clintard said:
Guys,
Ive ready about swapping the differential for one off a venture. I was wondering if anyone could explain some things about doing this.
First off, with a stock tire and rim, how would it effect your rpms and gas milage and speed?
Secondly, i dont like the look of the diff, can you just swap the internals?
Thirdly, how does this compare to getting another size of wheel? I thought about saving up for a 17 or 18 inch wheel for the back but read the wider tire would hurt the handling around curves worse.
Im a complete noob to this topic so can we get a discussion going about all the different aspects of it?
Thanks
With stock wheels your RPM will decrease, you will get say 50 mph at a lower RPM, that is good if you ride long distances traveling and your gas consumption will decrease a little, that said the bike will become slower in acceleration but long winded.
the tire size can also accomplish that, a bigger diameter tire will also reduce the RPM , a 170/80X15 tire will do that, to what extent vs a venture differential I really don't now
on the other hand if you put a smaller diameter tire as in the case of ONLY radials a 180/55x17 will make your RPM go up so that at 50 mph your RPM will be increased from stock, that translates into faster take off but a short winded bike maximum rpm comes sooner.
A smaller diameter rear tire will also lower the bike and affect the handling
good for straight bad for cornering.
Some of us get so annoyed from this rise in RPM after converting to 17 inch radials so they swap the differential with a venture to bring back the RPM to stock levels, but I found that using a 160/70X17 rear tire solves this problem nicely as it is only 9 mm shorter than stock and the added benefit of keeping the rear hight of the bike ~stock. Unless you insist on a Fat rear tire and don't care so much for cornering.
Now if you have a big bore engine and transmission work then a venture differential is a must because the motor has more power than stock.
Then what are the options available?
with stock wheels go stock tire size with and 80 profile, or go with the 170/80X15 for the rear if you ride on long opened stretches for most your riding, but the weight bias will be shifted slightly forward which is a good thing if your forks are not lowered or at least you took that into account when you lowered them
The big question is a 17 inch or an 18 inch wheel?
1- the 18 inch has its good and bad points, the good, though it is shorter than stock it is not as short as the 17 inch so the RPM will not be raised significantly
the bad thing is the available 18 inch tire sizes from all manufacturers is limited in the number of sizes
also people do not realize that a shorter tire profile= less sock absorption by the tire and more shock absorbing demand on the shocks so stock shocks have to go eventually
2- The 17 inch wheel good points, a big variety of sizes from all manufacturers
,Faster take off and acceleration
now the bad is if you are a fat tire fan it will lower the rear of the bike shifting the weight more to the back resulting in a light front that is unstable at speeds something like having a passenger
so front lowering has to be done either by sliding the forks up ( only if you replaced the stock springs with stiffer ones or else the fender will hit the radiator you have a stock front wheel? right.)
With sizes like a 170/60X17 or a 180/55X17 the RPM will be raised thus increasing vibration of the engine also you can't ride leisurely with RPM at higher levels and you are over taxing the engine for no reason.
With both 18 and 17 if a wide fat tire is desired your bike might not accommodate these sizes without swing arm notching(weakening) Bracing because of that. now if you want to fit a fat tire the wheel has to have an off set to move it away from the swing arm this is messing with the front to rear wheel alignment which will result in a poor handling nice looking bike
Now lets talk about the front leave it 18 or get a 17?
If you leave it 18 you will have to lower the front to shift the weight forward to correct the rear lowering that resulted from the fat rear.
If you get 17 the front will instantly be shorter by 2 inch, you will also have a big gap between the tire and fender which looks bad so a fender spacer is needed, now the speedometer is reading miles faster resulting in false higher than actual speed reading so you will need to replace the speedometer gear for ~ $30. the brake with 17 inch feels a little stronger ( it bites ) if not careful but not a deterrent from using a 17 inch.
I had a 120/70X17 front which is 600 mm in diameter replaced it with a 130/70X17 which is a 614 mm diameter and like it much better than the 120 , it has more rubber , damps potholes better and has the highest weight load to handle the forward wt bias I have the bike set at.
If you are starting from a bone stock I suggest you do race tech springs & emulator with one inch internal lowering FIRST before thinking of radials or differential.
as you can see you need to have a plan to accomplish what you want if you lower you have to compensate for it somewhere else.
having the weight bias to the rear will make bike unsteady, having it forward will need firmer front springs to a limit, if excessive front lowering is done the bike will do a stoppie in hard braking and front end dive increase to dangerous levels which increases the load on the front tire and might even exceed it in hard braking ( that is why I wanted a higher wt load rating on my front tire) moderation is key
I hope that helped
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