3.14 versus 3.38 diff ratio

[Ricky444]

Hi Folks currently run a 3.14 in my hayabusa sprints/Hillclimb car would it be a great benefit to change the ratio to a 3.38.

Thanks in Advance Richard

[stephenh]

What is your top gear ratio, and what size rear tyres?

What gear and revs do you pull on the fastest straight you get on on the tracks you visit? Or is this for future competition? 

Personally, when I was sprinting, the fastest I went was on the railway straight at Aintree (depending on the wind direction, which could make a big difference to something like a Westfield at those speeds) so I wanted gearing which meant that at that circuit I was pulling a bit less than max. revs in top as I hit the finishing line on that straight, given a following wind, the rev point at which I was getting max. power from my engine. From that, I worked backwards using maths to work out what diff. ratio I needed.

[K17 CAR]

I run a 3.21 wish I had the option of a 3.14, I bounce off limiter in top at Cadwell & Snetterton and that's with a longer 5th & 6th gear, I hit limiter at Snetterton even if I put 15" wheels on rear.

 

13" wheels? Don't change it.

[Ricky444]

Cheers I run 13 inch Toyos 

[Kingster]

10 minutes ago, Ricky444 said:

Cheers I run 13 inch Toyos 

In fairness that’s not as lot of help 😁

 

You need to add which size (width and aspect) as that has a rather big effect on diameter 👍

[Ricky444]

205/60/13 Toyo I always lose 0.1 to 0.2 on the 64ft line but have won both championships in Northern Ireland last year 

[K17 CAR]

Have a look on Avons Motorsport tyres page, there's a good list on there that gives diameter and revolutions of wheel per mile on all trye sizes, in 13" over the rim widths we tend to use there's not a huge difference in diameter/revolutions per mile.

Do you get near limiter in 6th on any of the circuits you run on?

[S2T]

Top Speed 3.14 diff 136mph (theoretical) with 13" 60 profile tyres, 126mph with 3.38. Acceleration would be better with a 3.38.  So in theory 3.38 better for the hills and 3.14 better for sprints especially those with long straights

[Ricky444]

Thank you folks I think I will just stay with the 3.14

[cast iron]

I ran a 3.14 albeit with a standard fire blade, similarly running 13" wheels. I couldn't get out of 4th gear! I run a 3.63 now and hit the limiter in 6th just braking for stowe at Silverstone seeing 125MPH according to their speed trap

I think your better off having the acceleration out of the corners over top speed, you always use acceleration!

[Terry Everall]

Remember that the gears on a Busa are different to a Fireblade. On my 1300, 1400 and 1548 Busa I always ran the 3.14 with no problems of acceleration or topped so I would stick with the 3.14