rpm in fifth is a warning to you that you are in gatso territory.

[ChimpofDarkness]

Quietlybonkers said:

If you ever lose the speedo on a journey (I have lost mine three times due to 100 amp fuse, faulty sender and mice), it is useful to know and easy to remember that 80mph in 5th is almost precisely 3000 rpm.

Of course you will never be doing this speed on the public road - seeing 3000 rpm in fifth is a warning to you that you are in gatso territory.

The best way to work out your speed from RPM is to just remember 2000rpm in a given gear is the gear number x 10:

Examples:

2000rpm in 1st = 10mph

2000rpm in 2nd = 20mph

2000rpm in 3rd = 30mph

2000rpm in 4th = 40mph

2000rpm in 5th = 50mph

Remembering this rule its easy to half the speed figure to give you the traditional MPH per 1000 rpm figure.

So 5th is 25mph per 1000rpm, or 3000rpm in 5th is actually nearer to a true 75mph (3 x 25) than 80mph

Well that's what I see when I compare the RPM displayed on my Canems software with the speed indicated by my TomTom sat nav.

In my opinion both my TomTom and Canems system are way more reliable than a TVR speedo & TVR rev counter.

Actually to be fair my TVR speedo is surprisingly accurate when checked against my TomTom, but my TVR rev counter definitely over reads by 200rpm.

[Alun Ivor]

Ok, great info chaps, thanks, bloody eck I've bin holding everyone up, my Tom Tom iPhone app, is also pretty accurate then, damn and blast, no wonder I've bin thinking of a good start and getting it to 60 in 4 secs easy, err not do sure now, presume the speedo can be re configured, think it's probably best to go by revs anyway, I've been so frustrated with the car, got it a year ago, thought it was good, soon realised everything was wrong with it, re built painted and repaired most of her now, at last I had a gentle run for 200 miles fri/sat, first time I've felt reliable. At times I've questioned my sanity.