Within 10%?

[Mudnguts]

Question on speedo gears. Checked the chart and worked out with my stock ratios and stock tyres I should have a 29 tooth gear. Was in right place at right time and scored a set of 5 31X10.5 for $150 all new:D
Chart says to get speedo correct I need a 27 tooth gear. How far out will it be if I stay with the 29? how much difference can 2 teeth make?

[bonza]

with a stock setup the speedo reads about 8% more than what your are actually traveling at whereas the odometer is pretty well spot on. this is deliberately designed into a lot of vehicles in order to be safe with the proliferation of speed cameras

by going to 31" tyres and with stock speedo gear it will now be reading lower than what you are actually doing by about 5% - 6% ie when speedo reads 100 kph you will actually be doing 106 kph. just be mindful of speed cameras

[Nezzy]

I have 31 x 10.5 and haven't changed the ratio's. I agree with Bonza - my GPS reads about 106 - 107k/h when the needle is on 100.

[Mudnguts]

Cheers guys.:D Where can I buy a 27 tooth gear from? Found them on E-Bay but average delivery time to Kalgoorlie is 4 weeks from the states.

[wes]

I'm sure individual results vary - have you checked your speedo with a GPS?

I used to have 32" tyres with the stock 29 tooth speedo gear - checked speedo with a GPS and couldn't tell the difference.

[Mudnguts]

That looks good to me Wess. Can you please message me your details. Wife is in Perth and can probably pick it up:)

[wes]

Have you checked your speedo with a GPS over a range of different speeds?

The point I was trying to make was I didn't have to change the stock speedo gear when I increased the tyre size to 32".
I'm sure individual results will vary with different tyre manufacturers having slightly different sizes but you may not need to change your speedo gear.

[Mudnguts]

No I haven't checked it with a GPS...I don't own one... yet

[Squall]

I run 31" maxis bighorns and my speedo is about 15% out. I use my scangauge II to apply a 15% change to the digital readout on the Scangauge. The Jeep speedo still reads low but I just don't pay any attention to it. I had to use my GPS in the calibration process to get the calibration right.

Another option is Heal Tech (http://www.stu-offroad.com/engine/speedohealer/speedohealer-1.htm) a mod you can do to change the ratios as required. It's more expensive then the speedo gear option but if you plan to change your tyre size in the future it's an option to future proof the system.

I have also been thinking that if my speedo is out then my odometer will also be out which could be bad for the service interval not to mention navigation when you are using the odometer to work out how far down a track you need to turn off. Not an issue on weekend trips but the longer trips could make this a factor. But that said tyre pressure and a bunch of other variables also have to be factored into that equation.

[Electric Monk]

They gears are easy to get on Ebay, Quadratec or put up a wanted add here. They are pretty cheap and it takes 10 minutes to swap around, very easy, no real reason not to.

[mattlee]

Running 33's and haven't changed the speedo. Reads about 10% out. Your right about the odometer being out to. I have missed quite a few turns until I think "dickhead, add 10%", but then that's 10% less k's I have to talk about if I ever wanted to sell :p

[SKU113]

Wes I think you might need a new GPS!