Hi guys
I'm wondering if anyone has experimented with a 40mm difference in front / rear tyres i.e. 205 front 245 rear, or 215 front 255 rear. Would this cause a significant amount of understeer?
 
I have a set of wheels with 205 (7.5") front, 225 (8.5") rear, both slightly stretched. The fronts are high quality summer tyres and the rears are basic economy. I'd like to replace the rears only with 245 and leave the 205s on front. When the fronts become worn I'd look at replacing with 215 to reduce the gap to 30mm.
 
Any thoughts? Would I be better off with 235 on rear to reduce the gap? I'd prefer 245 to fill out the wheelwell but appreciate this may not be best for handling...What about 'wide' 235's like Federal 595 RS-RR?
thanks        
 
 

What is your rim size and et (offset)?

8.5" rim, correct tyre size (based on sidewall) is 235-245 with a max 255.

Mr2 sw20 rear, 245/40/17 at et38-41 is ideal maximum (from memory). Maybe a little rub depending on ride hight and rolled guards and side strip mounted point.

Like you mentioned, later increase the front width.

Width is grip and friction; choose what u need for your driving style.

Significant understeer is another conversation and many variables (plus driver style).

TonyMR2
Width is grip and friction; choose what u need for your driving style.

Significant understeer is another conversation and many variables (plus driver style).

^ This is what I'm getting at. My rear wheels and offset will accommodate 225, 235, 245, or 255 so I have plenty of options. Given I'm planning to use 205 at the front (for the time being, no point in wasting RE003's) I'm undecided on 235 or 245 for the rear. 
 
My preference is 245 for grip and fit, but I understand that adding grip to the rear only will reduce front end grip and increase understeer. Most people seam to do a 20 or 30mm tyre stagger, so I'm curious to know if anyone has tried 40mm and how this affects handling.
 
The car isn't being driven at the moment but it will be a weekend / occasional track car. Currently on original shocks / springs but will be upgraded.     

I am running a 215 Front and a 255 rear currently and thinking of going to a 265 rear, I don't have any issues with under steer but I feel that changes to suspension geometry is what has the biggest effect to keeping the handling nice and neutral. 

thank guys. Sounds like 245 will be fine. I'm planning to upgrade and setup suspension early next year.