Speedo to tire size Error and Calculators

[SpiderJim]

Well I just ordered my Rota rims from Mark and trying to decide on tires and especially the size. The Rota rims are 15"x7" and look very much like the more expensive and period panasports. My original idea was to use the tire size of one of Marks customers which was 195/55R15 and was displayed in a picture that looked very nice. Before deciding it was time to get Kermit on the Hwy and check the speedo out against a couple of GPS systems. Each GPS showed a +5 KPH (Canadian Speedo) error at all speeds. This turns out to be +5% error @ 100 KPH. Turns out after researching euro cars tend to be 5-10% high to offset tire wear etc. So this is my thoughts. Increasing from 195/55/15 to 195/205/15 should get me closer to the mark and reduce my cruise RPM down by around 200 RPM. The negative side is approx loss in power probably equal to around 5%. However, I get to fill the wheel wells a little better and the wider tire takes away from the muscular upper body skinny legged man look. Am I full of BS or on the right track??. Would appreciate any expert advice.

Thx Jim

FYI
Misc tire/speed and gear ratio to RPM calculators
http://www.offroaders.com/info/tech-cor ... ph-rpm.htm

http://www.onlineconversion.com/bigger_tires.htm

[brad131a4]

Jim one of the things to check on is the offset of the rim. The 195 might be better as it might not rub when turning. A 7" rim in a 15" size gets pretty close to the inner fender well when at full lock. Not saying the 205 wouldn't work just check out how the rim looks first.

[narfire]

Jim, I have 205 50-15 toyos on my spider.(15 X 7 wheels) I found the height to be really close to the 27 inch total height of the original wheels (13 inch) and tires that were mounted before I bought the car.
I had a bit of a rubbing problem on one side but I just had to tighten and add a couple more screws to the plastic inner fender. No issues since.
Thats a good idea with the gps,I'll have to try that

[SpiderJim]

Whoops I made a boo boo I meant I was thinking of increasing from 195/55R15 (suggested) to 195/65R15 On a Champiro hi performance tire with directional V tread. Just wanted to gain about 5% more circumference to offset my speedo error and drop the RPM down a bit on cruise. it should also make the wheel fit the well a little better visually. (I hope)