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[MV6Matt]

Couple of things.....

The handy links to the sites that can tell you about variance/accuracy (of speedo) when putting different size rubber on different wheels

And

Does anyone have experience of different sizes (front and rear).

I used to have 235/45/17 all round when on the Prefacelift MV6  rim. I'm now on 19" rims and have 235/35/19 all round.

I'm aware that some people on here have put as large as 275 on the rear.

I'm pondering whether to go 225/35/19 on the front and 255/35/19 on the rear.

Will that completely throw me out speedo wise?

let me know your thoughts folks.
Ta
Matthew

[M0T0RVATE]

Hi there

235/45/17 = 25.32" diameter.
235/35/19 = 25.47" dia.
These are closely similar.

255/35/19 = 26.02" dia. therefore larger diameter.
These tyres will make your speedo 1mph error at 50mph.
And 1.5mph error at 70mph.

Hope that helps...

[Kevin Wood]

What are you trying to achieve?

Tyres that wide will be cosmetic IMHO.

Also, bear in mind that if you have a mismatch of circumference between front and rear your ABS ECU will take exception (not sure how much of a mismatch would be required, though).

Kevin

[MV6Matt]

hi thanks Motorvate!
does speed work off front/back/both axles/
(Haven't a clue)

Will having 225 on front make a difference with 255 on rear?

Matthew

[MV6Matt]

What are you trying to achieve?

Tyres that wide will be cosmetic IMHO.

Also, bear in mind that if you have a mismatch of circumference between front and rear your ABS ECU will take exception (not sure how much of a mismatch would be required, though).

Kevin

Hi Kev,

Any idea how I find out about ABS mismatches?

cosmetics/aesthetics have played a large part in the transformation of my car to its present look. And very pleased I am too.

[M0T0RVATE]

hi thanks Motorvate!
does speed work off front/back/both axles/
(Haven't a clue)

Will having 225 on front make a difference with 255 on rear?

Matthew

Hi Matthew

These equations work on the rear wheels only for a rear wheel drive car like an Omega. 

[Rockhampton]

My Omega had mismatched tyres front and rear when I bought it - 205/50/16 on the Front, and 225/55/16 on the rear. Caused me no end of problems, including the ABS cutting in on a regular basis on even gentle braking, ABS warning light from time to time, MID fuel consumption not reading correctly, and the AR35 would never lock up, which was a big problem going downhill at speed as the car would speed up dramatically. Also got the engine electronics light occasionally with a gearbox code. Changed the incorrect front tyres, all of the above stopped at once, and none of the problems have reappeared over the last ten months, so would not recommend mixing tyre sizes between axles 

[jordan681]

I have got 225/35/18 on the front and 285/30/18 on the rear, and i have no problems what so ever, my speedo is approx 1mph out, and i have no problems with the ABS...

[MV6Matt]

..........quite a contrast between Rockhampton and Jordan then............... :-?

Looks as though your tyre choice was intentional though Jordan?

Thanks for the input and insight guys.
 
Matthew

[jordan681]

my tyre choice was intentional mate, though it was mainly trial and error...  I found even with 255 on the rear i was losing traction when i put my foot down...  since i have gone for a wider tyre, not only do they look the business by filling the massive arches, they really help with traction and cornering...

[2woody]

OK Matt, some tyre stuff here....

there are only two real facts of importance - these are the "static laden radius" or hub-height and the "wheel revs per mile". The first one controls how the suspension works whilst the second provides the gearing.

If you're wanting to change the tyres, then you must ensure that the hub height is the same, or it won't handle at all well. Then there's the gearing, or more specifically making sure that the front is the same as the rear or your ABS won't work properly.

the tyre sizes you have mentioned are as follows :-

235/45 x 17 817wrpm and 11.7 inch hub height
235/35 x 19 817wrpm and 12.0 inch hub height
225/35 x 19 820wrpm and 12.0 inch hub height
255/35 x 19 801wrpm and 12.2 inch hub height

In theory, moving from the "original" 235/35 x 17 to the 235/35 x 19 hasn't cost much in suspension geometry or gearing - 0.3 inches is large, but acceptable difference in hub height.

moving to your choice of 225/35 fornt and 255/35 rear will give you some problems at the rear. Firstly, the 0.5 inch hub height will be enough to affect the suspension geometry and secondly, the front and rear tyres will be revolving at different speeds which will afect the ABS, so I wouldn't do it. Speedo error will be 1.2% over what you already have. I have been trying to find you an acceptable alternative - 265/30 x 19 seems good at 820wrpm and 11.9 inch hub height, but you'd have to be careful about wheel width and arch clearance - they must be fitted to 9 or 10 inch rims.

You will notice that I haven't really referred to handling, which is the opposite of grip. By choosing tyre sizes as wide as you have, I'm assuming that handling isn't your no.1 priority. Handling is really driven by tyre wall deflection, as the wall gets smaller (stiffer), the tyre doesn't deform and there becomes less opportunity to explore the handling. Sure, you get more grip, but handling is almost always poorer. Best handling seems to be around 215-section, depending on which steering you have (possibly even 205-section)

hope this helps

(and yes, you do know me !)

[MV6Matt]

OK Matt, some tyre stuff here....

there are only two real facts of importance - these are the "static laden radius" or hub-height and the "wheel revs per mile". The first one controls how the suspension works whilst the second provides the gearing.

If you're wanting to change the tyres, then you must ensure that the hub height is the same, or it won't handle at all well. Then there's the gearing, or more specifically making sure that the front is the same as the rear or your ABS won't work properly.

the tyre sizes you have mentioned are as follows :-

235/45 x 17 817wrpm and 11.7 inch hub height
235/35 x 19 817wrpm and 12.0 inch hub height
225/35 x 19 820wrpm and 12.0 inch hub height
255/35 x 19 801wrpm and 12.2 inch hub height

In theory, moving from the "original" 235/35 x 17 to the 235/35 x 19 hasn't cost much in suspension geometry or gearing - 0.3 inches is large, but acceptable difference in hub height.

moving to your choice of 225/35 fornt and 255/35 rear will give you some problems at the rear. Firstly, the 0.5 inch hub height will be enough to affect the suspension geometry and secondly, the front and rear tyres will be revolving at different speeds which will afect the ABS, so I wouldn't do it. Speedo error will be 1.2% over what you already have. I have been trying to find you an acceptable alternative - 265/30 x 19 seems good at 820wrpm and 11.9 inch hub height, but you'd have to be careful about wheel width and arch clearance - they must be fitted to 9 or 10 inch rims.

You will notice that I haven't really referred to handling, which is the opposite of grip. By choosing tyre sizes as wide as you have, I'm assuming that handling isn't your no.1 priority. Handling is really driven by tyre wall deflection, as the wall gets smaller (stiffer), the tyre doesn't deform and there becomes less opportunity to explore the handling. Sure, you get more grip, but handling is almost always poorer. Best handling seems to be around 215-section, depending on which steering you have (possibly even 205-section)

hope this helps

(and yes, you do know me !)

Wow - this is getting complicated!
I had also come to the same conclusion about the 265/30 tyre but have 8.5 all round so dont want to risk putting that size on.

Thanks all for your help.
More pondering to do....................

and is it you Chris? :-?

Matthew

[2woody]

stuart granger