Forums Forums Enthusiast Forums A - Z Autowirral Calculate your REAL top speed here....

As you may ot may not know, speedos are very inaccurate as you gain more speed, and, as a safety feature they overread

Not only that, but change your wheels and tyres and this also has an effect on your speedo reading.

Sooo, heres a top speed calculator - this uses your rpm, gear ratios, and wheel/tyre sizes to work out your genuine top speed and not an over reading speedos top speed.

There is however inaccuracy in your rev counter too (Though not as much as the speedo) and these also tend to over read. The only way to get a true rev readout is with a direct connection to ECU which reads on the rpm output wire - the apexi stuff is very good for this:



As a good example, my old 200, if you went by the speedo reading did 180+mph, however I hit the limiter in 5th a few time in it and this was set to 7200rpm - even though the rev counter read near 7500. Actual speed was 165mph with a reading of 7190 taken on an Apexi AVCR and Super AFC - this kind shows the inaccuracy in the speedo and rev counter.

Anyway, heres the Calculator - have fun

http://www.race-technology.com/WebPage2/Other/Utilities/GearCalculations/GearCalculation.html

what if you dont know the gear ratio's? anywhere we could find them out?

Erm, they may be available in a Haynes manual, failing that a search on the net for gearbox details of your car **should** turn something up

oke doke nice one, will have a go at searching for them on the net

Just worked mine out

At 8000rpm in 5th, she'll be doing 199.8mph

Rev limiter with the ECU I have is set at 8500

Just need a few more mods to get up there now

Blast from the past but the original link no longer works, so heres a new one

Top speed calculator.

As an example I entered my cars details:

1st 3.321
2nd 1.902
3rd 1.308
4th 1.000
5th 0.838
Rev 3.382

Max RPM at 7500 (Limiter is set at 8000)

1st 45mph
2nd 79mph
3rd 115mph
4th 151mph
5th 180mph
6th mph
rev 44mph

Gear ratios should be readily available for your car on the net, anyone else fancy posting their ratios, and results???

how true is that of yours stuey, whats ur indicated speed at 7500 in 4th? best to try 3rd as i dont think u wanna be doing 150+ on public roads.

Ill root out my handbook and give this a whirl later.

No idea lol, but mine reads just under 45mph at 2000rpm in 5th.

Ive only just got the speedo working as it should be since changing back to the original gearbox, but on the other gearbox which was all to pot, I had 7000rpm in 5th, and still pulling strong (On a nice long private road )a few weeks ago