07 Sprocket Size for Desert
Posted 23 April 2012 - 06:52 AM
I'm looking to change my sprocket size from a 13/51 to a 13/52 for the VCGP in Nevada this weekend. I'm wondering if the 52 in the rear will help me out in some of the slower rocky areas or should I just stick with a 51? Right now I seem to stall it from time to time in areas like that. I'm ordering a new chain and same size front sprocket but this might be the time to try a 52. I don't see a whole lot of 4th and 5th gear riding in this race... at least not by me. Thanks
Posted 23 April 2012 - 07:39 AM
Lowering the gearing that much doesn't help in the tight stuff nearly enough to make up for how bad it cuts off you peak speed, IMO.
Posted 24 April 2012 - 03:28 PM
If it were geared to the ground, a 13/51 would give you 85 mph at 10,500 RPM, and you'd be spinning about 5700 at 45 mph. Factoring in realistic tire slippage, your top end would come down to somewhere under 75, and you'd be close to 6K at 45 mph in 5th. Meanwhile, to run at 2500 with the clutch out, you'd need 10mph.
Changing to a 13/48 adds 6 mph to the top end, and lowers the 5th gear 45 mph cruise to around 5400. In low gear this means you'd need to go 10.6 mph to reach 2500.
You get the idea. Gearing changes have a much larger affect on things at the high end than at the low.
It's a straight, linear percentage. A 10% lower gear will cut your top speed by 10%, say from 100 to 90. Meanwhile, it only lowers your 2000 rpm low gear speed 10%, say from 10 to 9 mph.
Posted 24 April 2012 - 05:06 PM
Gearing your bike down reduces the effective MPH range of each gear and requires more shifting. It makes throttle response over-sensitive for offroad riding. And worst of all, it makes you a slower rider.
A 450 has more than enough low and midrange power to be effective at most all RPMs so there is no need to handicap the bike with low gearing. Having to do some clutching in the really tight spots far outweighs the disadvantages of low gearing IMHO.
I've never ridden the VCGP but I have friends that have and none of them gear down for it.