Where I live the country roads are full of large potholes, which the local council never get around to repairing

I have already replaced 2 alloys on one of my daughters cars (Ford Fiesta) which she bought 8 months ago, and am considering removing the alloys and replacing with steel wheels and decent wheel trims.

To avaoid damage to my alloys and suspension I'm thinking of fitting tyres with a bigger profile. At present I'm running on 275/40R20's fitted which were supplied with the car. I'm thinking of going to 275/60R20.

Has anyone here gone for a bigger profile? Will it dramatically affect the handling? Will I need to recalibrate the speedo?

Cheers guys

Jim

Not sure on the technical differences Jim, but have you thought about fitting 19" wheels. You could do that and as a by product get a larger profile tyre, without the need the recalibrate etc  ON THE WAY: BMW F21 M140i
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Ahhh BC thanks for that.

I may be a bit slow here but why would I need to swap to 19's? Can I just not fit tyres with a bigger sidewall to my 20's?

Jim

I'll be honest, I'm really not the one to comment, but I would imagine it's not as simple as just fitting bigger profile tyres.
Yes, you'd need 19" wheels, but I'm sure you could come out net net if you sold your 20's and bought some 19's.
Hopefully someone will be along to answer in a more technical manner.  ON THE WAY: BMW F21 M140i
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I would go for the 19's - I use them in winter and keep being tempted to leave them on but I do like the hse 20's

Changing profile sizes may invalidate insurance and warranty so be careful  Wanted a Series 2 LR since childhood but previously owned MY16 Disco Sport HSE TD4 Auto, MY13 RR Sport Black Edition TDV6 Auto, MY10 RR Sport HSE TDV6 Auto, 2007 Freelander 1 Freestyle TD4 Soft Top, 2009 Freelander 2 GS TD4 Auto, 2007 Freelander 2 GS TD4, 2004 Disco 2 Metropolis Auto, 2002 Disco 2 GS, 2000 Freelander 1 SE TD4 SW

Still hoping for a S2 one day!

If you drop the rim size down to 19 you gain extra sidewall due to the standard size of tyre fitted. The overall diameter of the wheel (tyre + rim) is the same regardless of whether you use the 19 or 20 inch rim as the reduced sidewall on the 20 keeps the rolling diameter the same as the 19 inch wheel. (also why the cars come with a 19 inch spare wheel).

If you run the tyres specified in the handbook then there is no need to re-callibrate your speedometer

So Simon, Jim can't just stick on bigger profiles on his 20's  ON THE WAY: BMW F21 M140i
MERCEDES GL350 - Metallic Navy Blue w/Grey interior

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@ Bean

There is nothing to stop Jim from putting bigger profile tyres onto his existing 20 inch rims, other than the fact that he would be running non-standard tyres (which potentially could have insurance and warranty issues - for sure you would need to declare the tyres to your insurer otherwise they would try to use it to wriggle out of any liability in the case of a claim) which would mean that either he accepts that his speedometer is no longer accurate or has it re-calibrated

i.e. with larger profile tyres comes a larger rolling diameter and as the speedometer is calibrated for a specific rolling diameter (used with standard rims and tyres as defined in the handbook) the speedo will under-read the actual speed. Not by much, but probably enough to get you 3 points if you're unlucky.

The safer/easier route is to get a good set of 19's and sell the 20's - you would probably break even

Thanks, wheels/tyres etc not a strong point of mine, thanks for the explanations. ON THE WAY: BMW F21 M140i
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GOING: BMW F31 335D MSport+ xDrive Touring
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GONE: BMW F10 520D MSport - Carbon Black
GONE:MY12 RRS SDV6 HSE Sumatra/Ivory/Grand Black Privacy glass

Guys

Thanks for your replies.

It would seem that the way forward would be to get a set of 19" rims and fit a tyre with a bigger profile. I had been considering buying another set of rims to fit a set of winter tyres on anyway.

I'll have a look at whats going on over on e-bay.

Jim

You need 255/50R19 Profile tyres on the sport - Disco have 55 profile so check before you buy  Wanted a Series 2 LR since childhood but previously owned MY16 Disco Sport HSE TD4 Auto, MY13 RR Sport Black Edition TDV6 Auto, MY10 RR Sport HSE TDV6 Auto, 2007 Freelander 1 Freestyle TD4 Soft Top, 2009 Freelander 2 GS TD4 Auto, 2007 Freelander 2 GS TD4, 2004 Disco 2 Metropolis Auto, 2002 Disco 2 GS, 2000 Freelander 1 SE TD4 SW

Still hoping for a S2 one day!

I had 255-55 profile on my 19" winter wheels and it was fine as recommended by AJS 4x4 site sponsor who i bought my tyres off, or was it just a sales tac tic just because he didn't have any 50 profile tyres in stock Either way they were great and gave great protection to the rims.

Check this site to see the difference in circumferences.

http://www.alloywheels.com/Tyre_Calculator

1. Make a claim against the Highway Authority for the damaged wheels/tyres. This is likely to be Bedfordshire County Council if you live in Bedfordshire. Easy to check though. You might get the cost of the damaged items refunded to you. Look on their website and/or phone them up and ask for the relevant form. If they haven't inspected the road within the correct time frame then they're liable for damage caused by unrepaired potholes.

2. Tyre sizes need to be matched in terms of rim size, tread width and aspect ratio (sidewall depth). A 275/40/20 is roughly equivalent to a 255/50/19. The code is as follows: tread width/aspect ratio/rim size.

The tread width is in mm, the aspect ratio is a % of the tread width and the rim size is in in inches. Nice mix of units, but that's the way it is. The relationship of tyre tread width, aspect ratio and rim diameter is important because it gives, roughly, the rolling circumference of the tyre as fitted to the car (I say roughly because detailed differences in tyre construction between manufacturers can give diffferent rolling circumferences for the same tyre size). Any change in rolling circumference will change the speedo reading and the overall drivetrain gearing. The former is noticeable, the latter less so.

Check your manual for the allowed sizes. My 2008 RRS manual shows 255/55/19 for winter tyre size even though the summer sizes are 255/50/19 or 275/40/20. The 2012 manual, I think, has 255/50/19 for winter tyres.

A 255/55/19 has a sidewall of 140.25mm, a 275/40/20 has a sidewall of 110mm. That's a big difference.

You should note that the 255/55/19 has a larger diameter over the 275/40/20 of about 5% (728mm (275/40) vs 763mm (255/55)). This lengthens the gearing and alters the speedo reading. Mine is pretty close to the speed given by a GPS though so not enough to be a worry.

You should also note that deepening the sidewall will "soften" the handling slightly but not enough to a worry and it can be resolved by tweaking the tyre pressures (adding a couple of psi to the front tyres to reduce the time it takes for them to "bite" will help to improve the steering response). This is a personal thing though and down to the driver to figure out (and be responsible for - get it wrong and the back end might be a little "playful" resulting in uncomfortable/nasty handling). 2012 SDV6 - it's missing a couple of cylinders
2008 TDV8 - it was a labour of love and is much missed

Quote:

Check your manual for the allowed sizes. My 2008 RRS manual shows 255/55/19 for winter tyre size even though the summer sizes are 255/50/19 or 275/40/20. The 2012 manual, I think, has 255/50/19 for winter tyres.

LR issued a revision as the handbook was wrong

Click image to enlarge

 Wanted a Series 2 LR since childhood but previously owned MY16 Disco Sport HSE TD4 Auto, MY13 RR Sport Black Edition TDV6 Auto, MY10 RR Sport HSE TDV6 Auto, 2007 Freelander 1 Freestyle TD4 Soft Top, 2009 Freelander 2 GS TD4 Auto, 2007 Freelander 2 GS TD4, 2004 Disco 2 Metropolis Auto, 2002 Disco 2 GS, 2000 Freelander 1 SE TD4 SW

Still hoping for a S2 one day!