20's on an EL.....speedo issues??

[cranners]

Hey everyone, considering buying 20's for my car but am concerned about my speedo being miles out and having to get it reset.....whats the story with this??

And also, how much am i looking at for a set of hub adaptors??

Thanks

Paul

[Kaddis]

Ringwood speedo's can make up a speedo correcter cog type thing, just tell them original size and new size overall.

[krisisdog]

Hub adaptors are about 250 new.

Whats the overall size of your new 20s?

[Kaddis]

The 20's have 35mm profile tyres, 225 front and 245 rear.

[BLCKED]

i want those wheels

buy my gts cranners

[cranners]

Haha do me a deal mate

[Commando]

Oi Paul what rubber did your XR8 rims have? You don't need to calibrate your speedo as it goes off the overall ROLLING DIAMETER of the tyre. So you can run 14s and high-profile rubber, or wrap a gilmer drive belt around some 22s, and as long as their rolling diameter is the same, you're laughing.

If the 245 tyres on the rears have a 35mm sidewall height, your overall rolling diameter would be 20" (~500mm) + (35mm x 2) = 570mm.
If the 245s are 245/35, the 35 means the sidewall height is 35% what the width of the tyre is... 20" (500mm) + (245 x 0.35 x 2) = 671mm

Standard example: 15" rims & 205/65 rubber: 15" (375mm) + (205 x 0.65 x 2) = 641mm

I'd say it's 245/35 rather than 35mm sidewall height. And assuming that, there's 30mm difference overall which will put your speedo out by 4-5% (in other words it'll be reading 95-96kph when you're actually doing 100, assuming it's calibrated spot on to start with).

30mm difference in rolling diameter is illegal (who gives a ****!) as the max allowed difference is 1" (25mm). I chewed out a pair of 205/65s on the wagon & replaced them with $22 205/60s which came to 20mm difference in rolling diameter (3% speedo difference). $22 tyres with tread FTW.

[Kilma]

FYI: The profile isn't a measurement of mm. It is dependant on the width of the tyre. For example, a 275/35/19 will have more sidewall than a 205/35/19.

There are heaps of diameter calculators that can be found on the net. Here is just the first one that came up in google.
http://www.1010tires.com/tiresizecalculator.asp

[sphell]

My speedo is dead accurate according to the radar thingy's on the Geelong fwy heading towards Melbourne. That is with 225/35 R20 tyres.

[Hybrid34]

As its to do with Diameter and so forth, can't you just get 20's that in total ad up to the same diameter overall (to the standard wheel)?
Bigger rim, smaller tyre..I thought thats how they did it so ur speedo doesn't go outta wack
- ASh

[Commando]

Correct