Going up a size on the tyre profile

[Dino D]

Bit of a tyre size dilemma.
I run 4 x 7,5j 17inch rims all around for road and have for years been shod with 235/40/17 tyres.

This size is no longer supported by decent brands - only 225/45 or 235/45 available in Michelin or Goodyear.
Not even Hancook do it anymore (I’ve got Ventus v12 currently).

Now 225/45 is too skinny for the rear - as it is the 235 is pretty skinny.

I believe one can’t properly mount a 245 on a 7,5j rim (need at a least 8j for that).

So I’m considering 235/45.

Now I’ve been here before ‘partially’.

i bought a pair of Hancook ventus in 235/45 to go on the rear along with 235/40 on the front.
It had a nice meaty look, not over top at all but a little less low profile.

there was an issue. The size (height/radius) difference between the taller rears and shorter front caused funny handling traits- pulling to one side when accelerating and a bit unsettled when coming off the power -a lot like when the tyres are way overinflated or you running the space saver.

so I took them off but still have them.

I also had this sensation when running 225/35/18 on the front and 245/40/17 on the rear when I was waiting for 18inch tyres once.
Clearly a big difference in radius between front and rear causes weird handling.

On track I run 245/40 AD08Rs track tyre all around and no issue (apart form them being stiff tyres).

so it seems as long as the radius is matched front to back, there should be no issue.

I’m just a little hesitant to go ahead and order 4 x 235/45/17 tyres and find out they still make for funny handling like when I had them on the rear only - logic dictates it was the mismatch that caused this issue. Not the 45 profile.

many else gone up a profile size all around and noticed anything.

I’m aware I’ll loose abbot of response by having 45 vs 40 but as these are my road tyres (and Kentish roads are shocking) the additional sidewalk and progressive handling should make up for it.

235/45 vs 235/50:

Not that noticeable in these pics, more obvious in person but didn’t look wrong at all.

 

[Dino D]

225/45 vs 235/45

 

[Dino D]

245/40 vs 235/45

 

[Dino D]

235/40 vs 235/45

 

[Toby]

Just run the AD08RS's all year round, rather than just on track A great tyre giving plenty of grip - just be careful pushing them on track continously.

They are a track focused tyre rather than a dedicated track tyre.

I run them all year round for fast road use, and the odd pootle around too have done for years

 

[Z Victor 1]

Curious that you say 225 s on 7.5j rims are too skinny. Standard rims on a 3.0l E85 Z4 from new are 8j fitted with 225 45 17 tyres. I have those on my Z4 2.2i and they don't look skinny at all. If BMW think they're ok that's good enough for me

 

[petecossie]

The Roadstar wheel as fitted to the Z3 MC & MR are 7.5" x 17" Front and 9" x 17" Rear
The fronts are fitted as standard with 225/45ZR17 tyres
The rears are fitted as standard with 245/40ZR17 tyres
I have slightly oversized Falken FK453 tyres on my Z3 MC which I did on the recommendation a lot of years ago of ZZZEMMCO on ZCoupe Forum as he used his car when instructing on the Ring with FK451s fitted at that time.
The fronts are fitted with 235/45ZR17 tyres
The rears are fitted with 255/40ZR17 tyres
I have informed my insurance company as it could be classed as a modification.
Never had any tracking/driving problems with my car in the 11 years I've owned it or in the 4 years I owned my first M Coupe with FK 451s fitted.
I thing the problems you have maybe related to the relationship the diameters of the tyres front & rear you have chosen as against the standard tyres fitted to the car which may have upset the handling. If you want a slightly staggered look with tyre sizes you'll still have to match up diameters to original setup.
I purchased my Falkens from a local Pro Tyre depot as Camskill who I'd previously purchased my Falkens from said they weren't available.

Hope this helps

 

[Dino D]

Just run the AD08RS's all year round, rather than just on track A great tyre giving plenty of grip - just be careful pushing them on track continously.

They are a track focused tyre rather than a dedicated track tyre.

I run them all year round for fast road use, and the odd pootle around too have done for years

I have a set of these in 245/40 on 8,5k rims I use for track.
They are good but there is a trade off with firmer sidewall and more ‘focused’ feel. Very high grip when warm but not as good when cold - they ok in the wet but not as good as a road tyre in the wet - possible but a bit of a compromise that I’ve tried and hope I can do better.

 

[Dino D]

The Roadstar wheel as fitted to the Z3 MC & MR are 7.5" x 17" Front and 9" x 17" Rear
The fronts are fitted as standard with 225/45ZR17 tyres
The rears are fitted as standard with 245/40ZR17 tyres
I have slightly oversized Falken FK453 tyres on my Z3 MC which I did on the recommendation a lot of years ago of ZZZEMMCO on ZCoupe Forum as he used his car when instructing on the Ring with FK451s fitted at that time.
The fronts are fitted with 235/45ZR17 tyres
The rears are fitted with 255/40ZR17 tyres
I have informed my insurance company as it could be classed as a modification.
Never had any tracking/driving problems with my car in the 11 years I've owned it or in the 4 years I owned my first M Coupe with FK 451s fitted.
I thing the problems you have maybe related to the relationship the diameters of the tyres front & rear you have chosen as against the standard tyres fitted to the car which may have upset the handling. If you want a slightly staggered look with tyre sizes you'll still have to match up diameters to original setup.
I purchased my Falkens from a local Pro Tyre depot as Camskill who I'd previously purchased my Falkens from said they weren't available.

Hope this helps

That’s good to know.
I used to use Falken, think they were 452.

I’m not looking to stagger them, the rims are are 7,5j all round and like the handling on a square set up and the ability to rotate for increased life.

I know that changing diameter on the rear too much in relation to front causes issues but wondering if the diameter is increased all around, equally, will it be fine.

 

[Dino D]

Curious that you say 225 s on 7.5j rims are too skinny. Standard rims on a 3.0l E85 Z4 from new are 8j fitted with 225 45 17 tyres. I have those on my Z4 2.2i and they don't look skinny at all. If BMW think they're ok that's good enough for me

That extra .5j makes a difference and the Z4 was better designed for the wheel to fill the arches I think - the 2.8 Z3 can hide massive wheel back there!

the 225 make it a bit too lively. The 235 has been a nice balance hence trying to stick with it.

 

[Z Victor 1]

I did think about fitting 235s last time I replaced the tyres, but then just stuck with the original size. I've got spacers on the back to bring them out nearer the arches.

 

[Jasn]

Ignore this post - I got this wrong. Sorry.

 

[Dino D]

Update.
I found a thread on bimmerforums USA with someone who’s run 245/45/17 on track tyres and was very happy.
This to my mind confirmed the increase ins diameter, as long as across both axles should work.

now he was running a track tyre which will have a stiff sidewall so negating the increased sidewall downsides somewhat

The tyres I had in mind were Michelin Pilot Sport 4 which appear to be quite stiff and offer very high grip.

In this size the PS4 is only 10% more than the Hankooks. The Hankooks used to be well under £100, think I paid about £80 per tyre, but now with Michelin promo of £30 off four four, the PS4 was only 10% so a no brainier.

tyres fitted and 60miles done and feedback is:

as expected:
Front tyres catch the liner on lock - was planning on raising the car by 10mm anyway.
More compliant ride.
Less direct steering - not numb but compare with the lower profile before, there is a bit more ‘give’.
Generally more ‘give’ and nicer ride.
None of the weird handling I experienced when only the rears where larger than the fronts.

unexpected change:
Massive amount of grip - I know PS4 are rated highly but this is next level - very confident and progressive tyre.
Kind of miss the Hankooks on this regards - they were not ditchfinders at all but they had lower limits, and very progressive.
These feel like the AD08RS (when warm) but much more compliance, which on bad roads means more grip.

Really like how they look too - kind of retro muscle car. The PS4 had a sort of smooth/rounded side wall that seems to accentuate the look.
Looks are a bonus but seriously impressed with the PS4.
Hoping they’ll make a good wet track tyre if needed.