[fattymatty]

Would like to lower the rpm on my Bonnie at speeds around 70mph, as i would not mind if i get a little less acceleration in return. So can anyone tell me if the standard front is a 17 and all i need do is fit a 18 or 19 or should i say get my dealer to fit this at my next service!!!!! :???: many thanks for any advise

 

[DickBender]

The standard would be 17. You should be able to go to an 18 without hurting acceleration too much. There have been a few recently that have gone back to 17s.
I have an 18 on mine with air flow mods and it is good.

Darcy

 

[fattymatty]

Thanks for your reply Darcy, Did you notice a drop in revs over 60mph with just the 18 fitted or only when you did the air flow mods also.....cheers :???:

 

[DickBender]

The revs are the same whatever the mods to the engine.
Revs only change due to gearing changes sprockets/tyre size.
The difference with taller gearing (ie18 or 19) is that with the reduction in revs you also get a reduction in torque.
If you free up the flow to and from the engine you get an increase in power/torque that overcomes the loss in torque caused by the gearing increase.
So in my case it actually has more torque with the 18th than it did with a 17th and a stock engine.

Darcy