Confused (and ignorant!) about tyres

ktc1

My Mondeo Titanium has Goodyear Excellence tyres with a spec of 235/45/R17 . I thought the R17 was the diameter of the wheel before you put on the tyres. The actual alloy wheel measurement is 18"?

I'm looking to change the front tyres as they are wearing quite quickly (22k kilometeres on the clock, partly my fault as they've been underinflated). Based on a bit of googling I was thinking of going with either the Uniroyal Rainspot 2 or the Goodyear Eagle FS1 Asymetric. Does anybody have any opinions on these or other recommendations?

Do I have to get the same size specs as I already have? I read somewhere about someone who changed to 215/55/R16 and got a smoother and quieter ride. Plugging that number into a tyre size selector comparison program I found on the 'net showed that there would be no difference on the speedometer. Would all four tyres need to be the same spec?

Sorry if the questions are daft, it merely reflects my ignorance of the subject !

mik_da_man

That sounds strange the R17 is the rim size, So I reckon you have 17" wheels on the car unless you asked for a specific upgrade to 18" which didn't happen.
The mondeo standard are 16 or 17 anyway not 18's

As for the tyres the Goodyear Eagle F1 are an excellent tyre, I have put a set of them on my focus and they offer better grip and are quieter than the Conti's which were on it.
They should be a good improvment over the Excellence you have currently.

Check www.camskill.co.uk for prices on the F1's - I saved €400 on a set Vs Irish prices

Also I'd say stick with what size is on the car.

Mr.David

ktc1 wrote: »

My Mondeo Titanium has Goodyear Excellence tyres with a spec of 235/45/R17 . I thought the R17 was the diameter of the wheel before you put on the tyres. The actual alloy wheel measurement is 18"?

Yes, the 17 is the actual wheel rim diameter. If its on 17" with an 18" rim theres something seriously fubar'd!

I'm looking to change the front tyres as they are wearing quite quickly (22k kilometeres on the clock, partly my fault as they've been underinflated). Based on a bit of googling I was thinking of going with either the Uniroyal Rainspot 2 or the Goodyear Eagle FS1 Asymetric. Does anybody have any opinions on these or other recommendations?

Try Continental and Vredestein too.

Do I have to get the same size specs as I already have? I read somewhere about someone who changed to 215/55/R16 and got a smoother and quieter ride. Plugging that number into a tyre size selector comparison program I found on the 'net showed that there would be no difference on the speedometer. Would all four tyres need to be the same spec?

I'd stick with the same spec, yes. You have to stay with 17s anyway or else get new wheels. You could change tyre width to a certain extent without changing wheels and then change the aspect ratio (in your case 55) which would increase the sidewall on the tyre. But its messy - dont change unless you cannot put up with the current ride quality.

Sorry if the questions are daft, it merely reflects my ignorance of the subject !

HashSlinging

+1 on Vredestein

Also get the XL (extra load) tyres when possible, find them a lot more forgiving than normal ones.

Neilw

Just so you know the details of the sizing.

235 is the width of the tyre.
45 is a percentage of the width, 45% of 235 is the height of the sidewall
17 is the rim size, in your case 17" rims

I have goodyears on mine, the new asymetric and they are very good.

Rovi

I suspect the OP is confused about how a wheel diameter is measured.


OP: wheel diameter (17 inches, in your case) is measured across the inner seating area where the tyre bead seals (the "Rim diameter" dimension in this image):


I'm guessing you've measured the outside diameter of the wheel, which would indeed be 18 inches or so for a 17 inch wheel.

peasant

The diameter of the rim is measured on the inside of the rim where the tyre sits, not at the most outer edge of the side flange.

This means your (tape) measured 18" rims are in reality 17".

(It would be physically unpossible to fit 17" tyres to an 18" rim )


EDIT...Rovi stole my thunder

Mr.David

Also, fyi you can tune the ride and handling balance yourself by trying different tyre pressures that deviate (within reason) from the manufacturers recommendations.

Also, trying varying the pressures from front - rear will be significant. Its no harm to play around with it to get the ride comfort/handling attributes that suit you as it will have been tuned to suit the "average" driver anyway.

CJhaughey

Generally the taller the sidewall is the more flex there will be in the carcass of the tyre and the better it will be for comfort.
You could change to 225/50 17s and be around 2% different in the speedo reading, 3% is the maximum recommended.
Low profile tyres can be very uncomfortable on roads that are less than perfect.

ktc1

Lads, thank you one and all for the responses. I did indeed in my innocence measure the outside diameter. Will definitely look into the options suggested and stick with the same measurements. Thanks again.