New Wheels; Speedometer Question

[Limey7]

OK, so I've searched lots of word combinations and I'm sure it's been covered here before but I can't find it. I'm about to put 14" minilite style wheels with 195/60/14's on my 7. Does anyone know how this will affect my speedo reading?

"The Flying Doorstop!"

[Hasbeen]

Limey, rolling diameter;

195 60 14 is 1825.28mm.

185 70 13 is 1851.03mm.

Thus the difference to stock is 1.25mm greater distance traveled per tyre rotation.

If your speedo was reading 100Km/h [62 mph], your actual speed would be 100.07 Km/h. Not even a cops radar could read that.

Hasbeen

[Limey7]

Thank you Hasbeen for the very precise and speedy answer! And this is why I love this forum. What a wealth of knowledge here!

"The Flying Doorstop!"

[stevie_a]

http://www.csgnetwork.com/speedocalibcalc.html

[;)]

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[Limey7]

OK, now time for a really dumb question....so if the difference is that minor can I get away with keeping a stock steel rim and a 185/70/13 for a spare. I'd only use it sparingly (pun intended[:)]) to get me off the side of the road and back home in case of a flat.

"The Flying Doorstop!"

[Hasbeen]

Yep, but remember to carry the right wheel nuts for it.

I have an MG F wheel as spare for the 8, as I can't get another of the wheels on it these days. I can only use it if I have the right nuts.

The same goes for the 7. I have an original Triumph alloy wheel as spare, & it requires different nuts to the aftermarket wheels.

Hasbeen

[Last TR]

Hmmm. I guess I had better check mine, as I also have after-market alloys and an original spare.

Ken Morton
Anchorage, Alaska

1980 TR8, 1973 TR6, 1965 Volvo PV544, 1958 MGA, Jeep Cherokees

[Limey7]

Thanks again Hasbeen. Thats what I figured. I was even thinking about the lugnut issues. I'll remember to throw four of those in the spare tire well.


"The Flying Doorstop!"

[Hasbeen]

Ken, the aftermarket wheel nuts have a thinner, slightly larger diameter washer than the original nuts. They can be used at a pinch, but the washers tend to get jammed in the recess in the wheel & actually bend, becoming cupped.

The original nuts have a much thicker better quality washer, which stays on the nut.

Hasbeen

[swifty]

I always use this useful little site for comparisons...

http://www.mintylamb.co.uk/?page=tyre.htm

[img][IMG]http://i728.photobucket.com/albums/ww281/swiftstuff/Tr8/029-1-1.jpg[/img]