I love these charts.
Over the years, we have been asked a time or two, “What makes the biggest difference for those of us who want a Bugeye that runs at highway speed?” The two charts shown in this post (originally made for a Morris Minor, but apply to Bugeyes just the same) will give you a sense of which ratio, which gearbox, and which tire size produces the best mix of results! Chart one above shows the RPM’s with a variety of different tire sizes when a stock transmission is used, with no overdrive.
Chart two, shown below, provides the RPM ranges using the same tire sizes as the first chart, but with an overdrive fifth gear. A Datsun B210 was used in sampling, which has a .82:1 overdrive ratio; all three of the major overdrive gearbox conversions, Datsun, Ford, and our newest option which will be available soon, Suzuki (contact us for more details!) use similar overdrive ratios to the B210, so the numbers will be pretty consistent throughout.
There is one other variable… comfort! We generally do not deviate from 13 inch wheels because we find 14 or even 15 inch wheels excessively harsh riding in a Sprite. Still, these charts provide you the ability to look to see how wheel size and tire size makes a difference.
You can also see how a wider tire also brings the RPMs down at speed. We generally do not use wide tires because they also make for a harsh ride and stiffer steering. One exception is the 185/60X13 Toyo tires we just put on our Bugeye build called “Kit” that you can see in the photos below, along with our VTO Black Classic 8 wheel. These performance 185 tires are a sufficiently soft compound that they ride nicely in spite of the extra width. They look cool and ride nicely with lots of grip! (If you’d like a set of these tires or wheels, you can find them in our parts catalog by clicking on the photos below!)
We are constantly rebuilding differentials too, so if you want a 3.9 limited slip differential for example, click on the photo below to order one and get your place on the waiting list secured! (Currently quoting December/January delivery).
Thank you to Brian Lane for creating this very useful document!
