RPM & Tires

OK Derek says that going from a 65 to 60 tire you increase RPM by 3%. I guess where I'm going with this is that the OEM tire was 25.65". The 195 70=25.75",195 65=24.98" and the 195 60=24.41" (according to Moss). So if you where cruising down the Highway @ 3000 RPM with the OEM tire then what is the RPM with the present tires available??? 70=3000 close to same RPM, 65=3100 100 gained and 60=3200 200 gained. I just have a hard time thinking that big of diameter change from stock to 60 is only 200 RPM difference. What do you guys think???? Maybe a little more low-end power with the smaller tire might be something to consider.

The reason I went with the 195SR65's on my K&R's back in 1997 was to come as close as possible to the original size. As I stated before, I personally ran into problems with fenderwell rubbing....and when I need replacement, will be looking for a suitable alternative. I have put thousands of miles (including long distance treks to Vancouver, Sebring, Dallas, etc) on the MGC since then with no problems (other than the shaving of the outer sidewall of the rear passenger.

I think you have to look at it as "how am I going to use the car and will the increased RPM's really hurt that much?"

These engines were made for high RPM's...and 3100 to 3200 is no where near Redline. Yes, the car will work a LITTLE harder to get you where you're going...and your fuel consumption will be a LITTLE higher....but I don't think it's worth losing a lot of sleep over.

FWIW - YOMV

:)

Kind of thinking the 195 60 15 may avoid the fender rub. What size are you going to try next time???

My brother-in-law is a machinist in California. I'm thinking of asking him if he can make me a couple of spacers (one for each MGC) for the K&R replicas per Greg Fast's recommendation if the bushings and/or Panhard rod doesn't do the trick.

To answer your question....probably a 185SR70...or perhaps a 185SR75 if the above tricks don't work out.

Think these are my current top choices. Tire size I'm thinking of now after reading some post is 185 65 15. Hoping this size will fit the car better without any mods. Couldn't find anything in 185 70 15 size without going to a vintage tire source.

http://www.tirerack.com/tires/tires.jsp?tireMake=General&tireModel=Altimax+HP&partnum=865HR5AMAXHP&vehicleSearch=false&fromCompare1=yes&place=2

http://www.tirerack.com/tires/tires.jsp?tireMake=Sumitomo&tireModel=HTR+H4&partnum=865HR5HTRH4&vehicleSearch=false&fromCompare1=yes&place=13

Never had either of these manufactures before. I've seen a couple guys on the board use the Sumitomo HTR H4 on B's, they seem to like them. Don't know if anyone has tried the Altimax, they are 2 lbs lighter and have a cool looking tread, are rated very high in their tire class with good reviews. Maybe I should try them out so we could have some sort of feedback on this board.

May have made an error in the Sumitomo, I actually think the guys on the board have HTR 200, summer only tire, the Sumitomo I saw in the 185 65 15 size is an all season type tire and doesn't rate as high in it's catagory.