R129 Tyre Widths

[l5foye]

I see that the recommended tyre size for a R129 (SL320) is 245 x 45 x 17. Would it be ok to fit 235 width? The reason for asking is that 235's seem a lot cheaper than 245's. Would the narrower width be immediately obvious? Out and out performance (speed) is not really a major factor.

 

[whitenemesis]

Tyre width will not determine speed....

Handling and grip YES!!

If that size is recommended then it is recommended for a reason.

 

[bolide]

Tyre width will not determine speed....

Handling and grip YES!!

If that size is recommended then it is recommended for a reason.

If you're suggesting that the narrower tyre would impair handling I disagree. It will probably make the car nicer to drive and give slightly better traction at the expense of a tiny bit of ultimate grip. Which l5foye is not worried about

I'd check the manual for recommended tyre sizes and look at what other models in the range use

A 225/50 17 is a better match than a 235/45 for rolling radius. You need to maintain the rolling radius within a couple of percent to keep the gearing (and speedo reading) the same as before

You can compare tyre sizes using my tyre size calculator
http://www.bolide.co.uk/actions/info.taf?page=tyresizecalculator

A 320 W124 runs on a 195/65 15 tyre, or a 205/60 15 tyre, and a R129 won't be appreciably quicker, so I'd say a 245 is overkill

Finally I'd check with your insurers to make sure they're happy

Nick Froome
www.w124.co.uk

 

[l5foye]

Thanks for the useful reply. I wonder if 1" less rolling radius would make much difference.
In case you wonder why I am looking at this, Goodyear Eagle G3-D3 in 235x45x17 cost £77.10, yet in 245x45x17 cost is £119. For such a small difference in width, the cost difference seems out of proportion.

 

[whitenemesis]

If you're suggesting that the narrower tyre would impair handling I disagree. It will probably make the car nicer to drive and give slightly better traction at the expense of a tiny bit of ultimate grip. Which l5foye is not worried about

No, I'm not suggesting that. I said tyre width would determine handling and grip, I did not imply any quality to those parameters.

Are grip and traction not the same? Or does grip refer to lateral forces (cornering?) and traction to straight line?

Personally I would consider them the same. The more rubber in contact with the road the more grip?

 

[television]

Personally I would consider them the same. The more rubber in contact with the road the more grip?

Sadly this is not always the case, under some conditions its the opposite

 

[whitenemesis]

Hence my ? at the end of the sentence

What conditions would reverse this asumption?

 

[l5foye]

1995 SLs would have come with 225 x 55 x 16 tyres. If 17" wheels are fitted,to keep the same rolling circumference, 245 x 45 x 17 tyres are required. Does anyone know if 1" less in rolling circumference would make a noticeable difference?

 

[bolide]

I would think one inch less circumference will make very little difference. What is it as a percentage?

You can easily change the aspect ratio to get a better match, hence my suggestion of 225/50 17

Nick Froome
www.w124.co.uk

 

[television]

I would think one inch less circumference will make very little difference. What is it as a percentage?

You can easily change the aspect ratio to get a better match, hence my suggestion of 225/50 17

Nick Froome
www.w124.co.uk

This is what I have had to do on my V70R to stop smashing wheels

 

[bolide]

It's a win-win situation, really: narrower tyres that ride better, make the car handle better, are more comfortable and are cheaper to buy!

Nick Froome
www.w124.co.uk

 

[Bazzle]

Thanks for the useful reply. I wonder if 1" less rolling radius would make much difference.
In case you wonder why I am looking at this, Goodyear Eagle G3-D3 in 235x45x17 cost £77.10, yet in 245x45x17 cost is £119. For such a small difference in width, the cost difference seems out of proportion.

You will need to fit the same diameter all around so ETC ABS tyre moniter etc dont give warnings or fail to work.

Also you wont get a ticket but may annoy other road users who have correctly reading speedos.

Best to stick to original diameter but vary width if thats what YOU wnat to do.

http://www.miata.net/garage/tirecalc.html

Bazzle

 

[Bazzle]

Thanks for the useful reply. I wonder if 1" less rolling radius would make much difference.
In case you wonder why I am looking at this, Goodyear Eagle G3-D3 in 235x45x17 cost £77.10, yet in 245x45x17 cost is £119. For such a small difference in width, the cost difference seems out of proportion.

You will need to fit the same diameter all around so ETC ABS tyre moniter etc dont give warnings or fail to work.

Also you wont get a ticket but may annoy other road users who have correctly reading speedos.

Best to stick to original diameter but vary width if thats what YOU want to do.

http://www.miata.net/garage/tirecalc.html

Bazzle