speedo not reading correct

[tigershark Lurker Find all posts View Profile Close tigershark]

Hello all. I have a problem with my speedo readings,has anyone had experience with their speedo reading being out after fitting larger tyres. I have recently installed a set of larger tyres to my pardo and found the the speedo reading is now out by 10ks { speedo reading 90 ks when actual speed is 100ks/hr}.

does anyone have a solution for this problem.


all comments and advise will be grealty appreciated.

[williade Avid PP Poster! Find all posts View Profile Close williade]

10% off is a big differnce. You must be running >33" tyres no?

Marks 4WD adapters make a speedo correction box that can be calibrated to larger tyres.
http://www.marks4wd.com/products/tyr...orrection.html

[glen_ep Addicted PP Member Find all posts View Profile Close glen_ep]

I've installed one of them, seen here:
http://www.pradopoint.com/showthread...l=1#post306087

[Brett1979 Avid PP Poster! Find all posts View Profile Close Brett1979]

10km/h difference? That's a lot. My speedo used to read 3-4km/h faster than what the car was doing at 100km/h and now it reads perfect. It's acceptable for the speedo to read slightly more than your actual speed with original sized tyres fitted, but not vice versa.

[Steve M Addicted PP Member Find all posts View Profile Close Steve M]

Both my 90's were out by about 3 to 4k eg 100 on speedo but actually doing 96/97 on GPS. When I put the A/T's on (bigger diameter, both vehicles) the speedo was spot on the dot to the GPS. My current 120 is about 1 to 2 k out the other way. speedo saying 100 GPS reading 101/102 running standard grandtreck tyres. Im keeping the standard size when I put muddies on the steel rims, main purpose is due to insurance. Not hard to work out if you need to knock a certian amount of klms off your reading if running bigger tyres. As mentioned in above posts, You certainly must be running some seriously bigger tyres to be out that much ?? Cheers Steve

[tigershark Lurker Find all posts View Profile Close tigershark]

Thanks for all the comments above. My tyre size is not that excessive { one size larger than standard. }. The speedo error must be due to another issue. I will set up a GPS and double check the error.

ps i was puzzled as well cause I did not think that the tyres would produce that much affect.

[Evo's 90 Lurker Find all posts View Profile Close Evo's 90]

Im running 285's and speedo reads 4-5km slow e.g GPS reads 100, speedo reads 95, this is consistent throughout the range. I think i will invest in a speedo correction at some point