Hi All, I need to replace the rear tyres on my 95 Ecotech V6 Commodore ute and would like o gear it up a bit. Factory is 205/65/15 and I recently replaced two and put on 215/65/15 and noticed no difference in cruising revs. I want to go to 225/70/15 on the rear but dont want to go to big and start effecting other things, like making it work too hard on take off etc. Ive worked out this would give a difference of about 6 to 7 km/hr at 100km/hr, and that doesnt seem much in the revs between those two. Anyone have any knowledge or experience of this! Anyone running these currently on their Commodore! Cheers for your thoughts.
morrisman1,
Jun 25, 5:06am
your speedo to revs ratio is not going to change, because the speedo only measures how fast the wheels are turning.
Why do you want to go larger again! I think that changing your speedo calibration by 7% is going to result in it under-reading significantly
skin1235,
Jun 25, 5:08am
bang a set of 205/90 commercials on it, they'll last forever and chjop the fuel bill by 20% too
40wav,
Jun 25, 5:10am
I would like more rubber on the ground because at the moment its is all over the place like an insane womans excrement (specially in the wet). I want larger circumference in an attempt to save a bit of fuel and cruise at 100km at slightly lower revs. Its really a commuter for me at the moment and I only occasionally tow or cart stuff.
morrisman1,
Jun 25, 5:18am
Remember that if you have more rubber on the road, there is less pressure on each square inch of contact area so the total grip may not change much at all. What you want is a better compound not a bigger tyre.
A wider tyre will be more susceptible to aquaplaning than a narrow one and in some circumstances may perform worse
llortmt,
Jun 25, 5:43am
Your science teacher may of told you that, but in the real world its never the case.
phillip.weston,
Jun 25, 5:46am
go for quality tyres over cheap nasty wider tyres. A decent 205 will outperform a crappy 225 all day long. I would be looking at other things which could be affecting traction and handling - bouncy shocks not holding firm to the road, saggy suspension bushes giving a squishy feeling etc. Wider tyres are more prone to aquaplaning too, so if you're driving in wet conditions a wider tyre will offer you less traction than a narrower tyre.
skin1235,
Jun 25, 5:54am
where did you dream up any validation in your comment, it could not be more wrong a narrower tyre will always give better adherence in the wet than a wide one
stevo2,
Jun 25, 1:16pm
The wider the tyre, the worse the roadholding will be on shingle and it will be noiser on the road. By going up in profile to a "70 series"you will get worse handling than you have at present due to more flex in the sidewalls. The difference between OE and what you propose is 7.5%, you should try to keep under 3%. Your overall diam will change from 647mm to 696mm and sidewall hieght from 133mm to 158mm. Your 215/65 gave you an extra 2% or 2kph at 100kph. Another option might be 225/60 for a 0.5% difference. Personally I would stick to 215/65 myself
40wav,
Jun 25, 1:57pm
All good comments, cheers guys. This is the sort of info I was hoping for. I'm having trouble finding a 225/70 anyway so might just go with the 215 65 again and know what I'm getting. Cheers all.
the-lada-dude,
Jun 25, 2:35pm
where in the devil did you dream that one up ! that's total crappolla !
smac,
Jun 25, 3:17pm
Tyres always bring out the absolute comments here.but there are no absolutes.
There's way more variables than just size. Sometimes wider tyres will have less traction than narrow in the wet.sometimes not. Sometimes not. Sometimes taller sidewall will mean worse handling than a lower profile, sometimes not.
It's everything to do with the make-up of the tyre and the suspension setup, way more so than the difference 10mm in width will make. As soon as somebody says "always" when talking about suspension or tyres, start ignoring them.
smac,
Jun 25, 3:18pm
Oh and as for the revs - is it manual or auto! This will effect the effect on revs.is a commy auto locked up at 100kph!
gedo1,
Jun 25, 3:59pm
While I can't offer any proveable knowledge about whether a narrow tyre gives more traction that a wider tyre I can offer this comment.I have noticed for motor rallies that the top level teams go to narrower tyres when the surface is known to be very loose, or particularly, when there is snow or icy conditions.Am I right you rally afficionados!
phillip.weston,
Jun 25, 4:27pm
Absolutely. Narrower tyres focus all their weight into a sharp line rather than a broad patch - much like ice skates! Same principle works with standing water, the narrower the tyre the quicker it displaces the water and sinks down gets traction with the surface underneath. Having said that a narrow tyre with no tread will perform worse than a brand new wider tyre with large channels to displace water.
the-lada-dude,
Jun 26, 12:15am
oh come on !there's way more to it than just saying that narrow tyres are better in gravel and snow than a wider tyreSMAC is on the case
alltorque350,
Jun 26, 12:44am
Why not get some 17 inch wheels from a ss or something and run 235/45/17
toot5,
Jun 26, 2:24am
just done that myself. handles better in the dry, and if i think it might let go in the wet i slow down. i get 400-450km per tank full, open road at 100kmh. even tho the tank is 63lt (read it somewhere) i only ever get round 50lt in when gauge is reading E
gedo1,
Jun 26, 4:35pm
And your vehemence is based on what evidence.!I tend to accept that money focussed rally teams may have some knowledge and considerable experience.
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