Tyre size & noise/ grip etc

[CDTi]

I just bought a set of 17" Starspokes for my CDTi from eBay and need to purchase new tyres.

I'm currently on 16" and have 215/55s fitted. I understand that the standard tyre for a 17" rim is 215/50.

I would like a slightly wider tyre if possible i.e. 225/50. The main reason for the extra width is to protect the alloys. The tyre will will be 10mm diameter bigger than the recommended. I don't think this will cause any problems with rubbing etc?

How about road noise and grip? The wider the tyre, the more road noise but would 10mm make much difference?

[bubs]

Off the top of my head I think mine has 225/45s fitted

[wuzerk]

Yes, the tyres should be 225X45 not 50. I personally found them to be too noisy and too harsh and reverted to 16" X215X55 which I think are a good compromise but you may well love them! I find that the rims are slightly more protected by the 16" tyres than they were with the 17".

[dln6376]

Standard fit for 17 inch rims are 225/45 however 215/50 can also be used which look better and offer a more comfortable ride.

Do plenty of research in order to find the quietest tyres available.

[versus]

215/55 R17 are ok too.

[Brabus]

Go for 225/50/17. These will be fine.served me well with no problems for the last few years.

[Duotone]

MG Rover changed their spec for the 17" alloys from 225 X 45 x R17 on the Mk1 Rover 75 to 215 X 50 x R17 on the facelift 75.

Dave T

[sikelsh]

Don't forget the 50 is percent of width, just stating in case you weren't aware.

Simon

[sjc]

215/50/17 is fine on the 75.Fills the arch gap better, offers a more compliant ride than 225/45/17 and with Barum Bravuris 2's fitted is probably as good as it gets.Unless your tyres have rim protectors, 225 isn't really going to offer anymore protection to the wheel than a 215.

[MG Tom]

I would stick with the Rover specified tyre size, but carefully check tyre ratings for noise first.

As correctly pointed out above (but I'll repeat for clarity!), the 2nd part of the tyre size is the height of sidewall as a % of the width. As a rule of thumb, going up 10mm in width means dropping 5% on the profile to keep the same rolling raidus. So the sidewall height would be the same on a 225/45 as a 215/50, therfore there would be no change in ride comfort whatsoever, assuming everything else is equal.

Industry guidelines recommend keeping rolling radius within 3% of the OEM specified, this is to ensure speedo accuracy is maintained within a reasonable tolerance, and to keep handling, unsprung weight etc within sensible limits.

Using a 225/45-17 instead of a 215/50-17 will result in a 2% difference in rolling radius, and remember that the sidewall height will be THE SAME, therefore so will the ride comfort.

I'd stick with the narrower width as specified by Rover, and concentrate efforts on finding a tyre with low noise levels and a rim-protection bead. :}

[CDTi]

Thanks for all the feedback, guys.

I'm a little reluctant to move away from the MGR tyre spec so I guess its either 215/50 or 225/45.

I like the look of a bigger wheel but I hate rims fitted with a rubber band, both from a comfort and aesthetic point of view.

225/45 have 17mm less sidewall than my current 16" tyres and I don't think I could live with that. 215/50 have over 10mm less and I think thats about as much as I would like to lose. One the other hand, 225/50's would have just 6mm less sidewall.

Decisions, decisions :)

[Greg]

Just fitted Dunlop SportMaxx RT on each corner (245/45/17). Very quiet tyre.

[CDTi]

Just when I thought I had decided on 215/50 :confused:

I have just noticed that the starspoke rim is 7.5, my current 16" forked alloy is 6.5 i.e. the starspoke alloy is 1 inch/25mm wider

So if I fit 215s, won't the starspokes "fill" the tires a lot more than the 6.5 rims?

Think I'll go with the 225/50s after all.

[Kedaha]

cdti, rim width has a relationship with tyre sidewall size (as a percentage of the tyre width) due to how tyres deform under lateral pressure and how deformable the sidewall is.

Yokohama suggest that a 215mm wide tyre is acceptable on anything from a 6" wide alloy to a 9" wide one, depending on the sidewall proportion.

Also, 225/50/17 is one of those rare tyre sizes that means that you're paying a ~40% premium over 225/45/17 for...what exactly? If you're worried about the alloys, buy a tyre with a tyre protector bead. Don't go messing with the only parts of your car that actually make contact with the road because of a gut feeling.

[James.uk]

Bear in mind the the larger the area of tyre on the road the softer your footprint. = you actually have less grip on the road surface... :o

Appearance will matter little if your choice of tyre leads to loss of control one day.... :o :o :o .. innit...

Please ignore appearances and make your choice based on your personal safety.. :}
...

[murphyv310]

Bear in mind the the larger the area of tyre on the road the softer your footprint. = you actually have less grip on the road surface... :o


Yes and of course this lack of grip is far far worse in the wet and other adverse conditions.

[CDTi]

Something that has puzzled me for a while is the claim that a narrower tyre gives better grip. I understand the theory behind this claim is that the narrower tyre has more pressure per sq inch.

While this may be the case, a wider tyre will obviously have more area to grip the road.

There is more physics at work with heat etc, have a read here: http://www.carbibles.com/tyre_bible_pg3.html

[Kedaha]

cdti, the link explains quite clearly that the total area of a tyre making contact with the road (contact patch) doesn't change as you change tyre size, only the shape of that contact patch changes.

I get the feeling that you aren't paying attention to any information that goes against your "wider = better" notion.

Also, wider = better dry grip, noisier(although the difference lessens as width grows), less comfortable(due to smaller sidewall), worse wet grip(due to wider contact patch aquaplaning).

[CDTi]

Thanks for all the input, lads.

Despite what my posts may have indicated here, I think I do understand the tyre width/profile/loading etc etc. Obviously the most important thing by far with tyres is safety and I would not take any chances with this.

Everything else is very much secondary to safety. How the wheels/tires look or the ride comfort due to side wall size doesn't really matter if you are dead because of fitting incorrect tires.

Bearing all this in mid, I have purchased Nankang AS-1 225/50 R17s with rim protection. These will give me an extra 5 mm sidewall over the recommended 215/50 so I will get a fuller tyre with a more comfortable ride (hopefully :}). Its all very marginal in any event and is unlikely to case any issues with safety.

My current tyres are Nankang NS2 and I'm very happy with them so hopefully the new AS-1s will give just as good service.

[Arctic]

225/45/17s bridgestone
http://i40.tinypic.com/28qfeh.jpg

[T16]

17's on a ZT ?

Boooo!!

leave those puny sized wheels to the grandads in the 75's!

:))


sorry, couldnt resist.

Still, I suppose your ride is better than my backbreaking one on Apex's

[CDTi]

225/45/17s bridgestone
http://i40.tinypic.com/28qfeh.jpgGlad I went for the 225s now after seeing that pic. Anything narrower wouldn't look right.

[CDTi]

New tyres now fitted: http://the75andztclub.co.uk/forum/showthread.php?p=1350610#post1350610