Jump to content
SAU Community

Recommended Posts

spaz moment, the 235/40 compared to the 45, this will increase spedo reading yes?

i know only by likr 3-4% but i have a 10% speedo error (always reading to high) anyway

Edited by GH05T

The higher profile will make the car go faster than the speedo is reading, so if your speedo currently reads higher than you're actually doing, it will correct this somewhat...but rather negligible as you say.

Let's not use confusing terms that could be interpreted differently.

Speedo runs off the gearbox output shaft, so it takes its reading based solely on engine rpm and the gear selected, irrespective of what's happening at the tyres and diff. Therefore, 2000rpm in 5th will always make the speedo read the same speed (say ~80km/h) no matter what size tyres or diff ratio you have.

Increase your tyre diameter and the vehicle physically goes faster but the speedo reading stays the same. So if your speedo reads high, putting on larger tyres will make it more accurate. If it reads low, putting on larger tyres will make it more inaccurate.

Manufacturers usually calibrate the speedo to the standard tyre diameter and make it read a little bit high so that they aren't responsible for people's speeding fines.

  • 2 weeks later...
  • 2 weeks later...

received the tires, unfortunately i stuffed up the tire speed calculation (yep did it backwards in my head....derp).
my speedo error reads to high already, the new diameter for my wheels means it will now read higher again not lower so they really dont suit which sucks.

still unfitted
which sucks cos the tread pattern looks so nice

re listed in sa :P

http://www.sau.com.au/forums/index.php?app=forums&module=post&section=post&do=new_post&f=12


Edited by GH05T

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now


  • Latest Posts

    • For once a good news  It needed to be adjusted by that one nut and it is ok  At least something was easy But thank you very much for help. But a small issue is now(gearbox) that when the car is stationary you can hear "clinking" from gearbox so some of the bearing is 100% not that happy... It goes away once you push clutch so it is 100% gearbox. Just if you know...what that bearing could be? It sounding like "spun bearing" but it is louder.
    • Yeah, that's fine**. But the numbers you came up with are just wrong. Try it for yourself. Put in any voltage from the possible range and see what result you get. You get nonsense. ** When I say "fine", I mean, it's still shit. The very simple linear formula (slope & intercept) is shit for a sensor with a non-linear response. This is the curve, from your data above. Look at the CURVE! It's only really linear between about 30 and 90 °C. And if you used only that range to define a curve, it would be great. But you would go more and more wrong as you went to higher temps. And that is why the slope & intercept found when you use 50 and 150 as the end points is so bad halfway between those points. The real curve is a long way below the linear curve which just zips straight between the end points, like this one. You could probably use the same slope and a lower intercept, to move that straight line down, and spread the error out. But you would 5-10°C off in a lot of places. You'd need to say what temperature range you really wanted to be most right - say, 100 to 130, and plop the line closest to teh real curve in that region, which would make it quite wrong down at the lower temperatures. Let me just say that HPTuners are not being realistic in only allowing for a simple linear curve. 
    • I feel I should re-iterate. The above picture is the only option available in the software and the blurb from HP Tuners I quoted earlier is the only way to add data to it and that's the description they offer as to how to figure it out. The only fields available is the blank box after (Input/ ) and the box right before = Output. Those are the only numbers that can be entered.
    • No, your formula is arse backwards. Mine is totally different to yours, and is the one I said was bang on at 50 and 150. I'll put your data into Excel (actually it already is, chart it and fit a linear fit to it, aiming to make it evenly wrong across the whole span. But not now. Other things to do first.
    • God damnit. The only option I actually have in the software is the one that is screenshotted. I am glad that I at least got it right... for those two points. Would it actually change anything if I chose/used 80C and 120C as the two points instead? My brain wants to imagine the formula put into HPtuners would be the same equation, otherwise none of this makes sense to me, unless: 1) The formula you put into VCM Scanner/HPTuners is always linear 2) The two points/input pairs are only arbitrary to choose (as the documentation implies) IF the actual scaling of the sensor is linear. then 3) If the scaling is not linear, the two points you choose matter a great deal, because the formula will draw a line between those two points only.
×
×
  • Create New...