I am trying to figure out what tire width is needed. 205 should be enough for an r1 engine, but I am considering adding a turbo at some point, and a 245 would be more appropriate, I think.
I just want to basically get away the with the least amount of rubber, but enough to hold traction, and it's hard to gauge from what cars use because of the torque/weight differences in a BEC.
Any suggestions?

Check out the Fibreglass you will be using and whether it is for road or race. 195 is generally acceptable on front's. Rears is more important as to whose rear arches/side panels you intent to go for.

IMHO I'd check this before I decided on tyre size's.

Hellfire

Is there not a balance between weight of the car and widthe of the tyre?

for example, if you have a 450 kg car and 295 width tyres, the mass per square inch of tread is very low. This means its easy to break traction. However, this is obviouslt compensated for by the width of the tyre, if you know what I mean.

Or is it simply a case of wider = more grip?

Mark

Perhaps read this for good advice:
http://www.chris-longhurst.com/carbibles/index.html?menu.html&a mp;tyre_bible.html
It's all good but see especially "Fat or thin? The question of contact patches and grip." about two thirds of the way down the page.

Dave

i am also looking to turbo my car in the future but will probably try it on the 205's before buying any wider wheels

Hellfire, glass isn't a big consideration-I own a composite business
Dave, thanks for the reading
I think I might just go with 205's and a wider wheel in back just in case, then I can just mount the 205 rubber up front when they wear out.
Thanks